The Novarupta-Katmai Eruption of 1912—Largest Eruption 

of the Twentieth Century: Centennial Perspectives

Professional Paper 1791

U.S. Department of the Interior

U.S. Geological Survey
COVER:

Katmai caldera and the Valley of Ten Thousand Smokes. During the 60-hour eruptive sequence of 6–8 June 1912, 13.5 km3

 of rhyolite, dacite, and andesite 

magma was released at a new vent, later named Novarupta. Withdrawal of magma from beneath Mount Katmai, 10 km east of Novarupta, caused syneruptive collapse of the 4-km-wide, kilometer-deep caldera, which has subsequently filled with a lake now >200 m deep. Plinian fallout blanketed southern 

Alaska, and aerosol was noticed as far east as Algeria. Synchronous with the first of three plinian episodes, nine successive packages of ash flows were 

emplaced over a 16-hour interval, filling a formerly brushy Alaskan valley with a thick ignimbrite sheet that produced myriad high-temperature fumaroles for a 

decade or longer. In the image, the terminus of the ignimbrite is seen in the distance, 29 km northwest of the center of the caldera.
The Novarupta-Katmai Eruption of 

1912—Largest Eruption of the Twentieth 

Century: Centennial Perspectives

Wes Hildreth and Judy Fierstein

Professional Paper 1791

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2012

This report and any updates to it are available online at:

http://pubs.usgs.gov/pp/1791/

For more information on the USGS—the Federal source for science about the Earth,

its natural and living resources, natural hazards, and the environment—visit 

http://www.usgs.gov or call 1–888–ASK–USGS

For an overview of USGS information products, including maps, imagery, and publications,

visit http://www.usgs.gov/pubprod

To order this and other USGS information products, visit http://store.usgs.gov

Suggested citation:

Hildreth, W., and Fierstein, J., 2012, The Novarupta-Katmai eruption of 1912—largest eruption of the twentieth 

century; centennial perspectives: U.S. Geological Survey Professional Paper 1791, 259 p.

Any use of trade, product, or firm names is for descriptive purposes only and does not imply 

endorsement by the U.S. Government.

Although this report is in the public domain, permission must be secured from the individual 

copyright owners to reproduce any copyrighted material contained within this report.
iii

Foreword

The Novarupta-Katmai eruption in early June 1912—the most powerful in the 

world in the 20th century—was surpassed in size during all of recorded history 

only by the 1815 eruption of Tambora Volcano (Indonesia). When this voluminous 

eruption occurred, however, Alaska was quite different from what it is today. The 

total population of the Alaska Territory in 1912 was only about 50,000, living in a 

vast, remote region that was terra incognita to most of the world. Alaska’s geology and volcanoes had been little studied, and the science of volcanology was 

nascent—even the early investigators at Katmai lacked the basic understanding of 

magmatic and volcanic phenomena that we take for granted today. Moreover, doing 

fieldwork—then as now—in the rugged Alaskan terrain posed daunting challenges, 

such as coping with the ever-present storms, icy streams, windblown dust and ash, 

and bears. However, such disadvantages of Alaskan field conditions are counterbalanced by the scientific bonus that the desolate, unvegetated Katmai volcanic landscape also presented exceptionally well exposed large pyroclastic deposits available 

for detailed investigations.

The initial information about the 1912 eruption was necessarily limited, consisting mostly of anecdotal accounts—of felt earthquakes, explosions, eruption plumes, 

and ashfalls—reported from places distant from the volcano. The full story of the 

eruption and what actually transpired at Katmai—above and below the ground 

surface—would only become clear after intensive scientific forensic work over 

subsequent decades, the results and implications of which are synthesized in this 

centennial volume. Wes Hildreth and Judy Fierstein are amply qualified and most 

experienced to undertake this synthesis, because of their own decades of substantial field and laboratory investigations on the eruption since the mid-1970s. Their 

encompassing synthesis is an encyclopedic and authoritative interpretation of all 

available data about the processes, products, and impacts of this eruption, within the 

context of modern scientific understanding of how volcanoes work.

With its in-depth discussion and diverse topical coverage, together with copious 

illustrations, this volume should be of immense utility to a wide variety of readers. 

For nonspecialists, the engaging narrative about the early investigations at Katmai 

makes for fascinating reading. For specialists in volcanology, the topics treated 

include stratigraphy of pyroclastic deposits, seismicity, caldera collapse, vent structure, chemical and isotopic composition of eruptive products, posteruption geomorphic evolution, and comparison of Novarupta-Katmai with other large historical eruptions. Indeed, detailed studies of the well-exposed and large-volume 1912 

pyroclastic deposits have provided diagnostic insights to decipher the emplacement 

processes of similar deposits (ignimbrites)—prehistoric and less well preserved—in 

other volcanic regions, whose origins long perplexed geoscientists. In addition, the 

volume traces the evolution of scientific thought about the causative mechanisms for 

large rhyolitic eruptions through progressive advances in the field of volocanology.

Hildreth and Fierstein mention that the Novarupta-Katmai eruption occurred 

about two months after the RMS Titanic struck an iceberg on 14 April 1912 and 
iv

sank, killing more than 1,500 passengers and crew. Although the huge 1912 eruption certainly had the potential to produce a massive volcanic disaster, it fortunately 

occurred in a sparsely populated region, causing only a single fatality (not directly 

eruption related) and minimal socioeconomic disruptions. Nowadays, even though 

the Alaska Peninsula is hardly densely populated, more people on the ground would 

be affected should another large eruption recur in the Katmai area. Because of the 

exponential increase in air traffic in the North Pacific region during recent decades, 

greater potential hazards are posed by possible encounters between jet aircraft and 

drifting clouds of volcanic ash from explosive eruptions.

 The broad scope and meticulous scholarship of this volume virtually guarantee 

a very long shelf life. Indeed, the detailed investigations of the 1912 NovaruptaKatmai eruption, as reviewed herein—in comprehensive and compelling fashion—

by Hildreth and Fierstein should be emulated at other Alaskan volcanoes to prepare 

the best possible assessments of potential hazards, on the ground and in the air. The 

future occurrence of another great explosive eruption in Alaska is not a question of 

if, but when, and we should be better prepared in such eventuality.

Robert I. Tilling

Senior Research Volcanologist, Emeritus

USGS Volcano Science Center

The SS Dora, a mail steamer of the Alaska Commercial Company, served 

coastal villages from Unalaska to Valdez for several decades. She was in 

Shelikof Strait in the early afternoon of 6 June 1912, when her crew and 

passengers became the first witnesses to report the great plinian eruption 

plume that ascended from Novarupta to the stratosphere. Photo by J.E. 

Thwaites, mail clerk of the Dora.
v

Contents

Foreword ........................................................................................................................................................iii

Abstract...........................................................................................................................................................1

Chapter 1. The 1912 Eruption and its Importance....................................................................................3

Overview of the Eruption........................................................................................................3

Volcanological Significance of the 1912 Eruption..............................................................3

Chapter 2. The Context of the 1912 Eruption ..........................................................................................13

Geographic Setting ...............................................................................................................13

Cultural Setting: Katmai Before 1912 .................................................................................13

Cultural Setting: The World in 1912 ....................................................................................14

Scientific Context of the Early Katmai Investigations .....................................................15

Geologic Setting of the Katmai Volcano Cluster..............................................................17

Chapter 3. 1912 Eruption Narrative: What Was Actually Recorded in 1912......................................19

Chronology of Observations in 1912...................................................................................19

Environmental Impact of the Eruption ...............................................................................22

Recovery of Flora and Fauna...............................................................................................22

Chapter 4. History of Investigations and Interpretations .....................................................................25

Chronology of Geologic Investigations at Katmai............................................................25

Principal Contributors to the Early Geologic Investigations at Katmai ........................42

Chapter 5. Products of the 1912 Eruption................................................................................................45

Eruptive Episode I ..................................................................................................................48

Layer A ...........................................................................................................................49

All-Rhyolite Ignimbrite.................................................................................................51

Layer B ...........................................................................................................................56

Compositionally Heterogeneous (Main) Valley-Filling Ignimbrite (VFI)...............57

Compositionally Heterogeneous High-Energy Proximal Ignimbrite (HEPI)........62

Time Constraints for Episode I ...................................................................................66

Eruptive Episodes II and III..................................................................................................68

Layer C............................................................................................................................70

Layer D ...........................................................................................................................71

Layer E............................................................................................................................71

Layer F............................................................................................................................73

Layer G ...........................................................................................................................74

Layer H ...........................................................................................................................76

Proximal Pyroclastic Density Currents.....................................................................77

Proximal Fall Deposits: Contrasting Facies..............................................................77

Eruptive Episode IV: Dacitic Phantom Dome and Block Bed.........................................78

Eruptive Episode V: Novarupta Rhyolite Dome.................................................................80

Chapter 6. Volcanological Aspects of the Primary Eruption Products ..............................................87

Volumes Erupted....................................................................................................................87

Coignimbrite Ash and Coplinian Ash..................................................................................87
vi

Atmospheric and Climatic Effects ......................................................................................88

Changes in Compositional Proportions During the Eruptive Sequence.......................91

Banded Pumice .....................................................................................................................94

Contemporaneity of Falls and Flows ..................................................................................96

Characteristics of the Eruption Columns...........................................................................97

Column Collapse and Emplacement of Pyroclastic Density Currents..........................98

Episode I Eruptive Sequence .....................................................................................98

Concurrent Deposition of HEPI and VFI..................................................................102

Particle Concentration Gradient..............................................................................105

Densification of Flow Units.......................................................................................105

Episode II and III: Small Density Currents from Column Margins......................111

Physical Features of VTTS Ignimbrite Sheet ..................................................................112

Aspect Ratio................................................................................................................112

Flow Units and Progressive Aggradation...............................................................112

Remobilized Flow Units .............................................................................................113

Diffusely Plane Laminated Ignimbrite.....................................................................114

“High Sand Mark”......................................................................................................114

Valley Margin Runups................................................................................................116

Induration and Welding.............................................................................................119

Degassing pipes .........................................................................................................122

Emplacement Over and Against Ice........................................................................123

Chapter 7. Vent Structure at Novarupta................................................................................................129

Asymmetry of the Proximal Ejecta Ring: The Turtle.......................................................132

Chapter 8. Caldera Collapse and Seismicity ........................................................................................135

Seismicity Accompanying the 1912 Eruption..................................................................135

Comparison with Other Seismically Recorded Caldera Collapses .............................139

Hydrothermal Explosion Breccia and Phreatically Ejected Mud Layers...................141

Chapter 9. The Ten Thousand Smokes ..................................................................................................143

Fumarolic Deposits .............................................................................................................147

Fumaroles in Novarupta Basin..........................................................................................153

Chapter 10. Secondary Deposits............................................................................................................155

Syneruptive Runoff and Remobilization...........................................................................155

Syneruptive Landslides ......................................................................................................157

Lakes Impounded ................................................................................................................158

Phreatic Craters and Deposits..........................................................................................165

Chapter 11. Posteruptive Evolution of the Landscape........................................................................167

Rapid Incision of Gorges....................................................................................................167

Alluvial Plains, Channels, and Veneers ...........................................................................168

Aeolian Deposits .................................................................................................................170

Behavior of Ash-covered Glaciers...................................................................................171

Katmai Caldera Lake and Intracaldera Glacier Development .....................................173

Photographic Comparisons: Then and Now...................................................................177

Chapter 12. The Katmai Volcano Cluster...............................................................................................179

 Alagogshak Volcano ...........................................................................................................179

Mount Martin .......................................................................................................................179
vii

Mount Mageik......................................................................................................................181

Trident Volcano and its Domes .........................................................................................182

Southwest Trident (Eruption of 1953-74)..........................................................................184

Mount Katmai.......................................................................................................................186

Snowy Mountain .................................................................................................................188

Mount Griggs........................................................................................................................188

Other Volcanoes Behind the Volcanic Front...................................................................190

Present-day Magma Distribution? ...................................................................................190

Typically Small Magma Batches.......................................................................................191

Chapter 13. 1912 Magma Compositions and Preeruptive Storage ...................................................193

1912 Bulk Compositions......................................................................................................193

Major Elements...........................................................................................................193

Trace Elements ...........................................................................................................196

Affinities to Nearby Volcanoes .........................................................................................196

Volatile Compositions .........................................................................................................203

Mineralogy of 1912 Products.............................................................................................203

Isotope Ratios ......................................................................................................................205

Experimental Petrology ......................................................................................................210

Preeruptive Magma Storage and Syneruptive Transport.............................................211

Plausible Storage Sites of 1912 Magmas...............................................................212

No Preeruptive Magma Storage Beneath Novarupta .........................................213

Data Bearing Upon Models of the 1912 Plumbing System..................................214

Origin of the Rhyolite Magma............................................................................................216

Alternatives to a Zoned Reservoir?..................................................................................217

Two Chambers?..........................................................................................................217

A New Magma Batch from Depth?.........................................................................218

Roof-Zone Remelting?...............................................................................................218

1912 Magma Storage Model .............................................................................................219

Chapter 14. Comparisons with Other Historic Eruptions....................................................................221

Chapter 15. Retrospective: Evolution of Ideas about the 1912 Eruption ..........................................225

Advances in Volcanology and Progress in Understanding the 1912 Eruption..........227

Acknowledgments.....................................................................................................................................231

References..................................................................................................................................................233

Appendix A. Major-element chemical analyses of eruptive products, Novarupta 1912 ...............246

Appendix B. Trace-element chemical analyses of eruptive products, Novarupta 1912................252

Appendix C. Trace-element analyses of 1912 eruptive products by Instrumental neutron 

activation analysis (INAA) ..........................................................................................................258 

Figures

1. Map of Alaska and adjacent North America, showing location of Novarupta, several 

geographic names mentioned in text, and region impacted by ashfall 

within a few days after 1912 eruption...........................................................................................5
viii

 2. Generalized 1912 Novarupta eruptive sequence and chronology of ashfall recorded at 

Kodiak village, 170 km downwind..................................................................................................6

 3. Aerial panorama of Valley of Ten Thousand Smokes, extending 20 km northwest from 

vent at Novarupta to ignimbrite terminus at base of Mount Katolinat....................................7

 4. Representative pumices from 1912 eruption.......................................................................................7

 5. Simplified geologic map of Valley of Ten Thousand Smokes (VTTS) and volcanoes of the 

Katmai cluster................................................................................................................................. 8

 6. Location maps of upper Alaska Peninsula and Kodiak Island group, showing many 

geographic locations mentioned in text.....................................................................................10

 7. Participants in 1919 Katmai expedition, at Kodiak ...........................................................................27

 8. Clarence Norman Fenner at Katmai, summer 1923, beside Yori’s pack........................................28

 9. Emanuel George Zies, 17 August 1919, at site of storm-wrecked camp on 

western bench of Baked Mountain.............................................................................................28

10. Werner Juhle, Howel Williams, and Ronald Kistler during 

 Katmai Project, summer 1953.......................................................................................................31

11. Participants in 1989 Novarupta Geophysical Expedition ................................................................36

12. Participants in 1991 Commission on Explosive Volcanism workshop at 

Valley of Ten Thousand Smokes ..................................................................................................37

13. Participants in 1999 expedition to Novarupta ...................................................................................40

14. Garniss Hearfield Curtis (right) with the authors near Three Forks in August 2003, on 50th 

anniversary of his first expedition to the Valley of Ten Thousand Smokes ..........................42

15. Novarupta pumice-fall section on south flank of Mount Katmai, 10 km 

southeast of Novarupta and 4 km south of rim of Katmai caldera.........................................45

16. Schematic sketches illustrating relations among 1912 pyroclastic deposits..............................46

17. Pumice-fall deposit of Episodes II and III in upper Knife Creek, 4 km 

northeast of Novarupta .................................................................................................................47

18. Novarupta rhyolite dome, 380 m across and 65 m high, beyond which, 

viewed westward, Novarupta basin merges into the upper 

Lethe arm of the Valley of Ten Thousand Smokes....................................................................48

19. Isopach diagrams for 1912 tephra falls..............................................................................................49

20. Representative fall-deposit sections measured at various distances 

and azimuths from Novarupta......................................................................................................50

21. Complete 1912 fallout section, 23 cm thick, including Layers A–H ...............................................51

22. All-rhyolite high-energy proximal ignimbrite (HEPI) deposits on northern ridge 

of Mount Cerberus, 3 km southwest of Novarupta and 250 m higher than 

margin of valley-filling massive ignimbrite at base of ridge ...................................................52

23. Whiskey Ridge and the Knife Creek Glaciers, viewed east-northeastward from near 

Novarupta........................................................................................................................................53

24. All-rhyolite high-energy proximal ignimbrite (HEPI) and dacite fallout 

section atop Buttress Range, in saddle above West Mageik Lake and 

8 km west-southwest of Novarupta ............................................................................................54

25. Pink all-rhyolite ignimbrite (Package 1) along axis of upper Griggs Fork, 9 km from 

Novarupta in an unobstructed northeasterly line-of-sight direction ....................................55

26. View southwestward across upper VTTS from high on Mount Griggs ........................................56

27. Distribution of nine successive packages of 1912 ignimbrite mapped 

by Fierstein and Wilson (2005) .....................................................................................................58

28. Katmai Pass viewed southward from summit of Falling Mountain ...............................................59
ix

29. Terminus of VTTS ignimbrite viewed westward from basaltic plateau 

(“Sayre Mesa” of Hildreth and others, 2004).............................................................................60

30. Aerial view of lower VTTS, Three Forks, and Ukak River corridor................................................60

31. Flow units and packages in massive nonwelded ignimbrite, 

southwest wall of Knife Creek, <1 km upstream from Three Forks ..................................... 61

32. Knife Creek gorge ~3 km upstream from Three Forks, cut largely in 

ignimbrite Packages 2 through 4 .................................................................................................61

33. Eutaxitic welded ignimbrite of Package 8 along Glacier 1 

fork of upper Knife Creek ..............................................................................................................62

34. Schematic diagram illustrating eruption chronology for Episode I and correlations 

among compositionally equivalent ignimbrite packages and fall units ................................63

35. Sintered to partially welded ignimbrite of Package 8, cut by upper Knife Creek ~400 m 

upstream from its confluence with Griggs fork.........................................................................64

36. Stream-scoured surface of sintered ignimbrite Package 9, rich in coarse dacite pumice 

(along with subordinate andesite and sparse rhyolite ............................................................64

37. Intercalated ash-flow and fall deposits 2.5 km southeast of Katmai Pass and 

~300 m south of terminus of 1959–60 Trident lava flow............................................................65

38. Contact between compositionally contrasting ignimbrite packages above 

west shore of West Mageik Lake ................................................................................................66

39. Massive nonwelded ignimbrite showing change in compositional 

proportions without any obvious depositional break...............................................................66

40. Matrix-rich oxidized ignimbrite containing abundant coarse clasts 

capping summit of Falling Mountain dome, 1.2 km from Novarupta dome ..........................67

41. Compositionally heterogeneous HEPI bedsets on crest of south ridge of 

Baked Mountain, 2.2 km northwest of Novarupta dome .........................................................67

42. Stratified oxidized HEPI deposits atop Whiskey Ridge, 5 km east of 

Novarupta and 400 m above valley-filling ignimbrite on floor of 

Knife Creek arm at foot of ridge...................................................................................................68

43. Conceptual sketch illustrating Episode I regional fallout from high plinian column and 

synchronous emplacement of massive valley-filling ignimbrite (VFI) and 

stratified high-energy proximal ignimbrite (HEPI) from radially collapsing 

currents that were graded in particle concentration ..............................................................69

44. Geologists examining high-energy fluvial beds of pumice and ash, reworked in 

part from Knife Creek Glaciers, during hours-long eruptive 

lull between Episodes I and II ......................................................................................................70

45. Complete section of dacite fall deposits, 11 km upwind northwest of Novarupta, 

near Lethe Hills at west margin of VTTS ....................................................................................72

46. Flow unit of ignimbrite Package 9 (lower left), its lateral margin exposed in 

cross section, near upper Knife Creek just downstream from Glacier 4..............................73

47. Photograph and annotated sketch of section in gulch ~1.1 km southeast 

of Novarupta dome, illustrating proximal intercalation of Episode II–III 

fall units with several thin pyroclastic density current (PDC) deposits ................................75

48. “S bed” atop the Turtle, ~600 m northeast of Novarupta dome.....................................................76

49. Structureless white fine ash, 20 cm thick, at Brooks Camp, 49 km upwind 

northwest of Novarupta ................................................................................................................78

50. Stratigraphic sections in three confluent forks of gulch system adjacent 

to east side of Falling Mountain, ~1.2 km south of Novarupta, illustrating complex 

ultraproximal deposits investigated in detail by Houghton and others (2004) .....................79
x

51. Grain size characteristics of the pyroclastic density current deposits 

(PDCs) intercalated ultraproximally with Episode II and III fall deposits 

within 1-3 km from Novarupta dome...........................................................................................80

52. Interbedded deposits of pyroclastic density currents (PDC) and 

pale-gray plinian dacite fallout on southeast spur of Baked Mountain, 

1.4 km northwest of Novarupta dome and ~100 m above 

floor of Novarupta basin ...............................................................................................................81

53. Cartoon illustrating four eruptive regimes capable of simultaneous operation from a 

sustained plinian column ..............................................................................................................82

54. Block of massive breadcrusted dacite on slope just northwest 

of rhyolitic Novarupta dome.........................................................................................................83

55. Novarupta and its ejecta ring ..............................................................................................................84

56. Vertical view (from tightly banking helicopter) of Novarupta dome, 65 m high, 

nearly circular in plan view, and 380 m across .........................................................................85

57. Flow foliation in Novarupta lava dome...............................................................................................85

58. Dispersal and thickness of 1912 fallout layers compared to those of a few 

other well-studied eruptions ........................................................................................................89

59. Variation of CaO, Al2O3, and TiO2 versus SiO2 content for ~265 samples of 1912 Novarupta 

pumice and dome lava ..................................................................................................................92

60. Eruptive sequence of June 1912, showing estimated timing and magma volumes of eruptive 

units, magnitudes (Ms) of earthquakes accompanying caldera collapse, stratigraphic 

positions of main mud layers ejected from collapsing caldera, intervals of ashfall at 

Kodiak, and fluctuating proportions of rhyolite, dacite, and 

andesite pumice that erupted concurrently ..............................................................................93

61. Banded pumice clasts from VTTS ignimbrite....................................................................................94

62. Block of recycled welded ejecta near Novarupta dome ................................................................95

63. Block of recycled welded ejecta ~1 km from Novarupta dome.....................................................95

64. Main VTTS ignimbrite banked against cross-valley moraine ~2 km 

northeast of Three Forks, 16 km from vent at Novarupta ........................................................99

65. Extreme development of diffuse lamination in distal VTTS ignimbrite 

~1 km upvalley from cross-valley moraine and 15 km from Novarupta ................................99

66. Diffuse layering in distal VTTS ignimbrite where it banks against 

moraine 16 km from Novarupta..................................................................................................100

67. Boundary between ignimbrite Packages 6 and 3 just east of Three Forks................................100

68. Classic flow-unit contact in nonwelded ignimbrite on left 

bank of Knife Creek just above Three Forks ............................................................................101

69. Jointed ignimbrite, sintered and vapor-phase indurated along Juhle fork, at northeast edge 

of VTTS ~600 m downstream from mouth of side valley where stream 

enters valley-filling tuff................................................................................................................102

70. Aerial view southeastward over Novarupta toward Trident and Mount Katmai......................103

71. View southwestward across Novarupta rhyolite dome from 

crest of Turtle to truncated face of Falling Mountain dacite dome, 

a distance of ~2.2 km ...................................................................................................................104

72. Mount Cerberus, late Pleistocene dacite dome, 1,500 m across and 360 m high, at foot of 

2,165-m Mount Mageik compound dacite stratovolcano......................................................106

73. Scarp of Whiskey Ridge, 400 m high, and panorama along Knife Creek arm of 

VTTS toward ignimbrite terminus 23 km away........................................................................106
xi

74. Aerial view of VTTS downvalley from above its narrowest reach (3 km wide), 

extending ~11 km to Ukak lobe terminus at foot of Mount Katolinat...................................107

75. Ignimbrite margin at southwest corner of VTTS, where tuff banks against 

Buttress Range adjacent to West Mageik Lake......................................................................108

76. Top of main VTTS ignimbrite (Package 4) wedging out against 

cross-valley moraine east of Three Forks................................................................................109

77. Thinly laminated ignimbrite on gorge wall of “Moraine Creek” just upstream 

of cross-valley moraine in northeastern part of VTTS...........................................................110

78. Ukak lobe terminus of ignimbrite at foot of Mount Katolinat, ~20 km 

from Novarupta.............................................................................................................................110

79. Distal ignimbrite exposure, ~7 m high, on wall of lower “Moraine Creek,” 

~18 km from Novarupta and 2 km east of Three Forks, showing 

contact of rhyolite-rich Package 4 overlain by compositionally 

heterogeneous Package 6..........................................................................................................113

80. Meter-scale distal flow units that developed near Ukak River 

terminus from what had been thick massive ignimbrite just upvalley ................................115

81. Lethe Hills: primary relief on Episode I ignimbrite surface draped 

by pale-gray stratified dacite fallout of Episodes II and III ...................................................115

82. “High sand mark”—ignimbrite bench along Buttress Range margin north of 

West Mageik Lake........................................................................................................................116

83. Fissured and faulted hingeline of the bench ~1 km north of West Mageik Lake 

seen in figure 82............................................................................................................................117

84. Overview of Fissure Lake....................................................................................................................118

85. Thin runup fringe of pink rhyolite-dominant ignimbrite along Buttress Range margin at 

narrowest part of VTTS, 11–12 km from Novarupta ...............................................................119

86. Close-up view of 15-cm-thick pink ignimbrite runup along Buttress Range margin, 

as viewed in figure 85..................................................................................................................120

87. Nonwelded ignimbrite that filled pre-1912 course of Windy Creek, forcing stream 

to incise new channel (toward left) through hyperconcentrated sandflow 

deposit of latest Pleistocene Lethe assemblage ....................................................................120

88. Gorge along mid-valley fork of Knife Creek (see fig. 74),

 ~10 km from Novarupta ..............................................................................................................121

89. Former natural bridge in partially welded tuff along main fork of Knife Creek, 

7 km north of Novarupta..............................................................................................................121

90. Block of vitrophyric welded tuff, 56 cm long, atop north ridge of Mount Cerberus, 3 km 

southwest of Novarupta and ~250 m above valley floor........................................................122

91. East Mageik Lake and fissured welded ignimbrite of Package 8, which banked against 

glacier that occupied lake basin in 1912 ..................................................................................123

92. Southwest margin of VTTS viewed eastward from crest of Buttress Range............................124

93. Breadcrusted block of sintered, oxidized, vapor-phase indurated 

bulk ignimbrite ejected by phreatic explosion along trough of former 

Fissure Lake...................................................................................................................................125

94. Floor of Fissure Lake............................................................................................................................126

95. View eastward across Knife Creek Glaciers 1, 2, and 3, all heavily 

ash-covered except in upland cirques where ice has cleared in a century of 

accumulation and flow............................................................................................................... 127

96. Conceptual cross section, to scale, of Novarupta vent area.......................................................129
xii

 97. Aerial view east-northeastward over Novarupta dome and its ejecta ring,

 which rises to form the Turtle on far side................................................................................130

 98. Stratified fall deposits that form inner south wall of ejecta ring 

only 25 m from margin of Novarupta dome..............................................................................132

 99. Extensional faults atop the Turtle....................................................................................................134

100. Mount Katmai beheaded ..................................................................................................................136

101. Southwestward aerial view of Mount Katmai caldera with ignimbrite-filled 

upper VTTS at right ......................................................................................................................137

102. Mount Katmai before and after the caldera collapse of 1912....................................................138

103. Aerial view northwestward over Katmai caldera and down 

ignimbrite-filled VTTS, terminus of which is 29 km 

from center of caldera.................................................................................................................138

104. Cumulative seismic energy release (in Joules) during June earthquake sequences 

accompanying caldera collapse at Katmai in 1912, Pinatubo in 1991, 

and Fernandina in 1968................................................................................................................139

105. Variation with distance from source of average maximum sizes 

of lithic fragments expelled concurrently from vents 

at Novarupta and Mount Katmai ...............................................................................................140

106. Hydrothermal explosion breccia as thick as 12 m on 

northwest rim of Katmai caldera ...............................................................................................141

107. Sketch of stratigraphic relations on northwest rim of Katmai caldera, 

showing breccia and mud layers expelled during caldera collapse 

and intercalated within the regional pumice-fall sequence from Novarupta....................142

108. Lethe arm of VTTS..............................................................................................................................144

109. Fumarolic fissure in welded tuff on southwest bench of Baked Mountain .............................145

110. Fractures in sintered ignimbrite that concentrated fumarolic 

emissions for about a decade after the eruption, 

leaching tuff of mobile constituents..........................................................................................146

111. Close-up view of fumarolically altered crack seen in figure 110...............................................147

112. Funnel fumarole in nonwelded ignimbrite east of 

Three Forks in lower VTTS..........................................................................................................148

113. Orifice of funnel fumarole in nonwelded ignimbrite just upvalley 

from cross-valley moraine in lower VTTS................................................................................148

114. Large focus of fumarolic alteration, 5–7 m wide, exposed on wall of 

River Lethe gorge, 12–15 m deep here, in lower part of central VTTS................................149

115. Natural cross section through hemicylindrical zoned fumarolic 

incrustations developed in dacite fall deposits, above a long-lived 

fumarolic fissure in underlying ignimbrite ...............................................................................150

116. Hemispherically zoned fumarolic incrustations formed in permeable 

dacite fall deposits directly atop sintered to partially welded ignimbrite ..........................150

117. Severe fumarolic alteration in sintered ignimbrite and overlying stratified dacite fall 

deposits exposed along River Lethe in upper Lethe arm of VTTS .......................................151

118. Orifice of fumarolic fissure vent near East Mageik Lake............................................................152

119. Advanced clay alteration along arcuate fissure system northeast of 

Novarupta dome (see fig. 97), where weak vapor emissions and near-boiling 

temperatures persist a century after the eruption .................................................................153

120. Katmai River pumiceous debris flow (lower right center) emerged from canyon fed by 

Metrokin Glacier on south slope of Mount Katmai.................................................................156
xiii

121. Katmai River pumiceous debris-flow deposit at its distal margin, 

where it overran willows and alders ........................................................................................157

122. Katmai River pumiceous debris-flow deposit (KRdf) resting on nearly 

complete Novarupta fallout section (Layers A–G) .................................................................158

123. Katmai Canyon landslide deposit....................................................................................................159

124. Hummocky avalanche deposit from slopes of Noisy Mountain that 

blocked upper Katmai Canyon and impounded upper Katmai Lake....................................160

125. Ash-dominant lacustrine and mudflat sediments deposited during 

first year or two after eruption and exposed along Griggs fork of 

Knife Creek opposite snout of Glacier 4 ...................................................................................161

126. Upright uncharred trees buried by ash-dominated debris-flow deposits 

as thick as 6 m, adjacent to Ukak terminus of ignimbrite, 20 km downvalley 

rom Griggs fork—the inferred source of the flows ................................................................162

127. Alignment of meter-scale blocks of welded tuff along northeast side 

of VTTS, interpreted as margin of flood flow across ignimbrite s

urface prior to incision of gorges that would have intercepted them.................................163

128. Griggs fork of Knife Creek.................................................................................................................164

129. One of ~60 phreatic craters rooted in ignimbrite and preserved along 

upper Knife Creek arm of VTTS..................................................................................................165

130. Surge-bedded deposits from phreatic explosion craters near confluence 

of main fork and Griggs fork of Knife Creek............................................................................ 166

131. View northwest down gorge of River Lethe, ~25 m deep, 

in central VTTS, ~4.5 km upstream from Three Forks ............................................................168

132. Braided Katmai River floodplain viewed south-southeastward 

from slope of Trident Volcano.....................................................................................................169

133. Ash-mantled snout of Knife Creek Glacier 1, 30–40 m high........................................................172

134. Katmai caldera, 4 km across at rim, viewed south-southwestward 

from helicopter in 1999 ................................................................................................................172

135. North and northeast wall of Katmai caldera viewed 

from southeast rim .......................................................................................................................174

136. Katmai caldera: North bench and Horseshoe Island ..................................................................175

137. Mud geyser with its own ejecta ring on northeastern floor of 

Katmai caldera when Yori and Fenner descended west wall in July 1923.........................176

138. View eastward of Katmai caldera floor mudflats from partway 

down west wall in July 1923, the only time the caldera was ever seen 

without a lake................................................................................................................................176

139. Crater floor of Mount Martin, where numerous fumaroles rich in 

sulfur gases and CO2 combine to produce prominent plume, 

which has persisted above cone since first reported in 1913 ..............................................181

140. Aerial view of ice-clad Mount Mageik toward south-southwest..............................................182

141. Trident volcanic group viewed northwestward from lower 

Mageik Creek near its confluence with Katmai River............................................................183

142. Southwest Trident in July 1979 (5 years after cessation of 

1953–74 eruptive activity), viewed eastward from glacier 

on Mount Mageik .........................................................................................................................184

143. Thick glassy rhyodacite lava capping southeast rim of Katmai caldera, 

draped by several meters of Novarupta fall deposits............................................................186

144. Aerial view of eastern flank of Northeast Katmai edifice 

looking northwestward ...............................................................................................................187
xiv

145. Southwestern inner wall of Katmai caldera from helicopter.....................................................189

146. Mount Griggs andesitic stratovolcano, highest peak in Katmai 

cluster at 2,332 m; aerial view northward across upper 

Knife Creek arm of VTTS .............................................................................................................189

147. Weight percent crystals versus whole-pumice weight percent SiO2 for 

~70 blocks of 1912 pumice and scoria ......................................................................................196

148. Compositional variations versus SiO2 content for ~265 samples of 

1912 Novarupta pumice and dome lava ...................................................................................197

149. Matrix glass compositions for three rhyolitic and two dacitic pumice clasts, visually 

homogeneous, determined by electron microprobe by Avery (1992)..................................198

150. Variation of Ba and Rb (in ppm) versus weight percent 

SiO2 for ~265 samples of 1912 Novarupta pumice and dome lava .......................................199

151. Variation of Sr and Zr (in ppm) versus weight percent SiO2 

for ~265 samples of 1912 Novarupta pumice and dome lava................................................200

152. Incompatible trace-element patterns for 1912 dacite and rhyolite, 

normalized to average primitive mantle composition of Sun 

and McDonough (1989) ...............................................................................................................201

153. Chondrite-normalized rare-earth-element abundances for 1912 pumice 

blocks and for high-purity matrix-glass separates thereof........................................................202

154. Values of 18O for coexisting quartz, plagioclase, orthopyroxene, and titanomagnetite 

separated from Novarupta lava and from individual 

pumice blocks of 1912 ignimbrite and fallout Layers A, C, D, and G.........................................206

155. Sr-isotope ratios plotted against reciprocal of Sr concentration (ppm-1), 

a convention that transforms a mixing hyperbola into a straight line......................................208

156. U-Th equiline diagram, combining Novarupta-Katmai data of 

Reagan and others (2003) and Turner and others (2010) for 33 samples.................................209

157. Summary of constraints on 1912 magma-storage conditions inferred 

from phase-equilibrium experiments of Coombs and Gardner (2001) 

and Hammer and others (2002), conducted on 1912 rhyolite and 

on end-member samples of the andesite-dacite continuum (ADC).........................................211

158. Katmai volcanic cluster magmatic plumbing system; schematic

illustration drawn to scale along N65oE volcanic axis, looking N25oW

 with no vertical exaggeration..........................................................................................................212

Tables

1. Physical data for Katmai cluster volcanoes...........................................................................................180

2. Compositional summary for 1912 eruptive products ............................................................................194

3. Comparison of some explosive eruptions...............................................................................................222
The Novarupta-Katmai Eruption of 1912—Largest Eruption 

of the Twentieth Century: Centennial Perspectives

By Wes Hildreth and Judy Fierstein

Abstract 

The explosive outburst at Novarupta (Alaska) in June 

1912 was the 20th century’s most voluminous volcanic eruption. Marking its centennial, we illustrate and document the 

complex eruptive sequence, which was long misattributed to 

nearby Mount Katmai, and how its deposits have provided key 

insights about volcanic and magmatic processes. It was one 

of the few historical eruptions to produce a collapsed caldera, 

voluminous high-silica rhyolite, wide compositional zonation 

(51–78 percent SiO2

), banded pumice, welded tuff, and an 

aerosol/dust veil that depressed global temperature measurably. It emplaced a series of ash flows that filled what became 

the Valley of Ten Thousand Smokes, sustaining high-temperature metal-transporting fumaroles for a decade.

Three explosive episodes spanned ~60 hours, depositing ~17 km3

 of fallout and 11±2 km3 of ignimbrite, together 

representing ~13.5 km3 of zoned magma. No observers were 

nearby and no aircraft were in Alaska, and so the eruption narrative was assembled from scattered villages and ship reports. 

Because volcanology was in its infancy and the early investigations (1915–23) were conducted under arduous expeditionary conditions, many provocative misapprehensions attended 

reports based on those studies. Fieldwork at Katmai was not 

resumed until 1953, but, since then, global advances in physical volcanology and chemical petrology have gone hand in 

hand with studies of the 1912 deposits, clarifying the sequence 

of events and processes and turning the eruption into one of 

the best studied in the world. To provide perspective on this 

century-long evolution, we describe the geologic and geographic setting of the eruption—in a remote, sparsely inhabited 

wilderness; we review the cultural and scientific contexts at the 

time of the eruption and early expeditions; and we compile a 

chronology of the many Katmai investigations since 1912. 

Products of the eruption are described in detail, including 

eight layers of regionwide fallout, nine packages of ash flows, 

and three lava domes that followed the explosive pyroclastic 

episodes. Changes in the proportions of coerupting rhyolite, 

dacite, and andesite pumice documented for the fallout and 

ash-flow successions, which are locally interbedded, permit 

close correlation of those synchronously emplaced sequences 

and their varied facies. Petrological correlation of the 

sequence of deposits near Novarupta with ash layers at Kodiak 

village, 170 km downwind, where three episodes of ashfall 

were recorded (to the hour), provides key constraints on timing of the eruptive events. 

Syneruptive collapse of a kilometer-deep caldera took 

place atop Mount Katmai, a stratovolcano centered 10 km 

east of the eruption site at Novarupta, owing to drainage of 

magma from beneath the Katmai edifice. Correlation of ~50 

earthquakes recorded at distant seismic stations (including 

14 shocks of magnitude 6.0 to 7.0) to fitful caldera collapse 

provides further constraints on eruption timing, because layers 

of nonjuvenile breccia and mud ejected from Mount Katmai 

during collapse pulses are intercalated with the pumice-fall 

layers from Novarupta. Structure of the Novarupta vent, a 

2-km-wide depression backfilled by welded tuff and inferred 

to be funnel-shaped at depth, is described in detail, as is the 

4-km-wide caldera at Mount Katmai. 

Discussions are also provided concerning: (1) the impact on 

global climate of the great mass of sulfur-poor but halogen-rich 

aerosol ejected into the atmosphere by the rhyolite-dominated 

eruption; (2) chemical and mineralogical effects of the fumarolic 

acid gases; and (3) the timing of several syneruptive landslide 

deposits sandwiched within the pumice-fall sequence. Secondary posteruption phenomena characterized include impounded 

lakes, ash-rich debris flows, phreatic craters on the ignimbrite 

sheet, responses of glaciers to the fallout blanket and to beheading by caldera collapse, growth of new glaciers inside the 

caldera, and gradual filling of the caldera lake.

Structure, composition, and ages of the several andesitedacite stratovolcanoes, closely clustered near Novarupta, all of 

which remain fumarolically and seismically active, are summarized. But among them only Mount Katmai extends compositionally to include basalt and rhyolite. The petrological 

affinities of 1912 magmas erupted at Novarupta with pre-1912 

Katmai lavas are outlined, and various chemical, mineralogical, 

isotopic, and experimental data are assembled to construct a 

model of preeruptive magma storage beneath Mount Katmai.

The monograph concludes by comparing the 1912 eruption with several other well-studied large explosive eruptions, 14 of them historical and 9 prehistoric. Finally, we 

retrospectively review the historical difficulties in understanding what had actually taken place at Katmai in 1912 and 

the century of progress in volcano science that has allowed 

most of it to be figured out.
2 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century:Centennial Perspectives

Campsite of Griggs expedition of 1917 on bench at north toe of Mount 

Cerberus. View to north-northwest down Lethe arm of the Valley of Ten 

Thousand Smokes. Photo courtesy of National Geographic Society.
Chapter 1

The 1912 Eruption and its Importance

The explosive eruptive sequence at Novarupta on 6–8 

June 1912 was the world’s most voluminous volcanic eruption 

of the 20th century (fig. 1), but its multifaceted significance for 

the developing science of volcanology involved far more than 

size alone. After summarizing the complex eruptive sequence, 

much of which was long misattributed to nearby Mount Katmai, we discuss how the 1912 events have remained scientifically important for 100 years and why the 1912 deposits 

continue in the 21st century to provide insights about volcanic 

and magmatic processes.

The first generation of posteruptive investigations of 

Mount Katmai, Novarupta, and the Valley of Ten Thousand 

Smokes was summarized in a splendidly illustrated book by 

Robert Fiske Griggs (1922), director of the 1915–1919 expeditions. The present volume is, in one sense, a sequel to Griggs’ 

book, updating a century of progress in learning how volcanoes work and in understanding, in particular, the complexities 

and wonders of the great eruption of 1912.

Overview of the Eruption

The greatest eruption of the 20th century began at 1300 

(Alaskan time) on 6 June 1912, continuing violently for ~60 

hours in three discrete explosive episodes (fig. 2) that produced ~17 km3

 of fall deposits and 11±2 km3 of ignimbrite, 

altogether representing ~13–14 km3 of zoned magma. The 

opening episode (I) released ~70 percent of the total volume, 

including plinian fallout Layers A and B and the main Valley 

of Ten Thousand Smokes (VTTS) ignimbrite (fig. 3), which 

were emplaced concurrently and have matching compositional zonation that extends from 100 percent rhyolite initially 

through to dacite-dominant with fluctuating fractions of andesitic scoria (fig. 4). The ignimbrite, which ranges from nonwelded to eutaxitic, was constructed during the first 16 hours 

by accumulation of nine compositionally distinct, sequentially 

emplaced flow packages.

Episode II began after a break of a few hours and produced 4.8 km3

 of dacite-dominant plinian fallout (Layers C 

and D), accompanied proximally by several sector-confined 

falls and small pyroclastic density currents. After another 

short break, Episode III produced 3.4 km3 of dacite-dominant 

plinian fallout (Layers F and G), accompanied proximally 

by several thin andesite-rich falls and pyroclastic density 

currents. All three explosive episodes issued from the 2-kmwide Novarupta depression (fig. 5), which is inferred to be 

a flaring funnel-shaped vent backfilled by welded Episode 

I ejecta and mantled by stratified deposits of Episodes II 

and III. Sometime after the final dust layer (Layer H) had 

settled, a dacite dome that plugged the Episode III vent was 

explosively destroyed and strewn about the depression as a 

block bed (Episode IV). It was subsequently replaced by a 

high-silica rhyolite dome (Episode V), slightly contaminated 

by andesite and dacite, the emplacement of which terminated 

the sequence.

Novarupta lies at the foot of an andesite-dacite stratocone group called Trident Volcano (figs. 5, 6), but the eruption broke out through horizontally stratified Jurassic marine 

sedimentary rocks. Caldera collapse at Mount Katmai, 10 km 

east of Novarupta, began around midnight, ~11 hours into the 

eruptive sequence, after escape of ~8.5 km3

 of magma. During the following 27 hours, fitful subsidence was accompanied 

by more than 50 earthquakes, of which ten were of magnitude 

6.0 to 7.0, and by phreatic ejections of hydrothermal mud and 

breccia that produced several circumcaldera layers intercalated 

with the contemporaneous plinian pumice-fall layers from 

Novarupta. No juvenile material erupted from Mount Katmai 

during formation of its kilometer-deep, 5.5-km3 caldera, but 

a small dacite dome extruded on the caldera floor sometime 

after the collapse. Modest earthquakes continued for months 

after the eruption ended.

Volcanological Significance of the 

1912 Eruption

The 3-day explosive eruption at Novarupta in June 1912 

was the world’s most voluminous volcanic event of the 20th 

century. For volcanologists and petrologists, it was also one 

of the most provocative. Long misinterpreted and in a region 

long difficult to visit, Mount Katmai and the Valley of Ten 

Thousand Smokes (VTTS) attracted rampant speculation but 

rather little fieldwork by experienced volcanologists, until 

1953. Since then, however, advances in understanding physical volcanology have gone hand-in-hand with numerous field 

studies, which have clarified the eruptive events and processes 

of 1912 and have turned the eruption into one of the most 

intensively studied in the world.
4 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Many aspects of the 1912 eruption made it extraordinary 

and of enduring interest: 

1. Its great volume, roughly 13 km3 of magma, places it 

among the five largest in recorded history. 

2. It was one of few historical eruptions during which a 

caldera collapsed. 

3. It was one of very few historical eruptions to eject voluminous rhyolite. 

4. The ashfall was global, an aerosol-dust veil was reported 

as far as the Mediterranean, and worldwide temperature 

depression was measurable. 

5. Pumiceous pyroclastic flows and pumiceous fallout were 

of roughly equal volume and were eventually shown to 

have been emplaced concurrently. 

6. The VTTS ignimbrite was the first large pumiceous pyroclastic-flow deposit of the scientific age to be emplaced 

on land. 

7. It was also the first known to have produced welded tuff. 

8. The eruptive products spanned a wide compositional 

range, with andesite, dacite, and high-silica rhyolite each 

representing an important proportion of the ejecta. 

9. Conspicuous and abundant compositionally banded pumice provoked speculative assimilation hypotheses, because 

such mingling had seldom been reported previously and 

magma mixing had not yet been widely recognized. 

10. “Ten thousand” fumaroles rose from the ignimbrite, 

and it took many years for observers to apprehend that 

the vapors owed their heat to the deposit, rather than to 

magma that was initially presumed to underlie all or much 

of the VTTS. 

11. High-temperature vapor transport of Fe, Pb, Zn, Cu, Sn, 

Mo, Mn, and other metals in halogen-bearing fumaroles 

and rapid precipitation of minerals containing such metals 

fascinated students of ore deposition. 

12. The eruption and caldera collapse were accompanied by 

extreme seismicity, later shown to include 14 earthquakes 

with magnitudes of 6.0 to 7.0. 

13. C.N. Fenner (1926) published analyses of 18 rocks from 

the Katmai region that became a focus of petrological 

debate (principally with N.L. Bowen) about the processes 

that produce magmatic diversity, particularly the relative 

importance of assimilation and fractional crystallization. 

Because Fenner’s suite included pre-Quaternary intrusive 

rocks as well as Pleistocene lavas and 1912 pumice, it was 

an inappropriate and unfortunate basis for that debate.

14. Lateral transport of magma to a vent some 10 km away 

from the site of caldera collapse raised as many questions 

as it solved. 

15. The major ignimbrite-producing episode and the largest 

of three plinian pumice-fall episodes were simultaneous, 

apparently at odds with the then-standard model of ashflow generation by column collapse (misinterpreted by 

many to imply column extinction). 

16. Two subsequent plinian episodes took place many hours 

after the large-scale ignimbrite emplacement, contrary to 

the expectations of conventional eruption scenarios.

17. Dispersal of plinian fallout was strongly eastward, reflecting the stratospheric jet stream, in contrast to more distributed dispersal from comparably great eruptions of the equatorial volcanoes, Tambora in 1815 and Krakatau in 1883. 

18. A high-silica rhyolite lava dome plugged the vent inside 

an ejecta ring composed of dacite and andesite. 

19. It became clear that the VTTS ignimbrite was not 

emplaced en masse but by a rapid succession of dozens 

of flow units, divisible into at least nine compositionally 

distinctive, mappable packages. 

20. Because the valley-filling ignimbrites were shown to have 

possessed neither great momentum nor high degrees of 

inflation during outflow, the VTTS came to be regarded 

as representing the low-energy extreme of a spectrum of 

ash-flow emplacement styles. 

21. Pioneering studies of melt inclusions in quartz from the 

1912 rhyolite provided insights about preeruptive magmatic conditions, helping initiate an expanding field of 

research on magmatic volatile contents. 

22. It surprised then-conventional petrological thinking that 

the 1912 high-silica (“minimum-melt”) rhyolitic magma 

contains quartz and plagioclase phenocrysts but lacks 

alkali feldspar. 

23. A compositional gap of ~8 weight percent SiO2 between 

1912 dacite and rhyolite stimulated a variety of models 

for the origin of such gaps, whether by secular crystal 

fractionation, by separation of rhyolitic melt from crystalrich intermediate magma, by partial melting of wall-rock 

granitoids, or by some independent origin of the rhyolite.

24. Application of the Fe-Ti-oxide geothermometer of Buddington and Lindsley (1964) yielded a thermal continuum 

for the 1912 andesite-dacite-rhyolite suite, despite the 

wide compositional gap, suggesting contiguity in the 

magma reservoir. 

25. Because the 1912 vent broke out through nonvolcanic 

basement rocks, any hydrothermal convection induced 

In later years, as more became known about the 1912 

deposits, additional extraordinary aspects attracted the attention of volcanologists: 
Chapter 1. The 1912 Eruption and its Importance 5

by the intrusive feeder beneath Novarupta would 

uniquely have a known age of initiation (1912). 

26. Because compensatory caldera collapse took place elsewhere and the Novarupta vent was cleanly reamed with 

only modest marginal slumping, complex pyroclastic 

deposits are preserved to within meters of the plug dome, 

providing virtually unique exposure of the ultraproximal 

products of high-energy sedimentation from the margins of 

a plinian jet and the lower part of its convective plume. 

27. Preservation of the vent structure, filled by its own ejecta, 

intruded only by the dome conduit, and reamed through 

horizontal Jurassic marine sedimentary rocks in a 3-day 

episode in 1912, provides an attractive target for geophysical investigation and scientific drilling; its relatively 

brief history offers insights about intrusion, decompression, degassing, fragmentation, and ejection of magma 

in a setting where the mechanical, chemical, and thermal 

consequences can be related to a short-lived episode.

Novarupta ash (1912)

Dawson

Juneau

Ketchikan

Anchorage

Cook Inlet

Shelikof Strait

Valdez

Chicken

Cordova

Seward

Seldovia

Port Graham

Homer

Kodiak

Unalaska

Dutch Harbor

Perryville

Aleutian Islands Alaska Peninsula

Vancouver 

Seattle Victoria

Kodiak

Island

Kenai Peninsula

Bristol

Bay

Fairbanks

Nome

120°

65°

55°

160° 140° ALASKA YUKON

Sitka

Novarupta

Aleutian Trench

0 1,000 KILOMETERS

0 400 MILES

500

200

Figure 1. Map of Alaska and adjacent North America, showing location of Novarupta, several geographic names 

mentioned in text, and region impacted by ashfall within a few days after 1912 eruption.
6 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

 upper B2

 No fall layer

 Hiatus

 Hiatus

 Hiatus

 lower B2

B1

B2

A

B3

C

D

E

F

G

H

{

Pkg 1

Pkg 4

Pkg 5

Pkg 6

Pkg 7

Pkg 8

Pkg 9

Pkgs 2+3

0600

2400

1800

1200

0600

2400

1800

1200

0600

6 JUNE

7 JUNE

8 JUNE

TEPHRA

FALL

LAYERS

HOUR OF ASHFALL

AT KODIAK

9 JUNE

2400

1800 ♦1700 

1300

ASH

FLOWS

Dora

sights column

♦0910 

☼2356 

♦1430

♦~1200 

Ash falls at Kodiak

collapse onset 

Ash falls at Kodiak

Ash falls at Kodiak

“Dawned clear”

at Kodiak

at Katmai

Episode I

Episode III

Episode II

♦

Figure 2. Generalized 1912 Novarupta eruptive sequence and chronology of ashfall recorded at Kodiak village, 170 km 

downwind. Four-hour offset at base represents time between initial sighting of eruption column by S.S. Dora and beginning of 

ashfall at Kodiak.
Chapter 1. The 1912 Eruption and its Importance 7

Figure 3. Aerial panorama of Valley of Ten Thousand Smokes, extending 20 km northwest from vent at Novarupta 

to ignimbrite terminus at base of Mount Katolinat. Baked Mountain (BM) and Broken Mountain (BR) are pumicemantled ridges of glaciated Jurassic siltstone that separate three arms of upper valley—River Lethe, Knife Creek, 

and a lesser valley between them. Ignimbrite surface slopes 1o-2o downvalley and is incised by several gorges 

as deep as 35 m. Scarps that truncate Broken and Falling Mountains define Episode I backfilled vent depression. 

Just beyond tip of Falling Mountain shadow (left center), where pumice-alluvial fan enters meandering gorge, tuff 

dips gently back toward Novarupta, owing to intravent compaction and welding, thus defining buried west rim of 

vent structure. Asymmetrical ejecta ring around Novarupta lava dome consists of products of eruptive Episodes 

II and III. Mount Griggs, upper right, is 2,330-m-high andesitic stratocone with several postglacial eruptions and is 

highest peak in district, 1,750 m above valley floor. Buttress Range and Mount Katolinat are subhorizontal siltstonesandstone strata of Jurassic Naknek Formation.

Figure 4. Representative pumices from 1912 eruption: White crystal-poor high-silica rhyolite, pale gray crystal-rich 

dacite, black crystal-rich andesite, and rhyolite-andesite banded pumice.
8 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Margot Creek

W

ni dy

Creek

1

2

3

4

3000

5000

Ikagluik Creek

Margot Creek

Windy

Creek

N

River Lethe

Knife Cree k

Ke

Kw 1

2

3

4

4

5

Te

Tsw

Tw

M a g

e i k

A

Martin

3000

5000

6000

4000

Griggs

Mt Juhle

Overlook

Hill

Mt Ikagluik

o

o

m

y

5000

6000

Angle Creek

VTTS

58°15'

58°20'

155°20' 155°10' 155°00'

Ukak

River

1000

MC

FM

LH

BM

KP

BR

WR

T

T I

KRdf

KC

NM

ML

hut

Camp IV

Island

Camp

Three

Forks

Martin Creek

Mageik Creek

Katmai River

Observation

Mtn

+

Mageik

Lakes

1

2

5

3

4

FL

JF

GF

Buttress

R

ange

Mt. Katolinat

X

X X

X

0 1 2 3 4 5 KILOMETERS

0 1 2 3 MILES
Chapter 1. The 1912 Eruption and its Importance 9

Figure 5. Simplified geologic map of Valley of Ten Thousand Smokes (VTTS) and volcanoes of the Katmai cluster. Contour interval 

500 feet (152 m). From hachured vent depression around Novarupta lava dome (N, black), Episode I ignimbrite (tan) extends northwest 

20 km along VTTS, as well as across Katmai Pass (KP) for 10 km down Mageik Creek on Pacific slope. Knife Creek Glaciers (blue 

pattern) are numbered 1-5; other glaciers are omitted for clarity. Alagogshak volcano (A), long extinct, is indicated only by its eroded 

crater. Mount Mageik consists of four overlapping centers (in shades of blue); only the youngest and easternmost center (for which 

individual lava flows are indicated) is Holocene. Mount Martin, entirely Holocene, consists of small fragmental summit cone and 

several overlapping coulees. Trident group consists of three Pleistocene cones, East Trident (Te), Trident I (TI), and West Trident (Tw), 

as well as historical Southwest Trident (Tsw) lavas and fragmental cone of 1953–1974; several peripheral Pleistocene lava domes, 

comagmatic with Trident, include Mount Cerberus (MC) and Falling Mountain (FM). Mount Katmai consists of two overlapping centers, 

Northeast Katmai (Ke) and Southwest Katmai (Kw), both truncated by 1912 collapse of hachured Katmai caldera, which is now partly 

filled by lake. Five youngest eruptive units of Mount Katmai are numbered (1–5) and discussed in chapter 12: 1, leveed dacite lava 

flows; 2, south-rim rhyodacite lavas; 3, zoned scoria fall atop unit 2; 4, dacite agglutinate sheet on caldera rim and correlative scoriaflow deposit at Knife Creek; and 5, Horseshoe Island dacite dome. Remnants of 22.5-ka plinian rhyodacite pumice-fall deposits (and 

ignimbrite) in Windy and Mageik Creeks (sites indicated by red X) are related to most evolved lava of unit 2. Products of Mount 

Griggs are subdivided by age into older (o, middle Pleistocene), middle (m, late Pleistocene), and younger (y, postglacial) exposures. 

Holocene debris-avalanche deposits are in bright yellow; those emplaced in 1912 are labelled: KC, Katmai Canyon landslide; KRdf, 

Katmai River pumiceous debris flow; ML, Mageik Landslide; NM, Noisy Mountain landslide. Uncolored basement rocks are Jurassic 

Naknek Formation or Tertiary porphyritic intrusions. Miscellaneous features: BM, Baked Mountain; BR, Broken Mountain; FL, site 

of Fissure Lake; GF, Griggs Fork of Knife Creek; JF, Juhle Fork of Knife Creek; T, Turtle; WR, Whiskey Ridge; hut, Baked Mountain Hut, 

research shelter; Island Camp and Camp IV were way stations between Katmai Bay and VTTS. 
10 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

ALEUTIAN TRENCH

6 cm/yr

Kodiak Island

Shelikof Strait

Seldovia

Homer

Iliamna

Redoubt

King

Salmon

The Gas Rocks

Ukinrek

Blue Mtn

Chiginagak

Yantarni

Kialagvik

Aniakchak

caldera

Gertrude

Creek

Dillingham

Cook

Inlet

Iliamna Lake

Becharof Lake

Bristol Bay

Kodiak

BRUIN BAY FAULT

158°

60°

58°

56°

156° 154° 152°

152o

P

Kj

A Mr

M

N

DP

T K S

F

Dg

DStKu KK

KF

KN

HB

KG

KM

IB

KB

KS

PU

PB

D2

Kaguyak caldera

Augustine Island

Mt

Griggs

Savonoski

cluster

Saddlehorn cluster

1

3

20

50

30

100

Afognak Island

Naknek

Nushagak

Kanatak

Cape

Uyak

KV

Kubugakli

Cape

Douglas

Kupreanof Strait

+

A

Naknek River

0 50 100 KILOMETERS

0 50 100 MILES

0 50

0 25 50 MILES

Figure 6. Location maps. A, Map of upper Alaska Peninsula and Kodiak Island group, showing many geographic locations 

mentioned in text and, in red, regional isopachs for total 1912 tephra-fall deposit (thickness contours in cm). Triangles indicate 

stratovolcanoes; hachured ovals indicate calderas. Abbreviations for volcanoes: A, Alagogshak; D, Denison; D2

, Devils Desk; 

Dg, Douglas; F, Fourpeaked; K, Katmai; Kj, Kejulik; Ku, Kukak; M, Mageik; Mr, Martin; P, Peulik; S, Snowy Mountain; St, Steller; T, 

Trident. Behind volcanic chain is Novarupta (N, black dot), vent site of 1912 eruption. The Savonoski and Saddlehorn clusters 

are rear-arc groups of small monogenetic cones, domes, and plugs described by Hildreth and others (2004). Abbreviations 

for other geographic features: DP, Dumpling Mountain; IB, Iliamna Bay; HB, Hallo Bay; KB, Katmai Bay; KF, Kaflia Bay; KG, 

Kaguyak Bay; KK, Kukak Bay; KM, Kamishak Bay; KN, Kinak Bay; KS, Kashvik Bay; KV, Katmai village; PB, Portage Bay; and PU, 

Puale Bay (called Cold Bay in 1912). At the Aleutian Trench, 350 km southeast of the volcanic line, the Pacific Plate subducts 

northwestward at 6 cm/yr. 

 B, Drainage system near Valley of Ten Thousand Smokes (VTTS, shaded); additional abbreviations here: B, Brooks Camp; BR, 

Brooks River; G, Mount Griggs; HP, Hagelbarger Pass; Kg, Kaguyak caldera; KjP, Kejulik Pass; KP, Katmai Pass; and YP, Yori Pass.
Chapter 1. The 1912 Eruption and its Importance 11

VTTS

154°

58°

58°15'

155°00' 155°30' 154°00'

155°

Rainbow River

Ikaglui k Creek

Iliuk Arm

North Arm

Lake Brooks

Uka k River

Katmai River

Katmai

Bay

Hallo

Kukak 

D2

Ku

St D

Katmai

caldera

T

M

Mr A

B

KP

YP

KjP

Kj

Kg

N

G

Shelikof Strai

Soluka

t

Creek

Hidden

Dakavak

Lake

Harbor

Geographic

Harbor

Snowy Mtn

Lake Grosvenor

Savonoski River

Alagogshak Creek

Barrier Range

Katmai

Lakes

HP

Noisy Mtn

Bay

Bay

Margot Creek

+

Savonoski

KV Takli

Island

58°30'

58°45'

Naknek Lake

Kejulik River

King Salmon River

BR

B

Becharof Lake

0 10 25 KILOMETERS

0 10 25 MILES

0 10 25 KILOMETERS

0 5 10 15 MILES

Figure 6 —Continued 
12 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Ashfall accumulation at Kodiak village, 170 km downwind from Novarupta, at the 

end of the 1912 eruption. Total deposit from three episodes of fallout at Kodiak 

during 6–8 June 1912 eventually compacted to a thickness of 25–30 cm. Photo by 

Wilbur J. Erskine, in charge of commerce at Kodiak.
Chapter 2. The Context of the 1912 Eruption 13

Chapter 2

The Context of the 1912 Eruption

In this section we describe where the eruption took 

place—in a remote, sparsely inhabited wilderness—and we 

provide synopses of the cultural and scientific contexts of the 

eruption and its subsequent investigations. These are followed 

by an overview of the geologic setting of the Katmai region, 

which completes the background information preparatory to 

launching into a detailed eruption narrative.

Geographic Setting

The Alaska Peninsula is the great 750-km-long arm 

that dominates the map of southwestern Alaska and extends 

southwestward into the Aleutian Islands chain (figs. 1, 6). 

From Cape Douglas to Becharof Lake, the Pacific half of the 

upper peninsula is a highland of basement rocks standing 

1,200 to 1,600 m above sea level, overlain by an ice-clad chain 

of active volcanoes and sculpted by active glaciers on both 

northwest and southeast flanks. Turbulent braided streams 

descend both flanks, those on the southeast side being much 

shorter and generally steeper than those to the northwest. The 

Pacific coastline is a rugged wonderland of narrow fjords and 

open bays with sandy beaches. The northwest half of the 

peninsula descends toward Bristol Bay through an ice-scoured 

hilly terrain of long spurs and outlying mountains of moderate relief and of large moraine-dammed lakes, merging into a 

broad coastal wetland of glacial and lacustrine deposits near 

sea level. The 1912 vent at Novarupta broke out at the head 

of a glacial valley, only 3 km northwest of the drainage divide 

along the volcanic axis, just north of Katmai Pass—one of the 

lowest saddles on the divide.

Novarupta is 450 km southwest of Anchorage, 250 km 

southwest of Homer, 170 km west-northwest of Kodiak, and 

100 km east-southeast of King Salmon, which is the nearest year-round town. Most of the 200-km-long reach of the 

peninsula from Cape Douglas to Becharof Lake lies within 

Katmai National Park and Becharof National Wildlife Refuge. 

Despite a few seasonal fishing and tourist resorts, most of 

the vast area is managed as wilderness and lacks either roads 

or permanent habitation. Access is by small boat or by float 

plane from King Salmon, where there is a regional airport.

The climate ranges from maritime to arctic-alpine. There 

are no weather records for the mountains, but long-term 

observations at King Salmon (near sea level in the Bristol Bay 

lowlands) yield average normal low and high temperatures of 

8oF and 22oF (–13oC and –6oC) in January and 46oF and 63oF 

(8oC and 17oC) in July. Average monthly water-equivalent 

precipitation is ~2.7 cm in January and 5.6 cm in July, but 

August is typically the wettest month, with an average of 7.5 

cm; the annual average is 50 cm (far below the average of 172 

cm recorded at Kodiak on the Pacific coast). Snow has fallen 

at King Salmon in all months except July and August and 

is, of course, far more frequent and severe in the mountains. 

Clouds and heavy morning fog are routine at King Salmon, 

which averages one clear day per month in summer and seven 

per month in January. Because the North Pacific storm track 

runs up the Alaska Peninsula, the region is exceptionally 

windy. At King Salmon, mean wind speed is ~18 km/hr every 

month of the year, and storm winds can reach 100-150 km/hr 

in the mountain passes.

Plant life in the treeless high country is limited to species resistant to cold, wind, and dessication—lichens and 

mosses, grasses and sedges, willows and dwarf birch, saxifrages, mountain sorrel, arnica, Oxytropis, and Dryas. In the 

lowlands, spruce forests are widespread, along with alder and 

willow thickets, grasses and sedges, fungi and mosses, and 

balsam poplar along streams. On the basis of three summers’ 

collections, Cahalane (1959) identified 273 plant species 

in Katmai National Monument. He also listed 117 species 

of summer birds, common among which are hawks and 

eagles, owls and ravens, ducks, loons, and grebes, geese and 

swans, gulls and shorebirds, woodpeckers and jays, grouse, 

thrushes, warblers, and sparrows. In high or open treeless 

country, one finds the raven and gyrfalcon, ptarmigan and 

snow bunting, Lapland longspur and rosy finch. Rare nests 

of Kittlitz’s murrelet were discovered in the VTTS by U.S. 

Geological Survey (USGS) geologists (Day, 1995).

Mammals include the wolf and wolverine, lynx and red 

fox, hares and lemming, ground squirrel and red squirrel, marten, 

mink, and weasels, porcupine and marmot, beaver, river otter, 

and muskrat, moose and caribou, and the preeminent brown bear. 

Furtive but abundant are shrews, mice, and bats. At the coast, one 

finds seals, sea lions, sea otters, and grey whales.

Cultural Setting: Katmai Before 1912

Native people of Eskimoan (not Aleut) linguistic, cultural, and ethnic stock had reached the upper Alaska Peninsula 

by ~10 ka and were distributed in a few villages and several 
14 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

seasonal camps on both sides of the mountain range when first 

contacted by Russian hunters and fur traders ~1750. The Russians reached Katmai village by 1782 and villages near today’s 

Naknek by 1791, and in 1784 they established headquarters 

on Kodiak Island. Savonoski had been occupied for several 

centuries by Alutiiq people related to those along Shelikof Strait 

and apparently hostile to the Aglurmiut people who had by 

1800 invaded the lower Naknek River and Bristol Bay from the 

north; Russian missionaries reached Savonoski by 1840 (see 

fig. 6). From the 1790s until the 1867 purchase of Alaska by 

the United States, the Russian American Company made Katmai village its principal trading post for the many small native 

encampments located on most of the coves and inlets along the 

rugged coast of Shelikof Strait. It ruthlessly organized most 

native men on both sides of the strait into annual hunting parties 

of hundreds of bidarkas (kayaks) in pursuit of sea otters and 

other marine mammals. The Alaska Commercial Company 

bought out the Russians in 1868 and had completed driving the 

sea otter to virtual extinction by 1900, after which the company 

declined. Its trading post at Katmai was neglected by 1906 and 

was certainly abandoned before the company sold its Kodiakbased holdings to Wilbur J. Erskine in 1911. Erskine took most 

of the photographs that documented the impact of the 1912 

eruption in and near Kodiak.

Traditionally, native economy had been based on hunting 

sea mammals, supplemented by hunting, fishing, trapping, and 

gathering shellfish, berries, and roots. Dwellings (barabaras) 

were semi-subterranean and sod-roofed, and seaworthy spruceframed sealskin bidarkas were built in great numbers. On 

the Naknek side of the divide, settlements were at key fishing 

locations, and the annual salmon run was critical for supplying 

fish to dry for the winter. The year-round village at Savonoski 

also relied on berries, bear, birds, and caribou; it was said that 

caribou were hunted in the valley that later became the VTTS.

By 1867, the natives were extensively Russianized 

culturally. Trading posts were central economically, priests 

were influential, chapels were built at Katmai and Savonoski, 

and most natives relied on Russian trade goods in exchange 

for furs and sea otter pelts. Unlike the Russians, the Alaska 

Commercial Company exercised no governmental authority, so leadership after 1868 reverted to local village elders. 

Depletion of sea otters by the 1890s impoverished the natives, 

many of whom became seasonal workers at fishing camps, 

salteries, and canneries, commercial enterprises that expanded 

rapidly after 1895. The cannery culture accelerated intermarriage among Alutiiq, Aglurmiut, Europeans, and Americans. 

The first cannery at Naknek opened in 1890. The town of King 

Salmon did not exist before construction of an Army Air Forces 

base there during World War II; the connecting road to Naknek 

was completed in the 1950s, and the base was closed in 1993.

Katmai village had a population of 457 in 1863. Its importance declined after the American takeover, but it still had 218 

residents in 1880 and 132 in 1890. Savonoski had a population 

of 162 in 1880 but only ~90 in 1912. Influenza contributed to 

the population decline of the late 1800s, and the pandemic of 

1918-19 again killed as many as half of the local population. 

The trail over Katmai Pass from Katmai to Savonoski had 

been a centuries-old link between the related peoples of the 

Shelikof coastline and the upper Naknek drainage. It became 

one of several alternative routes to Nome for gold seekers during the gold rush of 1899-1900, used especially in winter when 

sea and river routes were frozen. The U.S. Post Office provided 

mail service to western Alaska by way of Katmai Pass, using 

dogsleds in the winters of 1900–1902 and perhaps a bit longer. 

Savonoski and Katmai villages were both abandoned permanently in response to the eruption of 1912, as were numerous 

satellite villages and seasonal camps on both sides of the divide. 

Hussey (1971) and Dumond (2005) provide many details of 

the history and prehistory of the Katmai region, and their work 

formed the basis for the summary just made.

Cultural Setting: The World in 1912

Alaska was little known and almost mythical to most 

Americans in 1912. After its purchase from Russia in 1867, 

the inadequately explored region had been under the jurisdiction of the military and various Federal agencies. The U.S. 

Army, U.S. Coast and Geodetic Survey, Western Union, U.S. 

Geological Survey, and the Alaska Commercial Company 

contributed much to its exploration. By 1912, commercial 

fishing, canneries, and fur trapping had become important, 

replacing the hunting of dwindling marine mammals. Alaska’s 

population was ~50,000 in 1912, ~34 km2 per person territorywide. About 30,000 had come to Alaska in the Gold Rush of 

1899–1900. Congress reorganized Alaska as an incorporated 

Territory in 1912, roughly halfway between purchase and 

statehood in 1959. The first law passed by the Territorial legislature (1913) extended voting rights to women.

Travelers to Alaska in 1912 took the train to Seattle or 

San Francisco, where they could arrange transport on various 

commercial vessels, taking two weeks to Kodiak or a month to 

Naknek. The SS Dora, a mail steamer of the Alaska Commercial Company (and later of the Alaska Steamship Company), 

served coastal villages from Unalaska to Valdez for several 

decades and sometimes ran as far south as Sitka and Seattle; 

she transported mail, supplies, fishing and mining equipment, 

passengers, and cattle, and she played a key role in reporting 

the 1912 eruption. In 1918, the coastal passenger liner SS 

Princess Sophia ran aground north of Juneau and was lost with 

all 343 aboard, Alaska’s most deadly shipwreck.

The automobile was still a toy of the rich, but introduction of the Model T Ford in 1908 started its expansion into 

the middle class, culminating in a far more mobile society 

after World War I. The first modern electric traffic light was 

installed in 1912 (in Salt Lake City), and the Turkish Petroleum Company was founded in 1912 to exploit the oil reserves 

of Mesopotamia. Also in 1912, the United States issued its 

first postage stamp picturing an airplane, though commercial 

flight was still decades away. The first municipally owned 

streetcars began operation in San Francisco. In April, the 

RMS Titanic hit an iceberg and sank in the North Atlantic.
Chapter 2. The Context of the 1912 Eruption 13

In politics, 1912 saw the admission of New Mexico as the 

47th state and Arizona as the 48th. Also in 1912, the Massachusetts legislature enacted the first state law setting a minimum wage for women and children. Women’s suffrage was 

adopted that year by the voters of Oregon, Arizona, Michigan, 

and Kansas, which thus joined Utah, Idaho, Washington, and 

California, where women already had the vote; it was not made 

national until 1920 on ratification of the 19th Amendment. In 

1912, the “Bread and Roses” strike against the textile mills 

of Lawrence, Massachusetts, involved 20,000 workers and 

lasted for two months; Industrial Workers of the World (IWW) 

leadership appointed a strike committee with two members of 

every ethnic group in the mills and had its meetings translated 

into 25 languages. The successful strike defied assumptions of 

conservative unions that immigrant, largely female and ethnically divided workers could not be organized. Woodrow Wilson 

(Democrat) was elected president, beating Theodore Roosevelt 

(Progressive or “Bull Moose” Party), incumbent William Howard Taft (Republican), and Eugene V. Debs (Socialist). It was 

the “Progressive Era,” and three of the four main candidates 

advocated political and social reform, antitrust legislation, and 

more direct democracy. Alaskans were still half a century from 

being allowed to vote for president.

Internationally in 1912, Sun Yat-sen was inaugurated 

President of China, ending 2,000 years of imperial rule, and the 

Japanese Emperor Meiji died, ending the transformative Meiji Era. 

The British National Health Insurance Act took effect, requiring 

contributions from all wage earners and employers, and providing free medical attention and medicine as well as unemployment benefits. The Bolshevik faction led by Lenin split from the 

Russian Social Democratic Labour Party and printed the first issue 

of Pravda. Montenegro declared war against Turkey, starting the 

First Balkan War, and Bulgarian pilots soon performed history’s 

first aerial bombardment. The African National Congress was 

founded, 82 years before becoming the first postapartheid ruling 

party of South Africa. And the U.S. Marines invaded Cuba, Honduras, and Nicaragua (and in 1915, Haiti).

In the popular culture of 1912, Oreo Biscuits were 

introduced, Tarzan, Lord of the Apes was first published, W.C. 

Handy published the first “Blues” song (Memphis Blues), the 

mayor of Tokyo gave 3,000 cherry blossom trees to be planted 

in Washington, and the first annual “Cross-City Race” was run 

in San Francisco (renamed “Bay-to-Breakers” in 1965). Also 

in 1912, L.L. Bean opened in Freeport, Maine, and Fenway 

Park opened in Boston. Jim Thorpe won both the pentathlon 

and decathlon at the Olympic Games in Stockholm, where the 

host country refused to permit boxing.

In science in 1912, Alfred Wegener proposed the theory 

of continental drift, Max von Laue made the first observation 

of diffraction of X-rays by a crystal lattice, and Norman Levi 

Bowen joined the staff of the Geophysical Laboratory, beginning a fabled career in which he revolutionized petrology. 

Piltdown Man, famous “missing link” and paleontological 

hoax, was presented to the British Museum (but not exposed 

as a forgery until 1953). Robert Falcon Scott arrived on foot 

at the South Pole on 17 January, finding the tent of Roald 

Amundsen, who had reached the pole on skis 35 days earlier 

with five companions and 16 dogs. And the Hawaiian Volcano 

Observatory formally opened on the rim of Kilauea Caldera, 

largely on the initiative of Thomas A. Jaggar (professor of 

geology at MIT), who then served as its director for decades.

It can be added that during the 1915–1919 series of Katmai expeditions led by Griggs, many historic events took place 

elsewhere. The Mexican Revolution, the Armenian Holocaust, 

and World War I were ongoing. The year 1916 saw the Easter 

Rising in Ireland, creation of the U.S. National Park Service, 

election of the first woman to Congress, arrest of Emma Goldman for lecturing on birth control, and appointment of Louis 

Brandeis to the U.S. Supreme Court. The year 1917 saw U.S. 

intervention in World War I, the Balfour Declaration, and the 

Bolshevik Revolution. The year 1918 saw the Spanish Flu 

pandemic and the Armistice that stopped the First World War. 

The year 1919 saw the enactment of Prohibition in the United 

States, founding of the Fascist Party by Mussolini, the Paris 

Peace Conference, founding of the League of Nations, and the 

Versailles Treaty, terms of which ensured resurgence of populist nationalism in Germany, Yugoslavia, Iraq, and Palestine.

Scientific Context of the Early Katmai 

Investigations

The many publications of Griggs and Fenner made the 1912 

eruption famous, and their provocative interpretations attracted 

widespread skepticism and commentary. Difficulty of access, 

however, dissuaded scientific reinvestigation for another four 

decades. Their failure to understand fully what they observed is 

attributable in part to the unusual nature of the eruption, in part 

to botanist Griggs’ lack of geological experience, and in part to 

Fenner’s restless imagination, his compulsion to challenge orthodoxy, and his wistful hope that field observations could qualify or 

supplement the logic of Bowen’s petrological experimentation. 

(Bowen and Fenner were colleagues and rivals at the Geophysical 

Laboratory, which had been established by the Carnegie Institution 

in 1905.) Nonetheless, the insights and interpretations made by 

Griggs and Fenner, both mainstream scientists, were rooted in the 

scientific milieu, conventions, and ideas of their time. It may thus 

be useful to provide some background on the state of volcanological and petrological understanding during the decade of their field 

expeditions.

Microscopic petrography had long been sophisticated, 

and by 1912 bulk major-element analysis of igneous rocks was 

a thriving field. But little was known about magma sources, 

and awareness of plate tectonics and subduction lay a half 

century in the future (Yoder, 1993).

Influential books on igneous geology and petrology 

were published within a decade of the eruption by Alfred 

Harker (1909), Cambridge; Joseph Paxson Iddings (1909, 

1913), USGS, University of Chicago; and Reginald Aldworth 

Daly (1914), Harvard, all of whom were widely travelled 

experts. It was well known by then that most magmas are 
16 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

multicomponent aluminosilicate solutions, characterized by 

freezing-point depression, wide temperature ranges of crystallization, and orders of mineral crystallization that reflect 

pressure, temperature, and volatile content as well as bulk 

composition. Bowen’s experimental work was just beginning in the decade of the eruption, however, so many details 

of magmatic petrology remained nebulous and interpretations 

widely divergent. 

It was nonetheless already appreciated (by most petrologists) that dissolved water lowers magmatic viscosity and 

the temperature range of crystallization, that water is the 

dominant volatile component in most magmas, that much of 

the volatile content of a magma is lost on eruption, and that 

volatile retention under pressure at depth requires that plutonic crystallization extend to lower temperature than typical 

for extrusive equivalents. Although most geologists thought 

by then that silicic magmas crystallize at lower temperatures 

than mafic ones, the ambiguity of pioneering melting experiments and skepticism about inferences drawn from simple 

experimental systems left many unconvinced. Not until 1930 

was it proven that dry granite can melt at lower temperature 

than dry basalt, that its lower temperature range of crystallization is not solely dependent on magmatic volatile content, and 

that superheat is thus not required for basalt to remelt solid 

granite (Day, 1931).

Many had long inferred that basalts represent parental 

magmas globally, but only in 1916 did Arthur Holmes call 

basalts partial melts of peridotite, and not until 1928 did 

Bowen confirm that experimentally. Flux melting had been 

suggested but with no real notion of a volatile source nor any 

suspicion of subduction. Decompression melting was understood in principle, but presumption of a rigid earth prevented 

its acceptance until long after Holmes had proposed convective mantle upwelling in 1928.

Magmatic differentiation, the processes by which the 

great diversity of igneous rock composition originates, was 

then a key focus of research and debate. Iddings (1892) had 

summarized numerous potential alternative processes responsible for magmatic diversity.

Thoughts on more evolved magmas developed broadly 

along three lines—independent primary origins, assimilation 

of crustal rocks by basalt, or derivation from basaltic parents 

by liquid or crystal fractionation. Darwin made a strong case 

for the latter as early as 1844, suggesting both crystal settling 

and “straining” out the interstitial melt from crystal mush. 

Mixing of magmas was proposed by Bunsen as early as 1851 

and highlighted again by Harker (1909), but few had accepted 

it as common or important (Wilcox, 1999) by the time Fenner 

and Griggs neglected to invoke it for the banded pumice at 

Katmai. Several petrologists had proposed, nonetheless, that 

intermediate magmas in general were deep hybrids of independently generated mafic and silicic parents, although Iddings 

(1914) turned this around by arguing that the rhyolitic and 

basaltic extremes both differentiate from primitive intermediate parents, which he presumed fundamental to each region. 

Regional “petrographic provinces” had been discussed for 

decades by many petrologists, notably emphasizing distinctions between alkaline and subalkaline suites. 

Experimental petrology made great strides during the 

decade of the Katmai expeditions, principally at the Geophysical Laboratory, where phase-equilibria techniques were then 

being developed (Yoder, 2004). Bowen (1913) completed the 

phase diagram for plagioclase solid solutions and for numerous magmatically important binary and ternary systems during 

the following decade. Already in 1915, he argued that basalt 

is parental to most igneous rocks, that crystal fractionation 

controls differentiation, that assimilation is unimportant, that 

the Soret effect is negligible, and that experimental evidence 

was against a significant role for liquid immiscibility (Bowen, 

1915). At the time, most petrologists remained skeptical or 

reluctant to generalize his experimental inferences to igneous 

rock suites, particularly to voluminous continental granitoids 

(Holmes, 1916). In the communitywide debate that ensued 

in 1916, Fenner listened but remained silent (Yoder, 1992). 

Nonetheless, Fenner participated in the first experimental 

study of a hydrous system at elevated pressures and temperatures (Morey and Fenner, 1917), the first conducted above 

the critical point of water; they showed that mineral solubility increases with temperature, that water strongly lowers the 

melting point and viscosity of silicate magma, that crystallization of non-volatile-bearing phases raises system pressure, and 

that compressed vapor at high temperature readily transports 

chemical constituents of magmas. Such results certainly influenced Fenner’s later interpretations at Katmai.

Seismology had made major advances by 1912, but there 

was only one seismograph operating in Alaska at the time of 

the eruption. Although at least 30 Milne seismographs were 

by then distributed in Europe, Asia, Japan, Hawaii, North 

Africa, and North America (Abe, 1992), those closest to Katmai were at Sitka (Alaska) and Victoria (British Columbia). 

By 1912, studies of seismic-wave propagation had shown that 

most of the deep earth is solid, undermining age-old speculations about molten shells or global reservoirs of magma in the 

crust and mantle. Mohorovicic had discovered the seismic 

discontinuity defining the base of the crust in 1909.

As for volcanology in 1912, a fundamental distinction 

had been drawn between fissure and central-vent eruptions 

and among Hawaiian, Strombolian, Vulcanian, and Peléan 

eruption styles, and the importance of gas release for volcanic 

behavior was widely appreciated. It was generally acknowledged that vesiculation, fragmentation, and production of 

pyroclastic deposits owed to exsolution of water-dominated 

gas during shallow magma ascent. Harker emphasized the 

role of elevated viscosity for eruption of plugs, domes, and 

spines, and it was widely known that incandescent clouds 

(including pyroclastic density currents) are sometimes 

associated with such viscous extrusions. But there was little 

appreciation yet for the scale, abundance, nature, origin, or 

lithologic variability of ignimbrites. 

Large-scale stoping and assimilation of the sunken blocks 

at depth, as advocated by Daly (1914), was an idea adopted by 

Griggs for caldera formation at Mount Katmai. In the perennial 
Chapter 2. The Context of the 1912 Eruption 17

debate about the relative importance of magmatic differentiation versus assimilation, Daly had strongly favored the latter. 

He nonetheless postulated that differentiation accompanies and 

continues long after main-stage assimilation, and he accepted roles 

for fractional crystallization, assimilation of felsic wall-rock melts 

that ascend buoyantly within a chamber, expulsion of silicic melts 

from crystal mush, gaseous transport of some components, and 

liquid immiscibilty. Despite his broad perspectives, like others 

in his time, Daly greatly underestimated the abundance of silicic 

volcanic rocks, and he thus proposed that most volcanic rocks are 

mafic and most intrusive rocks granitoid. Noting that some large 

continental volcanoes are mafic, along with most oceanic volcanoes and most fissure-fed flood lavas, Daly inferred that basalt 

is the universal primitive magma and everything else derivative. 

Daly was also an advocate of the importance of sills and thus of 

lateral transport of magmas, perhaps in this respect influencing 

Fenner’s interpretation of the VTTS.

Pyroclastic density currents (pyroclastic surges and 

pyroclastic flows) were poorly understood during the early 

investigations at Katmai. Principal comparators at the time 

were the small-volume eruptions of May 1902—andesitic 

scoria flows generated by marginal collapse of a vertical 

column from the open crater of the Soufrière of St. Vincent 

(Anderson and Flett, 1903) and the nuée ardente generated 

by a sector-confined, laterally directed blast from an andesite 

dome in the crater of Mont Pelée, Martinique (Lacroix, 1904). 

At Krakatau, a more appropriate comparator for the 1912 

eruption, most of the 1883 flow deposits were underwater, and 

prevalent notions about the 1883 eruption (Verbeek, 1885) 

emphasized only its fall deposits, as was then likewise true for 

the 79 C.E. eruption of Vesuvius. Not until the 1930s did the 

volcanological community begin to appreciate the scale and 

eruptive style of ignimbrites and their abundance in continental volcanic belts worldwide.

Calderas also remained poorly understood, and there was 

no consensus on a collapse origin before the overviews by 

Reck (1928, 1936) and Williams (1941). Although Fouqué 

(1879) had made a strong case for subsidence of Santorini 

caldera, as had Verbeek (1885) for Krakatau, many still interpreted calderas as explosively excavated craters well into the 

20th century. As late as 1914, Iddings wrote that Krakatau 

had “blown up” in 1883. Tambora was a remote jungle island, 

little investigated. Clough and others (1909) had shown Glen 

Coe to be a subsided cylinder within a steep ring fault with 

felsic ring dikes, and they had compared it to the Askja caldera 

of similar size. For Mount Katmai, Griggs and Fenner thought 

partly in terms of explosive shattering of the edifice, although 

Griggs also speculated about magmatic stoping. Fenner’s recognition that the lithic ejecta were far from sufficient to match 

Katmai’s caldera volume may have helped lead to his radical 

hypothesis that the missing mass was melted, dissolved, or 

assimilated by the 1912 rhyolite magma.

Exothermic chemical reactions postulated to attend gas 

exsolution and shallow oxidation of magmas had a history dating back to Newton, so Fenner was hardly alone in proposing 

such reactions as the source of the excess heat that should be 

required for the 1912 rhyolitic magma to have assimilated solid 

andesite. Just earlier, Day and Shepherd (1913) had argued 

that such reactions made Kilauean magmas hotter, and Iddings 

(1914) agreed that they could be a “source of enormous volcanic energy.” Even Verbeek had suggested that “internal fusion,” 

wholesale remelting of the interior of the volcanic edifice, may 

have prepared Krakatau for caldera collapse.

Students of ore deposits and metallogenesis were by that 

decade generally agreed that most metallic ores were deposited 

by fluids, whether deep or shallow or at high or low temperature, that were heated by and in part emanated from igneous 

intrusions (Lindgren, 1913). Debate centered on what fractions 

of the fluids were meteoric versus magmatic and what fractions 

of the metals were recycled versus magmatically juvenile. Such 

uncertainties rendered the work of Allen and Zies on the VTTS 

fumarolic gases and precipitates of exceptional interest.

Institutionally, no national or state equivalent of the 

National Science Foundation existed in 1912, and university 

research budgets were lean or lacking. The Geophysical 

Laboratory was established in 1905 and the Hawaiian Volcano 

Observatory in 1911-12, organized and funded by exceptional 

individuals. The USGS had for 30 years supported research in 

geophysics and geochemistry, but on a modest scale without 

secure Congressional funding. Perret’s monitoring of eruptions at Pelée and Vesuvius were largely self-supported. It fell 

to the Research Committee of the National Geographic Society to sponsor Martin’s trip to Katmai in 1912 and the Katmai 

expeditions led by Griggs in 1915–1919.

Geologic Setting of the Katmai Volcano 

Cluster

The Quaternary volcanic chain of Katmai National Park 

is the most tightly spaced line of stratovolcanoes in Alaska 

(figs. 5, 6). Mount Katmai lies midway along a 95-km-long 

linear reach of the arc that extends from Devils Desk to Kejulik 

Volcano. Crater-to-crater spacing between adjacent (commonly contiguous) edifices here is typically 5 km or less. The 

frontal volcanoes of the arc segment are constructed along the 

preexisting rangecrest (the Shelikof Strait-Bristol Bay drainage 

divide), where the prevolcanic basement reaches elevations 

of 1,200 to 1,600 m. Because the volcanic summits reach 

1,830 to 2,290 m and lie in a region of high precipitation, all 

centers on the main chain are extensively ice-covered, as (to 

a lesser degree) is 2,330-m Mount Griggs, highest peak in the 

region but 12 km northwest of the frontal axis. Several rear-arc 

volcanoes lie 11 to 22 km behind the front (Hildreth and others, 

2004), all of them monogenetic except Mount Griggs.

 Beneath the Katmai volcanic cluster and adjacent to 

the VTTS, exposed basement rocks belong exclusively to 

the Late Jurassic Naknek Formation, which here averages 

1,700–2,000 m thick (Detterman and others, 1996). The 

Naknek Formation strata consist here of subhorizontal to 

gently warped marine siltstone, arkosic sandstone, and lesser 

lithic wacke and conglomerate that represent marine shelf, 
18 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

submarine fan-delta, and channelized prodelta slope facies of 

a forearc basin. Ranging in age from Oxfordian to Tithonian, 

they are thought to have been deposited synorogenically during crustal shortening and exhumation of the adjacent Jurassic 

batholith (Mullen, 1987; Trop and others, 2005). Although 

underlain regionally by an additional 3,500 m of Triassic and 

Jurassic sedimentary strata (Detterman and others, 1996), 

the Naknek Formation supplied all the nonvolcanic lithic 

fragments ejected at Novarupta in 1912, including sparse 

granitoid cobbles from its conglomerate members. Between 

Naknek Lake and Shelikof Strait, the Naknek strata are 

intruded by about 20 dioritic to granodioritic Tertiary plutons 

(Riehle and others,1993). 

The Mesozoic sedimentary rocks upon which the volcanic centers are built belong to a tectonostratigraphic package 

commonly called the Peninsular terrane, which is thought to 

have originated far to the south and to have been added to 

southern Alaska in middle or late Mesozoic time (Plafker and 

others,1994). The Mesozoic strata are altogether as thick as 

8,500 m and range in age from Late Triassic to Late Cretaceous; their base is nowhere exposed, although an islet of 

Permian limestone crops out near Puale Bay (Detterman and 

others, 1987, 1996). Tertiary volcanic-arc rocks have been 

eroded from the highland beneath the Katmai volcanic chain, 

but they are preserved outboard along Shelikof Strait as an 

800-m-thick section (Riehle and others, 1993) ~30 km wide 

that extends 60 km northeast from the Barrier Range at Katmai 

River to beyond Kukak Bay.

Crustal structure in the Katmai region is poorly known, 

and the nature of the basement under the subhorizontal 

Mesozoic marine section south of the Bruin Bay fault (fig. 

6) remains particularly uncertain. Alaska Peninsula crust is 

thought to be 30–36 km thick farther to the northeast (Moore 

and others, 1991), as well as near the southwestern extremity 

of the peninsula (Fliedner and Klemperer, 2000). Although 

the forearc and the subarc lower crust may be unusually mafic, 

having atypically high seismic velocities for normal continental crust (Fliedner and Klemperer, 2000), the many Tertiary 

granitoid plutons in the Katmai district indicate that much of 

the subarc crust here has become effectively continental. 

The Aleutian trench (5–6 km below sea level) lies 350 

km southeast of the Katmai volcanic front. Eocene seafloor is 

now being subducted there, nearly orthogonally, at a convergence rate of 6 cm/yr. The inclined seismic zone is well 

defined and 20 to 30 km thick (Kienle and others, 1983; Page 

and others, 1991). It dips only about 10 ̊ NNW for some 300 

km, then steepens to about 45 ̊ beneath the present-day arc, 

and persists behind the arc front to depths as great as 200 km. 

The top of the seismic zone lies about 100 km beneath the arc 

front near Mount Katmai, but it shallows northeastward to ~85 

km beneath Devils Desk, and it may deepen slightly along the 

front to the southwest (Kienle and others, 1983). 
Chapter 3

1912 Eruption Narrative: What was Actually Recorded in 1912

Before discussing the history of investigation and interpretation of the 1912 eruption and our own detailed characterization of the deposits and eruptive processes, it is appropriate to 

summarize what was actually reported by observers and instruments in 1912. All times cited are local Alaskan time in 1912. 

We call attention to what appear to be uncertainties, discrepancies, or yarns. Primary sources are largely Perry (1912) and 

Martin (1913), who interviewed and quoted many observers.

Chronology of Observations in 1912

1 June

Seismicity began? Martin (1913) stated (without citing 

his source) that earthquakes were felt at Katmai village “for at 

least five days prior to the eruption.” As there were no seismic 

instruments within 1,000 km of Katmai in 1912, no earthquakes were recorded instrumentally until the first of many at 

0508 on 6 June.

4 June

Severe earthquakes were felt at Kanatak, Uyak, Nushagak, and Katmai village. The only two families (six people) 

present at Katmai village evacuated, paddling down the coast 

toward Cold Bay (now called Puale Bay). It was inferred 

that their departure was prompted by the earthquakes. By 

June, most Katmai residents were away at Kaflia Bay and 

Cold Bay, fishing either privately or as employees of commercial fish camps. Most were probably at Cold Bay, 

explaining why the six evacuees headed that way two days 

before the eruption.

5 June

Severe earthquakes were felt at Kanatak, Uyak, and 

Nushagak.

6 June

Morning.—Explosions were reported, but only at Nushagak and Seldovia. At Seldovia they later became louder and 

more frequent, continuing all day. At least eight earthquakes 

(Ms 4.8–5.5) were instrumentally recorded remotely (and relocated by Abe, 1992) in the interval between 0508 and 1229, 

before the first sighting of the eruption plume at 1300.

1300.—A great explosion and earthquake were reported 

at Cold (Puale) Bay. The mail steamer Dora first viewed the 

eruption cloud at 1300, immediately after hearing a detonation. Captain C.B. McMullen reported that the Dora had left 

Uyak at 0830 and steamed up Shelikof Strait “in fine clear 

weather,” seeing no plume until entering Kupreanof Strait at 

1300, when he sighted a “heavy cloud of smoke” over Mount 

Katmai 55 miles (88 km) astern (Martin, 1913). First seen 

was an immense column ~1 km in diameter that was soon 

obscured by the dark ash cloud expanding above it. The ash 

cloud was overhead by 1500 (or 1600), ashfall began on the 

ship ~1800, and the vessel was enveloped in darkness soon 

after 1830. The ash raised the temperature on deck perceptibly, and the heavy, sultry, dust-filled air became stifling. 

Rather than risk landing at Kodiak, McMullen headed out to 

sea. He said that thunder and lightning had begun early in the 

afternoon and that helpless “birds of all species kept falling on 

the deck,” floundering and crying wildly.

1500.—A great explosion was heard for hundreds of 

miles around, as far as Juneau and Fairbanks. Detonations 

were first noted at 1900 at Cordova but as early as 1430 at 

Chicken, where they continued until 0600 on 9 June, sometimes in quick succession, sometimes at longer intervals. 

Griggs wrote that the three most violent of many reported 

explosions took place at 1500 and 2300 on 6 June and at 2240 

on 7 June. The most distant reports were from Dawson (1,050 

km) and Juneau (1,200 km). No explosions, however, were 

recorded at Kodiak, even during the interval before arrival of 

the ash cloud in late afternoon, after which thunder might easily have been confused with detonations.

1530.—Ashfall began at Uyak.

1600.—Captain K.W. Perry, aboard U.S. Revenue 

Service cutter Manning, already moored at Kodiak in clear 

weather, “observed a peculiar-looking cloud slowly rising 

to the southward and westward.” Distant thunder was heard 

soon after.

1700.—Light ash began falling at Kodiak and grew 

more severe by 1800, gradually increasing. Perry (1912) 

wrote that the “cloud bank had spread past the zenith when 

I observed another bank to the northward, and the two met 

about 30 degrees above the northern and eastern horizon.” 

There may thus initially have been two separate ash clouds 

spreading downwind at different altitudes on slightly different azimuths.
20 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

1900.—”A black night had settled down” at Kodiak, 

although long before sunset (Perry, 1912). Thunder and 

lightning had become frequent and at times very intense 

(unnerving to local people because normally rare in southern 

Alaska). Ball lightning was reported near the ground. Wireless apparatus on the Manning and at Woody Island naval 

wireless station nearby were rendered useless by the electrical 

conditions (severe static). Thunder and lightning diminished 

about midnight but continued intermittently until 8 June, when 

the fallout ceased. Sometime during the ashfall, the Woody 

Island station was destroyed by fire, presumed to have been 

caused by lightning.

2356.—The first major earthquake (Ms 6.5) was recorded, 

following the first 11 hours of the eruption, during which at 

least eight instrumentally recorded events (Ms 4.8–5.8) had 

taken place (1325 to 2253 on 6 June). This was soon followed 

at 0035 and 0223 (7 June) by earthquakes of magnitude (Ms) 

6.3 and 6.1, respectively.

The two native families who evacuated Katmai village on 

4 June were camped ashore somewhere near Cape Kubugakli 

at the start of the eruption. When they arrived at Cold Bay, 

people there saw rice-size pumice in their boat, and they were 

reported (third-hand) to have seen “the top of Katmai Mountain blown off.” If taken literally, this seems unlikely, because 

of the viewpoint from their campsite, the ashfall dispersal 

from Novarupta directly across Mount Katmai, and the timing 

of incremental collapse-related seismicity. 

A fourth-hand report that reached George Martin months 

later said that native residents of Savonoski had paddled 

away at the start of the eruption and, on reaching Naknek, 

reported “the upper half of Katmai Mountain gone.” The 

timing of their trip is poorly known, as is the location from 

which they might have seen Mount Katmai, which is not 

visible from Savonoski. How much of this testimony was 

later embellishment has never been clear. At Naknek in 1918, 

Paul Hagelbarger interviewed a Savonoski leader, who said 

that, in response to the earthquakes, he had been returning to 

Savonoski from a camp farther up the Ukak River when the 

eruption began. He spoke of hot ashfall and darkness while 

paddling down the lake to Naknek. His statement, later set in 

quotes by Griggs, that “fire came down the trail from Katmai” 

is likely to have been an inflated yarn. Decades later, his 

wife, who was born and raised in Savonoski, said most of the 

residents were already away working at the canneries; only a 

few remained at Savonoski, and she did not confirm that her 

husband, Petr Kayagvak (“American Pete”), had been among 

them. In 1923, Fenner met a prospector who said he had been 

at Savonoski when the eruption started, earthquakes were first 

felt, explosions were first heard, dust and darkness enveloped 

them, and the natives paddled away—all alleged to happen on 

the same morning. Inconsistencies with the regional record, 

conflict with other testimony, and conflation of all these 

phenomena to a single hour (“immediately”) make his story 

appear to be a latter-day concoction. In 1975, a National Park 

Service ranger interviewed a 68-year-old Perryville man, who

had lived as a child at Katmai village and had been at Kaflia 

Bay during the eruption; he stated that the Savonoski people 

(who included his relatives) had evacuated because of the 

earthquakes and that “they all move down to Naknek. They 

all ran away. Nobody left in Savonoski during that eruption” 

(National Park Service, 1975).

7 June

0300.— Ashfall began at Port Graham and Seldovia at 

the southwest end of the Kenai Peninsula. Light fallout continued there all day but without darkness, the main dispersal 

sector being farther south.

Dawn.—Ash was still falling at Kodiak. Out at sea, the 

Dora “cleared the black smoke” at 0430, “emerging into a 

fiery red haze, which turned into yellow,” and by 0600 ashfall 

ceased and the “horizon was perfectly clear from west to 

north” (Martin, 1913), although the ash cloud still filled the 

sky to the south and southwest.

Morning.—No ashfall had yet been reported (upwind) 

at Cold Bay, but “increasing noise of thunder and explosions, 

together with the growing violence of the earthquakes” drew 

attention to the great ash cloud to the northeast. Father Patelin 

at Kanatak (on Portage Bay) nonetheless reported dustfall in 

the morning and earthquakes nearly all day. Instrumentally 

recorded earthquakes before noon included a Ms

 6.5 event at 

0825 and two others, Ms 5.1 and 5.8.

0910.—After gradually diminishing since 0300, ashfall 

ceased at Kodiak. About 5 inches (13 cm) of ash had fallen 

there, forming the lower gray, coarsest layer (of three), fouling 

all the streams and wells, and prompting the Manning and 

another ship to furnish water to the local inhabitants.

1000.—People from Kodiak took shelter on the Manning

and in a warehouse on the wharf, the number rising the next 

day to 835; others arrived later from vessels, a salmon cannery, and Woody Island.

1200.—Ashfall resumed at Kodiak, increasing steadily 

in density until it was pitch dark by 1400, remaining so for 

the next 24 hours. Perry (1912) wrote that the ash now was 

“fine dust and flakes of a yellowish color,” and that sulphurous 

fumes were at times in the air. Avalanches of ash on nearby 

hills could be heard and “sent forth clouds of suffocating 

dust.” Crews worked vigorously with shovels and fire mains 

to clear the ship’s decks.

Noon.—Ashfall started near Cordova.

Evening.—At Kanatak, Patelin reported earthquakes so 

severe that barabaras were abandoned for tents and that the 

strongest earthquake yet was felt sometime after 2200, accompanied by heavy rumbling, rockslides all around, and a strong 

glare of light from the volcano. After midnight, there was a 

big noise like thunder, after which he went to sleep. 

2240.—Severe earthquakes were felt at Cold Bay. At 

Iliamna Bay, earthquakes persisted all night. The instrumentally recorded earthquakes relocated by Abe (1992) include 

events of Ms 6.0 at 2011, Ms 6.3 at 2049, Ms 7.0 at 2136, and 

Ms

 6.8 at 2248, as well as 11 others between Ms 5.4 and 5.9 
Chapter 3. 1912 Eruption Narrative: What was actually recorded in 1912 21

scattered between 1247 and 2029 on 7 June. These were soon 

followed by shocks of Ms 6.2 at 0029 and Ms 6.6 at 0300 on 

8 June, after which there was an apparent seismic lull of ~18 

hours until the next instrumentally recorded earthquake (Ms

5.4) at 2057 on 8 June.

8 June

0330.—The Dora reentered a “bank of volcanic ash” 

en route to Seward, having stopped under clear conditions at 

Seldovia at 2000 and Homer at 2300 the previous evening; 

by 0700 there was complete darkness again, which continued 

until 1600, when the ship emerged from the ashfall into “brilliant clear weather” (Martin, 1913).

Morning.—Two hours of darkness were reported in lower 

Cook Inlet, and ashfall continued all day at Seldovia, much 

heavier than the light ashfall there on 7 June. It was still dark 

at Kodiak.

1430.—Ashfall decreased at Kodiak, skies assumed a 

reddish color, and objects became dimly visible. Perry (1912) 

wrote that “seismic disturbances were still felt.” Ashfall 

“almost ceased” by late afternoon, and to this lull Martin 

attributed the top of the second ash layer, 4.5 inches (11.5 cm) 

thick and both browner and finer grained than the basal layer.

Evening.—Ashfall resumed at Kodiak, depositing the 

third and final ash layer, 1.5 inches (4 cm) thick, very fine 

grained, and light gray, and continued until an unrecorded hour 

that night. Following an 18-hour seismic lull, earthquakes 

resumed (less energetically) with instrumentally recorded 

events of Ms

 5.4 at 2057, Ms 5.1 at 2145, and Ms 5.6 at 2221.

9 June

0300.—A “dense cloud of dust came slowly” into Seldovia from the south. Ash fell from 0500 until nearly noon, 

causing a few hours of partial darkness. Accompanied by 

sulphurous fumes, fallout was heavier at Seldovia than on the 

previous days, “about 3⁄4 inch accumulating on the ground.” 

Intermittent explosions (or thunder?) continued to be heard 

there from the 9th through the 14th of June. Ashfall persisted 

at Seldovia until 13 June.

Dawn.—Ashfall had ceased at Kodiak and did not 

resume. Perry (1912) wrote that during “the 9th, 10th, and 

11th ...some substance was held in suspension, and at times 

the most unpleasant and strangling gases filled the air, making it difficult to breathe.” Wilbur J. Erskine, Alaska Commercial Company successor in charge of Kodiak commerce, 

took many photographs during the ensuing week—of the ash 

cover, slides and fans of remobilized wet ash, and collapsed or 

dislodged buildings.

Morning.—An “illuminated” funnel-shaped cloud was 

seen from Naknek and Iliamna, rising straight up before 

spreading into cloud banks at altitude. Only three instrumentally recorded earthquakes on 9 June were relocated to the 

Katmai area by Abe (1992)—events of Ms

 6.0 at 0714, Ms 5.7 

at 1138, and Ms 5.7 at 1210.

Evening.—Anne Olsen, an elderly refugee already suffering from tuberculosis and nephritis, died aboard the Manning

in Kodiak harbor, the only known death attributable to the 

1912 eruption (Hussey, 1971).

10 June

Three instrumentally recorded earthquakes took place 

here on 10 June—events of Ms

 5.1 at 0142, Ms 4.8 at 0200, 

and Ms 6.9 at 0606. Light ashfall was noted at noon at Tatoosh 

Island and also that day at Olga (both in Washington state).

11 June

Dustfall was noted at Dawson, Vancouver, Victoria, and 

Puget Sound. Atmospheric effects (haze, smoke, red twilights) 

had already been observed downwind, beginning in British 

Columbia on 6 June, Wisconsin on 8 June, Virginia on 10 

June, Algeria on 19 June, California on 21 June, and at various 

European locations starting 20–27 June (Kimball, 1913). Volz 

(1975a, b) later determined that mean atmospheric residence 

time of the aerosol was 9–12 months and that the main fraction that persisted for a year in the atmosphere was at altitudes 

of 15–20 km. In Seldovia and Cordova, acid rain caused painful burns, killed vegetation, and corroded metal on buildings; 

it tarnished brass and ruined linens on clotheslines as far away 

as Victoria and Puget Sound. Only one earthquake (Ms

 6.1) 

was recorded at Katmai on 11 June (Abe, 1992).

12 June 

About 2 cm of ash accumulated at Naknek, where (owing 

to wind direction) skies had remained clear during the eruption 

(Dumond, 2005). This and a second ashfall episode at Naknek 

on 15 June probably resulted from westward spreading of 

fine ash held aloft, perhaps augmented by ash associated with 

dome emplacement at Novarupta or Katmai caldera, phreatic 

plumes from the Katmai caldera floor or through the VTTS 

ignimbrite, or convective remobilization from ash-covered 

surfaces. Aeolian remobilization of fines from the VTTS during dry spells continues, a century later, to loft occasional dust 

clouds to elevations of thousands of meters. In 1912, dustfall 

was noted as far west as Nushagak later in the summer.

Summer

After the eruption, earthquakes were felt at Cold (Puale) 

Bay on 50 of the next 70 days through mid-August. According 

to Martin, they were “heaviest” on 8, 11, 13, 17, 21, 22, and 28 

June and on 4, 16, 21, 23, 24, 30, and 31 July. The most severe 

shocks felt there were said to be on 11 and 21 June and 30 July; 

the only one instrumentally recorded remotely, however, was that 

of 17 June, a Ms

 6.2 event at 0128. This was the final seismic 

event Abe (1992) was able to relocate to the Katmai area from the 

instrumental record. Dust remained in the air at Cold Bay until 

24 June, at times falling in sufficient amount to be seen on the 

ground. Griggs quoted the diary of C.L. Boudry, cannery agent 

at Cold Bay, who wrote of smoke, fumes, tremor, and shaking 

lasting all summer and an occasional roar or red clouds over the 

volcano. The earthquake at 1145 on 21 July was “hard enough to 

throw hat off table” and lasted 1–1.5 minutes. The same day
22 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Boudry wrote of “smoke from new crater like steam escaping 

or else light yellow” and “not a steady flow but puff every 2 

or 3 minutes.” He wrote (on 23 November) that he had tried 

three times to go to the volcano but was turned back each time 

by smoke and acid fumes that burned his hands and eyes. He 

added that dogs in Cold Bay were blinded by the acid.

12 August

From Takli Island, Martin (1913) saw “an immense column of steam ascending through the ordinary clouds” above 

the position of Mount Katmai (which was itself always in 

cloud during his expedition). While anchored there, he heard 

“an almost continuous roar.”

15 August

At the mouth of Katmai River, Martin (1913) saw the 

whole valley north of Katmai village “enveloped in a blue 

haze,” which by noon became so thick that visibility was limited. Acid rain stung the eyes and tarnished brass and silver. 

There were no earthquakes nor sounds from the volcanoes. 

Although even some of the trees had been killed at Katmai 

village, Martin encountered three dogs there that had survived 

the eruption and the summer-long desolation.

17 August

A sharp earthquake at Naknek upset lamps on the table.

20 September

Another strong earthquake was felt by Boudry at Cold Bay.

Environmental Impact of the Eruption

Beneath and adjacent to the ignimbrite in the VTTS 

and Mageik Creek, all living things were killed. Over a vast 

area, especially downwind to the southeast, pumiceous fallout 

blanketed shrubs and lesser vegetation, killing some of it right 

away. Trees, in general, were not killed by the fallout directly, 

but many subsequently died when partially buried by pumicerich alluvium, especially along the Katmai and Ukak Rivers 

(figs. 5, 6). Where fallout was less than ~1 m thick, many 

plant species were recovering well by 1915, as reported by 

Griggs (1917, 1918d) along lower Katmai River and Soluka 

Creek (figs. 5, 6), as well as on Kodiak Island. 

Intertidal organisms like barnacles, mussels, and kelp 

were killed from Katmai Bay to Afognak Island, in part by the 

abrasive action of floating pumice (Rigg, 1914). Land mammals were blinded by ash and acid rain and slowly starved, 

while birds and insects were exterminated outright. People 

on Kodiak Island suffered sore eyes and respiratory distress, 

and a few buildings collapsed (Griggs, 1918a, 1922); water 

was temporarily undrinkable. Seasonal settlements along the 

Katmai coast were evacuated and permanently abandoned, as 

were the villages of Katmai and Savonoski. Salmon populations dwindled in the principal fallout sector because of starvation, suffocation, and failure to spawn in ash-choked streams; 

because most salmon return to spawn in their fifth year, the 

run was lowest in 1916–1917, but it recovered well after 1920 

(Evermann, 1914; Eicher and Rounsefell, 1957). Acid aerosol 

remained perceptible in many Alaskan settlements for months, 

and the acid concentration in the 1913 ice layer on the Greenland icecap remained two-thirds as elevated as in that of 1912 

(Hammer and others, 1980).

Truly remarkable is the fact that the greatest eruption 

of the 20th century, as far as we know, killed no humans 

directly. A woman already suffering from tuberculosis and 

nephritis passed away aboard the Manning at Kodiak on 9 

June (Hussey, 1971), her condition probably exacerbated by 

ash-induced respiratory distress. Fewer than 200 people were 

displaced from their homes by the eruption, as the resident 

populations of the Savonoski area and the Katmai coast had 

each diminished to less than 100 by 1912 (Dumond, 2005). 

These impacts can be compared to those of the 1991 eruption 

of Pinatubo, which was comparable in size and style to that of 

1912—several hundred people dead and injured, mostly from 

roof collapse or lahars; >8,000 houses destroyed and ~75,000 

damaged; 50,000 people displaced and the livelihoods of two 

million (from 364 villages) severely impacted (Newhall and 

Punongbayan, 1996).

Recovery of Flora and Fauna

The ashfall generally did not kill underground parts of 

plants, so where fallout was thin or eroded, antecedent plants 

recovered quickly. True colonization of sterile inorganic 

ash surfaces, whether fallout or ignimbrite, was a far slower 

and site-restricted process. Around fumaroles in the VTTS, 

mosses and algae were conspicuous pioneers in 1917–1919, 

but they died of dessication or sandblast after extinction of the 

fumaroles. In 1919, most primary ash surfaces remained barren, and the most conspicuous pioneers on disturbed surfaces 

were lupines on hillslopes and grasses and sedges on ashchoked alluvial flats (Griggs, 1922). 

When he returned in 1930, Griggs (1933) found that little 

had changed except that extensive black mats of liverworts 

had pioneered some ashy surfaces. Cahalane (1959) reported, 

however, that most such mats had disappeared by 1953. Of 

major interest to Griggs was how soil forms from inorganic 

substrates and how nitrogen-fixation begins. Laboratory study 

of ash samples brought back in 1930 contained no fungi or 

actinomycetes, total bacteria counts very low relative to fertile 

soils, and no bacteria known to fix nitrogen, even beneath the 

liverwort mats; it was concluded that if any fixation of nitrogen was taking place in the VTTS ash, it could not be attributed to the microflora (Smith and Griggs, 1932). 

As of 2012, Griggs’ (1933) prediction of rapid revegetation in years to come has not been realized in the VTTS or on 

fallout-mantled terrain proximal to Novarupta. Farther than 

several kilometers from Novarupta, revegetation within the 

heavy fallout sector is unevenly distributed, depending principally on local erosion of the ash mantle, local exposure of 
Chapter 3. 1912 Eruption Narrative: What was actually recorded in 1912 23

pre-1912 substrate, and local stabilization of surfaces subject 

to aeolian or alluvial remobilization of ash and pumice.

In the VTTS, the principal obstacle to revegetation is 

persistent windscour and sandblast on the wide-open barren 

surface of the ignimbrite and on slopes mantled by coarse 

loose pumice. Along protected gullies and depressions, 

however, especially where sandy-silty substrate is available (either reworked ash or primary Layer H ashfall), many 

pioneering plant species have established a tenuous foothold. 

In 1953–54, Cahalane (1959) counted 35 such species in the 

upper VTTS, principally willows, sedges and grasses, wood 

rushes, horsetail, fireweed, mountain sorrel, snow pearlwort, 

and arctic poppy. In the upper VTTS in 1954, Cahalane 

surveyed six plots, each about 32 m by 16 m across, their 

corners marked by aluminum pipes, as a basis for long-term 

monitoring of revegetation. He photographed, described, 

and mapped the 1954 vegetation in all of them, three each 

in the Lethe and Knife Creek arms of the VTTS, but little 

followup work has been done. In the 1960s, Cameron 

(1970) sampled ashy surface “soil” at 10 sites in and adjacent to the VTTS; laboratory studies showed that the valley 

floor remained virtually sterile, with very low contents of 

organic matter, bacteria, algae, fungi, and nitrogen. As in the 

microbial ecology of extreme deserts, the limitation against 

establishing algal-lichen crusts in the VTTS is not moisture 

but, rather, porosity and instability of the substrate. And 

always the wind!

Mammals remain rare in the central and upper VTTS. 

Ground squirrels, hares, red fox, and mice are seen around 

the margins, and brown bears, wolverines, and moose occasionally cross Katmai Pass, typically in a hurry. By 1986, a 

porcupine had reached Baked Mountain Hut, and a mouse and 

a hare were seen at Novarupta, all far from food (and probably 

from survival).
24 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

C.N. Fenner, then 53, wading Mageik Creek en route to 

climbing the south slope of Mount Katmai to its caldera rim 

on 23 July 1923. Earlier that month, he and Charles Yori 

had ascended its west slope and became the only people 

ever to descend to the caldera floor, where the shallow lake 

seen in 1916–19 had temporarily been replaced by mudflats. 

Photo by Charles Yori.
Chapter 4. History of Investigations and Interpretations 25

Chapter 4

History of Investigations and Interpretations

We now summarize the 90-odd years of geological and 

geophysical research concerning the 1912 eruption and the 

volcanic system that gave rise to it. The chronological account 

that follows documents the succession of investigations, observations, and interpretations that bear upon the eruption itself 

and upon its products and the processes that affected them 

before, during, and after the eruption.

Chronology of Geologic Investigations 

at Katmai

1898

Josiah Edward Spurr (USGS party leader) left Savonoski 

village on 14 October, camped two nights in the valley of the 

later VTTS, crossed Katmai Pass on 16 October, and arrived at 

Katmai village on 17 October. Although there had been a few 

written accounts of crossing the pass between 1880 and 1898, 

Spurr’s general description of the geography and pre-eruption 

conditions were the first by a scientific observer. He noted hot 

springs at the south toe of Trident and introduced the name 

Naknek Formation for the principal basement rocks along the 

VTTS and Naknek Lake. Spurr was accompanied by Oscar 

Rohn and George Hartman (camp hands) and topographer 

William Schuyler Post, who made the first topographic map 

of the route. They were picked up by the steamer Dora at 

Katmai Bay on 31 October.

1908

A topographic sketch, Coast Survey Chart Number 

8555, of the Mount Katmai area was made by the U.S. Coast 

and Geodetic Survey, from a triangulation station at Cape 

Kubugakli, 15 km southwest of Katmai Bay. It was reproduced in part by Griggs (1922, p. 270–275) and by Fenner 

(1923, p. 8). There is no known photograph of Mount Katmai 

earlier than that taken by Griggs (1918e) in 1915.

1912

Eruptions at Novarupta 6–8 June. Initiation of the eruption column was witnessed from the Dora on Shelikof Strait in 

clear weather. Ashfall was reported across North America and 

as far as the Mediterranean. It was the world’s most voluminous eruption of the 20th century and the largest since that of 

Tambora in 1815.

George Curtis Martin (USGS), sent by the National Geographic Society to investigate the eruption, arrived at Kodiak 

in early July. Aboard a ship transporting refugees from 

mainland villages, he contacted most witnesses and compiled 

comprehensive accounts of the eruption impact, from Cape 

Douglas to Puale (then Cold) Bay and on Afognak and Kodiak 

Islands. Martin cruised the coast closest to Mount Katmai for 

two weeks in August and visited the site of Katmai village on 

13–16 August. The volcano remained in cloud all summer, 

but “an immense column of steam ascending through the ordinary clouds” was seen above Mount Katmai (Martin, 1913). 

Martin compiled a regional isopach map of total fallout and 

described three main layers of distal ashfall that fell during 

discrete intervals. He observed great fields of floating pumice.

1913

George B. Rigg (U.S. Bureau of Soils) cruised the coasts 

of Shelikof Strait in June and July, assessing the eruption’s 

impact on kelp and intertidal algae (mainly abrasion by floating pumice); he observed fields of pumice still floating as far 

as 241 km southwest of Katmai Bay.

Robert F. Griggs (Ohio State University botanist, attached 

to Riggs’ kelp expedition) studied the impact of ash burial 

upon onshore vegetation, mainly near Kodiak and Takli Bay 

(Griggs, 1918a, d).

William A. Hesse of Cordova and Mel A. Horner of 

Seldovia, hiking from Katmai village, failed in a June-July 

attempt to reach and photograph the eruption site. After defeat 

on the ash-covered approach to Mount Katmai, they went west 

to Martin Creek and obtained the first photograph (reproduced 

on p. 85 of Griggs, 1922) of a previously unmapped volcano, 

which Griggs later named Mount Martin.

1915

Griggs returned to Kodiak in June, sponsored by the 

National Geographic Society (NGS) with a $4,000 grant. He 

had been recruited by the NGS “out of the blue” in early 1915 

on the basis of his 1913 revegetation studies (Griggs, 1961). 

Surprised by rapid recovery of antecedent vegetation, Griggs 

chose to move his investigation of revegetation processes to 

more deeply buried areas closer to the volcano. Accompanied 

by Bentley B. Fulton (entomologist) and Lucius G. Folsom 

(Kodiak schoolteacher), Griggs landed at Katmai Bay 11 July 

1915; they hiked for a week up the east side of Katmai River, 
26 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

crossing ash-choked Soluka Creek with difficulty, naming the 

Barrier Range (which blocked their view of Mount Katmai), 

but failing to cross Katmai River (fig. 6) for lack of a rope. 

Camped 3 km below the mouth of Katmai Canyon, near the 

base of Mount Katmai, Griggs took the first photograph of 

beheaded Mount Katmai, noted the Katmai River debris flow 

(beyond the river), named Trident Volcano and Mount Martin, 

and noted steam plumes on Martin, Trident, and Mageik volcanoes. The party was picked up at Katmai Bay and returned 

to Kodiak the first week in August.

1916

Griggs, with Folsom, Donovan B. Church (photographer, 

Ohio State University student), and Walter Metrokin (packer), 

returned in July, again hiking up the east side of Katmai River. 

They based at what they called Island Camp (location shown 

in fig. 5) in the braided stream and (this trip carrying a rope) 

waded it below the mouth of Katmai Canyon. Their first ascent 

to the caldera rim on 19 July was up the south slope via the 

Katmai River debris flow, which Griggs recognized to postdate the stratified fallout and to contain uncharred wood. The 

second ascent was on 30 July up the southwest slope from the 

mouth of Mageik Creek canyon to the south-rim notch. Griggs 

reported a milky blue lake in the caldera with a horseshoeshaped island dome, a light-colored boiling upwelling, and 

many vigorous fumaroles all around the caldera floor margins. 

There were “two large bright-yellow spots of sulphur” low on 

the north wall (Griggs, 1922), but there was still no ice on the 

pair of benches where intracaldera glaciers later accumulated. 

On 31 July, Griggs and Folsom traversed Observation Mountain and ascended upper Mageik Creek to Katmai Pass (figs. 

5, 6). Lured on by fumaroles in the Pass, they discovered and 

named the “Valley of Ten Thousand Smokes” (VTTS) and 

hiked toward the lava dome (later named Novarupta). Griggs 

estimated that ~1,000 of the VTTS fumarolic plumes were more 

than 500 feet high. He misinterpreted the thin (by then fumarole-free) ignimbrite along Mageik Creek as a mudflow and 

the prominent crag (“tooth”) of rhyodacite lava in the caldera’s 

south-rim notch as a basaltic neck, but he correctly interpreted 

the Novarupta dome as a plug extruded within an ejecta ring. 

Lacking supplies for adequate further exploration, they returned 

to Island Camp, thence to Katmai Bay, waiting there 10 days for 

a boat to return them on 14 August to Kodiak (where Griggs’ 

family had awaited him for 5 weeks). Griggs began to plan and 

lobby for a major expedition the following year.

1917

Griggs returned, with a well-supplied party of ten (and a 

$12,000 grant from the NGS), basing for the first time at the 

west side of Katmai Bay on 15 June, relaying supplies up the 

west side of Katmai River via Martin and Mageik Creeks to 

the VTTS, and establishing three intermediate camps. Griggs 

crossed Katmai Pass with the packer Metrokin on 4 July and 

moved the whole party on 8 July to a camp on the bench north 

of Mount Cerberus (MC on fig. 5), where they remained well 

into August. Besides returnees Griggs, Folsom, Church, and 

Metrokin, the party included John Wesley Shipley (chemist), 

Clarence F. Maynard (topographer), James S. Hine (zoologist), 

Andrean Yagashof (packer), and Jasper D. Sayre and Paul R. 

Hagelbarger (botanical assistants from Ohio State University). Because Griggs, oddly, did not include a geologist, little 

geology was accomplished. In addition to general exploration of the VTTS, gas samples were collected by Shipley for 

analysis; a fine topographic map was surveyed by Maynard; 

Fissure Lake (FL on fig. 5) was named and photographed; and 

Katmai Canyon, Katmai Lakes (there were three at that time), 

and the Mageik Landslide on Martin Creek were investigated. 

Maynard, Griggs, and probably others climbed to the caldera 

rim from Camp IV (fig. 5) near the mouth of Mageik Creek 

canyon. The party was picked up by boat on 29 August and 

returned to Kodiak on 30 August.

Based on his 1917 observations and samples, Shipley 

wrote a (long overlooked) paper, published in 1920, about 

the fumarolic gases and the composition and mineralogy of 

their deposits. Unlike Griggs and Fenner, who speculated 

about hundreds of magmatic vents beneath the VTTS and 

who waffled about specific sources of the ignimbrite, Shipley 

stated flatly that the valley-filling flow deposit was “ejected by 

Novarupta volcano.”

1918 

Griggs’ plan for another large expedition was postponed 

owing to U.S. entry into World War I. Instead, he sent Sayre 

and Hagelbarger to pioneer a new route to the VTTS. After 

reaching Kodiak on 22 May, they shipped aboard the Dora via 

Dutch Harbor to Naknek, arriving 6 June. Ascent of Naknek 

River by motor boat, troubled by rapids, took them from 

9 June until 19 June. After climbing Dumpling Mountain 

(shown on fig. 6) for reconnaissance on 23 and 25 June, they 

reached the head of Naknek Lake on 26 June and hiked up the 

Ukak River to the VTTS on 27–29 June. They walked from 

their base camp across Katmai Pass all the way to Katmai 

Bay and back (1–8 July). From 13 July until 5 August, they 

recorded temperatures of VTTS fumaroles with pyrometers, 

measuring 86 vents hotter than 190oC and several hundred 

near the boiling point; 37 exceeded 290oC, 9 exceeded 390oC, 

and the hottest measured was 432oC. A mercury thermometer carried in 1917 had soon broken. Sayre and Hagelbarger 

noted a pre-1912 pumice-rich debris-flow deposit along lower 

Windy Creek (fig. 5), near the site where the 1912 ignimbrite 

had dammed what they called “Windy Lake” (which lasted 

only a few years). From 5 August to 17 August, they surveyed 

the Naknek Lake system and Naknek River while en route 

back to Naknek; eventually they shipped to San Francisco, 

arriving 22 September.

Katmai National Monument, to be managed by the newly 

established National Park Service (NPS), was created by 

presidential proclamation (under the Antiquities Act) on 24 

September 1918, in response to promotion by Griggs (1918b) 

and officers of the National Geographic Society. It may have 

helped that Secretary of the Interior Franklin K. Lane was on 
Chapter 4. History of Investigations and Interpretations 27

the NGS Board of Managers. The first “tourist” was Rodney 

L. Glisan, Portland (Oregon) attorney and a founding director 

of the American Alpine Club, who accompanied the Griggs 

expedition in 1919.

1919

Griggs, with a $35,000 appropriation by the Research 

Committee of the National Geographic Society, invited participation of Geophysical Laboratory scientists and outfitted an 

expedition of 19 men (fig. 7). Sayre returned via Naknek, 

assisted by three of Griggs’ students (A.J. Basinger, Richard E. 

Helt, and Harry E. Jacob), and hired Naknek Packing Company to transport the bulk of expedition supplies by motor 

boats (23 May to 2 June) to a base camp at the head of Naknek 

Lake. Griggs and a few others landed at Katmai Bay from 

Kodiak in late May, reestablished several relay camps via 

Katmai Pass, and reached the VTTS by 1 June. Along with 

returnees Folsom, Hine, and Paul Hagelbarger, Griggs was 

accompanied by Clarence Norman Fenner (petrologist; fig. 

8), Emanuel George Zies (fig. 9) and Eugene Thomas Allen 

(chemists), Emery C. Kolb (motion picture photographer), 

Julius Stone (boatman), Frank I. Jones (color photographer), 

and five assistants—Ralph Hagelbarger, William L. Henning, 

August E. Miller, H.M. Wallace, and Charles Yori. Griggs, 

Stone, and Miller joined Sayre at base camp near Savonoski 

on 9 June. New camps were set up at the northeast edge of 

the VTTS (“Ukak Camp”) and on the exposed bench at the 

southwest toe of Baked Mountain (fig. 5).

The Geophysical Laboratory contingent arrived at Katmai Bay on 13 June. Allen and Zies crossed Katmai Pass 16 

June, reached Savonoski Camp 19 June, set up a field laboratory there 20–26 June for gas analysis and microscopy, and 

studied fumaroles in the lower VTTS from Ukak Camp from 

27 June to 28 July. They moved to Baked Mountain Camp 

on 29 July to work on fumaroles in the upper VTTS but lost 

16 of 25 days in August to stormy weather, leaving the VTTS 

frustrated on 25 August and reaching Katmai Bay on 29 

August. Fenner spent the period 30 July to 12 August 

Figure 7. Participants in 1919 Katmai expedition, at Kodiak. From left, Richard Helt, Jasper Sayre, Paul Hagelbarger, Emery Kolb, 

Charles Yori, Robert Fiske Griggs, Lucius Folsom, Clarence Norman Fenner, Eugene Thomas Allen (swatting mosquito), August Miller, 

Emanuel George Zies, J.S. Hine, H.M. Wallace, A.J. Basinger, Julius Stone, and William Henning. Members not in photograph were 

Ralph Hagelbarger, Harry E. Jacob, and Frank Jones. Roles of each were mentioned by Griggs (1922). Photo courtesy of National 

Geographic Society.
28 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Figure 8. Clarence Norman Fenner at Katmai, summer 1923, 

beside Yori’s pack. Fenner marked his 53rd birthday at Katmai 

that summer when he and Yori spent two months alone together 

and altogether three months in the Katmai region. Photo by 

Charles Yori.

Figure 9. Emanuel George Zies, 17 August 1919, at site of stormwrecked camp on western bench of Baked Mountain. Photo 

courtesy of National Geographic Society.

at Camp IV, studying the south side of Mount Katmai and 

ascending to the caldera rim. Expedition accomplishments included measuring several fumarole temperatures in 

the range 500oC–645oC; collection of 18 gas samples and 

numerous samples of rocks and fumarolic incrustations; 

ascent to the crater rim of Mount Martin by Yori, Fenner, 

and Griggs on 16 August from Baked Mountain camp; and 

further topographic surveys of the Naknek Lake system and 

of a potential tourist route from Geographic Harbor across 

Hagelbarger Pass (fig. 6). Fenner noted that stream gorges 

incised into the ignimbrite were already nearly 100 feet deep. 

Griggs noted slackening, cooling, or disappearance of many 

1917 fumaroles and conversion of many former steam vents 

in the lower VTTS to boiling springs. Huts were built near 

Katmai Bay, Savonoski, and Brooks River (fig. 6). A movie 

outfit of two actors, an actress, and three packers arrived via 

Kodiak and Katmai Bay and spent a July week filming in the 

upper VTTS. The wives of Folsom, Kolb, and Griggs (Laura 

Amelia Tressel) came over from Kodiak to the VTTS in July 

and August (Griggs, 1961). Several participants, including 

Mrs. Griggs, Fenner, Hine, Basinger, and Sayre, reached 

the caldera rim from Camp IV. Between 26 August and 7 

September, most were shuttled from Katmai Bay to Kodiak 

in three trips, but a few others returned via Naknek. Ever the 

promoter, as the fumaroles faded, Griggs (1921) increasingly 

advocated tourism, scenery, salmon, and wildlife.

1920

Fenner rejected Griggs’ idea that the 1912 ignimbrite 

was a “great hot mud flow” and proposed instead that it 

had been a hot dry “ash- or sand-flow” analogous to nuées 

ardentes (Fenner, 1920, 1923). He argued, however, that fissure vents for the ejecta (and for the subsequently persistent 

fumaroles) issued from a sill that extended under the whole 

VTTS. Novarupta, he suggested, was similar to the spine of 

Pelée, representing stiff degassed magma later extruded from 

just one of the supposedly numerous earlier fissure vents. For 

Katmai caldera, he saw that lithic ejecta represented only a 

small fraction of the missing volume, and he granted that subsidence might have played a part, but he radically attributed 
Chapter 4. History of Investigations and Interpretations 29

formation of the crater principally to assimilation of older 

rocks by superheated rhyolitic magma, thermally aided by 

exothermic gas reactions.

1922

Publication of Griggs’ well-illustrated book “The Valley of Ten Thousand Smokes” by the National Geographic 

Society.

1923

Fenner (then 53) and Yori shipped to Kanatak on Portage Bay in early June, accompanying a USGS party, which 

lent them two packers, a dozen horses, and at least two dogs 

for transport to the VTTS. Via Kejulik Pass and Yori Pass 

(fig. 6), the packtrain reached the VTTS on 23 June and left 

them alone for two months at a well-stocked camp at the 

north toe of Mount Cerberus. They made the first ascent 

from the VTTS side of the range to the Katmai caldera rim 

on 6 July, traversing high from Novarupta across three 

Knife Creek Glaciers to the west-rim notch. Descending a 

snow-covered talus chute from the notch, they became the 

only people ever to stand on the caldera floor, where the 

shallow lake seen in 1916–19 had been replaced by mudflats. 

They photographed boiling mudpots, a large mud geyser, and 

myriad fumaroles around the base of the wall (Fenner, 1930), 

and they sampled the horseshoe-island dacite lava dome. 

On 14 July they climbed to the crater rim of Mount Mageik 

in poor weather. They camped for a week at Katmai River 

and climbed to the south rim of Katmai caldera on 23 July, 

accompanying a party of at least 11 tourists that included 

several women. They reclimbed Mageik on 4 August, when 

they were able to descend to its crater floor, site of roaring fumaroles and small pools of mud but at that time no 

crater lake. Yori made the first ascent of Knife Peak (now 

Mount Griggs) on 20 August. Fenner made many regional 

observations on intrusive rocks and undeformed Mesozoic 

sedimentary rocks that dominate the arc basement in this part 

of the Alaska Peninsula. Fissure Lake (FL on fig. 5) had by 

then drained, but a glacier still occupied the later site of West 

Mageik Lake. The packtrain picked them up at their Cerberus camp on 31 August.

Hundreds of the 1919 fumaroles were either dead or had 

cooled to near the boiling point, and most had vanished from 

the upper Knife Creek arm. In their photographs, ~50 steam 

plumes survived in the upper Lethe arm and nearly as many 

in the middle VTTS but only a few downvalley from Three 

Forks. Four discrete plumes were active along the western 

bench of Baked Mountain. The floor of Novarupta basin was 

steaming densely as far west as what we now recognize as the 

vent margin north of the nose of Falling Mountain; the Novarupta dome was steaming vigorously but the Turtle only weakly 

in a few places. Around Novarupta and in the upper Lethe 

arm, they found a few surviving superheated fumaroles, and 

what they identified as the hottest remaining one was along the 

arcuate graben ~1.2 km northeast of the dome.

The USGS party spent two months preparing a reconnaissance geologic and topographic map from Mount Peulik to Savonoski (fig. 6), using and naming Yori Pass. The 

party consisted of Walter R. Smith (geologist), R.K. Lynt 

(topographic engineer), C.S. Franklin (recorder), three camp 

hands, and 15 horses. Near Savonoski on 28 August, they met 

another USGS party, consisting of Kirtley F. Mather (geologist), R.H. Sargent (topographic engineer), and four assistants, 

that had landed at Iliamna Bay off Cook Inlet on 16 June and 

likewise reconnoitered the area from Kamishak Bay to the 

Savonoski drainage (fig. 6). After retrieving Fenner and Yori, 

the two parties together reached Kanatak on 9 September, 

whence they all shipped to Kodiak.

1923–1929 

Allen and Zies published a series of papers describing 

the composition of the fumarolic gases and the morphology, 

mineralogy, and chemistry of the vents and deposits. They 

tabulated 106 temperature measurements for fumaroles in all 

parts of the VTTS, noting that the hottest were in the central 

VTTS, with lower temperature vents distally and around the 

margins. They reported that many fumaroles measured in 

1918 had declined in temperature within a year and that hundreds had died out completely. They estimated that less than 

10 percent of stream runoff onto the ignimbrite was emerging at Three Forks, leading them to conclude that most of the 

fumarolic steam originated as surface waters infiltrating the 

hot tuff, vaporizing, and thus cooling the VTTS rapidly. The 

temperature of the glacier-fed River Lethe was 80-85oC at 

Three Forks in 1919.

1929 

Bernard R. Hubbard, S.J., “the Glacier Priest,” after failing to reach Mount Katmai from Kukak Bay in summer 1928, 

was dropped at Katmai Bay in late June (Hubbard, 1932, 

1935). With four college boys and two dogs, he climbed to 

the caldera’s south rim from the warm springs on Mageik 

Creek and also spent several days camped in the VTTS at the 

north toe of Mount Cerberus. The “milky turquoise blue” 

caldera lake had been restored and was by then deep enough 

that the Horseshoe Island was submerged. Hubbard reported a 

“whitish-blue boil” in the center of the lake, sporadic patches 

and streaks of “vivid yellow,” and several dozen fumaroles 

around the lakeshore. Ice had begun to accumulate on both 

intracaldera slump-block benches, and Hubbard and Frank 

Klatt descended a snow slope to the southern one. In the 

VTTS, only a few hundred fumaroles remained active, nearly 

all near or below the boiling point; none were left in the lower 

valley, but the Novarupta lava dome was still steaming vigorously. The party was picked up at Katmai Bay in late July.

1930

Griggs made his final visit to the VTTS, again via Katmai 

Bay, camping in the upper valley 3–9 July. He sprained his 

ankle badly in the VTTS and limped painfully all the way 

back to Lagoon Camp at Katmai Bay (Griggs, 1961). Of a 
30 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

few hundred fumaroles left, none were found to be above the 

boiling point, but he noted that some were still active on the 

face of Falling Mountain. He concluded that liverworts (not 

mosses, bacteria, or algae) were the principal pioneering plants 

on barren ash-covered surfaces. In a report to the Department 

of the Interior (22 November 1930), Griggs advocated expansion of the Monument as a wildlife preserve. On 24 April 

1931, a presidential proclamation doubled the size of Katmai 

National Monument.

Griggs was accompanied in 1930 by his 18-year-old son 

David Tressel Griggs (1911–1974). The trek helped inspire 

a career in experimental geophysics (at Harvard and UCLA), 

in which he pioneered studies of rock deformation, hydrolytic weakening, crystal dislocation, creep, oriented fabrics, 

earthquake mechanisms, and the role of mantle convection 

in mountain building. After the elder Griggs died in 1962, 

David climbed Mount Griggs to place his parents’ ashes on 

top in the summer of 1963. His own son added David’s ashes 

up there in 1975.

1932

Hubbard returned via Katmai Bay in March with two lads 

and a dogsled team. He made a brief trip into the VTTS and 

climbed to the caldera rim from the south, reporting that the 

“emerald lake” was unfrozen and that floating icebergs melted 

quickly. The icebergs calved from a “cascading glacier,” 

which may suggest that the narrow ice tongue on the west wall 

had originated by then. After waiting for 11 days at Katmai 

Bay, they were picked up on 16 April.

1934

Hubbard returned via Katmai Bay in September with six 

lads and four dogs, again climbing to the south rim of Mount 

Katmai and visiting the VTTS and Novarupta. The caldera lake 

remained blue and shallow, with no island; Hubbard (1935) 

mentioned rockfalls and waterfalls but no fumaroles on the 

caldera walls, and he said the intracaldera glaciers had grown 

and were calving into the lake. He reported that only “a few 

feeble” fumaroles were left (compared to hundreds in 1929), 

mostly in the upper Lethe arm and in Novarupta basin—especially adjacent to the lava dome. None survived in the lower or 

central VTTS. Most conspicuous was a pair of big steamers on 

the bench alongside Baked Mountain (down from four in 1923), 

but the corresponding bench along the west side of the Lethe 

arm lacked active fumaroles. Many fissures in the upper VTTS 

that had been open in 1929 were by 1934 filled with windblown 

pumice and sand. Hubbard noted how deeply the 1912 deposits 

along Mageik Creek and Katmai Pass had been incised since his 

1929 trip. He mentioned the odor of H2

S along Mageik Creek 

between Trident and Observation Mountain.

1940

Frank T. Been (superintendent of Mount McKinley 

National Park) and Victor H. Cahalane (Biological Survey, 

then a bureau in the U.S. Department of Agriculture) spent 

September reconnoitering by boat and plane the natural 

resources and the rampant poaching in Katmai National 

Monument. The National Park Service had never yet had any 

protective or interpretive personnel based in the Monument. 

They reported that only about ten fumaroles were still active.

1950

For the first time, the National Park Service stationed a 

ranger in the Monument, near the mouth of Brooks River (fig. 

6) for the summer. By arrangement with the NPS, Northern 

Consolidated Airlines initiated its first two fly-in fishing camps 

for tourists.

1951

The Alaska Recreation Survey, organized by the National 

Park Service, flew from Kodiak around Katmai National Monument for several days in June. The party consisted of George 

L. Collins, Adolph Murie, Thomas Williams, and Lowell 

Sumner. They reported seven steam plumes near Baked and 

Broken Mountains, fumaroles in the crater of Mount Martin and high on Knife Peak, and a “jade-green” color for the 

caldera lake at Mount Katmai. Their recommendations helped 

lead to the Katmai Project.

1953

Katmai Project: The National Park Service proposed to 

the Office of Naval Research comprehensive investigation of 

Katmai National Monument, in part to help prepare a master plan for management and interpretation. Studies would 

include geography, climate, glaciers, coastal geomorphology, 

flora, fauna, entomology, soils, volcanic activity, regional 

geology, mineral resources, and archaeology. Scientists 

from the USGS, Public Health Service, and five universities eventually took part. Eruption of Trident, beginning in 

February, helped draw the attention of the military, which 

provided rations, rifles, radios, field equipment and clothing, 

air transport, and even a helicopter. Beginning 19 June, field 

camps were outfitted on upper Knife Creek (VTTS), Kukak 

Bay, Brooks Lake, and near the site of Savonoski. Project 

headquarters on the Air Force Base at King Salmon was open 

all summer, closing for the season on 7 October.

Trident began erupting explosively on 15 February. Several andesite-dacite lava flows were emplaced between 1953 

and 1960, and numerous explosive events persisted as late 

as 1974, building a new fragmental cone. There were many 

observations during 1953 (Snyder, 1954), but only occasionally thereafter.

Howel Williams, Garniss Curtis, Ronald W. Kistler, and 

Rolf Werner Juhle (fig. 10) spent the last two weeks of June, 

camped on upper Knife Creek, reconnoitering the VTTS, 

Trident, and Mount Katmai. Correcting interpretations of 

Fenner and Griggs, they concluded that 1912 vents were not 

beneath the VTTS but at its head, that 1912 andesitic and 

rhyolitic magmas erupted simultaneously and mingled, that 

andesitic magma did not originate by fusion of older rocks by 
Chapter 4. History of Investigations and Interpretations 31

the rhyolitic magma, and that most fumaroles issued from the 

valley-filling ignimbrite sheet itself, not from an imagined sill 

or batholith beneath the valley. Williams introduced the place 

names for the Turtle and Whiskey Ridge (fig. 6). Poking fun 

at Fenner’s ideas, Curtis, Williams, and Juhle (1954) wrote 

that “No evidence was observed to support the hypothesis of a 

still under the valley floor.”

Juhle and Kistler (then a student at Johns Hopkins, later 

at Berkeley and the USGS) stayed on (fig. 10), conducting 

regional geologic mapping, until Juhle was lost into one of the 

torrent-filled gorges in the lower VTTS on 31 August (Donnay, 1956).

1954 

Curtis returned to the Knife Creek campsite in summer 1954, assisted by Jack Sheehan. Fenner and Griggs had 

assumed that most of the stratified fallout was ejected from 

Mount Katmai, even though they realized that the thickest 

and coarsest ejecta surrounded Novarupta. They believed that 

some subordinate fraction of the fallout had erupted at or near 

Novarupta, but Curtis keyed on the fact that they had never 

developed criteria to distinguish products of the two postulated 

vents. So Curtis subdivided the stratified fallout into eight 

principal layers, measured 30 sections between Novarupta and 

Mount Katmai, and showed that all eight thickened toward 

Novarupta, their true source vent. He was first to propose 

hydraulic interconnection between the collapsed caldera and 

the main vent at Novarupta, 10 km away. As for the ignimbrite, Curtis recognized that it had come from Novarupta 

basin, and he noted its gross compositional zonation, from 

rhyolite-rich distally to rhyolite-poor in the upper VTTS. 

Observing blocks of eutaxitic welded tuff ejected phreatically 

from deep in the ignimbrite and noting the differential compaction across the upper VTTS, Curtis constructed profiles for 

nearby streams and concluded by comparison that valley-filling ignimbrite in the VTTS might be more than 200 m thick.

A. Samuel Keller and Hillard N. Reiser (USGS) devoted 

two months of fieldwork to preparing a geologic reconnaissance map of Katmai National Monument (Keller and Reiser, 

1959), in collaboration with the NPS as a contribution to the 

Katmai Project. During July and August, eight field camps 

were put in for them by float plane supplied by the Air Force, 

at sites that included Iliuk Arm of Naknek Lake, Geographic 

Harbor, and Kinak, Kukak, Hallo, and Kaguyak Bays. 

Figure 10. Werner Juhle, Howel Williams, and Ronald Kistler during Katmai Project, summer 1953. 

Photo by Garniss Curtis.
32 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Emphasis was on basement rocks, but knowledge of the volcanic rocks was also extended.

1959

The Board of Geographic Names, on the initiative of the 

National Geographic Society, changed Knife Peak volcano to 

Mount Griggs.

1962

Pierre Bordet, G. Marinelli, M. Mittempergher, and 

Haroun Tazieff, European volcanologists, visited the VTTS in 

June after a scientific conference in Tokyo (Bordet and others, 

1963). Despite other misconceptions, they generally agreed 

with the 1953 observations of Williams and Curtis, inferring 

the mixing of separate silicic and intermediate magmas, which 

they postulated to have been stored respectively beneath 

Novarupta and Katmai. They were the first to explicitly apply 

to the VTTS deposit the word “ignimbrite” (which had originated in 1932; Marshall, 1935). Griggs had called it a “hot 

mud flow” and Fenner a “sand flow.” Williams and Curtis had 

considerable experience with ignimbrites, but Curtis chose 

to call it a “tuff flow” and Williams a “glowing avalanche 

deposit.” 

The National Park Service constructed a dirt road from 

Brooks River (fig. 6) to Overlook Hill near the VTTS, making 

access far easier.

1963

Robert W. Decker and Peter L.Ward of Dartmouth College, supported by the Geophysical Institute (University of 

Alaska), conducted a pilot project in July and August, proving 

the feasibility of seismology and gravity studies in the VTTS 

(Decker, 1964). Seismometers installed near Brooks River 

(fig. 6) and Overlook Hill (fig. 5) recorded 82 small earthquakes in 17 days. Gravity was measured at 35 stations, by 

boat along the lakes, on foot up the VTTS and through Katmai 

Pass to Mageik Creek, and by float plane near Dakavak Lake 

(fig. 6); their results defined a negative Bouguer anomaly of 

–35 mgal centered on Katmai Pass and flanked by positive 

anomalies on both sides of the volcanic axis. On 6–7 August, 

Ward and Decker climbed the new Trident cone, reporting a 

150-m-wide crater with abundant fumaroles, most of them 

hotter than 200oC and many on the crater rim encrusted with 

sulfur. They sketched a map of the 1953–1960 lava flows 

below the cone.

1965

Baked Mountain Hut (fig. 5; two contiguous cabins plus 

storage and generator sheds) was constructed for the Geophysical Institute (GI), University of Alaska, with Air Force helicopter support via Brooks Camp (fig. 6). The hut was built on a 

pumice-mantled wind-buffeted bench devoid of surface water, 

4 km northwest of Novarupta, fairly central to the upper VTTS 

but an uphill trudge from all directions. Ensuing geophysical 

research was undertaken during summers of 1965 to 1969.

Eduard Berg and Jürgen Kienle (GI), supported by NSF 

and the Air Force Office of Scientific Research, measured ~75 

new gravity stations along five helicopter-assisted profiles 

across the volcanic axis, extending the along-axis negative 

anomaly recognized in 1963 (Berg and others, 1967). The 

Bouguer gravity minimum centered on Katmai Pass was recalculated to reach –42 mgal.

Dipak Kumar Ray and Robert B. Forbes (University of 

Alaska) sampled Trident lavas and ejecta of the 1953–1963 

eruptions for Ray’s petrographic and chemical Ph.D. dissertation (1967). They reported little change in activity or configuration of the Trident cone since 1963. All four lava flows were 

still steaming.

In the VTTS, weak fumaroles (near or below boiling) 

remained only on Novarupta dome, on the west rim of its 

ejecta ring, along faults on and near the Turtle, and on the 

western bench of Baked Mountain. Fumarolic plumes were 

reported from Mageik, Martin, and the upper west flank of 

Mount Griggs.

Seismometers were installed for various intervals during 

summers of 1965–1967 near Brooks Camp, Overlook Hill, 

Katmai Canyon, Baked Mountain Hut, Savonoski, and Kodiak 

(figs. 5, 6). Participants included Berg, Kienle, Tosimatu 

Matumoto (Lamont), Ward (by then at Lamont), and Susumu 

Kubota (University of Tokyo). Hundreds of small earthquakes 

were recorded, nearly all shallower than 10 km, mostly magnitude 0–3, and the majority close to the volcanic axis from 

Mount Martin to Snowy Mountain. Screening of S-waves and 

attenuation of high-frequency P-waves on certain azimuths 

were interpreted as suggesting magma storage beneath the 

volcanic axis (Berg and others, 1967; Kubota and Berg, 1967; 

Matumoto and Ward, 1967; Ward and Matumoto, 1967; Matumoto, 1971).

1966

Ray returned to Trident in August, reporting no changes 

other than continuing growth of a plug in the crater, from ~3 m 

high in 1965 to ~15 m high in 1966.

Kienle (1970) measured 85 gravity stations along three 

profiles across the central VTTS in the summers of 1966 and 

1967. Uncertainties concerning density contrasts among basement rocks, variably welded ignimbrite, and unknown thicknesses of concealed pre-1912 valley fill led him to present two 

contrasting models. One model gave maximum tuff thicknesses of ~70 m; the second gave 140–160 m. In 1991, after 

the great range in VTTS ignimbrite density (r=1.0 to 2.1) was 

explained to him, he elaborated the second model, affirming 

the thickness estimate Curtis had based on stream profiles.

1967–1969

Attempts to determine thickness of the ignimbrite in 

the VTTS by seismic refraction profiles were made with a 

sledgehammer by Matumoto and M.L. Sbar (Lamont). Greatest calculated thickness in the lower Lethe arm was ~70 m; in 

Novarupta basin, it was thought thicker, but results were too 
Chapter 4. History of Investigations and Interpretations 33

complex to interpret (Sbar and Matumoto, 1972). In 1969, 

Larry Gedney, Charles Matteson, and Forbes (all University of 

Alaska) repeated such an experiment using explosives; their 

maximum inferred thickness was only ~50 m, in the lower 

Lethe arm (Gedney and others, 1970). Interpretation of such 

experiments was bedeviled by uncertainties about unexposed 

(and apparently unsuspected) welding zones in the ignimbrite 

and by subjacent glacial and alluvial deposits. Kienle (1991) 

later based his reinterpretations of those refraction profiles on 

new density data to give recalculated thicknesses of 120–167 

m (in the middle VTTS).

1975

Roman J. Motyka (GI) descended the Yori-Fenner chute 

to Katmai caldera lake in early July and, using an inflatable 

raft, recorded water temperatures at several sites that averaged 5.5oC at depths of 10–60 m. Measured pH was 2.5–3.0. 

Odor of H2S was strong, and a mid-lake yellowish bubbling 

upwelling contained particulate sulfur. Water samples were 

taken for chemical analysis. He had already surveyed the 

lake from the caldera’s west rim in August 1974. It was 

found to have deepened by 182 m between 1923 and drafting 

of the USGS topographic map in 1951, and by an additional 

47 m from 1951 to 1975. Motyka returned to the lake in 

August 1977 and found that its level had risen by an additional 6.5 m in two years. In 1977 he measured temperatures 

of 20.5oC at the lake floor and 8.8oC at depths of 10–60 m, 

and he noted that the lake had not frozen in winter 1975, 

although it had been photographed as largely frozen over in 

March 1967 (possibly for the first time).

1976

Wes Hildreth (then a Berkeley Ph.D. student working 

on ignimbrites, later at the USGS) spent five August weeks 

in the VTTS, assisted by Larry Jager and joined for a week 

by Daniel Kosco (U.C. Berkeley), and brought back 150 kg 

of samples for petrologic study. A single chimney fumarole 

(49oC) survived on the western bench of Baked Mountain; 

numerous centimeter-scale orifices with wispy odorless 

discharge (as hot as 88oC) were located on the Turtle and 

the northwest ejecta ring of Novarupta; and odorless vapors 

rose weakly from several spots atop the dome itself. They 

climbed to the caldera rim twice from the VTTS, observing 

three glaciers calving icebergs into a pale blue lake with a 

prominent yellowish upwelling in the middle. Depth of Knife 

Creek gorge south of Three Forks was measured by rope to be 

33 m. Pale gray dacite, rich in crystal clots, was recognized as 

a magmatic product distinguishable from coerupted andesite 

and rhyolite. They saw that proportions of the three pumice 

types changed greatly through the emplacement sequence, 

which could be defined by numerous apparent flow units in the 

ignimbrite (some subtle, some compositionally abrupt). Nonwelded in the lower VTTS, exposures of the tuff were found to 

be widely indurated in the upper VTTS, variously by sintering, partial welding, and vapor-phase crystallization. Phreatic 

craters had ejected welded, even eutaxitic, blocks from unexposed depths in the tuff. “High sand mark” benches alongside 

the VTTS were recognized to reflect differential compaction 

of welded tuff, with lesser contributions by marginal run-up 

during inflated emplacement and locally by axial drainaway. 

The eruption-initiating fallout layer of rhyolite pumice was 

found in Mageik Creek but nowhere under the ignimbrite on 

the VTTS side of the volcanic line. A pre-1912 debris-flow 

deposit rich in dacite pumice was sampled at Windy Creek. 

Relatively low-energy emplacement of the ignimbrite in the 

lower VTTS was inferred from the way it banked against and 

flowed around the modest cross-valley moraine near Three 

Forks. Familiar with zoned ignimbrites elsewhere, Hildreth 

envisaged that the entire rhyolite-dacite-andesite mixture 

could have issued from a continuous magma body.

1978

Kosco and David A. Johnston (USGS postdoc) spent 

two weeks in the VTTS, sampling fumarolic gases at Trident, 

Mageik, Griggs, and Novarupta dome. Kosco collected lavas 

from the volcanoes for his Ph.D. work at Berkeley, and Johnston began investigation of the stratified fallout. Mageik crater 

lake was measured at 70oC with pH ~1.

1979

Hildreth, Johnston, and Anita Grunder spent 22 June 

until 22 July on foot in the VTTS, following a 10-day helicopter-supported USGS field trip along the Alaska Peninsula, 

led by Thomas P. Miller and Robert L. Smith. Gas samples 

were again collected from Trident, Mageik, and Griggs. 

Temperatures measured for sulfurous fumaroles were 97oC 

on Trident, 108oC on Griggs, 172oC for a roaring jet on the 

north shore of Mageik’s crater lake, and 135oC for another 

issuing from talus on the northeast wall. The yellow-green 

lake itself was 71oC, roiling vigorously, and fringed with 

yellow sulfurous spindrift. Terry E.C. Keith, assisted by 

Peter Shearer (both USGS), spent 10 days with the party and 

initiated new studies of the (now-fossil) fumarolic deposits 

and the chemistry of spring waters. Pumice-type proportions 

were counted throughout the ash-flow and fallout deposits 

in order to document the complex compositional zonation of 

the 1912 eruptive sequence. Thin tephra layers in and near 

the lower VTTS were correlated with the meter-scale layers 

defined by Curtis in the area proximal to Novarupta. The 

basal rhyolitic pumice-fall layer was confirmed beneath the 

ignimbrite in lower Mageik Creek.

1980

The Monument was expanded and redesignated “Katmai 

National Park and Preserve,” much of it a Wilderness Area, 

under the Alaska National Interest Lands Conservation Act 

(ANILCA).

Hildreth, stunned by the death of Johnston at Mount St. 

Helens on 18 May, returned to the VTTS for the month of 

August, assisted by Judith Ellen Fierstein (USGS, on her first 
34 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

backpack trip). A tent was pitched for 10 days on the south 

fork of upper Knife Creek, to facilitate study of tuff-glacier 

relations, phreatic craters, and disrupted deposits along the 

Griggs fork (fig. 5) of Knife Creek. They began systematic 

inventory of maximum sizes of pumices and lithics in all 1912 

subunits. Logging of the complex proximal pyroclastic fall 

and flow deposits around Novarupta basin was initiated. They 

mapped phreatic, fluvial, and lake deposits in upper Knife 

Creek, near West Mageik Lake, and along the trough of former 

Fissure Lake. They also mapped a flood-margin track down 

the northeast side of the Knife Creek arm of the VTTS and 

ash-dominant debris-flow deposits near the VTTS terminus. 

A 3-day hike to Mageik Creek and Katmai River confirmed 

that the Katmai River debris-flow deposit (which overlies the 

stratified 1912 fallout) had engulfed uncharred trees (as noted 

by Griggs) and is thus a remobilized secondary deposit, not 

a hot pyroclastic-flow deposit from Mount Katmai (as interpreted by Fenner and Curtis). The Lethe Hills (fig. 5) and the 

“high sand mark” and its fissured hingeline were investigated 

(see chapter 6). 

By microbeam analysis at Berkeley and Menlo Park, 

Hildreth showed that the zoned 1912 eruption products 

recorded a preeruptive continuum in Fe-Ti-oxide temperatures (800oC–990oC), in spite of the wide bulk-compositional 

gap between the crystal-poor rhyolite and crystal-rich dacite. 

This was interpreted as support for a unitary zoned magma 

reservoir rather than mixing of magmas from two or more 

separate reservoirs.

1982

Hildreth and Fierstein returned to the VTTS from 11 July 

to 9 August, joined for a week by Christina Neal (Arizona 

State University, later USGS) and by Terry Keith and Michael 

Thompson (USGS) for two weeks. Fierstein began sieving 

pyroclastic samples at Baked Mountain Hut for grain size and 

componentry studies. Recording at the outcrop the maximum 

sizes of pumices and lithics continued for all 1912 subunits. 

Climbs of West Trident and Falling Mountain and traverses of 

the spurs of Baked Mountain involved logging the complex 

proximal pyroclastic-flow and fallout sequence. Sampling 

of thick plane-laminated ignimbrite east of Three Forks 

addressed the issue of distinguishing vent-derived flow units 

from those developed in the moving mass by internal shear, 

pulsatory remobilization, or incremental deposition. Sites of 

several 1915–1919 photographs were reoccupied to provide a 

record of geomorphic changes.

Keith and Thompson continued work on fumarolic deposits and spring waters. The whole party crossed Katmai Pass 

and sampled seeps and springs that issue from beneath the 

1953 and 1958 Trident lava flows; waters were near-neutral 

and ranged from 8oC to 42oC at their orifices. 

1983

Hildreth (1983) published an updated interpretation of the 

1912 eruptive sequence, integrating chemical petrology and 

microbeam mineralogy of the zoned eruptive products with 

advances in understanding pyroclastic processes, outflow and

welding of ignimbrites, and structure of the backfilled vent 

area in Novarupta basin.

1985

A Katmai Working Group was assembled, largely on the 

initiative of John Eichelberger (Sandia National Laboratories), to propose that the U.S. Continental Scientific Drilling Program (CSDP) should support research drilling into 

the 1912 ignimbrite and Novarupta vent. Grappling with 

ambivalence between his scientific and wilderness values, 

Hildreth joined the effort and sold the project to the CSDP 

at their Rapid City meeting in June 1986, advocating that 

the vent was the best thermal target to be drilled because it 

was “young, hot, and simple” (Eichelberger and Hildreth, 

1986). A formal proposal was developed as an interagency 

DOE-NSF-USGS effort, in need of authorization by the NPS 

(Eichelberger and others, 1987). There ensued meetings 

with the NPS and environmental societies, as well as numerous workshops that culminated in Geophysical Expeditions 

to Novarupta in 1989 and 1990 (Eichelberger and others, 

1990, 1991). A Science Plan was prepared with Eichelberger, Hildreth, and James J. Papike (1989) as Principal 

Investigators, and an Operations Plan was finalized in May 

1992. The NPS contracted with Dames and Moore, Inc., 

to prepare an Environmental Impact Statement, a 350-page 

draft version of which was reviewed by Hildreth and others 

in July 1993. Resistance mounted, and in 1994 the proposal 

to drill was withdrawn, apparently owing to complex politics 

that involved an order-of-magnitude escalation of estimated 

costs, fears about the perceived precedent of drilling in a 

Wilderness, and an announced requirement that authorization 

would need Congressional legislation.

1986

Hildreth and Fierstein returned to the VTTS from 18 

July until 18 August, joined by Keith and Gail Mahood 

(Stanford) who together continued work on fumarolic deposits. The emphasis this season was on documenting lithology 

and mass fraction of lithic ejecta in all 1912 subunits, as 

input for modelling the volume and shape of the backfilled 

vent structure beneath and around Novarupta. Special attention was given to the Novarupta ejecta ring and stratified 

deposits draping the walls of Novarupta basin and all sides of 

Falling Mountain. The party climbed to the Katmai caldera 

rim, recognizing there a thick 1912 explosion breccia banked 

against ice on the west rim. Soil atop a meter-thick pre-1912 

dacite pumice-fall deposit on the north slope of Mageik was 

collected and later radiocarbon dated at 2,140±60 14C yr B.P. 

In the course of regional geologic mapping, Robert L. Detterman and James R. Riehle arrived at Novarupta by helicopter 

to consult about the lithology, thickness, and stratigraphy of 

the Naknek Formation and deeper Mesozoic strata concealed 

beneath the 1912 vent.
Chapter 4. History of Investigations and Interpretations 35

1987

Fierstein hired a boat for a 9-day cruise along Shelikof 

Strait in June, measuring thickness and componentry of 1912 

fallout layers at many locations on Kodiak and Afognak Islands.

Hildreth and Fierstein returned to the VTTS from 2 July 

to 8 August, continuing detailed stratigraphic analysis and 

componentry of 1912 fallout and the sequence of ash flows. 

They climbed Whiskey Ridge, hiked the crest of the Buttress 

Range, and measured many sections on spurs of Baked Mountain and on the distal Ukak lobe of the ignimbrite. Two sorties 

were made down Mageik Creek, where they camped for a 

week and logged many complete fallout sections on slopes of 

Trident and Observation Mountain. The ash-flow sequence 

was mapped along the axis of Katmai Pass and Mageik Creek, 

where it is intercalated with rhyolitic and dacitic fall units, and 

where Layer B was shown to be its contemporaneous zoned 

equivalent. They later logged fallout sections atop Dumpling 

Mountain near Brooks Camp, by boat along Iliuk Arm, and 

by car from Naknek to Naknek Lake (fig. 6). Hildreth took 

USGS Director Dallas Peck on a helicopter tour of Novarupta 

and the VTTS, explaining the goals of the proposed scientific 

drilling initiative.

Terry Keith, assisted by Rick Hutchinson (NPS, Yellowstone), spent 10 July days working on fumarolic deposits and 

spring waters.

Lawrence G. Kodosky (University of Alaska) sampled 

fresh and fumarolically altered ejecta at 127 sites within 

Novarupta basin and analyzed them for elemental Hg content. 

It was hoped that the distribution of non-sulfide Hg, precipitated from vapor and adsorbed on clay-size particles, might 

help delineate structures that reflect configuration of the backfilled vent—generally inferred to be funnel shaped.

Peter Wallman, assisted by Larry Mastin (both then Stanford graduate students), began a structural study of Novarupta 

basin as part of his Ph.D. dissertation.

DeAnne Pinney camped for a month in Windy Creek, 

examining pre-1912 tephra and secondary deposits as a University of Alaska thesis project (Pinney and Beget, 1991).

Peter Ward deployed an array of 10 seismometers in September (enlarged to 14 in August 1988) on both sides of the 

volcanic chain; signals were telemetered to King Salmon. He 

located 1,900 earthquakes by December 1990 (mostly magnitude 1–2 and at 3–10 km depth), and he observed that P-wave 

delays were greatest near Katmai Pass (a formerly narrow 

defile filled by thick 1912 ignimbrite), coinciding there with 

the regional Bouguer gravity low. Although both P and S 

waves were attenuated along some paths that crossed the volcanic axis, S-wave screening like that noted in 1965–67 was 

not found. Most earthquakes occurred in four clusters—near 

Martin and Mageik, near Trident and Novarupta, near Mount 

Katmai, and northwest of Snowy Mountain.

1988

Fierstein hired a boat for a second week-long cruise 

along Shelikof Strait in July, measuring thickness and componentry of 1912 fallout layers at many locations along the 

Katmai coast from Kaguyak to Kashvik Bay (fig. 6). Jacob B. 

Lowenstern (Stanford, later USGS) joined Wallmann to study 

the rhyolite sills that intrude the Naknek Formation near West 

Mageik Lake (Lowenstern and others, 1991).

1989

The Geophysical Expedition party (fig. 11) established 

camp in an arcuate graben just east of the Turtle; starting 31 

July, three spacious fabric shelters and a ton of equipment 

and supplies were shuttled from King Salmon by helicopter. 

Surface studies were intended to help define the shape of the 

backfilled pyroclastic vent structure and conditions within it, 

preparatory to the proposed drilling project. Bench marks 

were established, and a 150-point grid was surveyed, spanning the vent region. Gravity and magnetic field strengths 

were measured at all grid points and the highly variable heat 

flow at selected ones. Wispy fumaroles were found to be as 

hot as 90oC. Electrical resistivity was measured along two 

profiles, and seismic refraction was recorded along lines 

west of Novarupta. A low-altitude aeromagnetic survey was 

flown by helicopter. The camp was dismantled 14 September. 

Participants included John Eichelberger, Vicki McConnell, 

Sanford Ballard, and Allan R. Sattler (all Sandia National 

Laboratories); James Papike (South Dakota School of Mines); 

John Power, Betsy Yount, John Paskievitch, Wayne Colony, G. 

DuBois, Peter Ward, Eugene Iwatsubo, and Jack Kleinman (all 

USGS); Paul Kasameyer, W. Daily, and M. Wilt (all Lawrence 

Livermore National Laboratory); David Pollard and Peter 

Wallmann (Stanford); and Chris Nye, Tim Redfield, Chris 

Larsen, and David B. Stone (all University of Alaska).

Hildreth and Maura Hanning (USGS) were taken from 

the camp on 2 August by helicopter to the south toe of Mount 

Katmai, just west of the mouth of Katmai Canyon, where they 

pitched a tent for two weeks. Climbing all over the south and 

southwest slopes of Mount Katmai and twice spending several 

hours on the caldera rim, they logged and sampled numerous 

fallout sections and the Katmai River debris flow. It was verified that no initial ash is present on either side of the volcanic 

axis that might have preceded onset of the rhyolitic plinian 

column that started the 1912 eruption. The big landslide that 

had blocked Katmai River canyon (and breached as a flood, 

possibly in 1915 according to Griggs, 1922) was shown to be 

syneruptive, intercalated within the sequence of dacite-rich 

fallout layers. Several layers of lithic-bearing stinking mud 

(and coarse breccia equivalents near the caldera rim) were 

logged, interbedded widely in the pumiceous fallout sequence 

from Novarupta but ejected from Mount Katmai by hydrothermal explosions during its caldera collapse. After a 2-day 

return hike via Katmai Pass, they joined 12 colleagues at the 

Geophysical Camp near Novarupta on 15 August and later 

hiked out to Three Forks Overlook.

Terry Keith, Mike Thompson, and Rick Hutchinson 

returned for two weeks in late August to continue work on 

fumarolic deposits and spring waters.

Julie M. Palais and Haraldur Sigurdsson published estimated masses of acid aerosols (H2

SO4, HCl, HF) released to 
36 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

the atmosphere by numerous large eruptions (including that of 

1912), based on a petrologic method that compares microbeam concentrations of such components in melt inclusions 

sealed in phenocrysts with those retained by the matrix glass 

of inflated pumice or dispersed ash. Unfortunately, their 1912 

samples (supplied by J. R. Riehle) were dacitic fallout from 

17 km northeast of Novarupta and did not include the volumetrically dominant rhyolite, which was dispersed southeastward. Accordingly, their whole-eruption values for HF are 

underestimated and for H2SO4 overestimated. Nonetheless, 

the acid fallout for 1912 measured in Greenland ice cores is 

less than a third that for 1783 (Hammer and others, 1980), 

which was produced by the basaltic Laki eruption in Iceland, 

despite the similar volumes and latitudes of the two eruptions; 

the silicic Katmai ejecta had far lower sulfur concentrations 

than the basalts at Laki.

1990

A second Geophysical Expedition, continuing surface 

studies of the Novarupta vent area, was based at Baked Mountain Hut 7–26 July, supplied by helicopter from King Salmon. 

Many gravity and magnetic stations were remeasured to 

assess any ongoing changes, and electrical, magnetic, and 

aeromagnetic surveys were extended beyond those of 1989. 

New bench marks completed a geodetic net encompassing 

the vent region (Kleinman and Iwatsubo, 1991). Samples 

were collected across 1912 fumarolic deposits and later 

analyzed for 50 elements to estimate mass gains and losses 

during alteration of primary pyroclastic material. Keith measured temperatures as high as 30oC for mid-VTTS springs 

issuing in a gorge of Knife Creek. The Hut was renovated. 

Participants included returnees Eichelberger, Papike, Hildreth, Fierstein, McConnell, Keith, Kasameyer, Kleinman, 

Paskievitch, and Redfield, as well as Andrew M. Goodliffe 

(GI), Chris D’Sa (University of Iowa), Don Felske (Lawrence Livermore National Laboratory), and Christina Neal, 

Game McGimsey, and Susan Walker (all USGS).

Hildreth and Fierstein were dropped by helicopter on 

9 July on the southeast slope of Trident, where they pitched 

a tent for 10 days against a glacier front as a windbreak. 

They climbed high on East Trident and Trident I, reached all 

the Trident saddles, and measured many Novarupta fallout 

Figure 11. Participants in 1989 Novarupta Geophysical Expedition. From left, Wayne Colony, Chris Nye, Gene Iwatsubo, Wes Hildreth, 

Vicki McConnell, John Power, Maura Hanning, Jack Kleinman, Tim Redfield, Jim Papike, Sandy Ballard, Chris Larsen, and John 

Eichelberger. Slope of Broken Mountain at left and Mount Griggs in distance. Photo by Paul Kasameyer.
Chapter 4. History of Investigations and Interpretations 37

sections with Katmai-derived mud layers intercalated. The 

500-m-wide Trident fumarole bowl (at the southeast toe of Trident I, first seen by Griggs in 1916) had ~80 sites of gas emission and a strong H2

S odor. After camp was moved to Mageik 

Creek basin north of Observation Mountain, detailed stratigraphy between there and Katmai Pass showed (1) that during the 

initial all-rhyolite phase of the 1912 eruption, thin ignimbrites 

and plinian fallout alternated; and (2) that emplacement of the 

subsequent compositionally heterogeneous main VTTS ignimbrite was contemporaneous with fallout of compositionally 

equivalent plinian Layer B. Fierstein’s region-wide stratigraphy and componentry had by now conclusively demonstrated 

contemporaneity and compositional equivalence of pyroclastic 

falls and pyroclastic flows throughout most of the 1912 eruptive sequence, contrary to the then-standard model whereby 

column collapse was presumed to replace the one by the other. 

She submitted this work as a thesis and published it in 1992 in 

the Bulletin of Volcanology.

Remnants of a late Pleistocene rhyodacitic plinian 

pumice fall and ignimbrite were mapped and sampled along 

Mageik Creek. Hildreth and Fierstein then met Colin J.N. 

Wilson (invited colleague, then at Cambridge University) 

at Baked Mountain Hut on 21 July, and they spent 9 days 

together examining most parts of the VTTS, engaged in vigorous discussion of pyroclastic-flow dynamics.

1991

Hildreth and Fierstein led a 12-day wilderness backpack 

trip for 12 members (fig. 12) of the Commission on Explosive Volcanism (International Association of Volcanology and 

Chemistry of the Earth’s Interior, IAVCEI). All parts of the 

VTTS were visited on foot, 12–23 July, as well as Katmai Pass, 

Trident, and the Katmai caldera rim, and many aspects of 1912 

eruption processes were discussed. Participants included HansUlrich Schmincke (Germany, then Secretary General of IAVCEI), Bruce Houghton (New Zealand), Mari Sumita (Japan), 

Jocelyn McPhie (Australia), Mauro Rosi (Italy), Stephen Self 

(UK), Armin Freundt (Germany), Robert L. Christiansen 

(USA), Paul van den Bogaard (Netherlands/Germany), and Tim 

Druitt (UK/France). Key issues included (1) discriminating

Figure 12. Participants in 1991 Commission on Explosive Volcanism workshop at Valley of Ten Thousand Smokes. From left, Jocelyn 

McPhie, Judy Fierstein, Tim Druitt, Mari Sumita, Hans-Ulrich Schmincke, Steve Self, Paul van den Bogaard, Bob Christiansen, Mauro 

Rosi, Bruce Houghton, and Armin Freundt. View down valley from near Baked Mountain Hut. Mount Katolinat on central skyline. Note 

British short-pants colonial tradition. Photo by Wes Hildreth.
38 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

discrete vent-derived flow units from layers deposited discontinuously by sedimentation at the base of flows or developed by 

internal laminar shear within them; (2) processes of emplacement of high-energy proximal deposits and their relationship to 

valley-filling ignimbrite of inferred low velocity; and (3) origin 

of the Lethe Hills (fig. 5) in the mid-VTTS.

Hildreth and Fierstein returned alone (26 July to 3 

August) to their tent at the toe of Knife Creek Glacier 3 and 

spent a week (roped up) visiting the caldera rim and the glacial 

north slopes of Trident and Mount Katmai. Hydrothermal 

explosion breccia and mud layers on the west rim were logged 

and sampled in a snowstorm. Pyroclastic flows rich in dacite 

pumice blocks that terminated Episode I were shown to be 

partially welded, and thus not secondary (as some had argued), 

and to have issued directly from Novarupta (not as a laharic 

slurry remobilized back down the Knife Creek Glaciers).

Keith sampled the mid-VTTS thermal springs in Knife 

Creek gorge when surface waters were largely frozen, landing 

with David Keith and Game McGimsey by fixed-wing aircraft 

on 15 March. Discharge was only slightly lower than in June 

1990 and water temperatures were similar, but the springs had 

been ~10oC cooler in July and August of 1987–1989 when 

diluted by cold infiltration. In 1992, Keith and coauthors published a data-rich paper that compared chemical compositions 

of (1) major VTTS creeks, (2) springs and streams outside 

the 1912 deposits, (3) the mid-VTTS thermal springs, and 

(4) thermal springs that emerge from beneath the 1953–1958 

Trident lava flows.

Keith and Papike published several papers (discussed 

in chapter 9) on physical and chemical features of VTTS 

fossil fumaroles, addressing contrasting alteration patterns of 

rhyolitic versus dacitic pumiceous protoliths, chemical gains 

and losses, mineralogical evolution during high-temperature 

vapor-phase processes and subsequent cooling, retrograde 

reactions, argillic alteration, and weathering. Within Novarupta basin, Keith mapped locations of dozens of warm areas 

and wispy fumaroles that ranged from 25oC to 90oC during her 

1979–1991 investigations.

A special issue of Geophysical Research Letters collected 

15 papers that presented diverse results of investigations by 

the 1989 and 1990 Geophysical Expeditions.

1992

Fierstein and Hildreth (1992) published a detailed 

analysis of the 1912 eruptive sequence, defining three explosive episodes and documenting synchroneity of compositionally equivalent fall and flow units, lateral equivalence of 

high-energy proximal ignimbrite (HEPI) and valley-filling 

ignimbrite (VFI), progressive changes in rhyolite/dacite/

andesite compositional proportions in successive emplacement units, and correlation of fall units from the VTTS all 

the way to Kodiak.

Transported by helicopter from King Salmon via Kejulik 

Pass on 7 July, Fierstein and Hildreth spent a week camped at 

the southeast toe of Mount Katmai, where the Noisy Mountain 

Glacier fork descends to Katmai River. The south and east 

slopes of Mount Katmai were mapped and sampled on foot, 

and the landslide that dammed Katmai Canyon (1912–1915) 

was shown, by its intercalation in the fallout sequence, to have 

been emplaced on the first day of eruption, midway through 

Episode I. They returned to King Salmon via Katmai Pass 

on 13 July. Fierstein met Colin Wilson in King Salmon and 

returned to the VTTS, together working on details of ignimbrite emplacement until 2 August.

1993 

The USGS published 1:250,000-scale geologic maps of the 

Mount Katmai quadrangle (Becharof Lake to Cape Douglas) by 

James R. Riehle, Robert L. Detterman, and associates, based on 

130 days of helicopter-supported fieldwork, 1983–1987.

Robert B. Symonds and Beatrice E. Ritchie (USGS) 

sampled fumarolic gases at Trident and Griggs, on foot in July.

Jacob B. Lowenstern (Stanford, later USGS) identified 

Cu-rich bubbles in melt inclusions within phenocrysts from 

1912 rhyolite. These were inferred to reflect entrapment during phenocryst growth of a fluid phase that had coexisted with 

the silicate melt before eruption. By FTIR, he also found the 

melt inclusions (in quartz and orthopyroxene) to contain 3.5 to 

4.7 weight percent H2

O. Its inferred vapor saturation indicates 

that the CO2-poor high-silica-rhyolite melt had been stored 

little deeper than 4 km before its 1912 outburst.

1994

Hildreth, Fierstein, Colin Wilson, and Bruce Houghton 

flew by helicopter to Baked Mountain Hut from King Salmon 

on 4 July; they were joined by Paul Wallace (University of 

Chicago) until 17 July. HEPI were logged in detail all around 

the upper VTTS—on spurs of Baked and Broken Mountains, 

in gulches south of Novarupta, inside its ejecta ring, and 

atop the Buttress Range crest, Mount Cerberus, and Whiskey Ridge. Dozens of layers in compositionally distinctive 

packages at each section were field sieved; coarse blocks were 

weighed at the outcrop, multi-kilogram samples sieved at the 

Hut, and remainders finer than 8 mm bagged for drying and 

sieving in the lab. Largest pumice and lithic sizes and component proportions were recorded for each layer. Brown pumice 

blocks atop the Turtle were collected to determine affinity with 

either dacite (normally pale gray) or andesite (normally black); 

chemical analysis later showed them to be both (61.8–65.6% 

SiO2

). Numerous pumice clasts were collected from every 

major layer for vesicularity and density determinations in the 

lab. A helicopter took out 300 kg of samples, and the party 

hiked out on 25 July.

Symonds and Ritchie again sampled fumarolic gases at 

Southwest Trident in mid-July but were prevented from doing 

so on Mount Griggs by exceptionally severe weather.

1995

Hildreth, Fierstein, and Houghton returned to Baked 

Mountain Hut by helicopter from King Salmon for the week 

of 21–27 July. Logging, sampling, and sieving of HEPI 
Chapter 4. History of Investigations and Interpretations 39

deposits continued on West Trident, Whiskey Ridge, and the 

several deep gulches south of Novarupta and adjacent to Falling Mountain. More pumice clasts were taken for vesicularity 

and density determinations from the stratified fallout on Baked 

Mountain and the south slope of Mount Katmai. Houghton 

recognized that, within ~1 km of Novarupta, the topmost unit 

of 1912 regional fallout (Layer H) was overlain by a field of 

scattered blocks of dacite lava, products of an extrusive dome 

that had been explosively destroyed before extrusion of the 

rhyolitic Novarupta dome. Cirque headwalls on the north 

faces of Trident were photographed and sketched by helicopter. Between helicopter lifts, 1912 fallout sections were 

logged and sampled high on the east, north, and west sides 

of Mount Katmai, while Hildreth was shuttled to numerous 

landing sites on the edifice, including most notches around the 

caldera rim, to collect Katmai lava flows. On the southwest 

rim, a dacite agglutinate sheet was found to be >60 m thick 

and to drape inboard into a pre-1912 crater. On the south rim, 

a thick scoria fall deposit, partly agglutinated and zoned from 

dacite to andesite, was found to overlie a 50-m-thick rhyolite 

lava flow (later dated at 22.5 ka).

John Power, Elliot Endo, Art Jolly, and John Paskievitch 

(Alaska Volcano Observatory, AVO) reoccupied the fivestation geodetic network centered on Novarupta and undertook 

simultaneous 12–15 hour observations with five GPS receivers. They detected no deformation in the vent area, relative 

to EDM and GPS surveys in 1990 and 1993 by Jack Kleinman and Eugene Iwatsubo, who had installed the stations 

in 1989–90 (Kleinman and Iwatsubo, 1991; Kleinman and 

others, 1997). Five seismic stations from Ward’s 1987–1991 

network were reactivated and upgraded.

Symonds and Ritchie returned and sampled fumarolic 

gases at Mount Griggs on foot and at Mageik crater and the 

southeast flank of Trident with helicopter assistance. 

1996

Hildreth and Fierstein were asked by AVO to prepare a 

geologic map and hazards assessment of the whole Katmai 

volcano cluster (Fierstein and Hildreth, 2001), extending by 

helicopter their previous Novarupta-Katmai-Trident work, 

which had largely been on foot. Assisted by Michelle Coombs 

(University of Alaska) and David Tucker (Western Washington University), they set up three successive tent camps at the 

heads of the east and southeast forks of Angle Creek and of 

the east fork of Kejulik River (fig. 6). The eroded edifice of 

Alagogshak Volcano was recognized and mapped, along with 

parts of Martin and Mageik. Coombs sampled 1953–1974 

eruptive products of Trident, which became a focus of her petrologic Ph.D. work, and Fierstein began her study of the pre1912 tephra layers of the Katmai region. Fieldwork extended 

from 14 July to 1 August.

John Paskievitch and Art Jolly spent 14–28 July extending the regional seismic monitoring array by helicopter; they 

enclosed five existing and six new seismic stations in fibreglass huts (for protection from wind, snow, and bears).

1997

Hildreth, Fierstein, Wilson, Houghton, and Coombs flew 

by helicopter to Baked Mountain Hut from King Salmon on 

16 July, basing there until 15 August. Detailed attention was 

devoted to logging, field sieving, and correlating proximal 

pyroclastic fall and flow layers among the many gulches south 

and east of Novarupta. Hildreth and Fierstein tent camped for 

a few days in lower Mageik Creek, where complex pre-1912 

valley-fill deposits were logged. They spent many days by 

helicopter advancing the regional tephra and geologic mapping efforts; progress was made on Mageik, Martin, and 

Griggs Volcanoes by landing at numerous high points on all 

three. The valleys of Alagogshak, Martin, Soluka, Ikagluik, 

Windy, and Margot Creeks were cruised for tephra layers, as 

were Katmai Canyon, Noisy Mountain, and the Ukak River; 

the sites of Savonoski and Katmai villages were visited. 

Before departure on 15 August, shorelines of Iliuk Arm were 

cruised by boat for tephras and glacial deposits.

Symonds and Ritchie again collected fumarolic gases at 

Griggs, Trident, and Mageik. Since their earlier visits, highest 

recorded temperatures at Griggs had declined from 105oC to 

99oC and at Trident from 97oC to 94oC; the highest at Mageik 

crater lake remained in the range 167–173oC. All had cooled 

slightly relative to Johnston’s measurements in 1979.

Paskievitch, Jolly, and Tim Plucinski restored the array of 

seismic stations, several of which had been down from April 

until July.

Using satellite-based synthetic aperture radar interferometry (InSAR), Zhong Lu (USGS) and associates detected several 

centimeters of inflation that took place between 1993 and 1995 

within a 7-km2

 area that included the still-fumarolic Southwest 

Trident cone (Lu and others, 1997). No further inflation was 

detected there subsequently through at least 2010.

1998

Hildreth, Fierstein, Wilson, Houghton, and Coombs 

returned by helicopter to Baked Mountain Hut from King 

Salmon on 14 July, basing there until 31 July. Logging and 

sieving proximal 1912 deposits continued, as did the regional 

search for pre-1912 tephras, this year in Angle and Margot 

Creeks and Rainbow River. With ample helicopter support, mapping and sampling of Griggs, Trident, Mageik, and 

Martin Volcanoes was completed, Mount Katmai nearly so, 

and Snowy Mountain was reconnoitered. Rear-arc lavas were 

collected near Savonoski River, Rainbow River, Mount Juhle, 

and Gertrude Creek (fig. 6). A reconnaissance fly-around at 

Kaguyak caldera and landings on its two intracaldera domes 

assessed logistics for a major effort there the following year 

(Fierstein and Hildreth, 2008). After others departed, Fierstein, Wilson, and Hildreth tent-camped near Three Forks 

Overlook from 31 July until 8 August, logging in detail distal 

1912 deposits, pre-1912 tephras, and glacial deposits.

Paskievitch, Jolly, Plucinski, and Seth Moran spent two 

July weeks replacing batteries and installing seven new seismic stations, bringing the Katmai seismometer array to 
40 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

18 stations and a few repeaters. Signals were telemetered in 

real time via line-of-sight radio transmission to King Salmon, 

thence via commercial phone circuits to AVO in Anchorage 

and Fairbanks.

Symonds and Ritchie again sampled fumarolic gases 

on Griggs, Trident, and Mageik, all of which had maximum 

temperatures similar to those of 1997. They installed a lakemonitoring package in Mageik crater lake, intended to record 

temperature, pH, conductivity, and lake level every two hours 

for the following year. At the time, lake water pH was 1.6 and 

temperature 72oC.

1999

Fierstein and David Tucker picked up a Zodiac inflatable 

boat in Anchorage, met Hildreth in King Salmon on 12 July, 

and were dropped by two Cessna float planes at the islet in 

Kaguyak caldera lake. After photographing and sketching the 

walls from the islet, the three sampled all lavas and fragmental 

deposits exposed on the walls and rim, by Zodiac and on foot. 

Soundings of lake depths were made and lake waters collected 

for analysis. From 22 July until 2 August, the outer slopes 

of the Kaguyak edifice, the ignimbrite outflow, and tephras 

exposed in coastal bluffs were sampled by helicopter. Additional sampling was done at Snowy Mountain, Devils Desk, 

and the several Savonoski volcanic cones. 

Houghton, Wilson, and Julia Eve Hammer (Brown University petrology postdoc) arrived at King Salmon on 3 August 

and were flown to Baked Mountain Hut (fig. 13). Houghton 

and Hammer did further work on Novarupta proximal deposits until 14 August, and Fierstein and Wilson worked on the 

valley-filling ignimbrite in the upper and lower VTTS until 

23 August. Numerous pyroclastic samples were sieved at the 

Figure 13. Participants in 

1999 expedition to Novarupta. 

From left, Julia Hammer, Bruce 

Houghton, Colin Wilson, Judy 

Fierstein, and Jim Sink. Pumicecovered slopes and ice-filled 

crater of Mount Griggs at upper 

right. Photo by Wes Hildreth.
Chapter 4. History of Investigations and Interpretations 41

Hut, and the sub-8-mm fractions were flown out for lab work 

by helicopter in several duffle bags. All four hiked out to 

Three Forks Overlook.

Paskievitch replaced batteries and performed system 

checks for the Katmai seismic array. Several stations had been 

inoperative during the winter months. The network became a 

mainstay of Alaska Volcano Observatory operations, locating 1,000 to 2,000 earthquakes per year in the Katmai region 

(Mount Steller to Mount Martin) for the whole decade through 

2010. Nearly all have been in the ML range –0.5 to 2.5 and 

shallower than 10 km, most of them clustered in the same 

four areas identified by Ward in 1987–1991—Martin-Mageik, 

Trident-Novarupta, Mount Katmai, and northwest of Snowy 

Mountain. Rare events have been ML 2.8 to 4.5.

2000

Fierstein and Hildreth spent a week (16–23 July) doing 

helicopter geology from King Salmon, principally along Angle 

Creek, on the Savonoski cones, and on the Rainbow River 

cone and debris-avalanche deposit. Local problems concerning the pyroclastic deposits were reexamined along Mageik 

Creek, Windy Creek, the Griggs fork of Knife Creek, and near 

Three Forks. 

Michelle Coombs and associates published her petrological dissertation work on lavas and ejecta of the 1953–1974 

Trident eruptions, collected during her 1996–1998 fieldwork. 

Eruptive products were shown to range from 55.8 to 65.5 

percent SiO2 and from ~1,000oC (andesite) to 890oC (dacite) 

in Fe-Ti-oxide temperature. H2O contents of melt inclusions 

in phenocrysts and phase-equilibria experiments indicated that 

pre-1953 magma storage had been as shallow as 3 km and that 

mixing of ascending andesite into resident dacite may have 

taken place just before the 1953 eruption.

Hildreth and Fierstein published an overview article that 

summarized the eruptive sequence, caldera collapse chronology, and 1912 magma storage model, establishing the compositional affinity of the 1912 suite to Mount Katmai.

2001

Fierstein and Hildreth spent 12 days (28 July to 9 August) 

doing helicopter geology from King Salmon, principally along 

Margot Creek and the Griggs fork, on Snowy Mountain and 

Mount Denison, and on the several lava remnants between 

Mounts Ikagluik and Juhle. Spot checks were made on Mageik 

and Griggs, and several rim stops around Katmai caldera. The 

helicopter was shared with John Paskievitch, who was installing 

new batteries and servicing the far-flung seismometer network, 

so, on flightless days, Fierstein and Hildreth investigated glacial 

and tephra deposits by truck between Naknek and Lake Camp. 

A boat was hired to examine exposures along bluffs of the 

Naknek River, where they learned why Sayre and Hagelbarger 

had a hard time ascending the rapids in 1918. While Hildreth 

recuperated from an injury, Fierstein devoted a day to reconnoitering Ukinrek Maars, The Gas Rocks, and Blue Mountain, all 

on the southwest side of Becharof Lake.

Coombs ran phase-equilibria experiments on 1912 rhyolite in the lab of James E. Gardner (University of Alaska) and 

Hammer on 1912 dacite and andesite in the lab of Malcolm J. 

Rutherford (Brown University). Results suggested preeruptive 

storage of the rhyolite in the depth range 1.6 to 4.4 km, and of 

the zoned dacite-andesite continuum at 4 to 5 km. Uncertainties include quartz stability, the effects of ranges in magma 

temperature, and the influence of preeruptive CO2

 and SO2

contents of the fluid phase on pressure inferences.

2003

Fierstein, Wilson, and Hildreth arrived at King Salmon 

on 16 July and remained in the area until 15 August. Fierstein 

and Wilson based much of the time at Baked Mountain Hut, 

completing mapping of the compositionally distinctive packages that make up the 1912 ignimbrite in the VTTS, Katmai 

Pass, and Mageik Creek. Nine sequential packages of flow 

units, each with different proportions of rhyolite, dacite, and 

andesite pumice, were mapped, many with sharp mutual contacts. Pumice proportions and local intercalation of flow and 

fall deposits were used to link ignimbrite formation and coeval 

fall deposition. The compositional zonation permitted documentation of how a major ignimbrite sheet is incrementally 

assembled, as published by Fierstein and Wilson (2005).

Houghton and Nancy Adams (University of Hawaii) 

based at Baked Mountain Hut between 27 July and 10 August 

and concentrated on collecting pumice suites from upper Knife 

Creek, Novarupta basin, and the south slope of Mount Katmai; 

they also mapped in detail the Episode IV dacite block bed in 

Novarupta basin. Hildreth devoted 2 days to Mount Denison, 

and he flew to the Katmai caldera rim on three different days, 

variously with Fierstein, Adams and Houghton, or Andrew 

Calvert (USGS). Calvert visited 21–25 July and spent a day 

with Hildreth at Kaguyak caldera, scouting for samples suitable for Ar dating. Hildreth also sampled most of the Tertiary 

granitoid plutons in the Katmai region. Fierstein and Hildreth flew together to Kaguyak for a day and, on another day, 

beyond Kaguyak to reconnoiter and sample Fourpeaked and 

Douglas Volcanoes. They sampled all units at The Gas Rocks 

and many at the Blue Mountain dacite dome complex, and 

Hildreth and Houghton returned a week later to complete the 

sampling and mapping of Blue Mountain (Hildreth and others, 

2007). Families and friends of Hildreth and Fierstein gathered 

at Brooks Lodge 13–15 August for a walk to Three Forks that 

celebrated completion of the project; participants included 

Garniss Curtis and Ian Carmichael, Berkeley professors who 

had encouraged Hildreth’s rookie trip to the VTTS, a month 

on foot in 1976. It was the 50th anniversary of Curtis’ first trip 

to the VTTS in 1953 (fig. 14).

A volcanological geologic map of the Katmai volcanoes 

and VTTS was published by Hildreth and Fierstein (USGS 

Map I-2778).

Seth Moran (AVO) determined first-motion fault-plane 

solutions for 140 earthquakes (1995–2001) and inverted the 

solutions for stress tensors. He was thus able to discriminate 
42 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Figure 14. Garniss Hearfield Curtis (right) with the authors 

near Three Forks in August 2003, on 50th anniversary of his first 

expedition to the Valley of Ten Thousand Smokes. Curtis always 

wore tennis or running shoes during fieldwork. Photo by Julie 

Donnelly-Nolan.

(1) seismicity related to regional tectonics (near Snowy 

Mountain and off the volcanic axis) from (2) seismicity along 

and near the axis that he attributed variously to hydrothermal 

convection, edifice loading, or activation of fractures that may 

have been created during the many 1912 earthquakes of magnitude 6.0–7.0 (Moran, 2003).

2004

Houghton, Wilson, Fierstein, and Hildreth published a 

stratigraphic and dynamic analysis of the 1912 ultraproximal deposits of Episodes II and III around Novarupta. This 

was the most comprehensive characterization yet undertaken 

of complex proximal deposition during a plinian eruption 

because such deposits are seldom both preserved and exposed. 

Simultaneous with the buoyant plinian plume, sedimentation 

from margins of the jet and lower plume produced local pyroclastic flows and sector-confined fallout wedges that intercalated only proximally with the region-wide plinian pumice-fall 

layers. Relative to the regional falls, most such proximal 

deposits are enriched in andesitic and banded pumice and in 

denser lithic fragments, reflecting lateral heterogeneities in 

particle concentration and componentry around the periphery 

of the emerging jet. It was inferred that a concentrated annular 

zone surrounding the jet core was more susceptible to fountaining and collapse because of its higher density and lower 

velocity. Confluence of dacite and andesite magmas and the 

shift from lateral conduit flow to vertical flow beneath the vent 

were implicated as contributing to the heterogeneities and thus 

to jet-margin instabilities. Four concurrent transport regimes 

were identified for the pyroclasts ejected.

2004–2010 

AVO continued to amass seismic data from its 18-station array, serviced annually by John Paskievitch. Jolly and 

associates applied traveltime inversion tomography to >1,000 

local earthquakes (1996–2001) to produce a 3-dimensional 

P-wave-velocity structural model for the Katmai volcano 

cluster (Jolly and McNutt, 1999; Jolly and others, 2007). 

They confirmed a Mageik-to-Trident low-velocity zone centered on Katmai Pass (extending to depths of at least 8 km) 

and demonstrated absence of such an anomaly beneath Griggs 

and Snowy Mountain Volcanoes. Stephanie Prejean (AVO) 

and associates relocated >7,000 earthquakes using the doubledifference method to sharpen images of seismic clusters 

beneath Martin and Mageik volcanoes and planar structures 

near Snowy Mountain, and to suggest that the low-velocity 

body under Katmai Pass and Trident extends to depths shallower than 5 km and reaches toward Novarupta at its shallowest level. In summer 2008, they installed 11 temporary 

seismometers near Trident in an effort to acquire still better 

resolution of the velocity anomaly.

Principal Contributors to the Early 

Geologic Investigations at Katmai

George Martin

George Curtis Martin (1875–1943) was an intrepid field 

geologist with the Alaska division of the USGS for 20 years. 

A son of Massachusetts, he graduated from Cornell in 1898 

and earned a Ph.D. in 1901 at the Johns Hopkins University, 

where he was a paleontology instructor 1901–1904. After 

studies of the geology and mineral resources of Maryland for 

the Maryland Geological Survey (1898–1904), he led three 

USGS Alaskan expeditions (1903–1905), investigating petroleum and coal resources of Controller Bay, Cold (Puale) Bay, 

and the west shore of Cook Inlet. In 1905 and 1910 Martin 

mapped the coal fields of the Matanuska Valley, in 1906 he 

returned to Controller Bay (Katalla oil field) and Bering River 

coal field, and in 1908 he reconnoitered the coal resources of 

Colorado east of the Front Range. His 1903 and 1904 trips 

to Cold Bay in an open boat made him uniquely familiar with 

the remote Katmai coast and thus the choice by the Research 

Committee of the National Geographic Society to investigate 

the Katmai eruption in the summer of 1912 (Martin, 1913). 

From 1909 to 1923, he spent 2–4 months in Alaska almost 
Chapter 4. History of Investigations and Interpretations 43

every summer, mapping the Lake Iliamna-Lake Clark region, 

Kodiak and Afognak Islands, the Kenai Peninsula, and the 

Matanuska and Nenana coal fields, as well as investigating 

gold-bearing placers near Cape Yakataga and in the Shumagin 

Islands. During the 1920s, he undertook expeditions to the 

Yukon and Koyukuk regions, the upper Kuskokwim drainage, 

and the Chignik district, as well as intensifing his study of the 

stratigraphy and petroleum resources of the Alaska Peninsula. 

Martin published numerous reports, notably a 1926 monograph 

on the Mesozoic stratigraphy of Alaska and a 1921 report on 

petroleum in Alaska. While Alfred Hulse Brooks served with 

the Army in Europe during World War I, Martin was acting 

Geologist-in-Charge of the USGS Alaska Division. While 

he was in charge, Martin examined the mines of the Chitina 

Valley and the Fairbanks district, and the USGS opened its first 

Alaskan office (in Anchorage). He retired from the USGS in 

1924 and became a consulting geologist, investigating among 

other things the petroleum resources of Mexico. In 1935, while 

living in Corvallis, Oregon, Martin was appointed Executive 

Secretary of the Board of Geographic Names by the Secretary 

of the Interior. He had travelled to 47 states, Canada, Mexico, 

and Central America. Mount Martin Volcano and several Martin Creeks are named for one of Alaska’s most adventurous and 

productive pioneering geologists, one who added much to both 

mineral wealth and pure science.

Robert Griggs

Robert Fiske Griggs (1881–1962) was a field-based 

botanist who graduated from Ohio State University in 1903 

and earned a Harvard Ph.D. in 1911. He served on the botany 

faculties at Ohio State (1906–1921), George Washington 

University (1921–1947), and the University of Pittsburgh 

(1947–1952). He was a founding member of the Ecological Society of America (1915) and its President in 1943. His 

research included the cytology of fungi, the willows of Ohio, 

and the systematics of kelp. His expeditions sponsored by the 

National Geographic Society led to discovery and exploration 

of the Valley of Ten Thousand Smokes and to his leading role 

in establishment of Katmai National Monument. The Alaskan 

years turned him into an ecologist with interests principally in 

the colonization dynamics of marginal environments, including in his later career timberline studies at Mount Washington 

(New Hampshire) and in the Rocky Mountains. During World 

War II, he was Chair of the Division of Biology and Agriculture, National Research Council. In 1959, Knife Peak volcano 

adjacent to the VTTS was renamed Mount Griggs. In a sense, 

the present monograph is an update of Griggs’ well-illustrated 

1922 book, “The Valley of Ten Thousand Smokes,” published 

by the National Geographic Society.

Clarence Fenner

Clarence Norman Fenner (1870–1949) was an analytical and field petrologist who graduated from Columbia as a 

mining engineer in 1892 and for 15 years studied ore deposits 

in Canada, Mexico, the western United States, and South 

America. Returning to Columbia in 1907, he completed his 

Ph.D. in 1910 and then joined the staff at the Geophysical 

Laboratory (1910–1938). His thesis on the Mesozoic basalts 

of the Watchung Mountains (New Jersey) included study of 

zeolites and secondary replacement minerals; these investigations and those on ore deposits fired a lifelong interest in 

hydrothermal and pneumatolytic processes involving “gaseous 

emanations” (Wright, 1952). This fascination predisposed him 

at Katmai to hypothesize exothermic reactions related to rhyolitic magma ascent and volatile escape, to which he attributed 

both large-scale assimilation and the explosive eruption. The 

Mesozoic sills of New Jersey may also have influenced his 

postulation of a shallow magmatic sill beneath the VTTS as the 

source of its tuff and fumaroles. In the lab, Fenner established 

the stability relations among the polymorphs of silica, and 

during World War I he pioneered the use of optical pyrometers in controlling glass furnaces when assigned to improve 

and extend U.S. capacity in producing optical glass (formerly 

imported from Germany). In the early years of U-Th/Pb 

geochronology, he made a study of U-Th minerals and devised 

chemical methods for separation and analysis. He also recognized the Fe-enrichment trend in differentiation of tholeiitic 

basalts, widely called the “Fenner Trend.” At Yellowstone, 

he pioneered core drilling in the geyser basins, reached 180oC 

at 124-m depth, and investigated alteration minerals, compositional gains and losses, and relative meteoric and magmatic 

contributions to hydrothermal fluids. For the Gardiner River 

mixed lava complex at Yellowstone, Fenner again invoked his 

“gaseous emanations” hypothesis, suggesting that solid basalt 

had been permeated and corroded by “tenuous rhyolitic solutions”—liquid and gaseous—causing “replacement analogous 

to granitization.” He also advocated reconsideration of liquid 

immiscibility as an important magmatic process. At age 66, 

Fenner joined a research expedition to Antarctica (1936–1937). 

In retirement, Fenner returned to Peru (1938–1939) where 

he mapped the “incandescent tuff deposits” (ignimbrites) of 

the Arequipa region, likened them to the VTTS deposits, and 

adopted the local term sillar for nonwelded ignimbrites indurated by vapor-phase crystallization (and sintering). Fenner 

was one of America’s most versatile, energetic, and imaginative 

geologists. He spent 2 months at Katmai in 1919 and nearly 3 

months there with Yori in 1923 (fig. 8).

E.T. Allen

Eugene Thomas Allen (1864–1964) was a geochemist of 

exceptional breadth who was based at the Geophysical Laboratory for 37 years. Another son of Massachusetts and descended 

from its earliest colonists, he graduated from Amherst College in 1887 and completed a Ph.D. in chemistry at the Johns 

Hopkins University in 1892. Allen spent two years at Harvard 

(1893–95) as what would now be called a postdoctoral fellow, and he taught at the Women’s College of Baltimore (now 

Goucher College), the University of Colorado, and Missouri 

School of Mines (Rolla) until 1901, when he joined the U.S. 

Geological Survey. In 1906, he transferred to the Geophysical 

Laboratory where he remained a research chemist (and repeatedly its acting director) until his retirement in 1933. Allen was 
44 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

a superior analytical chemist and a pioneer in high-temperature 

experimental methods and the synthesis and stability fields of 

silicate minerals. From 1910 to 1917 he shifted his emphasis to the stability of metallic sulfides and sulfates, clarifying 

processes of secondary enrichment of ore deposits. During 

World War I, along with Fenner and Zies, Allen researched 

the trace-element composition and production of optical glass, 

supply of which from Germany had been cut off. Participation in the 1919 expedition to Katmai confirmed another career 

shift, which had begun at Lassen Peak in 1915. The remainder 

of Allen’s research career was devoted to field and chemical 

investigations of volcanic gases and thermal waters. His classic chemical study of fumaroles in the Valley of Ten Thousand 

Smokes (Allen and Zies, 1923) was followed by landmark 

papers on the fumaroles, geysers, and hot springs of Lassen, 

The Geysers (California), and Yellowstone. Allen was elected 

to the National Academy of Sciences in 1930. He died at home 

in Arlington, Massachusetts, 106 days after his 100th birthday.

E.G. Zies

Emanuel George Zies (1883–1981) was a geochemist, 

mineralogist, and pioneer investigator of volcanic gases and 

their sublimates. Born in Baltimore, he graduated from the 

Johns Hopkins University in 1906 and completed his Ph.D. 

in chemistry there in 1909 with a dissertation entitled “The 

osmotic pressure of cane sugar solutions at 0o.” Zies joined 

the staff of the Geophysical Laboratory in 1913 as a geochemical volcanologist, retired formally in 1949, but remained an 

active emeritus researcher there until 1967. After participating 

in the 1919 expedition to the Valley of Ten Thousand Smokes 

(fig. 9), he conducted field studies at volcanoes in Java, Bali, 

Hawaii, South America, El Salvador, Guatemala (Santa 

María), Mexico (Parícutin), and Italy (Pantelleria). Ziesite 

is a copper vanadate deposited by fumaroles in the summit 

crater of Volcán Izalco (El Salvador), which was born in 1770. 

After Robert L. Smith published his classic 1960 review “Ash 

Flows,” he and Zies met for lunch at the Cosmos Club, and 

Zies was highly congratulatory about Smith’s understanding of 

pyroclastic flows and his insights about trace-metal transport 

by the VTTS fumaroles. Because Smith had written, however, 

that “Unfortunately, for students of pure magma chemistry, 

these deposits are formed from a mixed magma...” (Smith, 

1960, p. 835), Zies genially jabbed him—”What the hell’s a 

“pure magma”?

Garniss Curtis

Garniss Hearfield Curtis (1919–) is a field geologist, 

volcanologist, and geochronologist who graduated from the 

University of California at Berkeley in 1942 and worked 4 

years as a mining engineer and geologist before returning to 

Berkeley in 1946, where he completed his Ph.D. and joined 

the Berkeley faculty in 1951. For his thesis he mapped a 

large area of the Sierra Nevada near Markleeville and Topaz 

Lake and investigated the origins of the extensive andesitic 

breccia deposits of the Mehrten Formation. As a member of 

the Katmai Project (1953–1954), he helped reinterpret the 

1912 eruption in a modern volcanological framework and isopached the medial pumice-fall deposits, proving that Novarupta (not Mount Katmai) was their source vent. He was a 

pioneer in K-Ar dating, first at the University, later as founder 

of the Berkeley Geochronology Center. His ages calibrated 

the Tertiary land-mammal stages of North and South America 

and the fossil hominid stratigraphy of East Africa and of 

Homo erectus in Java. Curtis is also an authority on the 

geology of the Berkeley Hills, where he taught field methods 

to generations of geologists. He returned to Katmai with the 

authors (fig. 14) in 2003, the fiftieth anniversary of his initial 

summer in the VTTS.
Chapter 5. Products of the Eruption 45

Chapter 5

Products of the Eruption

The 60-hour-long explosive sequence at Novarupta consisted of three discrete episodes (fig. 2), separated by lulls of at 

most a few hours duration (Martin, 1913; Hildreth, 1983; Fierstein and Hildreth, 1992). Episode I began with plinian dispersal 

of purely rhyolitic fallout (Layer A) and synchronous emplacement of rhyolitic ignimbrite. Nowhere has any initial ash or phreatomagmatic deposit been found beneath Layer A, indicating that 

the plinian column first witnessed at 1300 h (Alaskan local time) 

on 6 June indeed marked the onset of eruption. Vent opening was 

accompanied, however, by a blast that spread sheets of highenergy proximal ignimbrite as far as 9 km radially. After ejection 

of ~3 km3

 of rhyolitic magma over the course of a few hours, 

small amounts of andesitic and dacitic magma began contributing to the sustained eruption column, marking (by definition) the 

onset of plinian Layer B (fig. 15). The juvenile ejecta in Layer 

B are zoned from >99 percent rhyolite at its base to only about 

15 percent at its top, matching the progressive shifts in (andesite/dacite/rhyolite) pumice proportions in the main sequence of 

zoned ignimbrite (fig. 16) emplaced concurrently in the Valley of 

Ten Thousand Smokes (Fierstein and Hildreth, 1992; Fierstein 

and Wilson, 2005). Only a few thin andesite-dacite flow units 

capping the Episode I deposits lack a widespread fallout equivalent, suggesting that ignimbrite emplacement barely outlasted the 

plinian phase. Episode I lasted ~16 hours and produced almost 

all of the ignimbrite (~11 km3) and roughly half of the fall deposits (8.8 km3 out of 17 km3

).

Episode II began after an eruptive lull no longer than 

a few hours and consisted principally of plinian dispersal of 

phenocryst-rich dacite that deposited regional fall Layers C 

and D. Intercalated within these layers proximally are minor 

Figure 15. Novarupta pumice-fall section on south flank of Mount Katmai, 10 km southeast of Novarupta and 4 km south of rim of 

Katmai caldera. Vaguely shower-bedded Layer A is 1.4 m thick, tripartite Layer B is 1.0 m thick, and bevelled Layer C is 1.6 m thick to its 

eroded surface. Deposit rests directly on glacial till.
46 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

intraplinian pyroclastic-flow and surge deposits made up 

predominantly of dacite and andesite (Fierstein and Hildreth, 1992; Houghton and others, 2004). Subordinate rhyolite (identical to that of Episode I) accompanied the dacite 

during deposition of the lower part of Layer C but was very 

sparse thereafter.

Episode III began after another lull as long as several 

hours, during which fines-rich Layer E settled from lingering ash clouds of composite origin (Fierstein and Hildreth, 

1992). It was similar to Episode II in depositing plinian 

dacite Layers F and G regionally, along with thin, proximally 

H

H

E

FG

CD

FG

CD

FG

CD

E

B3

B2

B1

A

H

E

B3

B2

B1

A

BRU

Andesite-rich 

falls Intraplinian

PDCs

90% rhy VFI

50% rhy VFI

andesite-rich VFI

All-rhy VFI

All-rhy VFI

valley-filling

ignimbrite

Rhydominant

Rhypoor

Pkg 8

Pkg 9

Pkg 7

Pkg 6

Pkg 5

Pkg 4

Pkg 3

Pkg 2

Pkg 1

HEPI

Time-equivalent fallout

(no thickness

significance)

DOWN

MAGEIK

CREEK

KATMAI

PASS NEAR VENT DOWN-VTTS A

B

intercalated, sheets of andesite-dacite ignimbrite and sectorconfined lobes of fallout (Fierstein and others, 1997; Houghton and others, 2004). Layer H is another postplinian ashfall 

deposit, finer grained and more widespread than Layer E, 

that also settled from ash clouds of composite origin (Fierstein and Hildreth, 1992). The dacite pumice that dominates 

the products of plinian layers C, D, F, and G shows similar 

ranges of bulk and mineral compositions in all four layers (fig. 17). Eruptive styles were likewise similar, though 

Layers C and D were more strongly dispersed toward the 

southeast (Fierstein and Hildreth, 1992).

Figure 16. Schematic sketches illustrating relations among 1912 pyroclastic deposits. A, Cartoon summarizing 

ignimbrite facies and time-equivalent fall deposits (Layers A through H). Nine compositionally distinguishable ashflow packages (Pkg) are represented in valley-filling ignimbrite (VFI) and eight of the nine in high-energy proximal 

ignimbrite (HEPI). Rhyolite is abbreviated, rhy. BRU, block-rich flow units that dominate small-volume Package 9, 

which was emplaced only on valley floor, not as HEPI. Thicknesses not to scale; vertical dimension scaled to depict 

time equivalence. B, Generalized sketch illustrating influence of topography on landscape-mantling fall deposits and 

contemporaneous ignimbrite packages (patterned) that are intercalated near Katmai Pass and along Mageik Creek. 

Episode I subunits are colored identically in both panels. Episode II and III regional fall deposits are uncolored, but 

intercalated ultraproximal falls and pyroclastic-density-current deposits (PDCs) are gray.
Chapter 5. Products of the Eruption 47

G

F

E D

C-D

C

Figure 17. Pumice-fall deposit of Episodes II and III in upper Knife Creek, 4 km northeast of 

Novarupta. Geologist stands on fluvial pumice beds reworked during eruptive lull between 

Episodes I and II; they rest on sintered ignimbrite packages 8 and 9 at gulch floor. Coarse base of 

Layer C, just above geologist’s head, contains subordinate rhyolitic pumice, but rest of 12-m-thick 

fallout sequence is 99 percent dacitic. Fines-rich layer, 2-3 cm thick, that crosses middle of 

image is “C–D parting,” which separates 2.4 m of Layer C from 1.6 m of Layer D. Fines-rich Layer 

E, 10-15 cm thick, represents lull between Episodes II and III. Coarse Layer F grades up into 

Layer G, most of which is eroded here.
48 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

This threefold framework (fig. 2), worked out by stratigraphic analysis of proximal, medial, and distal deposits, fits 

well with the three timed intervals of ashfall at Kodiak (170 

km downwind) and with the three downwind ash layers measured by Martin (1913) and correlated by microprobe analysis 

of shards by Fierstein and Hildreth (1992).

Fallout volumes calculated for Episodes II and III are 4.8 

km3 and 3.4 km3 (Fierstein and Hildreth, 1992; Fierstein and 

Nathenson, 1992). Added to 8.8 km3 for Episode I fallout, 

the total 17 km3 of tephra is equivalent to ~6.5 km3 of magma 

emplaced as fallout. Because the thickest ignimbrite deposits 

in the upper VTTS are welded and not deeply incised, their 

volume can only be approximated as 11±2 km3, equivalent to 

~7±2 km3 of magma. For the three-episode magma total of 

~13.5 km3, we estimate that 55 percent was rhyolite, 35 percent dacite, and no more than 10 percent andesite.

The explosive episodes were followed by extrusion of 

three lava domes. No evidence is recognized that pins down 

the timing of these extrusions, but records of silicic eruptions elsewhere suggest that they could have taken place 

within days or as long a year or so after the plinian events. 

A small dacite lava dome that plugged the Episode III vent 

was subsequently destroyed by vulcanian explosions that 

scattered an 8-km2

 block bed atop Layer H (fig. 4 of Adams 

and others, 2006a). The same vent was then plugged by the 

rhyolitic Novarupta dome, which survives a century later 

(fig. 18). On the floor of Katmai caldera, which collapsed 

fitfully during the eruptive sequence at Novarupta (Hildreth, 

1991; Hildreth and Fierstein, 2000), another dacite dome 

was extruded and then partially disrupted explosively. This 

was the crescentic or Horseshoe Island dome first seen by 

Griggs in 1916 and sampled by Fenner in 1923 before it was 

covered by the deepening caldera lake (fig. 5).

Eruptive Episode I 

Reconstructing stratigraphic relationships between the 

main VTTS ignimbrite and plinian Layers A and B was surprisingly difficult. The opening plinian ejecta that produced 

Layer A were strongly dispersed east-southeastward in a 90o 

sector (fig. 19) across the snow-covered glaciers and ridges of 

Trident and Mount Katmai. Layer A is widely intact on the 

southern slopes of those peaks, but the ignimbrite did 

Figure 18. Novarupta rhyolite dome, 380 m across and 65 m high, beyond which, viewed westward, Novarupta 

basin merges into the upper Lethe arm of the Valley of Ten Thousand Smokes. Buttress Range rises on skyline, 

pumice-cloaked Baked Mountain at right, and northern spur of Falling Mountain at left. Just right of that 

spur, in middle distance, where light-colored alluvial pumice fan (just left of center) abruptly enters narrow 

snow-filled gorge, compacted pyroclastic deposits dip gently back toward Novarupta, marking west margin of 

Episode I vent structure, which is backfilled with welded tuff. Unlike many lava domes, Novarupta is a simple, 

subcircular, axisymmetrical extrusion, not much wider than the orifice of its conduit.
Chapter 5. Products of the Eruption 49

Figure 19. Isopach diagrams for 1912 tephra falls: Layers A and B of Episode I; combined Layers C, D, and E for Episode II; and 

combined Layers F, G, and H for Episode III. Thickness contours in cm. Outline of VTTS is shown for reference. Dots are sites of 

measured sections; for abundant proximal and medial sites, see Fierstein and Hildreth (1992). See figure 6 for wider geographic context 

of Shelikof Strait and Kodiak Island. NL, Naknek Lake.

not extend that far. On the northern slopes, serial pulses of 

high-energy proximal ignimbrite scoured fall deposits from 

highland ridges, ice movement disrupted most supraglacial 

pyroclastic deposits, and ignimbrite filling the upper VTTS 

is so thick that its base is nowhere exposed. Only in upper 

Mageik Creek south of Katmai Pass and at a few marginal 

sites where ash flows feathered out in the Trident saddles, 

on Mount Katmai, and in the Griggs fork of Knife Creek are 

intercalations of all-rhyolite fallout and all-rhyolite ignimbrite 

preserved and exposed. Because Fenner’s 1923 ascent to the 

caldera rim was across the Knife Creek Glaciers (where 1912 

deposits are disrupted) and all previous ascents had been from 

the south side of Mount Katmai, the early investigators appreciated neither that fallout and ignimbrite were interlayered nor 

that the pumice-fall deposits thinned and fined toward Mount 

Katmai, away from Novarupta.

Layer A

The all-rhyolite plinian fall deposit is as thick as 1.5 m 

near Katmai River (figs. 15, 20). It may have been thicker 

on the northern slopes of Trident, where it was intercalated 

with and scoured by ash flows or was subsequently eroded or 

sloughed over snow. Along its narrow east-southeasterly 

1912 FALLOUT

Layer A Layer B

Layers C+D+E Layers 

F+G+H

VTTS

0 50 km
50 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

FG

E

F2?

F2

F1

G

G

D D

D

D

D

D

D

B3

B1

B1

B

CD

FGH

A 1

2

3

4

5

6

B2

B3 B3

B1

Brhy dom

Bdac dom

CD

FGH

B1

E

E

A

H

G?

G

F1?

F1

F1

F2

F1

G

H

H

H

H

H

F2

C

C

C

C

C

C C

100

50

0

cm

A

A A

A

B3 C

B3

B3

B2

B2

B2

830 cm

3.8 km

300 cm

80 cm

100 cm

160 cm 375 cm

~125 cm

240 cm

200 cm

130 cm

not exp Jn soil not exp soil till soil

K-mud

soil

soil

60-100 cm

strat

fall/flow

sequence

surge

E

pf

pf

HEPI

ig

Pkg 9

ig

strat pf

rwkd

2 m

2 m

Pkg 8

ig

Pkg 7

ig

Pkg 1

1

3

4

5

6 7

2

Knife Ck Baked Mtn Upper Mageik Ck Katmai Pass Lower Mageik Ck So. Trident Katmai River Geographic Harbor

Kodiak Island

40 ̊ ( ) 1.7 km350 ̊ ( ) 7.8 km

140 ̊ ( )

13 km

130 ̊ ( )

36 km

120 ̊ ( )

110 km

120 ̊ ( )

8.5 km

180 ̊ ( )

8.9 km

160 ̊ ( )

5.8 km

180 ̊ ( )

2 1 3 4 5 6 7 8

9

Figure 20. Representative fall-deposit sections measured at various distances and azimuths from Novarupta, as indicated at top of 

each column. Selected layers color coded for clarity of correlations. Inset shows numbered section locations on outline of VTTS 

ignimbrite and Katmai caldera (as in figure 5). For far-downwind section 9, color zones 1–6 in distal ash were correlated as indicated by 

microprobe and discussed by Fierstein and Hildreth (1992). Abbreviations: Jn, Jurassic Naknek Formation; rwkd, reworked; HEPI, highenergy proximal ignimbrite; ig Pkg, ignimbrite package; strat, stratified; K-mud, layer of hydrothermal mud ejected from Katmai caldera 

during its collapse.

dispersal axis, Layer A constitutes the basal 15 percent of 

intact fallout sections on Trident at distances of 6–8 km downwind, ~30 percent near Katmai River (10–15 km), and >60 

percent on Kodiak Island (100–180 km). As far as ~13 km 

from vent, Layer A is a pumice fall that tends to be vaguely 

shower-bedded, exhibiting a few slightly coarser intervals 

within meter-thick sections. On the mainland the deposit is 

everywhere fines-poor, having ≤1 percent ash finer than 63 μm 

as far as 36 km downwind. 

Medial deposits are dominated by white crystal-poor 

high-silica-rhyolite pumice, much of which has a lustrous 

silky sheen owing to finely elongate vesicles that impart a 

fibrous texture. Some pumice has more equant vesicles or 

has equant vesicles superimposed on the tubular or stretched 

generation. Maximum pumice size (average of 5 largest at 

each site) decreases from 17 cm on the south flank of Trident 

(7 km from vent), to 1.5 cm at Geographic Harbor (36 km), 

and to 0.2 cm on the west coast of Kodiak Island (110 km). 

Corresponding average maximum lithic sizes measured at 

the same locations are 9 cm, 0.4 cm, and <0.1 cm. Scattered 

pumice clasts as large as 25 cm and lithics up to 15 cm can 

be found near the dispersal axis on the south slopes of Trident 

and Mount Katmai. Representing the vent-opening outburst 

of ejecta, Layer A contains as much as 24 weight percent lithic 

fragments as far as 13 km downwind, but lithic content drops 

off to ~10 weight percent along the Shelikof coast (40–42 km) 
Chapter 5. Products of the Eruption 51

and to only ~1 weight percent at Kodiak (170 km). The lithics 

are predominantly sedimentary rocks of the Naknek Formation, but they also include Trident andesites and Falling Mountain dacites, all three being lithologies that crop out adjacent to 

the vent at Novarupta.

The rhyolite pumice has only 0.5 to 3 weight percent phenocrysts, but liberation of crystals during eruptive fragmentation resulted in Layer A containing 2-3 weight percent free 

crystals on the south slopes of Trident and Katmai (5–13 km 

downwind), 4–9 percent at the Shelikof coast (40–42 km), and 

~10 percent at Kodiak (170 km). Layer A is fairly well sorted 

(sø=0.6–2.0), and sorting improves downwind (fig. 21). At a 

site 7 km from vent where median grainsize (Md) is 6.5 mm, 

sø is 1.6, and at Kodiak where Md is 0.2 mm, sø is 1.0. The 

quantitative data for this summary are tabulated in Fierstein 

and Hildreth (1992). 

The only phenocrysts (Hildreth, 1983; Avery, 1992) 

common in the crystal-poor rhyolite pumice of Layer A are 

subequal amounts of plagioclase (≤1.2 mm; An25–29) and 

dipyramidal quartz (≤0.8 mm), which contains abundant 

Figure 21. Complete 1912 fallout section, 23 cm thick, including Layers A–H. Location is well south of dispersal axis, at site of Katmai 

village, 30 km southeast of Novarupta. Knife is 8.5 cm long. Section overlies organic-rich soil and is overlain by wind-reworked tephra.

melt inclusions (Clocchiatti, 1972, 1975; Lowenstern, 1993). 

These are accompanied by sparse orthopyroxene (En49–50) and 

titanomagnetite, much sparser ilmenite, apatite, and pyrrhotite, and rare zircon. There is little or no clinopyroxene in 

the rhyolite, although a trace is present within some Layer B 

rhyolite pumice, where contamination by coerupted dacite is 

a possibility. Although absent in most of the rhyolite pumice, 

trace amounts of unrimmed amphibole euhedra, as long as 0.4 

mm, have been found in mineral separates from Novarupta 

lava-dome rhyolite, where dacite contamination is also a likelihood (Hildreth, 1983; Avery, 1992).

All-Rhyolite Ignimbrite

Accompanying fallout of Layer A during the first several hours of the eruption was emplacement radial to Novarupta of ash flows containing exclusively rhyolitic juvenile 

material. Because most of the all-rhyolite ignimbrite was 

soon covered by more voluminous ignimbrite that contains 
52 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

a wide range of juvenile compositions, exposures of the 

former are limited to the periphery of the upper VTTS and 

to wind-stripped ridgecrests surrounding Novarupta basin. 

We described the all-rhyolite ash-flow deposits (Fierstein 

and Hildreth, 1992) as comprising three facies—high-energy 

proximal ignimbrite, valley-filling ignimbrite, and a thin 

marginal fringe facies—all emplaced concurrently with fallout of Layer A from the plinian column.

Rhyolitic High-Energy Proximal Ignimbrite (HEPI).—

Within several kilometers of Novarupta, the only basal exposures of 1912 deposits are on windswept ridgecrests where 

the thick mantle of dacitic fall deposits (Layers C to H) have 

been stripped. At such locations, Episode I exposures are of 

stratified, lenticular, moderately to poorly sorted, pyroclasticdensity-current deposits with wavy and lensoid bedding, 

scour and truncation of lower bedsets by overlying ones, and 

sparse ballistic ejecta. Many of the coarser layers and lenses 

are surgelike, reflecting high-velocity turbulent flow over 

proximal ridgecrests, and fairly well sorted (sø

=1–2). Most, 

however, represent more concentrated flows that left finesrich, poorly sorted (sø

=2–4) deposits that drape the ridges and 

merge downslope into the thick valley-filling ignimbrite of the 

upper VTTS. Such high-energy strata were emplaced throughout Episode I, successive bedsets reflecting the compositional 

zonation of the overall sequence. The all-rhyolite bedsets are 

always basal, resting on basement rocks or on thin sections of 

Layer A fallout.

Good exposures of rhyolitic HEPI survive on Baked and 

Broken Mountains, Mount Cerberus (fig. 22), several northern spurs of Trident and Mount Katmai, atop Whiskey Ridge 

(fig. 23), and atop the Buttress Range (fig. 24). The all-rhyolite HEPI deposits range in thickness from 5–10 cm intervals 

interbedded with Layer A fallout in the saddles between the 

peaks of Trident, to 70 cm on the Buttress Range and as much 

as 4 m on Whiskey Ridge. Individual layers and lenses are 

typically 3–30 cm thick, lithic-rich, and commonly inversely 

graded; adjacent layers commonly exhibit contrasts in sorting, 

grain size (Md ~0.5 to 7 mm), and fine-ash contents (5 to 25 

weight percent). As vent-opening proximal deposits, 

Figure 22. All-rhyolite high-energy proximal ignimbrite (HEPI) deposits on northern ridge of Mount Cerberus, 3 km southwest of 

Novarupta and 250 m higher than margin of valley-filling massive ignimbrite at base of ridge. At top, darker heterogeneous HEPI deposit 

(containing andesite, dacite, and rhyolite pumice) overlies light-colored bedsets in which juvenile pumice is wholly rhyolitic. Both 

contain abundant lithic fragments. Ice-axe is 81 cm long. View is roughly westward.
Chapter 5. Products of the Eruption 53

the rhyolitic HEPI contain an abundance of lithic fragments, 

most layers having 10–15 weight percent, the extremes 

measured being 3 and 32 weight percent. As in Layer A, the 

lithics include sedimentary rocks of the Naknek Formation as 

well as lavas of Trident and Falling Mountain. In successive 

layers of various exposures, either Trident or Naknek lithics can predominate. Lithic fragments of Falling Mountain 

dacites are most abundantly exposed in basal HEPI sections 

on Baked Mountain.

Nearly all HEPI exposures lie along unobstructed direct 

lines from vent and are thought to have been deposited by 

moderately concentrated but turbulent upper parts of pyroclastic density currents that had developed gradients in particle 

concentration and were synchronously depositing valleyfilling massive ignimbrite. Most HEPI exposures lie within 4 

km of Novarupta, within lateral-blast range or close to the toe 

of a collapsing column. The all-rhyolite deposits on Whiskey 

Figure 23. Whiskey Ridge and the Knife Creek Glaciers, viewed east-northeastward from near Novarupta. Black, horizontal, marine 

Jurassic strata of Whiskey Ridge (right center) form steep-walled cleaver separating Glaciers 3 and 4, ~5 km east of Novarupta. 

Slender light-colored strip atop Whiskey Ridge is high-energy proximal ignimbrite (HEPI) deposit ~5 m thick (see fig. 42), which rests 400 

m higher than margin of valley-filling ignimbrite on floor of Knife Creek valley in center of image. Two kilometers farther east, beyond 

tan ash-covered Glacier 4, another black cleaver separates Glaciers 4 and 5; along its narrow crest, HEPI deposit has thinned to ~1 m. 

In foreground is Glacier 1, overlain and surrounded by pumice-fall deposits of Episodes II and III, many meters thick. Glacier 2 is hidden 

from view between Glaciers 1 and 3.

Ridge (5 km from the Novarupta dome) and on the Buttress 

Range (8 km), however, were emplaced atop steep-walled 

ridges, respectively 400 m and 250 m above the adjacent 

VTTS floor, apparently demanding at least that thickness for 

the transporting, inferentially graded, blast-initiated currents. 

The thin all-rhyolite fringe deposit (described below) that 

extends across the slopes of Mount Griggs as far as 9 km from 

Novarupta is at least in part distal HEPI that was emplaced by 

a vent-opening lateral blast.

Rhyolitic Valley-Filling Ignimbrite (VFI).—Massive 

pink all-rhyolite ignimbrite is as thick as 13 m along the 

Griggs fork (fig. 25), ~6 m thick just south of Katmai Pass, 

and 4.5 m along Mageik Creek near Observation Mountain. 

In the Knife Creek and Lethe arms of the VTTS, such deposits are concealed by the main compositionally heterogeneous 

VFI, but the all-rhyolite VFI was certainly deposited earlier 
54 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Figure 24. All-rhyolite high-energy proximal ignimbrite (HEPI) and dacite fallout section atop Buttress Range, in saddle above 

West Mageik Lake and 8 km west-southwest of Novarupta. Cross-stratified and lenticular HEPI deposit has alternating layers 

rich in fines or in rhyolite pumice granules. Resting on organic-rich soil, HEPI was emplaced ~200 m higher than nearby 

margin of valley-filling ignimbrite in Lethe arm of VTTS. Subsequent compositionally heterogeneous HEPI currents did not 

reach crest of Buttress Range. The all-rhyolite HEPI (R–HEPI), variously 20–70 cm thick (~30 cm here), is overlain by ~30 cm 

of Episodes II and III upwind dacite fall deposits (layers as labelled), which are here separated by prominent Layer E, which is 

fine-grained, cream-colored, and 3–4 cm thick. Shovel is 58 cm long.

throughout the upper VTTS because its all-rhyolite fringe 

facies flanks the Knife Creek margin of the main VFI as far 

down valley as the Juhle fork. In gorges incised to the base 

of the ignimbrite in the lower VTTS, however, no purely 

rhyolitic ignimbrite is exposed. Because the thin all-rhyolite 

VFI was emplaced more energetically than the later heterogeneous VFI, it extends laterally well beyond the uppervalley margins, but the heterogeneous VFI was far more 

voluminous and thus advanced incrementally twice as far 

down the valley. Lack of deep incision in the upper VTTS 

renders estimates fairly uncertain, but the volume of allrhyolite ignimbrite is probably no more than 1 km3

 and that 

of the heterogeneous VFI roughly 10 km3.

Rhyolitic VFI is poorer in pumice lapilli than most 

of the overlying heterogeneous VFI, pumice clasts larger 

than 1 cm rarely making up as much as 10 weight percent 

of it. Concentrations or trains of pumice that might mark 

flow-unit boundaries or depositional pulses are correspondingly uncommon in the massive rhyolitic ignimbrite, which 

contains 30–50 weight percent fines (≤63 μm). A few 

representative samples sieved yield Md~0.1–0.5 mm and 

sø~2–3. Like Layer A and the rhyolitic HEPI, rhyolitic VFI 

is rich in lithic fragments, Naknek clasts generally exceeding lavas; measured lithic contents are in the range 13–15 

weight percent.

At many places in the Mageik Creek drainage, the rhyolitic VFI is underlain, overlain, or intercalated with thin strata 

of plinian Layer A, but the fallout is commonly missing at the 

base, apparently having been synchronous with or scoured by 

the first flow. Along the Griggs fork, lenses of Layer A fallout 

are preserved locally within sections of all-rhyolite VFI. Such 

intercalations may be what led Curtis (1968) to interpret the 

pink rhyolitic VFI near Glacier 5 and the foot of Mount Griggs 

as Layer A fallout.
Chapter 5. Products of the Eruption 55

C

D E

F-G mudflow

Figure 25. Pink all-rhyolite ignimbrite (Package 1) along axis of upper Griggs Fork, 9 km from Novarupta in an unobstructed 

northeasterly line-of-sight direction. It was far more mobile than all subsequent ignimbrite packages. Ignimbrite is ~8 m thick here 

but as thick as 13 m just downstream (to left). It is overlain successively by a thin brown ashy mudflow deposit, 2.4 m of Layers 

C–D dacite fallout, a prominent 4-cm-thick rib of Layer E, and remnants of Layers F–G, which are interrupted by mudflows and 

overlapped by pumice-rich scree and alluvium.

Marginal Fringe Facies of All-Rhyolite Ignimbrite.—In 

contrast to the later-emplaced main heterogeneous ash flows 

(which outside the near-vent region were strictly valleyconfined), the rhyolitic ash flows were more energetic and 

swept far up the surrounding slopes. The all-rhyolite HEPI 

grade into thin fringe deposits in and beyond the Trident 

saddles, and a fringe of rhyolitic ignimbrite 5–20 cm thick 

widely mantles the lava-flow benches at the eastern base of 

Mount Mageik (fig. 26). The latter are best exposed on lavaflow benches up to 250 m higher than the valley-confined 

ignimbrite along Mageik Creek, but they can locally be traced 

downslope to their merger with the 5-m-thick massive rhyolite ignimbrite along the valley axis.

A massive or vaguely stratified pink deposit on the 

lower flanks of Mount Griggs forms a run-up fringe continuous with the thick all-rhyolite VFI along the Griggs fork. It 

thins gradually from 13 m along the stream axis to only a few 

centimeters at distances 1–2 km upslope, and it extends ~7 

km across the southwest slope of Mount Griggs as far as the 

Juhle fork at elevations up to 450 m above the VTTS floor. 

Across-slope transport of the feather edge of the ignimbrite 

is recorded by charred 1912 willows flattened in the downvalley direction. Snowmelt on the lower slopes of Mount 

Griggs remobilized parts of this fringe deposit, producing 

many small all-rhyolite gulch-confined debris flows that 

underlie and interfinger with the dacite pumice-fall deposits 

of Episodes II and III.

The rhyolitic fringe deposits, sampled and sieved to 

record their apparent diversity, have wide ranges in grain size 

(Md~0.5 to 3 mm), sorting (sø

~1.7 to 3), and structure, ranging from massive to crudely stratified. Samples sieved have 

~5 weight percent lithics and 3–6 weight percent free crystals.

A few centimeters of fine rhyolitic ash beneath thin 

Layer A on Observation Mountain suggests that an ash flow 
56 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Figure 26. View southwestward across upper VTTS from high on Mount Griggs. Knife Creek arm in foreground, River Lethe arm in 

right distance, and between them the intermediate valley separating siltstone ridges of Baked Mountain and Broken Mountain (nearer 

camera); all three valleys are floored by ignimbrite, margins of which are marked by abrupt color change. Baked and Broken Mountain 

basement rocks are draped by pale gray pumice-fall deposits. On center skyline, four-peaked Mount Mageik stands 19 km from the 

camera and rises 1,500 m above the valley floor. To its right are the black cone of Mount Martin and glacier-clad Alagogshak Volcano, 

both along the rangecrest. At left toe of Mount Mageik, a pair of dacite domes, Mount Cerberus (farther from camera) and Falling 

Mountain, frame the entrance to Katmai Pass, through which the VTTS ignimbrite extends. Overlying ignimbrite on valley floor in right 

distance, black fans are andesite-dacite alluvial gravels from Mount Mageik.

with a superjacent ash cloud went through Katmai Pass at the 

onset of eruption, at least minutes before fallout of plinian 

Layer A had expanded broadly enough to cover that area, at 

the southwest edge of its dispersal sector. Similar rhyolitic 

ash, probably likewise elutriated from the initial all-rhyolite 

ash flows, is locally the basal deposit atop the Buttress Range 

and on the cross-valley moraine near Three Forks (upwind 

sites where Layer A was not deposited). Thin ash at all 

three sites probably resulted from turbulent ash clouds that 

detached and extended beyond the termini of their associated 

valley-confined all-rhyolite flow units.

The evidence that the several kinds of purely rhyolitic deposits just described are depositional facies produced in common 

by an eruptive episode only a few hours long is summarized by 

Fierstein and Hildreth (1992, p. 662). Synchronous with a powerful sustained plinian column that produced regionally dispersed 

rhyolite fallout, voluminous density-stratified ash flows moved 

radially in all directions from Novarupta basin, distributing massive VFI along the valleys, wavy lenticular strata on ridgecrests, 

and fine rhyolitic ash dispersed laterally by billowing clouds. 

Layer B

Use of this term has a confusing history because Curtis 

(1968) first applied it to fine-grained pink ignimbrite deposits 

along and near the Griggs fork of Knife Creek that contain both 

rhyolite and andesite-dacite components. These valley-fringing 

deposits are compositionally heterogeneous but still rhyolitedominant; they thin rapidly away from the main heterogeneous 

VFI that fills the Knife Creek arm, and they nowhere overlie it. 

We now assign them to ignimbrite Packages 2 and 3 (Fierstein 

and Wilson, 2005). The more extensive fringe of all-rhyolite 

ignimbrite (fig. 25) that underlies these “Layer B” ash-flow 

deposits in that area was assigned by Curtis to Layer A. Sparse 
Chapter 5. Products of the Eruption 57

lenses of fallout did locally survive scour during emplacement 

of these marginal-facies ignimbrites along the Griggs fork, but 

only small fractions of Curtis’ units A and B in this sector are 

true fallout layers. Hildreth (1983) referred to these deposits as 

the “feather edge” of all-rhyolite and compositionally heterogeneous ignimbrites emplaced successively. When we later 

studied in detail the 1912 deposits south of Trident and Mount 

Katmai, however, it became clear that true plinian fall deposits 

of heterogeneous composition accumulated atop Layer A in the 

downwind sector (figs. 15, 20). The fall deposits south of the 

volcanic axis thus provided a firm basis for redefining Layer B, 

independent of Curtis’ original sites on the Griggs fork (Fierstein and Hildreth, 1992).

Layer B was accordingly restricted to the plinian fallout 

that accompanied emplacement of the main compositionally 

heterogeneous ignimbrite sequence that filled the VTTS and in 

part spilled through Katmai Pass into Mageik Creek (Hildreth, 

1983; Fierstein and Hildreth, 1992; Fierstein and Wilson, 

2005). Layer B was divided into three subunits (figs. 15, 16, 

21) on the basis of grain size and compositional proportions 

(as elaborated in table 1 of Fierstein and Wilson, 2005), even 

though no depositional break is recognized within Layer B or 

between it and purely rhyolitic Layer A. 

Layer B1 is a conspicuous terra-cotta horizon 1–11 cm 

thick that caps the white pumice-fall deposit of Layer A. Its 

pumice lapilli show little difference in size from subjacent 

Layer A, but they include for the first time sparse dacitic and 

andesitic pumice as well as 35–45 weight percent oxidized coignimbrite ash, which coats lapilli and imparts the color. The 

layer is related to the first heterogeneous ash flows (Package 

2) to spill into Katmai Pass. It thins laterally away from the 

valley-confined deposit of those ash flows (fig. 16), as well as 

downstream, where it is identifiable no farther than the lower 

slopes of Trident and Mount Katmai (presumably the limit of 

the co-ignimbrite ash cloud). Layer B1 is very poorly sorted 

(sø~4-5) owing to its co-ignimbrite ash contaminant, but it 

remains fairly coarse (Md~2 to 5 mm) owing to its plinian 

lapilli-fall component. As in Layer A, its lithic fragments are 

predominantly from the Naknek Formation but include subordinate Trident and Falling Mountain lavas. Pumice counts 

for Layer B1

 yield 82–99 percent rhyolite, similar to pumice 

proportions in ignimbrite Packages 2 and 3, which were the 

first to reach the lower VTTS near Three Forks.

Layer B2 is a compositionally mixed fall deposit as thick 

as 73 cm on higher slopes of Trident and 30–50 cm thick at the 

south base of Trident and Mount Katmai. It typically shows 

slight inverse grading, and its top several centimeters is typically burnt orange in color owing to a small contribution of 

oxidized andesite-dacite co-ignimbrite ash. Numerous field 

and lab counts show pumice in its lowest part to be as much 

as 93 percent rhyolitic, the proportion declining upward to as 

little as 40 percent, as dacite and andesite pumice become progressively more abundant. Rhyolite dominance is maintained 

for half to two-thirds of Layer B2

 as dacite pumice increases 

from <5 percent near the base to as much as 60 percent in 

the upper third; the andesite proportion is small and varies 

erratically. The upward change in clast proportions in Layer 

B2

 is consistent and well documented from the proximal area 

all the way to Geographic Harbor and Kodiak Island (Fierstein and Hildreth, 1992). On the south slopes of Trident and 

Mount Katmai, average maximum pumice clasts are 9–12 cm 

and maximum lithic clasts ~5 cm. Lithic content is as great as 

17 weight percent on the slopes of Trident but decreases to ~6 

weight percent at Katmai River and Dakavak Bay. The lithic 

suite is still dominated by Naknek, Trident, and fewer Falling 

Mountain clasts, but fragments of welded-tuff vitrophyre recycled from vent-filling fallback ejecta (Hildreth, 1987) make 

their first appearance. Layer B2 is moderately or well sorted 

(sø~0.7–2.7), despite containing ~8 to 20 weight percent fine 

ash (≤63 μm), which is most abundant near its top. Its content 

of free crystals increases from ~5 weight percent on the slopes 

of Trident and Mount Katmai (7–13 km from vent) to 14 

weight percent at Dakavak Bay (40 km downwind), a common 

pattern as the fraction of pumice lapilli declines and grain size 

diminishes with distance. A few centimeters of Layer B2 that 

survived scour in upper Knife Creek are intercalated within 

ignimbrite Package 7 (Fierstein and Wilson, 2005).

Layer B3 is a compositionally mixed fall deposit that 

extends the trend in pumice proportions represented by Layers 

A, B1, and B2. Numerous pumice counts give 20–38 percent rhyolite near its base and 11–25 percent near its top; the 

subunit contains as much as 6 percent andesite scoria and is 

the earliest fall deposit to be dacite-dominant (59–87 percent) throughout. Pumice proportions are like those of late 

(but not final) ash-flow packages in the VTTS. Layer B3 is 

30–50 cm thick on the southern slopes of Trident and Mount 

Katmai, where it is distinguished by a slightly finer-grained 

base, which separates it from B2, and by a dusting of oxidized 

co-ignimbrite ash that coats lapilli and imparts a burnt-orange 

color throughout but most prominently at the top. Although it 

contains ~10 weight percent fine ash and ~25 weight percent free crystals, sorting is good to fair (sø

~0.9–2.5), even 

at the most proximal exposures. The subunit is coarsest in 

its middle, where extreme pumice clasts reach 20 cm, average maximum pumice reaches 16 cm, and average maximum 

lithic values are 4–7 cm on the southern slopes of Trident and 

Mount Katmai. The lithic suite still contains Naknek, Trident, 

and sparse Falling Mountain clasts, but for the first time in the 

fallout sequence, recycled welded fallback ejecta predominate. 

Thin remnants of Layer B3 are locally preserved on the VTTS 

side of the volcanic axis, outside its main southeasterly dispersal sector; they occur directly beneath Layer C on Broken 

Mountain, Mount Griggs, the Buttress Range, and near Glacier 

4, but wherever the main VTTS ignimbrite was deposited, 

compositionally equivalent Layer B3 is absent.

Compositionally Heterogeneous (Main) ValleyFilling Ignimbrite (VFI)

The main sequence of ash flows that filled the VTTS was 

compositionally equivalent and synchronous with fallout of 
58 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Layer B. In the upper VTTS their marginal fringe directly 

overlies the all-rhyolite ignimbrite described earlier. The 

emplacement progression from rhyolite-dominant to rhyolitepoor ash flows has been characterized in progressively increasing detail by Curtis (1968), Hildreth (1983), Fierstein and Hildreth (1992), and Fierstein and Wilson (2005), who mapped 

the limits of nine successive compositionally distinguishable 

100% rhyolite

< 5% dacite

< 3% andesite

92%_99% rhyolite 90%_99% rhyolite

< 5% dacite

<10% andesite

< 5% dacite

10%_40% andesite

60%_88% rhyolite

< 5% dacite

40%_60% andesite

40%_55% rhyolite

12%_20% dacite

25%_45% andesite

25%_45% rhyolite

20%_70% dacite

20%_70% andesite

5%_30% rhyolite

45%_90% dacite

15%_70% andesite

<10% rhyolite

40%_60% dacite

<1% andesite

40%_60% rhyolite

Pkg 1 Pkg 2 Pkg 3

Pkg 4 Pkg 5 Pkg 6

Pkg 7+7a Pkg 8 Pkg 9

155o20' 155o10' 155o 155o20' 155o10' 155o 155o20' 155o10' 155oW

58o20'

58o15'

58o20'

58o15'

58o20'

58o15'

58o10'N

58o10'

58o10'

A B C

D E F

G H I

0 5 km 0 5 km

0 5 km 0 5 km

0 5 km

0 5 km

0 5 km 0 5 km 0 5 km

N

Figure 27. Distribution of nine successive packages of 1912 ignimbrite mapped by Fierstein and Wilson (2005) on basis of changes in 

pumice proportions, as given in insets. For each panel, gray shows extent of all previously emplaced packages. Black stipple indicates 

distribution of high-energy proximal facies (HEPI) that accompanied valley-filling deposits. Red stipple in panel G shows limits of 

Package 7a, deposit of a short-lived blast during eruption of Package 7. Emplacement sequence of nine packages is estimated to have 

taken 16 hours.

packages of ignimbrite (fig. 27). Of the nine exposed in the 

VTTS, four also passed southward into Katmai Pass (figs. 16, 

28), and of those four, two feathered out shortly south of the 

pass, and two extended as far as 10 km down the Pacific slope 

to the foot of Observation Mountain. Of the latter pair, the 

first was the energetic all-rhyolite package, which is 3–6 m 

thick along the valley of Mageik Creek, and the other was 
Chapter 5. Products of the Eruption 59

Figure 28. Katmai Pass viewed southward from summit of Falling Mountain. Mount Cerberus is just out of view to right. Fumaroles 

from thick ignimbrite at lower right lured Griggs and Folsom into VTTS in 1916 and remained active when Fenner returned in 1923. 

Benches along pass are lava flows from Mageik (right) and Trident (left). All benches are veneered by thin ignimbrite and draped by 

dacite fall deposits, with exception of black 1958 and 1959 Trident lavas on left rear side of defile. 1912 ignimbrite Package 7 penetrated 

7 km beyond the pass and is 10–20 m thick along axis of Mageik Creek at foot of Observation Mountain (left distance).

the seventh package, which is as thick as 20 m along Mageik 

Creek and is compositionally unique in having roughly equal 

proportions of dacite and rhyolite pumice but only a trace of 

andesite. In the VTTS, two of the packages (the third and 

fourth) extended at least 23 km down the glaciated valley of 

the Ukak River (fig. 29), and three more packages (the second, 

fifth, and sixth) extended as far as Three Forks (fig. 30), 17 km 

from Novarupta.

The combined valley-filling ignimbrite probably ranges 

between 100 m and 200 m thick in the upper VTTS (Curtis, 

1968; Hildreth, 1983); it is ~35 m thick in the lower VTTS 

where incised to its base and 10–20 m thick at eroded distal 

termini (fig. 31). Because the sheet is not deeply incised in 

either the River Lethe arm or the Knife Creek arm of the upper 

VTTS, its total volume is poorly established but estimated to 

be 11±2 km3. Of this total, no more than 10 percent is attributable to the opening all-rhyolite package and only ~1 percent 

to the later packages along Mageik Creek, so the compositionally heterogeneous ignimbrite in the VTTS has a volume of 

roughly 10 km3. 

Where exposed, much of the medial to distal sheet is 

nonwelded, but steep-walled gorges in the middle and upper 

VTTS are cut in indurated ignimbrite (fig. 32), both sintered 

vitric tuff and tuff indurated by vapor-phase crystallization. 

Welded tuff with flattened fiamme (fig. 33) is exposed in situ 

at only a few places, all in the upper VTTS, but blocks of 

such welded ignimbrite ejected at phreatic explosion craters 

provide evidence for widespread welding below the level of 

stream incision in both arms of the valley.

Following the initial all-rhyolite package, all eight 

subsequent packages contained andesite, dacite, and rhyolite 

pumice in varied proportions (fig. 34). Chemically analyzed 

rhyolite pumice from the main VTTS ignimbrite ranges 

in SiO2

 from 77.1 to 77.8 percent, and the accompanying 

andesite and dacite pumice form a compositional continuum 

extending from 57.9 to 68.6 percent SiO2. Packages 2 through 

4 are rhyolite-dominant with subordinate dacite and progressively increasing andesite; Packages 5 and 6 carried subequal 

amounts of rhyolite and andesite with subordinate dacite; 

Package 7 had subequal dacite and rhyolite with only sparse 

andesite; and, finally, Packages 8 and 9 (figs. 35, 36) carried 

abundant andesite and dacite but only minor rhyolite. Banded 

pumice is present throughout Packages 2 to 9, constituting 3–5 

percent of pumice clasts overall but ranging locally between 0 

and 37 percent. 

Correlations of fallout layers and ignimbrite packages that 

erupted concurrently (Fierstein and Wilson, 2005) are based on 

field counts of pumice proportions (rhyolite, dacite, andesite, 
60 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Figure 29. Terminus of VTTS ignimbrite viewed westward from basaltic plateau (“Sayre Mesa” of Hildreth and 

others, 2004). Far side of valley-filling ignimbrite (light colored) is 10 km from the camera and 1,000 m lower. 

Deposit is 10–15 m thick where Ukak River is eroding its terminus at right. In middle distance, ash flows were 

blocked by moraines and largely diverted to far west margin, where narrow Ukak River corridor fed terminal Ukak 

lobe. A few ash-flow lobes passed though saddles in moraines and feathered out into brush-covered hills of 

glacial debris. Margot Creek in distance; Mount Katolinat at upper right. Basalt on Sayre Mesa was studied and 

dated by Hildreth and others (2004).

Figure 30. Aerial view of lower VTTS, Three Forks, and Ukak River corridor. Windy Creek at left, River Lethe in 

center, and Knife Creek at right conjoin at Three Forks to form Ukak River. Ignimbrite here is nonwelded and 10–25 

m thick. Base is exposed atop till along Knife Creek at right center. Beyond Knife Creek, ash flows banked against 

brown moraine and were diverted into narrow (400-m-wide) Ukak River corridor at left. In distance, white deposits 

are aeolian sand winnowed from 1912 deposits, and pink strips are tongues of ignimbrite that bypassed moraines 

and feathered out into brush.
Chapter 5. Products of the Eruption 61

Figure 31. Flow units and packages in massive nonwelded 

ignimbrite, southwest wall of Knife Creek, <1 km upstream from 

Three Forks. Its base resting on dark brown till, multipackage 

ignimbrite is here ~12 m thick and overlain by a thin white layer of 

dacite fallout, which is capped at surface by brown mudflows ~1–2 

m thick. Dark brown ignimbrite Package 5 fills swale eroded into 

white Package 4 beneath it.

Figure 32. Knife Creek gorge ~3 km upstream from Three Forks, cut 

largely in ignimbrite Packages 2 through 4. Gorge here is ~30 m deep; 

stream cut down through nonwelded tuff into sintered or partially 

welded tuff, hackly jointed, that walls inner gorge. Flow units and 

variously sorted layers and lenses are conspicuous on walls. Leftbank rim is capped by thin white layer of dacite fallout, overlain in turn 

by thin brown mudflow deposit. Mount Katolinat on skyline.

and banded) as well as on physical intercalations (fig. 37). Flow 

packages, however, generally have higher andesite fractions 

than time-correlative fallout, reflecting the fact that little andesite pumice was distributed by the high plinian plume but most 

was, instead, preferentially partitioned into lower fountains 

ejected around the periphery of the plinian column (Hildreth, 

1983). The same annular pattern recurred during Episodes II 

and III, when andesite-enriched flows, surges, and small proximal falls were released sectorially around the base of plinian 

columns that carried aloft little other than dacitic ejecta (Fierstein and others, 1997; Houghton and others, 2004).

The issue of what constitutes an ignimbrite “flow unit” 

has remained under discussion for decades, and nowhere 

is it more ambiguous than in the VTTS. Hildreth (1983, p. 

52–3) called attention to several late flow units or packages 

thereof (figs. 31, 38) but thought that much of the ignimbrite exposed in the VTTS was emplaced by a continuously 

zoned outflow (fig. 39) that partitioned only distally into 

numerous secondary flows as it fitfully ground to a halt. 

Fierstein and Hildreth (1992, p. 664–5) illustrated and discussed further the problems of distinguishing among ventderived flow units and secondary units produced by 
62 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Figure 33. Eutaxitic welded ignimbrite of Package 8 along Glacier 1 fork of upper Knife Creek. Fiamme are both andesitic and dacitic. 

Ice axe is 81 cm long.

budding, internal shear, overlapping flow paths, and discontinuous deposition from the base of moving ash flows. 

Because persistent interflow partings are seldom seen on 

gorge walls in the middle VTTS, they thought that “as much 

as 90 percent of the exposed sheet was emplaced quasicontinuously.” Detailed mapping by Fierstein and Wilson 

(2005) of nine distinguishable packages of flows made an 

important advance in understanding the processes of outflow and deposition. Questions about distal partitioning of 

secondary units remain, but Fierstein and Wilson demonstrated contacts between successive packages, some sharp 

and some cryptic, as defined variously by changes in pumice 

proportions or ignimbrite matrix color, finer-grained bases of 

flow units, lobate accumulations of distinctive composition, 

compaction swales filled by later packages, shallow erosional channels filled by the flows that scoured them, slump 

surfaces left by remobilized ignimbrite and filled by a later 

package, and (largely south of the vent) fall deposits intercalated between flow units. Emplacement processes and flow 

units are discussed in more detail in chapter 6, below.

Compositionally Heterogeneous High-Energy 

Proximal Ignimbrite (HEPI)

Within ~3 km of Novarupta, the more widely distributed 

all-rhyolite HEPI is overlain by thicker deposits of compositionally heterogeneous HEPI. Like their earlier rhyolitic 

counterparts, these are stratified, lenticular, and highly varied 

in grain size and sorting. They are exposed on windswept 

proximal ridges wherever Episode II and III fallout has been 

eroded away—on Trident, Falling Mountain, Mount Cerberus, Whiskey Ridge, and all spurs of Baked and Broken 

Mountains. Deposited by high-velocity currents radial to 

Novarupta, the HEPI represent a dynamic facies that contrasts 

with time-equivalent VFI flows that were emplaced rather 

sluggishly by the time they reached the middle and lower 

VTTS (Hildreth, 1983). Nonetheless, the sequence of HEPI 

layers exhibits pumice proportions similar to most (but not 

all) of the sequence of VFI packages that filled the VTTS.

Most exposures are 1–5 m thick and consist of 5–25 

discrete layers, each typically 1–15 cm thick but in places as 
Chapter 5. Products of the Eruption 63

Pkg 9

R D A R D A

<10 45_90 15_70

Pkg 8 (top)B3

B1

5_30 20_70 20_70

10_30 70_87 0_6

Pkg 7

(upper)B2

(lower)B2

40_60 40_60 <1

40_60 30_70 0_35

Pkg 6 35_55 12_20 25_45

Pkg 5 40_55 <5 40_60

Pkg 4 60_88 <5 10_40

90 <5 <10

Pkg 3 90_99 <5 <10 90_99 <12 <10 Pkg 2 92_99 <5 <3

Pkg 1 100 0 0 Layer A 100 0 0

 Layer C <5 95_99 <2

Flow Packages Fallout Sequence

Flowed southward

Flowed northward

Begin Episode II

2

4

6

8

10

12

14

16

Eruption

hours

Figure 34. Schematic diagram illustrating eruption chronology for Episode I and correlations among compositionally equivalent 

ignimbrite packages and fall units. Ranges in proportions of pumice clasts—R, rhyolite, D, dacite, and A, andesite—based on 

field and laboratory counts, are indicated for all. Vertical scale is time; no thickness data intended. Inferred durations of plinian 

fall phases were elaborated by Hildreth and Fierstein (2000) and Fierstein and Wilson (2005), and they are summarized in figure 

60, below. Durations of compositionally distinguishable plinian subunits provide constraints on time intervals available for 

emplacement of ignimbrite packages.
64 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Figure 35. Sintered to partially welded ignimbrite of 

Package 8, cut by upper Knife Creek ~400 m upstream 

from its confluence with Griggs fork. Welded platform 

is overlain by 1.5-m-thick ledge of sintered Package 

9, rich in coarse dacite and andesite pumice. This in 

turn is overlain by ~2 m bedded sequence of fluvially 

remobilized pumice and ash (on which geologist is 

squatting) that marks eruptive lull between Episodes 

I and II. At upper left, dacitic Layer C and a remnant 

of Layer D are fumarolically oxidized. Terrace gravels 

at top were deposited before gorge incision into 

ignimbrite here.

Figure 36. Stream-scoured surface of sintered 

ignimbrite Package 9, rich in coarse dacite pumice 

(along with subordinate andesite and sparse rhyolite). 

Underlying welded dark-gray Package 8 crops out 

behind geologist, along Knife Creek near confluence 

with Griggs fork.

◄

◄
Chapter 5. Products of the Eruption 65

Figure 37. Intercalated ash-flow and fall deposits 2.5 km southeast of Katmai Pass and ~300 m south of terminus of 1959–60 Trident 

lava flow. All-rhyolite ignimbrite Package 1 is ~1.5 m thick and has layers and lenses of all-rhyolite (Layer A) fallout within and above 

it. Bright salmon Layer B1

 is 8 cm thick here and consists of mixed fall and flow material. Ignimbrite Package 7 is 30 cm thick here, near 

the pass, but it thickens to 10–20 m downstream along Mageik Creek. It is sandwiched here by 8 cm of rhyolite-dominant Layer B2

 below 

and 10 cm of heterogeneous Layer B3

 above, which is in turn capped by >1 m of dacitic layer C. Knife (near center) is 8.5 cm long.

thick as 35 cm. HEPI sections on Falling Mountain (fig. 40) 

and the long south spur of Baked Mountain (fig. 41) are as 

thick as 10–15 m and consist of as many as 110 layers. Atop 

Whiskey Ridge, 5 km from Novarupta, where the all-rhyolite 

HEPI is 4 m thick, the mixed HEPI is only ~1 m thick (fig. 

42); and 2 km farther northeast, atop the cleaver separating 

Glaciers 4 and 5 (fig. 23), these packages thin to 104 cm and 9 

cm, respectively. Successive pulses commonly scoured earlier 

layers, leaving numerous unconformities. Most layers are planar or gently undulating, but, because many pinch out laterally 

within 5–15 m, they are lenticular or lobate at outcrop scale. 

Layers are variously (1) fines-rich and matrix-supported, (2) 

dominantly coarse to medium ash with pumice granules, or (3) 

clast-supported beds rich in pumice lapilli. 

Sieve data and componentry for the VTTS ignimbrite 

were given by Fierstein and Hildreth (1992). As in most 

ignimbrites, sorting in the VFI is generally poor (sø~3–4), 

ash finer than 63 μm makes up 30-50 weight percent of the 

deposits, and ash finer than 1 mm 60 to 80 weight percent, 

although pumice blocks and lapilli are ubiquitous. In HEPI, 

however, the variance in fine ash content is great, ranging 

from <10 to ~50 weight percent, even among adjacent layers. Median grain size ranges widely between 0.1 and 1 mm 

in most of the VFI but is as coarse as 4 mm in some HEPI 

layers and probably also in a few coarse VFI intervals not 

sieved. Sorting in the many lensoid HEPI layers is quite 

variable (sø

~1.5–4), as is their lithic content, which can 

be lower than 1 weight percent or as great as 5–16 weight 

percent; in most VFI, lithic content ranges from 1–6 weight 

percent. Free crystals are generally 2–7 weight percent of 

VFI but locally are as abundant as 20–30 weight percent; 

in the lensoid HEPI, they range even more widely, from 10 

to 50 weight percent. Many HEPI layers show coarse-tail 

inverse grading of pumice, but only a minority exhibit 
66 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Figure 38. Contact between compositionally contrasting ignimbrite 

packages above west shore of West Mageik Lake. Nonwelded 

rhyolite-dominant Package 4 is overlain by sintered andesite-rich 

Package 5. Thin contact zones are locally vaguely stratified (as at 

right) and commonly scoured (as at left). Ice axe is 81 cm long.

Figure 39. Massive nonwelded ignimbrite showing change in 

compositional proportions without any obvious depositional 

break. Exceptional exposure, ~10 m high, is near northeast edge 

of VTTS where Juhle fork of Knife Creek turns abruptly from 

valley margin toward its interior.

cross-bedding. No accretionary lapilli or other evidence of 

involvement of external water were noted in the HEPI.

The compositionally heterogeneous HEPI were less 

mobile than their all-rhyolite predecessors. They failed to 

crest the Buttress Range or to run up the lower slopes of 

Griggs and Mageik, and on Whiskey Ridge and Mount Cerberus they are much thinner than the rhyolite HEPI beneath 

them. As with the all-rhyolite HEPI, we envisage deposition 

on ridges well above the valley floor from turbulent but fairly 

concentrated upper levels of density-graded currents that 

were depositing poorer sorted VFI just downslope (fig. 43). 

The turbulence that favored scour, wavy bedding, and abrupt 

changes in sorting may have been enhanced by topographic 

roughness, by hydraulic jumps off ridgecrests, and by location within or near the deflation zone of collapsing fountains, 

consistent with a small ballistic contribution in some layers.

Time Constraints for Episode I

Intercalations of plinian fall Layers A and B1-3 with pyroclastic flow deposits in Katmai Pass, along Mageik Creek, and 

locally in upper Knife Creek show clearly that these falls and 

flows were produced by the same source column and emplaced 

contemporaneously (Fierstein and Hildreth, 1992). Details 

of compositional fluctuations linking the fallout sequence 

with the sequence of ignimbrite packages are elaborated by 

Fierstein and Wilson (2005). They graphically summarized 

the fall-flow correlations (fig. 34) and placed the sequences 

in a temporal framework spanning 16-hour-long Episode I. 

General constraints on emplacement times are imposed by 

recorded intervals of ashfall at Kodiak (Hildreth, 1983), seismicity recording fitful collapse of Katmai caldera (Abe, 1992; 

Hildreth and Fierstein, 2000), and phreatic syncollapse Katmai 
Chapter 5. Products of the Eruption 67

Figure 41. Compositionally 

heterogeneous HEPI bedsets on crest 

of south ridge of Baked Mountain, 

2.2 km northwest of Novarupta dome. 

Variably sorted, oxidized strata are 

10–15 m thick here, consisting of ~110 

layers and lenses, each 1–30 cm thick. 

Ridgecrest is 250 m above valleyfilling massive ignimbrite on adjacent 

valley floor and lies directly athwart 

main western outlet from Novarupta 

basin. In background, section wedges 

out ~100 m higher against Jurassic 

bedrock; on summit pinnacle (180 m 

higher than camera) is preserved a 

remnant of earlier all-rhyolite HEPI 

but none of these heterogeneous 

packages. Off-white dacite fall 

deposits, once several meters thick 

here, have been widely stripped by 

windscour. Ice axe (left) is 81 cm long. 

Figure 40. Matrix-rich oxidized ignimbrite containing abundant coarse clasts capping summit of Falling 

Mountain dome, 1.2 km from Novarupta dome. Pyroclastic deposits are underlain by dacite dome 

lava, which was sheared off in 1912 eruption, forming steep scarp. Section is overlain by white dacite 

pumice falls of Episodes II and III. Ignimbrite is 4–5 m thick here but thickens downslope to >13 m where 

plastered against scarp nearby (see fig. 71); lower part of section consists of stratified HEPI with highly 

variable sorting and fines contents. At upper left is scarp marking southeast wall of vent structure, here 

consisting of Trident-derived andesite lava flows heavily mantled by 1912 ejecta.
68 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Figure 42. Stratified oxidized HEPI deposits atop Whiskey Ridge, 5 km east of Novarupta and 400 m above valleyfilling ignimbrite on floor of Knife Creek arm at foot of ridge (see figs. 23, 73). Resting on Jurassic bedrock, section 

consists of ~4 m of all-rhyolite HEPI, ~1 m of heterogeneous HEPI, and coarse lag of windscoured dacite pumicefall at surface. Mount Griggs at upper right.

mud layers intercalated within the Layer B fallout sequence 

(Hildreth, 1991). Interpretive linkage of the Katmai seismicity 

and mud layers places the B2-B3 transition near midnight, ~11 

hours into the plinian eruption (Hildreth and Fierstein, 2000). 

Because the distinctive seventh package is directly overlain by 

Layer B3, it can thus be inferred that at least 80 percent of the 

VTTS ignimbrite was emplaced within the first 11 hours. If 

accumulation times for the B1-3 intervals were approximately 

proportional to fallout thickness, then Layer A represents ~3.5 

hours, and Layer B1 would represent ~1 hour, Layer B2 ~6.5 

hours, and Layer B3 and ignimbrite Packages 8 and 9 together 

~5 hours (Fierstein and Wilson, 2005).

Episode I ended with a complete eruptive hiatus, marked 

by deposition of water-reworked pumice and ash atop sintered 

Packages 8 and 9 in upper Knife Creek (figs. 35, 44).

Eruptive Episodes II and III

A sequence of fall units, predominantly dacitic, rests 

directly upon the main VTTS ignimbrite (both VFI and HEPI), 

or upon Layer B3, or locally upon water-reworked deposits 

below the snouts of the Knife Creek Glaciers. Curtis (1968) 

divided this fall sequence into six units (Layers C through H), 

largely on the basis of the relatively simple medial fall succession in the upper Knife Creek arm, 3–10 km northeast of 

Novarupta. Despite a few complexities, Fierstein and Hildreth 

(1992) were able to extend Curtis’ framework northwestward 

beyond Three Forks and southeastward across Mount Katmai to Shelikof Strait and Kodiak Island (figs. 19, 20). They 

recognized that the C–D and F–G pairs were each deposited 

virtually continuously but that fine-grained Layer E, which 

separates the pairs in the VTTS, represented a time break of 

hours—probably longer than the break between Layers B and 

C. On this basis, the C–D and F–G time intervals were defined 

as Episodes II and III, respectively. Proximally to medially, 

all four of these pumice-fall layers (figs. 17, 45) have faint 

plane-parallel internal bedding, moderate to good sorting, and 

aerodynamic equivalence among pumice and lithic clasts, 

characteristics of material deposited from the umbrella cloud 

of a high sustained buoyant plinian plume. Layers E and H 

are ash-rich beds of composite origin, formed principally by 

slow-settling coplinian fines, as well as by ash that had been 

elutriated from small proximal pyroclastic density currents 

during C–D and F–G plinian episodes and that settled after 

termination of those episodes. 

Using regional isopach data and microprobe analysis of 

coplinian ash partitioning, Fierstein and Hildreth (1992) 
Chapter 5. Products of the Eruption 69

Figure 43. Conceptual sketch illustrating Episode I regional fallout from high plinian column and synchronous emplacement of massive 

valley-filling ignimbrite (VFI) and stratified high-energy proximal ignimbrite (HEPI) from radially collapsing currents that were graded in 

particle concentration. Modified from Fierstein and Hildreth (1992). Near-vent Baked and Falling Mountains (schematically drawn at 

right) were overwhelmed by such stratified currents. Represented at left, Whiskey Ridge (5 km from vent) blocked and diverted denser 

parts of currents (as VFI) while turbulent upper parts deposited 5 m of HEPI on ridgecrest 400 m higher.

calculated eruptive volumes of 4.76 km3 and 3.44 km3 for 

Episodes II and III, respectively; these reduce to magma 

volumes of 2.0 km3 and 1.66 km3. Duration of Episode II 

ashfall at Kodiak was 26 hours and of Episode III ~10 hours. 

There need be no simple correlation, however, between 

fallout intervals 170 km downwind and the duration of eruptive episodes at vent, owing to altitudinally varied transport 

velocities and azimuths, wind shear, progressively slower 

settling of ash that becomes finer with distance, and turbulent retention of fine coplinian ash aloft. Ashfall intervals 

recorded at Kodiak are certainly longer than plinian eruptive 

intervals, but they may not be far wrong if settling times for 

Layers E and H are included.

Unlike Episode I deposits, in which compositional 

equivalence permits confident correlation of ignimbrite 

packages with regional fall deposits, there is considerable compositional contrast between the dacitic plinian fall 

deposits (Layers C–D and F–G) and coeval proximal deposits intercalated with them near Novarupta. Within ~3 km 

of the Novarupta lava dome, proximal products of Episodes 

II and III include alternations and mixtures of locally and 

regionally dispersed fall ejecta and several thin deposits of 
70 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Figure 44. Geologists examining high-energy fluvial beds of pumice and ash, reworked in part from Knife Creek Glaciers, during 

hours-long eruptive lull between Episodes I and II. Geologists stand on main Episode I ignimbrite, which floors gulch cut along Glacier 

1 fork of upper Knife Creek. Fluvial beds are overlain by coarse base of dacitic Layer C. On far wall, two fine-grained dark ribs are C–D 

parting and Layer E, which is overlain in sequence by coarse Layer F, finer pumice-fall Layer G, and thick section of surge-bedded strata 

emplaced explosively from post-eruption phreatic craters.

pyroclastic density currents (PDCs—flows and surges) that 

have no regional equivalents (Fierstein and others, 1997; 

Houghton and others, 2004). The locally dispersed components of the fall deposits form sector-confined lobes and 

wedges for which thicknesses halve radially away from the 

vent within 100-300 m (in contrast to several kilometers 

for the medial-distal plinian falls). Both the locally dispersed fall material and most of the proximal PDCs are far 

richer in lithics and in andesitic and banded pumice than the 

coeval plinian falls (C–D and F–G). The near-vent deposits are interpreted by Houghton and others (2004) in terms 

of four transport regimes: (1) sustained buoyant plume, (2) 

column-margin collapse to produce PDCs, (3) fountaining, 

where coarser fractions decouple on parabolic trajectories 

to produce conical deposits, and (4) direct lateral (ballistic) 

ejection. Here, we first describe the plinian layers and then 

summarize the complex proximal deposits.

Layer C

The first of the postignimbrite plinian fall deposits, Layer 

C, is the thickest and coarsest among them, and, like the 

Episode I falls, its dispersal was strongly east-southeastward. 

Layer C is ~3 m thick (figs. 17, 46) in upper Knife Creek 

(4–6 km from vent) and still ~2 m thick on the southern 

slopes of Trident and Mount Katmai (fig. 20; 7–10 km from 

vent). Close to Novarupta, it may be as thick as 6 m but is 

interrupted by one or more PDCs. Downwind distally, Layer 

C merges indistinguishably with Layer D (Fierstein and 

Hildreth, 1992), and they are together ~15 cm thick near the 

Shelikof coast (50 km) and ~5 cm at Kodiak (170 km). 

In the upper VTTS, Layer C is coarsest in its lower half, 

where dacite pumice as large as 50 cm and welded-tuff lithics 

as big as 20 cm are present, along with sparse andesitic and 

banded pumice and 5–20 percent rhyolite pumice. The 
Chapter 5. Products of the Eruption 71

upper half is a lapilli fall weakly graded to a thin crystal-rich 

coarse-ash top, and its pumice is almost entirely dacitic. The 

lower part of Layer C marks the last eruption of an appreciable 

amount of rhyolite until extrusion of the Novarupta lava dome. 

South of Trident and Mount Katmai, Layer C is a single lapilli 

fall, poorly graded except in its top ~10 percent, which is likewise crystal-rich coarse ash. Upwind to the northwest, Layer 

C splits into two normally graded subunits, and it fines and 

thins rapidly to ~1 m in the central VTTS (fig. 45) and to only 

a few centimeters near Three Forks.

Dacite pumice of Episodes II and III is unusually crystalrich (27–42 wt %), and the fraction of free crystals in Layer 

C along upper Knife Creek (4–7 km from vent) is also within 

that range. There is, however, for each of the plinian dacite 

Layers C, D, F, and G, an annular crystal-enrichment zone in 

which the free crystal content of the deposit exceeds that in 

pumice clasts, generally at distances where Md is close to 1 

mm, the size typical of the abundant feldspar phenocrysts. In 

the lower VTTS and at Katmai River, Layer C thus contains 

50–70 weight percent crystals. The fraction drops back to 

4550 weight percent near Shelikof Strait (40 km downwind) 

and to 22 weight percent on Kodiak Island (110 km), as glass 

shards become dominant distally. Median grain size of 

Layer C is typically 4–16 mm in upper Knife Creek, as great 

as 50–80 mm close to Novarupta, ~1.5 mm at Katmai River, 

~0.5 mm at Geographic Harbor, and <0.1 mm on Kodiak 

Island. Sorting for Layer C shows a remarkably wide range 

(sø

~0.5–3.3), owing in part to the high crystal content and 

the unusually proximal distribution of some sites from which 

samples were sieved. Lithic content is 2–7 weight percent, 

predominantly welded-tuff vitrophyre recycled from Episode I vent fill. The 5-cm lithic isopleth for Layer C extends 

~13 km southeast and 7 km north of the vent (Fierstein and 

Hildreth, 1992).

Although the top 10 cm or so of Layer C commonly 

grades normally to coarse ash and small lapilli, it does not 

grade to fines that might indicate a lull in plinian activity. 

Instead, it is capped by a thin bed of fines-bearing crystal-rich 

ash, 1–5 cm thick, that separates plinian Layers C and D in the 

upper VTTS (fig. 17). This bed appears to incorporate the fine 

ash associated with emplacement of a poorly sorted ignimbrite (<1 m thick) that formed by partial column collapse and 

is exposed only within 2.5 km south and west of Novarupta 

(PDC 5 of Houghton and others, 2004). This finer grained 

“C-D parting” is present only in the upper VTTS.

Layer D

Layer D represents a continuation and resurgence of the 

dacite plinian episode that began with eruption of Layer C. In 

the upper Knife Creek arm (3–6 km from vent), Layer D is 

1–1.7 m thick. It may exceed 2 m closer to Novarupta, but it 

is interrupted there and shaved by PDCs. Still ~1 m thick just 

west of Katmai caldera, it thins downwind from ~60 cm on 

the upper south slopes of Trident to ~20 cm at Katmai River, 

and, still farther southeast, it merges with the graded top of 

Layer C. Like all plinian layers that preceded it, Layer D 

was strongly dispersed east-southeastward. Off-axis, it thins 

to only 10–15 cm along Mageik Creek, and upwind it thins 

rapidly to ~40 cm in the central VTTS and to only 1–2 cm at 

Three Forks and the Ukak River. 

Much of Layer D is a massive lapilli fall rich in free 

crystals and normally graded to coarse and medium ash only 

in the top ~10 percent of its thickness. Unlike Layer C, it was 

followed by a temporary cessation of plinian activity, as it 

grades up normally to coarse ash and is overlain throughout 

the VTTS and on adjacent peaks by fines-rich Layer E (fig. 

17). In the upper VTTS, Layer D rests on the fines-bearing 

C–D parting, and on the southern slopes of Trident and Mount 

Katmai its lapilli-rich base rests on the normally graded 

crystal-rich top of Layer C. Sorting is only fair in Layer D, 

again owing to the high crystal content of the dacite pumice; 

the matrix of medium-to-coarse crystal-rich ash fluctuates in 

abundance vertically, contributing to vague internal stratification. In upper Knife Creek (3–6 km from vent), Layer D 

contains 40–45 weight percent free crystals and 2–4 weight 

percent lithics. Its lithic content is smaller than in Layer C 

but is similar in consisting predominantly of recycled welded 

vent-filling ejecta. The largest pumice clasts are 15–30 cm 

in the upper VTTS and 8–10 cm at Katmai River; average 

maximum lithic sizes at corresponding locations are 4–8 

cm and 2–4 cm. The pumice is predominantly dacitic, but 

~1 percent of small pumice lapilli are crystal-poor rhyolite 

proximally, and this fraction increases to ~10 percent at 

Katmai River (where most lapilli in Layer D are small). The 

scarcity of rhyolite pumice proximally, the near-absence of 

coarse lapilli and blocks of rhyolite pumice, and the rarity of 

banded rhyolite-dacite pumice suggest that much or all of the 

rhyolite in Layers D, F, and G was entrained by the column 

from near-vent surfaces and that little or none of it coerupted 

with the dacite.

Analysis of vesicularity and bubble-wall textures of 

dacite pumice from Layers C and D (Adams and others, 

2006b) shows little evidence for slowing of magma ascent or 

a trend toward open-system outgassing as a precursor to the 

break in plinian activity at the end of Episode II. More likely 

is an interruption by conduit blockage caused by vent-wall 

collapse, which was soon cleared by an explosive blast that 

radially emplaced a lithic-rich PDC deposit and permitted 

resumption of plinian activity as Episode III.

Layer E

Layer E is an ash bed, variously 3–9 cm thick throughout 

the VTTS, that accumulated during temporary shutdown of the 

stable plinian plume between Episodes II and III. It is recognizable between coarser layers D and F (figs. 17, 24, 45) for at 

least 23 km northwest of Novarupta, as well as in the Trident 

saddles and along Mageik Creek. Farther downwind, from 

Katmai River to Kodiak, it is not separable from the normally 
72 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Figure 45. Complete section of dacite 

fall deposits, 11 km upwind northwest of 

Novarupta, near Lethe Hills (fig. 6) at west 

margin of VTTS. Fine-grained pale-gray 

Layer E, here 9 cm thick, separates deposits 

of Episodes II and III. Layers C and D are 

together only 13 cm thick, while Layers F and 

G are together ~70 cm thick. Southeast of 

vent, C–D versus F–G thickness proportions 

are opposite, with Episode II deposits (C–D) 

always thicker than those of Episode III (F–G). 

At bottom of image, Layer C rests directly on 

oxidized ignimbrite (ig) of Episode I with no 

intercalation of coignimbrite ash. At top, finegrained dacite-dominant Layer H (4 cm thick) is 

overlain conformably by a pumice-rich debrisflow deposit (df). Ruler is 16 cm long.

graded ashy top of the Episode II (C–D) plinian deposit. In 

the VTTS, it stands out in relief as a fines-rich rib that separates the enclosing pumice-fall deposits (Curtis, 1968). 

In and near the VTTS, Layer E maintains fairly constant 

thickness (fig. 6 of Hildreth, 1983), whereas the enclosing plinian dacite layers thin rapidly away from Novarupta. 

Except within ~3 km of the vent, 50 weight percent or more 

of Layer E consists of ash finer than 63 μm, sorting is good 

(sø=1–2), lithic content is <1 weight percent, and pumice as 

big as 2–16 mm is rare. Componentry shows that Layer E 

consists of 81–96 weight percent vitric ash, and microprobe 

analysis of the glass shards shows 86–95 percent of them to 

be derived from dacite magma (Fierstein and Hildreth, 1992). 

Rhyolite shards contribute 3–11 percent and andesite shards 

1–5 percent of the vitric ash fraction. Crystal content ranges 

from 9 to 19 weight percent, declining with distance from 

vent, and most crystals are smaller than 0.25 mm. By comparison, the enclosing plinian layers contain 35–70 weight 

percent free crystals (many of which are ≥1 mm), and their 

dacite pumice has 27–42 weight percent phenocrysts.

The ash constituting Layer E had at least three separate sources (Fierstein and Hildreth, 1992): (1) The plinian 

plumes of Episode II dacite left slow-settling fines aloft. 

(2) Lesser fractions of rhyolitic and andesitic shards suggest that coignimbrite and coplinian ash contributions were 

left over from Episode I. As Episode I products were about 

two-thirds rhyolitic, however, they could have contributed 

no more than ~10 percent of the shards in dacite-dominant 

Layer E. (3) A multiflow package of ignimbrite, 1–3 m 

thick, is intercalated proximally at the level of Layer E, 
Chapter 5. Products of the Eruption 73

Figure 46. Flow unit of ignimbrite Package 9 (lower left), its lateral margin exposed in cross section, near upper Knife Creek just 

downstream from Glacier 4. Flow unit is rich in coarse dacite (and subordinate andesite) pumice blocks (see figure 36), some of which 

were here concentrated toward edge of flow lobe. Lobe is overlain by pale-gray ash-cloud deposit 14 cm thick, which settled during 

the lull between Episodes I and II. Ash is overlain by coarse base of dacite-dominant Layer C, which opened Episode II and is as thick 

as 3.5 m where intact nearby. Hammer is 28 cm long.

extending 1–3 km radially away from Novarupta. This 

represents the most laterally extensive PDC deposit of 

Episodes II and III (PDC 4 of Houghton and others, 2004), 

a thin landscape-mantling radially distributed veneer, which 

may have been produced by the outburst that reopened the 

vent, initiating Episode III. Although dominantly dacitic, 

this poorly sorted, lithic-rich ignimbrite also contains 10–20 

weight percent andesitic and banded pumice and smaller 

fractions of rhyolite pumice. Ash clouds generated by these 

small proximal PDCs certainly contributed to Layer E, especially in the upper VTTS, but the fairly constant thickness 

of Layer E from Mageik Creek to the Ukak River suggests 

that its regional deposition was in large part from lingering 

clouds of coplinian dacite ash from Episode II.

Layer F

After the few-hours-long lull recorded by accumulation of Layer E, Episode III began with plinian dispersal 

of crystal-rich dacite compositionally identical to that of 

Episode II. Just as Layer C is coarser and more widely 

dispersed than D, Episode III was most vigorous in its opening phase, causing Layer F to be thicker and coarser than 

subsequent Layer G. In the upper Knife Creek area, Layer 

F is a lapilli fall 3–6 m thick, rich in crystal ash and consistently marked by a coarser lower half (fig. 17). Closer still to 

Novarupta, Layer F maintains its integrity (Fall 3 of fig. 9 of 

Houghton and others, 2004), although it is sandwiched there 

by proximal PDC deposits. Its coarser and better sorted 

lower half is weakly graded normally, and its moderately 

sorted upper half is richer in crystal-ash matrix, which fluctuates on a decimeter scale, imparting a weak plane-parallel 

internal stratification. Dacite pumice coarser than 30 cm is 

common in the lower half, within 4 km of Novarupta. Farther than ~5 km from vent, this twofold division transforms 

into a pair of normally graded subunits (F1 and F2 of fig. 20; 

Fierstein and Hildreth, 1992) that remain distinguishable as 

far as Three Forks and Katmai River. Altogether, Layer F 
74 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

is thicker than 1 m on Trident and 50–80 cm along Katmai 

River; as it fines downwind, it merges with Layers G and 

H to yield a combined thickness of ~10 cm along Shelikof 

Strait and 2-3 cm on Kodiak Island. Northwest of Novarupta, Layer F thins to ~60 cm in the central VTTS and to 

~20 cm near Three Forks. Because it thins northwestward 

less rapidly than do Layers C and D, Curtis (1968) inferred a 

change in wind direction between Episodes II and III. More 

regional isopach data (Fierstein and Hildreth, 1992), however, show that Layers F and G were still dispersed preferentially toward the east-southeast (as during the Episodes 

before them) but not so strongly. That the proximal isopachs 

for Episode III are more equant may reflect lower column 

height as well as slackening of wind velocity (Fierstein and 

Hildreth, 1992).

Field counts show the pumice clasts in Layer F to be 

97–99 percent crystal-rich dacite in the VTTS and 84–94 

percent dacite south of Trident and Mount Katmai. As in 

Layers C, D, and G, downwind dilution by several percent 

of small lapilli and granules of rhyolite pumice (inconspicuous in the coarser proximal deposits) is probably caused by 

reentrainment of nonwelded Episode I material from nearvent surfaces. 

In the upper VTTS the largest pumice clasts in Layer 

F commonly exceed 30 cm and are as coarse as 50–90 cm 

proximally. Average maximum pumice size is still ~25 cm in 

the Trident saddles and 8–12 cm along Katmai River, where 

corresponding average maximum lithic sizes are ~12 cm and 

3–4 cm, respectively. Lithics make up only ~1 weight percent 

of the deposit in upper Knife Creek and merely a trace at the 

Shelikof coast 40 km downwind; they are predominantly 

recycled welded-tuff vitrophyre. Free crystal content of Layer 

F exceeds 50 weight percent in the VTTS and remains 48–56 

weight percent at the Shelikof coast. Owing to the crystalrich nature of the dacite, median grain size (Md~1 to 32 mm) 

and sorting (sø

~1.8–3.0) range widely (by sublayer, distance, 

and azimuth) in the upper VTTS, but Md declines to 0.6 mm 

in the central VTTS and, downwind, to 1.2 mm at Katmai 

River, ~0.25 mm at Geographic Harbor, and 0.06 mm on 

Kodiak Island (110 km). Within 15 km of vent, the deposit is 

fines-poor throughout and grades only to crystal ash at the top 

where overlain by Layer G.

Layer G

The final plinian deposit of the Episode II-III sequence 

is also the most irregular and complex (figs. 45, 47). Curtis 

(1968) observed two or more ashy partings within his Layer 

G lapilli-fall deposit along upper Knife Creek, where rapid 

thickness variations (<0.5 m to 3.5 m) forced him to draw 

peculiar isopachs for that limited area, only 3–6 km from 

vent. Our work on more proximal deposits equivalent to 

Layer G shows that it consists of two parts separated by a 

set of thin ignimbrites that extend only ~2 km radially from 

Novarupta but supplied ash clouds for partings within the 

medial lapilli falls. The lower half proximally is a wellsorted lapilli fall (Fall Unit 2 of Houghton and others, 2004), 

coarser than the falls above and below it and ~2–3 m thick, 

that contains dacite pumice as coarse as 50 cm and only subordinate crystal ash. This lower half is itself partitioned into 

two parts, each with a weakly normally graded top, by thin 

ignimbrites and derivative ash laminae; each part is typically 

1–2 m thick but exhibits rapid sectorial changes in thickness 

and coarseness. The upper half (Fall Unit 1 of Houghton and 

others, 2004) is not quite as coarse, though it locally contains 

dacite pumice as big as 40 cm; it is subdivided into three 

parts by very thin ignimbrites and derivative ash laminae, and 

its thickness varies sectorially from typically 1–1.5 m to as 

much as 4 m. Much of the ejecta ring around the Novarupta 

dome, including the sector-confined andesite-rich “S-bed” 

(fig. 48) of Fierstein and others (1997), is time-equivalent to 

this uppermost part of Layer G. The complex stratigraphy 

of this closing stage of the plinian sequence is illustrated and 

described in detail by Houghton and others (2004).

The proximal intricacy grades laterally into medial 

lapilli-fall deposits as thick as 3.5 m along upper Knife Creek, 

where grain-size fluctuations suggest three pulses. The three 

intervals, however, are defined by variation in proportions of 

pumice lapilli and coarse crystal-rich ash, not by grading to 

fines that might indicate time breaks in plinian emission. Likewise, south of Trident and Mount Katmai, Layer G consists of 

two (and locally three) weakly graded subunits, each 5–35 cm 

thick. Only the top interval grades up into fines-rich Layer H, 

which accumulated after final extinction of the plinian column.

In the VTTS, pumice clasts in Layer G are >99 percent 

dacite, but south of Trident and Mount Katmai (where most 

rhyolitic pumice is 0.5–4 mm) as many as 12 percent are rhyolite, probably reentrained from Episode I material. Average 

maximum pumice size exceeds 20 cm in the upper VTTS and 

declines to 7 cm on Trident and 3–4 cm at Katmai River; corresponding average maximum lithic sizes are 7 cm, 2 cm, and 

only 1–2 mm. As throughout Episodes II and III, most lithics 

are welded tuff recycled from Episode I vent fill. The fraction of free crystals in Layer G is 40–60 weight percent in the 

VTTS, along Mageik Creek, and all the way to Shelikof Strait 

(40 km downwind). Median grain size ranges widely in the 

proximal falls (Md~1–64 mm), as does sorting (sø

~1.7–3.3), 

depending on proportions of crystal ash and pumice lapilli 

in successive sublayers (Houghton and others, 2004). Sorting improves downwind, and Md declines from ~1 mm in 

upper VTTS medial deposits to ~0.2 mm in distal deposits 

at Three Forks and ~0.1 mm at the Shelikof coast. As grain 

size diminishes between Katmai River and Shelikof Strait, 

dacite-dominant Layers F, G, and H merge indistinguishably 

and become contaminated by fallout of coplinian fines left 

over from Episode I (table 3a of Fierstein and Hildreth, 1992). 

Although principal downwind dispersal of Episode III ash was 

still east-southeastward, part of the cloud was driven northeastward toward Cook Inlet (fig. 14 of Fierstein and Hildreth, 

1992). The vitric shards that dominate the 4-cm-thick layer of 

1912 ash on Augustine Island (160 km northeast of Novarupta) 
Chapter 5. Products of the Eruption 75

snow

PDC 4

PDC 4

PDC 3

PDC 2

PDC 1

PDC 5

PDC 4

Fall 1

Fall 2A

Fall 2B

Fall 3

Fall 4

sloughed

sloughed

Section 94-F

Novarupta ejecta ring 

ballistic

block

Figure 47. Photograph and annotated sketch of section in gulch ~1.1 km southeast of Novarupta dome 

(seen at top), illustrating proximal intercalation of Episode II–III fall units with several thin pyroclastic 

density current (PDC) deposits. For scale, total Fall 2 is 2.8 m thick. Several such gulches radial to 

Novarupta expose such sequences, in which coarseness and thickness of fall and flow units change 

sectorially, as documented in detail by Houghton and others (2004). Falls 1 and 2 here are equivalent to 

regionally dispersed Layer G; Fall 3 to Layer F; PDC 4 to Layer E; Fall 4 to Layer D; PDC 5 to the C–D parting. 

Layer C and Episode I ignimbrite are below level of exposure in this gulch. 
76 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Figure 48. The “S bed” atop the Turtle, ~600 m northeast of Novarupta dome. Rich in andesite scoria, the layer is enclosed within 

dacitic Layer G of Episode III and extends as a 150-m-wide lobe for only 1.1 km northeast of vent (Fierstein and others, 1997). The 

bed thins with distance, and its andesite proportion is progressively diluted by dacite pumice, ultimately fading into a scattering of 

sparse clasts among the dacite. Distance over which its thickness halves is ~70 m, in contrast to many kilometers for dacite-dominant 

fall layers. Containing 50–90 percent andesitic clasts, S bed is andesite-richest unit of whole 1912 eruption. It may reflect viscous 

segregation of low-viscosity andesite along conduit margin, resulting in a sector-confined collar of low-fountaining ejecta peripheral to 

a high-velocity core that simultaneously fed dacitic plinian column. Best exposed here on wall of radial graben atop the Turtle. View 

westward toward spurs of Baked Mountain. Geologist is 1.63 m tall.

are >88 percent dacitic, ~10 percent rhyolitic, and ~1 percent 

andesitic (table 3a of Fierstein and Hildreth, 1992).

The fluctuations of Layer G were followed by termination 

of plinian activity and transition to effusion of the lava domes 

of Episodes IV and V. Analysis of vesicularity and bubble-wall 

textures of dacite pumice from Layer G (Adams and others, 

2006b) shows a progressive shift toward smaller bubbles, 

thicker vesicle walls, and teardrop shapes, indicating onset of 

bubble-wall collapse with open-system degassing. Unlike the 

temporary plinian stoppage after Episode II, which was probably caused by conduit blockage, this final cessation of plinian 

activity reflects slowing of magma ascent and maturation of 

vesicular melt, permitting freer escape of gas, transition to 

open-system outgassing, and accumulation of degassed magma 

that ultimately blocked the conduit, precursory to effusive 

dome growth.

Layer H

Throughout and near the VTTS, on Trident and Mount 

Katmai, and from Mageik Creek to Katmai Canyon, Layer H 

is widely preserved as a bed of muddy vitric ash that caps the 

1912 primary deposits (figs. 21, 45). The blue-gray or terra 

cotta (oxidized) mud is typically 5–50 cm thick, but its thickness appears not to vary systematically with distance from 

Novarupta. Its primary thickness, however, is typically hard 

to assess, owing to disturbance by scree, mudflows, windscour, and other surface processes. Sections thicker than 40 

cm have been measured in upper Knife Creek, high on the 

flanks of Mount Katmai, and at Katmai Canyon. Farther 

from vent than 20 km northwest or 40 km southeast, Layer H 

is not separable from the fine-grained top of Layer G. Accretionary lapilli are locally conspicuous in Layer H, as 
Chapter 5. Products of the Eruption 77

are vesicles that probably reflect syndepositional incorporation of atmospheric moisture.

Even proximally, Layer H includes >50 weight percent 

ash finer than 63 μm and contains ≤10 weight percent crystals 

and a negligible fraction of lithics. Microprobe analysis shows 

that, in and near the VTTS, 85–100 percent of the glass shards 

are dacite derived. Relative to the phenocryst-rich dacite 

pumice of Episode II and III, therefore, Layer H is strongly 

depleted in crystals. Downwind near Shelikof Strait, however, microprobe data indicate that about a third of the glass 

shards in the top few centimeters of the ashfall are rhyolitic, 

evidently Episode I fines that were held aloft since the first day 

of the eruption (Fierstein and Hildreth, 1992). Upwind to the 

northwest, where the expanding ash cloud did not bring ashfall 

at Naknek until 12 June (Dumond, 2005), the rhyolitic shard 

fraction falls off from 19 percent at Brooks Camp (fig. 49; 50 

km from vent) to only ~1 percent at King Salmon (100 km).

Clearly, then, most of Layer H is coplinian dacitic ash and 

dust that settled slowly after the dacite plinian eruptions of Episodes II and III. Mass balance indicates that no more than 10 

percent of Layer H in and near the VTTS can be coignimbrite 

ash, although far downwind roughly a third of Layer H fallout 

is coplinian ash left over from Episode I (Fierstein and Hildreth, 1992). Detailed investigation of the proximal deposits 

(Houghton and others, 2004) shows that no pyroclastic density 

currents were emplaced subsequent to Layer G that might have 

contributed ash to Layer H. 

Sieving of Layer H indicates median grain size between 

0.05 and 0.1 mm and moderate to good sorting (sø

~1–2). 

Locally, however, as many as three medium-to-coarse crystalash laminae are intercalated within dominantly vitric Layer 

H. On Mount Katmai, some of these are related to the phreatic 

mud layers expelled from the fitfully collapsing caldera (Hildreth, 1991). In upper Knife Creek and the uppermost Lethe 

arm of the VTTS, some are probably related to the numerous 

phreatic explosion craters in the ignimbrite there (Hildreth, 

1983; Hildreth and Fierstein, 2003). On and adjacent to many 

slopes, uncommon sandy layers thicker than several millimeters (some containing sparse rounded pumice granules) may 

in many cases have been wind deposited. No ultraproximal 

evidence is recognized for postplinian explosions at the Novarupta vent that might have deposited coarse ash laminae during 

settling of Layer H, but there is little doubt that small outbursts 

could have occurred.

Proximal Pyroclastic Density Currents

Within 3 km of the Novarupta dome, which plugs the Episode III vent, the sequence of dacite fallout deposits equivalent 

to medial-distal Layers C through G contains thin packages 

of pyroclastic density current deposits (figs. 47, 50) intercalated at five different horizons (Houghton and others, 2004). 

Most are sector-confined multiflow packages that show rapid 

radial and sectorial changes in thickness and grainsize. All are 

dacite-dominant, but nearly all also contain more andesitic and 

banded pumice (and lithics) than the medial fall deposits. The 

various packages range in thickness from 0.1 to >3.5 m and 

pinch out within 1.5 to 2.5 km of Novarupta, although most 

also generated ash clouds that deposited thin ashfall layers 

extending a kilometer or two farther. They include (1) matrixrich channel-confined ignimbrites, typically 1–2 m thick and 

generally consisting of a few thin massive flow units defined 

by pumice-concentration zones; some are rich in dacite pumice 

blocks, but all contain more andesite pumice than the enclosing fall deposits; (2) radially distributed, thin bedded ash-rich 

packages that show pinch-and-swell lamination, interbedding 

with thin lapilli falls, and dacite-andesite-rhyolite pumice 

proportions similar to enclosing thin fall deposits; (3) radially 

distributed massive landscape-mantling ash-rich veneers deposited by concentrated but energetic currents; and (4) channelconfined matrix-poor grain-flow avalanche deposits formed by 

local slumping of coarse pumice-fall deposits. These complex 

proximal deposits are described, illustrated, and interpreted by 

Houghton and others (2004), and their grain size characteristics 

are illustrated in figure 51. Their total volume is small (<0.05 

km3

), but their importance for revealing the processes of proximal sedimentation from the margins of the gas-thrust jet and 

the base of the convecting column is profound. 

The variety of thin sector-confined flow deposits radial 

to Novarupta (fig. 52) and intercalated within deposits of sustained plinian pumice fall suggests column-margin instabilities 

on very short spatial and time scales. It indicates a variety of 

transporting currents initiated from a range of heights and on 

a range of trajectories, reflecting sporadic heterogeneities—in 

particle density and in lithic and andesite proportions—within 

an annular collar around the emerging column (fig. 53).

Proximal Fall Deposits: Contrasting Facies

Within 3 km of Novarupta, in addition to the proximal 

flow deposits just discussed, there are also several coarsegrained locally dispersed fall deposits interbedded with the 

regionally dispersed dacite fall deposits of Layers C, D, F, 

and G. Even ultraproximally, the latter remain moderately 

sorted lapilli-to-block falls that are radially distributed and 

pass gradationally in grain size and thickness into their medial 

equivalents; thicknesses halve over distances of several 

kilometers. Subtle fluctuations in grain size and in fraction 

of crystal-rich coarse-ash matrix define faint shower bedding. 

Like the medial-to-distal plinian fall deposits, the material in 

these “normal” proximal fall units was derived from high in 

convective plumes and their ensuing umbrella clouds. 

The locally dispersed proximal fallout facies is identified as six narrow wedge-shaped lobes that halve in thickness within only 100–300 m, terminate 1.5–2 km from vent, 

and pass radially and laterally into the normal fall deposits. 

These lobes are generally coarser (Md~8–64 mm) than the 

normal facies (Md~2–6 mm), apart from crystal-enriched 

intervals that are similar (Md~1–3 mm) in both facies. Neither proximal facies, however, is well sorted (sø

~1.7–3.2), 
78 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Figure 49. Structureless white fine ash, 20 cm thick, at Brooks 

Camp, 49 km upwind northwest of Novarupta (fig. 6). Coin is 2.4 

cm across. Point counts by microprobe showed dacite shards 

to make up 87 percent of this deposit at base and 79 percent at 

top (Fierstein and Hildreth, 1992). Sparse andesite shards are 1–4 

percent, and rhyolite shards 9–19 percent. Rhyolite-rich plinian 

ash was driven strongly southeastward from vent, and rhyolite-rich 

ignimbrite produced rather little coignimbrite ash. Upwind ashfall 

continued for several days after eruption ended and consisted 

predominantly of fine fractions of plinian dacite of Epiodes II and 

III. Lush herbaceous plant life rapidly recolonized ashfall blanket.

owing to the crystal-rich nature of their dacite and andesite 

pumice and to concurrent sedimentation from diverse parts 

of the eruptive jet and plume. The lobate facies is much 

richer than the normal fallout in andesitic pumice and lithic 

fragments, both of which decrease rapidly away from vent. 

The andesite-rich “S-bed” (fig. 48) of Fierstein and others 

(1997) is a striking example that extends narrowly northeastward for ~900 m from Novarupta, across the Turtle sector 

of the ejecta ring. Like the “S-bed,” the several larger lobes 

mapped by Houghton and others (2004) were emplaced by 

intermittent processes limited to local sectors of the periphery of the eruptive jet and lower plume. Rapid lateral and 

radial changes in proportions of andesite pumice and lithic 

fragments within such fallout lobes further emphasize the 

role of small-scale transient heterogeneities around the margin of the emerging jet.

The excessive proportion of lithics and especially of 

andesite in the ultraproximal fall and flow lobes may be explicable in terms of inhomogeneous two-phase flow in dikes and 

conduits, both before and after fragmentation of the magma, 

as explored by Carrigan and others (1992) and Houghton and 

others (2004 and references therein). Viscous segregation of 

lower-viscosity andesite magma into lateral zones during joint 

sheet flow with dacite or rhyolite may have been succeeded, 

following fragmentation, by lateral zones of higher-density 

high-concentration particulate material along the sheet or conduit walls. Changes in direction or from sill to dike or from 

dike to pipe-like conduit could also promote inhomogeneities 

during transport. At the vent, such a dense annular collar 

would emerge at lower velocity than the turbulent core and 

thus be more likely to contribute to marginal fountains than 

to the central plinian plume (fig. 53). Some such processes 

certainly influenced distribution of near-vent ejecta during 

Episodes II and III, and they probably operated during Phase 

B of Episode I as well (producing the greater fractions of 

andesite in ignimbrite packages than in coeval fall deposits).

Eruptive Episode IV: Dacitic Phantom 

Dome and Block Bed

Sometime after cessation of the pyroclastic eruptive 

sequence, following the days or weeks required for complete 

accumulation of fines-rich Layer H, a small dacite dome that 

plugged the Episode III vent was explosively destroyed. The 

resulting apron of decimeter-to-meter-sized fragments covers an elliptical 4-km by 2-km dispersal area that surrounds 

Novarupta and is elongate north-south (fig. 6 of Adams and 

others, 2006a). The approximately 700 blocks studied represent four main lithologies—pumiceous, dense, flow-foliated, 

and variably welded breccia. All lithologies are crystal-rich 

dacite compositionally like that erupted as pumice during the 

preceding Episodes II and III (62.2–66.7% SiO2; n=8). Many 

blocks of all lithologies became breadcrusted after fragmentation and dispersal, indicating that the plug material was still 

hot and capable of exsolving residual gas after explosive 

disruption (fig. 54). The distribution of blocks of different size 

and density suggests complex or serial ejections, and fanshaped dispersal of blocks that shattered on impact indicates 

ballistic trajectories for many. 
Chapter 5. Products of the Eruption 79

?

?

95-4 97-11

95-5

Trident

Turtle

dome

Falling

Mtn

172°

1,125 m

from vent

178°

1,200 m

from vent

185°

1,230 m

from vent

0

2 m

175 m 135 m

Distance between sections

95-4

B-ig

PDC-5

PDC-4

PDC-3

PDC-2

PDC-1

dacite block bed

Layer H

Fall 1

Fall 2a

Fall 2b

Fall 3

Fall 4

Fall 5 Fall 5

Fall 6

III

II

I

IV

Fall

Regional

G

F

E

D

C

Postplinian

Episode

Layer 97-11 95-5

Figure 50. Stratigraphic sections in three confluent forks of gulch system adjacent to east side of Falling 

Mountain, ~1.2 km south of Novarupta, illustrating complex ultraproximal deposits investigated in detail by 

Houghton and others (2004). At least five pyroclastic density current (PDC) deposits are intercalated (only 

proximally) in the fallout sequence, for which regionally dispersed equivalents are indicated at right, along 

with eruptive episode sequence. Distances between sections and azimuths and distances from Novarupta 

are given at bottom. Inset sketch shows locations of sections relative to Novarupta dome, ejecta ring 

(dotted), rim of vent structure (dashed), and Falling Mountain scarp (see photo figure 70). Compare 

sequence with that of Section 94-F, which lies 1.1 km east, as illustrated in figure 47.
80 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

4

3

2

1

-6 -4 -2 0 +2 +4

0

Mean grain size 

Sorting 

phi units

(64 mm) (16 mm) (4 mm) (1 mm) (1/4 mm) (1/16 mm)

Massive ignimbrite

Thin-bedded pdc layers

Veneer-like units

Avalanche deposits

Fall within PDC unit

Main VTTS ignimbrite

Medial-distal fall

Proximal fall

Figure 51. Grain size characteristics of the pyroclastic density current deposits (PDCs) intercalated ultraproximally with Episode 

II and III fall deposits within 1-3 km from Novarupta dome. For comparison, red lines enclose fields of abundant data for proximally 

and regionally dispersed dacite fall deposits (Layers C, D, F, G). For elaboration of PDC facies distinguished in key, see Houghton and 

others (2004). Sorting is conventional sedimentological parameter sf.

Vesicle population studies (Adams and others, 2006a, 

b) indicate for Episode IV dacite a continuation of the trends 

toward bubble coalescence and collapse already underway 

late in Episode III, marking the transition from closed- to 

open-system degassing of conduit magma. A short interval of 

passive extrusion culminated in explosive disruption of a lowpermeability plug as pressurized gas was suddenly released 

after accumulating from subjacent dacite that was incompletely degassed and still somewhat permeable. Modelling 

ballistic ejection of Episode IV blocks by transient Vulcanian 

explosions suggests a role for excess trapped gas or for external water, augmenting the gas provided by the vesicular facies 

of the ejected material alone. Explosion could have been 

triggered by gravitational carapace collapse, by build-up of 

internal pressure of trapped gas, or by infiltration of rainwater 

through cracks toward the hot interior.

Episode IV material dispersed across the strewnfield adds 

up to a hard-to-estimate volume that is certainly less than a tenth 

that of the subsequent Novarupta dome (~5 million m3

). What 

is remarkable is that this small destructive event cleared the vent 

and upper conduit of mobile dacite magma, permitting egress of 

the rhyolite magma that then formed the Episode V Novarupta 

dome without further ejection of pyroclastic material.

Eruptive Episode V: Novarupta Rhyolite 

Dome

The Phantom dacite dome of Episode IV was never 

observed, and the subsequent rhyolitic dome (Novarupta) 

was not observed until July 1916, when Folsom and Griggs 

first entered the VTTS. Although it has cooled substantially 

and virtually ceased steaming, the morphology of the dome is 

essentially unchanged since it was first seen. Nestled within 

an extraordinarily asymmetrical ejecta ring (fig. 55), the 
Chapter 5. Products of the Eruption 81

Figure 52. Interbedded deposits of pyroclastic density currents (PDC) and pale-gray plinian dacite fallout on southeast 

spur of Baked Mountain, 1.4 km northwest of Novarupta dome and ~100 m above floor of Novarupta basin. All layers are 

products of Episode III. Note that topmost PDC crosscuts all below it. Layer G pumice-fall deposit tops section here as 

well as on Baked Mountain ridge in background. For scale, backpacks are ~1 m high.

Novarupta dome is ~380 m in diameter, circular in plan, and 

65–70 m high, and it plugs the vent of Episodes III and IV 

(and less certainly II). Its coarsely blocky surface is almost 

entirely glassy and flow-foliated, steep-sided and rugged on 

top, where there is no sign of any tephra (either uplifted by 

the dome or deposited subsequently). Spreading of the dome 

opened numerous fissures on its upper surface, some with 

5–20 m of relief. Principal among these radiate 80o, 235o, and 

295o from a small 20-m-deep pit just south of the dome’s center (fig. 56); a few more trend northeast across the northeast 

rim, and a concave-outward arcuate set marks the northwest 

slope of the dome. Exposed deep on the wall of one fissure is 

an abrupt transition from glassy carapace into a denser devitrified interior facies (Cowee and others, 1999). The dome has a 

peripheral apron of coarse angular talus blocks, most of which 

were shed during extrusion and have remained undisturbed 

since first observed. Many early photographs published by 

Griggs (1922) and Fenner (1923, 1950) show the dome and its 

talus much as they are today.

The exposed part of the dome has a volume of roughly 

5,000,000 m3. The dome surface is ~95 percent rhyolitic, and 

most of its ubiquitous flow foliation reflects textural variation 

in the rhyolite. Much of the exposed rhyolite is pale gray 

and finely vesicular to microvesicular, but some layers and 

lenses are coarsely vesicular and oxidized brown, while fewer 

are variously pink, massive, incipiently devitrified, or finely 

spherulitic. The rhyolite lava carries the same assemblage 

of sparse phenocrysts present in the rhyolite pumice erupted 

earlier (quartz, oligoclase, orthopyroxene, Fe-Ti oxides), as 

well as traces of augite and amphibole that are probably contaminants from interlaminated andesite and dacite. As pointed 

out by Fenner (1950, p. 720) and Curtis (1968), crystals from 

the intermediate components are sparsely but widely disseminated within the deceptively clean-looking dome rhyolite. 

Such contamination explains why most (normalized) chemical 

analyses of dome rhyolite (sampled for apparent purity) yield 

74.5–76.9 percent SiO2

, whereas virtually all samples of 1912 

rhyolite pumice have more than 77.1 percent.

Conspicuous layers, lenses, and rounded to angular chunks 

of dark-brown to black intermediate lava are included within the 

dome rhyolite (fig. 57). They make up ~5 percent of exposures 

around the dome margins and appear to be much sparser in the 

dome core, but the rugged top of the dome has not been as thoroughly examined. Many of the dark layers are 1–15 cm 
82 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

REGIME 3

REGIME 1

REGIME 2 (generating PDCs)

REGIME 4

Dominated by clasts

not adequately supported

by upward gas flow

Buoyant plume

Dominated by fountaining of all grain sizes,

low, small-scale collapses around 

plume margins, and overspill from vent

to generate density currents

Direct lateral ejection,

detached from

rising eruptive plume

(generating ballistic ejecta)

(generating locally confined fallout)

(generating regionally distributed fallout)

Figure 53. Cartoon illustrating four eruptive regimes capable of simultaneous operation from a sustained plinian column. Model was 

elaborated in detail by Houghton and others (2004) to account for deposition of ultraproximal sector-confined falls and thin pyroclastic 

density currents (PDCs) concurrent with regional plinian fallout.
Chapter 5. Products of the Eruption 83

Figure 54. Block of massive breadcrusted dacite on slope just northwest of rhyolitic Novarupta dome. Hundreds of such 

dacite blocks, variously dense, pumiceous, flow-foliated, or brecciated, are strewn across an area of 8 km2

, overlying 

Layer H and representing explosive destruction of a small plug-dome (Episode IV) that preceded extrusion of Novarupta 

(Adams and others, 2006a). Knife is 8.5 cm long.

thick and meters long, and some are bundles of thin parallel 

laminae that intimately alternate with rhyolite. All dark layers 

are at least finely vesicular, and some are coarsely scoriaceous 

or vuggy and contain vapor-phase minerals. Discrete pieces of 

dark intermediate lava are mostly 0.5–10 cm across and rarely 

as long as 15–25 cm. Most are within or associated with the 

dark layers and lenses, but such clasts occur in rhyolite layers as well. They include clasts that are angular and solitary, 

broken and slightly separated, rounded, lenticular, or viscously 

distended. Like the dark layers and lenses, most clasts are 

glassy, phenocryst-rich, and variably vesicular. Much of the 

clast population may form a deformation continuum with the 

dark layering, their brittle through viscous behavior depending 

on local cooling rate and strain rate. Rare clasts of dark lava are 

crystal-poor (unlike any 1912 andesite-dacite ejecta) and may 

be true xenoliths. Xenoliths of Naknek sandstone and siltstone, 

undeformed and usually oxidized, make up fewer than 5 percent 

of the non-rhyolite clasts in the dome.

Nearly all of the dark layers, lenses, and clasts are 

crystal-rich pyroxene-plagioclase lava, compositionally 

indistinguishable from the andesite-dacite juvenile continuum 

previously erupted during Episodes I through IV. Layers and 

clasts chemically analyzed range in SiO2

 content from 55.2 to 

65.1 percent.

Bulk densities measured for numerous rhyolite samples 

from Novarupta range from 1,300 to 2,170 kg/m3 (Adams and 

others, 2006a). These values compare with ranges of 310 

to 1,250 kg/m3 for the pumiceous facies of the Episode IV 

block bed and 600 to 1,300 kg/m3 for pumice in Episode III 

fallout (Layers F and G). A few Novarupta rhyolite samples 

representative of the density range measured were selected 

for textural analysis, yielding 18–38 volume percent vesicles 

and 3–6 volume percent crystals (Adams and others, 2006a), 

significantly more crystals than held by rhyolite pumice. As in 

the Episode IV dacites, it was found that bulk density increases 

as vesicle size decreases and glass walls thicken. Novarupta 

vesicles, however, are usually foliated, with vesicles of all sizes 

elongate in the same direction but generally not segregated into 

layers. The low-density dome sample (1,490 kg/m3) studied in 

detail has vesicle diameters ranging in size from 8 μm to 630 

μm, with a median diameter near 100 μm (0.1 mm). Absence 

in Novarupta dome of the very-low-density pumiceous facies 

present in Episode IV dacite probably reflects days to months 

of open-system degassing of rhyolite stored shallowly in the 

conduit system, possibly since the close of Episode I. After the 

Episode IV dacite was flushed, such rhyolite was thus able to 

extrude passively without major build-up of overpressure by gas 

still exsolving beneath the plug.
84 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

A

B

Figure 55. Novarupta and its ejecta ring. Views northeastward of the 380-m-wide lava dome and 

its asymmetrical ring of Episode III ejecta: A, 1919 and B, 1982. Above the dome-encircling moat, 

the ejecta ring ranges in height from a low of ~7 m in the southwest to 225 m in the northeast, 

where it broadens into the 1-km-wide northeast-elongate mound called the Turtle. Configuration 

of the dome, ring, faults, and fissures has changed little since 1919. The dome steamed vigorously 

for decades, as did several fumarolic areas along the ring that are now conspicuously discolored. 

Measured temperatures of acid fumaroles in 1918–19 were as high as 290oC on the west rim of the 

ring and 166oC–264oC along faults atop the Turtle (Sayre and Hagelbarger, 1919; Allen and Zies, 1923). 

In the same areas, wispy emissions were visible only close at hand and gave temperatures of only 

25oC–90oC in the 1980s (Keith, 1991a). At lower right of both images, a fallen block of shattered dacite 

of Falling Mountain crumbled in place to form a 12-m-high hummock that has sometimes been 

mistaken for a domelet or “volcanette.” 1919 photo courtesy of National Geographic Society, taken 

from toe of Falling Mountain; 1982 photo by authors, taken from summit of Falling Mountain.

A

B
Chapter 5. Products of the Eruption 85

W

E

N

S

Figure 56. Vertical view (from tightly banking helicopter) of Novarupta dome, 65 m high, nearly circular 

in plan view, and 380 m across. Note fumarolic alteration outside and along crest of fissured ejecta ring. 

Dome surface is almost entirely glassy, flow-foliated, coarsely blocky, and tephra-free. Spreading of 

dome on extrusion opened variously oriented fissures on its upper surface, some with 5–20 m local relief. 

Apron of coarse talus fringes steep sides of entire dome. Orientation indicated at margins of image.

Figure 57. Flow foliation in Novarupta 

lava dome. Medium- and light-gray 

layers are rhyolite, dense to finely 

vesicular. Darker brownish layers and 

laminae are both dacitic and andesitic. 

Dark enclaves are variously crenulate, 

deformed, or broken, and they include 

some of the most mafic andesite 

released in whole 1912 eruption. Only a 

few percent of dome surface is visibly 

contaminated with such nonrhyolitic 

material, but even apparently clean 

rhyolite has ubiquitous xenocrysts. 

Knife is 8.5 cm long.
86 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Graffito inscribed in oxidized sintered ignimbrite along a hinge-line fault 

on the rim of the “high sand line” bench near the northwest base of Mount 

Cerberus. The “Glacier Priest,” Bernard Hubbard, a faculty member at 

the University of Santa Clara, California, led small teams of rugged male 

students on several summer expeditions to Alaska in the 1920s and 1930s. 

The first of his three trips into the Valley of Ten Thousand Smokes (VTTS) 

was in July 1929. Fault fissures like this one have provided many VTTS 

expeditions with shelter from the severe sandblast attending storm winds 

intensified by funneling through adjacent Katmai Pass. July 1982 photo of 

one of the present authors by the other.
Chapter 6. Volcanological Aspects of the Primary Eruption Products 87

Chapter 6

Volcanological Aspects of the Primary Eruption Products

In this section we summarize the volumes of material that 

erupted during the five episodes of the 1912 eruption. Following 

that, we discuss interesting physical aspects of the fall and flow 

deposits, their emplacement, distribution, and consolidation. 

Volumes Erupted

Griggs (1922) estimated 4.75 cubic miles (19.8 km3) of 

regional fallout, which he attributed to Mount Katmai, plus 

~0.5 mi3 (2.08 km3) of proximal fallout attributed to Novarupta, and ~1 mi3 (4.17 km3

) for the VTTS ignimbrite, yielding 

a total ejecta volume of ~26 km3. Curtis (1968) estimated ~20 

km3 of fallout and, modelling much thicker tuff concealed in 

the upper valley, ~11 km3 of ignimbrite, giving a total ejecta 

volume of ~31 km3. 

By logging 382 fallout sections from Bristol Bay to 

Katmai River (on foot) and on both sides of Shelikof Strait (by 

boat), Fierstein refined the volume estimates and subdivided 

them by episode (Fierstein and Hildreth, 1992). Estimates 

included integration to vanishing thickness (Pyle, 1989; 

Fierstein and Nathenson, 1992), showing that 9–14 percent of 

each fallout layer lies beyond its 1-cm isopach. As determined 

by microprobe, proportions of rhyolite shards in the fine-ash 

fraction of each layer varied considerably by azimuth and 

with distance from vent. Owing to atmospheric turbulence 

and intrinsically slow settling velocities for low-density glass 

shards of irregular shape, considerable volumes of Episode I 

rhyolitic ash ultimately accumulated within dacitic Layers C 

through H, requiring complex reapportionments to obtain true 

eruptive volumes for each episode (Fierstein and Hildreth, 

1992). As so adjusted, the fallout volumes are 8.8 km3

 for 

Episode I (6.1 km3 for A; 2.7 km3 for B), 4.8 km3 for Episode 

II, and 3.4 km3 for Episode III, yielding a total of 17 km3. 

The 11-km3 volume estimate by Curtis (1968) for the 

120-km2 VTTS ignimbrite is as good as the uncertainties warrant; addition of the Mageik Creek lobe and the eroded Ukak 

terminus would raise the estimate by only 0.1 to 0.2 km3. The 

base of the ignimbrite is not exposed in the middle or upper 

parts of either the Knife Creek or River Lethe arms of the 

VTTS. Weaker development of marginal benches (attributable to differential compaction; see section titled “High Sand 

Mark,” below) along the Knife Creek arm and an abundance 

of phreatic craters that burst through the ignimbrite sheet in 

upper Knife Creek suggest that the sheet might be thinner there 

than in the Lethe arm. If so, the ignimbrite volume might be as 

much as 20 percent smaller than estimated by Curtis.

Equivalent magma volumes are about 6.5 km3 emplaced 

as fallout and 7±2 km3 emplaced as ignimbrite, yielding a total 

of ~13.5 km3 of magma erupted as ejecta in 1912. The subsequent lava domes added trivially to the total, and neither was 

accompanied by significant additions of tephra. The Episode 

V Novarupta Dome has a volume of ~0.005 km3

 (5 million 

m3), and the Episode IV Phantom dome (the plug destroyed to 

produce the block bed) was an order of magnitude smaller still. 

The observation that roughly equal proportions of explosively fragmented magma were emplaced as fall and flow 

deposits in 1912 contrasts strongly with some other 20th century plinian eruptions. In both the Santa María (Guatemala) 

eruption of 1902 and the Quizapu (Chile) eruption of 1932, 

pyroclastic density currents provided only trivial fractions of 

voluminous plinian outbursts that deposited widespread tephra 

falls. During Episode I, fall Layers A and B accumulated 

continuously, nowhere showing any evidence for a significant 

interruption in deposition from the plinian column. Nonetheless, the transition from Phase A to B represented not just 

a compositional change but a fundamental shift in eruptive 

style, in that ~90 percent of Phase A was emplaced as fallout 

and ~80 percent of Phase B as ignimbrite. Episodes II and III 

were again predominantly fallout, as the several accompanying flow deposits amount to no more than 1 percent of their 

respective volumes.

Coignimbrite Ash and Coplinian Ash

Compositional proportions (rhyolite/dacite/andesite) of 

glass shards, determined by microprobe for numerous distal 

ash samples (40–155 km from vent; table 3a of Fierstein and 

Hildreth, 1992), show that downwind fallout (on both sides 

of Shelikof Strait) equivalent to dacite-dominant Layers C-D 

and F-G-H incorporate 23–40 percent rhyolitic ash that had 

stayed aloft after Episode I. The 1912 dacitic glass shards are 

far richer in Ti, Fe, Mg, and Ca than the rhyolitic glass shards 

and are thus readily distinguishable. From Katmai River to 

Geographic Harbor (13–36 km from vent, where coarse ash and 

pumice granules still permit visual clast counts), the rhyolite 

fraction added to these dacite fall layers is 7–16 percent (table 

2 of Fierstein and Hildreth, 1992). Although a limited fraction of rhyolitic ash and lapilli was no doubt entrained from 
88 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

near-vent surficial material by the Episode II and III columns, 

this was probably a modest contribution, because most of the 

near-vent Episode I rhyolite was by then welded (as represented 

by the lithic suite predominant in the Episode II and III deposits). Phase B of Episode I (Layer B and the main VFI) was the 

only interval during which voluminous rhyolite and dacite (and 

andesite) erupted concurrently.

The abundance of rhyolite shards in downwind ashfall 

deposits of Episodes II and III could thus be attributable to 

(coignimbrite) ash elutriated from rhyolite-rich packages of 

the main Episode I ignimbrite or to slow-settling (coplinian) ash that remained aloft after deposition of Layers A and 

B. The former is unlikely to have provided a large fraction 

of the rhyolite shards that settled with the Episode II and III 

downwind dacite fallout because (1) Layer C lies directly on 

the main ignimbrite (fig. 45) with no coignimbrite intercalation, and (2) in proximal and medial sections from the VTTS 

to Katmai River, fine-grained Layer H (which caps the Episode 

III pumice falls) contains little rhyolite ash (0–15 percent; table 

3 of Fierstein and Hildreth, 1992). Scarcity of coignimbrite ash 

near the VTTS and downwind may reflect (1) persistence of 

the Phase B column during generation of the main ignimbrite, 

favoring updraft of circum-vent ash clouds into the plinian 

column itself; (2) relatively low-energy emplacement of VTTS 

ignimbrites, promoting rather limited elutriation of fines; (3) 

flushing of lingering Episode I fines by the dacite pumice falls, 

and (4) muffling of any coignimbrite plume from the ignimbrite 

sheet itself by the blanket of Episode II-III fallout. 

There is no discrete coignimbrite ashfall layer (rhyoliterich or otherwise) between lapilli-fall Layers B and C (representing the lull between Episodes I and II) proximally, 

medially, or downwind. Upwind (northwest) of the VTTS, 

where most of the rhyolite shards might be expected to be of 

coignimbrite origin, they make up only 3–19 percent of the 

unitary layer of fine ash (17–30 cm thick) at distances of 20–50 

km from vent (fig. 49) and only ~1 percent of shards in the 

2-cm-thick distal layer at King Salmon (100 km northwest of 

vent). Moreover, medially and distally, downwind Layers A, 

B1

, and rhyolite-dominant B2 are actually enriched in crystals 

relative to the crystal content of rhyolite pumice, indicating 

that they do not contain a significant contribution of (typically 

crystal-depleted) coignimbrite ash. Likewise, as far downwind 

as Shelikof Strait (~40 km from vent) Layers C-D and F-G 

themselves remain enriched in free crystals (relative to the 

crystal content of their dacite pumice), despite their downwindincreasing contamination by rhyolite shards. It can thus be 

concluded that most of the rhyolitic fines that mixed with the 

dacite-dominant downwind ashfall of Episodes II and III were 

leftovers from the Episode I plinian phase, which reached a 

greater elevation, was more voluminous, and had a greater fraction of fines than the subsequent dacitic plinian outbursts.

Shards that settle together distally thus need not, as a 

generality, be all from the same eruptive episode. As the 1912 

rhyolitic downwind shards (mostly finer than 125 μm) were 

predominantly plinian in origin, their settling was delayed and 

decoupled from fallout of coarser coerupted ejecta. By analogy 

with the term coignimbrite ash, such suspended fines have been 

called coplinian ash. Atmospheric turbulence and intrinsically slow settling velocities of raggedly fractured tubular and 

bubble-wall shards inevitably decouple some fraction of the 

fines from the bulk of coerupted ejecta that settles systematically to produce a deposit that thins exponentially with distance. 

Figure 58, reproduced from Fierstein and Hildreth (1992), 

illustrates isopach data for the 1912 fall deposits and for three 

others that all yield two-segment best-fit lines (Pyle, 1989; 

Fierstein and Nathenson, 1992). The breaks in slope between 

medial and distal deposits occur at distances where slow-settling 

fines become an important or dominant fraction; the flatter 

segments represent distal tephra deposits where the exponential 

fallout is augmented by fines that remain aloft longer and are 

thus transported farther downwind than would be predicted by 

terminal fall velocities (Fierstein and Hildreth, 1992). Because 

many plinian eruptions, especially rhyolitic ones, produce ejecta 

consisting of ≥50 weight percent fine ash (finer than 63 μm), 

such a two-segment medial/distal fallout pattern is common. 

And, in the 1912 eruption and elsewhere, such a pattern may 

be intrinsic to the plinian plume and need not always reflect 

dispersal of coignimbrite ash elutriated from ash flows or rising 

as a secondary buoyant plume above hot ignimbrite sheets. 

The voluminous 1932 rhyodacite eruption of Quizapu (Chile) 

produced a continent-wide plinian deposit with ~50 weight percent of ejecta finer than 63 μm (Hildreth and Drake, 1992) and 

a similarly inflected thickness-area relationship (fig. 58), even 

though ash-flow generation was negligible.

A small fraction of the finest ejecta remained aloft longer still. Volz (1975a, b) reviewed 1912–1914 atmospheric 

records and solar-radiation data for Europe and North America, 

concluding that (1) tropospheric dust was largely washed out 

within a few months; (2) stratospheric aerosol was concentrated 

at 15–20 km altitude and, though diminishing gradually after 

September 1912, persisted measurably through late 1914; and 

(3) mean atmospheric residence time for the aerosol was 9–12 

months. Although the records could not distinguish proportions 

of silicate dust and acid aerosol, Volz inferred from atmospheric 

turbidity measurements that 12.7 M metric tons of material 

remained aloft in September 1912 and 2.8 M metric tons still in 

September 1913. Taking an average magma density of 2,500 

kg/m3

, such estimates would mean that in September 1912, 

~100 days after the eruption, roughly 0.08 weight percent of the 

6.5 km3 of the magma erupted as fallout remained suspended in 

the atmosphere. If, after three months, the dust had settled and 

most of the stratospheric aerosol remaining had converted to 

sulfuric acid droplets (density 1,788 kg/m3), the mass fraction 

aloft would still be ~0.06 weight percent. 

Atmospheric and Climatic Effects

Kimball (1913) summarized advance of the ash and gas 

cloud driven eastward by stratospheric winds and reported 

over Wisconsin on 8 June, Virginia 10 June, Algeria 19 June, 
Chapter 6. Volcanological Aspects of the Primary Eruption Products 89

Average maximum lithic clasts, in centimeters Square root of isopach area, in kilometers

Area, in square kilometers

Thickness, in centimeters

A

B

Figure 58. Dispersal and thickness of 1912 fallout layers compared to those of a few other well-studied eruptions. A, Area in km2

enclosed by isopleths of average maximum lithic clasts (ML) for Layers A, C, and F. B, Plots of thickness (log scale) versus square 

root of isopach area (A1/2)for Layers A, B, CDE, and FGH. Straight-line segments define exponential thinning (Pyle, 1989; Fierstein and 

Nathenson, 1992). Breaks in slope represent changes in settling regime with diminishing grain size (Fierstein and Hildreth, 1992). For 

ultraproximal data, also see figure 24 of Houghton and others (2004).

and at various European cities 20–27 June. Precise measurements demonstrated for the first time that the volcanic haze, 

which had spread widely across the Northern Hemisphere, 

attenuated the solar radiation reaching the surface (Abbot, 

1913). Abbot proposed insightfully that the haze affected the 

radiation budget by reflection, absorption, and scattering; the 

haze was at that time generally assumed to consist mainly of 

silicate dust rather than sulfuric-acid aerosol, the importance 

of which was not widely appreciated until the 1960s. 

Satellite measurements of the mass of aerosol, its 

particle-size distribution, and its latitudinal, altitudinal, and 

temporal distribution were unavailable in 1912, and estimates 

of atmospheric optical density, radiation budget, and average 

surface cooling were still fairly primitive. It is instructive 

to ponder the 1912 aerosol in light of multifaceted analyses 

of the globe-encircling aerosol from the 1991 eruption of 

Pinatubo, based on satellite data and summarized by Sparks 

and others (1997). Despite important differences in latitude 

and sulfur content, masses of volcanic aerosol that entered the 

stratosphere in 1912 and 1991 were similar. 

It is now well established that the role of volcanic silicate 

dust in affecting the radiation budget is complex but small 

and short-lived, because most of it falls out within weeks to 

months (Rampino, 1988; Lacis and others, 1992). Longer 

lived stratospheric aerosols are predominantly liquid droplets 

(<0.1 to 1 μm) that nucleate homogeneously as sulfuric acid 

formed by complex oxidation of SO2

 gas, principally involving reaction with OH radicals produced by photo-dissociation 

of water vapor. Conversion of SO2 to H2SO4 proceeds slowly 

over many months, probably maximizing optical depth 3-6 

months after an eruption. Optical depth, which measures 

depletion of incoming solar radiation and is closely related to 

aerosol mass, is the most important factor in aerosol climatic 

forcing.

Volz (1975a, b) compiled a large body of written observations and solar radiation data for 1912–14, principally from 

Europe and North America, suggesting that atmospheric dust 

had completely disappeared by October 1912 but that colorful twilights persisted at least until December 1913. From 

atmospheric turbidity records, Volz inferred that the persistent 
90 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

fraction of Katmai aerosol was largely at altitudes of 15–20 

km and predominantly north of 44oN latitude, that mean 

atmospheric residence time was 9–12 months, and that stratospheric aerosol remained significant at least as late as December 1914. Settling rates for spherical droplets of sulfuric acid 

from a stratospheric injection altitude of 25–30 km (Fierstein 

and Hildreth, 1992) suggest cumulative settling times to the 

tropopause (~10 km) of about 1 month for radii of 1 μm, 1 

year for radii of 0.1 μm, and more than a decade for radii of 

0.01 μm (Sparks and others, 1997). Progressive aggregation 

of aerosol droplets increases settling velocities sufficiently to 

induce thorough removal to below the tropopause within 2 

years. In the troposphere, aerosols are flushed quickly with 

normal precipitation. Scrutiny of ice-core records in Greenland suggests that acid fallout from the Katmai eruption lasted 

~1.5 years there (Hammer, 1977).

From the mean acidity of annual layers in Greenland ice 

cores, global fallout of acid aerosol from the 1912 eruption 

was estimated at 20 million metric tons (Hammer, 1977) or 30 

million metric tons (Hammer and others, 1980), whereas calculations based on global-average peak optical-depth measurements suggest 13–20 million metric tons of stratospheric sulfate aerosol (Rampino and Self, 1984; Palais and Sigurdsson, 

1989). Palais and Sigurdsson (1989) applied the microbeambased “petrologic method” of calculating the mass of acid 

aerosol emitted by subtracting the amounts of S, Cl, and F left 

in the matrix glass of ash or pumice from those contained by 

pristine melt inclusions sealed in phenocrysts, and then multiplying by the total mass of magma erupted. Unfortunately, all 

of their 1912 samples (supplied by J. R. Riehle) were dacitic 

fallout from 17 km northeast of Novarupta and did not include 

the volumetrically important Episode I rhyolite, which was 

dispersed southeastward. Applying the sulfur-yield data of 

Palais and Sigurdsson (1989) to the ~4 km3

 of dacite magma 

erupted as plinian fallout during Episodes I, II, and III reduces 

their estimate from ~7.9 to ~3.5 million metric tons of H2SO4

released to the atmosphere. The 2.5 km3 of rhyolite magma 

erupted as fallout was neglected, but similar microbeam work 

by Westrich and others (1991) found sulfur contents of melt 

inclusions in 1912 rhyolite phenocrysts to be below their 

detection limit (<65 ppm). Accordingly, their petrologic estimate of H2

SO4 released in 1912 is ~3.5 million metric tons for 

the entire eruption, similar to the mass recalculated from the 

data of Palais and Sigurdsson for dacite fallout alone.

On the other hand, because Westrich and others (1991) 

analyzed the rhyolite, which is halogen-rich (though sulfurpoor), their estimate of HCl released to the atmosphere is 

2.5 times that of Palais and Sigurdsson. As for HF, analytical imprecision (at 400–600 ppm F) and rather small differences between F contents of melt inclusions and matrix glass 

weakens application of the “petrologic method” for estimating 

the HF yield to the atmosphere in 1912. Nonetheless, the 

1912 eruption is one of few historic events to have produced a 

strong HF signal in ice cores on the Greenland icecap (Lyons 

and others, 1990); others include Tambora (1815) and several 

Icelandic eruptions. If HF yield to the atmosphere was 25 

percent that of HCl, then the petrologic data of Palais and Sigurdsson (1989) and Westrich and others (1991), recalculated 

for the compositional proportions and total fallout volume (6.5 

km3 DRE) estimated by Fierstein and Hildreth (1992), yield 

4.3 M metric tons of HCl, 1.1 M metric tons of HF, and 1.6 

M metric tons of H2SO4, for a total of 7 million metric tons of 

acid gases.

All the estimates discussed above deal with the acid gases 

released by the 6.5 km3 of magma erupted as plinian fallout. 

If the ~7 km3 of 1912 magma emplaced as ignimbrite, which 

has a much greater ratio of rhyolite to dacite than the total fallout, released comparable fractions of its acid volatiles to the 

atmosphere, then the total acid gases emitted could be more 

than double that estimated above, thus at least 15 metric tons. 

Some unknown fraction of the gases emitted from collapsing ash flows would have ascended to the stratosphere with 

the column, and another unknown fraction would have been 

evolved during outflow of successive valley-filling packages; 

the latter may or may not have reached the stratosphere if a 

large coignimbrite plume failed to develop from the sheet (as 

argued by Fierstein and Hildreth, 1992). For the whole eruption, fallout plus ignimbrite, we recalculate ~9 million tons of 

HCl, ~4 million tons of H2SO4, and 2.3 million tons of HF, for 

a total of ~15 million tons of acid gases. The dominance of 

halogen acids is striking. Cl species are known to react with 

ozone in the stratosphere, potentially thinning the ozone layer 

(Sigurdsson, 1990; Symonds and others, 1988), but the impact 

(if any) of halogen gases in augmenting the role of sulfate 

aerosol in depleting transmissivity of solar radiation remains 

poorly known.

The microbeam data of Westrich and others (1991), 

augmented by that of Lowenstern (1993) and Wallace (2005), 

recalculated for a total erupted magma volume of 13.5 km3, 

indicate that at least 700 million tons (7x1014 g) of H2O was 

released to the atmosphere by the 1912 eruption. Lowenstern 

found <50 ppm CO2 in melt inclusions in both rhyolite and 

dacite, and Wallace measured 20–50 ppm CO2 in quartzhosted melt inclusions in the rhyolite. Owing to cracking or 

crystallization of melt inclusions in 1912 andesite, their preeruptive CO2

 content has not been established. Nonetheless, 

the small fraction of andesite among the 1912 ejecta and the 

low CO2 contents of rhyolite and dacite indicate that the CO2

released was trivial compared to the vast atmospheric CO2

reservoir and thus of no climatic consequence.

If the 20–30 million metric tons of total 1912 acid aerosol 

estimated from Greenland ice cores (Hammer and others, 

1980) and the 13–20 million tons of stratospheric aerosol 

(presumed to be largely H2SO4) estimated by optical density 

(Rampino and Self, 1984) are not greatly exaggerated, then 

estimates by the petrologic method are too low. The latter 

method assumes that all gases released were derived from the 

magma erupted and that there were negligible contributions to 

volatile emissions from (1) unerupted magma left in the reservoir, (2) gas bubbles dispersed in the magma before eruption, 

(3) the preeruptive hydrothermal system that collapsed with 

Mount Katmai, or (4) ignimbrite-derived fumaroles. Failure 
Chapter 6. Volcanological Aspects of the Primary Eruption Products 91

of any such assumptions would cause underestimation by the 

petrologic method. Because sulfur is strongly partitioned into 

any vapor phase coexisting with low-temperature silicic melt, 

and because 1912 rhyolite probably contained dispersed gas 

bubbles (Lowenstern, 1993; Wallace, 2005), there may well 

have been a significant preeruptive mass of excess sulfur not 

accounted for by the petrologic method. On the other hand, 

estimates from ice-core acidity and optical density require 

assumptions about latitudinal distribution of the globe-encircling aerosol (Hammer, 1977) that might lead to overestimation. Aerosol dispersal from the 1912 vent at 58oN appears to 

have been strongly latitude-parallel, tending at high elevations 

to migrate poleward, probably accounting for observation of 

strong turbidity peaks in 1912–13 only north of 40oN (Volz, 

1975a), and perhaps enhancing the aerosol fraction deposited 

at 65o–77oN in Greenland. For high-latitude eruptions, upper 

tropospheric winds could also favor acid deposition in Greenland (Hammer and others, 1980), leading to overestimation 

of total global aerosol from the ice-core record. Because the 

tropopause is lower than ~10 km at high latitudes, such winds 

might also have transported fumarolic gases to Greenland, 

helping further to reconcile the differences between emissions 

estimated by petrologic and ice-core methods.

The acid fumaroles from the ignimbrite sheet were 

observed to have continued issuing halogen-rich gas for a 

decade after the eruption, though much of this is likely to 

have suffered tropospheric rainout. Zies (1929) estimated 

that in 1919 the VTTS fumaroles were annually emitting 1.25 

million tons of HCl, 0.2 million tons of HF, and 0.3 million 

tons of H2

S; if such outputs approximated the average for 10 

years (1912–21), they would represent 17.5 million tons of 

acid gases from fumaroles alone. Indeed, the microbeam data 

of Westrich and others (1991) indicate that potential yields of 

halogens remaining in ignimbrite glass (after decompressive 

losses during eruption) were on the order of 7 million tons 

of HF and 20 million tons of HCl, available for release to the 

vapor phase during devitrification and leaching of the sheet. 

How much of this gas might have reached the stratosphere 

(above a 10-km tropopause) is unknown.

Crystallization of glass (devitrification) in the ignimbrite 

was recognized by Fenner as one source of the halogen gases. 

Smith (1960) discussed Fenner’s inferences, pointed out that 

halogens in the glass greatly exceeded the mass of free acid 

gases trapped interstitially in the tuff, and reasoned that gas 

liberation from crystallizing glass should long outlast the 

welding process, as field evidence has verified. 

Acid aerosol in the stratosphere certainly reduces solar 

transmissivity, thus lowering surface temperature, and evidence is good that sulfuric-acid droplets are more effective in 

doing so than halogen gases. Surface cooling was recorded 

widely in the Northern Hemisphere during summers of 1912 

and 1913, reaching a maximum measured deficiency of –0.9oC 

for September 1912 (Kimball, 1913; Humphreys, 1913; 

Griggs, 1922, p. 39). Average daily deficiency for the whole 

Northern Hemisphere for the 16-month interval following 

the eruption was reported to be –0.16oC. Modern analysis of 

monthly mean surface-temperature data for stations throughout the Northern Hemisphere (Jones and others, 1982) found 

striking anomalies (relative to a 1946–60 reference period) of 

–0.37oC to –1.18oC for nearly every month from July 1912 

through October 1913. Rampino and Self (1984), however, 

attributed to the eruption a Northern Hemisphere mean temperature decrease of only –0.2oC.

Yields of acid gases to the atmosphere have been estimated by the petrologic method for numerous other large 

eruptions (Devine and others, 1984; Palais and Sigurdsson, 

1989). A log-log plot of sulfur yield versus Northern Hemisphere temperature decrease produces a good linear relation 

embracing the data for most of the eruptions studied (Palais 

and Sigurdsson, 1989; fig. 18.1 of Sparks and others, 1997). 

For example, a sulfur yield of 30 million tons by the Laki 

eruption of 1783 was followed by a cooling of 1oC; a yield of 

17 million tons by the Tambora eruption of 1815 produced a 

cooling of 0.7oC; and a yield of 1 million tons by the Krakatau 

eruption of 1883 cooled Northern Hemisphere surface temperature by 0.3oC. On those plots, however, data for the 1912 

eruption fall far below the trend defined by most eruptions 

studied, plotting at either too small a cooling or too great a 

sulfur yield. The anomalous position for Katmai can be eliminated either by doubling the cooling to 0.4oC (as the 1912–13 

data suggest) or lowering the sulfur yield to half a million tons 

(1.6 million tons of plinian H2

SO4)—as we recalculated above, 

based on the data of Westrich and others (1991) and our own 

compositional proportions and eruptive volumes (Fierstein and 

Hildreth, 1992).

Changes in Compositional Proportions 

During the Eruptive Sequence

Few eruptions worldwide have produced a compositional 

range of ejecta as wide as that of 1912—57.9 to 77.8 percent 

SiO2, plus sparse blocks of mafic scoria down to 50.4 percent SiO2

. The tight andesite-dacite compositional array is 

continuous (fig. 59), though pumice less silicic than 62 percent 

is typically black while pumice having 63–68 percent SiO2 is 

generally pale gray (fig. 4). None of the 250 or so (nonmixed) 

1912 pumice clasts analyzed contains between 68.6 and 77 

percent SiO2, manifesting a broad compositional gap that 

separates 1912 dacite and rhyolite. Numerous field counts of 

pumice clast proportions in all ignimbrite packages and all 

fallout layers (Hildreth, 1983; Fierstein and Wilson, 2005), 

combined with shard proportions in distal ash layers counted 

by microprobe (Fierstein and Hildreth, 1992), allow us to 

estimate that at least 55 percent of the 1912 magma released 

was high-silica rhyolite, 35 percent dacite, and no more than 

10 percent andesite.

Although the first ~3 km3

 of magma erupted was strictly 

rhyolite, the coerupting proportions of andesite, dacite, 

and rhyolite fluctuated greatly from the middle of Episode 

I onward (fig. 60). Neither the rhyolite magma nor the 
92 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

52 56 60 64 68 72 76

0.2

0.4

0.6

0.8

1.0

52 56 60 64 68 72 76

Pyroclastic flows

Layer A

Layer B

Layer C

Layer D

Layer F

Layer G

Scoria fall

Phantom dome blocks

Novarupta dome

Katmai

Mount

CaO, in weight percent Al2O3, in weight percent TiO2, in weight percent

SiO2, in weight percent

Figure 59. Variation of CaO, Al2O3, and TiO2 versus SiO2 content (all 

in weight percent) for ~265 samples of 1912 Novarupta pumice and 

dome lava, subdivided as indicated in inset key. Principal features 

are continuity of andesite-dacite array, wide compositional gap 

from dacite to rhyolite, slight contamination of dome samples, and 

five (rare) mafic scoria outliers. Outlined enclosure is field for ~150 

samples from Mount Katmai, illustrating its compositional affinity 

with Novarupta. Data in appendix A. For more chemical data and 

discussion, see chapter 13.
Chapter 6. Volcanological Aspects of the Primary Eruption Products 93

A

All

rhyolite

Rhyolite

Dacite

Andesite

HI

N

Lava

Domes Episode I II III

0

12

10

8

6

4

2

7

6

5

0.5

1.0

Seismicity

Pumice fraction erupted

6 June 7 June 8 June 9 June 10 June

Ms

Mount Katmai Mud Layers ~13.5 km3 Magma

~7 km3 as ignimbrite

6.5 km3 as fallout

3 Ashfall intervals

at Kodiak

Cumulative Magma Volume

Dark Ig

Mxd Ig

Lull

Lull

CDE

FGH

B3

B1-2 A

Rhy Ig

1300 h

onset Magma volume erupted, in cubic kilometers

PD

Figure 60. Eruptive sequence of June 1912, showing estimated timing and magma volumes of eruptive units, magnitudes 

(Ms

) of earthquakes accompanying caldera collapse, stratigraphic positions of main mud layers ejected from collapsing 

caldera, intervals of ashfall at Kodiak, and fluctuating proportions of rhyolite, dacite, and andesite pumice that erupted 

concurrently. Compare with figures 2 and 34. Rhy Ig, all-rhyolite ignimbrite Package 1; Mxd Ig, compositionally 

heterogeneous main ash-flow sequence; Dark Ig, late Packages 8 and 9, both rich in andesite and dacite pumice. Fall units 

A and B represent Episode I. Segment CDE is Episode II; segment FGH is Episode III. Mount Katmai mud layers are sheets 

of lithic ejecta expelled by hydrothermal explosions. Three lava domes were emplaced at unknown times after Episode 

III: PD, Phantom dome, dacite plug explosively distributed to produce block bed that overlies Layer H; HI, Horseshoe 

Island dacite dome on caldera floor; N, Novarupta dome, ~95 percent rhyolite but streaked with andesite and dacite. Stars 

emphasize earthquakes of magnitude 6.0 or greater.
94 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

andesite-dacite magmatic continuum was exhausted during the 

series of explosive eruptions, as shown by subsequent extrusion of three lava domes. The Horseshoe Island dome on the 

Katmai caldera floor was dacite (66% SiO2; Fenner, 1930, 

1950). The Phantom dome that transiently plugged the Episode III vent was also dacitic but was explosively destroyed 

and never observed; texturally varied samples from the derivative block bed (Adams and others, 2006a), scattered as far as 

2 km from Novarupta, range from 62.2 to 66.7 percent SiO2

(n=8). The succeeding Novarupta dome, which is predominantly rhyolite (76-77% SiO2

) but streaked with ~5 percent 

andesite and dacite (55-65% SiO2), plugged the same vent and 

was first observed in 1916.

The compositionally varied nature of the deposits and the 

rapid fluctuations in proportions of coerupting pumice types 

facilitated (1) extraordinarily detailed correlations between fall 

units and contemporaneous ash flows (fig. 34); (2) subdivision 

of the main Episode I ash-flow sequence into nine successive, compositionally distinct, packages of flows (fig. 27; 

Fierstein and Wilson, 2005), illustrating stepwise assembly 

of a 120-km2

 ignimbrite sheet over an interval of ~16 hours; 

(3) linkage of compositional packages in the HEPI facies on 

near-vent ridges to particular packages in the voluminous 

valley-confined facies (Fierstein and Hildreth, 1992; Fierstein 

and Wilson, 2005); (4) quantitative discrimination of mixed 

contributions from different eruptive episodes to fine-grained 

ash layers, upwind, far downwind, and in VTTS (Layers E and 

H, as elaborated above; Fierstein and Hildreth, 1992); and (5) 

recognition of narrow lobes of proximal fallout and sectorconfined proximal PDC deposits intercalated with regional fall 

deposits of Episodes II and III (figs. 47, 48, 52), and inference 

therefrom of column-margin instabilities and processes of 

ultraproximal sedimentation from lower margins of the emerging jet and convective eruption column (Fierstein and others, 

1997; Houghton and others, 2004).

For the first ~3.5 hours of the eruption, the magma 

released was exclusively rhyolitic. For the next ~5 hours, 

andesite gradually increased its proportion from trace amounts 

until it rivaled rhyolite as the principal component, while 

dacite consistently contributed only a small fraction of the 

ejecta (<5%). After the 8th hour, the fraction of dacite began 

to increase, and after the tenth hour, dacite became the dominant component, fluctuating in its fraction of the eruptive mixture until the end of Episode 1 (figs. 34, 60). During Episodes 

II and III, from shortly after the 16th hour until the end of the 

explosive sequence on the third day, dacite was consistently 

predominant, with small bursts of andesite largely limited to 

ultraproximal falls and flows shed from the periphery of the 

main dacite column.

Banded Pumice

Syneruptive mingling of the 1912 rhyolite, dacite, and 

andesite magmas produced an abundance of banded pumice 

(fig. 61) as well as conspicuous dark-colored lenses and layers 

in the light-colored rhyolitic Novarupta lava dome. Banded 

pumice is most abundant in Layer B and in ash-flow Packages 

4 through 9 that make up the VTTS ignimbrite sheet. Field 

counts of pumice clasts at hundreds of sites, including all 

subunits, yield wide ranges of banded pumice content—0–25 

(count) percent in VFI, 0–18 percent in HEPI, and 0–24 

percent in Layer B (Hildreth, 1983; Fierstein and Hildreth, 

1992; Fierstein and Wilson, 2005). Banded pumice is absent 

in Layer A and concurrent all-rhyolite flow deposits, and it is 

rare in regionally dispersed dacitic fall Layers C–D and F–G. 

Intercalated proximally with the dacite pumice falls, however, most of the thin sector-confined fall and flow deposits 

of Episodes II and III (Houghton and others, 2004) are rich 

in banded pumice, including as much as 27 percent in the 

andesite-rich S bed (Fierstein and others, 1997). We estimate 

that, for the entire 1912 eruptive sequence, 3–5 percent of 

pumice clasts are banded.

The banded pumice was provocative during the early 

Katmai investigations because products of magma mixing had 

by then seldom been described. Fenner advanced a radical 

interpretation that dark components of the banded pumice and 

lava dome had been solid andesite of the Katmai edifice and 

of valley-floor moraines that were melted and assimilated into 

juvenile rhyolite magma by virtue of exothermic reactions that 

he imagined were linked to delayed liberation of magmatic 

gases. He attributed sieve-textured plagioclase in andesite 

bands to attack by such gases, and he interpreted xenoliths in 

the dome lava as fragments of the rocks being melted. Xenolith-bearing clasts of variably welded vent-filling tuff recycled 

as lithic ejecta during Episodes II and III were interpreted 

by Fenner as “obsidian” (fig. 62) and “scum” (fig. 63) from 

the surface of a lava lake he imagined to occupy a crater on 

Mount Katmai while part of the edifice was being dissolved. 

Fenner seems also to have thought that the dacite pumice was 

Figure 61. Banded pumice clasts from VTTS ignimbrite. Knife is 

8.5 cm long.
Chapter 6. Volcanological Aspects of the Primary Eruption Products 95

Figure 62. Block of recycled welded ejecta near Novarupta dome. One of many textural varieties 

of Episode I vent-filling tuff expelled from nested inner vent during Episodes II and III, this type was 

called “obsidian” by Fenner. Welded block contains abundant lithic fragments of Jurassic siltstone, 

a discrete pale-gray ejected block of which lies at upper right. Pen is 13.5 cm long.

Figure 63. Block of recycled welded ejecta ~1 km from Novarupta dome. Such agglutinated 

pumice breccia, rich in rhyolite, dacite, and andesite pumice clasts, is a common variety of recycled 

vent-filling tuff that was expelled as lithic ejecta during Episodes II and III. Called “scum” by 

Fenner, lapilli of such material are the principal lithic component of fallout Layers C, D, F, and G and 

are identifiable as far as 25 km downwind. Geologist is 1.63 m tall.
96 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

a thoroughly hybridized result of such assimilation. How he 

rationalized complete hybridization while dismissing simple 

syneruptive mixing of different liquids is not clear. Fenner 

nonetheless persuaded Griggs (1922) of his hypothesis and 

defended assimilation of solid mafic lavas by rhyolitic magma 

for the rest of his life (Fenner, 1923, 1926, 1934, 1937, 1938a, 

1938b, 1944, 1950). 

By 1953, petrologic and thermal relations of rhyolite and 

andesite were better appreciated, Fenner’s mechanism had been 

discounted, and Williams and others (1953) reinterpreted the 

banded pumice in terms of mingling of confluent magmas. Curtis (1968) went on to point out that most contacts between bands 

were sharp (with gradations only microns thick), that glassy 

andesite was chilled against rhyolite, and that sieved and nonsieved variably zoned plagioclase had coexisted in the andesite 

before encountering the rhyolite, which has its own nonsieved 

unzoned, easily distinguishable, more sodic plagioclase.

The “bands” in the banded pumice are extremely varied, 

ranging from hairline streaks to layers many centimeters thick 

and including isolated blebs and blobs, multistrand stringers, 

and sparser convolutions. Individual banded pumice blocks 

and lapilli consist predominantly of either rhyolite, dacite, or 

andesite, or they can have subequal proportions of any two of 

them. Pumice clasts consisting of all three are rare. Rhyoliteandesite and dacite-andesite combinations are abundant, but 

dacite-rhyolite banded pumice is uncommon except in ignimbrite Package 7 (Fierstein and Wilson, 2005). Proportions of 

the three compositional combinations generally reflect those of 

the nonbanded pumice clasts in each emplacement unit. 

The sharpness of compositional contacts within clasts is 

consistent with syneruptive confluence in the magma feeding 

system and with contiguity for only minutes or hours prior to 

fragmentation. Wide fluctuations in proportions of andesite, 

dacite, rhyolite, and varieties of banded pumice in successive 

eruptive packages indicates that feed rates of the three magmas from reservoir(s) to their ultimate mutual conduit were 

unequal and not steady. Although joint conduit transport was 

able to produce extensive mingling of the viscous magmas in 

a short time interval, the interval was long enough for andesite 

to be partitioned preferentially into a peripheral collar around 

the emerging jet and thence into fountains and flows collapsing around the margins of plinian columns, the interior cores 

of which carried far smaller proportions of andesite into the 

regional fallout (fig. 53).

Syneruptive mingling of the compositionally different 

magmas is not known to have produced any homogeneously 

hybridized pumice, but limited mutual contamination by 

phenocryst transfer is not uncommon. Sparse quartz grains 

have been identified in a few andesite and dacite pumice 

clasts, where they evidently lacked time to be resorbed or 

rimmed before eruptive quenching. Sparse hornblende prisms 

in a small fraction of the dacite pumices and in the Novarupta 

rhyolite dome are compositionally identical, and in neither 

host have they developed reaction rims, even though they 

were in equilibrium with neither (see section below titled 

“Experimental Petrology”). Rare clinopyroxene crystals, 

mostly fragments, have been found in a few rhyolite pumices and in the rhyolite dome but are absent in most rhyolite 

samples. Subordinate populations of Fe-Ti-oxide minerals 

that give much higher equilibration temperatures than most of 

the accompanying titanomagnetite-ilmenite pairs are present 

sparsely in some dacite pumices and in the dome rhyolite. 

Some pairs in an andesite host were found to have developed 

Ti gradients at their contacts (Hammer and others, 2002), but 

most such transferred oxide crystals remained homogeneous 

and unmodified. Such contaminants, widely scattered and easily overlooked, require cautious sample selection and scrutiny 

of mineral microbeam data. The general absence of reaction 

between such transferred crystals and their new host melts 

supports the interpretation that the mingling that produced 

both the subtle contamination and the conspicuous banding 

was syneruptive and thus occurred over only hours or days.

Contemporaneity of Falls and Flows

Plinian fallout, high-energy proximal ignimbrite (HEPI), 

and voluminous valley-filling ignimbrite (VFI) were deposited contemporaneously throughout most of Episode I. This 

is demonstrated by (1) comparably progressive changes in 

rhyolite/dacite/andesite pumice proportions in the sequences 

of fall layers and flow packages (fig. 34); (2) intercalation of 

layers and lenses of Layer A with all-rhyolite HEPI and VFI 

deposits; (3) intercalation of compositionally heterogeneous 

HEPI and VFI packages with compositionally similar parts of 

Layer B (fig. 37); and (4) absence of the Episode I fall deposits in the VTTS wherever equivalent ignimbrite is present. 

Irrespective of whether the A–B fallout near Novarupta and on 

the VTTS floor was incorporated by concurrently emplaced 

flows or scoured by them, the flow/fall intercalations that crop 

out nearby, atop peripheral ridges, in the Trident saddles, and 

along the Mageik Creek valley from Katmai Pass to the toe of 

Observation Mountain, prove their contemporaneity. 

During Episodes II and III, on a lesser scale, intercalation of several small proximal PDC deposits within the stack 

of regionally dispersed plinian pumice falls (Layers C–D and 

F–G) likewise demonstrates generation of laterally emplaced 

flows from various heights in a sustained column (figs. 47, 

52). These were mostly sector confined, just a few meters 

thick, and extended only a few kilometers, but they nicely 

illustrate radial generation of pyroclastic currents by transient 

instabilities in an annular collar around the emerging jet and 

sustained column. 

During Episode I, such lateral currents were proximally 

turbulent, far more voluminous, and represented greater mass 

fractions of the ongoing eruption column than during Episodes 

II and III; some were blast like and others soon densified in the 

valleys, where some extended >20 km from vent. Despite the 

complexly changing compositional proportions in the 16-hour 

sequence of discrete packages of flows that built up the VTTS 

ignimbrite (fig. 34), and despite the 4:1 volume dominance of 
Chapter 6. Volcanological Aspects of the Primary Eruption Products 97

Phase B ignimbrite over Layer B fallout, no hiatus is recognized within Layer B (fig. 15) that might suggest discontinuous accumulation of plinian fallout during assembly of the 

main VTTS ignimbrite.

Characteristics of the Eruption Columns

Initial rise of the plinian column was seen in clear 

weather from the S.S. Dora in Shelikof Strait at 1300 Alaskan 

time on 6 June. No observers were able to see any column 

after a few hours, but the three intervals of ashfall recorded 

at Kodiak (170 km downwind) correlate well with the three 

layers discernible there on the ground (Martin, 1913; Griggs, 

1922; Hildreth, 1983; Fierstein and Hildreth, 1992). The three 

fallout intervals lasted ~20 h, ~26 h, and ~10 h at Kodiak, but 

there need be no simple correlation between fallout intervals 

downwind and duration of eruptive episodes at vent, owing to 

altitudinally variable transport velocity, wind shear, progressively slower settling of ash that systematically fines with 

distance, and turbulent retention of fine ash aloft. Ashfall at 

Kodiak first ceased between 0910 and noon on 7 June, but it 

was reported to have diminished gradually after 0300. If so, 

and if a 4-hour transport time (based on first sighting of the 

column at 1300 and onset of fallout at Kodiak at 1700) can 

be generalized, then the A and B plinian phases of eruptive 

Episode I may have together lasted only 10–14 hours. This 

possibility is supported by an additional time constraint—the 

first of several layers of nonjuvenile lithic debris ejected during caldera collapse at Mount Katmai is intercalated between 

Novarupta Layers B2

 and B3 and is thought to coincide with 

the first major teleseism (Ms 6.5) at 2356 on 6 June, apparently the onset of major collapse (Hildreth, 1991; Abe, 1992; 

Hildreth and Fierstein, 2000). By that hour, all of Phase 

A, two-thirds of Layer B, and as much as 85 percent of the 

main Phase B ignimbrite had erupted, equivalent to a magma 

volume of ~8.5 km3 (figs. 34, 60). For an average magma 

density of 2,400 kg/m3 and a duration of 11 hours, these data 

suggest an average mass eruption rate of 5x108

 kg/s, our best 

constrained estimate for most of Episode I. For the plinian 

fraction alone (~2.6 km3 of magma dispersed as fallout), the 

mass eruption rate would be ~1.6x108 kg/s.

No similar narrative or geophysical constraints can be 

applied with any confidence in estimating durations of eruptive Episodes II and III. Local flooding and reworking of 

pumice atop the ignimbrite along upper Knife Creek (fig. 44) 

indicates a time break of unknown duration before opening of 

Episode II. One interpretive possibility is that the interval of 

extraordinary seismicity from the evening of 7 June through 

0300 on 8 June (including six earthquakes of magnitude 6.0 to 

7.0) represented fitful caldera collapse, during which Episode 

II dacite was withdrawn from under Mount Katmai. Such 

a scenario could mean that the main eruptive interval that 

produced Layers C and D lasted only 7–9 hours and that the 

26-hour-long ashfall interval at Kodiak included slow settling 

of fines both before and after eruptive Episode II. If the ~2 

km3 of Episode II dacite magma were released in 8 hours, then 

its average mass eruption rate was 1.7x108 kg/s.

The time break between eruptive Episodes II and III 

permitted accumulation of Layer E, dominantly fine dacitic 

vitric ash, which is 3–9 cm thick proximally and medially out 

to at least 23 km from vent. Layer D grades up normally from 

lapilli fall to a fine-ash top, showing that fallout of pumice 

lapilli ceased entirely, the only clear lull in the Episode II–III 

sequence. The eruptive hiatus is inferred to have ended with 

radial blast like emplacement of lithic-rich PDC 4 (Houghton 

and others, 2004), which reopened the vent for resumption of 

dacite magma release as plinian Layers F and G. Vent blockage by wall collapse was probably responsible for the hiatus, 

rather than the slowing of magma ascent and the shift to opensystem degassing (inferred from vesicle textures) thought to 

have terminated Episode III (Adams and others, 2006b).

At Kodiak, the second ashfall hiatus lasted less than 6 

hours and was followed by the final period of fallout ~10 

hours long, roughly equivalent to Episode III. During this 

interval, seismicity resumed after a 20-hour lull, and two final 

phreatic mud layers were ejected from the enlarging caldera of 

Mount Katmai and intercalated within the pumice falls of Layers F and G (fig. 60). There are no tighter constraints on the 

duration of eruptive Episode III. If it truly lasted 10 hours, the 

average mass eruption rate for its 1.63 km3

 of dacite magma 

was 1.1x108 kg/s (or twice that for a duration of 5 hours).

The mass eruption rates estimated above (1.6, 1.7, and 

1.1x108 kg/s for Episodes I, II, and III, respectively) are based 

on volumes of the plinian fall deposits and their approximate 

eruption durations. The model of Wilson and Walker (1987) 

provides a relation between mass eruption rate and column 

height: H = 0.236 (M0)1/4 where H is column height in kilometers and M0

 is mass eruption rate in kilograms per second. 

This yields column heights of 27, 27, and 24 km, respectively, 

for plinian Episodes I, II, and III.

An alternative method developed by Carey and Sparks 

(1986) reconstructs characteristics of the source plume from 

measurements of clast dispersal in the fall deposits. Dispersal pattern is controlled mainly by column height, local 

winds at various altitudes, and grain-size distribution of the 

ejecta. Apart from ultraproximal deposits augmented by lower 

column-margin fallout (Houghton and others, 2004), regional 

fall deposits typically display exponential decay of thickness 

and grain size away from vent, reflecting sedimentation from 

the umbrella region of the spreading plume. As reviewed by 

Sparks and others (1997), dispersal of clasts of a given size is 

quite sensitive to column height, especially lithic clasts that 

are less varied in density than pumice and less susceptible to 

breakage on impact. Plotting the lithic-isopleth data (fig. 58) 

of Fierstein and Hildreth (1992) on the nomograms of Carey 

and Sparks (1986) yields column heights of 28, 28, and 24 

km, respectively, for plinian Episodes I, II, and III. The data 

also yield rough estimates of maximum wind velocities (at the 

tropopause), respectively >30 m/s, 30 m/s, and <10 m/s for the 

three successive episodes. The more symmetrical distribution, 
98 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

less vigorous plume, and weaker southeastward dispersal of 

Episode III ejecta, relative to those of I and II, were noted by 

Curtis (1968) and Fierstein and Hildreth (1992).

Column Collapse and Emplacement of 

Pyroclastic Density Currents

Buoyant plinian columns commonly collapse, partially 

or extensively, into fountains that generate pyroclastic flows. 

Wilson and others (1980) analyzed eruptive conditions that 

favor collapse—decreasing exsolved magmatic gas content 

and increasing vent radius, or, closely linked respectively, 

decreasing vent-exit velocity and increasing mass eruption 

rate. Many subsequent theoretical and field studies of explosive eruptions and their deposits were reviewed by Sparks 

and others (1997). During Episode I in 1912, a sequence of 

pyroclastic flows filled the VTTS and was more voluminous 

than the plinian fallout that preceded and accompanied it. 

On the other hand, during Episodes II and III, several small 

pyroclastic density currents (flows, surges, and blasts) were 

largely sector confined, extended only 1–3 km from vent, and 

amounted in total volume to less than 1 percent of concurrently deposited plinian dacite Layers C to H.

Episode I Eruptive Sequence

In the VTTS, valley-filling ignimbrite (VFI) extends 

~23 km northwest from Novarupta and has been shown to 

consist of nine successive, compositionally distinguishable, 

packages of ash flows (figs. 16, 27). Of the nine, several 

also entered Katmai Pass, and two of them (1 and 7) thence 

extended southward as far as 10 km down Mageik Creek. In 

Package 1, the pumice is entirely rhyolitic but generally small 

(few clasts larger than 2 cm), and lithics are abundant owing 

to initial vent-reaming and vent-wall collapse. Package 1 is 

distributed radially, extending 9 km from Novarupta, in part as 

a blast like vent-opening HEPI. In Packages 2 through 5, the 

fraction of andesite pumice progressively increased from ~3 to 

~50 percent, while dacite pumice maintained a fairly constant fraction (<5 percent); each of these four packages filled 

the upper VTTS and reached at least as far as Three Forks. 

Taken together, Packages 3 and 4 volumetrically dominate the 

VTTS sheet; they were partly diverted around the Three Forks 

moraine (figs. 30, 64), becoming the only packages that extend 

all the way to the Ukak terminus (fig. 29). Where it banked 

against the moraine, a thick section of Package 4 developed 

diffuse laminae (fig. 65), most layers being 1–10 cm thick (fig. 

66). The distal tongues of dark-colored andesite-rich Packages 5 and 6 were confined to swales that were produced on 

a time scale of hours by axial compaction of earlier packages 

and commonly enhanced by active basal scour (figs. 31, 67). 

Package 6 was the first to contain abundant dacite pumice 

(12–28 percent), along with subequal proportions of rhyolite 

and andesite. Although not as widespread as earlier packages 

around the upper VTTS (presumably because less energetically emplaced), it nonetheless issued swale-confined darkcolored andesite-rich tongues, which, like those of Package 5, 

reached Three Forks (figs. 27, 30). 

Package 7 is compositionally unique in consisting of 

equal proportions of dacite and rhyolite pumice with only a 

trace of andesite. It marks the arrival of dacite as a major contributor to the eruptive mixture, an importance that expanded 

in Packages 8 and 9 and became predominant in Episodes II 

and III. In the VTTS, Package 7 is distributed only within 

6 km of Novarupta, but it flowed at least 10 km down the 

valley of Mageik Creek. Intercalated within it proximally is 

a thin blast like deposit, confined to the southwest sector and 

containing abundant andesite scoria and blocks of welded 

vitrophyric lithics (Fierstein and Wilson, 2005). Package 

8, though rather variable in composition, contains grossly 

equal proportions of dacite and andesite pumice and is the 

first ignimbrite unit in which rhyolite is clearly subordinate 

(5–30 percent). It is limited to and caps much of the upper 

and middle VTTS, where it is dark gray (or locally brightly 

oxidized), 5–10 m thick, widely sintered or vapor-phase 

indurated, and locally welded and eutaxitic (fig. 35). Package 9, which terminated Episode I, is a set of small-volume 

ignimbrite lobes and tongues rich in dacite pumice blocks but 

typically only 0.5–3 m thick (fig. 46). Dacite is dominant, 

but andesite scoria is abundant and the rhyolite fraction is less 

than 10 percent. Variously nonindurated or sintered, scoured 

exposures of Package 9 locally form blocky pavements (fig. 

36) on the floors of the upper Lethe and Knife Creek arms. 

Although no HEPI equivalent is recognized, currents of Package 9 also crossed the low saddle between Baked and Broken 

Mountains, leaving deposits on the floor of the narrow valley 

that trends northwest from that saddle (fig. 26).

With the exception of block-rich Package 9 and local 

pumice-concentration zones in other packages, most of the 

VTTS contains familiar massive fines-rich ignimbrite, with 

poor sorting (sø

~2.5–4.5), median grain size generally 0.1–0.5 

mm, modest lithic fractions (1–6 weight percent), and varied 

fractions of scattered pumice lapilli and blocks. Much of the 

sheet is nonwelded (fig. 68), but many exposures in the middle 

and upper valley are sintered, vapor-phase indurated (fig. 69), 

or rarely eutaxitic (fig. 33). Ignimbrite blocks ejected from 

postemplacement phreatic explosion craters are commonly 

dense and some have flattened pumice, indicating widespread 

welding at levels deeper than that of present-day stream incision. Exposed total thickness ranges from 10 to 20 m distally 

to as much as ~33 m in some lower valley gorges (fig. 32) and 

on marginal benches. In most of the central and upper VTTS, 

however, where the sheet is indurated and certainly thickest, 

streams have cut only a few meters deep (fig. 35). Along the 

Lethe arm, differential welding (Hildreth, 1983) and comparative stream profiles (Curtis, 1968) suggest an axial total thickness of at least 150 m, perhaps locally >200 m. 

The near-vent ignimbrite facies called high-energy 

proximal ignimbrite (HEPI) by Fierstein and Hildreth (1992) 
Chapter 6. Volcanological Aspects of the Primary Eruption Products 99

Figure 64. Main VTTS ignimbrite banked against cross-valley moraine ~2 km northeast of Three Forks, 16 

km from vent at Novarupta. Ignimbrite, ~20 m thick just to right of moraine, failed to override it, but thin 

ash-flow tongues penetrated a few low saddles like that in foreground. Backside of moraine at left has 

15–25 m relief and is veneered by thin ash-cloud, plinian, and aeolian ash deposits.

Figure 65. Extreme development of diffuse lamination in distal VTTS ignimbrite ~1 km upvalley from crossvalley moraine and 15 km from Novarupta. Layers are 1–10 cm thick, and exposure is ~8 m high. Mount 

Katolinat on skyline.
100 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Figure 66. Diffuse layering in distal VTTS ignimbrite where it banks against moraine 16 km from Novarupta. 

Layers are 5–10 cm thick. Ice axe is 81 cm long. Layering continues to top of deposit, which does not extend 

beyond moraine.

Figure 67. Boundary between ignimbrite Packages 6 and 3 just east of Three Forks. Package 6 (above) has 

diffuse internal layering and its own thin fine-grained basal layer, which crosscuts subhorizontal layering in 

rhyolite-richer Package 3 (below). Broad swale is not compactional; earlier partial drainaway of upper Package 

3 is not excluded, but swale was at least partly scoured by currents emplacing Package 6. A modest time break 

is implicit. Ignimbrite is overlain by ~0.5 m of stratified white dacite fallout of Episodes II and III, then by several 

meters of brown ashy mudflow deposits. Shovel just left of center is 58 cm long.
Chapter 6. Volcanological Aspects of the Primary Eruption Products 101

Figure 68. Classic flow-unit contact in nonwelded ignimbrite on left bank of Knife Creek just above Three 

Forks. Fine-grained basal layer of ignimbrite Package 4 (upper third of cliff) conformably overlies Package 

3. Exposure ~12 m high; base rests on glacial and fluvial deposits. At top, thin strata of white dacite fallout of 

Episodes II and III are capped by tan ashy mudflow deposits.
102 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Figure 69. Jointed ignimbrite, sintered and vapor-phase indurated along Juhle fork, at northeast edge of VTTS 

~600 m downstream from mouth of side valley where stream enters valley-filling tuff. Waterfall is ~25 m high. 

Fumarolic alteration of ignimbrite in foreground. Jointed zone grades down into massive ignimbrite that ranges 

locally from nonindurated to sintered.

was deposited on all ridgecrests within 6 km of Novarupta. 

Typically 1–5 m thick but as thick as 12–15 m on Baked and 

Falling Mountains, these stratified veneers were deposited by 

high-velocity turbulent currents in all directions from Novarupta basin. The wide ranges in median and maximum grain 

size, fines fraction (5–50 wt percent), lithic fraction (1–16 

wt percent), sorting (sø~1–4), and thickness (1–35 cm) of 

individual layers, which number from 5 to >110 in various 

sections, were described in chapter 5. The compositional 

sequence of pumice proportions in HEPI sections roughly 

matches that of the sequence of packages that make up the 

main VFI, although the final VFI package (Package 9) apparently lacks a HEPI equivalent. If HEPI deposits mantle a 

liberally estimated area of ~50 km2 in the upper VTTS and if 

their average thickness is 5 m, then their total volume would 

be ~0.25 km3 or only 2–3 percent that of the VFI emplaced 

during Episode I (~11 km3).

Concurrent Deposition of HEPI and VFI

Concurrent production of HEPI and VFI at Novarupta 

exemplifies some of the issues that underlie various models 

of ignimbrite deposition, particularly those concerning solids 

concentration in the depositing currents, the degree to which 

such currents are turbulent, the mechanisms of particle support 

in such currents, whether currents are stratified (graded in particle concentration) or have sharp upper surfaces, and whether 

currents deposit incrementally at the base or slide to a halt 

(more or less) en masse (Fisher, 1966; Sparks, 1976; Wilson 

and Walker, 1982; Druitt, 1998; Freundt and Bursik, 1998; 

Branney and Kokelaar, 2002). 

Properties of gas-charged particulate masses as they 

collapse from an eruption column and initiate the currents 

that deposit ignimbrite remain inadequately known. At 

Novarupta it can be inferred that collapse was not complete, 

because intercalation of plinian Layer B with packages of the 

main ignimbrite and their mutually equivalent compositional 

sequences indicate sustained coexistence of a (reduced but 

substantial) buoyant plume with the more voluminous collapsing fountains. It can also be inferred that the Phase B fountains were not very high because most currents had insufficient 

momentum to flow more than ~2 km laterally (and 300 m in 

elevation) up the adjacent slopes of Trident. Phase A currents, 

however, though far less voluminous, passed through the Trident saddles (~800 m higher than Novarupta) and swept across 

the slopes of Mount Griggs (as much as 450 m higher than 

Phase B VFI in the Knife Creek arm). The radial distribution 
Chapter 6. Volcanological Aspects of the Primary Eruption Products 103

of the Phase A all-rhyolite ignimbrite, its greater momentum, 

greater proportion of stratified HEPI, and sparsity of coarse 

pumice probably reflects a radial blast like component to its 

initial momentum rather than simply a greater collapse height 

relative to the currents of Phase B. This may in turn reflect the 

greater gas content of the rhyolite and perhaps, too, a component of lateral momentum owed to decompression of the 

abruptly unconfined mass emerging from an immature vent at 

the eruptive onset. 

Absence of Phase B HEPI on the upper vent-facing 

slopes of Trident and on the summit of Baked Mountain (only 

~1.5 km laterally and ~250 m higher than the vent-funnel 

rim) suggests that vertical momentum of the gas thrust phase 

was unable to carry the fountaining mass more than a few 

hundred meters above the vent. Instead of initially discrete 

currents collapsing from column margins at heights of a few 

kilometers, there may have been a broad low fountain flooding 

Novarupta basin and disgorging radially from it. Rapid excavation of a flaring vent funnel 1–2 km wide, further confined 

between Broken Mountain and Trident, may have so limited 

radial air entrainment relative to mass discharge that fountain 

collapse was atypically low. There is no evidence for asymmetrical collapse during Episode I, as all nine ignimbrite 

packages are distributed radially into the Knife Creek and 

Lethe arms (as well as the narrow valley separating Baked and 

Broken Mountains, fig. 26), including even Package 9, which 

was laid down by short-lived lobate currents of low mass flux. 

The north and south sides of Novarupta basin are 

hemmed in by highlands (fig. 70), but the slopes west and east 

of the vent were gently sloping valleys broadened by Pleistocene glaciation. The western outlet now slopes only ~1.7o 

W toward the Lethe arm (fig. 18) and is unlikely to have been 

much steeper before the eruption. The eastern outlet now 

slopes 5o–6o NE toward the Knife Creek arm, but its (probably 

Figure 70. Aerial view southeastward over Novarupta toward Trident and Mount Katmai. In foreground, vent depression (commonly 

called Novarupta basin) extends 2.5 km from pumice-covered fissured scarp of Broken Mountain at left to 400-m-high bedrock scarp 

of Falling Mountain dacite dome at right. Vent funnel was backfilled by ignimbrite and fallback ejecta, deformed by compaction and 

welding, and plugged by 380-m-wide Novarupta rhyolite dome, which is surrounded by an asymmetrical ejecta ring that consists mostly 

of fallout from Episodes II and III. At extreme upper left, Katmai caldera is centered 10 km east of Novarupta. Tephra-covered Knife 

Creek Glaciers (1 to 3) descend at left from four ice-sculpted peaks of Trident group. Partly hidden at right is black cone of Southwest 

Trident (1953–74) and its lava-flow apron in Katmai Pass and Mageik Creek. In far right distance is Katmai River floodplain and Katmai 

Bay. On remote horizon lies Kodiak Island, beyond Shelikof Strait.
104 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

gentler) preeruptive gradient is hard to estimate because of 

the thick Episode II and III deposits in that sector. Densifying underflows encountered no barriers emerging east or west 

from fountains collapsing in Novarupta basin, and the gentle 

slopes away from the vent would have reduced their initial 

momentum. Coarse lithic lag breccias, representing vent-funnel excavation and collapse of the Falling Mountain scarp 

(fig. 71), are presumed to have been dumped in Novarupta 

basin during Episode I, but none are exposed owing to the 

thick proximal deposits of Episodes II and III. Dense clasts 

lifted by the gas thrust but unsupported by the fountain would 

have been dropped promptly by initially dilute currents emerging on such gentle slopes. Clasts in traction-stratified HEPI 

(and sparse ballistics) on circum-vent ridgecrests include 

dense lithics as big as 25–35 cm and abundant pumice blocks 

as big as 40–60 cm.

During most of Phase B, a pulsating fountain filled 

Novarupta basin and discharged concentrated pyroclastic 

Figure 71. View southwestward across Novarupta rhyolite dome from crest of Turtle to truncated face of Falling Mountain dacite 

dome, a distance of ~2.2 km. Novarupta is 65 m high and Falling Mountain ~400 m. Ignimbrite as thick as 13–15 m is plastered 

on east (left) shoulder and part of steep face of Falling Mountain, indicating syneruptive loss of vent-facing side of dome early in 

1912 eruptive sequence. Dacite of Falling Mountain makes up a modest fraction of lithic fragments among Episode I ejecta, as 

does andesite of Trident volcano, lava flows of which were truncated by the vent-margin scarp to left of Falling Mountain. Icecapped Mount Mageik rises 1,000 m higher and 8 km beyond Falling Mountain. Mount Cerberus, a dacite dome much like Falling 

Mountain, stands 1 km to its west (right). Both are of late Pleistocene age, and both are lapped by 1912 valley-filling ignimbrite in 

upper Lethe arm at right.

underflows into both arms of the VTTS. The laterally expanding fountain may have been little thicker than the highest 

HEPI deposits, a few hundred meters above Novarupta. Concurrently, a plinian convective column partially survived and 

deposited equivalently zoned Layer B fallout downwind as far 

as Kodiak Island. More speculatively, the column might have 

been augmented by thermal plumes rising from the periphery 

of the fountain, their resurgent buoyancy owing to peripheral 

ingestion of air during collapse. Another possibility is alternation of collapsing fountains and convecting plumes, perhaps 

punctuating the ignimbrite packages, owing to variations in 

discharge rate, in gas content released from changing proportions of the different magmas, or in fluctuating exit pressures 

caused by vent-wall instabilities. In any event, persistently 

low fountaining during Phase B is consistent with the low 

momentum of VFI packages, which failed to ride far up sidewalls in the upper VTTS or to overrun the low valley-blocking 

moraine at Three Forks (fig. 64). Progressive excavation of a 
Chapter 6. Volcanological Aspects of the Primary Eruption Products 105

wider vent and increasing proportions of dacite and andesite, 

at the expense of gas-richer rhyolite, would favor extensive 

fountain collapse during Phase B, when ignimbrite greatly 

exceeded fallout, following rhyolitic Phase A, when only a 

modest fraction of the ejecta contributed to lateral currents.

Particle Concentration Gradient

Proximity of (1) thinly stratified bedsets of variably 

sorted HEPI draping ridgecrests and (2) massive poorly sorted 

VFI on valley floors a few hundred meters downslope provides good evidence for vertical gradients in the concentration of solid particles in the currents that discharged laterally 

from the collapsing fountain(s) in Novarupta basin (fig. 43). 

General equivalence of the succession of compositional proportions making up the sequence of HEPI and VFI packages 

(and intercalated fall layers that locally avoided ingestion and 

scour) attest to contemporaneity of deposition. Graded pyroclastic density currents have been called “stratified” by some, 

following Valentine (1987). 

In a turbulent suspension current, a concentration gradient inevitably develops, as differential settling of particles 

experiencing a wide range of turbulent support should rapidly 

produce vertical gradients in the masses transitioning from 

fountain collapse to outflow currents (Sparks and others, 1978; 

Druitt, 1998; Choux and others, 2004). Not clear, however, is 

whether stratification is in part intrinsic to the collapsing fountain nor how rapidly the emerging currents develop an interface between a dilute turbulent cloud and a denser underflow. 

Nonetheless, even at high radial velocity around Novarupta, 

sedimentation from an expanded turbulent current should soon 

have produced a poorly sorted dense underflow, which could 

be diverted or channelled by topography, while the radially 

expanding dilute cloud concurrently laid down a thin-bedded 

set of variably sorted, lenticular, stratified deposits upon ridges 

only a few hundred meters higher (fig. 43). Certainly, such 

a dichotomy had developed here within a few kilometers of 

outflow, as massive VFI deposits bank around the bases of 

Mount Cerberus (fig. 72) and Whiskey Ridge (fig. 73), which 

are capped by stratified HEPI that lie 250 m and 400 m higher, 

respectively, than VFI on the adjacent valley floors (but only 

250 m higher than Novarupta). After proximal HEPI deposition, turbulent ash clouds may have become so dilute that 

much of their remaining fine ash lofted and dispersed or was 

convectively drawn back inward and upward to join what 

survived of the buoyant plinian column.

Currents that deposited the most voluminous of the nine 

ignimbrite packages may have been sustained for an hour or 

more. However, viewed as a whole, the Phase B sequence 

was episodic rather than continuous, as suggested by (1) scour 

and truncation of successive HEPI bedsets, (2) varied range 

and distribution of successive VFI packages, (3) intercalation 

of fall layers between some VFI packages, and (4) compaction 

swales that had time to develop between successive packages. 

Such episodicity is likely to have reflected spasmodic fountain 

collapse and vent-wall spallation that caused repeated discharge fluctuations, including radial blasts during deposition 

of Packages 1 and 7 (Fierstein and Wilson, 2005). 

Alternating HEPI beds range from fines-rich and poorly 

sorted (much like thicker massive VFI) to fines-poor and better 

sorted layers rich in lithics and coarse pumice (figs. 22, 41, 

42). They reflect fluctuations in velocity, capacity, competence, shear rate, tractional effects on bedload, and degree of 

turbulence in the pulsating currents. Sedimentation was from 

turbulent suspension currents with or without traction at the 

depositional surface. Some matrix-richer layers may have been 

virtually plastered by current pulses breaking like waves over 

the ridgecrests, the roughness of which influenced fluctuating 

degrees of local turbulence. Alternation of massive beds and 

lensoid traction-dominated layers on a decimeter scale suggests 

abrupt rapid fluctuations in solids concentration—vertically, 

laterally, and temporally—in the turbulent currents passing.

Densification of Flow Units 

The dense granular underflows (with solids concentrations probably up to several tens of volume percent), retained 

most of the particulate mass, flowed gravitationally into the 

different arms of the valley, were channelled and diverted by 

surrounding terrain, filled and masked the prior topography, 

and continued much farther than the dilute lofting clouds from 

which each had separated. The latter deposited thin HEPI 

veneers only out to ~6 km from vent, whereas some of the 

VFI-depositing currents extended at least 23 km. Turbulent 

support was soon replaced by particle interactions and partial 

fluidization in each underflow. Currents were not “ponded” 

but, instead, were topographically guided down gently sloping, 

open-ended valleys with steep sidewalls. 

Although gradually deflating and losing momentum along 

valley floors, each current retained modest mobility owing 

to reduction of interparticle friction by partial fluidization 

promoted by excess pore pressure and hindered settling associated with upward-escaping interstitial gases (Fenner, 1923, 

p. 63; Sparks, 1976; Wilson, 1980, 1984; Druitt and others, 

2004, 2007; Girolami and others, 2008). High temperature 

and internal shear during transport would have helped maintain expansion of the gas-rich particulate currents. In addition 

to ingestion of air by the collapsing fountain and continuing 

diffusive exsolution of magmatic gas from glassy particles, 

gas content of the currents would be partially replenished 

by pumice attrition, burning vegetation, boiling of overrun 

surface waters, and perhaps by additional frontal entrainment 

of air where currents encountered rough terrain, all helping to 

sustain mobility.

The high fines contents of the VFI-depositing currents 

would have enhanced partial fluidization and hindered settling 

(self-fluidization not requiring gas replenishment) by reducing 

permeability, thus extending gas-retention times. Predominance in the ignimbrite of rhyolite pumice and ash, which had 

high magmatic gas content and thin fragile bubble walls, no 
106 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Figure 72. Mount Cerberus, late Pleistocene dacite dome, 1,500 m across and 360 m high, at foot of 2,165-m Mount 

Mageik compound dacite stratovolcano. High-energy proximal ignimbrite (HEPI) deposits cap both ridges of Mount 

Cerberus as well as south ridge of Baked Mountain in foreground. Where valley-filling ignimbrite laps against 

base of Cerberus, its tan (oxidized) margin is sharply defined against pale-gray pumice-fall scree. Some ignimbrite 

packages flowed around both sides of Mount Cerberus en route to Katmai Pass, which lies 2 km to left of image and 

is drained by prominent arroyo at left. East Mageik Lake, barely visible at right center, was occupied in 1912 by the 

glacier now hanging ~1 km above it.

Figure 73. Scarp of Whiskey Ridge, 400 m high, and panorama along Knife Creek arm of VTTS toward ignimbrite 

terminus 23 km away. Atop great wall of Jurassic siltstone at upper right is 5-m-thick intact section of HEPI deposits 

capped by Layer C (see figs. 23, 42).
Chapter 6. Volcanological Aspects of the Primary Eruption Products 107

doubt helped produce a large initial fraction of fines. Fines 

replenishment by attrition of fragile pumice during outflow 

would have compensated in varying degree for the elutriation 

of fines by escaping interstitial gas. 

Currents in the VTTS propagated 9–23 km downvalley 

along low gradients, infilling the prior topography to produce 

generally planar sheets that slope only 0.9° in the Lethe arm 

and 1.2° in the Knife Creek arm. Beyond the constriction 

where the VTTS is narrowest, ~10 km from Novarupta (fig. 

74), the ignimbrite surface steepens to ~1.5° as far as the 

Three Forks moraine, probably because some of the later 

packages terminate near the head of that narrow reach (Fierstein and Wilson, 2005). Such modest slopes are gentler than 

normal angles of repose for granular materials, underlining 

that excess mobility was imparted by retention of interstitial 

pore pressure, despite the low momentum indicated by failure 

of most packages to run up sidewalls (fig. 75) or to surmount 

the cross-valley moraine (fig. 76).

Deposition of the valley-filling VTTS ignimbrite was an 

incremental process that lasted 14–16 hours (figs. 2, 34, 60; 

Hildreth, 1983; Hildreth and Fierstein, 2000; Fierstein and 

Wilson, 2005). Each of the nine compositionally distinguishable packages consists of the deposits of several discrete 

currents (flow units), and each or most of the currents may 

have deposited material incrementally at its base by progressive aggradation (Fisher, 1966; Branney and Kokelaar, 2002), 

at least in the upper VTTS. As stressed by Wilson and Walker 

(1982) for pyroclastic currents in a partially fluidized state, the 

thickness of a deposit bears no simple relation to the thickness 

of the current that passed, and the processes of sedimentation 

and particle segregation that take place during outflow cause 

the grain size and componentry of a deposit at any point to 

bear no simple relation to either those of the original eruptive 

mixture or to those of the current that passed.

Progressive densification of currents downvalley, however, increased intergranular friction, leading to unusually 

Juhle Fork

Hills Lethe Hills

Figure 74. Aerial view of VTTS downvalley from above its narrowest reach (3 km wide), extending ~11 km to Ukak lobe terminus 

at foot of Mount Katolinat. At left, ignimbrite wraps nose of Buttress Range into Windy Creek lobe. In center distance, narrow 

Ukak River corridor connects Ukak lobe with 5-km-wide ignimbrite sheet that was elsewhere blocked by moraine belt crossing 

lower valley. Four stream gorges are prominent: River Lethe at left margin, mid-valley fork of Knife Creek, main fork of Knife 

Creek (with gray overbank alluvium), and Juhle fork at right. Chains of pinkish ignimbrite hills along Lethe and Juhle fork margins 

contrast with elsewhere planar surface of sheet; hilly marginal strips have 10–15 m of primary local relief that formed during 

Episode I ignimbrite emplacement (see figure 81) before being draped by Episode II fallout.
108 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Figure 75. Ignimbrite margin at southwest corner of VTTS, where tuff banks against Buttress Range adjacent to West Mageik Lake. Dark 

ignimbrite ledge near rim is illustrated in figure 38, where it overlies thick rhyolite-rich ignimbrite that extends beneath lake level. Lightcolored deposits above dark ledge include dacite fallout but are mostly pumice-rich scree sloughed from steep bedrock slope above. Gray 

material veneering cream-colored tuff above lakeshore is till left by glacier that occupied lake basin in 1912. In distance, ignimbrite bench 

stands as high as 60 m above valley floor axis at right, owing to differential compaction-welding of thick valley-filling tuff.

sluggish medial-to-distal advance. Densification and early 

depletion of interstitial gas may likewise account for failure 

of the depositing currents to loft buoyantly at their runout 

extremities or to produce a volumetrically important cloud of 

coignimbrite ash. As each current flowed out into the valley, 

its expanded condition would have gradually deflated, and 

basal sedimentation would have progressively reduced its 

moving mass. After outflow of several kilometers, each densifying ash-flow current would first have developed a sharp 

density discontinuity and eventually have left behind most 

of its turbulently dilute upper clouds. Development of free 

surfaces on some currents is implicit in the intercalation of 

pumice falls (but no fine ashfall layers) between ignimbrite 

packages at medial runout distances in upper Knife Creek 

and the Katmai Pass/Mageik Creek area. Such intercalations 

are absent more proximally, where the turbulent currents 

would have incorporated contemporaneous fallout.

In its progress from fountain collapse to the lower 

VTTS, each current would thus have transitioned from 

turbulent suspension to fluidized laminar flow to shearing 

flow with partial gas support by hindered settling to shearing granular mass flow with increasing matrix strength and 

density (Druitt, 1998; Freundt and Bursik, 1998; Iverson 

and Vallance, 2001). On reaching the central VTTS, most 

currents had evidently lost enough of their interstitial fluid 

pressure that intergranular friction greatly reduced velocities. 

Downvalley, some discrete currents took on the characteristics of model flow units (Sparks and others, 1973) with finegrained and/or lithic-rich layers at the base, buoyant pumice 

concentrated at or near the top, and free surfaces attended 

only by billowing ash clouds produced by ongoing elutriation. Reduction of internal agitation as fluid escape lessened 

would have increased particle collisions (leading ultimately 

toward interlocking), increasing rigidity toward plug flow 
Chapter 6. Volcanological Aspects of the Primary Eruption Products 109

Figure 76. Top of main VTTS ignimbrite (Package 4) wedging out against cross-valley moraine east of Three Forks (see figure 64). 

Within 50 m upvalley (to left of image), ignimbrite is 10–20 m thick. Ruler, 16 cm long, rests against brown soil containing charred willow 

roots. Oxidized ignimbrite here is overlain by thin Layers C–D, fine-grained pale-gray Layer E, and thicker Layers F–G at top. Ignimbrite 

lacked sufficient momentum, 16 km from Novarupta, to run up modest slope of soil-covered moraine.

and promoting alternation of stalling and surging of the flow 

front, perhaps stimulated by the ongoing seismicity and/

or slight resurgence of pore pressure by gas flux from wet 

substrate. Such densifying flow units, though perhaps still 

aggrading basally, might ultimately glide to a halt, not quite 

en masse but by internal laminar shear. Even at the extremity of outflow, such flow units probably would not undergo 

plug flow but move instead by laminar flow with organized 

shear, perhaps pulsatorily. Each distal current may have 

ground to a halt from the base up, shear propagating upward 

as the granular mass stalled and its upper levels moved 

onward in unsteady pulses (fig. 77). At the ultimate Ukak 

terminus, the VFI feathers out in tapering wedges less than a 

meter thick (fig. 78).

Rhyolite-rich distal ignimbrite in the lower VTTS is not 

strongly crystal enriched relative to phenocryst-poor (0.5–3 

wt percent) rhyolite pumice, indicating that loss of fine vitric 

ash was limited. Small fractions of phenocryst-rich (25–42 

wt percent) andesite and dacite pumice render calculation of 

free-crystal enrichment uncertain distally and nearly impossible upvalley, where proportions of the three pumice types are 

large and varied. Nonetheless, componentry yields only 2–4 

wt percent free crystals in rhyolite-rich nonwelded Packages 

3 and 4 in the lower VTTS, 14–20 km from vent (Fierstein 

and Hildreth, 1992). Both rhyolite-rich and compositionally 

more heterogeneous ignimbrite packages in the VTTS contain 30–50 wt percent ash finer than 63 μm, supporting the 

inference that elutriative loss of fines was not large during 

downvalley flow. Moreover, the all-rhyolite plinian pumicefall deposit, Layer A, likewise contains 2–4 wt percent free 

crystals at medial downwind distances of 7–13 km. (Crystal 

content of Layer A is greater than this on Kodiak Island, 

170 km downwind, by which distance the deposit is entirely 

ash-grade and aeolian fractionation had kept a larger fraction 
110 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Figure 77. Thinly laminated ignimbrite 

on gorge wall of “Moraine Creek” just 

upstream of cross-valley moraine in 

northeastern part of VTTS (Hildreth 

and Fierstein, 2003). Exposure here 

is 7–8 m high, but gorge is locally as 

deep as 20 m, cut entirely in rhyolitedominant packages of Episode I 

ignimbrite. Note that laminae, mostly 

3–10 cm thick, continue to top of 

deposit. Distal deposit here, 15–16 

km from Novarupta, represents 

entire transporting current, no higher 

part of which existed to pass over 

moraine barrier. It is thus inferred 

that lamination developed within 

dense sluggish current itself, not 

by incremental deposition at base 

of a current that continued farther 

downvalley.

Figure 78. Ukak lobe terminus of ignimbrite at foot of Mount Katolinat, ~20 km from Novarupta. Gray-brown flats 

at center are posteruptive deposits of ashy mudflows. White deposits are primary rhyolite-dominant nonwelded 

ignimbrite that feathered out into brush with little or no run-up.
Chapter 6. Volcanological Aspects of the Primary Eruption Products 111

of vitric fines aloft). The similarly modest losses of fine ash 

in plinian fallout and distal ignimbrite inferred from equivalently small degrees of crystal enrichment suggests that most 

of the fines were lost by violently agitated fluidization of the 

dilute mass around the vent (Wilson, 1980) as it transitioned 

from collapsing fountain into radial currents. If so, and if 

subsequent elutriation of fines from downvalley currents was 

unimportant, this further implies only weak fluidization, in 

accord with the inference of low velocity and low momentum of nearly all VTTS ash flows. 

Further support for very slow distal advance comes from 

the scarcity of ground layers enriched in crystal and lithic 

components. Widely interpreted as deposited from flow fronts 

diluted by turbulent entrainment of air (Walker and others, 

1981), basal ground layers (2–4 cm thick) have been observed 

just beyond Katmai Pass and along the Ukak River corridor, 

both rough, steepening pitches where turbulent entrainment 

might provide exceptions to otherwise sluggish advance of the 

distal currents. The only other ground layers observed are in 

thin all-rhyolite flow units that banked into the cul-de-sac at 

the snout of Glacier 5. Consistent too with slow and halting 

progress of flows near the downvalley terminus is absence in 

their well-exposed basal deposits of any bones of large mammals, several species of which would be expected here in June. 

They got away.

Episodes II vs III: Small Density Currents from 

Column Margins

The several pyroclastic density currents (PDCs) produced during Episodes II and III (fig. 47) were very different from the sustained ignimbrite-depositing currents 

of Episode I. Each current was only minutes in duration, 

trivial in volume (≤0.01 km3), and generally sector-confined. 

The deposits crop out in five packages, ~0.1 m to ~3.5 m in 

aggregate thickness, that each consist of several thin layers or flow units; none extends more than 3 km from vent, 

though a few pass laterally into ashfall layers a few centimeters thick. The laterally emplaced PDC deposits are intercalated with the proximal parts of regional plinian Layers C 

through G and with a few locally dispersed sector-confined 

wedges of andesite-rich proximal fallout (Fierstein and others, 1997; Houghton and others, 2004). Like the ultraproximal fall deposits, the PDC deposits are enriched (relative 

to the coeval dacite-dominant plinian falls) in andesitic and 

banded pumice and in vent-wall lithic fragments. As their 

total aggregate thickness averages ≤3 m, total volume of the 

five packages is probably <0.05 km3

, even accepting that a 

modest fraction of each current may have been lost as dilute 

turbulent ash clouds overwhelmed by synchronous plinian 

fallout. Altogether, then, the PDC deposits make up less than 

1 percent of the Episode II–III ejecta, which include ~8.2 

km3 of regional plinian fallout (Fierstein and Hildreth, 1992).

During Phase B of Episode I, the main VTTS-filling 

multipackage ignimbrite accounted for ~80 percent of the 

material being erupted and the subordinate convective 

plume that produced Layer B only ~20 percent. No largescale collapse into a radially spreading fountain took place, 

however, in either Episode II or III, during each of which the 

high convective column was sustained. Rather than from 

a fountain, PDCs were initiated by spasmodic sedimentation from external margins of the emerging jet and/or lowest 

margins of the convective plume, each in a limited sector 

and from probably less than 1 km above the vent. Collapsing spasmodically and highly asymmetrically, the PDCs are 

inferred to have resulted from column-margin instabilities 

caused by annular overloads rich in andesitic and lithic ejecta 

that emerged in irregular short-lived pulses. Such instabilities took place on a time scale of minutes, such that many of 

the multipulse currents were separated by short intervals of 

fallout, producing deposits of falls and flows that alternate on 

a thickness scale of decimeters to meters.

The PDC deposits range widely in thickness, grain 

size, sorting, fraction of fines retained, and in abundances of 

andesite scoria and vent-wall lithics, showing such contrasts 

even within packages emplaced simultaneously in different 

sectors. As documented in detail, illustrated, and interpreted 

by Houghton and others (2004), the Episode II and III PDC 

deposits include at least four facies. (1) Channel-confined 

matrix-rich, multipulse ignimbrites with sharp lateral and 

terminal boundaries and containing abundant pumice blocks. 

Largely confined to the western outlet of Novarupta basin, 

these probably originated as laterally ejected slugs or smallscale local collapses of the lower column margin. (2) Thinly 

bedded ash-rich deposits with pinch-and-swell lamination 

and a wide range of sorting, interbedded with thin pumicefall layers that share their pumice-composition proportions. 

These are distributed widely and probably represent dilute 

suspension currents that lofted distally and graded out into 

thin ashfall deposits. (3) Channel-confined matrix-poor lenses 

of pumice lapilli and blocks largely confined to slopes of the 

Turtle, interpreted as local grain-flow avalanches of pumicefall material remobilized by seismicity and/or compactioninduced sagging and faulting of the vent-fill.

Finally, (4) a radial blast-like deposit (PDC 4 of Houghton and others, 2004) that extends symmetrically as far as 2.5 

km issued from the same vent but during a temporary shutdown of the high plinian plume. Proximally, it is temporally 

equivalent to regional Layer E, deposited during the interval 

between Episodes II and III. The deposit is a 1–3.5-m-thick, 

matrix-supported, massive, landscape mantling, poorly sorted 

ignimbrite that has as many as five flow units with pumiceconcentation zones and elutriation pipes. Although more even 

in thickness and distributed more radially than the other PDC 

deposits, it is nonetheless sectorially varied in grain size, fines 

retention, lithic fraction, and degree of welding. Its abundant 

welded vitrophyre lithics (including some ballistic blocks) 

indicate major vent erosion, and its 350-m runup height on the 

slopes of Trident suggests energetic lateral transport. Its radial 

outburst was probably the result of sudden clearance of the 

vent blockage that had shut down plinian Episode II.
112 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Physical Features of VTTS Ignimbrite 

Sheet

Aspect Ratio

Walker and others (1980) proposed that aspect ratio is a 

measure of “violence”—lateral dispersal by momentum—and 

defined it as the ratio of average thickness to the diameter of 

a circle with the area of the deposit. The VTTS sheet (fig. 

74) has commonly been cited as a prime example of a highaspect-ratio ignimbrite. The fact, however, that the 1912 

sheet is a composite product of nine packages (and certainly 

dozens of flow units) that merged into the main valley from its 

three arms means obviously that such citation addresses the 

whole deposit and does not concern the thickness, velocity, or 

runout of its many component currents. Masking of topography by early packages and deposition of smooth degassing 

surfaces would clearly have enhanced the mobility and runout 

of later currents. Duration of the multipackage eruption also 

influenced aspect ratio, because maximum runout area was 

achieved by Package 3, and Packages 4–9 only served to 

thicken the whole, thereby progressively increasing the aspect 

ratio. Moreover, even neglecting HEPI veneers and VFI near 

valley margins, the thickness of axial VFI ranges at least 

5-fold and possibly 20-fold, rendering average total thickness 

rather difficult to estimate. As an exercise, nonetheless, for an 

area of 120 km2

 for the main VFI, a (very uncertain) average 

total thickness of ~50 m gives an aspect ratio of 4 x 10-3. By 

comparison, the (likewise composite) HEPI veneers, which 

drape rather than fill topography, have an average thickness of 

~5 m over ~50 km2 (or ~2 m over ~100 km2), giving arguable 

aspect ratios of 2–6 x10-4—an order of magnitude thinner, for 

facies of the same eruption.

Flow Units and Progressive Aggradation

Numerous flow units can be identified within the VTTS 

ignimbrite sheet, some of which are thin with well-defined 

contacts and some of which are thick and structureless and 

may have been deposited continuously or incrementally at the 

base of passing currents. Conceptually, we consider a flow 

unit to be the deposit of a single vent-derived current, initiated 

by a discrete eruption, collapse pulse, or major fluctuation in 

discharge during a sustained eruptive interval, while further 

recognizing that some currents can subdivide laterally or 

vertically during outflow. In practice, we follow Wilson and 

Hildreth (1997) in mapping “packages” of ignimbrite with 

similar components, compositional proportions, and lithologic 

characteristics (exclusive of welding style) that were emplaced 

as one or many pulses or flow units. This usage skirts the 

uncertainty in interpreting whether such common features as 

discontinuous partings or stringers of pumice or lithics represent unsteady deposition from a continuous current or flow 

units separated by time breaks between discrete episodic currents. Thick sections of massive ignimbrite, either structureless or with a few such discontinuities, have been variously 

interpreted in terms of progressive aggradation or as a succession of flow units at intervals so short that batches amalgamated by shearing along their contacts before each lower batch 

had time to degas and consolidate sufficiently to provide a firm 

substrate for the next. These depositional modes may themselves essentially merge if discrete pulses follow one another 

rapidly enough. The better demarcation of flow-unit contacts 

distally, as commonly observed, may reflect longer setup times 

between batches and/or more advanced defluidization. Mixing 

and merging at boundaries between successive fluidized pulses 

may so obscure the contact that a seamless join is either indiscernible or marked only by subtle textural changes and particle 

trains hard to distinguish from products of unsteady deposition 

from a continuous current.

Flow-unit boundaries (Sparks, 1976; Wilson, 1980; 

Druitt, 1998) are fairly unequivocal where marked by (1) layers of intercalated fallout, (2) truncation of degassing pipes, 

(3) inversely graded fine-grained basal layers, or (4) ground 

layers strongly enriched in dense components—crystals and 

lithics. In addition, (5) major pumice swarms and (6) normally graded lithic-rich zones are usually clear indicators 

of upper and lower parts, respectively, of flow units. Small 

clusters or trains of pumice or lithics, discontinuous on a meter 

scale, and vague impersistent stratification, however, are more 

ambiguous. Not all such discontinuities need reflect discrete 

pulses with time breaks, as opposed to short-lived irregularities in deposition (or nondeposition) at the base of a continuing current (Branney and Kokelaar, 2002).

The nine successive packages of Episode I ignimbrite 

are the cumulative product of 14–16 hours of eruptive activity 

(Hildreth and Fierstein, 2000; Fierstein and Wilson, 2005). 

Flow-unit boundaries between and within packages are well 

marked in the upper VTTS and Mageik Creek by pumice-fall 

intercalations (fig. 37) or stratified intervals between massive units of contrasting composition and induration (fig. 38). 

The lack of coignimbrite fine-ash layers at flow-unit contacts, 

however, means either that they were scoured, that intervals 

between currents were short, or that the fallout of plinian pumice was uninterrupted. As illustrated by Fierstein and Wilson 

(2005; their fig. 6), sharp contacts between flow units are 

variously marked by compactional swales filled by later units 

or erosional channels cut by the units that fill them (figs. 31, 

67), and, in the central and lower VTTS, by fine-grained basal 

layers (fig. 68) that occur commonly (but not exclusively) 

between nonsuccessive packages. Andesite-rich Package 8 

may have been partially welded before the thin block-rich flow 

units of postplinian Package 9 overran it (fig. 35). 

Striking compositional changes (fig. 79) that define 

packages usually also coincide with flow-unit boundaries, 

but exposures in the central and lower VTTS are common 

in which a compositional change, either sharp or gradational 

within a meter or two, is accompanied by no visible discontinuity or grain-size change (fig. 39) to indicate a depositional 
Chapter 6. Volcanological Aspects of the Primary Eruption Products 113

Figure 79. Distal ignimbrite exposure, ~7 m high, on wall of lower “Moraine 

Creek” gorge (Hildreth and Fierstein, 2003), ~18 km from Novarupta and 2 

km east of Three Forks, showing contact of rhyolite-rich Package 4 overlain 

by compositionally heterogeneous Package 6.

hiatus between currents. In particular, transitions between 

voluminous rhyolite-rich Packages 2, 3, and 4 in the lower 

VTTS are commonly featureless except for abrupt upward 

increases in proportions of andesite pumice. Some of the 

discontinuous stratification and clast trains may well reflect 

incremental aggradation within thick flow units that by midvalley had become dense grain flows that were extensively 

defluidized, advancing in pulses, and halting layer-by-layer. 

Rather than stopping en masse as plug flows ~10 m thick, 

distal flow units apparently sheared out laminarly, depositing progressively or spasmodically and feathering out thinly 

at their termini—in the Windy Creek embayment, beyond 

saddles in the Three Forks moraine, and at the base of Mount 

Katolinat. Engulfment of charred but upright trees in distal 

ignimbrite several meters thick suggests creeping velocity and 

near-exhaustion of momentum.

Remobilized Flow Units

Stringers of pumice or lithic fragments and subtly discontinuous layering that extends only a few meters, not uncommon features on gorge walls in the central and lower VTTS, 

may represent traces of amalgamated contacts between closely 

successive flow units or, alternatively, products of unsteady 

sedimentation at the base of a unitary current depositing incrementally. Distally, however, where Packages 3 and 4 bypassed 
114 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

the Three Forks moraine and flowed down the narrow Ukak 

River corridor (fig. 30) to the terminal lobe, numerous meterscale flow units are well developed (fig. 80). Called “segregation units” by Hildreth (1983) and “pseudo-flow-units” by 

Fierstein and Hildreth (1992; their fig. 10a), these have no 

visible equivalents upstream and appear to have originated 

distally by budding or surging of massive unstratified ignimbrite that was by then halting or advancing very slowly. Many 

of these strata are inversely graded, with fine-grained basal 

layers and coarse pumice preferentially buoyed toward the 

top. Downstream from the Three Forks moraine, the slope of 

the ignimbrite surface (where uneroded) increases from ~1.5o 

to ~2.1o for 3.5 km and to as steep as 3.2o for one 500-m-long 

reach (figs. 29, 30). 

After 16 km runout from vent, the internal fluid pressure 

may have been so depleted that intergranular friction increased 

matrix strength sufficiently to resist further advance. After 

burying a stream valley and beginning to stall on a slope of 

a few degrees, however, upper parts of the deposit may have 

been intermittently remobilized gravitationally by slight 

renewal of pore gas pressure or perhaps by the strong seismicity continuing during caldera collapse. Although developed 

within the same ignimbrite package and similarly associated 

with slowing or stoppage of a granular mass flow, these meterscale remobilized flow units (fig. 80) appear to reflect a process rather different from the systematic internal shear thought 

to have produced the centimeter-scale lamination (figs. 65, 

66, 77) where the flow was stopped and diverted by the Three 

Forks moraine (fig. 64).

There are at least three places in the VTTS where the 

upper few meters of ignimbrite were remobilized after the 

sheet had clearly come to rest, leaving concave scarps and 

drainaway channels in nonwelded tuff that had developed 

sufficient rigidity to preserve them. Each location is adjacent to the margin of the main VFI: (1) along the southeast 

margin of the Ukak terminal lobe; (2) the northeast margin of 

the central VTTS along the Juhle fork; and (3) the southwest 

margin of the central VTTS where the River Lethe hugs 

the bend in the Buttress Range (fig. 74). The last involves 

a kilometer-long area, the Lethe Hills (fig. 5), where the 

ignimbrite piled up in a cluster of mounds and ridges as 

much as 15 m higher than the elsewhere smoothly planar 

surface of the sheet (fig. 81). It seems likely that the hills 

were deposited where lobes of Packages 3 and 4 that flowed 

out of the Knife Creek arm collided with the Buttress Range. 

Pronounced narrowing of the VTTS at this location may 

also have played a role (Hildreth, 1983), as the lobes coming 

down the Lethe arm converged with those from Knife Creek. 

Directly across the valley constriction, where the Juhle fork 

hugs the northeast wall of the VTTS, the Lethe Hills have 

a counterpart in a cluster of ridges and hummocks showing 

7–10 m of primary local relief on the ignimbrite surface. 

Both hilly areas were affected by local drainaway, the upper 

few meters of ignimbrite having been remobilized within 

hours of emplacement, before the fall of dacite Layers C–H, 

which drape them.

Whatever the origin of the hills, the internal friction and 

rigidity suggested by such primary relief indicates that some 

of the granular currents were poorly fluidized by the time 

they reached the central VTTS. At several places in the Lethe 

Hills, scalloped embayments provide evidence for drainaway 

of ignimbrite that remobilized obliquely downstream toward 

the lateral margin of the VFI. Both the hills and the drainaway scarps (which added only slightly to the hilly relief) 

are draped by the dacite fall deposits of Episodes II and III, 

showing that hills are primary constructional features and 

that remobilization took place within a day after Episode I 

ignimbrite deposition.

Diffusely Plane Laminated Ignimbrite

In the lower VTTS, dense flow units of at least two 

Packages (3 and 4) ran straight into the Three Forks moraine, 

banking against it (fig. 76), diverting laterally into low gaps 

through it (figs. 29, 30) but failing to override the barrier that 

lay only a few meters higher than the surface of each current 

(fig. 64). The deposits, there pervasively marked by diffuse parallel stratification (figs. 65, 66, 77), had previously 

condensed into a dense sluggish current with a free surface. 

Condensation had concluded earlier and, though the mass was 

still moving slowly, no separate transporting current was left 

to continue across the moraine. The evenly spaced, well-organized, centimeter-scale stratification (fig. 65) is exposed from 

the uneroded top surface to the bottom of gorges 10–15 m 

deep. Occurring within packages of elsewhere-massive ignimbrite, the thin layering is best developed within 300 m of the 

moraine barrier, but subtler manifestations are also exposed as 

far as 1 km upstream of the moraine and down on the terminal 

Ukak lobe. Any incremental aggradation had been complete 

farther upvalley, so the systematic lamination of these densely 

granular avalanche-like flow units was apparently accomplished by internal shear as they banked into the barrier and 

ground fitfully to a halt nearby (Hildreth, 1983).

“High Sand Mark”

The elevated bench around the upper VTTS where the 

ignimbrite sheet is thickest was called the “high sand mark” 

by Griggs (1922) and Fenner (1923, 1925), who thought it 

was either a veneer or a valley-margin runup. However, it 

was deposited neither by passage of an inflated current nor a 

high-velocity current that drained away downvalley. Instead, 

it represents a marginal bench (figs. 75, 82) around most of the 

Lethe arm that formed in thick ignimbrite by differential welding-compaction (Fenner, 1923; Hildreth, 1983). The benches 

change gradually into side slopes in the central VTTS and 

then fade out completely as the sheet thins downvalley and 

becomes nonwelded. Around the upper Lethe basin, however, 

an elevation difference of 30–60 m between the valley floor 

and the fissured hingeline of the bench suggests an axial thickness as great as 150–200 m, in agreement with Curtis’ (1968) 
Chapter 6. Volcanological Aspects of the Primary Eruption Products 115

Figure 80. Meter-scale distal 

flow units that developed 

near Ukak River terminus from 

what had been thick massive 

ignimbrite just upvalley. 

Hammer is 30 cm long. Budding 

of such distal secondary flow 

units is interpreted to have 

taken place within densified, 

extensively defluidized currents 

that were discontinuously 

stalling and pulsing, 

preferentially near their tops. 

Figure 81. Lethe Hills: primary relief on Episode I ignimbrite surface draped by pale-gray stratified dacite fallout of 

Episodes II and III. Hills have as much as 15 m relief above planar surface of sheet. Such hills developed only along 

margins of narrowest reach of VTTS, here only 3 km wide (see figure 74). View is northeastward across gorge of River 

Lethe at base of Buttress Range, 11 km northwest of Novarupta.
116 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Figure 82. “High sand mark”—ignimbrite bench along Buttress Range margin north of West Mageik Lake. 

Fissured hingeline along rim of bench reflects bending of indurated ignimbrite sheet owing to differential 

compaction and welding. Elevation difference between bench and valley-floor axis is variously 30–60 m. 

Valley-filling ignimbrite along valley axis is more densely welded and thicker than along its margins. Lake 

was occupied in 1912 by snout of glacier from Mount Mageik. Recession of ice front by ~1 km has exposed 

3.1-Ma rhyolite sill complex (white ledge at lower left) cutting stratified Jurassic siltstone. Lake outlet is 

origin of River Lethe.

estimate based on comparative stream profiles. Although 

less well developed, comparable benches and inward slopes 

around the upper Knife Creek arm (fig. 26) suggest 100–150 

m of variably welded ignimbrite there as well. Some have 

speculated that the benches might conceal lateral moraines, but 

Neoglacial moraines in the VTTS lie 15 km downvalley near 

Three Forks, and glacier-fed valleys that parallel the VTTS 

nearby (Ikagluik Creek, Rainbow River) lack such proximal 

lateral moraines (Hildreth and Fierstein, 2003).

Compaction faults with decimeters to meters of displacement are common on the benches in the upper VTTS, especially along hingelines, where indurated ignimbrite adjacent to 

antithetic faults is commonly tilted 15o–30o toward the valley 

axis (fig. 83; Fenner, 1923, p. 40). Such faults and fissures 

intercepted surface precipitation, runoff, and groundwater, 

leading to vigorous fumarolic discharge and alteration along 

the benches (as observed when active in 1916–1923; Griggs, 

1922, p. 216, 225, 232) and to explosive phreatic excavation of 

craters and fissures (fig. 84) concentrated along the hingelines 

(probably all before 1916). 

Because many of the faults displace the dacite fall deposits as well as the ash-flow tuff, compaction deformation of the 

ignimbrite sheet certainly persisted for at least 2 days after 

Episode I deposition. From another perspective, however, 

because some of the later ignimbrite packages were channelled 

along broad axial swales atop the thick packages emplaced 

only hours earlier, axial compaction was clearly underway 

almost immediately after emplacement.

Valley Margin Runups

Not to be confused with the marginal benches that marked 

the deposit surface in the upper VTTS before compaction and 

welding, there are also a few locations where momentumdriven runup deposited thin wedges of nonwelded ignimbrite 

still higher than that surface. Apart from the initial blast-like 

radial emplacement of the all-rhyolite Package 1, however, the 

subsequent packages underwent significant runup in only a few 

topographically special situations. The sparsity of evidence for 

runup is consistent with the sluggishly halting advance inferred 

for the ash flows that reached the lower VTTS. The most 

voluminous packages, 3 and 4, which alone flowed all the way 

to the Ukak terminus, exhibit marginal runups of less than 10 

m where exposed in the upper VTTS (fig. 75).
Chapter 6. Volcanological Aspects of the Primary Eruption Products 117

Figure 83. Fissured and faulted hingeline of the bench ~1 km north of West Mageik Lake seen in figure 82. 

Bending in response to differential compaction produced dips as great as 25o toward valley axis. Fissures 

focussed intense fumarolic discharge and alteration for a decade after eruption. Visible relief 1–3 m along 

trough, now partly filled with reworked pumice and ash.

Package 1 was uniquely mobile in veneering the ventfacing slopes of Trident to elevations >700 m higher than 

Novarupta basin and in sweeping across the slopes of Mount 

Griggs as high as 450 m above the margins of subsequent 

VFI packages that filled the Knife Creek arm. A massive to 

vaguely stratified tongue of pink nonwelded rhyolite tuff (fig. 

25) that extends ~5 km up the narrow Griggs fork canyon 

(to ~500 m higher than the valley floor at Knife Creek) was 

deposited by unobstructed outflow directly from Novarupta, 

which lies 6 km from the canyon mouth. Along the Griggs 

fork, Package 1 ignimbrite is as thick as 13 m, but it feathers 

out upslope on Mount Griggs and thins northwestward across 

slope to <1 m at the Juhle fork, 9 km from vent, where it then 

vanishes. A similar veneer of pink all-rhyolite ignimbrite, 

vaguely stratified and typically thinner than 20 cm, mantles the 

lava-flow benches of Mount Mageik, west of Katmai Pass and 

upper Mageik Creek (figs. 26, 28); the veneer extends as much 

as 250 m higher than the tongue of Package 1 ignimbrite (4–6 

m thick) that fills the axis of Mageik Creek. These Package 1 

veneers on Trident, Griggs, and Mageik have a runup quality 

to them, but they were all probably deposited from turbulent 

overcurrents rather than the dense undercurrents that deposited 

ignimbrite along the canyon floors.

Package 2, predominantly rhyolitic, also ran ~3 km (and 

300 m in elevation) directly up the Griggs fork but did not 

veneer the adjacent slopes of Mount Griggs as Package 1 had. 

None of the subsequent packages left evidence for significant 

runups in the upper VTTS. However, the southwest margin 

of the (composite multipackage) ignimbrite sheet that fills the 

upper Knife Creek arm extends smoothly along the Broken 

Mountain slope, paralleling the northwesterly flow direction 

30–50 m higher than the valley floor (fig. 26). This feature, 

only 2 km downhill from the vent, is certainly not a result of 

runup but is, instead, a combined product of deposition from 

proximally expanded currents that passed and subsequent 

differential welding, as in the Lethe arm. Similarly, for Package 7 to be limited to the upper VTTS (fig. 27) but to have 

poured through Katmai Pass more voluminously than any 

other package requires not runup around a left-turn corner but 

some process otherwise unique in the 1912 eruptive sequence. 

Much of its fountain collapse is likely to have enveloped Falling Mountain, allowing Package 7 currents to go both south 

and north from that obstacle (figs. 70, 71).

Where the Lethe and Knife Creek arms merge in the central VTTS and the valley floor narrows to only 3 km, there are 

runups of Packages 3 and 4 on both walls of the valley (fig. 

74). At this constriction, adjacent to the Lethe Hills and just 

downstream from fadeaway of the marginal bench, a wedge 

of pink to terra cotta nonwelded ignimbrite (fig. 85) extends 

up the Buttress Range sidewall to elevations 30–60 m higher 
118 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

A

B

A

B

Figure 84. Overview of Fissure Lake. Views westward along trough occupied by Fissure 

Lake (Griggs, 1922, pp. 212, 244) for the first decade after eruption: A, 1917 and B, 1982. 

Trough was excavated by phreatic explosions along hingeline of compactional bench 

at southwest edge of VTTS. Fumarolically altered ignimbrite dips ~20o N at right but is 

almost horizontal at left and in distance where banked against Buttress Range. Scarp at 

right is ~20 m high; note two men on rim in 1917 image. Lake silted in by 1923. Terminus of 

glacier, ~1 km from camera, occupied present-day site of West Mageik Lake. Since 1951, 

glacier has retreated ~1 km upslope to left, exposing rhyolite sill complex that intrudes 

Jurassic siltstones. White sill at upper left in 1982 image is 10 m thick, dips 15o NNE along 

with enclosing Jurassic strata, has ~77 percent SiO2

, and yielded a K-Ar age of 3.08±0.07 

Ma (Hildreth and Fierstein, 2003; Lowenstern and Mahood, 1991; Lowenstern and others, 

1991). 1917 photo courtesy of National Geographic Society; 1982 photo by authors.
Chapter 6. Volcanological Aspects of the Primary Eruption Products 119

than the hills and the planar surface of equivalent units on the 

valley floor. The massive unstratified deposit is ash-rich and 

rhyolite-dominant and contains abundant pumice lapilli where 

it is still a few meters thick, but it becomes lapilli-poor where 

it feathers out upslope to <20 cm thick (fig. 86). This elevated 

fringe extends along the Buttress Range for ~1.5 km but is 

absent along the same slope immediately upstream and downstream. Only 4 km farther downvalley, the ignimbrite filled 

the 1912 channel of Windy Creek (fig. 87), but it was moving so sluggishly that the sidewall and overbank turf, though 

charred, was not scoured away. 

A similar but less well preserved runup fringe of pink 

ignimbrite is present directly across the narrows of the VTTS 

above the Juhle fork (fig. 74), where the main VFI also exhibits a cluster of ridges and hummocks mirroring those of the 

Lethe Hills. The runups apparently represent a local phenomenon related to narrowing of the VTTS. 

Because Package 3 and 4 currents failed to surmount the 

low moraine only ~5 km farther downvalley, their evidently 

Figure 85. Thin runup fringe of pink rhyolite-dominant ignimbrite 

along Buttress Range margin at narrowest part of VTTS, 11–12 km 

from Novarupta. Brush was killed up to 60 m above planar surface 

of valley-floor ignimbrite. Deposit overlies dark brown organicrich soil. Shovel is 58 cm long.

poor mobility makes it unlikely that, when they passed the 

narrows, they could have been inflated to twice the thickness 

of their deposits in this part of the valley. From the general 

lack of significant runups elsewhere in the VTTS, it can be 

inferred that valley-confined currents here were seldom much 

thicker than their nonwelded deposits. More likely, currents 

from the two converging arms of the VTTS either crossed 

paths and ran directly up the opposing walls or promoted a 

temporary elevation of the confluent flow surface, limited to 

the narrow VTTS constriction (Hildreth, 1983; Fierstein and 

Hildreth, 1992; Fierstein and Wilson, 2005).

Induration and Welding

In the lower VTTS, the rhyolite-dominant ignimbrite is 

wholly nonwelded where exposed top to bottom in gorges 

10–20 m deep (figs. 31, 68, 79, 87). Mechanical compaction 

nonetheless promoted induration by matrix packing (with 

or without traces of fumarolic or groundwater precipitates) 

sufficiently strong to permit the massive nonwelded tuff 

(bulk density 1,100–1,300 kg/m3) to stand in vertical cliffs 

for decades. Within 3 km upvalley from Three Forks, lower 

walls of 30-m-deep gorges begin to exhibit weak sintering 

(figs. 32, 88), and in the central and upper VTTS most surface 

exposures (figs. 35, 36, 69, 89) become moderately sintered 

to partially welded (1,400–1,700 kg/m3). Because sintering represents fusion of point contacts among vitric shards 

without macroscopic deformation, sintered ignimbrite remains 

permeable and subject to vapor percolation. As a result, there 

is widespread overlap between near-surface zones of vaporphase crystallization and sintering (or weak welding) in the 

VTTS. Along the mid-valley forks of Knife Creek, such zones 

developed slender cooling-joint columns that extend down the 

gorge walls to depths of 5–20 m, where they grade down into 

massive sintered or nonwelded tuff. Columnar jointed vaporphase-indurated tuff is also widely exposed on the benches 

fringing the upper Lethe arm.

Partial welding (1.7–2.0 g/cm3), marked by incipient to 

moderate flattening of pumice, is exposed in relatively few 

areas of the upper VTTS, where stream cuts into the ignimbrite are only 3–7 m deep (figs. 35, 89). Most of the dark-gray 

surface exposures there, largely of rhyolite-poor Packages 8 

and 9, are strongly sintered or incipiently welded (fig. 35), but 

Package 8 displays flattened pumice near West Mageik Lake 

and has a strong eutaxitic (planar foliation) texture near Knife 

Creek Glacier 1 (fig. 33), ~2 km east of Novarupta basin. 

Blocks of welded tuff ejected from the many phreatic craters 

in the upper Knife Creek arm (Hildreth and Fierstein, 2003) 

range from tack-welded to eutaxitic, some having measured 

densities of 1.8–1.9 g/cm3

 (Curtis, 1968; Hildreth, 1983). 

Most such blocks are of rhyolite-poor ignimbrite, indicating 

shallow sources, but some are rhyolite-rich, evidently blasted 

out from earlier packages concealed deep in the deposit. 

Similarly, the vitrophyric blocks of welded vent-fill recycled 

as the principal lithic component of Episodes II and III range 
120 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Figure 86. Close-up view of 15-cm-thick pink ignimbrite runup along Buttress Range margin, as viewed in figure 

85. White base chilled against substrate of dark brown soil, avoiding oxidation. Note that ignimbrite coarsens 

upward. Pink rhyolite-dominant ignimbrite is overlain by white dacite fallout of Episode II. Knife is 8.5 cm long.

Figure 87. Nonwelded ignimbrite that filled pre-1912 course of Windy Creek, forcing stream to incise new 

channel (toward left) through hyperconcentrated sandflow deposit of latest Pleistocene Lethe assemblage 

(Hildreth and Fierstein, 2003). Streambank here is 8–10 m high. Note that sluggishly emplaced ignimbrite did 

not scour mat of charred vegetation from upland surface it overran (at left) and only partially scoured it from 

sidewall of channel it filled. Mount Katolinat on skyline.
Chapter 6. Volcanological Aspects of the Primary Eruption Products 121

Figure 88. Gorge along mid-valley fork of Knife Creek (see fig. 

74) , ~10 km from Novarupta. Upper ~5 m is nonwelded, weakly 

sorted ignimbrite with vague meter-scale layering. Lower 10–12 

m is sintered and jointed, grading to partial welding at depth. 

Stream originates in central VTTS and is fed in part by mid-valley 

thermal springs of Keith and others (1992).

Figure 89. Former natural bridge in partially welded tuff along 

main fork of Knife Creek, 7 km north of Novarupta. Later 

ignimbrite packages (5 through 9), rich in andesite and dacite 

pumice, are typically sintered or welded in upper and central 

VTTS and seldom incised deeper than 8 m. Bridge collapsed at 

unknown time in interval 1986–1989.

from weakly to densely welded (figs. 62, 63, 90), presumably 

reflecting a range of excavation depths.

Densely welded ignimbrite (2.1–2.4 g/cm3) is nowhere 

exposed in the VTTS, but it may underlie axial parts of the 

upper Lethe and Knife Creek arms, as suggested by 30–60 m 

of differential welding compaction. It is inferred that rhyoliterich Packages 2, 3, and 4, which extend farthest downvalley, 

make up the bulk of the unexposed welded tuff beneath the 

upper and central VTTS. The partially welded or strongly 

sintered material capping much of the upper VTTS, however, 

belongs to later rhyolite-poor ignimbrite packages dominated 

by dacite and andesite (Fierstein and Wilson, 2005). Because 

magma temperature of the andesite was at least 100oC higher 

than that of the rhyolite (Hildreth, 1983) and because the 

gas-poorer andesitic ejecta collapsed from generally lower 

heights (with less air entrainment) than rhyolite and dacite 

ejecta (Houghton and others, 2004), the andesite-richer flow 

units were intrinsically more subject to welding. During the 

break between Episodes II and III, a pair of andesite-rich flow 

units ~2 km east of Novarupta welded moderately (PDC 4 of 

Houghton and others, 2004), even though each is only ~1 m 

thick and overlain only by ~8 m of pumice-fall deposits.

Welding of ignimbrite entails the viscous deformation of vitric fragments under load. Glass has its viscosity 

reduced (and is thus made more susceptible to welding) by 

higher emplacement temperature, greater alkalinity, and more 

retained (or resorbed) water and halogens. It has been shown 

experimentally that (1) high-silica-rhyolite ignimbrite (comparable to that of the 1912 eruption) requires temperatures of 

550o–600oC to permit welding and that (2) under load pressure of 5 MPa (50 bars) with 0.4 weight percent water, such 

material can achieve partial welding with fiamme in 2-day 
122 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Figure 90. Block of vitrophyric welded tuff, 56 cm long, atop north ridge of Mount Cerberus, 3 km southwest of 

Novarupta and ~250 m above valley floor. Fiamme are all rhyolite, and abundant small red lithics are oxidized 

Jurassic siltstone. Material is welded vent fill equivalent to ignimbrite Package 1. Block was excavated and 

probably transported in blast-like current that punctuated emplacement of ignimbrite Package 7 (Fierstein and 

Wilson, 2005). Knife is 8.5 cm long.

runs (Grunder and others, 2005, and references therein). 

These conditions were probably met or exceeded by those 

inferred for the thick rhyolite-dominated ignimbrite buried in the upper VTTS. Rhyolite magma temperature was 

800o–850oC, and fumarolic gases were still as hot as 645oC 

in 1919. H2O retained by dense dome rhyolite at Novarupta 

is ~0.25 weight percent and was certainly greater for rhyolite 

pumice within the ash flows. And 100–200 m of overlying 

compacting tuff would have applied loads similar to that of 

the experiments cited.

Rapid onset of welding in thick upper-valley ignimbrite 

is inferred from the compaction swales that must have formed 

within an hour or two after emplacement of Package 4 on the 

first day of the eruption in order to have partially channeled 

subsequent packages. Hingeline faults along the compactional benches, however, are observed to offset Package 9 as 

well as some pre-Episode II reworked deposits and the dacite 

fall Layers C-H, demonstrating that welding compaction 

also continued beyond the third day of the eruptive sequence 

(Hildreth, 1983; Fierstein and Wilson, 2005). Many of the 

long fissures that controlled fumaroles in the upper and central 

VTTS are transverse to the valley axis, suggesting that viscous downvalley creep at depth influenced the brittle fracture 

in sintered tuff at the surface. For voluminous Packages 2 

through 4, the fines-rich crystal-poor rhyolite-dominant ash 

flows that issued as dense currents from a low fountain (and 

overran streams, ponds, marshes, and snowbanks in the upper 

VTTS) probably accumulated, compacted, and lost permeability rapidly enough to retain heat and pore fluids (Sparks and 

others, 1999) adequate to promote dense welding at depth on a 

timescale of only hours to days.

Degassing Pipes

Gas escape pipes, variously known as elutriation pipes, 

segregation pipes, or degassing pipes, are remarkably uncommon in the 1912 ignimbrite. Where small clusters of them are 

exposed near Mageik and Windy Creeks and along the Griggs 

fork, they are typical of pipes widely reported in massive 

nonwelded ignimbrite—nearly vertical, 5–15 cm in diameter, 

and 0.5–3 m high. Rarely, some are inclined, branching, or 

curtain-like in three dimensions. Gas escape has flushed them 

of fine ash, leaving openwork concentrations of crystals, lithics, and pumice lapilli, much better sorted than their host tuff. 

Because gas can be gathered internally from the host, no external fluid source (wet substrate or burning vegetation) need be 
Chapter 6. Volcanological Aspects of the Primary Eruption Products 123

required; the few pipes observed are rooted either within the 

ignimbrite or in permeable fall material at its base. Nonetheless, all of those found in the 1912 sheet are in nonwelded 

tuff less than 10 m thick that had clearly buried streams and 

willow thickets. None of the pipes observed had leached, 

oxidized, or otherwise visibly altered their walls; none had 

precipitated incrustations at their upper ends; and none have 

been found in sintered or welded tuff. In these respects, they 

contrast strikingly with the “ten thousand” fumaroles discussed in chapter 9.

How can scarcity of elutriation pipes be reconciled 

with the abundant fossil fumaroles so ubiquitous in the 1912 

ignimbrite? Although less abundant and shorter-lived than in 

the thick ignimbrite of the upper and central VTTS, fumaroles 

were indeed present in the nonwelded tuff of the lower VTTS, 

where some persisted for a decade. If the granular currents 

had lost most of their interstitial gas before distal deposition, 

thus rarely producing elutriation pipes, were distal fumarolic 

gases almost entirely meteoric water that became acid by 

leaching the hot tuff? Distal fossil fumaroles appear to be 

more common over buried stream courses, but this is likewise 

true for the sparse elutriation pipes.

Emplacement Over and Against Ice

The five Knife Creek Glaciers lie within 1.5 to 6 km east 

of the Episode I vent rim, their termini adjoin the valley floor, 

and their lower reaches are at elevations lower than Novarupta. The snouts of none have receded significantly since 

1912. Two glaciers from the north side of Mount Mageik also 

extended in 1912 to the valley floor, where their snouts were 

4 km and 6 km southwest of Novarupta and 100 m lower in 

elevation. Both have receded more than 1 km since 1912, 

leaving their former terminal reaches occupied by East and 

West Mageik Lakes, each bordered by bluffs of ignimbrite that 

had banked against the ice.

Around East Mageik Lake, the sheet of partially welded 

ignimbrite has slumped back toward the lake, opening a set of 

arcuate fissures (fig. 91), presumably in response to withdrawal of the ice front against which it had been deposited. 

West Mageik Lake is enclosed on three sides by ignimbrite 

that is widely altered fumarolically and pitted with phreatic 

craters, has collapsed into aprons of ignimbrite talus, and is 

locally lapped by lake sediments (fig. 92). The lake periphery 

is littered with brightly oxidized blocks of ignimbrite, some 

Figure 91. East Mageik Lake and fissured welded ignimbrite of Package 8, which banked against glacier 

that occupied lake basin in 1912. Snout of glacier from Mount Mageik has now receded ~1 km (see figure 

72), withdrawing support for tuff margin, which has slumped back toward lake, opening complex fissure 

system. View is northwest across Lethe arm of VTTS to Buttress Range margin, where “high sand mark” 

bench stands as high as 60 m above valley axis. Thin black veneer of alluvium in middle of Lethe arm 

overlies ignimbrite and is largely derived from andesite-dacite lavas of Mount Mageik.
124 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

prismatically jointed, that were expelled explosively (fig. 93). 

Many such blocks are associated with the fissured hingeline 

of the compactional bench nearby (figs. 84, 92), but others 

may have been ejected from the ice-contact zone at the glacier 

front itself. Lakeward tilting, fissuring, and slumping of the 

ignimbrite bluffs may also reflect melting away of buried 

snowbanks and ice-cored moraine. 

When first visited in 1917, a narrow lake extended from 

the glacier front for 600 m northeast of the present lake along 

a defile excavated phreatically along the fissured hingeline. 

Called “Fissure Lake” by Griggs (1922), this extension had 

silted up by 1923, and today its 10-m-thick deposit of ashy 

lacustrine and alluvial fill has been incised by a stream flowing 

back southwest into the modern lake (fig. 94), which was not 

fully formed by glacial recession until the 1950s. The lower 

reaches of the two Mageik glaciers have now disappeared, 

but photographs from 1917 show that the lower kilometer of 

the western one was still mantled by a few meters of eruption 

products, thick enough to require an ignimbrite veneer as well 

as fall Layers C–H. The lower kilometer or two of the eastern 

glacier was surely veneered with ignimbrite, as shown by the 

thin runups (largely of Package 1) still present on Mageik lava 

benches adjacent to the deglaciated trough.

All five Knife Creek Glaciers remain heavily mantled 

with 1912 fallout (fig. 95), which is as thick as 10 m atop 

their lower lobes and still 6.5 m at the Katmai caldera rim. 

Much of it has been disrupted by ice movement and wasting, 

but sections complete from Layer A to Layer H are locally 

intact. Intercalated within some supraglacial fall sections 

are (1) layers and pods of pyrite-bearing hydrothermal mud 

ejected from Mount Katmai during caldera collapse (Hildreth, 

1991) and (2) meter-thick deposits of pumiceous debris flows 

that were remobilized down snowclad slopes during the eruptive sequence. 

At the western edge of Glacier 1, an ice-marginal stream 

has cut a narrow slot ~20 m deep, along which at least 12 m 

of stratified fines-poor ignimbrite rich in andesite is exposed 

beneath 10 m of dacite fall deposits, both of which had banked 

against the ice and are still in local contact with it. Across 

the chasm to the east, 3–5 m of ignimbrite are locally visible 

extending across the glacier under a hummocky mantle of 

disrupted fallout. In a few places atop the steep flow front of 

Glacier 1, supraglacial ignimbrite is seen to consist of several 

meters of rhyolite-dominant material overlain by a few meters 

of compositionally heterogeneous darker material, capped 

in turn by the stratified dacite fall deposits. The supraglacial 

Figure 92. Southwest margin of VTTS viewed eastward 

from crest of Buttress Range. Outlet of West Mageik Lake 

at lower left is origin of River Lethe. Trough across center 

of image was excavated by chain of phreatic explosions 

along hingeline of compaction-related bench similar to 

that seen in figure 82. Wide silt-floored central segment 

of trough was site of Fissure Lake (figs. 84, 94), which 

ultimately drained toward modern lake at right. Three 

discrete phreatic craters mark foreground peninsula. Blue 

East Mageik Lake is visible at ignimbrite margin in left 

distance, 2 km from seasonally muddy West Mageik Lake 

in foreground. Ignimbrite packages banked against dark 

slopes of glacially scoured lavas of Mount Mageik with 

hardly any run-up. In left background, black cone and lava 

flows that erupted at Southwest Trident in 1953–1974 rise 

above Katmai Pass, 10 km from camera.
Chapter 6. Volcanological Aspects of the Primary Eruption Products 125

Figure 93. Breadcrusted block of sintered, oxidized, vapor-phase indurated bulk ignimbrite ejected by phreatic explosion along 

trough of former Fissure Lake (figs. 92, 94). Shovel is 58 cm long.

pumice-fall deposits, though now widely chaotic, are little 

altered; most are gray or tan, but they locally exhibit red or 

yellow staining caused by diffuse steaming, which was variously promoted by the heat of the pumice deposits themselves 

or that of the Katmai mud layers or the thin ignimbrite veneers 

intercalated near the base of the fall section.

A few kilometers farther east, on lower reaches of Glacier 

3, thin remnants of disrupted ignimbrite are exposed within 

thick fall material chaotically disarrayed by severe wasting of 

the glacier, which had been beheaded by caldera collapse. On 

the cleaver separating Glaciers 3 and 4, ~3 km east and 670 m 

higher than the snout of Glacier 3, a complete fall section has 

three all-rhyolite ignimbrite flow units of Package 1 intercalated within Layer A. Separated by fall intervals, the three 

are successively 30, 60, and 60 cm thick, and all are matrixsupported but fines-poor, perhaps owing to excess gas flux 

during transport over snow and ice. The site, 6 km east and 

500 m higher than the vent rim at Novarupta, was not reached 

by any of the voluminous (but less mobile) ignimbrite currents 

of Phase B—Packages 2 to 9.

Knife Creek Glacier 4 is laterally confined by a pair of 

steep cleavers (fig. 23), the tops of which are, respectively, 5 

km and 7 km from Novarupta. Atop the first (Whiskey Ridge) 

were deposited 4 m of all-rhyolite HEPI and ~1 m of mixed 

HEPI; atop the second cleaver these packages had thinned to 

104 cm and 9 cm, respectively. Both ridgetop deposits are 

~400 m above the VTTS floor and ~200 m above the sloping 

surface of Glacier 4. Upper levels of blast-like pyroclastic 

currents passed over both steep-sided cleavers (fig. 73) and the 

trough-filling glacier between them. On both ridgecrests the 

PDC deposits are overlain directly by Layer C (fig. 42).

Fed from cirques high on Trident, Knife Creek Glaciers 

1 and 2 advanced 250–300 m between 1951 and 1987 (as 

shown by comparing sets of aerial photographs). Fed from 

Mount Katmai, Glacier 4 advanced ~150 m and Glacier 3 

(despite beheading by caldera collapse) ~225 m between 

1951 and 1987. Moreover, examination of a 1919 photograph 

shows that by 1951 Glacier 4 had already advanced 500 m 

and Glacier 5 ~1,300 m (see section below titled “Behavior of 

Ash-covered Glaciers” in chapter 11). Since 1951, however, 

the distal 700 m of Glacier 5 has thinned and stagnated but not 

receded noticeably; any former ice-ignimbrite contact there 

was, in any case, overrun by glacial advance before 1951 or 

masked by alluvium.
126 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

A

A

Figure 94. Floor of Fissure Lake. Views westward along 100-m-wide trough of Fissure Lake: A, 

1917 and B, 1982. Admiring its “clear green water,” Griggs (1922, p. 244) called it “one of the most 

picturesque spots in the whole Valley.” Ignimbrite scarp at right is ~20 m high and was locally still 

steaming in 1917; scarp at left is more than 30 m high. Sediment from the glacier (center distance, 

~1 km from the camera) was already by 1919 filling the lake, which was largely silted in by 1923. 

Later withdrawal of glacier terminus created present-day West Mageik Lake (not in view), which 

now drains north (right) to the River Lethe. Fissure Lake trough then suffered drainage reversal 

(toward West Mageik Lake), permitting incision of a westerly outlet stream to expose ~10 m of ashy 

lake sediment. 1917 photo courtesy of National Geographic Society; 1982 photo by authors.
Chapter 6. Volcanological Aspects of the Primary Eruption Products 127

The termini of Glaciers 1, 2, 3, and 4 have thus all overrun margins of the 1912 ignimbrite sheet. No further changes 

in terminal positions have been noticed since 1987 (Hildreth 

and others, 2003a), but small ones could easily have escaped 

detection. It can be inferred that most of the ignimbrite packages had banked against the first four glaciers and that some 

currents flowed a short distance up their surfaces. Only allrhyolite Package 1, however, was energetic enough to climb 

the glaciers and reach the Trident saddles and the middle 

slopes of Mount Katmai. 

Advance of the glaciers and incision of streams 

along their fronts have removed most evidence for direct 

ignimbrite-ice interaction. At one exposure across the stream 

from the snout of Glacier 3, ~4 m of cross-bedded but poorly 

sorted tuff rich in andesite and dacite pumice rests directly 

upon sintered ignimbrite of Package 8 and probably represents 

pyroclastic-flow material thrown back from the ice front by 

steam blasts. Many phreatic craters were blasted through the 

ignimbrite sheet in the upper Knife Creek arm, a few of them 

close to the glacier termini (Hildreth and Fierstein, 2003); 

because their surge-bedded deposits (discussed in chapter 

10) overlie the dacite pumice falls, however, these explosive 

interactions between meltwater and hot tuff took place at least 

a few days after ignimbrite emplacement.

1

3 2

Figure 95. View eastward across Knife Creek Glaciers 1 (right), 2 (center), and 3 (left), all heavily ash-covered except in upland cirques 

where ice has cleared in a century of accumulation and flow. Glaciers 1 and 2 issue from opposite flanks of East Trident volcano (peak 

6010). Glacier 3 descends trough from skyline saddle, which is caldera rim of Mount Katmai. Twin peaks on center skyline are Peaks 6128 

and 6200 on west rim of caldera. In foreground, undisturbed complete 7-m-thick section of dacite fallout of Episodes II and III overlies ~8 

m of Episode I ignimbrite; same deposits have been chaotically disarranged on glacier surface. Fine-grained ribs of Layers E and H are 

conspicuous in intact fallout remnant. In July 1923, Yori and Fenner contoured across these glaciers at about this elevation to reach Glacier 

3 and Katmai caldera rim, achieving first ascent from VTTS side of Mount Katmai. 
128 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Katmai Project campsite on south bank terrace of Griggs Fork of Knife Creek in 

June 1953. View northward toward Knife Peak (now Mount Griggs). Geological 

parties were based here in 1953 and 1954, supplied by fixed-wing aircraft. Garniss 

Curtis bends over the camp stove. Others standing, from left to right, are John B. 

Lucke (University of Connecticut), bush pilot Schmiel, Howel Williams, and Ronald 

Kistler (Johns Hopkins University). Curtis and Williams were faculty members at 

the University of California at Berkeley, and Kistler soon after became a graduate 

student there. Photo courtesy of Ron Kistler, U.S. Geological Survey.
Chapter 7

Vent Structure at Novarupta

The failure of the first generation of investigators to define 

clearly the source vent for the 1912 pyroclastic deposits is 

attributable to late-stage backfilling of nested vent craters by 

their own ejecta and to poorly developed notions of magma 

storage and pyroclastic eruption. Griggs and Fenner assumed 

incorrectly that most of the fallout came from the summit crater 

of beheaded Mount Katmai, but they did observe that the ignimbrite had not descended from that edifice and inferred correctly 

that it originated in the VTTS. Both were impressed by the valley-filling fumarole field, leading Griggs to postulate a batholith 

beneath the VTTS and Fenner to imagine a rhyolite sill extending under much of the valley. Although both acknowledged 

Novarupta to be one of the chief sites of emission, they thought 

that the swarms of fumarolic fissures throughout the VTTS also 

ascended directly from a subjacent magma body. Even as late 

as 1953, a new generation of observers attributed the ignimbrite 

to fissure swarms at the head of the VTTS, thought to extend 

from the base of Mount Mageik as far as Falling Mountain 

(Williams and others, 1953). An extended field season in 1954 

allowed Curtis (1968) to appreciate the structural significance 

of the fault scarps that surround Novarupta basin and to propose 

that the postulated fissure vents were restricted to that 2-kmwide hollow (fig. 70).

Rather than fissure vents, we envisage an open flaring funnel-shaped vent for the great Episode I outpouring, which released plinian Layers A and B, all of the main 

VTTS ignimbrite, and ~70 percent of the magma erupted in 

1912. A cylindrical vent created by piston-style subsidence 

is very unlikely here because of the small diameter, silo-like 

geometry required, and evidence against a shallow, directly 

subjacent, magma chamber. The presumed vent funnel was 

flared explosively, was backfilled by Episode I ejecta toward 

the close of that episode, was partly reamed out a day later to 

form the smaller nested vent for Episodes II and III, and was 

then concealed deeply by the ejecta of those episodes—Layers 

C through H and the ring of complex proximal deposits that 

encircles the still-later lava dome (fig. 96). 

The rim and steeply inward sloping upper walls of the 

Episode I vent funnel are defined by truncated scarps of Falling 

Mountain, distal Trident lava flows, and southwestern Broken 

Falling Mtn

SW NE

Novarupta Turtle Broken Mtn

Episode II-III

Episode I

Jurassic siltstone

Mesozoic sedimentary rocks

horizontally stratified

Naknek Formation

welded tuff

Knife Creek

Base of Naknek Fm.

fallout

intrusion?

70 ka

dacite dome

500 m

500 m

?

Figure 96. Conceptual cross section, to scale, of Novarupta vent area. Representation is based on surface exposures, geophysical 

interpretations, regional Mesozoic stratigraphy, and estimates of volumes of basement lithic ejecta and recycled welded ejecta. No 

vertical exaggeration.
130 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Mountain (figs. 70, 71). The northeast rim is defined by a set 

of arcuate fissures and a shallow graben that probably reflect 

compaction and welding of the thick multiepisode ejecta blanket 

where it drapes the buried rim (fig. 97). The western rim of the 

funnel is more subtly defined by a gentle monocline that dips 

~5o inward toward Novarupta (fig. 18), probably reflecting differential compaction of the thick vent fill. Just north of Falling 

Mountain, the monocline occupies the topographically lowest 

side of the vent complex, a pre-1912 valley excavated by Pleistocene ice that truncated the southern spurs of Baked Mountain 

and flowed into what is now the Lethe arm of the VTTS. A 

1917 photograph (p. 194 of Griggs, 1922) illustrates abrupt lessening of fumarolic discharge outside the buried west rim, just 

north of the toe of Falling Mountain. The Episode I vent funnel 

is ~2.5 km wide at its ejecta-mantled rim and 1.7-2.0 km wide 

at its present-day floor (fig. 14 of Hildreth, 1983; Wallmann and 

others, 1990).

The truncated wall is best exposed as the shattered 

425-m-high north face of Falling Mountain, where, as recognized by Griggs and Fenner, a large slice of the dacite dome had 

spalled and disappeared into the ignimbrite early in Episode I 

(fig. 71). Frequent rockfalls persisted from the face at least as 

late as 1923 (Fenner, 1938a), inspiring the name of the dome 

(Griggs, 1922). Ample post-1912 talus that accumulated below 

the face includes great blocks that disintegrated into hummocks 

as tall as 12 m, which have repeatedly been mistaken by casual 

observers for independent mini-domes (Hubbard, 1932, p. 90); 

the largest (fig. 55) was already there in 1917. Fumaroles high 

on the face of Falling Mountain persisted until the 1980s, but 

most issued from talus or from the thick sheet of ignimbrite 

draping its east end (fig. 71; also see photo on p. 136 of Griggs, 

1918f) and only a few came from cracks in the dacite lava 

itself. A row of craters and troughs, with 5–8 m of local relief 

and rimmed by crossbedded surge deposits, was excavated by 

phreatic explosions through talus and tuff along the toe of the 

scarp, marking the buried structural margin of the vent funnel 

(see photo-fig. 8 of Fenner, 1925).

The depth of the backfilled Episode I funnel is poorly 

known but can be roughly limited by the volume and types of 

lithic fragments ejected. Episode I deposits are unusually rich 

Figure 97. Aerial view east-northeastward over Novarupta dome and its ejecta ring, which rises to form the Turtle on far side. In 

distance, floor of upper Knife Creek valley lies 4 km from dome. Mutually perpendicular sets of graben cut Episode II fall deposits 

across summit of Turtle, resulting from viscous spreading of thick welded-tuff pile. Beyond Turtle, ~1 km from dome, elongate arcuate 

fissures and graben define outer margin of backfilled vent structure, which is inferred to be funnel-shaped.
Chapter 7. Vent Structure at Novarupta 131

in lithics, dominantly fragments of the sedimentary Naknek 

Formation, with lesser fractions of Trident andesites and Falling Mountain dacites, the three bedrock units truncated by 

Novarupta basin. Layer A contains 9–24 weight percent lithics 

on the mainland, rhyolite HEPI 9–14 weight percent, and allrhyolite VFI 5–15 weight percent. Layer B has 6–17 weight 

percent lithics on the mainland, heterogeneous HEPI 1–16 

weight percent, and the (main) heterogeneous VFI 1–6 weight 

percent (Fierstein and Hildreth, 1992). On Kodiak Island, 

however, Episode I fallout has only ~1 weight percent lithics, 

and the fraction no doubt continues to diminish still farther 

downwind (out to sea). Because the lithics in all these deposits are predominantly Naknek Formation lithologies, derived 

from a well-studied regional formation predicted to extend 

to a depth of ~1,500 m here (Detterman and others, 1996), 

and because Mesozoic formations that regionally underlie the 

Naknek are absent in the 1912 lithic suite, the reamed-out vent 

funnel likely does not extend deeper than 1.5 km (and could 

be much shallower). Sparse granitoid cobbles among the 1912 

ejecta are from conglomerate members of the Naknek Formation, not from any subjacent pluton.

If the volume fraction of lithics were a third of its weight 

fraction in the ejecta, then lithics would make up an average of 

~1 volume percent of all Episode I fallout (8.8 km3

) and heterogeneous VFI (~8 km3

) and ~3 volume percent of all HEPI, 

rhyolite VFI, and concealed proximal VFI (~3 km3). Such 

approximations, based on volume estimates and measured 

lithic fractions (Hildreth, 1987; Fierstein and Hildreth, 1992), 

yield an Episode I lithic volume of only ~0.26 km3, the volume of an inverted cone only 350 m deep, if 1.7 km in diameter at the surface (the floor of Novarupta basin). If, instead, 

the volume fraction of lithics were half its weight fraction 

in the pyroclastic deposits, similar calculations yield a lithic 

volume of ~0.39 km3 and a cone depth of ~500 m. Calculation 

of such modest volumes suggests either strong near-surface 

flaring of a shallow vent funnel above a narrow conduit or a 

much larger proximal fraction of (concealed) lithics. The latter is not observed recycled into the ejecta ring (fig. 98) close 

to the dome nor in the recycled welded-tuff material (figs. 62, 

63, 90) reamed from the Episode I vent fill that dominates the 

lithic fraction in Episode II and III ejecta. 

Rim benches north and south of Novarupta appear to be 

pre-1912 surfaces, ejecta-mantled but little deformed, that 

were sharply truncated by the Episode I eruption. The benches 

are now ~200 m higher than the floor of Novarupta basin west 

of the dome. This 200 m of visible relief could account for 

half of the lithic volume calculated, rendering the apparent 

depth of the backfilled Episode I crater shallower still. 

Gravity and magnetic surveys of Novarupta basin (Goodliffe and others, 1991), tied to a geodetic grid with a 200-m 

spacing, support a strongly flaring, rather shallow backfilled 

crater. The crater is not defined at all by the gravity contours, 

owing in part to the small density contrast between Naknek 

Formation basement and welded vent fill. A subtle gravity low 

(–1 mgal) over the Turtle is likely to reflect the great tephra 

thickness of that asymmetrical pile of ejecta. The buried 

crater is well defined by the magnetic contours, owing to the 

enormous susceptibility contrast between Naknek Formation 

sandstones and welded andesite-dacite ejecta. The magnetic 

contours define a high that dips radially outward on all sides 

of Novarupta basin, reflecting the shallow radially inward dip 

of the base of the high-susceptibility vent-filling ejecta. Lack 

of a magnetic low over the Turtle disproves the hypothesis that 

it is underlain by a siltstone slide mass from adjacent Broken 

Mountain. Three modest magnetic highs (+200 nT) in the vent 

area, notably one located 500 m northeast of the dome and 500 

m south of the Turtle top, are likely to reflect, not cryptic intrusions, but sector-confined emplacement of andesite-rich fallout 

and PDC lobes as well as local variations in degree of welding 

(Fierstein and others, 1997; Houghton and others, 2004).

Compaction and welding of vent-filling ejecta hundreds 

of meters thick provide the best explanation for the fault and 

fissure patterns atop the Turtle as well as for the arcuate graben 

and fissures in the thick Episode II and III deposits rimming 

Novarupta basin (fig. 97). The Turtle is an integral part of 

Novarupta’s ejecta ring (figs. 55, 97), stratigraphically continuous with it but 200 m thicker owing to strong asymmetry 

in accumulation of proximal Episode II and III fallout (fig. 

96). The Turtle is clearly not a structural uplift. The mutually 

perpendicular sets of extensional faults crossing its summit 

probably reflect shallow spreading of the steep-sided 1-km-wide 

mound of ejecta during viscous deformation accompanying the 

welding of its interior (Hildreth, 1983). Although wispy fumaroles and warm ground are still present along some of the Turtle 

faults, the Turtle was never a major focus of fumarolic discharge. Photographs taken in 1917–1919 (Griggs, 1922) show 

only modest emissions on the Turtle (fig. 55A), compared to 

vigorous plumes then issuing nearby, variously from Novarupta, 

its lower ejecta ring, the Falling Mountain scarp, and many of 

the arcuate fractures marginal to the wider depression. Relatively weak fumarolic activity only 5 years after the eruption 

is inconsistent with existence of a cryptic intrusion beneath the 

Turtle (Hildreth, 1983; Goodliffe and others, 1991). 

Within Novarupta basin, extreme variations in conductive and convective heat flow were measured over horizontal 

distances of only a few meters (Ballard and others, 1991), 

and the several surviving warm areas (25o–90oC) are largely 

confined to faults and fractures, as are the areas of former 

acid alteration (Keith, 1991b). Such warm areas dominate 

heat flow in Novarupta basin, and a few still emit near-neutral 

wet steam, weakly from tiny orifices. It is inferred that the 

fractures provide high-permeability pathways that guide 

ascent of water vapor (previously also acid gases), which in 

turn dominates heat transport and arises from depths where 

infiltrating groundwater is heated to boiling by proximity to 

the still-cooling magmatic conduit.

The lithic fractions of Episodes II and III consist predominantly of welded ejecta that had backfilled the wider vent during Episode I (Hildreth, 1987). Fragments range in size from 

centimeters to several meters, in composition from rhyolite 

to andesite, and in texture from dense eutaxite to tack-welded 

pumice agglutinate (figs. 62, 63, 90). Most of the fragments
132 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Figure 98. Stratified fall deposits that form inner south wall of ejecta ring only 25 m from margin of Novarupta 

dome. Section exposed is ~10 m thick, consisting mostly of coarse fall deposits and a few thin fines-rich 

pyroclastic density current (PDC) deposits; juvenile material in all layers is rhyolite-poor and rich in dacite, 

andesite, or both. Lithics are predominantly recycled welded-tuff vitrophyre along with sparse basement 

siltstone and rare fragments of Trident lavas. Section was deposited entirely during Episode III. A few large 

dacite blocks scattered on top surface are part of Episode IV block bed.

are poorly sorted tuff that consists of a variety of juvenile (and 

lesser lithic) components; some are breadcrusted or have prismatic joints, and others have a hackly fracture pattern characteristic of densely welded vitrophyres. Virtually all are glassy, 

and most contain angular to rounded fragments of Episode I 

lithics—andesite, dacite, and Naknek Formation lithologies, 

the last commonly oxidized to brick-red. Although these three 

lithic types are also sparsely present as discrete clasts, the 

rarity of free basement lithics among the Episode II-III ejecta 

shows that these episodes contributed little to further excavation of the bedrock envelope. Their conduits were nested 

well inside the broader backfilled vent for Episode I. Low 

H2O contents of matrix glass in the vitrophyre ejecta (0.2±0.1 

weight percent; Westrich and others, 1991) confirms that 

they consist of material that decompressed to one atmosphere 

before falling back, welding, and being re-ejected.

Residence time of the recycled vent fill was evidently 

long enough for it to weld but too short to devitrify before 

being blasted out during excavation of the smaller nested vent 

for plinian Episode II. It is not known whether the Episode 

II vent was thickly backfilled before plinian Episode III, but 

similar radial distribution of their products does suggest that 

their vent sites were the same. Episode III strata dip radially 

inward and enclose a low-relief moat ~450 m in diameter that 

surrounds the lava dome. The volume of welded recycled 

material for Episodes II and III combined is estimated to be 

~0.05 km3 (Fierstein and Hildreth, 1992). Such a volume 

could represent a 450-m-wide cylinder about 300 m deep, or 

an inverted cone three times as deep, or a geometrically less 

regular structure of intermediate depth.

Asymmetry of the Proximal Ejecta Ring: The Turtle

In the northeast sector of Novarupta basin, the ejecta 

ring surrounding the inner vent plugged by the Novarupta 

dome grades into a northeast-elongate hill of coarse Episode 

III ejecta, 225 m high and 1 km long, first called “the Turtle” 

by Howel Williams in 1953. The hill is cut by sets of mutually perpendicular graben (and other faults) that cross its crest 

(figs. 70, 97). The faults (fig. 99) were fully developed when 

the Turtle was first visited in 1917, and they still influence 

the distribution of wispy fumaroles (as warm as 90oC) today 

(Keith, 1991a, b). Photographs taken in 1917–1919 (Griggs, 

1922) show, however, that the Turtle was not a major focus of 

fumarolic discharge (fig. 55A). Compared to the vigorous 
Chapter 7. Vent Structure at Novarupta 133

plumes then emitted from other nearby sites, emissions atop 

the Turtle were unimportant.

The Turtle is not a structural uplift but, instead, a stratigraphically continuous sector of an extraordinarily asymmetrical ring of ultraproximal ejecta (figs. 55, 97, 98). The ejecta 

ring ranges in exposed height from ~7 m in the southwest 

sector to 225 m in the northeast. Inside the ring, the narrow 

moat surrounding the dome is inferred to represent the vent 

active during Episodes II and III. On the Turtle itself, erosive 

incision is minimal and only the last few proximal fall layers of Episode III are exposed, including fine-grained Layer 

H, which caps the fallout sequence. However, outer fringes 

of the ejecta ring are seen to rest on a thin andesite-bearing 

ignimbrite equivalent to the ashy parting between plinian Layers C and D (Fierstein and others, 1997; Houghton and others, 

2004). Most or all of the ring deposits therefore accumulated 

during the last full day of the explosive sequence (the latter 

half of Episode II and all of Episode III), and they consist of 

the proximal facies of regional Layers D, F, and G, along with 

ultraproximal intercalations of several sector-confined fall 

beds and pyroclastic density current deposits (summarized on 

p. 104-105 of Houghton and others, 2004).

Why the overthickening should here be so asymmetrical 

and why such asymmetrical deposition should have been 

sustained toward the northeast sector for ~24 hours remains 

uncertain. Overthickening of ultraproximal (but nonballistic) pumice deposits may generally be attributable to (1) 

vortices in the emerging jet; (2) inefficient reentrainment of 

ejecta released from greater heights and swept inward by 

surrounding air drawn toward the buoyant convective plume; 

(3) roughness of conduit walls, decelerating margins of the 

emerging jet; and (4) excess andesite and lithics partitioned 

into a boundary layer around the core of the jet. The last 

two could create an unstable collar of low-fountaining ejecta 

marginal to the higher-velocity core feeding the plinian 

column (fig. 53). Such peripheral fountaining evidently produced the several sector-confined, locally dispersed fallout 

lobes and small pyroclastic density current deposits (mostly 

andesite-enriched) close to Novarupta (Fierstein and others, 

1997; Houghton and others, 2004). 

There are at least two components to the northeastward 

overthickening of the ring around Novarupta: (1) In contrast 

to southeastward dispersal of all the earlier regional fall 

units, isopachs for Layers F and G exhibit a lobate bulge to 

the northeast (Fierstein and Hildreth, 1992), and (2) intercalated, locally dispersed, fall and flow units are more numerous to the northeast and tend to be thicker in that direction 

(Houghton and others, 2004). Factors that might have 

contributed to asymmetry of the ring deposits include: (1) 

Low-altitude winds drawn into the base of the convecting 

column preferentially from the Lethe arm and Katmai Pass 

on the wide-open southwestern side of Novarupta basin (fig. 

18), potentially resulting in (2) slight bending of the plume 

and preferential sedimentation from the lower northeast 

part of the column; (3) asymmetry of the flaring vent funnel, distorting axisymmetrical emergence of the jet; and (4) 

asymmetrical semiannular distribution of andesite magma 

in the conduit during flow that was otherwise dominated by 

dacite magma during Episodes II and III. A strongly asymmetrical ultraproximal deposit was also produced by the 

plinian rhyodacite eruption of Quizapu in 1932 (Hildreth 

and Drake, 1992), but there a compositionally contrasting 

component like the andesite at Novarupta is not conspicuous 

in the main-stage crater-rim deposit.

It has occasionally been suggested that the Turtle might 

be a displaced slump block of Broken Mountain basement 

draped by 1912 ejecta. This idea may well have inspired the 

name Broken Mountain, and it is clear that Griggs (1922, 

p. 244) intended the name to include both hills. However, 

there is no amphitheater-like scarp on Broken Mountain that 

could be the source of a 1-km-long block. Although blanketed by ejecta, the south face of Broken Mountain, which 

rises more than 600 m above the saddle separating it from the 

Turtle, appears to have been sculpted by glacial erosion in 

the same manner as adjacent Baked Mountain and the other 

sides of Broken Mountain. Moreover, a Bouguer anomaly 

map (Goodliffe and others, 1991) shows a weak gravity low 

(–1 mgal) over the Turtle, more likely to reflect the thick pile 

of low-density tephra (1,000–2,000 kg/m3

) near the surface 

there than a slide block of basement siltstone (2,500–2,600 kg/

m3). Absence of a magnetic low over the Turtle (Goodliffe 

and others, 1991) casts severe doubt on the hypothesis that it 

is underlain by a slide mass of Naknek Formation siltstone (of 

low magnetic susceptibility: ~1.1x10-3 SI units) surrounded by 

andesite-rich 1912 ejecta (14-30x10-3 SI units).

Another idea advanced by Goodliffe and others (1991) 

was that a shallow cryptodome was emplaced beneath the 

Turtle after the ejecta had accumulated. Their speculation 

was based on magnetic data, but in fact their magnetic contours run parallel and undeflected across most of the Turtle. 

They identified three modest magnetic highs (+200 nT) 

within Novarupta basin, the closest of which is centered 125 

m lower and 500 m south of the top of the Turtle. Rather 

than intrusions, the highs are likely to reflect the concentration of proximal fall and flow lobes in the northeast sector 

that are rich in andesite (30x10-3 SI units) as well as local 

variations in degree of welding (Fierstein and others, 1997; 

Houghton and others, 2004). The sets of extensional faults 

crossing the summit of the Turtle (fig. 97) probably reflect 

shallow spreading of the steep-sided mound of ejecta during 

viscous deformation accompanying the welding of its interior 

(Hildreth, 1983). Some of the faults continue well beyond 

the Turtle to the east margin of the vent funnel, where they 

likewise represent extensional spreading in vent fill that was 

compacting and welding where it drapes the rim. The fault 

displacements atop the Turtle (fig. 99) range from <1 m to 

~20 m, fairly modest had a cryptodome caused the extension. 

Finally, the rather subdued fumarolic activity on the Turtle 

only 5 years after the eruption, compared to the abundant 

high-temperatures plumes all around it, is more consistent 

with a thick impermeable lens of welded tuff than with a 

cryptodome intruding a shallowly flaring vent funnel.
134 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

A

Figure 99. Extensional faults atop the Turtle. Views toward northwest along southern set of northweststriking faults near crest of the Turtle, ~1 km northeast of Novarupta dome: A, 1919 and B, 1982. Taken from 

near intersection with northeast-striking fault set (see fig. 97). Lower scarp represents ~3 m displacement, 

upper scarp ~20 m. Dacite-dominant pumice fall exposed is proximal deposit of Episode III, locally capped 

by a thin remnant of fine-grained Layer H. Degradation of scarps by 1982 reflects 63 years of sloughing 

induced by wind and snowmelt. For a profile perpendicular to these scarps, see figure 6 of Fierstein and 

others (1997). 1919 photo courtesy of National Geographic Society; 1982 photo by authors.

A

B
Chapter 8

Caldera Collapse and Seismicity

Collapse of the summit of Mount Katmai during the 

eruption at Novarupta was one of the few caldera-forming 

events of the scientific age. Owing, however, to syneruptive and summer-long ash clouds, lack of nearby observers, 

and the obstructed perspectives of remote observers, no one 

witnessed the collapse. During the summer investigations of 

1912 and 1913, Mount Katmai was obscured in cloud, so the 

first record of its beheaded summit is Griggs’ photograph of 

July 1915 (fig. 100A). Nonetheless, study of circum-caldera 

deposits intercalated with Novarupta pumice-fall layers (Hildreth, 1991) and analysis of the seismic record for June 1912 

(Abe, 1992) together permit a fairly good reconstruction of 

the fitful collapse sequence (Hildreth and Fierstein, 2000).

Before 1912, the Katmai edifice was a compound 

stratovolcano that consisted of two large contiguous cones 

(fig. 5), both beheaded by the caldera collapse (fig. 101). On 

the caldera walls are exposed separate foci of hydrothermal 

alteration and abutting stacks of lavas and ejecta that dip 

toward each other from discrete northeast and southwest 

centers. A coastal survey in 1908 (Griggs, 1922, p. 270–275) 

sketched four summits (fig. 102), three of which were lost 

in 1912. The westernmost of the four survived the collapse 

and forms present-day twin peaks 6128 and 6200. These rise 

above the western edge of a marginally preserved remnant 

of a pre-1912 filled crater of the southwest cone; the eastern 

margin of that crater apparently included the main summit, 

former peak 7500. The two other pre-1912 summits (peaks 

7360 and 7260; fig. 102) belonged to the northeast cone and 

were probably high points on the rim of its summit crater, 

now wholly destroyed. 

Katmai caldera, described by Griggs (1922), Fenner 

(1930), Hildreth (1983, 1991), and Hildreth and Fierstein 

(2000, 2003) has an area of 4 km2

 at the floor and 8.8 km2 at 

the rim. Its floor lay at an elevation ~990 m in 1916, and its 

jagged rim has a highest elevation of 2,047 m and a lowest 

of about 1,488 m. Caldera walls exposed above lake level 

generally have average inward slopes of 52o–62o, interrupted 

by slump-block benches in two sectors and by a 35o chute in a 

western scallop, which alone provides (hazardous) foot access 

to the lakeshore (fig. 103). Internal volume of the caldera is 

today about 4 km3

, and the foundered superstructure amounted 

to an additional 1.1 to 1.5 km3, giving a total collapse volume 

of ~5 to 5.5 km3. The Horseshoe Island dome and numerous 

fumaroles on the caldera floor (Fenner, 1930) were by 1929 

covered by rising lakewater, which is now deeper than 200 m 

and more than 1 km3 in volume. 

Seismicity Accompanying the 1912 Eruption

There were no seismic instruments within 1,000 km of 

Katmai in 1912. Abe (1992), however, studied the records of 

about 40 seismological stations worldwide and was able to 

assign magnitudes to 50 earthquakes associated with the eruption. Of these 50 shocks, 33 had surface-wave magnitudes 

(Ms) greater than 5.5, and 14 were in the range Ms 6.0 to 7.0. 

A plot of Ms vs cumulative frequency for the sequence (fig. 8 

of Abe, 1992) shows a deficiency of recorded events smaller 

than Ms 5.5 and suggests that there could actually have been 

as many as 100 Katmai earthquakes with Ms ≥ 5.0. If so, 

about half either failed to register on 1912 instruments or did 

not meet Abe’s selection criteria.

Many precursory earthquakes were said to have been felt 

locally for at least 5 days before the eruption (Martin, 1913; 

Fenner, 1925), but none of them were recorded instrumentally. 

Similarly, following the eruption, although shocks were felt (at 

a village 60 km southwest of the caldera) on 50 of the next 70 

days (Martin, 1913, p. 158), Abe’s search detected only two 

Katmai earthquakes later than 10 June and none after 17 June. 

Since the detection threshold of the station at Victoria, B.C., was 

about Ms 5.0 (Abe, 1992), the absence of an instrumental record 

of the precursory and posteruptive felt seismicity suggests that 

all such earthquakes were of lesser magnitude. (Because large 

events so dominate the total energy released, an additional 

50 earthquakes of Ms~5.0 would add only 0.22 percent to the 

cumulative energy of the 1912 seismic sequence.)

Figures 60 and 104 show the sequence of earthquakes 

evaluated by Abe in relation to our analysis of the eruptive 

sequence. The first of the 50 instrumentally recorded earthquakes (Ms 5.4) took place at 0508 (local time) on 6 June, 

about 8 hours before the plinian eruption began. Seven additional shocks (Ms 4.8 to 5.5) were recorded during the next 7.5 

hours, before the first sighting of the plinian column at about 

1300. During the opening 10 hours of the eruption, eight more 

shocks (Ms 4.8 to 5.6) were recorded, culminating in the 11th 

hour with the first major seismic event (Ms 6.5) at 2356 on 6 

June. This event may have signalled the first strong pulse of 

caldera collapse, which was probably associated with ejection 
136 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives A

Figure 100. Mount Katmai beheaded. Views northward from alluvial floodplain 11 km south (1915) and 13 km southsouthwest (1989) of caldera rim. Rhyodacite crag in south rim notch at center; Peak 6200 on west rim at left. A, 1915 

photo was taken from Katmai River floodplain, ~2 km east-northeast of B, 1989 photo site on Mageik Creek alluvial 

fan. Ghost forests have today largely been destroyed by aggrading gravels of both streams. 1915 photo courtesy of 

National Geographic Society; 1989 photo by authors.

A

B
Chapter 8. Caldera Collapse and Seismicity 137

Figure 101. Southwestward aerial view of Mount Katmai caldera with ignimbrite-filled upper VTTS at 

right. Snow patch on wall across lake is where Yori and Fenner descended to caldera floor from west 

notch in 1923. Lake level is ~250 m above 1912 caldera floor, but sedimentation may have reduced 

present water depth to ~200 m. West wall now rises as little as 275 m above lake, whereas northeast wall 

(hidden by summit ridge at right) is ~800 m high. Several small glaciers still drape outer slopes despite 

loss of summit in 1912. Ice shelf on southwest rim predates caldera, but it took decades for its narrow 

ice appendage to extend down west wall. Beyond caldera, two tongues of Pacific sea fog are about to 

envelop Trident group, the more distant tongue invading Katmai Pass at toe of iceclad Mount Mageik.

of the first phreatic mud layer from Mount Katmai (intercalated in the Novarupta fallout at the B2

/B3 boundary; fig. 60). 

Moreover, the debris avalanches described by Griggs (1922) at 

Katmai Canyon, Noisy Mountain, and Martin Creek (“Mageik 

Landslide”) all broke loose about this hour, as each deposit is 

draped directly by all or part of Layer B (see section below 

titled “Syneruptive Landslides” in chapter 10. About 8.5 km3

of magma had by then been released at Novarupta (Fierstein 

and Hildreth, 1992), so, if our correlation is correct, it indicates an average magma discharge rate of ~5 x 108 kg/s (8.5 

km3 x 2,400 kg/m3 x 11 h-1) for the initial 11 hours leading up 

to the onset of major collapse-related seismicity.

Soon after the Ms 6.5 event at 2356, three more major 

shocks took place early on 7 June (Ms 6.3 at 0035, Ms 6.1 

at 0223, and Ms 6.5 at 0825). The seismic energy released 

during this 8.5-hour interval amounted to 10.2 percent of the 

total for the 50-event 11-day series (fig. 104). After 0825 on 7 

June there was a 6.5-hour interval marked by four earthquakes 

of Ms ≥ 5.1 but none greater than Ms 5.6. This interval of 

lesser seismic-energy release ended with a Ms 5.8 event at 

1457, opening a remarkable 6-hour series of earthquakes of 

magnitudes 5.8, 5.7, 5.8, 5.9, 5.4, 5.8, 5.7, 6.0, 5.8, and 6.3 (at 

2049), culminating with a 7.0 at 2136. This powerful event 

was succeeded an hour later by a magnitude 6.8 earthquake (at 

2248 on 7 June), followed by events of Ms 6.2 at 0029 and 6.6 

at 0300 (8 June). The five big earthquakes between 2049 and 

0300 on the night of 7–8 June account for 61.3 percent of the 

cumulative seismic energy released by the 11-day series (fig. 

104), the Ms 7.0 shock alone representing 37.4 percent of the 

total seismic energy. Much of the structural collapse of Mount 

Katmai probably took place during these hours.

Surprisingly quiet by contrast, a 28-hour seismic respite 

(interrupted by modest shocks of Ms 5.4 at 2057, 5.1 at 2045, 

and 5.6 at 2241) ensued from 0300 on 8 June until 0714 on 

9 June, when the “lull” was broken by another Ms 6.0 event. 

This was followed by another extended interval of relatively 

low seismic-energy release, 23 hours long and marked by only 

four recorded earthquakes (Ms 4.8 to 5.7), that ended with a 

magnitude 6.9 shock at 0606 on 10 June. 

This earthquake, second largest of the entire series, took 

place 24-30 hours after the main eruptive activity ceased. Relocated by Abe (1992; p. 177) about 12 km west of Mount Katmai 

(apparently near Novarupta if located accurately), this major 

shock could conceivably have reflected posteruptive failure of a 

distal part of the plumbing system or (less likely) fault dislocation of vent fill around Novarupta, instead of additional caldera 

subsidence at Mount Katmai. The faults atop the Turtle 0.7–1 

km northeast of Novarupta have vertical displacements as great 

as 20 m (fig. 99; also Griggs, 1922, p. 244; Fenner, 1925, p. 

203). The seismic moment (Mo) implied by a Ms 6.9 earthquake demands, however, that the rupture surface area or the 

vertical displacement have been at least an order of magnitude 
138 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

X X X

7260

7360

7500

6000

5000

5000

4000

4000

3000

3000

6250

3260

6715

6128

6200 6000

Elevations in feet 0 5 KILOMETERS

1908 USCGS 1951 USGS

Figure 102. Mount Katmai before and after the caldera collapse of 1912. Left panel is adapted from Coast Survey 

Chart 8555 (U.S. Coast and Geodetic Survey, 1908; also reproduced by Griggs, 1922, and Fenner, 1923); summit 

elevations were triangulated from the coast 25–42 km south of Mount Katmai, and contours were apparently 

sketched visually with little additional control. Right panel is adapted (for the same area at the same scale) 

from U.S. Geological Survey quadrangles Mt. Katmai A–3, A–4, B–3, and B–4 (1:63,360 series, 1951), which were 

prepared by photogrammetric methods from aerial photographs taken in 1951. Elevations in feet. Horseshoe 

Island dacite dome, on sublacustrine caldera floor at an elevation of about 3,260 feet, is now covered by as much 

as 820 feet (250 m) of sediment and still-deepening lakewater.

Figure 103. Aerial view 

northwestward over Katmai caldera 

and down ignimbrite-filled VTTS, 

terminus of which is 29 km from 

center of caldera. Muddy deposit 

mantling shelf on northwest rim 

consists of caldera-collapse 

phreatic ejecta and ablation 

diamict left by beheaded glacier 

that has receded >500 m from rim 

since 1912. Narrow intracaldera 

glacier draping west wall (at left) 

and glacier that mantles slumpblock bench at base of north wall 

(at right) both originated in 1920s. 

Isolated snow shelf just right 

of narrow glacial tongue marks 

descent route from west rim notch 

taken by Yori, Fenner, and Motyka.
Chapter 8. Caldera Collapse and Seismicity 139

Cumulative seismic energy, in joules

Date

+

+

+

+

++ ++ +++ ++

+++ + ++ + +

+

++

+

++

+++

++

+

2 x 1013 J

FERNANDINA

6.2 X 1013 J

PINATUBO

KATMAI

1,575 x 1013 J

DAY 1 2 3 4 5 6 7 8 9 10 11 12

Katmai: June 6 7 8 9 10 11 12 13 14 15 16 17

Pinatubo: June 15 16 17 18 19

Fernandina: June 12 13 14 15 16 17 18 19 20 21 22 23

1012

1013

1014

1015

1016

M5.1

M5.2

M5.0

M5.0M5.1 M5.0 M5.1

M5.1 M5.5

M5.7

18 events (M4.5-5.0)

M5.7

M5.5

M5.5

M6.5

M6.5

M6.3

M7.0

M6.8

M6.6 M6.9 M6.1 M6.2

13 events (M5.1-6.0)

Figure 104. Cumulative seismic energy release (in Joules) during June earthquake sequences accompanying 

caldera collapse at Katmai in 1912, Pinatubo in 1991, and Fernandina in 1968. Note log scale. Energy for each 

event recalculated by revised energy-magnitude relation of Kanamori and others (1993) as employed by Mori 

and others (1996). Data from Abe (1992), Scott and others (1996), and Filson and others (1973). Sequence of 

Katmai earthquakes (with magnitudes shown here) is plotted relative to eruptive sequence in figure 60.

greater than discernible for any posteruptive faults within or 

surrounding the Novarupta depression (fig. 70). The event is 

likely to have taken place at Mount Katmai or elsewhere in the 

plumbing system.

Unlocated adjustments in the vent, caldera, caldera-fill, or 

magma-storage and plumbing systems continued for more than 

two months, as recorded by a magnitude 6.1 earthquake at 2104 

on 11 June, a magnitude 6.2 earthquake at 0128 on 17 June, and 

an abundance of felt seismicity (not recorded instrumentally) 

that persisted at least through mid-August (Martin, 1913).

Comparison with Other Seismically Recorded 

Caldera Collapses

Figure 104 illustrates the earthquake sequences for the 

three caldera-forming eruptions for which adequate seismic records exist. Table 2 of Hildreth and Fierstein (2000) 

summarizes comparative volcanological and seismological 

data for the three eruptions, collapses, and their host edifices. 

Although the volume collapsed and the volume of magma 

erupted at Katmai were each only about twice as large as at 

Mount Pinatubo (Philippines) in 1991, the cumulative seismic 

energy released at Katmai was 250 times greater. No fewer than 

24 Katmai earthquakes were as large or larger than the greatest shock at Pinatubo (magnitude 5.7). Likewise, during the 

1968 caldera subsidence at Isla Fernandina (Galápagos Islands), 

which was similar to Pinatubo in volume collapsed, more than 

600 earthquakes were assigned magnitudes (Filson and others, 

1973), but none was larger than Ms 5.2, and the total seismic 

energy released was 800 times smaller than at Katmai. What 

factors can explain such discrepancies?

In attempting to account for the far greater seismic energy 

released during the collapse at Mount Katmai, factors to consider logically include the structure and strength of the precaldera volcanic edifice, the location, depth, and configuration of 

the magma reservoir, the conduit geometry and flux of magma 

removal, and perhaps the viscosity and volatile content of the 
140 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

0 2 4 6 8 10 12

4 2 25

20

15

10

5

20

15

10

5

0

Distance southeast of Novarupta, in kilometers

Maximum size of lithics, in centimeters

Novarupta

Katmai

Caldera

(to

50 cm)

Novarupta

Lithics

Katmai

Lithics

A

D

G

F

B

C

Kilometers from

caldera rim Figure 105. Variation with 

distance from source of average 

maximum sizes of lithic fragments 

expelled concurrently from vents 

at Novarupta and Mount Katmai. 

The hydrothermal/phreatic mud 

layers that contain Katmai-derived 

lithics were expelled during caldera 

collapse and intercalated within 

sequence of Novarupta-derived 

pumice-fall layers (A–G). “Maximum 

size of lithics” is average of three 

axes of five largest lithic clasts at 

each station. Katmai data are largely 

from south and southwest slopes of 

Mount Katmai edifice.

magmas. At Fernandina, as at Mount Katmai, magma was 

withdrawn from beneath the collapsing edifice rather than erupting through it, but the Fernandina magma was basaltic and the 

edifice a basaltic shield (Simkin and Howard, 1970). At Pinatubo, however, the climactic eruption issued from vents at the 

site of caldera collapse, expelled predominantly dacitic magma, 

and took place at a long-lived andesite-dacite stratovolcano 

(and dome complex) somewhat larger than Mount Katmai and 

marked by numerous ignimbrite-forming eruptions in the past 

~35 kyr (Newhall and others, 1996). 

Because the volumes of collapse differ by at most a factor of three and the bulk densities of collapsed material are 

unlikely to differ substantially, we speculate that the following factors were implicated in producing the seismic-energy 

discrepancy. (1) In contrast to Pinatubo and Fernandina, both 

of which had older calderas, Mount Katmai lacked preexisting 

caldera faults and shear zones, requiring that all breakage be 

new. Many earthquakes may have taken place on older faults 

at Pinatubo and Fernandina. (2) Subsidence may have been 

buffered at Pinatubo by buoyant viscous magma vesiculating 

and rushing upward to escape at fissure vents surrounding or 

within the foundering block. To the extent that the cauldron 

block was broken up and the subsidence piecemeal, such 

cushioning might have been still more effective in limiting 

the seismic energy generated. At Katmai (and Fernandina), 

because the magma was withdrawn from below, no such 

subsidence-opposing magma flow took place. At Katmai there 

were no magmatic ring dikes serving to lessen friction around 

the subsiding cauldron block. (3) At Katmai, about 8.5 km3 of 

magma had erupted before the first cluster of large earthquakes 

(Ms > 6) 11–13 hours into the eruption, and nearly 12 km3 had 

been released by the time of the second major cluster 32–38 

hours after the eruption started (fig. 104). The strength of the 

previously unfaulted Katmai edifice may have permitted greater 

stress accumulation during withdrawal of magmatic support, 

resulting in individually greater stepwise vertical dislocations 

of the ultimately collapsing block(s) and, accordingly, fewer but 

larger earthquakes than at the already faulted Pinatubo and Fernandina edifices. Moreover, the horizontally layered Mesozoic 

siltstones and sandstones, at least 5 km thick beneath Mount 

Katmai (Detterman and others, 1996), could have contributed to 

greater average stress drops for each event by initially bending 

(with interbed slip, phonebook-like) before finally breaking. (4) 

The high-silica rhyolite magma that dominated the 1912 eruption, probably at least as viscous as crystal-rich Pinatubo dacite, 

certainly more so than Fernandina basalt, and proportionately 

more retentive of the excess volume contributed by vesiculation, 

may have played a role in slowing magma transfer within the 

plumbing system and slowing withdrawal of support, thereby 

contributing to the stress accumulation and overstepping that 

resulted in larger individual dislocations.

At Katmai in 1912, seismic-energy release was concentrated into a few short intervals (fig. 104), reflecting principally 

the distribution of the few Ms 6.5–7.0 earthquakes. The three 

largest earthquakes alone accounted for 76.5 percent of the total 

seismic energy released: The Ms 7.0 shock in the 33rd hour of 

the eruption contributed 37.4 percent of the cumulative seismic 

energy, the Ms 6.8 event 72 minutes later about 15.2 percent, 

and the Ms 6.9 event on 10 June about 23.8 percent. By comparison, the largest earthquake at Fernandina (Ms 5.2) contributed only 8.9 percent of the total seismic energy for the swarm, 

and the largest at Pinatubo (Ms 5.7) about 27.1 percent. 
Chapter 8. Caldera Collapse and Seismicity 141

Figure 106. Hydrothermal explosion breccia as thick as 12 m on 

northwest rim of Katmai caldera. Ice axe (lower right) is 81 cm 

long. Derived from altered zones inside Mount Katmai edifice, 

material was ejected at onset of caldera collapse, thought to 

coincide with first major seismic event (M 6.5) in 11th hour of 

eruption. Deposit rests on 1.5 m of Novarupta plinian pumice fall 

(Layers A through B2

), which in turn rested on glacial ice, which 

has since melted (fig. 107).

Three main intervals of seismic activity at Katmai produced 

95.3 percent of the total seismic energy. (1) Between 2356 

and 0825 on the first night (11 to 19.5 hours into the eruption), 

10.2 percent was released. (2) Between 2049 and 0300 on the 

second night (32 to 38 hours into the eruption), 61.3 percent was 

released. And (3) the lone shock (Ms 6.9) at 0606 on 10 June (89 

hours after the eruption began and 24–30 hours after it ended) 

produced 23.8 percent. Hildreth and Fierstein (2000) further 

elaborated the timing of seismic-energy release as spread over 

the multiday earthquake sequences, and their figure 7 shows 

the percentages of total seismic energy released for successive 

4-hour intervals during the three caldera subsidences.

As discussed by Abe (1992), the total moment estimated 

from the collapse geometry of Katmai caldera can be approximated as Mo=mDV. Taking DV=5.0–5.5 km3

 as the caldera 

volume displaced and taking m, the shear modulus for shallow 

events, to be 3x1010 N/m2, then S Mo= 1.5–1.65x1020 Nm, a 

satisfactory approximation to the cumulative seismic moment, 

1.4x1020 Nm, estimated from the magnitudes of the 50 Katmai 

earthquakes interpreted. There is thus no need to invoke major 

additional release of seismic energy or large displacements 

elsewhere in the plumbing system or at Novarupta. The cumulative seismic moment for the Fernandina collapse was roughly 

equivalent to that of a single earthquake of M 5.9, the Pinatubo 

seismic sequence to one of M 6.2, and the 1912 sequence at 

Katmai to one of M 7.4.

Hydrothermal Explosion Breccia and 

Phreatically Ejected Mud Layers

On and near the caldera rim at Mount Katmai, several 

layers of massive, poorly sorted, unconsolidated “mud,” studded with Katmai-derived lithic fragments, were ejected by 

phreatic-hydrothermal explosions during caldera collapse and 

intercalated within the sequence of widespread plinian fallout 

layers from Novarupta (Hildreth, 1991). No juvenile material 

has been recognized in the Katmai-derived mud layers, which 

thin from 10–200 cm near the rim to ≤1 cm at radial distances 

of 5–8 km from the rim. In contrast, the pumiceous plinian 

layers (A through G) thicken and coarsen toward Novarupta, 

away from Mount Katmai (fig. 105). We call them “mud layers” because under conditions prevailing at Mount Katmai these 

fines-rich deposits are always wet (or frozen), even gooey, and 

contain a hydrothermal clay component that imparts a faintly 

sulfurous odor. They are best exposed on the southern slopes of 

Trident and Mount Katmai, but a few intact remnants have been 

identified on and adjacent to the glaciers west of the caldera. 

Abundant crystals and centimeter-scale lithics occur within the 

dominant muddy matrix, and sparser large lithics (as big as 17 

cm, as far as 5.8 km from the rim) were probably emplaced 

ballistically (Hildreth, 1991). The several mud layers identified 

are interpreted as a series of explosive ejection events released 

by unloading the hydrothermal system inside the cone during 

stepwise caldera collapse.

The first (and most voluminous) of the Katmai-derived 

mud layers lies between Novarupta plinian layers B2

 and 

B3, providing the earliest evidence for onset of caldera collapse. The chronology of fallout reported at Kodiak (Martin, 

1913) and of seismicity reevaluated by Abe (1991) supports 

correlation of this stratigraphic horizon with the first major

syneruptive earthquake (Ms 6.5), at 2356 h on 6 June, 11 

hours into the eruption (fig. 60). By that time, ~8.5 km3 of 

magma had vented at Novarupta, suggesting an average mass 

eruption rate of ~5x108

 kg/s for the first 11 hours. Some 

or all of this had been withdrawn from beneath the Katmai 

edifice, which then began to collapse. 

Two mud layers near the B2–B3 contact are each a few centimeters thick on lower southern slopes (where the upper one 
142 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

S T A G N A N T I C E

A

B

CD

FG

Dacite

NW SE

Fallout

Complex “H” muds

Grey mud

Blue grey mud Graded 

hydrothermal

explosion breccia

Ablation

rubble

Caldera

Rim

Rhyolite

Fallout

KATMAI

5 m dacites +

andesites

contains accretionary lapilli), but they thicken and merge into a 

common layer 0.5–2 m thick where it overlies a breccia sheet 

(described next) on the west rim. This mud layer is 65–85 cm 

thick on a 4,600-ft lava-flow shelf ~2.5 km west of the rim. A 

thin mud layer is locally present at the B3–C contact, and as 

many as eight mud layers (each 3–30 cm thick) are intercalated 

within the dacite pumice-fall sequence near the caldera rim. The 

thickest of these is within Layer F, where its thickness is 30–80 

cm on the south rim, 14–45 cm near the west rim, and 6 cm on 

the 4,600-ft western shelf. At least three more mud layers, rich 

in sand and granules, are intercalated around the rim near the 

top of Layer G and within what appears to be an extraordinarily 

thick (~3 m) accumulation of Layer H. Capping the 1912 section, this near-rim fines-rich accumulation is apparently composite, consisting in part of Novarupta-derived vitric ash (normal 

Layer H), in part of contributions from continuing phreatic 

outbursts, and in part of deposits from dustclouds attending 

caldera collapse and continuing slumps and rockfalls. No ashfall 

layer has been identified that might correlate with eruption of the 

Horseshoe Island dacite dome on the caldera floor.

A wedge of coarse yellow-brown breccia as thick as 12 

m is widespread on the caldera’s northwest rim (fig. 106). It 

directly underlies the B2

/B3 mud layer, which is here 0.5–2 m 

thick, though only 22 cm thick on the south rim. Confined to 

a 20-degree sector, the breccia was deposited atop ~1.5 m of 

plinian fallout (Layers A through B2), which in turn rests on 

glacial ice that has since wasted away owing to destruction 

of its accumulation area by caldera collapse (fig. 107). Intact 

fallout sections have nonetheless survived disruption atop a 

few unmelted seracs. The breccia sheet thins westward across 

hummocky ablating ice and disappears about 800 m from the 

rim, where the glacial ice is still mobile.

Fragments in the breccia are angular to subrounded, as 

large as ~1 m, and include ~10 percent fresh (basaltic, andesitic, and dacitic) Katmai lavas. Most clasts, however, are 

hydrothermally altered lavas and tuffs, some of which contain 

disseminated sulfides. Identified by x-ray diffraction in the few 

clasts sampled were smectite, gypsum, albite, pyrite, hematite, 

magnetite, cristobalite, and chalcedony. Oxidized fracture films 

and rinds on both (internally) fresh and grey-to-black sulfidebearing clasts attest to hot emplacement and subsequent steaming. A few hydrothermally altered blocks developed prismatic 

joints after emplacement of the breccia. Neither nonvolcanic 

nor juvenile clasts have been observed in it. The breccia deposit 

is unconsolidated, poorly sorted, and unstratified,; where thickest, it fines upward from >10 m of coarse clast-supported breccia (with <10 percent sandy-muddy matrix) through ~0.5 m of 

matrix-supported breccia into 0.5–2 m of blue-grey lithic-poor 

mud, which is overlain by Novarupta Layers C–H. The coarse 

zone thins to <1 m within 250 m northwest of the rim, but the 

associated mud layer extends radially as far as 8 km. Several 

kilometer-scale zones of hydrothermal alteration on the caldera 

walls extend beneath present lake level, had precollapse vertical 

dimensions greater than 500 m, and are an obvious source for 

the hydrothermal explosion breccia. Depressurization of an 

active hydrothermal system within the Katmai edifice where it 

was displaced abruptly along caldera faults caused explosive 

ejection of a relatively small fraction of the collapsing mass. 

Figure 107. Sketch of stratigraphic relations on northwest rim of Katmai caldera, showing breccia 

(fig. 106) and mud layers expelled during caldera collapse and intercalated within the regional 

pumice-fall sequence from Novarupta. Deposited upon a glacier that was beheaded by collapse, 

section has been widely disrupted by a century of ablation of subjacent ice, margin of which has 

locally receded as much as 500 m from rim.
Chapter 9. The Ten Thousand Smokes 143

Chapter 9

The Ten Thousand Smokes

The VTTS was discovered by Griggs in 1916, who then 

named it the “Valley of Ten Thousand Smokes” for its myriad 

fumarolic plumes (fig. 108), among which he estimated 1,000 

to be more than 500 feet high. He also observed fumaroles in 

Katmai Pass but reported none still active in the thin ignimbrite tongue farther south along Mageik Creek. During the 

1917 expedition, the first to actually study the VTTS, Shipley 

(1920) noted fissural and point-focused orifices over the entire 

ignimbrite, but he also stressed ubiquitous diffuse steam emanations from surfaces with no visible orifices. Pits dug into 

cold surfaces everywhere reached boiling-point temperature 

(~97oC) within 1 m. Shipley observed that some fumaroles 

were largely water vapor, but many others consisted of acid 

gases rich in Cl, F, and S, and he was first to study the mineralogy and composition of the fumarolic incrustations. During 

the 1919 expedition, Allen and Zies made extensive collections of the acid gases and the incrustations (Allen and Zies, 

1923; Zies, 1924a, b; 1929).

In 1918, temperatures greater than 190oC were measured 

for 86 vents (Sayre and Hagelbarger, 1919), the hottest found 

being 432oC in the central VTTS. In 1919, 54 vents were 

found hotter than 200oC, of which 11 were in the range 400-

645oC (Allen and Zies, 1923). In the lower VTTS near Three 

Forks, the hottest was 274oC, while in the upper VTTS fumarole temperatures were as high as 397oC in the Lethe arm and 

438oC in the Knife Creek arm. Some were as hot as 403oC 

near Novarupta but no hotter than 260oC on the faulted top of 

the Turtle. None were measured on the forbiddingly steaming 

Novarupta lava dome itself. Highest temperatures measured 

were again in the central VTTS, 1–3 km north of the noses of 

Baked and Broken Mountains, including all values in excess 

of 500oC (Allen and Zies, 1923). There was a wide range in 

volume and velocity of fumarolic plumes, from wispy to brisk 

to roaring jets and from pinhole fumes to columns 10–20 m 

wide that ascended >100 m and rarely >500 m. Also noteworthy in 1919, in the near-vent area, were a few feeble 

fumaroles that issued from bedrock shale on the south and 

west faces of Baked Mountain (diagram on p. 263 of Griggs, 

1922) and from the face of dacitic Falling Mountain (photo 

on p. 202 of Griggs, 1922); the latter site continued to steam 

weakly into the 1980s.

Already in 1919, however, Griggs noted slackening, cooling, or disappearance of many 1917 fumaroles and conversion 

of many former steam vents in the lower VTTS to boiling 

springs. The great majority of fumaroles measured in 1918 

and reoccupied in 1919 had declined in temperature (Allen 

and Zies, 1923). Fumarole 1 on the distal Ukak lobe of the 

ignimbrite cooled from >357oC in 1917 to 220oC in 1918 to 

95oC in 1919. Fenner (1950) found that by 1923 hundreds of 

former fumaroles were either dead or had cooled to near the 

boiling point; hardly any survived along the Knife Creek arm, 

and the few superheated fumaroles remaining were either in 

the upper Lethe arm or around Novarupta, where some could 

still melt zinc (>419oC). Fenner noted that weak fumaroles 

were still active in 1923 high on Broken Mountain and in 

Katmai Pass south of Mount Cerberus, indicating that surprisingly thick ignimbrite is concealed there beneath the blanket 

of dacite fallout. 

By 1929, only a few hundred fumaroles survived (Hubbard, 1932), nearly all near or below the boiling point. In 

1930, Griggs (1933) could locate none above the boiling 

point, but he noted a cluster still active on the face of Falling 

Mountain (see 1918 photograph there on p. 280 of Griggs, 

1922). When Hubbard returned in 1934, he reported that 

only “a few feeble” fumaroles were left, mostly in the upper 

Lethe arm and around Novarupta, compared to the hundreds 

he had seen in 1929; most conspicuous was a pair of big 

steamers on the western bench of Baked Mountain (Hubbard, 

1935). In 1940, an aerial reconnaissance by the National 

Park Service reported only about 10 fumaroles still active in 

the VTTS. During geophysical investigations coordinated by 

the University of Alaska in the mid-1960s, weak fumaroles 

(near or below boiling) remained only on the Novarupta 

dome, on the west rim of its ejecta ring, along faults on and 

near the Turtle, and on the western bench of Baked Mountain. All but the last of these areas were still active in the 

1990s, though most continued to weaken and cool; a few 

wispy ones remained as hot as 80oC–90oC (Keith, 1991b). 

The Baked Mountain bench fumarole, the lone survivor 

outside the 1912 vent area, kept steaming passively from a 

deep open fissure during the 1980s but died out in the 1990s; 

we obtained a temperature of 49oC in 1976 by dangling a 

maximum thermometer into a narrow linear orifice (fig. 109) 

about 6 m below its rim, and Keith (1991a) measured 32oC 

there in 1989. In its prime in 1917, it was photographed with 

a mighty plume (p. 128 of Griggs, 1918f).

Infiltration of ample rainfall and snowmelt directly into 

the ignimbrite, contributions of several modest side 
144 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

A

A

B

Figure 108. Lethe arm of VTTS. Views northwest to north across Lethe arm of upper VTTS to Buttress 

Range (at left): A, 1917 image, where distance from camera on bench at northwest toe of Mount 

Cerberus to steaming bench across valley at left is 4 km; fissure control of many (not all) fumarolic 

emissions in upper valley is conspicuous. B, 1982 image from lower slope of Mount Mageik (~1 km west 

of Mount Cerberus) overlaps 1917 image and shows axial River Lethe, fissured hingeline of marginal 

benches (left and foreground), and post-1912 dark alluvial sheet (at right) from Mount Mageik. Distance 

down VTTS, entirely fumarole-free in 1982, is ~14 km to narrows where valley bends left. 1917 photo 

courtesy of National Geographic Society; 1982 photo by authors.
Chapter 9. The Ten Thousand Smokes 145

Figure 109. Fumarolic fissure in welded tuff on southwest bench of Baked 

Mountain. Ignimbrite is overlain by dacite pumice-fall deposits (at surface), 

aeolian redistribution of which has filled or hidden many such fissures, 

creating an enduring hazard. This was site of longest-lived fumarolic 

emissions outside of Novarupta basin. It was still producing a weak vapor 

plume at 49oC in 1976 and at 32oC in 1989.

streams that disappear into it, and large contributions from 

the glacier-fed forks of Knife Creek and the River Lethe all 

helped sustain the fumaroles and greatly advanced cooling of the ignimbrite sheet. In 1919, Allen and Zies (1923) 

observed that total stream outflow from the sheet at Three 

Forks, though far greater than in 1917, was less than a tenth 

of the water they estimated to be entering the sheet from the 

various sources. Just above Three Forks, the River Lethe 

gave temperatures of 80oC–85oC in summer 1919. Allen and 

Zies further noted that fumaroles along the valley margins 

were generally of lower temperature than those near the 

valley axis, probably owing to direct marginal runoff from 

the valley walls, as well as to lateral thinning of the ignimbrite sheet. Their observation that the ratio of acid gases 

to steam declined downvalley can likewise be attributed to 

accumulative infiltration and to thinner tuff. 

Gases sampled from many fumaroles in 1917 and 1919 

(Shipley, 1920; Allen and Zies, 1923) were all >99.5 volume percent water vapor, but they also contained significant 

amounts of HCl, CO2

, H2S, and HF (generally in that order of 

abundance), as well as atmospheric N2 and Ar. Shipley mentioned SO2

, but it was not detected by Allen and Zies, which 
146 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

(for higher temperature gases) may reflect their analytical 

procedures. Sheppard and others (1992) critically reviewed 

the early methods of Allen and Zies and noted that the modest 

CO2 contents relative to the halogens reflected the sources of 

the nonaqueous gases within the tuff itself. Found principally 

in Novarupta basin were CH4 and NH3, the latter precipitating 

white crusts of ammonium chloride within fumarolic orifices. 

Like Shipley before them, Allen and Zies observed a tarry 

black precipitate of aromatic hydrocarbon close to Novarupta 

dome. The presence of HF in concentrations comparable to 

those of H2S and HCl was surprising, probably because gases 

associated with high-silica rhyolite had not been sampled 

previously. Fresh rhyolite pumice from Layer A contains ~500 

ppm F and ~1,500 ppm Cl. Along with the eruptions of Tambora in 1815 and Hekla in 1947, the 1912 eruption was one 

of the few historical events to produce a fluorine spike in ice 

cores on the Greenland icecap (Lyons and others, 1990).

Fossil fumarole deposits and structures, though 

degraded, are still ubiquitously exposed on the floor of the 

VTTS and in Novarupta basin (Keith, 1991a, b). Several 

types of fumarole morphology were described by Sayre 

and Hagelbarger (1919), Allen and Zies (1923), and Keith 

(1991a). In the upper and middle VTTS, where the ignimbrite is well indurated and fractured, fissure fumaroles tens 

to hundreds of meters long predominated (figs. 110, 111). 

Many fumarolic fissures are roughly perpendicular to the 

valley axis, others are parallel to the valley margins (notably 

along the hingeline of the marginal benches produced by 

differential compaction of the VFI), and still other fumaroles 

took advantage of columnar joints and networks of variably oriented fractures in devitrified vapor-phase tuff. In 

the lower VTTS and Mageik Creek, where the ignimbrite is 

poorly indurated, slightly permeable, and thinner than ~25 m, 

fissure control is less common, and most fossil fumaroles are 

funnel shaped (figs. 112, 113), 1–5 m across at the surface, 

and commonly more concentrated above buried pre-1912 

stream courses. Discrete altered zones—fissural, funnel-like, 

or irregular—are exposed on gorge walls to depths of 1–20 

m (fig. 114), showing that focused gas ascent was gathered 

from within the tuff, where some fraction of the volatiles 

had been trapped interstitially during emplacement and more 

were liberated by secular devitrification. Many discrete 

pathways have light-colored leached rinds at depth in the 

ignimbrite, but many flare shallowly into varicolored zones 

of mineral precipitation near the surface of the ignimbrite 

and especially within the overlying stratified pumice falls 

(figs. 115, 116). Where well indurated by incrustations, 

many fumarolic orifices are still marked by mounds and 

Figure 110. Fractures in sintered ignimbrite that concentrated fumarolic emissions for about a decade after the 

eruption, leaching tuff of mobile constituents. Lethe arm of VTTS near course of River Lethe. Backpacks for scale.
Chapter 9. The Ten Thousand Smokes 147

Figure 111. Close-up view of fumarolically altered crack seen in figure 110. 

In well-indurated (sintered) ignimbrite, strong leaching was commonly limited 

to narrow zones only 5–10 cm wide; but note wider grayish zones of lesser 

alteration outboard of cream and pink strip. Notorious Katmai winds have 

widely scoured indurated ignimbrite surface, especially along Lethe arm of 

VTTS, stripping away formerly overlying fall deposits. Knife is 8.5 cm long.

ridges resistant to erosion (Keith, 1991a). Precipitates at 

some orifices included mounds of amorphous silica “several 

feet high” (Shipley, 1920; Allen and Zies, 1923), a few of 

which have survived a century of erosion.

Fumarolic Deposits

Most fumarolic deposits are complexly zoned in mineralogy, color, and degree of alteration of the host ignimbrite 

or fall deposit (Keith, 1991a). An axial throat of high-temperature acid-gas release was surrounded on a meter scale by 

successive zones of boiling and condensing steam that permeated the tuff. As each fumarole cooled, such zones collapsed 

inward, converting the orifice to a hot spring or mudpot within 

a few years and replacing in full or in part the original fumarolic minerals with lower-temperature assemblages. Most of 

the fluorides, chlorides, and sulfates, originally ubiquitous, 

were dissolved and removed by aqueous condensate and by 

secular weathering in a cold wet climate. 
148 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Figure 112. Funnel fumarole in nonwelded ignimbrite east of 

Three Forks in lower VTTS. Orifice flares to ~2 m wide at surface. 

Note concentrations of lapilli along irregular cracks, from which 

fine ash was flushed by gas flux.

Figure 113. Orifice of funnel fumarole in nonwelded ignimbrite 

just upvalley from cross-valley moraine in lower VTTS. Note 

contrast between pervasive mild oxidation of tuff and restriction 

of white and bright red alteration to margins of fossil fumarole.

Higher temperature vents produced anhydrite, corundum 

(Shipley, 1920), ammonium chloride, ammonium silicofluoride, molybdates (Zies, 1929, p. 28), and abundant vaporphase magnetite (much of which was gradually replaced by 

hematite). Ramdohr (1962) later identified bornite, chalcopyrite, zincite, molybdenite, pyrrhotite, and pyrite as inclusions 

in magnetite taken by Zies (1924a) from mid-VTTS Fumarole 

148 (239oC in 1919). In 1923, Fenner found that Fumarole 

148 had cooled to 97oC and that the abundant clusters of magnetite crystals had been replaced by hematite.

Every incrustation studied contained abundant F, analyses 

yielding 0.1–15 weight percent F. Hard opaline mounds at 

Fumaroles 108 (238oC) and 134 (298oC) were impregnated by 

fluorides (as well as chlorides and sulfates, including barite), 

and the latter site (in the middle VTTS) had 12 weight percent F (Zies, 1929). Extensive bluish deposits along a hightemperature fissure just north of Baked Mountain (Fumarole 

127; 264oC) contained 700–3,500 ppm Mo (Zies, 1929), a 

remarkable degree of concentration from the 3 ppm Mo in 

1912 rhyolite pumice (Hildreth, 1987). Borate minerals were 

not identified, and B contents of gases were not measured. 

But incrustations at 22 fumaroles (97oC to 414oC) contained 

0.01–0.21 weight percent B2

O3, and those at three additional 

high-temperature fumaroles had 0.72–2.17 weight percent B2O3

(table 9 of Zies, 1929); these values can be compared with 

31–58 ppm B in the rhyolite pumice, 28–41 ppm in dacite 
Chapter 9. The Ten Thousand Smokes 149

Figure 114. Large focus of fumarolic alteration, 5–7 m wide, exposed on wall of River Lethe gorge, 

12–15 m deep here, in lower part of central VTTS. Rhyolite-dominant ignimbrite grades down from 

nonwelded to weakly sintered.
150 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Figure 115. Natural cross 

section through hemicylindrical 

zoned fumarolic incrustations 

developed in dacite fall deposits, 

above a long-lived fumarolic 

fissure in underlying ignimbrite 

(exposed in foreground). View 

westward toward Buttress 

Range from draw that drains 

northward from Katmai Pass 

between Mount Cerberus and 

Falling Mountain (see fig. 72). 

Fumarolic structure is ~20 m 

across. Backpack and shovel at 

left center for scale. See Keith 

(1991a) for more on this site.

Figure 116. Hemispherically zoned fumarolic incrustations formed in permeable dacite fall deposits directly 

atop sintered to partially welded ignimbrite. Fissure in brown indurated tuff that fed sustained gas flux is 

exposed at base of structure. Pale-gray fall deposit is ~3 m thick here in upper Lethe arm of VTTS. 
Chapter 9. The Ten Thousand Smokes 151

pumice, and <4 ppm in andesite pumice (Hildreth, 1987). Shipley, Allen, and Zies were well aware that some fraction of most 

metals they detected in the fumarolic deposits (B, Cu, Zn, Pb, 

Ti, Mn, Fe, Co, Ni, Mo, Ag, Cd, Sn, Sb, Te, Ga, As, Se, Bi) had 

been extracted from the pyroclastic deposits by the acid gases, 

but the great enrichments of such elements as Mo, Tl, and Bi 

persuaded them to accept the view of Griggs and Fenner that the 

gases and much of their metallic cargo issued directly from a 

magmatic intrusion beneath the valley. 

Lower temperature fumarolic vents had deposits of 

elemental sulfur, realgar, orpiment, gypsum, halite, alunite, tarry 

aromatic hydrocarbons, and multicolored oxides, chlorides, and 

hydroxides of iron (Shipley, 1920; Allen and Zies, 1923). Sulfur was not present in vents hotter than 97oC but was conspicuous along lower temperature fissures and ubiquitous in fringing 

zones within ~1 m of hotter orifices. Pyrite was widespread in 

mudpots, and vivianite (hydrous iron phosphate) was found in 

a few (Shipley, 1920). Methane, ammonia, and tarry hydrocarbons were detected mostly within Novarupta basin, site of the 

deeply reamed vent structure and not a site where exceptional 

stands of pre-1912 vegetation might be expected to have grown 

or to have been buried. Perhaps these compounds were distilled 

out of the fossiliferous Mesozoic siltstone that surrounds the 

vent and spalled into it, a possibility raised by Zies (1929).

Keith (1991a) investigated in detail the mineralogy of 

the deposits that remained seven decades after extinction of 

most of the fumaroles (figs. 117, 118). Black zones typically 

reflect surviving magnetite or hematite that replaced magnetite. White zones may be enriched in silica, alunite, fluorite, 

barite, clay minerals, and hydrated aluminum hydroxyfluoride 

(AHF), but some are simply the leached ashy protolith with 

little added. Dark red and purple zones are usually enriched 

in hematite and goethite, and pink zones contain a little of 

these. Orange to yellow zones typically reflect abundant 

limonite, goethite, or sulfur, in addition to varied amounts 

of the white-zone minerals just cited. Within the coarse 

pumice-fall deposits, fine-grained Layers E and H served as 

low-permeability barriers, causing rising vapors to spread out 

laterally, creating diffuse zones of red, orange, and yellow 

precipitates in the pumice and thin multicolored crusts of 

Figure 117. Severe fumarolic alteration in sintered ignimbrite and overlying stratified dacite fall deposits exposed along River 

Lethe in upper Lethe arm of VTTS. Black and red lineation on stream-scoured surface of ignimbrite reflects closely spaced cracks 

that governed gas emission. Blackening of originally near-white dacite fallout reflects high-temperature fumarolic deposition of 

magnetite (now widely retrograded) where gases emerged from fissures in ignimbrite into cold permeable fall deposits of pumice 

and crystal-rich ash. Black fall section is ~2 m thick here.
152 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Figure 118. Orifice of fumarolic fissure vent near East Mageik 

Lake. Ignimbrite is severely altered, but overlying white dacite 

pumice fall deposit only weakly so. Hammer is 28 cm long.

silica, limonite, and amorphous Fe-hydroxide directly beneath 

the barrier layers (Keith, 1991a).

Chemical studies of fossil fumaroles have shown 

intense leaching of most elements adjacent to fissures in 

indurated ignimbrite, resulting in residual enrichment of 

Si and Ti. In contrast, the far more permeable stratified 

pumice falls that overlie the ignimbrite provided favored 

sites for precipitation of incrustations and enrichment of 

most elements transported by the fluids (Papike and others, 

1991a; Keith, 1991a). Lovering (1957) studied a sample 

transect collected by Ray Wilcox in 1952 from roughly 

concentric zones around Fumarole 1 in nonwelded rhyoliterich ignimbrite on the Ukak lobe of the distal VTTS; the 

fumarole had been hotter than 357oC in 1917, 220oC in 

1918, 95oC in 1919 (Allen and Zies, 1923), and was cold 

and dead in 1952. Because the ignimbrite protolith was 

rhyolite-dominant, gas expelled had been halogen-rich and 

sulfur-poor, in contrast to gases from andesite-richer tuff in 

the upper VTTS, where S may locally have exceeded F + Cl. 

Lovering documented complex multistage remobilization of 

many elements and concluded that, in general, halogen-acid 

alteration promotes greater loss of silica relative to alumina 

than does sulfuric-acid alteration. 

It is hard, however, to extract systematic generalities 

about chemical redistribution in the several fumarolic deposits 

investigated (Papike and others, 1991a,b; Papike, 1992; Keith, 

1991a; Lovering, 1957) because of (1) the temporal succession through decadal cooling of the acid-gas phase to aqueous 

boiling and eventually liquid-water alteration; (2) instantaneous 

lateral and vertical gradients in the thermal zonation implicit 

in those stages; (3) the multipackage (fig. 27) compositional 

(andesite-dacite-rhyolite) complexity of the VTTS ignimbrite, 

much of which exhibits great heterogeneity on a 10-m scale; 

and (4) downvalley (upwind) fining of the supra-ignimbrite 

dacite fallout (Layers C–H) from coarse pumice to crystal-rich 

medium ash. Slight enrichment in alumina and loss of alkalies 

were fairly general, and most metallic elements were transported from ignimbrite to surficial incrustations—many to be 
Chapter 9. The Ten Thousand Smokes 153

Figure 119. Advanced clay alteration along arcuate fissure system northeast of Novarupta dome (see fig. 97), where weak 

vapor emissions and near-boiling temperatures persist a century after the eruption. Broken Mountain at upper left, mantled 

by dacite fall deposits; Mount Griggs stratovolcano on distant center skyline.

dissolved and lost subsequently to lower temperature alteration 

and secular weathering.

Fumaroles in Novarupta Basin

Within the vent area of Novarupta basin, fumarolic 

activity was longer lasting but no hotter than in thick parts of 

the VTTS ignimbrite sheet. In 1918, Sayre and Hagelbarger 

(1919) measured temperatures of 166oC and 264oC atop 

the Turtle and 294oC west of the dome; in 1919, Allen and 

Zies (1923) measured 238oC to 414oC at nine fumaroles in 

Novarupta basin, where exposures are predominantly of the 

thick coarse fallout of Episodes II and III with thin ignimbrites intercalated. Keith (1991a, b) studied the fumarolic 

deposits and alteration around Novarupta in detail, describing the overprinting of high-temperature vapor-phase suites 

(magnetite-hematite-silica), first by lower temperature 

(<400oC) vapor-phase minerals (fluorides-chlorides-sulfatesgoethite-orpiment-NH4

Cl-silica) and then by argillic suites 

(<200oC; alunite, kaolinite, pyrite, smectite, goethite, gypsum, and silica). Argillically altered areas are mostly aligned 

along faults and fissures where surface waters were acidifed 

by fumarolic gases, attacking the ash and pumice from the 

surface downward and creating impermeable clay-rich caps 

mostly <50 cm thick (fig. 1 of Keith, 1991b). The clayey 

areas are mostly white, yellow, pink, or red (fig. 119), but 

the few that are dark gray typically have visible pyrite. They 

overlie brightly colored fall deposits, coarse and permeable, 

that had been altered only modestly during diffuse hightemperature gas flux. 

Residual warm areas today (25oC–90oC; fig. 10 of Keith, 

1991a) lie along the fissures that governed major fumaroles 

in 1917–1919 and subsequently became sites of argillization. 

From the warm areas, numerous wispy fumaroles still emit wet 

steam, which at pH 5.7–7.0 precipitates a little silica from its 

condensate but accomplishes little further alteration. Although 

no cinnabar or other Hg-bearing sulfide has been recognized, 

elemental mercury was measured (~0.1–7 ppm) in Novarupta 

basin by Kodosky (1989), concentrated principally in the warm 

wet areas mapped by Keith, where it is probably adsorbed on 

clay minerals. On the Novarupta lava dome itself, thin films of 

vapor-phase hematite and silica remain along cracks and faces 

of glassy blocks, but subsequent alteration is not discernible, 

and the wisps of vapor still sometimes seen atop the dome (on 

foggy mornings) are water vapor and warm air—pH 6–7 in 

1978 and 49oC in 1986 (Keith, 1991a, b). 

Thermal springs (21oC–30oC) in the middle VTTS discharge on gorge walls deep within the ignimbrite. As far as 11 

km from Novarupta and certainly diluted by cold infiltration, 

their century-long persistence suggests either underflow from 

the vent region or residual heat in the thick welded tuff of the 

upper VTTS (Keith and others, 1992).
154 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

“Glacier Priest” Bernard Hubbard and his malamute “Katmai” at a fumarolic 

pit just west of Novarupta in September 1934, the third summer he camped in the 

Valley of Ten thousand Smokes with dogs and football players. With experience 

accrued, he came well equipped this time, even though he knew the fumarolic 

gases had by then diminished greatly. Photo courtesy of University of Santa 

Clara archives.
Chapter 10

Secondary Deposits

Emplacement of ignimbrite and fall deposits upon rugged 

terrain—barren or brushy, much of it snowclad or ice-covered, 

and drained by braided glacier-fed streams in broad valleys—

inevitably produced rapid and sustained alluvial, phreatic, and 

sedimentary responses. Here, we describe secondary effects 

that took place during or soon after the eruption, and in chapter 11 we summarize longer lasting secular responses.

Syneruptive Runoff and Remobilization

In early summer, the upper VTTS usually retains extensive snowbanks, and the north-facing slopes of Trident, 

Mageik, and Katmai are almost always snow covered. Deposition of warm pumice falls and hot ignimbrite on surfaces 

of snow and ice thus inevitably led, on 6–8 June 1912, to 

widespread remobilization of eruption products by meltwater, 

principally as ashy mudflows and pumice-rich slurries. Little 

evidence for this survives at the north base of Mount Mageik, 

where fallout was thin, later phreatic cratering was extensive, 

and the two large glaciers have receded ~1 km since 1912, 

with attendant fluvial erosion.

However, at the foot of the Knife Creek Glaciers, which 

were blanketed with many meters of ejecta, the evidence for 

remobilization is extensively preserved. In a deep narrow 

gorge incised along the lower west wall of Glacier 1, ~12 

m of stratified pumice-rich alluvium is sandwiched between 

the ignimbrite and a complete section of Layers C–H. In a 

coarse matrix of crystal sand, the pumice blocks and lapilli 

are mostly dacitic and andesitic, derived from final ignimbrite 

Packages 8 and 9. At the snout of Glacier 3, remnants of 

a small proglacial pond include dropstones and accretionary mudballs (2–25 cm in diameter) in a very poorly sorted 

massive deposit rich in vitric silt, crystal sand, pumice lapilli 

and blocks, and angular lithics as big as 20 cm. Just downstream, massive exposures of hyperconcentrated crystal sand 

are as thick as 5 m. And for 2 km downstream from Glacier 

3 to its confluence with the Griggs fork, the proglacial stream 

provides extensive exposures of plane- and cross-stratified 

high-energy fluvial beds of pumice and crystal sand (figs. 35, 

44), in layers 1–20 cm thick and altogether 1-8 m thick. Like 

the similar reworked section adjacent to Glacier 1, rhyolite 

pumice is sparse and small, dacitic pumice dominates over 

andesitic, and successive sets of steep cross beds truncate 

earlier ones. Because the fluvial section here overlies the sintered ignimbrite (Packages 8 and 9) and underlies (typically 

complete) sections of Layers C–H, it was clearly deposited 

during the hours-long pause between eruptive Episodes I 

and II. Where the main proglacial stream reemerges from 

a 300-m-long tunnel under the edge of Glacier 4, the fluvial 

beds also overlie a 50-cm-thick remnant of Layer B3

 pumice 

fall, confirming that meltwater runoff from the ejecta-mantled 

glaciers commenced only after the end of eruptive Episode I.

Below the snout of Glacier 5, secular stream erosion 

has removed any deposits reworked syneruptively from the 

glacier, but slopes on the north side of its outlet stream provide 

a record of several decimeter-scale debris-flow deposits, 

all dominated by rhyolitic pumice and ash, that ran back 

downslope to intercalate with Layer B and lowermost Layer 

C. There is also evidence here that fluvial erosion had cut a 

sidewall into an A–B fall-and-flow section ~7 m thick before 

the unconformity was draped by Layer C.

Along the lower Griggs fork, similarly, a few pink mudflow deposits, 0.5–2 m thick, are intercalated within the A–B 

section of fallout and valley-fringing ignimbrite. These were 

remobilized by snowmelt on the slopes of Mount Griggs and, 

largely confined by swales, flowed down to interfinger with the 

primary pyroclastic deposits still accumulating on the valley 

floor. Juvenile components in the earliest such mudflows were 

almost exclusively rhyolitic pumice and ash, but later ones intercalated with the dacite fallout also contain a little andesitic and 

dacitic pumice and lenses of crystal sand. Small sparse lithics 

are mostly Jurassic shale originally emplaced with ignimbrite 

Packages 1 and 2, from which the mudflows were remobilized.

Along the Noisy Mountain Fork of Katmai River, on the 

southeast side of Mount Katmai, ~15 km from Novarupta, 

remnants of several matrix-dominated pumice-rich debris 

flows crop out downstream from the glacier front. The earliest 

is pale gray, rhyolite-dominant, and 4–6 m thick; it truncates 

Layer A and is capped by Layer B3

. Another, 1–5 m thick, 

contains both rhyolite and dacite pumice and is overlain 

directly by the upper half of Layer C. A third, 5–6 m thick, is 

terra cotta, contains all three pumice types, and overlies Layer 

G. The timing of these ashy debris flows is roughly consistent 

with that inferred from seismicity and fall stratigraphy for 

major pulses of caldera collapse (see chapter 8, above). The 

Noisy Mountain Glacier just upstream, though actively 
156 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

crevassed, is still heavily pumice covered, right to its snout. 

The pumiceous debris flows were remobilized, not from the 

glacier, but from the steep snowclad southeast slope of the 

Katmai edifice.

The Katmai River Debris-Flow Deposit.—This deposit

at the south toe of Mount Katmai was recognized by Griggs 

(1918c, p. 124, 130) as a secondary pumiceous diamict 

emplaced at low temperature atop the stratified dacite fallout 

of Episode II and III, but several subsequent observers interpreted it as a hot pyroclastic-flow deposit, which it resembles 

(fig. 7 of Hildreth, 1983). The deposit is an unstratified sheet 

of poorly sorted 1912 ash and pumice lapilli. As thick as 18 m, 

the sheet slopes ~3oS and today covers an area of ~0.75 km2, 

but before erosion it was at least twice as extensive (fig. 120). 

It debouched from a single steep gorge fed from Metrokin 

Glacier, which mantles the south and southwest slopes of the 

Katmai edifice all the way to the caldera rim (Hildreth and 

Fierstein, 2003). The deposit overlies nearly complete fallout 

Figure 120. Katmai River pumiceous debris flow (lower right center) emerged from canyon fed by Metrokin 

Glacier on south slope of Mount Katmai (summit in cloud, upper left). Pink deposit remnant, much eroded in a 

century, is ~2.5 km long and as thick as 18 m; dark stream alluvium (lower center) has replaced about half of the 

original deposit. Repeatedly mistaken for a pyroclastic density current deposit, which it resembles, it contains 

uncharred wood and consists of Novarupta fall deposits that were remobilized from snowclad slope of Mount 

Katmai and emplaced as a cold wet debris flow sandwiched between fall Layers G and H. For a close-up view, 

see figure 7 of Hildreth (1983). At left and center, thick Katmai andesitic lavas; Katmai Canyon in right distance. 

Tephra-mantled knolls at lower right are Tertiary granitoid pluton.

sections of Layers A through G, although G is partly scoured in 

places. Layer H is widely preserved atop the primary uneroded 

surface of the debris-flow deposit, indicating that the flow was 

emplaced right at the end of eruptive Episode III. Field pumice 

counts yield a 7:3 ratio of dacite to rhyolite lapilli, similar to 

that of the bulk fallout mantling Mount Katmai and unlike 

that of any 1912 ignimbrite package (Hildreth, 1983; Fierstein 

and Wilson, 2005). Andesitic and banded pumice are rare, 

consistent with their extreme scarcity in fallout farther than ~4 

km from Novarupta. In several exposures the deposit contains 

uncharred branches and twigs, as well as rooted bushes that are 

bent over downhill and retain intact bark (fig. 121). The source 

area was a snow-mantled glacier ~4 km2 in area that sloped 

11o–14o southward and was blanketed by at least 5 m of pumiceous fallout. Such supraglacial fall deposits, representing at 

least 0.02 km3 of material, would be nearly double the volume 

originally constituting the debris-flow deposit (Hildreth, 1983). 

Beneath the main dacite-rhyolite debris flow, an all-rhyolite 
Chapter 10. Secondary Deposits 157

pumiceous debris flow left a deposit 0.5–1 m thick (Hildreth, 

1991) that is intercalated within the pumice-fall section at the 

level of Layer B2 (fig. 122).

Syneruptive Landslides

Seismicity attending caldera subsidence triggered collapse of at least three substantial extracaldera landslide masses 

(fig. 5), in addition to many minor slumps and rockfalls. 

Numerous pumice-rich debris flows (described in the previous 

section) during or soon after the eruptive sequence may likewise have been shaken loose from fallout deposited on steep 

snowy slopes by the severe earthquakes that continued at least 

as long as 10 June.

The Mageik Landslide.—This feature, described at length 

by Griggs (1920, 1922), broke loose from a glacially eroded 

stack of dacite lava flows on the south side of Mount Mageik, 

leaving behind a 120-m-high scarp with a rim at the 3,000-ft 

level. The rugged deposit extends ~6 km down the valley of 

Martin Creek to an elevation of 650 ft and consists predominantly of angular blocks of fresh dacite, along with sparse 

chunks of basement sandstone. It has millions of dacite blocks 

larger than 1 m, slabs as long as 20 m, and hummocks as high 

as 20 m. It locally left 30-m-high superelevated trimlines and 

impounded drainages along its steep margins. About 800 m 

wide proximally, the deposit spread out to ~1.5 km medially 

and covers an area of ~6 km2. Griggs (1920) estimated an 

area of 10 km2, but this included parts of pre-1912 avalanche 

deposits mapped separately by Hildreth and Fierstein (2003). 

Although the thickness (5–30 m) is hard to average, the volume is probably in the range 0.05 to 0.1 km3

. The avalanche 

took place during eruptive Episode I, on the night of 6/7 June, 

because the deposit is overlain by only the upper part of Layer 

B and later fall units (Hildreth and others, 2000).

The Katmai Canyon Landslide.—This deposit likewise 

broke loose on the night of 6/7 June, after deposition of Layers 

A and part of Layer B. It is overlain directly by Layers B3

through H. Near the south toe of Mount Katmai, the headwall 

scarp extends ~500 m above the canyon floor, exposing a stack 

of andesite-dacite lavas with thin scoriaceous interlayers. The 

chaotic 0.08-km3 slide mass covered ~1.2 km2, was as thick 

as 125 m, and consists entirely of shattered debris from the 

Katmai edifice. The deposit blocked the narrow gorge of Katmai Canyon (fig. 123), impounding a 5-km-long lake, which 

breached by 1915 (Griggs, 1922); see section below titled 

“Lakes Impounded.”

The Noisy Mountain Landslide.—This deposit in upper 

Katmai Canyon is avalanche debris consisting of Tertiary(?) 

Figure 121. Katmai River pumiceous debris-flow deposit at its distal margin, where it overran willows and alders. Branches 

retain uncharred bark. Shovel (center) is 58 cm long.
158 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Figure 122. Katmai River pumiceous debris-flow deposit (KRdf) resting on nearly complete Novarupta fallout section (Layers A–G). 

Layer H is locally preserved atop the debris flow deposit, indicating that the flow took place within days after eruptive Episode III. At 

base, 1.2 m of Layer A rests on bouldery alluvium and is overlain by Layers B1

 (3 cm) and B2 (48 cm). Brown boulder-bearing next layer is 

a syneruptive mudflow deposit (105 cm) in which all pumice clasts are rhyolite (rhy df). This is overlain by 2.8 m of stratified fall deposits 

(Layers B3

 through G), capped by ~10 m of main compositionally heterogeneous debris-flow deposit, which includes two principal flow 

units. Geologist at center for scale. Barrier Range on skyline to east.

andesite from Noisy Mountain, on the south slope of which 

the headwall scarp extends as high as 900 m above the valley 

floor. The 6.5-km2 deposit is studded with numerous barren 

hummocks 10–20 m high (Griggs, 1922, p. 128) and a few 

shattered megablocks as wide as 30–80 m. Like the other 

landslides, large parts of this avalanche broke loose during 

eruptive Episode I, because the lowest unit of the pumice-fall 

section overlying it is the upper part of Layer B2, even though 

Layer A is 30 cm thick directly adjacent to the landslide 

deposit. Griggs (1922) noted that, when his party camped 

there in 1917, rockfalls large and small continued on the scarp 

every few minutes, inspiring the name Noisy Mountain. It 

was quiet when we investigated the area in the 1990s. The 

deposit impounded Upper Katmai Lake, which was ~2 km 

across in 1917 (Griggs, 1922) but only a shallow pond ~600 

m long in 1997 (fig. 124) and still shrinking as a pumice fan 

gradually encroaches on its eastern end (see next section, titled 

“Lakes Impounded”).

Lakes Impounded

Windy Creek was blocked by the ignimbrite at the north 

end of the Buttress Range. An unpublished National Geographic Society photograph taken from the top of the Buttress 

Range in 1917 shows a shallow lake extending from the blockage for ~1.4 km upstream, where it was fed by a broad braided 

stream much like today’s. It was called “Windy Lake” in the 

1918 diary of Jasper Sayre and mentioned by Griggs (1918c, 

p. 128). The pre-1912 channel of lowermost Windy Creek was 

filled by the ignimbrite (fig. 87) and can be traced as a gentle 

swale on the tuff surface for 1.3 km northward to its former 
Chapter 10. Secondary Deposits 159

A

Figure 123. Katmai Canyon landslide deposit. A chaotic 0.08-km3 slide mass broke loose from south toe of 

Mount Katmai on night of 6/7 June, after deposition of Layer A and part of Layer B. It is overlain directly 

by Layers B3

 through H. Headwall scarp (outlined in white) extends ~500 m above canyon floor, exposing a 

stack of andesite-dacite lavas with thin scoriaceous interlayers. Covering ~1.2 km2

 and as thick as 125 m, the 

shattered andesitic debris blocked the narrow gorge of Katmai Canyon, impounding a 5-km-long lake, which 

breached by 1915 (Griggs, 1922, chapters IX, X). A, 1917 photo courtesy of National Geographic Society; B, 

1998 photo by authors.

A

B
160 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

confluence with the River Lethe. The former channel was never 

reoccupied, as Windy Creek cut a gorge ~250 m long through 

the blockage and established a new course around the western 

margin of the ignimbrite, ~1 km west of its original one. The 

ignimbrite is only ~10 m thick and wholly nonwelded in this 

area, and it is presumed that the outlet gorge was cut to lake 

level and Windy Lake was drained within a few years after 

1918, but the actual date is unknown.

Fissure Lake.—Named by Griggs (1922, p. 212), this 

feature extended ~600 m east from the site of present-day 

West Mageik Lake (fig. 92), which was then still occupied 

by the snout of West Mageik Glacier (fig. 84). The lake was 

as wide as 100 m, and in 1917 it was filled with “clear green 

water.” Despite being fed by meltwater from the nearby 

glacier, the lake was warm in 1917–1919, owing to its steep 

walls of steaming ignimbrite. The broad “fissure” had been 

excavated as a chain of coalescent phreatic explosion craters 

along the hingeline (fig. 92) of the compactional bench marginal to the Lethe basin (see “High sand mark” in chapter 6). 

Accordingly, its south rim is at least 10 m higher than its north 

rim, and both sides are strewn with multicolored tuff blocks 

that had been sintered or welded and fumarolically altered 

before phreatic ejection. June snowbanks and the glacial 

outlet stream buried by the ignimbrite may have promoted 

exceptionally vigorous fumarolic and explosive phreatic activity here. It was noted by Griggs (1922, p. 244) that a delta 

then building out into Fissure Lake from the ice front would 

lead to its early extinction. Indeed, the lake silted up by 1923, 

and today its 10 m of ash-rich lacustrine and alluvial fill (fig. 

94) have been incised by a stream that flows back into the 

modern lake (fig. 92), which was not fully formed by glacial 

recession until the 1950s.

East Mageik Lake and West Mageik Lake.—These lakes 

filled the bowls left by recession of the termini of glaciers at 

the north toe of Mount Mageik (see “Emplacement over and 

against ice” in chapter 6). When the earliest set of aerial photographs was taken in 1951, the eastern lake had fully formed 

but the western one was still a pair of ponds not yet coalesced 

into the present-day lake. The lakes are now, respectively, 400 

m and 700 m across, and their color varies from blue-green 

to mud-brown, depending on the influx of silt-laden seasonal 

runoff from the nearby glaciers (figs. 91, 92).

Griggs Fork Lake.—This feature may have been the 

largest of the new or temporary lakes in the VTTS. Its deposits are 10–15 m thick and crop out as steep bluffs along the 

Griggs fork for ~1.5 km, from north of the snout of Glacier 

4 nearly to the confluence of the forks of Knife Creek. The 

lower half of the lake-sediment section (fig. 125) consists 

Figure 124. Hummocky avalanche deposit from slopes of Noisy Mountain (out of view to right) that blocked upper 

Katmai Canyon and impounded upper Katmai Lake (foreground). View westward down canyon, 6 km to narrows 

where Katmai Canyon landslide deposit blocked gorge. Both these avalanches took place during eruptive 

Episode I; their deposits overlie Layer A and part of Layer B, and both are overlain by part of Layer B and Layers 

C-H. Barrier Range at left; Mount Katmai lavas at right; snowclad Mount Mageik on central skyline.
Chapter 10. Secondary Deposits 161

of plane beds of gray to tan massive mud, poorly sorted and 

50–200 cm thick, separated by thinner layers of pumicebearing sand (1–10 cm) or gray silt (1–3 cm). The upper 

half is thin bedded to laminated mud with pumice-rich lenses 

and layers of alluvium and mudflow deposits. We envisage 

shallow still-water ponds and seasonal mudflats that intermittently received ash-rich mudflows and pumice-rich slurries, 

some of which slightly scoured their muddy substrate. Sparse 

pumice blocks and coherent clusters of pumice lapilli (probably frozen when deposited) may have been emplaced as 

dropstones from floating ice or from mudflows or snowbank 

slurries. Water depth probably fluctuated seasonally from 

several meters to empty or frozen.

Along this reach of the Griggs fork, which is now a gravelly braided stream ~100 m wide, the stratigraphically lowest 

exposures are of dark gray ignimbrite, sintered to partially 

welded, which is widely disrupted, faulted, tilted, or shattered 

into a chaos of blocks. Because the disrupted welded tuff is 

separated from the snout of Glacier 4 by terraces of undisturbed deposits, it seems clear that the disruption was caused 

by phreatic explosions, not by advance of the ice front. Surgebedded phreatic deposits are indeed locally exposed between 

the ignimbrite and the overlying lake sediments. We think the 

trough along which the sediments were deposited was a combined product of axial compaction of the welded tuff, proglacial high-energy fluvial erosion of the overlying dacite fallout 

section, and blockage of the downstream end by a thick pile of 

phreatically ejected rubble.

The lake deposits variously rest directly on the sintered 

ignimbrite (Package 8) or upon overlying remnants of crossbedded stream gravels, surge-bedded phreatic deposits, or 

the stratified dacite pumice falls of Episodes II and III. At 

the upstream end of the lake-basin deposits, there are more 

outcrops of disrupted welded tuff, overlain by interstratified 

deposits of lake mud, stream alluvium, and pumiceous mudflows, into which had calved rotated blocks (several meters 

across) of the layered dacite fallout. The lake deposits are 

overlain by 5–20 m of later, post-Episode III, explosive phreatic deposits that issued from many nearby craters and by 

1–5 m of wavy-bedded terrace gravels. Parts of the sedimentary pile are fumarolically altered, particularly in their more 

permeable pumice-bearing lenses, attesting to enduring fluid 

flux from the hot underlying ignimbrite. The lacustrine section, ignimbrite, and varied deposits between them (but 

Figure 125. Ash-dominant lacustrine and mudflat sediments deposited during first year or two after eruption 

and exposed along Griggs fork of Knife Creek opposite snout of Glacier 4. Exposure is 10 m thick and also 

includes pumice-rich sandy alluvium and mudflow deposits. Top 1–2 m is alluvial terrace deposit. Ephemeral 

or seasonal lakes were impounded by phreatic explosion deposits that blocked drainage just downstream near 

confluence of forks. Abrupt breakout transported debris flows and trains of welded-tuff blocks to lower VTTS 

before incision of deep gorges into midvalley ignimbrite.
162 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

not the overlying terrace gravels and upper phreatic deposits) 

are cut by several small faults, probably the result of welding 

deformation and/or adjustment to nearby phreatic cratering.

The Griggs fork lake was the apparent source of an outburst flood that scoured the central VTTS and laid down ashy 

mudflow deposits all the way to the Ukak River terminus (Hildreth, 1983). Distal deposits are typically 1–8 m thick, poorly 

sorted, and massive; although the thickest Ukak sections do 

consist of a few conformable flow units, emplacement appears 

to have largely been a continuous event. The mudflows 

overlie both the ignimbrite and Episode II–III fall deposits; 

they poured beyond the ignimbrite terminus, engulfed upright 

uncharred trees, and feathered out into the brush (fig. 126). 

The deposits are pumice-rich diamict with pumice blocks as 

big as 35 cm, diorite and andesite cobbles up to 15 cm, and 

abundant fragments of Jurassic shale, all in a muddy matrix 

of crystal-vitric ash. Also conspicuous in the deposit are 

blocks of dark-gray sintered or welded tuff, material exposed 

only in the upper VTTS and widely disrupted and phreatically shattered along the Griggs fork. Energetic runoff might 

also at times have issued from the glacier-fed streams and the 

Juhle fork, but the only location satisfactory as a source of 

the pre-1912 clasts, the welded-tuff blocks, and the abruptly 

released volume of water required by high-energy transport 

for 20 km to the Ukak terminus is the Griggs fork lake. The 

River Lethe arm is not nearly as widely scoured of dacite fall 

deposits as parts of upper Knife Creek and the broad Knife 

Creek floodplain of the central VTTS, where both the Episode 

II-III fallout and the top meter or two of the sintered Episode 

I ignimbrite were stripped. The right margin of the flood path 

can be tracked for kilometers along the central and northeastern VTTS as a 10-m-wide mudflow veneer strewn with 

blocks of welded tuff (fig. 127). Gorges on several forks of 

Knife Creek were already more than 20 m deep in the central 

VTTS by 1917 and would have intercepted and confined the 

flood flow had it not taken place earlier. Moreover, a 1917 

photograph of the Griggs fork shows it much as it is today (fig. 

128). Rapid sedimentation along this short-lived proglacial 

trough is not surprising because the rugged landscape was 

everywhere mantled with unstable unconsolidated eruption 

products. Breakout and drainage of the lake took place in one 

of the first summers—1912 to 1916. 

Katmai Canyon Lake.—This ephemeral feature was 

impounded behind the Katmai River landslide deposit, which 

blocked the narrow gorge at the south base of Mount Katmai 

(fig. 123). The 0.08-km3

 slide mass consists of shattered lavas 

from the Katmai edifice, covered ~1.2 km2, and was as thick 

as 125 m; its headwall scarp extends ~500 m above the canyon 

floor. Although a complete pumice-fall section (Layers A–H) 

is intact alongside it, the slide mass is overlain by only part of 

Layer B, all of Layers C–H, and minor secondary slide debris; 

clearly therefore it was emplaced during the seismically 

Figure 126. Upright uncharred trees buried by ash-dominated debris-flow deposits as thick as 6 m, adjacent to 

Ukak terminus of ignimbrite, 20 km downvalley from Griggs fork—the inferred source of the flows (see fig. 125).
Chapter 10. Secondary Deposits 163

Figure 127. Alignment of meterscale blocks of welded tuff 

along northeast side of VTTS, 

interpreted as margin of flood flow 

across ignimbrite surface prior 

to incision of gorges that would 

have intercepted them. Inferred 

source was ephemeral lake 

impounded along Griggs fork 12 

km upvalley (see figs. 125 and 126). 

Gray-brown gravel veneer on 

surface of ignimbrite is lag deposit 

left by deflation of debris-flow 

deposits and of nonwelded top 

of ignimbrite by perennial Katmai 

winds. Backpack at lower center 

provides scale.

vigorous eruptive Episode I. Canyon blockage led to growth 

of a 4-km2 lake, ~5 km long, as wide as 800 m, and as deep 

as 70 m, which was never witnessed but was inferred from 

field evidence by Griggs (1922, chapter IX). The strandline 

illustrated by Griggs (1922, p. 120) stood ~64 m above a 

small lake remnant in 1917 (called “Lower Katmai Lake” by 

Griggs). The lake remnant has since vanished, the strandline 

has been obscured by scree, and scant trace of any lake sediment remains. When the landslide dam breached, the outburst and subsequent fluvial erosion cut a steep-walled trench 

through the blockage (Griggs, 1922, p. 116), removing about a 

third of the deposit (fig. 123). Nonetheless, north-bank terrace 

remnants ~1 km upstream of the blockage preserve ~15 m of 

plane-bedded sand-dominant strata with intercalated pumice 

lenses and layers of laminated mud. Foreset bedding is locally 

exposed, but most of the strata are horizontal (unlike alluvium 

of the steep present-day streams adjacent), supporting their 

interpretation as lakeshore deposits. Their elevation is ~60 m 

higher than the present-day floor of the breach, thus acceptably consistent with Griggs’ estimate of lake depth.

When Griggs (1922, chapters VIII, IX) first landed at 

Katmai village in June 1915, he was so impressed with the 

alluvial devastation that he assumed the outbreak flood had 

just occurred. He illustrated swamped barabaras, bent-over 

brush, trees uprooted or snapped off, and the sandy lowland 

at the village site covered by a sheet of wet mud all the way 

to the toe of the adjacent mountain. The village chapel had 

floated loose from its foundation and was marked by a highwater mark 3 m above its floor (Griggs, 1922, p. 104). The 

river-mouth estuary, which had extended 3–4 km inland to 

the village dock and up which Martin (1913) had sailed in a 

35-foot schooner as late as August 1912, had by 1915 completely silted up. The 8-km-wide floodplain of Katmai River 

was a sheet of ashy mud and pumice with wide expanses of 

shallow water and quicksand, rather than the braided plain of 

coarse gravel restored today. Griggs reported flood runups of 

3–8 m along the floodplain margins, a bedrock ridge athwart 

the lower-canyon flood path that had been stripped of its soil 

and pumice mantle, and a train of huge boulders extending 

3–5 km out from the canyon mouth. His evidence was convincing for recent passage of a great flood, and his inference 

of its occurrence in 1915 (three years after the blockage) 

is fairly persuasive. Of course, aggradation of the Katmai 

River floodplain continues today, a century after the eruption 

choked the whole drainage system with pumice. Comparable 

aggradation of tributary Soluka Creek, where there was no 

flood, suggests that some of the sedimentational devastation 

illustrated by Griggs was secular.

Upper Katmai Lake.—This lake survives today as a shallow pond ~600 m long, but Griggs (1922) mapped it as being 

~2 km across in 1917. Along Katmai River canyon, between 

Noisy Mountain and the Barrier Range, the lake lies 6 km 

upstream from the slide mass that impounded the lower lake 

and only 2 km downstream from the snout of Princess Glacier 

(Hildreth and Fierstein, 2003). The lake is impounded by a 

6.5-km2

 expanse of avalanche debris studded with numerous 

barren hummocks 10–20 m high (Griggs, 1922, p. 128) and a 

few shattered megablocks as high as 30–80 m. The avalanche 

rubble is andesite of Noisy Mountain, on the south slope of 

which the headwall scarp extends as high as 900 m above the 

valley floor. Large parts of the avalanche cut loose during 

eruptive Episode I, because the lowest unit of the pumice-fall 
164 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

A

B

Figure 128. Griggs fork of Knife Creek. Views eastward from north-bank rim at lower end of Griggs fork up its 

3-km-long braided floodplain: A, 1919 and B, 1982. At head of valley in center distance, Glacier 5 has advanced 

1,300 m. Glacier 4 at right has advanced 650 m. Both glaciers remain heavily tephra-covered a century after 

1912 eruption. Cutbanks consist of ashy fines-rich ponded sediments overlain by terrace gravels and phreatic 

surge beds. Floodplain has widened modestly at expense of south-bank terrace (right, middle distance). 

Foreground terrace at right served as airstrip and Katmai Project campsite in 1953–54, occupied by Curtis, Juhle, 

Williams, Kistler, and others. 1919 photo courtesy of National Geographic Society; 1982 photo by authors.

A

B
Chapter 10. Secondary Deposits 165

section overlying it is the upper part of Layer B2, even though 

Layer A is 30 cm thick directly adjacent to the avalanche 

deposit. Griggs (1922) noted that, when his party camped 

there in 1917, rockfalls large and small continued on the scarp 

every few minutes, inspiring the name Noisy Mountain. The 

lake had no surface outlet when we examined it in 1997, all 

drainage being through the permeable subsurface of the blocky 

avalanche (fig. 124). Lake area was shrinking, owing to 

encroachment of a pumice-rich alluvial plain at its eastern end. 

The only strandline observed was ~1 m above the August lake 

level, presumably representing seasonal fluctuation.

“Horseshoe Pond.”—This feature, illustrated and so 

named by Griggs (1922, p. 142), is a shallow lake ~500 m 

long that was impounded on the south side of Martin Creek 

by the Mageik Landslide, which (like several other mass 

movements) was emplaced during eruptive Episode I in 1912 

(Griggs, 1922, chapter XI; Hildreth and Fierstein, 2003). The 

lake has changed little in size or configuration since studied by 

Griggs in 1917. What he assigned to the Mageik Landslide, 

however, includes two older avalanche deposits as well as that 

of 1912 (Hildreth and others, 2000; also see section above 

titled “Syneruptive Landslides”).

Two temporary lakes also formed along the braided plain 

of the Ukak River (fig. 6), as documented by unpublished 

National Geographic Society photographs taken in 1917. One 

was ~5 km long, only a few hundred meters wide, and headed 

~4 km downstream from the ignimbrite terminus. The other, 

6–8 km farther downstream, was more equant but larger in 

area, flooding the brushy marshland just above the mutual 

delta of the Ukak and Savonoski Rivers. Summer discharge 

down the Ukak in 1917–19 was less than a tenth of what it is 

today, owing to boiling away of its principal inputs (Allen and 

Zies, 1923), and it was probably nearly dry in winter. Pileup 

of sandy pumice-rich alluvium along the braided courses of 

both rivers (and lower Ikagluik Creek), temporarily severely 

overloaded with eruption products, are presumed to have 

caused the transient impoundments.

Phreatic Craters and Deposits

Phreatic explosions within the VTTS ignimbrite produced numerous craters surrounded by tuff rings and aprons 

of poorly sorted, cross-bedded, remobilized pyroclastic debris 

(Hildreth, 1983). Many craters are circular, most are 20–60 

m across, but some are as wide as 150 m. Crater depths were 

3–20 m in 1919 (Allen and Zies, 1923, p. 87, 108), but most 

have since been partly filled with sediment (fig. 129). About 

60 craters are identifiable along a 6-km-long swath adjacent 

to upper Knife Creek, and conspicuous clusters of craters are 

also present near the snout of Glacier 3 and along the compactional bench at the north base of Mount Mageik (Hildreth 

and Fierstein, 2003). A few small craters also formed between 

the Buttress Range and the River Lethe, opposite Baked 

Mountain. Most craters are in areas where some level of the 

ignimbrite was welded or otherwise well indurated, suggesting 

the importance of an impermeable seal adequate to permit 

buildup of steam overpressure. Although some phreatic explosions took place at glacier fronts during or immediately after 

ignimbrite emplacement against them, most crater formation 

occurred after the dacite pumice falls of Episodes II and III, 

indicating delays of at least two days before steam blasted 

through the ignimbrite. In each of the three principal areas of 

craters, welded tuff had buried streams and snowbanks. 

Downvalley, though the tuff is nonwelded, craters formed 

in a few places where defeated streams poured against and 

over the hot tuff, inducing explosions. Resulting deposits are 

well preserved along the Juhle fork, along the southeast edge 

of the distal Ukak lobe, and where Windy Creek enters the 

ignimbrite. The diamictic explosion deposits at Windy Creek 

are 1–4 m thick, extend as high as 45 m above the ignimbrite 

surface on both banks, contain sparse stream cobbles, and 

consist predominantly of remobilized ignimbrite material.

Figure 129. One of ~60 phreatic craters rooted in ignimbrite and 

preserved along upper Knife Creek arm of VTTS (Hildreth and 

Fierstein, 2003). Craters range from 7 m to 30 m in diameter; this 

example is ~20 m wide, ~5 m deep, and holds ephemeral ponds 

that have cut encircling rings. Ejecta aprons of such craters are 

1–20 m thick. View is southwestward across main fork of Knife 

Creek toward base of Broken Mountain, where abrupt change 

from brown to pale gray marks upper limit of ignimbrite, 30–50 m 

above valley floor; dark brown slope is equivalent to “high sand 

mark” around Lethe arm (see figs. 72, 82).
166 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

The principal phreatic explosion deposits in the upper 

VTTS are generally 2–5 m thick but 15–25 m thick near 

snouts of Glaciers 3 and 4 and around the confluence of the 

Griggs fork with Knife Creek. These deposits consist of 

poorly to moderately sorted thin beds and laminae that are 

alternately enriched in crystals or in pumice lapilli, both kinds 

having a crystal-vitric matrix of muddy ash. Parallel bedding is common, but dunes, antidunes, festooned cross-sets, 

pinch-and-swell bedding, and extensively rippled bedding are 

also present. Truncated bedsets provide evidence of repeated 

outbursts and mutal interference of deposits from adjacent 

craters (fig. 130).

The deposits contain abundant blocks of sintered to 

partially welded tuff, some of which are denser than most 

ignimbrite surface exposures. Such blocks are commonly 

0.5 m across, and some are as large as 3 m (see photo on p. 

195 of Curtis, 1968). A few show impact sags and thin zones 

of thermal alteration of the enclosing diamict. Most of the 

phreatic debris is derived from rhyolite-poor packages that 

were emplaced late in the ignimbrite sequence, but a few 

craters near Glacier 4 and along the Juhle fork expelled material that is as much as 80 percent rhyolite. Although these few 

suggest a somewhat deeper (or valley marginal) source, most 

of the outbursts ejected material from upper and intermediate 

levels of the ignimbrite. Nonetheless, the low-permeability 

welded zones that favored buildup of steam pressure (and, by 

ultimately failing, initiated the blasts) were generally at deeper 

levels than the bulk of the material ejected.

Two linear troughs were excavated from indurated 

ignimbrite, which was shattered and heaved by explosive 

formation of chains of coalescent craters, along what became 

Fissure Lake and along the Griggs fork of Knife Creek. 

These were not ice-contact features but formed, instead, 

hundreds of meters away from the glacier fronts, probably 

above outlet streams buried by the ignimbrite. Along the 

Griggs fork, surge-bedded deposits on both banks of the 

present-day braided stream are as thick as 20–25 m and 

dip oppositely away from the stream. At the site of Fissure 

Lake (now drained) and around West Mageik Lake, phreatic 

deposits as thick as 5 m dip away from the trough and are 

studded with abundant blocks of tuff, commonly as big as 1 

m (fig. 93). Close to the present-day lake, however, which 

was occupied by the glacier front in 1912, ash-dominated 

proglacial pond sediments contain radially columnar blocks 

of indurated ignimbrite. The local evidence there suggests 

that blocks of hot ignimbrite calved into a meltwater-filled 

gap that had opened quickly between ice and ignimbrite, 

probably explosively.

Figure 130. Surge-bedded deposits from phreatic explosion craters near confluence of main fork and Griggs 

fork of Knife Creek. USGS geologist Dave Johnston stands atop primary nonwelded ignimbrite, which was 

source of the phreatic ejecta. Numerous craters each produced bedsets that mutually truncate and overlap 

each other. Johnston was swept away by the 18 May 1980 eruption of Mount St. Helens, nine months after our 

joint work in the VTTS.
Chapter 11

Posteruptive Evolution of the Landscape 

The principal geomorphic impacts abruptly introduced by 

the 1912 eruption were (1) inundation of Knife Creek, the River 

Lethe, and upper Mageik Creek by ignimbrite; (2) mantling of 

the rugged landscape with fall deposits—pumice-rich tephra out 

to 10–15 km but crystal-vitric ash beyond; (3) caldera collapse 

at Mount Katmai; and (4) fluvial aggradation of the Ukak, Ikagluik, Rainbow, Savonoski, and Katmai River systems. 

Only a tiny fraction of the 1912 ignimbrite transformed 

or was subsequently remobilized downstream into pumiceous 

debris flows. The Ukak River and Mageik Creek ignimbrite 

termini were certainly so affected, but terrace remnants of 

laharic deposits farther downstream are rare and small. We 

did find terraces with modest hyperconcentrated streamflow 

deposits along Rainbow River (northeast of Mount Katmai; 

see fig. 6), but these were derived from crystal-rich fallout, not 

ignimbrite. Debris flows transported from the Griggs fork and 

Katmai Canyon were mentioned in chapter 10, but these were 

abrupt events caused by lake breakouts. 

The contrast with the fluvial response to the 1991 eruption of Pinatubo, which emplaced a volume of ignimbrite comparable to that of 1912, could not be more striking. Within 

months, the radial ignimbrite sheets at Pinatubo were intricately dissected, and within three years, a third of the ignimbrite had been swept away as lahars (Punongbayan and others, 

1996; Newhall and Punongbayan, 1996). Typhoons and 

monsoons were important intensifiers at tropical Pinatubo, but 

the dearth of lahars at Katmai was a complex result of several 

factors: (1) Summer drizzle is frequent but downpours uncommon, and streams are frozen for half the year. (2) Despite the 

glacier-fed streams, more than 90 percent of streamflow over 

and into the ignimbrite boiled away for the first decade. (3) 

Upvalley the ignimbrite is welded and poorly permeable, and 

it was widely covered by several meters of coarse permeable 

pumice-fall deposits. (4) Differential compaction and welding, proportional to ignimbrite thickness, favored immediate 

establishment of axial trunk streams in each branch of the 

VTTS. These are joined intermittently by sheetwash but by 

only a few (mostly shallow) tributaries across the welded 

surface. Characteristics of the 1912 deposits and the Katmai 

climate thus combined to retard intricate dissection and extensive erosion of the VTTS ignimbrite. The few major drainages 

had been incised into its surface as narrow gorges before 1917 

when the valley was first explored, and they have changed 

rather little ever since.

Rapid Incision of Gorges

Because three branches each of Knife Creek and the 

River Lethe are fed by glaciers at the head of the VTTS, 

streams rapidly began to establish new courses across the 

valley-filling ignimbrite, and the trunk streams were forced 

down the middle of each arm of the upper valley by the differential axial welding-compaction. When the first real exploration of the VTTS was conducted in 1917, Griggs (1918c, p. 

118; 1918f, p. 132) photographed mid-valley gorges that he 

said were already “nearly 100 feet [30 m] deep,” though those 

illustrated were only ~20 m deep. In 1919, the outlet channel west of Novarupta basin was at least 7 m deep northwest 

of Falling Mountain (Griggs, 1922, photo facing p. 240), and 

it is no deeper today. Also in 1919, gorges on the forks of 

Knife Creek in the central VTTS were said by Griggs (1922) 

to be “100 feet deep” in places, though the gorge he illustrated (p. 254) was again closer to 20 m deep. He noted that 

canyons did not cut through the tuff to the underlying substrate 

anywhere except in the lower valley. Fenner (1923) repeated 

100-foot (30 m) estimates for some of the gorges he witnessed 

in 1919, but those he illustrated (p. 32, 34) were likewise no 

more than ~20 m deep. 

The stratified fall deposits of Episodes II and III had 

been eroded away along the main stream channels by 1917, 

and incision of the underlying ignimbrite was generally only a 

few meters in the upper valley but widely ~20 m in the central 

valley. There have been no quantitative measurements of 

erosion rates, but there is no doubt that erosion slowed greatly 

after the first few years. A century after the eruption, streams 

in the upper River Lethe and Knife Creek arms of the valley 

have narrow, steep-walled gorges still only 2–8 m deep (figs. 

35, 89) into sintered or welded ignimbrite. In the lower valley where the tuff is nonwelded and 10–20 m thick, the base 

is widely exposed (figs. 31, 68), but for only 2 km upstream 

from Three Forks. Today the gorges are deepest in the central 

VTTS, where the tuff grades from sintered to nonwelded (fig. 

131). The greatest depths we measured (by rope) are 30–35 

m, along the gorges of the main and Juhle forks of Knife 

Creek, 1–2.5 km above their confluence.

In the narrowest reach of the central VTTS there are 

four principal gorges, ultimately convergent, that are sheer, 

of similar depth, and floored within the tuff—from west to 

east, the River Lethe and the mid-valley, main, and Juhle 
168 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

forks of Knife Creek (fig. 74). The Juhle fork drains a glacier 

on Mount Griggs, the River Lethe drains glaciers on Mount 

Mageik, and the main fork integrates drainages from all five 

Knife Creek Glaciers. The mid-valley fork is now spring-fed 

where its gorge heads abruptly in the center of the valley; it 

had been for half a century the principal channel of Knife 

Creek before capture of its headwaters by what is now the 

main fork, sometime between 1951 and 1976. In the lower 

VTTS, there are shorter gorges, 10–20 m deep, along Moraine 

Creek and two minor tributaries of Knife Creek (see map of 

Hildreth and Fierstein, 2003).

Alluvial Plains, Channels, and Veneers

Extensive braided plains of alluvial gravel had been laid 

down by the Ukak and Savonoski Rivers and by Katmai River 

and its tributaries long before 1912, but the abrupt introduction of eruption products caused severe aggradation for years 

afterward. Aggradation of the broad Katmai River floodplain 

(fig. 132) and conversion of the former Katmai Bay to braided 

alluvium and mudflats were extensively illustrated by Griggs 

(1917, 1918f, 1922). Comparison of the 1908 U.S. Coast 

and Geodetic Survey Chart No. 8555 (Fenner, 1923) with 

Figure 131. View northwest down gorge of 

River Lethe, ~25 m deep, in central VTTS, 

~4.5 km upstream from Three Forks. Upper 

half of exposed ignimbrite is nonwelded 

to weakly sintered where jointed; inner 

gorge is sintered to partially welded, with 

base not exposed. Large oxidized zone of 

fumarolically indurated tuff on far right wall. 

Brown mudflow deposit overlies thin white 

layer of dacite fallout on right rim. Mount 

Katolinat in cloud in background. Geologist 

at lower left.
Chapter 11. Posteruptive Evolution of the Landscape 169

Figure 132. Braided Katmai River floodplain viewed south-southeastward from slope of Trident Volcano. 

Coastline of Shelikof Strait at Katmai Bay is 23 km from camera, and Kodiak Island lies an additional 55 km 

beyond it. At right, lower gorge of Mageik Creek opens onto floodplain to join Katmai River. Barrier Range 

at upper left. Ash-covered glacier tongue at lower left separates Trident lavas from brown Jurassic siltstone 

overlain by dark-gray lavas of Mount Katmai on far wall of gorge. Near-white Novarupta pumice-fall deposits 

and derivative pumiceous screes mantle countryside far and wide. Floodplain was initial route taken by Griggs 

and his companions in approaching Mount Katmai in 1915–16. Before severe aggradation and complex braiding 

of floodplain in response to 1912 eruption, it had also provided principal trail from Savonoski to Katmai village.

Maynard’s topographic map of 1917 (Griggs, 1922) suggests 

that, even though the Katmai River estuary and former anchorage had been severely infilled, any general advance of the 

shoreline had been modest. By 1951, the coastal sandspit and 

sandbars had changed little since 1917, but tidal mudflats had 

apparently advanced ~1 km seaward (USGS 1:63,360-scale 

topographic map Mt. Katmai A–3). The gravel plain of the 

lower Ukak River likewise advanced ~1.5 km at the expense 

of the Iliuk Arm of Naknek Lake between the mapping of 1917 

and 1951 (USGS 1:63,360-scale topographic map Mt. Katmai

C–5). Morphological changes at the mouths of the Ukak and 

Katmai Rivers appear to have been modest since 1951, but no 

quantitative observations have been maintained.

In the VTTS, there were also a number of rapid posteruption alluvial responses that are interesting enough to record. A 

shallow pond ~400 m across formed in Novarupta basin west 

of the dome, impounded by the subtle east-dipping monocline north of Falling Mountain that marks the west rim of the 

vent structure. Still there in 1919, the pond drained due west 

toward the River Lethe along a shallow gorge that remains 

little changed today. The pond was later covered by a fan of 

alluvial pumice (fig. 18) that grew outward from the mouth of 

a gulch draining several ravines on the vent-wall scarp ~1 km 

southeast of Novarupta dome. 

In the uppermost Lethe arm, a dark-colored composite 

alluvial fan (fig. 26) that extends2 km northward from the compactional bench at the head of the valley had already formed 

by 1919. Fed by three streams that cut through the ignimbrite 

bench, the confluent fans are rich in clasts of andesite-dacite 

lavas from Mount Mageik. The fans scoured away the stratified dacite fall deposits and rest directly on the ignimbrite. 

Farther down the Lethe arm, the fall deposits are widely intact 

on the valley floor, except close to the River Lethe itself, which 

has incised a gorge 2–8 m deep into the ignimbrite. 

Likewise, in uppermost Knife Creek an alluvial fan in front 

of Glaciers 1 and 2 rapidly extended ~2 km northward atop the 

ignimbrite, scouring away most of the dacite fallout. Pre-1912 

clasts of lava (from Trident) are present here as well, but, compared to the Lethe fans, a much larger share of the alluvial gravels here are 1912 eruption products reworked off the glaciers.
170 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Downstream from the confluence of the Griggs fork, 

Knife Creek rapidly fashioned a shallow braided alluvial 

channel 150–300 m wide, floored by sintered ignimbrite and 

walled principally by the stratified dacite fall deposits. For 

~4 km below the confluence, its general configuration has 

changed little since 1919, as shown by National Geographic 

Society photographs. Just northwest of the nose of Broken 

Mountain, however, Knife Creek spread out across the central 

VTTS into a braided fan, 1.7 km wide and 3.5 km2 in area, that 

lasted more than four decades. The fan funnelled distally into 

the mid-valley gorge of Knife Creek and split off a minor left 

distributary to the River Lethe, as documented on the 1951 

USGS 1:63,360-scale topographic map Mt. Katmai B-4. The 

fan gravels are 1–7 m thick and rest directly on indurated 

ignimbrite, from which the fallout had already been stripped in 

the central VTTS by 1919 (Allen and Zies, 1923). Sometime 

between 1951 and our first visit in 1976, however, the fan 

was abandoned and the principal course of Knife Creek was 

captured by what is today the main fork, parallel but farther 

northeast (fig. 74).

The terminal Ukak lobe of the ignimbrite below Three 

Forks (fig. 29) records a complex fluvial history of erosion and 

sedimentation. The narrow corridor of the Ukak River (fig. 

30), which runs 2 km downstream from Three Forks, was rapidly stripped of its thin ignimbrite cover, exhuming a steep pre1912 channel cut in Jurassic shale. Another pre-1912 channel 

along the east side of the corridor has been only partly cleared 

of ignimbrite by incision of present-day Moraine Creek (see 

map of Hildreth and Fierstein, 2003). After emplacement of 

mudflow deposits atop the Ukak lobe ignimbrite, the exhumed 

Ukak River channel spread a thin sheet of gravel across both of 

them. Subsequently, as the river cut deeper into the ignimbrite 

barrier at the lower end of the corridor, at least three sets of terrace gravels were inset before gorge incision reached the base 

of the 1912 deposits, establishing a drainage configuration that 

has now persisted for decades.

Moraine Creek, which bends northeast at the toe of 

the steep corridor and becomes the marginal stream along 

the southeast edge of the Ukak lobe, was the site of various 

tuff-water interactions during and after ignimbrite emplacement—phreatic explosions, gravel stringers and insets 

between ignimbrite flow units, and ignimbrite remobilization 

and drainaway. Subsequently, two right-bank tributaries of 

Moraine Creek, temporarily blocked by the ignimbrite before 

incision of Moraine Creek, distributed sheets of coarse gravel 

atop and against the ignimbrite. These gravels were at least 

in part derived from nearby glacial till deposits. Because one 

of the tributaries was never overrun by the ash flows and the 

other only thinly so, it is unlikely that breakout of temporarily 

impounded ponds caused remobilization of the till. The severe 

seismicity that continued until at least 17 June suggests an 

alternative mechanism.

The pre-1912 channel of lowermost Windy Creek was 

buried by ~10 m of nonwelded ignimbrite (fig. 87) but is still 

marked by a gentle swale on the tuff surface that extends ~1.3 

km northward to its former confluence with the River Lethe. 

Windy Creek never reoccupied its former channel but instead 

cut a gorge ~250 m long through the blockage and established 

a new course around the western margin of the ignimbrite, 

~1 km west of its original one. The blockage temporarily 

impounded a lake that lasted at least through the summer of 

1918 (see “Lakes Impounded” in chapter 10).

Aeolian Deposits

A century of notorious Katmai wind has relocated and 

sorted millions of tons of pumice and phenocryst sand from 

the 1912 eruptive products. Much of the crystal-dominant 

ashfall in the central and lower VTTS has been stripped from 

the ignimbrite surface and redeposited in part as dunes and 

sand sheets along the northeast margin of the valley and in 

the hilly morainal terrain northeast of Three Forks. There the 

aeolian deposits variously overlie the layered dacite fallout, 

thin ignimbrite, 1912 soils, or glacial deposits. Behind the 

Three Forks moraine (figs, 29, 64), longitudinal dunes 6–8 

m high, now stabilized by willow growth, are separated by 

gravel-armored chutes with veneers of rippled sand. Some 

of the sand deposits expose as many as 70 pairs of coarse/

medium sand laminae. One sand sheet is gradually encroaching on a swamp impounded by the ignimbrite. Aeolian sand 

sheets locally climb up and over kames and irregular hills of 

till, around which the sluggish ignimbrite had merely banked.

Around the site of Katmai village, a pre-1912 dune field 

has been augmented by as much as 3 m of post-1912 sand that 

overlies complete fallout sections (Layers A-H) as thick as 23 

cm (fig. 21). Much of the sand spit that shelters the former 

estuary and anchorage (now mudflats), however, predates the 

eruption.

The pumice-fall deposits have been extensively stripped 

from ridgecrests by the region’s severe and frequent winds, 

which are intensified by the arterial role of Katmai Pass, one 

of the lowest saddles along the volcanic axis. Wedges of 

reworked pumice have piled up below the walls enclosing the 

upper and central VTTS, as well as in the downwind fallout 

sector to the east and southeast—along Ikagluik Creek, Katmai 

River, and Soluka Creek. Nearly every gully that descends 

to the VTTS from the Buttress Range, Mount Griggs, and the 

valley’s northeast wall has built a fan of pumiceous alluvium 

(Hildreth and Fierstein, 2003). From the fans, pumice then is 

frequently remobilized as slurries down the local drainages, so 

that floating clasts can still today be distributed tens of kilometers down the Naknek Lake system. 

The central VTTS is a wind-abraded desert marked by 

sandy windrows, sculpted pumice-block ventifacts, and etched 

surfaces of sintered ignimbrite. Pioneering vegetation cannot 

survive the sandblast and is able to establish a toehold only in 

the most sheltered gullies. Despite a century of wind scour, a 

few dry summer days will loosen ashy substrates sufficiently 

to permit intense duststorms in and near the VTTS. Windstorms still occasionally loft white vitric ash from the barren 

surface to elevations of many kilometers. Such high-altitude 
Chapter 11. Posteruptive Evolution of the Landscape 171

plumes of remobilized 1912 dust have been the cause of several spurious eruption reports (Hildreth and others, 2000), and 

such misleading reports still recur almost annually.

Behavior of Ash-covered Glaciers

We earlier discussed some effects of the pumice-fall 

mantle on the Knife Creek Glaciers and the glaciers on the 

north slope of Mount Mageik, as well as local evidence for 

ignimbrite interactions with the glacial termini (see “Emplacement over and against ice” in chapter 6). Here we summarize 

more broadly the behavior of glaciers affected by the 1912 

eruption. 

Mount Mageik has a substantial icecap that extends radially into nine glaciers, of which two terminated in 1912 on the 

floor of the Lethe arm at elevations lower than 2,100 ft (640 

m). Termini of all nine have retreated 500–1,200 m (in plan 

view) since 1951 and a few as far as 1,700 m since 1912 (Hildreth and others, 2000). The generality of 20th century recession here is no doubt dominated by climatic control of the ice 

budget and not significantly influenced by the mantle of 1912 

fallout. The fall deposits thinned across Mount Mageik from 

~50 cm on its northeast to ~5 cm on its southwest, and nearly 

all of it was removed from the glaciers within a few decades.

Mount Griggs, highest peak in the Katmai region, has 

six active glaciers, which are thin, narrow, and distributed 

radially around its summit. Elevations of their termini during 

the 20th century were in the range 3,000–3,800 ft (915-1,160 

m), except for the one south-facing glacier (5,000 ft; 1,525 m). 

All were thickly mantled with 1912 fall deposits, but all were 

too high to be reached by ash flows. Today only the lower 

third or so of each glacier is still covered with tephra, and this 

has generally been disrupted chaotically by ice movements. 

The upper reach of each glacier is steep, active, crevassed, and 

now free of its 1912 pumice cover. All six may have thinned 

a bit, but comparison of 1951 and 1987 aerial photographs 

shows that the terminal positions of three had retreated, one 

had advanced, and two had changed little. The lack of systematic glacial behaviour on Mount Griggs is likely to reflect a 

combination of climatic and edifice effects, with little influence attributable to the fallout (Hildreth and others, 2002).

Snowy Mountain, 25–32 km east of Novarupta, is 

blanketed by an icefield from which a dozen glaciers extend 

radially. Comparison of aerial photographs taken in 1951 and 

1984 shows that during that 33-year interval, termini of nine 

glaciers retreated, two were stationary, and the southwesternmost advanced ~150 m (Hildreth and others, 2001). The 

blanket of crystal- and pumice-rich 1912 fallout had a cumulative thickness of 1–2 m on the Snowy Mountain edifice, thinning to the north and east but thickening southwest to more 

than 3 m at the head of Katmai River. There, the southwestern 

glacier from Snowy Mountain (called Princess Glacier by 

Griggs, 1922, p. 131) is a major source of Katmai River, as 

is nearby Noisy Mountain Glacier, and both advanced ~150 

m between 1951 and 1984. Ice motion and surface erosion 

stripped the tephra from most of the Snowy Mountain glaciers 

decades ago, but those to the southwest and west still retain 

thick fallout blankets, especially atop their distal reaches. 

The ash-free glaciers to the east have all retreated, while the 

ash-covered ones to the west and southwest of Snowy Mountain have advanced or stagnated (Hildreth and others, 2001). 

Where thick enough and enduring for decades, the pale gray to 

tan tephra mantle evidently retards ablation.

The Trident group, closest to Novarupta, received a 

thicker blanket of 1912 fallout than any other edifice in the 

Katmai cluster. In addition, Knife Creek Glaciers 1, 2, and 3 

on the north side of Trident (fig. 133) were covered distally 

by thin ignimbrite, and the all-rhyolite ash flows (Package 

1) ran all the way up Glacier 1 to feather out in the saddles 

between Trident summits. Glaciers 1 and 2, which each issue 

from multiple cirques on the north face of Trident, have been 

largely cleared of 1912 ejecta along steep upper reaches ~800 m 

long, by a combination of flowage and new ice accumulation. 

Medial and distal parts of both remain covered by as much as 

12 m of 1912 material, supplemented locally by more recent 

avalanche rubble (Hildreth and Fierstein, 2003). Comparison 

of 1951 and 1987 aerial photographs shows that Glacier 1 

advanced 250 m and Glacier 2 at least 300 m during that interval (Hildreth and others, 2003a). Along with nearby Glaciers 

3 and 4, which head on Mount Katmai, both have thus overrun 

the edge of the 1912 ignimbrite sheet in the upper Knife Creek 

arm. In contrast, glaciers on the south side of Trident, where 

supraglacial fall deposits are 4–5 m thick, have thinned and 

wasted, though changes in terminal positions have been inconsistent (Hildreth and others, 2003a).

Behavior of glaciers on Mount Katmai involves the 

complication that some (not all) were partly beheaded by caldera collapse (fig. 134). Nonetheless, all of the dozen radial 

extracaldera glaciers around Mount Katmai were blanketed 

with several meters of Novarupta fall deposits. Some aspects 

of Knife Creek Glaciers 3, 4, and 5 were discussed earlier 

in the context of their interactions with 1912 ignimbrite (see 

“Emplacement over and against ice” in chapter 6). Glacier 

3, although still partly fed from Peak 6128, lost at least half 

its catchment area to collapse of the summit. The glacier has 

since thinned and disrupted its thick ejecta blanket, but its 

upper reach remains active and crevassed; although its lower 

half looks hummocky and stagnant, its terminus actually 

advanced ~225 m between 1951 and 1987. Glacier 4 is fed 

from the extensive North Katmai Icefield, which was partly 

beheaded but remains robust, not shrinking. The vigorously 

lobate terminus of Glacier 4 advanced ~150 m between 1951 

and 1987, and a National Geographic Society photograph 

taken in 1919 (fig. 128) shows that Glacier 4 had already 

advanced 500 m before 1951, for a total of 650 m since 

1919. Knife Creek Glacier 5 is supplied from an isolated 

cirque 2.5 km northeast of the caldera rim and was thus not 

affected by caldera formation. Between 1919 and 1951, its 

terminus advanced ~1,300 m, but since 1951 its distal 700-m 

reach has thinned and stagnated, although its terminal position has changed little.
172 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Figure 133. Ash-mantled snout of Knife Creek Glacier 1, 30–40 m high. Pyroclastic density currents crossed 

this glacier in 1912, and Novarupta fall deposits draped it; both have been attenuated and disarranged in a 

century of ice movement. At lower right, intact pale-gray dacite fall deposits many meters thick are capped by 

fine-grained Layer H and by a veneer of white pumiceous alluvium but are otherwise undisturbed.

Figure 134. Katmai caldera, 4 km across at rim, viewed south-southwestward from helicopter in 1999. Several 

extracaldera radial glaciers persist in spite of loss of mountain’s summit in 1912. Icefield at upper right mantles 

slope of twin peaks 6128 and 6200, and since 1920s it has extended a narrow intracaldera tongue down west 

wall. Slump-block bench (at center) on southwest wall progressively accumulated an intracaldera glacier that 

now reaches lake level. South-rim rhyodacite lavas form crest and crag above that glacier. Thick dacite lava 

flow caps north-ridge cleaver in right foreground.
Chapter 11. Posteruptive Evolution of the Landscape 173

Two substantial glaciers west and south of the caldera 

exhibit inconsistent behavior. The Wishbone Glacier, fed 

from the Katmai-Trident saddle, divides into two tongues that 

extend several kilometers southward into narrow gorges. The 

southeast tongue advanced 200 m between 1951 and 1989, 

while the southwest tongue thinned and receded slightly, 

although it has a small western lateral lobe that advanced 110 

m (Hildreth and others, 2003a). Due south of the caldera rim, 

Metrokin Glacier was partly beheaded but continues being 

supplied by the west-rim ice shelf below Peaks 6128 and 6200 

(Hildreth and Fierstein, 2003). Its canyon-confined terminus 

retreated ~600 m between 1951 and 1989 and another 400 m 

between 1989 and 2001. This is the glacier that shed the Katmai River pumiceous debris flow (fig. 120), so its insulating 

blanket of fallout was substantially less than on other glaciers 

of Mount Katmai.

The steep southeast slope of Mount Katmai supports 

three isolated glaciers, all beheaded by collapse and today 

respectively 1.8, 2.1, and 1.2 km long (Hildreth and Fierstein, 

2003). The northern one fills the valley below the east notch 

in the caldera rim. Termini of all three have retreated more 

than 1 km since 1951.

The East Katmai Icefield (Hildreth and Fierstein, 2003) 

is largely fed by three ice tongues on the steep east slope of 

the postcaldera summit of Mount Katmai (Peak 6715). Only 

its upper parts have been cleared of 1912 ejecta, but the whole 

icefield is actively crevassed. It contributes northward to 

Ikagluik Glacier, the terminus of which has moved little since 

1951, and contributes southward to Noisy Mountain Glacier, 

which has advanced ~150 m since 1951.

The North Katmai Icefield (Hildreth and Fierstein, 2003) 

is also robustly active, feeding icefalls that descend toward 

Glacier 4 and toward Ikagluik Creek. The icefield is partly 

supplied by a series of small cirque glaciers on the steep north 

rim of the caldera. Although these were deprived of contributions from higher on the foundered edifice, each remains 

actively crevassed and shrinkage is limited to notches on the 

caldera rim. 

Katmai Caldera Lake and Intracaldera Glacier 

Development

Caldera collapse left a sheer jagged rim, which was 

initially capped by ice cliffs of the beheaded glaciers in four 

sectors, 90o–150o, 190o–260o, 280o–350o, and 0o–10o, thus 

fringing ~60 percent of the caldera’s upper margin (Griggs, 

1922; photos on p. 175, 178). Because much of the ice had 

been fed from higher on the vanished edifice, the ice cliffs 

wasted over a period of decades, thinning and receding 

50–800 m from the rim and leaving rubbly deposits of ablation 

debris—largely consisting of what had been 1912 supraglacial 

ejecta. On the southwest side, however, Peak 6200, which 

stands 275 m higher than the rim, has continued to sustain an 

ice shelf (fig. 134). Much of the shelf has receded from the 

rim, but a narrow ice tongue has extended from its north end 

into a rim scallop and partway down the west wall toward the 

lake (figs. 103, 134). 

Complex collapse left kilometer-wide slump blocks that 

rose to inward-sloping benches 300–400 m above the caldera 

floor at its north and southwest margins. The benches had 

accumulated snow patches by 1917 (Griggs, 1922, p. 172) and 

still only modest snowfields by 1923 (figs. 12, 17 of Fenner, 

1930). By Hubbard’s first trip to the rim (1929), the snowfields had turned to ice and he reported a bergschrund (Hubbard, 1932), but the earliest record of extensively crevassed 

glaciers on the benches is a set of 1951 aerial photographs. 

As observed in 1953–54 by Muller and Coulter (1957a), the 

southwest intracaldera glacier terminated in ice cliffs 50–80 m 

above the lakeshore, the north glacier mantled only the upper 

half of its bench, and the narrow ice tongue on the west wall 

reached halfway down to the lake. In 1976, the western edge 

of the southwest glacier had barely reached the lake, but later 

it wasted back. Although all three intracaldera glaciers have in 

the past calved icebergs into the lake, a set of 1987 aerial photographs shows all of them terminating atop steep rocky slopes 

just shy of entering the lake. By 1999, however, small tongues 

of both slump-block glaciers had reached the lakeshore (figs. 

134, 135). The steep western ice tongue had surged in 1976 

and did so again in 2001, twice temporarily reaching the 

lakeshore but subsequently wasting back upslope. Regional 

snowline was estimated by Muller and Coulter (1957a) to be 

about 1,675 m (5,500 ft), which is higher than both iceclad 

benches and higher even than some segments of the caldera 

rim. Snow that accumulates directly on the benches is clearly 

augmented by drift and avalanching from the rim.

The lake itself has a complex century-long filling history. Although a turquoise lake was 10–15 m deep during the 

expeditions of 1916–19 (fig. 136), it had disappeared by 1923 

when Fenner and Yori descended to a caldera-floor mudflat 

(Fenner, 1930). Fenner described numerous steam columns 

rising from the floor and the fringing talus; fumarolic incrustations and the odor of H2

S; boiling mudpots as wide as 8 m that 

produced gigantic bursting mud bubbles; and a mud geyser 

(fig. 137) that erupted at short intervals in jets as high as 60 m 

with loud detonations. He also showed that Horseshoe Island 

was a dome of platy to blocky dacite lava ~350 m in diameter 

with ~20 m of visible relief (fig. 138). It had a steep-walled 

central lagoon, ~75 m wide, >20 m deep, and open to the 

northwest (figs. 15, 16 of Fenner, 1930), that had been explosively reamed through the dome; Fenner described stratified 

deposits dipping radially from the dome that may have been 

related to such an event. He suggested but could not confirm 

that Jurassic sedimentary rocks cropped out near the base of 

the caldera wall. While this is not unreasonable in view of the 

elevations and extracaldera distribution of Naknek Formation 

exposures (Riehle and others, 1993), such rocks have not been 

identified in the breccias deposited explosively on the caldera 

rim. The question remains unresolved because the base of the 

wall now lies beneath at least 200 m of lake water.

By 1929, Horseshoe Island was fully concealed by 

the rising lake (Hubbard, 1932), implying a filling rate of 
174 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

at least 3–4 m/yr after 1923. When it was 10–15 m deep in 

1917, Maynard had surveyed the elevation of the lake level 

to be ~1,003 m (Griggs, 1922), but by 1951 it was ~1,188 m 

(Motyka, 1977), yielding an average filling rate of 5.4 m/yr for 

34 years. For the short interval 1951–53, Muller and Coulter 

(1957a) also estimated a change of ≥5 m/yr. In 1974, Motyka 

(1977) surveyed lake level at 1,235 m (and 1.2 m higher in 

1975), giving a reduced rate of ~2 m/yr (47 m in 23 years) for 

the interval 1951–74. Returning in 1977, however, Motyka 

(1978) found the level to have risen to 1,242 m, implying an 

increase in rate to ~3 m/yr for 1975–77. We are not aware of 

any precise measurements since 1977, but observations on 

our many trips to the caldera rim (1976–2001) suggest that 

additional deepening of ~10 m had taken place. 

From an inflatable raft on the lake in 1977, Motyka 

(1978) measured a depth no greater than 200 m, an apparent 

discrepancy of ~50 m with the 1917 survey: [(1,242–1,003 

m)+(10–15 m) = 249–254 m depth by 1977]. The discrepancy 

could reflect large uncertainties in one or both surveys or as 

much as 50 m of lake-floor sedimentation in 60 years. Whether 

adequate to account for the discrepancy or not, sediment 

accumulation is still substantial in the 21st century, as shown 

by continuing rockfall from unstable walls, several muddy 

meltwater waterfalls, and aeolian and sheetwash transport of 

1912 ejecta and glacial ablation debris across the rim.

According to pilots quoted by Muller and Coulter 

(1957a), the lake had not frozen over in winter as late as 

1953. Motyka (1977) reported that it did freeze in 1967 but 

not in 1975, suggesting variations in heat flux through the 

lake floor. Winter and spring freezing has become common 

in recent decades, however. Since 1953, summer observers 

have witnessed calved icebergs circulating around the lake 

and melting within hours. A yellow-green upwelling in the 

northeastern part of the lake has been observed intermittently 

for decades, roughly over the site of the mud geyser photographed in 1923 by Fenner (1930). In 1975, Motyka (1977, 

1978) paddled through the upwelling, reporting a flux of 

small sulfur particles, bubbles, and the odor of H2S. In 1977, 

he measured a lake-bottom temperature of 20.5oC, which 

declined to 12oC only 10 m above the floor, then remained 

nearly constant at 8.8oC at depths between 150 m and 10 m. 

Motyka noted that this represented a substantial temperature 

increase from the 5.5oC recordings he had made at depths of 

10–60 m only 2 years earlier. 

Figure 135. North and northeast wall of Katmai caldera viewed from southeast rim. Slump-block bench at foot 

of north wall progressively accumulated an intracaldera glacier that now reaches lake level. Hydrothermally 

altered wall below east rim notch (right) is one of several such internal zones that supplied acid-altered ejecta 

during caldera collapse (see fig. 106). Northwest-dipping lavas of true summit (peak 6715 on central skyline) are 

cut by vertical dike complex; southeast-dipping strata above east notch (at right) are part of same edifice, gutted 

in 1912. Pedestal on skyline rim above glacier is head of north-ridge dacite lava flow prominent in figure 134.
Chapter 11. Posteruptive Evolution of the Landscape 175

A

Figure 136. Katmai caldera: North bench and 

Horseshoe Island. Views northward from south rim 

showing intracaldera lake and slump-block bench on 

north wall: A, 1917 and B, 1989. Lake was ~10 m deep 

in 1917, >200 m in 1989. North bench had thin snow 

shelf in 1917, but no glacier was seen before 1929. By 

1989, however, the glacier was >50 m thick and locally 

flowed into lake. Crest at right is true summit (Peak 

6715 at 2,047 m); lake level in 1917 was 3,290 ft (1,003 

m), and snow shelf on north bench was at 4,800–4,900 

ft (1,463–1,493 m). Volcanic strata above glacier dip 

northwest away from dike complex (upper right) at core 

of eviscerated edifice. Horseshoe Island was a dome 

of platy to blocky dacite lava ~350 m in diameter that 

extruded before 1916 and has been wholly submerged 

since 1929 at latest. When the lake temporarily 

disappeared in 1923, the dome had ~20 m of visible 

relief. It also had a steep-walled central lagoon, open 

to the northwest, which was ~75 m wide, >20 m deep, 

and is presumed to have been reamed explosively (see 

fig. 138). For several views of caldera floor when lakefree in 1923, see Fenner (1930).

A

B
176 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Figure 137. Mud geyser with its own ejecta ring on northeastern floor of Katmai caldera when Yori and 

Fenner descended west wall in July 1923 (Fenner, 1930). Caldera lake, ~10 m deep during all previous 

ascents to rim (1916–1919), had drained by 1923, but by next known ascent in 1929, lake was tens of 

meters deep and floor was submerged for good. Note numerous fumaroles in talus at base of north wall, 

which is now draped by intracaldera glacier (figs. 134, 135). Fenner wrote that geyser threw mud as high 

as 60 m in frequent roaring explosions.

Figure 138. View eastward of Katmai caldera floor mudflats from partway down west wall in July 1923 

(Fenner, 1930), the only time the caldera was ever seen without a lake. At center is Horseshoe Island 

dacite dome, ~350 m in diameter with ~20 m of visible relief; its steep-walled central lagoon, probably 

reamed out explosively, was ~75 m wide and >20 m deep. See figure 136 for 1917 view of dome as 

island in lake.
Chapter 11. Posteruptive Evolution of the Landscape 177

Two water samples taken at a depth of 60 m in 1975 and 

analyzed at the USGS in Menlo Park contained (in mg/L) 

1,350–1,750 Cl, 1,200–1,250 SO4, 590–760 Na, 120–140 

SiO2, and 12–14 B; their pH was 2.5–3.0 as measured in the 

field or 2.05 as calculated in the lab (Motyka, 1977). Another 

sample taken in the summer of 1989 had a similar composition 

(Cameron and Larson, 1992). The acidity suggests dissolution 

of gaseous CO2 in the lake water and little or no bicarbonate 

ion. Such chloride-sulfate waters are typical of volcanic crater 

lakes and are consistent with meteoric meltwater mixed with a 

substantial input of fluids from drowned fumaroles.

Photographic Comparisons: Then and Now 

We made intermittent efforts over the years (1982–2001) 

to photograph features in and near the VTTS for which the 

National Geographic Society had provided images from 

1917–19. Paired images are distributed throughout the text 

as appropriate to the subject matter, but they are all cited, 

abstracted, and highlighted here.

Mount Katmai Beheaded (fig. 100A, B).—Images of 

postcaldera Mount Katmai taken in 1915 and 1989 from the 

Katmai River floodplain show little change in its southern 

flank and caldera-rim profile.

Katmai Caldera: North Bench and Horseshoe Island (fig. 

136A, B).—Views northward from south rim showing intracaldera lake and slump-block bench on north wall of caldera, 1917 

and 1989. Lake was ~10 m deep in 1917, more than 200 m 

in 1989. North bench had thin snow shelf, but no glacier was 

seen before 1929. Crest at right is true summit of present-day 

Mount Katmai, which is cut by a dike complex (upper right) 

at the core of the eviscerated edifice. Horseshoe Island was a 

20-m-high dome of platy to blocky dacite lava ~350 m in diameter that has been wholly submerged since before 1929.

Katmai Canyon Landslide Deposit (fig. 123A, B).—A 

chaotic 0.08-km3

 slide mass broke loose from the south wall 

of Mount Katmai on the night of 6/7 June after deposition 

of Novarupta fallout Layer A and part of Layer B. Covering 

~1.2 km2 and as thick as 125 m, the shattered andesitic debris 

blocked the narrow gorge of Katmai Canyon and impounded 

a 5-km-long lake, which breached by 1915. Views from 1917 

and 1998.

Novarupta and its Ejecta Ring (fig. 55A, B).—Views 

northeastward of the 380-m-wide lava dome and its asymmetrical ring of Episode III ejecta, 1919 and 1982. Above the 

dome-encircling moat, the ejecta ring ranges in height from 

~7 m in the southwest to 225 m in the northeast, where it 

broadens into the 1-km-wide northeast-elongate mound called 

the Turtle. Configuration of the dome, ring, faults, and fissures 

has changed little since 1919. The dome steamed vigorously 

for decades, as did several fumarolic fissures along the lower 

ring, but emissions were modest atop the Turtle and are weak 

and wispy today. At lower right of 1919 image, a fallen block 

of shattered dacite of Falling Mountain crumbled in place to 

form a 12-m-high hummock that has sometimes been mistaken 

for a domelet or “volcanette.”

Extensional Faults Atop the Turtle (fig. 99A, B).—Views 

toward northwest along southern set of northwest-striking 

faults near crest of the Turtle, ~1 km northeast of Novarupta 

dome, 1919 and 1982. Taken from near intersection with 

northeast-striking fault set (fig. 97). Lower scarp represents 

~3 m displacement, upper scarp ~20 m. Degradation of scarps 

reflects 63 years of sloughing induced by wind and snowmelt. 

Griggs Fork of Knife Creek (fig. 128A, B).—Views 

eastward from north-bank rim at lower end of Griggs fork up 

its 3-km-long braided floodplain, 1919 and 1982. At head of 

valley in center distance, Glacier 5 has advanced 1,300 m. 

Glacier 4 at right has advanced 650 m. Both glaciers remain 

heavily tephra-covered a century after the eruption. Cutbanks 

consist of ashy fines-rich ponded sediments overlain by terrace 

gravels and phreatic surge beds.

Overview of Fissure Lake (fig. 84A, B).—Views westward along trough occupied by Fissure Lake (Griggs, 1922, 

p. 212, 244) during first decade after eruption, 1917 and 1982. 

Trough was excavated by phreatic explosions along hingeline 

of compactional bench at southwest edge of VTTS. Glacier 

occupied present-day site of West Mageik Lake.

Floor of Fissure Lake (fig. 94A, B).—Views westward 

along 100-m-wide trough of Fissure Lake, 1917 and 1982. 

Ignimbrite scarp at right is ~20 m high and was locally still 

steaming in 1917; that at left is more than 30 m high. Sediment from the glacier (center distance, ~1 km from the camera) was already by 1919 filling the lake, which was largely 

silted in by 1923. Later withdrawal of the glacier terminus 

created present-day West Mageik Lake (not in view), which 

drains north (right) to the River Lethe.

Lethe Arm of VTTS (fig. 108A, B).—Views northwest and 

north across Lethe arm of upper VTTS to Buttress Range (at 

left), 1917 and 1982. Distance from bench at northwest toe 

of Mount Cerberus to steaming bench across valley at left is 

4 km; fissure control of many (not all) fumarolic emissions in 

upper valley is conspicuous. From just west of Mount Cerberus, 1982 image shows River Lethe and 14-km-long reach 

of VTTS, fumarole-free. 
178 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Horses of a U.S. Geological Survey pack train departing the Valley of Ten 

Thousand Smokes after leaving C.N. Fenner and Charles Yori and a wellsupplied base camp at the foot of Mount Cerberus on 23 June 1923. The 

horses brought Fenner and Yori to the area from Kanatak via Kejulik and Yori 

Passes for two months of fieldwork. No other geologists are known to have 

ridden to the area on horseback. Novarupta dome and surrounding fumaroles 

are seen in upper right. Photo by Charles Yori.
Chapter 12

The Katmai Volcano Cluster

An extraordinary aspect of the greater Katmai magmatic 

system is the clustering of andesite-dacite volcanoes close to 

the 1912 eruption site (figs. 5, 6). Along the volcanic chain 

here, crater-to-crater spacing between adjacent, mostly contiguous, edifices is typically 5 km or less, one of the world’s 

most tightly spaced lines of arc stratovolcanoes. Discrete 

eruptive edifices far outnumber the stratocones and lava domes 

formally named. Mount Martin is a relatively simple cone 

and Mount Griggs a fairly symmetrical cone, but both overlie ruggedly eroded remnants of older edifices. Both Mount 

Katmai and Snowy Mountain consist of pairs of contiguous 

cones, and Mount Mageik and Trident Volcano each have 

four overlapping cones. In addition, five dacitic lava domes 

form an array around the Trident edifice. There are thus no 

fewer than 21 separate volcanic vents in the Katmai cluster, of 

which 16 lie within 11 km of Novarupta and 7 are within 8 km 

(Hildreth and Fierstein, 2003). Numerous K-Ar and 40Ar/39Ar 

ages for most of these volcanoes were presented by Hildreth 

and others (2003) and are summarized in table 1. Martin, 

Mageik, Trident, Katmai, Griggs, and Snowy have all had 

Holocene eruptions, but not one of the 21 pre-1912 vents ever 

produced high-silica rhyolite—the dominant product of the 

1912 eruption. Mount Katmai has produced modest amounts 

of rhyodacite (68-72% SiO2) and basalt, but all the rest have 

produced exclusively andesite-dacite. Coincidence of such 

an anomalous clustering of intermediate-composition vents 

with the anomalous site of rhyolitic magma generation, each a 

rarity on the Alaska Peninsula, induces inference of a relationship. The unusual degree of magmatic focussing, particularly 

beneath the Katmai-Trident cluster, may have provided the 

thermal environment necessary for intracrustal production and 

storage of phenocryst-poor high-silica rhyolite magma.

Here we provide overviews of the morphology, composition, and eruptive history of each of the principal volcanoes of 

the Katmai cluster (table 1). 

Alagogshak Volcano

Oldest edifice in the Katmai cluster, Alagogshak lies 

on the rangecrest 15 km southwest of Katmai Pass (Hildreth 

and Fierstein, 2003) and is centered only 3 km southwest of 

Mount Martin (figs. 5, 26). Originating by 680±20 ka, the 

glacially dissected volcano produced 14±4 km3 of andesitedacite eruptive products during several episodes in the middle 

and late Pleistocene (Hildreth and others, 1999). From a 

central vent marked by hydrothermal alteration and remnants 

of a cratered fragmental cone on the drainage divide, glacially 

incised stacks of lava flows dip radially and extend 6–10 km 

in most directions. The basal flow in the northwest sector, 

resting on Jurassic basement, gave a K-Ar age of 680±20 ka. 

In the southwest sector, intracanyon lava flows yielded ages of 

394±46 ka and 389±71 ka, and to the south, the top flow of a 

stack of seven andesite lavas gave an age of 104±10 ka. 

The youngest unit at Alagogshak is an andesitic lava flow 

(61% SiO2

) that descended steeply southeastward from the 

rangecrest and spread into upper Alagogshak Creek, where 

its 100-m-thick distal lobe now forms a glacially scoured 

plateau. Originating at an ice-clad knob, which is probably a 

flank-vent dome 1.5 km east of the crater, the lava flow gave 

an age of 43±8 ka. No evidence is known for subsequent 

activity until construction of the nearby cone of Mount Martin 

in the Holocene. The medium-K calcalkaline eruptive suite 

(57–66% SiO2) of Alagogshak Volcano is compositionally 

varied, probably reflecting independent evolution of different 

magma batches supplied intermittently over a lifetime of more 

than 600,000 years, much longer than that of other volcanoes 

in the Katmai cluster.

Mount Martin

Youngest stratocone in the Katmai cluster, Mount Martin consists of a 2-km-wide fragmental cone (fig. 26) and ten 

overlapping coulees of blocky dacite (fig. 5), each lobe 75–100 

m thick, that descend northwest for 10 km (Hildreth and Fierstein, 2000, 2003). Although it exceeds 1,860 m in elevation, 

the cone itself has local relief of only ~500 m, owing to its 

construction upon a high ridge of Jurassic basement rocks. Of 

the 7-km3 present-day volume estimated for Mount Martin, the 

cone makes up only 5 percent and the 31-km2 lava-flow field 

about 95 percent. Despite a cone-encircling collar of small 

active glaciers, erosion of the cone and coulees is insignificant, indicating that Mount Martin is a Holocene volcano in its 

entirety. Because the topmost flow distally is overlain by soil 

and tephra layers as old as 6 ka (Fierstein, 2007), the package 

of lava flows must have been emplaced in the early Holocene, 

conceivably in an effusive episode only years or decades 

long. The cone has been marked by a steam plume persistent 

throughout the century since the edifice was 
Table 1. Physical data for Katmai cluster volcanoes. [Present volumes for Mount Katmai are calculated for edifices prior to 1912 caldera collapse. Volume erupted from Southwest Katmai includes ~25 km3 for edifice, 5±2 km3 

pyroclastics, and 12±5 km3 for 22.5-ka rhyolite pyroclastics] Volcano/edifice SiO2 range Age range of Present area Volume today Volume Notes of products activity (km2) (km3) erupted Alagogshak Volcano 57–66 680–43 ka 20 5 14±4 Central-vent stratocone plus outliers Mount Martin 58–64 Holocene 33 7 8 Vigorous fumaroles in crater atop co

Mount Mageik 56–68 Since 93 ka 80 20 30 Four overlapping subedifices, each w

Southwest Summit 56–68 93–80 ka 32 9 17 Central Summit 58–66 80–60 ka 10 4 6 North Summit 60–64 60–10 ka 13 1.5 2 East Summit 60–64 Holocene 25 5 5.5 Trident Volcano 53–72 Since 143 ka ~10 22±3 Four contiguous cones and several d

East Trident 58–65 142±15 ka 7–8 2.3 6–9 Trident I 53–64 101–58 ka 14–15 4 7–10 Pyroclastic-flow remnants 57–72% S

West Trident 55–64 44±12 ka 8–9 2.4 3–4 Trident domes 54–65 late Pleistocene 5 0.7 1 Six domes include Mount Cerberus a

Southwest Trident 57–65 1953–1974 8.5 0.65 0.7 Cone and lava apron built since 1953 Mount Katmai 51–72 Since 100 ka 43 Two overlapping cones, both cut by 

Northeast Katmai 52–66 100–50 ka 25 10 15±3 Early basaltic cone followed by ande

Southwest Katmai 51–72 60 ka to 1912 61 20 42 Horseshoe Island dome concentric w

Novarupta 51–78 1912 only 3 13 13 New flank vent drained magma from 

Snowy Mountain 55–64 200 ka to Holocene 7 Two contiguous cones; two vents 4 km 

Northeast Snowy 61–64 180 ka to Holocene 20 5 8±2 Dome plugs amphitheater of HoloceSouthwest Snowy 55–62 20090 ka 13 2 5±2 Glacially dissected aretes and windo

Mount Griggs 51–63 292 ka to Holocene 60 20–25 35±5 Sector collapse refilled by Holocene 
Chapter 12. The Katmai Volcano Cluster 181

first observed in 1913. The plume coalesces from as many as 

20 fumaroles, rich in CO2, H2S, and SO2, that are precipitating sulfur in the talus northwest of a shallow lake on the floor 

of its steep-walled 300-m-wide crater (fig. 139). Scoriaceous 

and massive glassy blocks of the cone are andesitic (59–61% 

SiO2), whereas the stairstep sequence of coulees is dacitic 

(62.5–64.2% SiO2). Eruptive products yield a tight compositional array that is similar to the andesite-dacite suite erupted 

at Novarupta in 1912 but is poorer in Sr and marginally more 

potassic (Hildreth and Fierstein, 2000). Mount Martin is 

essentially a Holocene successor to Alagogshak Volcano, their 

craters being only 3 km apart (figs. 26, 140). Long persistent earthquake activity and recurrent small swarms beneath 

and near Mount Martin were punctuated by a strong swarm 

in January 2006; Alaska Volcano Observatory located 860 

events, mostly ML 0–1.5 and largely at depths of 1–4 km, 

but they were accompanied by no other evidence of volcanic 

unrest (Dixon and Power, 2009).

Mount Mageik

An ice-capped compound andesite-dacite stratovolcano, 

Mount Mageik is one of the most extensive (80 km2) and 

voluminous (30 km3) edifices in the Katmai cluster (fig. 140). 

Each of its four summits is a discrete eruptive vent (Hildreth 

and others, 2000), and each is the source of numerous lava 

Figure 139. Crater floor of Mount Martin, where numerous fumaroles rich in sulfur gases and CO2 combine to 

produce prominent plume, which has persisted above cone since first reported in 1913 (see photos in Griggs, 1922). 

flows (56–68% SiO2). At least 57 lava flows are exposed, 

many of them 50–200 m thick distally (owing to ice-contact 

emplacement). Three of the four overlapping centers are 

severely eroded glacially, but the East Summit is a Holocene 

edifice, from which a dozen leveed lava flows (60–64% SiO2) 

have descended toward Katmai Pass (figs. 5, 28), where 

blocky terminal lobes are 60–150 m thick. Ice-filled craters 

mark three of the summits, but the Central Summit is capped 

by an ice-clad dacite dome. An ice-free 350-m-wide phreatic 

crater between the East and Central Summits contains an acid 

lake (pH ~1) and many superheated fumarolic jets. Holocene 

debris avalanches have broken loose from three different sites 

on the south slopes of Mount Mageik, the youngest triggered 

by seismicity attending collapse of Katmai caldera in 1912 

(Hildreth and others, 2000).

The four crowded cones of Mount Mageik epitomize the 

close clustering of the Katmai volcanoes. Physical overlap 

and relative erosion show the Southwest Summit cone to be 

the oldest, followed in order by the Central, North, and East 

Summit cones. The Southwest Summit subedifice is larger, 

longer lived, and compositionally more varied than its companions. Basal lavas of the Southwest Summit, resting on 

Jurassic basement rocks along Martin and Alagogshak Creeks, 

respectively, yield K-Ar ages of 93±8 ka and 89±8 ka. The 

lowest lava flow from the Central Summit in the southeast sector gave 71±11 ka, and a 150-m-thick andesite lava from the 
182 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

North Summit, which rests on basement rocks at the northwest 

toe of the mountain, gave 59±11 ka. No attempt was made 

to date the Holocene lavas of the East Summit, but tephras 

overlying them suggest that some could be as young as 2,500 

years (Fierstein, 2007). Judging by their relative degrees of 

degradation, the dozen Holocene lava flows represent several 

discrete episodes (Hildreth and others, 2000). The postglacial 

eruptive volume is ~5–6 km3, to which dacitic fallout and a 

small andesitic pyroclastic-flow deposit contribute no more 

than 0.1 km3.

All products of Mount Mageik are plagioclase-rich 

pyroxene-dacites and andesites that form a calcic medium-K 

arc suite (Hildreth and Fierstein, 2000; Hildreth and others, 

2000). We estimate eruptive volumes of 17, 6, 2, and 5.5 km3

for the Southwest, Central, North, and East Summit edifices, 

respectively, yielding a total of ~30 km3.

Mount Mageik’s fumarolic plume is often conspicuous, 

but none of the sporadic reports of 20th century tephra eruptions (for example, Jaggar, 1927) are plausible. Configuration of the crater has not changed since it was first photographed in 1923 (Fenner, 1930; Hildreth and others, 2000), 

Figure 140. Aerial view of ice-clad Mount Mageik toward south-southwest. Each of its four summits is an 

independent eruptive vent for andesite-dacite lavas as old as 93 ka and as young as middle Holocene (Hildreth 

and others, 2000). At right are Mount Martin and Alagogshak Volcano. At lower left is Mount Cerberus dacite 

dome, guarding entrance to Katmai Pass. At lower right, 1912 ignimbrite banks against toe of Mount Mageik 

and displays well-developed “high sand mark” bench that rises ~50 m above valley floor.

and the only tephra deposits younger than 2 ka on the flanks 

of Mount Mageik are the Novarupta pumice falls of 1912 

and Trident ash of 1953–74.

Trident Volcano and its Domes

 Like Mount Mageik, Trident consists of four contiguous andesite-dacite cones (fig. 141), only one of which was 

constructed in the Holocene. That cone, Southwest Trident, 

erupted from 1953 to 1974 but was largely built in the 7-year 

interval 1953–60, during which four lava flows and most of 

the fragmental cone were emplaced. The three Pleistocene 

edifices young from east to west, and all three are severely 

eroded glacially (Hildreth and others, 2003a). 

East Trident, a small andesite-dacite cone (Peak 6010; 

58–65% SiO2) almost contiguous with Mount Katmai, is 

gutted by five glacial cirques, which expose a hydrothermally 

altered core and stacks of 10–20 radially dipping lava flows 

and breccia sheets. Most are silicic andesites 10–30 m thick, 

but 100-m-thick lavas that support the southwest ridge 
Chapter 12. The Katmai Volcano Cluster 183

Figure 141. Trident volcanic group viewed northwestward from lower Mageik Creek near its confluence with 

Katmai River. Four separate eruptive vents are visible. Two peaks at right are parts of East Trident; high peak 

at center is Trident I; and at left, black cone of Southwest Trident (1953–74) largely obscures snowclad cone 

of West Trident. Trident cluster is as old as 143 ka (Hildreth and others, 2003a, b). At far left is Observation 

Mountain. At right, black bench of glaciated andesite from Mount Katmai overlies brown bench of Jurassic 

siltstone along canyon of Mageik Creek. Pale-gray pumice-fall deposits from Novarupta mantle most slopes.

and cap the northeast ridge are dacites (63–65% SiO2). The 

northeast ridge dacite, which extends nearly to the summit 

(indicating that most of East Trident is older) yields a K-Ar 

age of 142±15 ka. An analytically indistinguishable age of 

143±8 ka for a basal andesite lava low on the north-northwest 

arête suggests, however, that activity at the small East Trident 

cone was short lived. Peak 5700, central prong of the “trident” as viewed from the southeast (the aspect that inspired 

the volcano’s name; Griggs, 1922, p. 98–9), is not a separate 

cone but simply the ruggedly eroded southwest flank of East 

Trident. Reconstruction suggests that the cone may once have 

exceeded 6,600 ft in elevation, which may have once made it 

the highest of the Trident summits.

Trident I is a discrete andesitic cone (Peak 6115; 

53–63% SiO2) that forms the central and highest edifice (1,864 

m) of the Trident group. Its lavas bank against East Trident 

at their mutual saddle. The core of the edifice is eviscerated 

by a north-face cirque, the sheer headwall of which reveals 

~200 m of crudely stratified andesitic breccia overlain by 

a 150-m-thick near-summit lava (63% SiO2), which yields 

a K-Ar age of 101±12 ka. This dacite lava may be a dome 

remnant that overlies crater fill and dome breccia on its north 

side. The southwest slope consists of a mafic (53–55% SiO2) 

pyroclastic complex that gives an age of 58±15 ka. Activity at 

Trident I is thus loosely bracketed between approximately 142 

and 58 ka. Although the edifice is glacially ravaged, its lower 

southeast flank has a field of sulfur-depositing fumaroles. 

Another large fumarole on the southwest ridge of Trident I 

became the vent for the Southwest Trident cone of 1953–74.

West Trident (Peak 5605), smallest and youngest of the 

prehistoric Trident stratovolcanoes, is the closest cone in the 

Katmai cluster to Novarupta. Its lavas are heavily mantled 

by 1912 fallout. Those exposed are silicic andesite to dacite 

(58–64.4% SiO2), and many are unusually rich in chilled 

enclaves (1 to 20 cm) of phenocryst-poor mafic andesite 

(54–58% SiO2). The summit lava (61% SiO2) is >125 m thick 

and may be a dome remnant. Summit-derived lavas dip east 

against Trident I at their mutual saddle. An andesite lava flow 

30-40 m thick that dips 20 ̊ down the north ridgeline yields a 

K-Ar age of 44±12 ka. Although largely ice-free today, West 

Trident is everywhere glacially modified. Some lava flows 

bank against Falling Mountain dome (70±8 ka), and, just east 
184 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

of there, the distal parts of adjacent lavas were destroyed on 6 

June 1912 by collapse into the Novarupta vent, thereby providing the andesitic lithics among the 1912 ejecta.

As many as eight lava domes of pyroxene dacite (62–

65% SiO2), all glacially scoured, were emplaced within and 

adjacent to the West Trident and Trident I edifices. The two 

largest domes, 425-m-high Falling Mountain and 365-m-high 

Mount Cerberus (each 0.3–0.4 km3), are compositionally similar to the smaller (unnamed) domes, the volumes of which 

are in the range 0.015–0.12 km3. Like West Trident, the 

domes contain chilled enclaves (1 to 20 cm) of phenocrystpoor andesite (54–58% SiO2

). Falling Mountain and Mount 

Cerberus, which frame the entrance to Katmai Pass (figs. 5, 

26), appear to be little modified by ice in gross morphology 

and were once suspected of being fairly young (Hildreth, 

1983). Repeated search, however, turned up few remnants 

of glassy carapace, and late Pleistocene K-Ar ages were later 

measured for both domes: 70±8 ka for Falling Mountain and 

114±46 ka for Mount Cerberus (Hildreth and others, 2003b). 

The superficiality of glacial erosion may reflect their compact 

profiles and locations close to the drainage divide. Attempts 

to date other late Pleistocene domes along the southwest 

periphery of the Trident group failed.

Glacial ice and the blanket of 1912 fallout obscure so 

much of Pleistocene Trident that counting lava flows is an 

uncertain exercise; we estimate roughly 40 for the eastern 

edifice, 25 for the central, and 10 for the western. Eruptive 

volumes, as reconstructed (table 1), were roughly 8 km3 each 

for East Trident and Trident I, only 3–4 km3 for West Trident, 

a total of 1 km3 for the several domes, and 0.7 km3 for the 20th 

century eruption of Southwest Trident, giving a total eruptive 

volume for the Trident group of 22±3 km3.

Southwest Trident (Eruption of 1953-1974)

Beginning in February 1953, a new andesitic edifice (0.7 

km3) was built at the southwest margin of the Trident group 

(Snyder, 1954; Ray, 1967). Although sometimes referred to 

informally as “New Trident,” we have called it Southwest 

Trident, in anticipation of the day it ceases to be Trident’s 

youngest component. During two decades of sporadic activity 

(vulcanian and effusive), a new 3-km2 composite cone was 

constructed of block-and-ash deposits, scoria, agglutinate, 

stubby lava lobes, and the intercalated proximal parts of the 

main lava flows that spread as an apron around the cone (fig. 

142). The cone grew to an elevation of 1,515 m (GPS 

Figure 142. Southwest Trident in July 1979 (5 years after cessation of 1953–74 eruptive activity), viewed eastward from 

glacier on Mount Mageik. Fragmental cone, asymmetrically built on slope of glaciated Trident lavas, rises 750 m above 

Katmai Pass in foreground; its crater is 350 m wide and still weakly fumarolic. Leveed lava flow at left erupted in 1959–60, 

and overlapping flows at right in 1953 and 1958. Petrology of andesite-dacite eruptive products was reported by Coombs 

and others (2000) and geology by Hildreth and others (2003a).
Chapter 12. The Katmai Volcano Cluster 185

measurement reported by Coombs and others, 2000) on the 

former site of a 100-m-wide fumarolic pit at an elevation 

of about 1,175 m on the steep southwest flank of Trident I. 

Although relief on its south side exceeds 700 m, the slopedraping new cone has a central thickness of only 340 m and a 

volume of about 0.3 km3 (Hildreth and others, 2000, 2003a). 

At successive stages of cone construction, four blocky leveed 

lava flows effused from its central vent, in 1953, 1957, 1958, 

and during the winter of 1959–60. Each flow is 25–60 m thick 

and 2.5–4 km long, and altogether they add about 0.35 km3 to 

the eruptive volume. The cone’s summit is today marked by a 

shallow crater 350 m wide (Hildreth and others, 2000, 2003a) 

that was the site of several small ephemeral plugs, which 

were emplaced after the final lava flow and were repeatedly 

destroyed by intermittent explosive activity (1960–74). 

Black ash clouds rose 6–9 km at least 10 times between 

1953 and 1974 and perhaps to 12 km once or twice. Several 

times during the first month of activity, light ashfall dusted 

areas as far as 30–50 km from the vent, in all sectors. By far 

the most voluminous fallout appears to have resulted from the 

initial outburst of 15 February 1953 (Snyder, 1954). A single 

nongraded scoria-fall layer (5–17 cm thick) deposited during 

that event is preserved at a few protected sites as far away as 

Mount Katmai and upper Knife Creek. Sieve data for bulk 

samples of this layer yield median and maximum particle sizes 

of 6.5 mm and 10 cm, respectively, in the saddle 1 km north 

of the vent and 2.1 mm and 2 cm in the saddle 7 km northeast 

of the vent—between the twin western summits of Mount 

Katmai. Thin sheets of finer ash that fell during the many subsequent events have been almost entirely removed or reworked 

by wind and runoff. Abundant ballistic blocks, variously 

breadcrusted, densely vitrophyric, or scoriaceous, are scattered 

as far as 3 km from the vent and are products of many discrete 

explosive episodes (none of which were closely observed) 

distributed over two decades. Liberal estimates of total fallout 

yield no more than 0.05 km3

, contributing less than 10 percent 

of the total eruptive volume of 0.7±0.1 km3. 

 The period of most frequent observation was from February to September 1953, principally by military reconnaissance aircraft during the early months (Snyder, 1954) and by a 

U.S. Geological Survey party that camped at Knife Creek during the summer (Muller and others, 1954). When the vent was 

first seen through the cloud layer on the fourth day of activity 

(February 18, 1953), an effusive lava flow (then already 250 

m wide) was upwelling centrally and spreading radially (fig. 

15 of Hildreth and others, 2003a). Although a fumarolic pit 

as deep as 40 m was conspicuous at the impending vent site 

on aerial photographs taken in 1951 (and had probably been 

further excavated by the explosive outburst of February 15), 

any such crater was soon filled and buried by the effusive lava, 

which continued to extrude and spread slowly throughout the 

seven months of intermittent observation in 1953. At different times, lava lobes emerged laterally through the chilled 

carapace at the foot of the pile, or the pile itself “expanded like 

a balloon” and extruded lobes by overflow from the vent, or 

small slumps and slide masses detached from the steep flow 

margins (Snyder, 1954). By June 1953, the main southerly 

tongue of lava, ultimately 4.2 km long, had advanced only 

1,250 m from the vent. Snyder (1954) estimated the volume 

of fallout and lava produced by June 17, 1953, to have been 

between 0.23 and 0.3 km3

, roughly a third of the eventual 

output. During the summer, steady steaming and continued 

spreading of the lava was punctuated sporadically by steam 

bursts or occasional “smoke columns” (Muller and others, 

1954) that rose 1–3 km and dusted various proximal sectors 

with minor additional ashfall. 

Observations after September 1953 were sporadic and 

few. A general chronology of major events was compiled by 

Decker (1963) and augmented by Ray (1967), largely from 

intermittent National Park Service reports. The 1953 lava 

flow may not have attained its final dimensions until early 

1954 or later. It appears that there were no observations at all 

during eruption and outflow of the lava flows of 1957, 1958, 

and 1959–60, merely aerial snapshots taken in the summer 

seasons following emplacement of each. Time of emplacement of the lava flow attributed to the winter of 1959–60 is 

the least well known, because no photographs are known 

to have been taken between September 1958 and August 

1960. The 1958 lava flow partly overran the 1953 flow and 

impounded a small lake on upper Mageik Creek that soon 

filled in with pumiceous alluvium, becoming a mudflat (“Ferruginous Flat”) now marked by numerous iron-precipitating 

warm springs (Keith and others, 1992).

Growth of the fragmental cone only began after much or 

all of the 1953 lava flow had been emplaced. It accumulated 

progressively during the later 1950s, as shown by emergence 

of the successive lava flows at different levels of the fragmental edifice. National Park Service photographs show that the 

cone had attained nearly its full height by 1960, but explosive 

showers of blocks continued to augment the cone until 1974. 

In addition to the four main lava flows, cone construction 

included emplacement of several stubby lava lobes limited to 

its proximal southwest slope. The southeast side of the cone 

completely buried a 1-km2

 cirque glacier, producing no recognized effects on eruptive behavior or edifice structure, though 

it is possible that enhanced steaming could have contributed to 

the stronger fumarolic emission and alteration on that side of 

the cone. Explosive ejections of tephra, some involving blowout of plugs and at least one spine, took place from 1960 to 

1974, but volumetrically significant eruptions ended by 1963. 

Numerous sulfurous fumaroles, superheated in the 1960s but 

below or at the boiling point today, persist on upper parts of 

the cone. Dark-gray bouldery debris flows reworked from the 

pyroclastic deposits have built a proximal fan and thin distal 

sheets (1 to 4 m thick) that cap stream terraces for 3 km downstream along Mageik Creek. Some debris flows resulted from 

the initial February 1953 fallout over snow, others in later years 

by avalanching of rubble from the steep slopes of the cone.

The lava flows and ejecta are olivine-poor, two-pyroxene 

andesite and dacite that span a compositional continuum from 

56 to 65.5 percent SiO2. All products are plagioclase-rich and 

contain 33 to 45 percent phenocrysts, many of them complexly 
186 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

zoned, resorbed, and overgrown (Ray, 1967; Kosco, 1981; 

Coombs and others, 2000). The least evolved bulk material 

identified is the initial scoria fall of February 1953 (56–57 

%) SiO2). Andesitic enclaves are abundant, relatively mafic 

(56–59 % SiO2), contain the same phenocryst species as the 

host material, and fall mostly in the size range from 1 to 30 

cm (Coombs and others, 2000). No evidence of contamination by leftover 1912 magma (such as jacketed quartz phenocrysts) has been found, and small but consistent compositional differences (Hildreth and Fierstein, 2000) indicate that 

the andesite-dacite magmas erupted in 1912 and in 1953–74 

were different batches. For the Southwest Trident batch, 

Coombs and others (2000) presented experimental and analytical evidence for mixing between resident dacite magma 

stored at 890 ̊C at a depth of about 3 km and a newly arrived 

batch of 1,000 ̊C andesite magma. They interpreted diffusion 

profiles in phenocrysts to suggest that extensive mixing could 

have produced the linear compositional array within about a 

month before the eruption began.

Mount Katmai

Centered 10 km east of Novarupta and adjacent to 

Trident, Mount Katmai is a compound stratovolcano that 

consisted of two contiguous cones, both beheaded by caldera 

collapse in 1912, as discussed above in chapter 8. On the caldera walls are exposed separate foci of hydrothermal alteration 

and abutting stacks of lavas and ejecta that dip against each 

other from discrete Northeast Katmai and Southwest Katmai 

centers (figs. 5, 103, 135). The caldera has an area of 4 km2 at 

the floor and 8.8 km2 at the rim (Hildreth, 1991; Hildreth and 

Fierstein, 2000). Its internal volume is today about 4 km3, and 

the foundered superstructure amounted to an additional 1.1 

to 1.5 km3, giving a collapsed volume of about 5.5 km3. The 

Horseshoe Island dacite dome (figs. 136, 138) and numerous 

fumaroles on the caldera floor (fig. 137; Fenner, 1930) were by 

1929 covered by rising lakewater, now deeper than 200 m and 

more than 1 km3 in volume. 

 Eruptive products of the Katmai edifice (Hildreth and 

Fierstein, 2000) range from basalt to rhyolite (51.6–72.3% 

SiO2), an array wider than that of any other stratovolcano in 

the cluster (table 1) and surpassed only by the zoned pyroclastic eruption of 1912 (50.4–77.8% SiO2

). Andesitic lava flows 

are the dominant material of both Katmai cones, and products 

more mafic than 55 percent SiO2 are limited. Silicic lavas 

(63–72% SiO2) are common, dominating the stratigraphically 

youngest products of both cones. No lava domes are recognized in the caldera walls, though some of the thick silicic lava 

flows truncated by the walls could have issued from summit 

domes obliterated by the 1912 collapse. The most silicic 

materials identified in the Northeast Katmai edifice are dacite 

lava flows (66% SiO2) as thick as 60 m that cap the north rim 

(figs. 134, 136). The Southwest Katmai cone likewise has 

many dacites but additionally produced several rhyodacitic to 

rhyolitic lava flows (68–72% SiO2) that armor its upper southern slopes and cap much of its south to southeast rim 

(fig. 143). The most evolved of the south-rim lavas yielded 

Figure 143. Thick glassy rhyodacite lava capping southeast rim of Katmai caldera, draped by 

several meters of Novarupta fall deposits. Geologist stands 600 m above lake level. Beyond 

east rim notch (center) is Northeast Katmai edifice (see figs. 5, 135, 144).
Chapter 12. The Katmai Volcano Cluster 187

a 40Ar/39Ar age of 22.5±1.6 ka, but a zoned dacite-andesite 

scoria fall and several rhyodacite lavas overlie it (Hildreth and 

Fierstein, 2003). 

The highest point surviving on the caldera rim belongs 

to the oldest component of Mount Katmai, a 1-km-thick 

dike-laced pile of rubbly mafic lava flows (52–55% SiO2) that 

makes up the northeast wall of the caldera (fig. 135) and dips 

steeply outward (fig. 144). The core of the Northeast Katmai 

edifice consists entirely of this structurally simple mafic cone, 

the base of which is exposed only distally, not within the 

caldera. A basaltic lava midway through the cone sequence 

(where cut by the caldera rim) gave a 40Ar/39Ar age of 89±25 

ka. An andesite lava flow resting (with apparent conformity) 

on the pile of mafic lavas at the northeastern toe of the cone 

gave a K-Ar age of 70±13 ka. Several ridge-capping andesitedacite lavas are stratigraphically younger still.

Caldera-wall stratigraphy shows that the two Katmai 

cones overlap in age but that the southwest edifice is in large 

part younger. A basal andesite lava flow of the Southwest Katmai cone, resting on basement at Katmai River, gave a K-Ar 

age of 39±12 ka, and a dacite lava flow (also basal or nearly 

so) west of the caldera gave 47±13 ka. The Southwest Katmai 

cone erupted at least twice postglacially (Hildreth and Fierstein, 2000, 2003), as well as producing the Horseshoe Island 

dacite dome on the caldera floor after the 1912 collapse.

Along and near Katmai River, several lava flows relatively 

low in the Mount Katmai pile are 50–150 m thick, pervasively 

glassy and columnar, and display entablatures of slender curving columns, many of which are subhorizontal and locally form 

rosettes. Such features, which occur in both silicic and mafic 

andesites of Southwest Katmai and even in a few basaltic lavas 

of Northeast Katmai, suggest ponding of many early Katmai 

lavas against ice near paleocanyon floors. Despite persistence 

of active glaciers on both cones, the stacks of generally thinner 

andesite-dacite lavas higher on the compound edifice rarely 

display such pervasive ice-contact features.

Off-edifice pyroclastic deposits erupted at Mount Katmai (Fierstein, 2007) include the following: (1) Valley-floor 

remnants of a late Pleistocene plinian pumice-fall deposit 

and associated ignimbrite are chemically (71–72% SiO2) and 

mineralogically similar to the hornblende-bearing rhyolite 

lava flow on the south rim, 40Ar/39Ar-dated at 22.5±1.6 ka. 

Organic material at the base of the plinian deposit gave an age 

of 19,240±70 14C yr BP, equivalent to a calendar age of 22.8 

ka (Hildreth and Fierstein, 2000). (2) In upper Knife Creek, 

sintered remnants of a dacitic scoria-flow deposit (Hildreth 

and others, 2002), 4–10 m thick, are compositionally similar (64–66% SiO2

) to an agglutinated scoria-fall deposit that 

drapes the west rim of the caldera (figs. 5, 134, 145) and 

ponded inside a paleocrater (Hildreth and Fierstein, 2003). 

(3) Debris flows and hyperconcentrated sand deposits rich in 

dacite pumice are as thick as 25–30 m where exposed in the 

lower VTTS (Hildreth and others, 2000). These deposits and 

those described in (2) have not been dated directly but were 

Figure 144. Aerial view of eastern flank of Northeast Katmai edifice (fig. 5) looking 

northwestward. Foreground relief ~400 m. Steeply dipping lavas and red scoria layers are 

largely mafic, in contrast to products of Southwest Katmai edifice, which range from andesite to 

rhyolite. For intracaldera view of steep inner wall of these crags, see figure 135. Beyond knifeedged caldera rim rises andesitic cone of Mount Griggs, 15 km from camera.
188 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

emplaced during end-Pleistocene deglaciation, probably 16–8 

ka (Fierstein, 2007). (4) Remnants of an undated quartz-bearing ignimbrite (76.6% SiO2

) as thick as 100 m cap a divide ~6 

km northeast of the caldera rim (Hildreth and Fierstein, 2003). 

Although this ignimbrite is not confirmed to have issued from 

Mount Katmai, the only center known to have produced Quaternary products more silicic than dacite, no alternative source 

has been identified anywhere in the district.

Snowy Mountain

Snowy Mountain consists of two contiguous edifices 

(Hildreth and others, 2001; Hildreth and Fierstein, 2003) that 

were supplied by long-lived central vents only 4 km apart. 

Because glacial ice still covers nearly 90 percent of both 

edifices, rock exposures are limited to narrow ice-bounded 

arêtes at higher elevations and ice-scoured lava-flow benches 

at lower elevations. Each cone appears to consist of only 

12–15 andesite-dacite lava flows, apparently erupted as a few 

packages at widely spaced intervals. Many products of the 

southwest vent are olivine-bearing andesites (55–62% SiO2), 

whereas those of the northeast vent are largely pyroxene 

dacites (62–64% SiO2). 

For Southwest Snowy, a basal andesite lava flow resting 

on basement rocks at the north toe of the cone gave a K-Ar 

age of 199±9 ka, and the summit-capping andesite gave 196±8 

ka. However, another andesitic lava flow exposed through the 

ice on the southeast flank (probably also basal in its sector) 

yielded an age of 92±10 ka. For Northeast Snowy, the second 

flow of a basal stack of dacite lavas on the north apron gave an 

age of 171±8 ka, which is probably close to the inception age 

of that center. Sporadic activity apparently alternated from 

the paired vents during the first half of the eruptive lifetime 

of Snowy Mountain, but only the northeast cone remained 

active through the late Pleistocene into the Holocene. The 

only known Holocene eruption was emplacement of a dacite 

dome within the amphitheater of the northeast cone shortly 

after a sector collapse about 1.5 ka (Hildreth and others, 

2001). Eruptive volumes are estimated to be 8±2 km3 for the 

northeast edifice, 5±2 km3 for the southwest, and 13±4 km3 for 

the Snowy Mountain center as a whole. As much as half has 

been removed by glacial erosion.

Mount Griggs

Highest peak in Katmai National Park, Mount Griggs 

is a fumarolically active andesitic stratovolcano that stands 

alone 12 km behind the main volcanic chain (Hildreth and 

others, 2002). Symmetry of the apparently little-dissected 

cone (fig. 146) reflects postglacial effusions of andesitic lava 

that have healed and concealed older scars of glacial erosion. 

Mount Griggs consists of three main parts: (1) Remnants of 

a middle Pleistocene edifice as old as 292 ka, exposed in only 

a few windows; (2) a late Pleistocene cone consisting of at 

least 50 lava flows, well-preserved except for its southwest 

quadrant, which underwent postglacial sector collapse; and (3) 

a Holocene inner edifice that filled the collapse amphitheater 

by building a cone with nested inner craters, a 12-km2 fan of at 

least 20 blocky andesite lava flows, and a volume of about 2.2 

km3. Bedded scoria falls and layers of poorly sorted phreatomagmatic ejecta are exposed on rims of the inner craters but 

rarely elsewhere. In contrast to the compound volcanic-front 

centers, Mount Griggs has maintained a stable central-vent 

position throughout its multi-stage history. Present volume is 

20–25 km3, but reconstruction of the eroded components of 

the edifice yields an estimate of 35±5 km3 for the total volume 

erupted (Hildreth and others, 2002). 

Eruptive products define a typically Ti-poor, mediumK calcalkaline arc suite, largely in the range 55–63 percent 

SiO2; most units are andesitic, ranging from olivine-rich 

mafic andesite to two-pyroxene silicic andesite and dacite. 

Olivine-rich andesite makes up a larger fraction of Mount 

Griggs than of the other volcanoes in the Katmai cluster. All 

lavas are plagioclase-rich. Relative to products of the arcfront centers, those of Mount Griggs are generally enriched in 

Na, Rb, Sr, Ba, Al, and P, and consistently enriched in K, Zr, 

Hf, Ta, Th, and U (Hildreth and Fierstein, 2000; Hildreth and 

others, 2004). Fumarolic gases at Mount Griggs are richer in 

He than those at other Katmai volcanoes and have 3He/4He 

values as high as 7.7 Ra (Poreda and Craig, 1989; Sheppard 

and others, 1992). The magmatic plumbing system of Mount 

Griggs is independent of those beneath the main volcanic 

chain, apparently well down into the mantle. Consistent 

chemical differences from all the volcanic-front centers indicate that magma typical of Mount Griggs did not contribute to 

the 1912 eruption.

Mount Griggs is as old as 292±11 ka and thus predates 

inception of all the nearby volcanic-front centers except Alagogshak. The basal lava flow at the north toe of the volcano 

yields that age, and two windows of a dissected andesitic edifice yield K-Ar ages of 160±8 ka (crags on the mountain’s west 

shoulder) and 133±25 ka (a southerly kipuka). Such a range of 

ages for widely spaced glaciated remnants, respectively 1,600 

m, 500 m, and 1,300 m lower than the modern summit, signify 

that a large fraction of the long-lived middle Pleistocene edifice 

was eroded away before being covered by the late Pleistocene 

cone, which, in contrast, is only slightly eroded. 

The stratigraphically lowest lava on the east side of the 

late Pleistocene cone ponded in an older glacial canyon and 

yields a K-Ar age of 90±7 ka. Another thick basal lava flow 

resting on basement rocks at the northeast edge of the cone 

gave 54±8 ka. Attempts were made to date three additional 

lava flows from other parts of the late Pleistocene cone. To 

the north, a thick distal andesite flow that rests on basement 

rocks gave an age of 15±18 ka. On the west slope, the topmost andesite flow beneath the debris-avalanche deposit that 

resulted from the Holocene sector collapse gave 21±11 ka. 

Adjacent to the latter flow, the lone dacitic lava flow exposed 

at Mount Griggs (also overlain by the debris-avalanche 

deposit) failed to yield measurable radiogenic Ar despite 

repeated extractions, apparently because it is very young, 
Chapter 12. The Katmai Volcano Cluster 189

Figure 145. Southwestern inner wall of Katmai caldera from helicopter. Bench-forming rim cliff is 

massive to layered dacite agglutinate, here as thick as 60 m, that dips modestly inboard where it filled a 

precaldera crater. Stack of andesitic lavas on lower wall dips ~25oSW (opposite to the agglutinate) and 

is part of Southwest Katmai edifice (fig. 5) that held the crater. Lithologically described and mapped 

by Hildreth and Fierstein (2003), the agglutinate also drapes ridge at upper right to elevations as much 

as 225 m higher than rim ledge here. Narrow glacier tongue at right extends from rim bench nearly to 

lakeshore (see fig. 134).

Figure 146. Mount Griggs andesitic stratovolcano, highest peak in Katmai cluster at 2,332 m; aerial 

view northward across upper Knife Creek arm of VTTS. Exposed products range in age from 292 ka to 

Holocene (Hildreth and others, 2002). Pumice-covered leveed lavas of southwest sector (at left) and 

summit crater are postglacial. Mount Juhle at far left; Griggs fork and snout of Glacier 4 at far right.
190 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

possibly early Holocene. The dacite is also overlapped locally 

by the fan of leveed Holocene lavas (55–62% SiO2) that cover 

a fourth of the volcano’s surface. Flows of the fan retain rugged near-primary surfaces (fig. 146).

Other Volcanoes Behind the Volcanic Front

In addition to Mount Griggs, there are several additional 

rear-arc volcanoes, isolated or clustered, well behind the 

closely spaced, single-file chain of volcanic-front centers (fig. 

6). These include the Savonoski River cluster, the Saddlehorn Creek cluster, and the Gertrude Creek cone (all on fig. 

6A), for all of which radioisotopic ages have been determined 

(Hildreth and others, 2004). Most are of Pleistocene age, and 

all are small and either monogenetic or short-lived, except 

Mount Griggs. Analytical data and geologic descriptions 

are given for all by Hildreth and others (2004), and supplementary electronic files accompanying that article illustrate 

several of them.

Present-Day Magma Distribution?

Here we review what can be inferred about magma distribution beneath the Katmai cluster today, and we summarize 

what is known about the sizes and compositions of prehistoric 

magma batches in the cluster.

Gravity and seismic data that identify a low-density lowvelocity region centered near Katmai Pass were summarized 

by Ward and others (1991). A southeasterly gravity traverse 

that crossed the volcanic axis by way of Katmai Pass showed 

cross-axial width of the anomalous region to be about 15 km, 

but the data are insufficient to know how far it extends along 

the axis. Of the several seismic stations in the Katmai array, 

only the one in Katmai Pass (central to the gravity anomaly) 

consistently showed traveltime delays for deep local and 

regional earthquakes. The delays suggest great thickness for 

the low-velocity domain, which may well extend deeper than 

20 km (Ward and others, 1991), thus involving most or all of 

the crust. Their seismic data also indicated significant attenuation of P and S waves, but they found no screening of S waves 

(in contrast to seismic reconnaissance studies 25 years earlier). 

To explain the data, they invoked present-day crustal magma 

storage, favoring scattered small magma bodies rather than a 

large chamber.

The pattern of seismicity recognized by Ward and others (1991) has persisted during the past two decades; the 

Alaska Volcano Observatory continues to locate 40–130 

earthquakes each month along and near the volcanic axis of 

the Katmai cluster (Jolly and McNutt, 1999). Most of the 

earthquakes fall into three persistent clusters: (1) beneath 

the volcanic line from Martin to Mageik; (2) beneath Katmai 

Pass and the northwest slope of the Trident group; and (3) 

beneath Mount Katmai, especially its northern slopes. In 

a fourth area, north of Snowy Mountain, the seismicity is 

less abundant and more scattered. Nearly all the earthquakes 

in all four areas are smaller than magnitude 2.5, and only 

a few events have been in the range M 3.0–4.5. Many are 

shallower than 5 km, and nearly all are shallower than 10 

km. The dense shallow seismicity seems inconsistent with 

present-day upper-crustal storage of voluminous magma 

and is more likely to reflect fluid flow, volume changes, and 

hydraulic microfracturing in hydrothermal systems, along 

with slip-threshold reduction in altered rocks. If magma 

bodies other than small pods and dikes are really present 

in the seismically active, evidently brittle, top 10 km of the 

crust, they are more likely to underlie the gaps between the 

seismic clusters. If shallow chambers exist, they could lie 

beneath East Mageik or between Trident and Mount Katmai. 

Beneath the seismic clusters themselves, any magma bodies 

today are probably deeper than 10 km. Nonetheless, shallow components of the pre-1912 reservoir might once have 

occupied what are now seismically active domains that were 

effectively drained by the 1912 eruption, any residues having 

subsequently crystallized. 

Vigorous fumaroles in the Katmai cluster are evidence 

that magma stored somewhere below is actively degassing, 

though this provides little or no control on depths, distribution, volume, or degree of crystallization of such magma. 

Superheated jets high on Griggs and around the crater lake 

of Mageik are steam-dominated but rich in CO2

 and H2S and 

have magmatic He-isotope ratios 7–8 times the atmospheric 

value. Boiling-temperature fumaroles on the southeast flank 

of Trident I have similarly magmatic signatures and have 

discharged vigorously since at least 1916 when first recorded 

(photo on p. 99 of Griggs, 1922). Though not yet sampled 

directly, many fumarolic jets in the crater of Mount Martin 

are precipitating abundant sulfur, are probably superheated, 

and combine to discharge the biggest and (olfactorily) H2Srichest plume in the Katmai district. USGS flights through 

the Martin plume have measured high levels of CO2 and SO2

(Doukas and McGee, 2007).

From the point of view of resolving the magmatic 

plumbing puzzle for the Katmai cluster, there are too many 

“smoking guns.” The vigorous fumaroles on Martin, Mageik, 

Trident I, and Griggs have apparently been continuously 

active with little change in style or configuration since they 

were first photographed in the period 1913–17 (Griggs, 

1922), but there is no evidence that any of these volcanoes 

produced any ejecta in 1912 or erupted at any time since. In 

contrast, fumaroles at the three vents that did erupt in the 20th 

century have been in decline.

Those on the Southwest Trident cone were superheated 

during the 1953–74 eruptive episode and were still depositing 

sulfur and remained at or above the boiling point during our 

sampling in 1979, but they have since declined both thermally 

and in H2

S output (R.B. Symonds, oral commun., 1998). The 

many fumaroles on the Katmai caldera floor (Fenner, 1930), 

although drowned under rising lakewater by 1929, continued 

for decades to discharge beneath the lake. Yellowish-green 

upwellings and failure of the lake to freeze over fully in winter attested for many years to their survival and to
Chapter 12. The Katmai Volcano Cluster 191

concomitant thermal flux through the caldera floor (Muller 

and Coulter, 1957a; Motyka, l977). Our own visual observations (1976–2003) suggest, however, that these chemical and 

thermal fluxes weakened appreciably during the 1990s. In 

the 1912 vent area, within 1.5 km of the lava dome, numerous 

high-temperature fumaroles (Allen and Zies, 1923) declined 

gradually, passing through an acid-argillic alteration phase 

and leaving today only odorless wisps of near-neutral wet 

steam that discharge weakly at 20 ̊C–90 ̊C (Keith, 1991b). 

Declines in temperature and magmatic-gas flux at the three 

20th-century vents (in contrast to sustained discharge at Trident I, Griggs, Mageik, and Martin) may signify that Mount 

Katmai, Southwest Trident, and Novarupta are no longer 

linked by fracture networks to deep magma reservoirs. If so, 

does this reflect self-sealing of fluid-filled fractures, cooling 

and crystallization of magma conduits, or nearly complete 

removal of the magma formerly under each of them? For 

Novarupta, the rapid fumarolic decline supports the likelihood that no part of the voluminous magma reservoir directly 

underlay the 1912 vent, bolstering the case for transport by 

dike or sill from reservoir components elsewhere (Hildreth, 

1987; Wallmann and others, 1990).

Although modulated by passage through upper-crustal 

hydrothermal systems, the magmatic gases discharging at so 

many sites indicate that cooling magma is distributed widely 

and discretely at indeterminate depths beneath the Katmai 

cluster. Depletion or exhaustion of local upper-crustal magma 

bodies by eruption need have little impact on coexisting independent components of deep-crustal magma storage systems 

distributed beneath the volcanic line.

Typically Small Magma Batches 

Eighteen vents distributed along the 25-km volcanic 

line from Mount Martin to Mount Katmai have built the 

chain of cones and domes by sporadic eruption of many 

small batches, mostly of pyroxene-plagioclase dacite and 

andesite rich in phenocrysts. Volumes of lava domes here 

are in the range 0.01 to 0.3 km3, most lava flows 0.01 to 

0.4 km3

, and quasi-conformable stacks of compositionally 

similar lava flows generally in the range 0.1 to 1 km3. The 

whole 1953–74 eruptive episode that built Southwest Trident 

amounted to only 0.7 km3. The most voluminous individual 

lava flows of East Mageik are smaller than 0.4 km3, but sets 

of morphologically and compositionally similar ones may 

have erupted in short order from magma batches as large as 

2 km3

.

 As an extreme possibility, the ejecta cone and ten 

Holocene lava flows making up 7-km3 Mount Martin are 

similar enough that they might have been derived from an 

effectively monogenetic magma batch. Most exceptional of 

all are the two major plinian eruptions, of 1912 and of late 

Pleistocene rhyodacite at Mount Katmai. Each released on 

the order of 10 km3 of magma, but they involved the most 

silicic magmas ever erupted in the Katmai cluster, providing 

the exceptions that illustrate the rule—small phenocryst-rich 

andesite-dacite batches rather than large magma chambers 

undergoing strong internal differentiation. Accordingly, the 

two large plinian events produced the only phenocryst-poor 

eruptive products in the later history of the Katmai cluster. 

All other late Pleistocene and Holocene products of Martin, 

Mageik, Trident, Katmai, and Griggs Volcanoes contain at 

least 20 percent phenocrysts (plagioclase >> pyroxenes > 

Fe-Ti oxides ≥ olivine), and many have 30–50 percent.

Widespread incidence of chilled magmatic enclaves 

(varied but generally of mafic to silicic andesite) in most of the 

andesitic and dacitic lava flows of Mount Katmai and Trident 

is further evidence of repeated mingling of separate magma 

batches, supporting the idea of a continually changing plexus 

of dikes, sills, and modest irregular or podiform magma bodies. Such enclaves are conspicuously absent in the voluminous 

rhyolite of Layer A (which initiated the 1912 zoned sequence), 

as they typically are in early-emplaced parts of many major 

pyroclastic deposits erupted from thick zoned chambers. 

Intermediate lava flows here characteristically have 

several populations of complexly zoned phenocrysts (Coombs 

and others, 2000), suggesting disorderly histories of mingling 

and changing physical conditions. Many flows are internally 

heterogeneous (in the 1 to 2 percent SiO2

 range) rather than 

having the homogeneity or simple zonation that might be 

expected from a large chamber. If large reservoirs of intermediate magma do exist here, they probably lie in the mid-todeep crust and sporadically yield ascent batches, typically 

smaller than 1 km3, as dikes that erupt, stall, or augment an 

upper-crustal plexus. Only occasionally would the ascent flux 

be sufficient that parts of such a plexus would enlarge into 

shallow chambers big enough to undergo sustained systematic 

zonation and evolution of silicic roof zones capable of voluminous plinian eruptions and attendant caldera collapse.
192 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Baked Mountain Hut, the only fixed shelter in the Valley of Ten Thousand Smokes 

(VTTS), stands 4 km northwest of Novarupta. Built in 1965 by the Geophysical 

Institute of the University of Alaska as a research station, the facility lacks water 

and power, but through the years it has accommodated scores of academic and 

U.S. Geological Survey scientists and countless visiting backpackers. Windblown 

sand and pumice have scoured the walls and piled up against the upvalley (right) 

side of the hut. View is northeastward across the Knife Creek arm of the VTTS 

toward Mount Griggs. Photo by Wes Hildreth in August 1976.
Chapter 13. 1912 Magma Compositions and Preeruptive Storage 193

Chapter 13

1912 Magma Compositions and Preeruptive Storage

The ~13 km3 of magma released in 1912 consisted of 

~4.5 km3 of dacite and ~1 km3 of andesite (both having 25–42 

weight percent phenocrysts) and 7–8 km3 of crystal-poor highsilica rhyolite with only 0.5–3 weight percent phenocrysts (fig. 

147). A large compositional gap separates the slightly zoned 

rhyolite from the strongly and continuously zoned andesitedacite (figs. 59, 148). A second apparent compositional gap 

suggested by our first 30 pumice analyses (Hildreth, 1983)—

separating black andesite and light grey dacite (fig. 4)—was 

an artifact of limited sampling and does not exist. The 1912 

ejecta include neither rhyodacite nor phenocryst-rich rhyolite 

comparable to the products of many other large zoned ignimbrite eruptions. Homogeneous pumice containing 69–77 

percent SiO2 is absent. 

1912 Bulk Compositions

Major Elements

Major element contents were determined by XRF for 

~265 samples of 1912 eruptive products, including ~70 

pumice blocks from the ignimbrite, 8 lava samples from 

Novarupta dome, 8 blocks from Phantom dome, and ~180 

pumice clasts representing all fall units. Data are tabulated in 

appendix A, and several elements are plotted in figures 59 and 

148. Apart from the very unusual coeruption of high-silica 

rhyolite, the 1912 intermediate suite represents an ordinary 

subalkaline, low-Ti, medium-K, calcalkaline arc array. The 

narrow array (fig. 148) is strongly calcalkaline by the criterion of Miyashiro (1974) but calcic by the alkali-lime index 

of Peacock (1931), and it straddles the low-Fe/medium-Fe 

boundary of Arculus (2003). Table 2 summarizes and compares the compositional ranges for all rhyolite, dacite, and 

andesite samples analyzed.

The phenocryst-rich andesite-dacite array forms a dense 

continuum, with no discernible compositional distinction 

between pumice clasts emplaced as fallout or ignimbrite. The 

conventional boundary between andesite and dacite at 63 

percent SiO2

 happens to coincide roughly here with a change 

in pumice color from black to pale gray (fig. 4), but it should 

not be inferred that they represent different magma batches 

or that 63 percent SiO2 represents any kind of compositional 

discontinuity. SiO2

 contents range continuously from 57.9 to 

68.6 percent whereas Al2O3 drops from 17.1 to 14.6 percent. 

Across the array from andesite through dacite, K2O rises from 

1.2 to 2.2 percent and Na2O from 3.3 to 4.3 percent; contrarily, 

FeO* declines from 7.4 to 4.2 percent, MgO from 4.6 to 1.5 

percent, CaO from 7.8 to 3.9 percent, and TiO2 from 0.75 to 

0.51 percent. The minor components MnO and P2O5 likewise 

decline with SiO2

 enrichment within the low concentration 

ranges 0.15–0.09 percent and 0.22–0.09 percent, respectively. 

Although most black scoria clasts (fig. 4) fall within the array 

at 58–63 percent SiO2, two that we took from the S bed (fig. 

48) atop the Turtle were uniquely mafic among 1912 products 

in having only 54.6 and 50.4 percent SiO2; only the second 

was noticeably enriched in olivine. In addition, three mafic 

enclaves within Novarupta dome rhyolite gave SiO2 contents 

of 57.1, 56.5, and 55.5 percent, significantly outside the main 

array (fig. 148; table 2).

The phenocryst-poor, volumetrically dominant rhyolite 

of 1912 shows limited but real compositional variations. SiO2

is in the range 76.5–77.8 percent, but only (slightly contaminated) Novarupta dome samples have less than 77.1 percent. 

Al2O3 ranges from 11.9 to 12.6 percent, and alkali data are 

tightly grouped at 4.0–4.4 percent Na2O and 3.1–3.3 percent 

K2O. Other major element data define quite limited ranges for 

the 1912 rhyolites: 0.13–0.23 percent TiO2; 1.2–1.5 percent 

FeO*; 0.04–0.07 percent MnO; 0.09–0.19 percent MgO; 

0.81–1.16 percent CaO; and 0.02–0.09 percent P2O5. 

Major-element compositions of matrix glass from 1912 

pumice clasts have been determined by electron microprobe 

by Avery (1992), Westrich and others (1991), Fierstein and 

Hildreth (1992), and Hammer and others (2002). For the phenocryst-poor rhyolite, glass composition is not much different 

from bulk composition. For the crystal-rich dacite pumice, 

glass composition is high-silica rhyolitic, but (despite a little 

overlap) it is generally distinguishable by microprobe from 

the slightly more evolved glass of the rhyolite pumice (fig. 

149). For the crystal-rich andesite scoriae, glass compositions 

reported are far more varied, ranging from dacitic to rhyolitic 

(65–73% SiO2

). A summary of the abundant glass data follows, for rhyolite, dacite, and andesite, respectively, in weight 

percent for each oxide: SiO2 77–79, 76–79, 65–74; TiO2

0.08–0.21, 0.20–0.35, 0.6–0.8; Al2O3 11.9–12.2, 11.7–12.8, 

13.5–15.5; FeO* 1.0–1.4, 1.3–1.85, 2.5–4.6; MgO 0.09–0.14, 

0.2–0.28, 0.55–1.4; CaO 0.7–0.9, 0.8–1.4, 2.2–3.6; Na2O 

4.0–4.4, 4.0–4.1, 4.1–4.6; and K2

O 3.1–3.3, 2.8–3.2, 2.2–2.7.
194 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Table 2. Compositional summary for 1912 eruptive products.

[The 10 major-element oxides are in weight percent; trace elements in parts per million; —, not analyzed . Chemical data are from Appendices A–C. Isotope data are in Hildreth, 1983, 1987; Reagan and others, 2003, Hildreth and others, 2004; and Turner and others, 2010.]

Rhyolite Dacite Andesite 5 Mafic Samples

Major elements

SiO2 76.5–77.8 63.0–68.6 57.9–63.0 50.4–57.1

TiO2 0.13–0.23 0.51–0.71 0.67–0.75 0.69–0.81

Al2

O3 11.9–12.6 14.6–16.2 16.1–17.15 14.0–17.9

FeO* 1.20–1.53 4.2–5.95 5.9–7.35 7.7–10.1

MnO 0.04–0.07 0.09–0.13 0.12–0.15 0.14–0.17

MgO 0.02–0.34 1.5–2.7 2.65–4.6 4.1–11.4

CaO 0.81–1.16 3.85–5.7 5.7–7.8 7.6–10.1

Na2

O 4.0–4.4 3.6–4.3 3.2–4.0 2.0–3.7

K2

O 3.10–3.28 1.56–2.18 1.17–1.57 0.50–0.92

P2

O5 0.02–0.09 0.09–0.22 0.12–0.22 0.09–0.16

Trace elements

Rb 54–79 24–50 23–37 8–23

Cs 2.3–3.0 1.1–1.7 0.9–1.2 0.36–0.72

Sr 58–95 210–280 260–330 270–360

Ba 790–1025 370–800 330–580 155–340

Y 40–48 30–42 20–31 14–25

Zr 120–165 120–170 100–140 42–102

Hf 4.3–5.2 4.1–4.9 2.9–3.7 1.6–2.5

Nb 4.0–5.4 3.0–3.9 2.5–3.5 1–2

Ta 0.40–0.44 0.26–0.42 0.20–0.34 0.08–0.19

Th 4.8–5.4 2.8–3.5 1.1–3.1 1.0–1.9

U 2.1–2.5 1.3–2.0 0.5–1.5 0.4–0.8

La 14–21 8–16 6–15 5–7.5

Ce 32–38 22–26 19–22 11–16

Nd 18–21 13–15.5 11.5–14 7.5–11

Sm 5.0–5.9 3.8–4.4 3.3–4.0 2.3–3.1

Eu 0.71–0.86 0.97–1.14 0.94–1.07 0.8–0.9

Gd 5.2–6.1 4.0–4.7 3.5–4.3 2.4–3.5

Tb 0.94–1.11 0.72–0.84 0.62–0.74 0.43–0.56

Yb 3.8–4.9 2.7–3.9 2.3–3.0 1.6–2.5

Lu 0.62–0.72 0.44–0.51 0.37–0.45 0.24–0.38

Sc 7–9 17–23 23–28 29–46

V 1–12 44–120 120–175 —

Cr 0–2 4–18 18–55 28–230

Co 0.5–0.7 10–14 17–19 23–54

Ni 0–3 1–12 4–32 11–64

Cu 1–3 6–31 13–36 —
Chapter 13. 1912 Magma Compositions and Preeruptive Storage 195

Rhyolite Dacite Andesite 5 Mafic Samples

(Trace elements)

Zn 30–44 47–90 64–113 69–84

Ga 12–16 16–28 17–29 —

Li 31–56 17–26 16–21 —

Be 1.5–2.0 0.5–0.8 0.6 —

B 31–58 28–41 <4 —

Mo 2.9–2.9 1.6–1.7 1.4–1.5 —

Sn 1.8–2.0 0.6–1.0 0.9–1.8 —

Sb 0.9–1.2 0.5–1.2 0.3–0.7 0.1–0.3

W 0.86–0.98 0.40–0.46 0.36–0.50 —

Pb 10–14 6–13 5–7 2.4

Ratios

FeO*/MgO 7–19 2.2–2.9 1.6–2.2 0.9–2.0

K2

O/Na2O 0.71–0.80 0.38–0.56 0.35–0.43 0.24–0.31

K/Ba 25–32 20–35 21–34 22–27

K/Rb 340–505 320–530 320–530 320–480

Rb/Cs 22–28 20–23 20–22 24–35

Rb/Sr 0.90–0.94 0.11–0.17 0.08–0.11 0.03–0.07

Ba/Sr 13–14 1.8–3 1.3–1.8 0.6–1.0

Ba/La 47–55 42–52 37–48 37–52

Ba/Nb 190–200 130–160 120–160 144

Ba/Zr 5–6.5 2.6–4.5 2.6–4.4 2.8–3.3

Zr/Hf 27.5–29 33–34.5 33–34.5 35–42

Sr/Nd 3.0–3.2 13–20 19–25 32–36

Ce/Yb 8.3–8.9 7.5–8.6 7.5–8.5 5.6–8.1

La/Sm 3.0–3.9 2.6–3.6 2.3–3.4 2.1–2.5

Sm/Yb 1.1–1.3 1.2–1.4 1.3–1.5 1.55

Eu/Eu* 0.4–0.5 0.7–0.8 0.8–0.9 0.8–0.9

Th/U 2.05–2.11 2.09–2.17 2.15–2.21 2.2–2.6

87Sr/86Sr 0.70368 0.70354 0.70352 0.70338

0.70374 0.70362 0.70374 0.70348

143Nd/144Nd 0.512987 0.512967 0.512995 0.512952

0.512996 0.513010 — 0.513035

206Pb/204Pb 18.85 18.88 — 18.88

207Pb/204Pb 15.57 15.57 — 15.58

208Pb/204Pb 38.375 38.38 — 38.39

Table 2. Compositional summary for 1912 eruptive products.—Continued
196 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives Crystal content, in weight percent 

SiO2, in weight percent

60

40

50

30

20

10

65 70 75

Figure 147. Weight percent crystals versus whole-pumice weight percent SiO2 for ~70 blocks of 1912 pumice and scoria. After 

cleaning of their surfaces, individual blocks were halved—one fraction for chemical analysis, the other for mineral separation in 

heavy liquid. Phenocryst-poor rhyolite contrasts with unsystematically phenocryst-rich andesite-dacite continuum.

Trace elements

Trace element contents of the 1912 magmas were listed 

by Hildreth (1983, 1987) and Turner and others (2010), and 

abundant additional data are tabulated in appendices B and 

C and summarized in table 2. Some trace-element data for 

matrix-glass separates from 1912 rhyolite, dacite, and andesite pumices were given by Lowenstern (1993). Across the 

andesite-dacite continuum, the following ranges (all in ppm) 

have been determined for individual pumice clasts: 1.1–1.7 

Cs, 23–50 Rb, 210–330 Sr, 330–800 Ba, 100–170 Zr, 2.5–3.9 

Nb, 6–16 La, 2.3–3.9 Yb, 5–13 Pb, and 1.1–3.5 Th. The 1912 

rhyolites are more enriched than the dacites in these and most 

other incompatible elements (table 2; figs. 150, 151, 152) with 

the exceptions of Sr (58–95 ppm) and Zr (120–165 ppm), the 

relative declines of which are attributable to fractionation of 

abundant plagioclase and traces of zircon. Trivalent rare earth 

elements (REE) are enriched progressively from andesite 

to dacite to rhyolite (fig. 153), but their normalized patterns 

remain nearly parallel across the whole compositional range, 

while Eu deficiency increases toward rhyolite (table 2; fig. 10 

of Hildreth, 1983, Turner and others, 2010). Ni and Cr are 

quite depleted, 1–32 ppm and 4–55 ppm, respectively, in the 

dacite-andesite array and are, of course, still more impoverished in the low-MgO rhyolites. 

Incompatible trace-element patterns as displayed on 

primitive-mantle-normalized diagrams (Hildreth and others, 

2004; Turner and others, 2010) are typical of those from many 

magmatic-arc suites, showing spikes in fluid-mobile Cs, Ba, 

Sr, Pb, and U and troughs in less mobile Ti, Nb, Ta, and Th 

(fig. 152). Accordingly, the elevated values (table 2) of such 

ratios as Ba/La, Sr/Nd, Ba/Nb, Ba/Th, U/Th, and Cs/Rb are 

characteristic of the geochemical signature of the slab-derived 

fluid flux beneath arc volcanoes globally. For the Katmai 

region in particular, the across-arc waning of such geochemical subduction indicators was investigated in detail by Hildreth 

and others (2004), who compared compositions of volcanicfront magmas (including Novarupta and Mount Katmai) with 

those of several rear-arc volcanoes nearby.

Affinities to Nearby Volcanoes

In the course of mapping all eruptive components of the 

Katmai cluster (Hildreth and Fierstein, 2003), we assembled 

compositional data for more than 700 samples in an effort to 
Chapter 13. 1912 Magma Compositions and Preeruptive Storage 197

0.5

1.0

1.5

2.0

2.5

3.0

52 56 60 64 68 72 76

3

4

5

6

7

2

4

6

8

10

12

52 56 60 64 68 72 76

K2O

Na2O+K2O

SiO2, in weight percent

FeO*/MgO

Pyroclastic flows

Layer A

Layer B

Layer C

Layer D

Layer F

Layer G

Scoria fall

Phantom dome blocks

Novarupta dome TH

CA

basaltic

andesite

andesite

a l k a l i n e

s u b a l k a l i n e

dacite

rhyolite

Low-K

Mount

Med-K

High-K

Katmai

high-Fe

medium-Fe

low-Fe

Content, in weight percent

Figure 148. Compositional variations 

versus SiO2

 content (all in weight percent) 

for ~265 samples of 1912 Novarupta pumice 

and dome lava, subdivided as indicated 

in inset key. Principal features are 

continuity of andesite-dacite array, wide 

compositional gap from dacite to rhyolite, 

slight contamination of dome samples, 

and five (rare) mafic outliers. Outlined 

enclosures are fields for ~150 samples from 

Mount Katmai, illustrating its compositional 

affinity with Novarupta. Alkaline/subalkaline 

boundary and named fields follow LeBas and 

others (1986). Tholeiitic/calcalkaline (TH/

CA) boundary after Miyashiro (1974). Low-, 

medium-, and high-Fe fields after Arculus 

(2003). Data in appendix A.
198 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

77 77.5 78 78.5 79

77 77.5 78 78.5 79

0.4

0.3

0.2

0.1

0

1.8

1.6

1.4

1.2

1.0

3.3

3.2

3.1

3.0

2.9

2.8

1.2

1.1

1.2

0.9

0.8

0.7

TiO2

Content, in weight percent

SiO2, in weight percent

Fe2O3*

K2O

CaO

Matrix glass

of pumice

Rhyolite

Dacite

Figure 149. Matrix glass compositions for three rhyolitic and two dacitic pumice clasts, 

visually homogeneous, determined by electron microprobe by Avery (1992). SiO2

, TiO2, K2O, 

CaO, and total iron as Fe2

O3, all reported in weight percent after normalization of analytical 

totals to 100 percent. In spite of wide compositional gap (69–77 percent SiO2

) between 

whole-pumice data for dacite and rhyolite, glass compositions are virtually continuous. 

A more extensive data set for pumice clasts and ash shards would extend the rhyolite 

range above 79 percent SiO2

 and the zoned dacite range below 77 percent SiO2 (table 3b of 

Fierstein and Hildreth, 1992).
Chapter 13. 1912 Magma Compositions and Preeruptive Storage 199

10

20

30

40

50

60

70

80

52 56 60 64 68 72 76

200

400

600

800

1,000

52 56 60 64 68 72 76

SiO2, in weight percent

Content, in parts per million

Rb

Ba

Pyroclastic flows

Layer A

Layer B

Layer C

Layer D

Layer F

Layer G

Scoria fall

Phantom dome blocks

Novarupta dome

Katmai

Figure 150. Variation of Ba and Rb (in ppm) versus weight percent SiO2 for ~265 samples of 1912 Novarupta 

pumice and dome lava, subdivided as indicated in inset key. Outlined enclosures are fields for ~150 samples 

from Mount Katmai.
200 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

50

100

150

200

250

300

350

400

450

52 56 60 64 68 72 76

50

100

150

200

250

52 56 60 64 68 72 76

SiO2, in weight percent

Sr

Zr

Pyroclastic flows

Layer A

Layer B

Layer C

Layer D

Layer F

Layer G

Scoria fall

Phantom dome blocks

Novarupta dome

Katmai

Content, in parts per million

Figure 151. Variation of Sr and Zr (in ppm) versus weight percent SiO2 for ~265 samples of 1912 Novarupta 

pumice and dome lava, subdivided as indicated in inset key. Outlined enclosures are fields for ~150 samples 

from Mount Katmai. Note pronounced effect of zircon fractionation on Zr content of rhyolites.
Chapter 13. 1912 Magma Compositions and Preeruptive Storage 201

1

Cs Rb Ba Th U Nb Ta K La Ce Pb Sr Nd Sm Zr Hf Eu Ti Tb Y Yb Lu

10

100

primitive mantle model

glass

dacite

9 rhyolites

17 dacites

Ratio of sample/primitive mantle

Figure 152. Incompatible trace-element patterns for 1912 dacite and rhyolite, normalized to average primitive mantle composition 

of Sun and McDonough (1989). Red bars represent nine rhyolite pumice clasts and yellow bars 17 dacite pumice clasts. Bold blue 

line represents two glass separates from crystal-rich dacite pumice clasts; within analytical errors, their plots coincide except for 

Cs and Rb. Diagram illustrates that melt extracted from bulk dacite is similar to bulk rhyolite, except that rhyolites contain lower 

Sr, Zr, Eu, and Ti, inferentially as a result of further fractionation of plagioclase, zircon, and Fe-Ti oxides.
202 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

50

40

30

20

10

50

40

30

20

10

La Ce Nd Sm Eu Gd Tb Dy Yb

3 rhyolites

2 dacites

2 andesites

Lu

La Ce Nd Sm Eu Gd Tb Dy Yb Lu

8 rhyolites

17 dacites

13 andesites

WHOLE PUMICE

GLASS

Ratio of sample/chondrite

Figure 153. Chondrite-normalized rare-earth-element abundances for 1912 pumice blocks and for high-purity matrix-glass 

separates thereof, arranged by ionic radius. For whole-pumice blocks, dacite field (lined) partly overlaps that for andesites. 

For glass separates, two dacite samples are, within analytical errors, virtually identical and plotted as a single bold line.
Chapter 13. 1912 Magma Compositions and Preeruptive Storage 203

assess magmatic affinities of the 1912 products with those of 

the several stratocones and domes nearby. Novarupta lies at 

the toe of the Trident complex, and the 1912 vent cuts across 

one of its peripheral lava domes (Falling Mountain). But it 

also lies close to Mageik and Griggs Volcanoes and, of course, 

Mount Katmai collapsed nearby during the 1912 eruption. All 

of these, and Mount Martin and Snowy Mountain as well, consist predominantly of andesite-dacite, and all have produced 

Holocene eruptions. Not one has erupted any late Quaternary 

high-silica rhyolite.

The analysis of Hildreth and Fierstein (2000) showed 

that all products of Mount Griggs and all Pleistocene products 

of Trident and Mageik are unambiguously distinguishable 

geochemically from the andesite-dacite continuum of 1912. 

Some Holocene dacites of Mount Mageik are similar to 1912 

dacites, but many others are relatively enriched in K, Fe, and 

Zr. The Southwest Trident lavas and ejecta of 1953–74 are 

similar in many respects to the 1912 andesite-dacite array, 

but they are consistently lower in K and the andesites are 

lower in Fe. Geochemical affinity of the 1912 suite is closest to the products of Mount Katmai (figs. 59, 148, 150, 151), 

in particular to the dacite-rhyodacite array erupted from its 

southwest cone in the interval ~23–10 ka. Moreover, Southwest Katmai is the only Quaternary vent in the Katmai cluster 

to have erupted both basalt and rhyodacite (51.6–72.3% SiO2

) 

in addition to its andesite-dacite array. Its caldera floor, of 

course, also provided the vent site for the Horseshoe Island 

dacite in the aftermath of caldera collapse synchronous with 

the eruptions at Novarupta. It thus appears most plausible that 

the andesite-dacite magma released at Novarupta came from 

beneath Mount Katmai, even though its transport path may 

have led under parts of the older Trident edifice. What was 

the preeruptive storage site of the 1912 rhyolite, and whether 

it was conjoint with the andesite-dacite or not, are questions 

addressed at length below.

Volatile Compositions

Preeruptive water contents were estimated by Fourier 

transform infrared spectroscopy (FTIR) and ion-probe analysis 

of melt (glass) inclusions (MI) trapped in phenocrysts, presumably during crystal growth in the magma reservoir prior to 

syneruptive decompression (Westrich and others, 1991; Lowenstern, 1993; Wallace, 2005). For MI in quartz and orthopyroxene phenocrysts from 1912 rhyolite, the three studies measured ranges of 3.8±0.7, 3.0–4.7, and 4.2–4.5 weight percent 

H2

O, respectively. Lowenstern (1993) found overlapping 

ranges and no consistent differences in water contents of MI 

in 1912 rhyolite emplaced as fallout, ignimbrite, or lava dome. 

For MI in plagioclase from 1912 dacite pumice, Westrich and 

others (1991) measured 2.3±0.6 weight percent H2O by ion 

probe and Lowenstern (1993) 2.2–3.1 weight percent H2O by 

FTIR. If such values accurately represent pre-eruptive water 

content of the dacite melt, the dissolved water content of the 

crystal-rich dacite magma would have been ≤2 weight percent. 

For 1912 andesite pumice, nearly all MI examined (in several 

laboratories) have been found to be partly crystallized and/

or fractured; nonetheless, Westrich and others (1991) reported 

1.0±0.1 weight percent H2O in eight bubble-bearing MI in 

andesite plagioclase, although it remains unresolved whether 

such low water contents might reflect gas loss during preeruptive magma ascent or posteruptive modification of MI. 

CO2 content of MI in 1912 rhyolite quartz has been 

determined only by Wallace (2005), who found a low range of 

20–50 ppm by FTIR spectroscopy (using a CO2-purged system 

with a very low detection limit). Lowenstern (1993) reported 

CO2 contents to be below his 50 ppm detection limit in MI 

from both dacite and rhyolite. The combined H2O–CO2 data, in 

conjunction with experimentally determined vapor-saturation 

isobars (fig. 8 of Wallace, 2005; Newman and Lowenstern, 

2002), suggest preeruptive storage of the rhyolite magma at 

100–130 MPa (1–1.3 kb), consistent with the phase-equilibrium experiments of Coombs and Gardner (2001). Lowenstern 

(1993) independently made a strong case for preeruptive gas 

saturation (in all 1912 magmas), based on the presence of Curich bubbles in MI, the low CO2

 and S contents of MI, and the 

need for partitioning into a fluid phase to account for marked 

decreases of S and Cu concentrations and suppression of Cl 

enrichment from andesite to dacite to rhyolite.

Halogen contents of MI were determined by microbeam analysis by Westrich and others (1991), who reported 

1,930±120 ppm Cl and 630±210 ppm F for MI from rhyolite 

pumice; 1,790±220 ppm Cl and 640±220 ppm F for MI from 

dacite pumice; and 1,690±180 ppm Cl and 530±200 ppm F 

for MI from andesite pumice. They also emphasized that 

large fractions of the magmatic Cl and F were retained by the 

matrix glass of the ejecta, leaving them available for release 

by leaching or devitrification during the subsequent decade of 

acid-gas fumarolic activity. Palais and Sigurdsson (1989) also 

determined halogen contents of MI (by electron microprobe) 

from several samples of 1912 dacite (only), obtaining ranges 

of 1,710–2,220 ppm Cl and 220–420 ppm F.

Sulfur contents of MI in 1912 dacite, as measured by 

electron microprobe by Palais and Sigurdsson (1989), range 

widely, 48–359 ppm S. By the same method, Westrich and 

others (1991) obtained the following concentrations for MI in 

1912 ejecta: <65 ppm S for rhyolite, 120±40 ppm S for dacite, 

and 170±60 ppm S for andesite. All 1912 ejecta contain pyrrhotite (Fe1-xS), implying magmatic sulfur saturation across the 

whole compositional range.

Mineralogy of 1912 Products

Mineral separations from individual pumice blocks have 

yielded 0.5–3 weight percent crystals in 1912 rhyolite and a 

remarkably wide range of 25–42 weight percent crystals in the 

dacite and andesite (fig. 147). All ejecta contain plagioclase, 

orthopyroxene, titanomagnetite, ilmenite, apatite, and pyrrhotite, in that order of abundance. In addition, euhedral quartz is 

only slightly less abundant than plagioclase in the rhyolite, 
204 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

and clinopyroxene is comparable in abundance to orthopyroxene in the dacite and andesite (Hildreth, 1983). Rare zircon 

occurs in the rhyolite as tiny inclusions in other crystals, and 

inclusions of Fe-Cu sulfide (cubanite-like “intermediate solid 

solution”) occurs within titanomagnetite in some andesitic 

scoriae (see table 5 of Lowenstern, 1993). Sparse olivine 

accompanies the abundant pyroxenes in eight andesites and 

one dacite—about half the scoria blocks from which minerals 

were separated.

Rare euhedral hornblende has been observed in mineral 

separates from nine pumice blocks and in the rhyolitic lava 

of the Novarupta dome. All the hornblende-bearing pumice 

blocks were taken from Layer B or from Packages 3 to 7 of the 

main ignimbrite, thus from compositionally mixed parts of the 

eruptive sequence. Four of the pumice blocks turned out to 

have bulk compositions (66.9–68.6% SiO2) at the high-silica 

end of the andesite-dacite continuum, but two were rhyolites 

(77.1–77.4% SiO2), two were lower-silica dacites (63.2–65.9% 

SiO2), and one an andesite (59.1% SiO2). Hornblende was not 

found in rhyolite pumice from Layer A.

Abundances of mineral phases in pumice are hard to 

estimate optically and seldom satisfactorily precise even in 

mineral separates. The following data represent the combined 

efforts of Hildreth (1983) and Avery (1992). In 1912 rhyolites, plagioclase is euhedral, generally smaller than 1 mm, and 

makes up 0.5–2 weight percent of the rock, while dipyramidal quartz is 0.2–0.8 mm across and typically somewhat less 

abundant (0.3–1 weight percent) than plagioclase. Orthopyroxene prisms are as long as 0.5 mm and roughly 0.2–0.5 

weight percent in abundance. Clinopyroxene is absent in most 

rhyolite samples, but traces (often broken and probably transferred from coerupted intermediate magmas) were observed 

in mineral separates from the Novarupta lava dome and from 

a few rhyolitic pumices taken from Layers B, C, and D, but 

not from Layer A. Euhedral unrimmed hornblende found 

in Novarupta and in two rhyolite pumice blocks is stubby, 

0.1–0.4 mm long, and (where present at all) is less than 0.1 

weight percent in abundance. Titanomagnetite is generally 0.1–0.3 mm across and quite sparse in the rhyolite, ≤0.2 

weight percent. Ilmenite is of similar size but at least an order 

of magnitude sparser than titanomagnetite. Apatite, sulfide, 

and zircon inclusions are tiny (≤0.1 mm), rare in the rhyolites, 

and have not been observed as free crystals.

In 1912 dacite and andesite, quartz is absent or very rare 

and presumed xenocrystic; plagioclase is by far the dominant 

phenocryst, constituting 20–35 weight percent of the rock. 

Plagioclase ranges in length from ~0.1 mm to 2.5 mm in 

dacites and rarely up to 4 mm in andesites. Orthopyroxene 

prisms are 0.1-1 mm long and make up 1.5–4 weight percent 

of dacites and 1–3 weight percent of andesites. Clinopyroxene 

prisms are typically 0.2–1 mm long and make up 1–3 weight 

percent of dacites and 4–8 weight percent of andesites. In 

mineral separates, opx:cpx ratios are estimated to be as great 

as 2:1 in some dacites, 1:1 in others, and as small as 1:3 in 

many andesites. Hornblende prisms are euhedral, unrimmed, 

and typically 0.1–0.4 mm but rarely ~1 mm long; absent from 

most pumice blocks examined, they are as abundant as 0.6 

volume percent in a few (Avery, 1992). Fe-Ti oxides are as 

big as 0.5 mm in dacites and 0.3 mm in andesites, but they 

also occur as tiny inclusions (commonly ≤0.1 mm) in other 

phenocrysts (except quartz). Ilmenite is very sparse in andesites but may be half as abundant as titanomagnetite in some 

dacites, as estimated by microprobe in heavy-mineral concentrates (Hildreth, 1983). Olivine is rare, ≤0.5 mm, identified 

only in andesite scoriae (and one dacite pumice), and may or 

may not have reaction rims. Sulfides and apatite are widespread as tiny inclusions (≤0.1 mm), the former most common 

in pyroxenes and oxides, the latter as needles in plagioclase.

Compositions of most mineral phases were summarized 

by Hildreth (1983) and Avery (1992), who conducted extensive analytical work by electron microprobe. Plagioclase in 

1912 rhyolite is unzoned or very weakly so and limited to the 

oligoclase range An25-29. In dacites and andesites, most plagioclase is optically zoned and euhedral, though many crystals 

are broken. Plagioclase with sieve texture (myriad interconnected glass inclusions) is uncommon in dacites but abundant 

in andesites. Individual isolated melt (glass) inclusions (MI) 

are typically 20–80 μm across in both andesites and dacites. 

Zoning is generally normal in dacites, but internal dissolution 

discontinuities are common and zoning reversals present in 

many plagioclase grains in andesites. Avery (1992) illustrated 

and documented various styles of oscillatory, discontinuous, 

and irregular zoning, weak and strong, in andesitic and dacitic 

plagioclases. In general, plagioclase core compositions are 

An36-82 in dacites and An48-89 in andesites, whereas rims are 

An35-53 in dacites and An36-83 in andesites (Hildreth, 1983; 

Avery, 1992). A sparse subpopulation of highly calcic plagioclase—discrete grains almost unzoned in the range An87-94—was 

found principally in andesitic scoriae (Hildreth, 1983) but also as 

rare contaminants in Novarupta dome rhyolite. No grains or 

overgrown cores of oligoclase transferred from 1912 rhyolite 

have been identified in 1912 andesite or dacite (or in Trident 

products erupted nearby in 1953–74).

Orthopyroxenes are virtually unzoned in rhyolites at En49-50

and have low contents of CaO (~1.1%) and Al2O3 (~0.3%). 

Across the dacite-andesite continuum, orthopyroxenes are 

modestly zoned but show no compositional overlap with those 

in the rhyolites. Core compositions are En61-65 in dacites and 

En62-73 in andesites, whereas rims are En59-63 in dacites and 

En59-74 in andesites. CaO content ranges from 1.2 to 1.9 percent (Wo2.0-3.7) and Al2

O3 widely from 0.6 to 2.6 percent.

Clinopyroxenes are unzoned or weakly zoned in Ca-MgFe but fairly heterogeneous in minor elements. Compositions 

cluster tightly in the augite field at Wo40-45 for both andesites 

and dacites. Clinopyroxene cores are En40-43 in dacites and 

En40-45 in andesites, whereas rim compositions are En39-42 in 

dacites and En41-46 in andesites. Al2O3 contents of the clinopyroxenes are more varied, 1–2 percent in dacites and 1.4–4.4 

percent in andesites; thin reversely zoned (Mg-richer) rims in 

some clinopyroxenes in andesite scoriae have Al2O3 contents 

as great as 5.0–6.7 percent. In an ion-probe reconnaissance, 

Shearer and others (1991) found such Mg+Al-enriched 
Chapter 13. 1912 Magma Compositions and Preeruptive Storage 205

pyroxene rims (25–75 μm thick) to be depleted in REE relative to their cores, suggesting late interaction with a more 

primitive magma batch. Such mafic recharge not long before 

the eruption is also consistent with the An-rich rims of many 

plagioclase crystals (and the sparse unzoned An90 grains) in 

the 1912 andesite.

Olivines, found sparsely in about half the andesite scoria 

blocks separated, are in the compositional range Fo73-82 and 

contain 0.09-0.18 percent CaO.

Quartz in the rhyolite is euhedral and shows subtle (if 

any) cathodoluminescence zoning and no significant zoning in 

Ti content (Payne and Eichelberger, 2009), providing temperature estimates consistent with the range determined from 

coexisting Fe-Ti-oxide geothermometry (Hildreth, 1983). The 

quartz dipyramids contain abundant melt inclusions, mostly 

20–150 μm in diameter and exclusively high-silica rhyolite 

in composition (Clocchiatti, 1972, 1975; Westrich and others, 

1991; Lowenstern, 1993).

Hornblendes from dacite pumice blocks analyzed by 

Avery (1992) and Hammer and others (2002) are magnesian 

and calcic, low in alkalies and alumina, and only weakly 

zoned. Even in the glassy dome lava of Novarupta, as in 

the pumice clasts, hornblende prisms lack reaction rims. 

Nonetheless, experimental work (Hammer and others, 2002) 

indicates that the sparse hornblende found in a few 1912 

rhyolite samples is a magmatic contaminant transferred from 

the commingled dacite. By weight, MgO/(MgO+FeO*) in 

the hornblendes is 0.49–0.54, and by cations per formula unit, 

the range of Mg/Fe is 1.75–2.1. The following ranges were 

measured by electron microprobe: 10.8–11.2 percent CaO; 

1.45–1.7 percent Na2

O; 0.23–0.38 percent K2O; 1.3–1.6 percent TiO2

; and 5.5–7.0 percent Al2O3.

Iron-titanium oxide minerals were analyzed by Hildreth 

(1983), Coombs and Gardner (2001), and Hammer and others (2002) by electron microprobe, emphasizing coexisting 

titanomagnetite-ilmenite pairs. In titanomagnetites, Xusp is 

0.29–0.31 in rhyolites, 0.25–0.29 in dacites, and 0.23–0.27 

in andesites. In ilmenites, Xilm is 0.85–0.975 in rhyolites, 

0.76–0.81 in dacites, and 0.72–0.75 in andesites. Minor elements range widely in both phases. In the titanomagnetites, 

as MgO increases from 0.7 to 3.1 percent (from rhyolite to 

andesite), Al2

O3 increases from 1.0 to 3.5 percent, and MnO 

declines from 0.8 to 0.35 percent. Likewise, in the ilmenites, 

as MgO increases from 1.6 to 3.7 percent, Al2O3 increases 

from 0.1 to 0.5 percent and MnO declines from 1.1 to 0.35 

percent. Because of such compositional ranges and because 

coeruption of rhyolite, dacite, and andesite has introduced 

mixed populations of oxide minerals into some samples, all 

pairs were screened for equilibrium by the Mg/Mn partitioning test of Bacon and Hirschmann (1988), and touching pairs 

were preferred (but not always found). Using the QUILF 

algorithm of Andersen and others (1993), equilibration values 

of temperature and oxygen fugacity (fO2

) were then calculated 

for numerous preferred pairs, values inferred to represent magmatic conditions just prior to eruptive quenching. For 1912 

rhyolites, the method yields 800oC–857oC and log fO2 values 

of –13.5 to –12.0. For dacites, the ranges are 848oC–950oC 

and –11.7 to –10.0. And for andesites, they are 952oC–990oC 

and –9.2 to –10.1. 

As emphasized by Hildreth (1983), such data imply a 

thermal continuum across the pre-eruptive magmatic spectrum in spite of the wide bulk-compositional gap between 

the rhyolite and the dacite-andesite continuum. It should be 

noted, however, that only four rhyolitic pumice samples have 

given oxide temperatures between 835oC and 857oC (whereas 

~20 pairs yield 800oC–833oC). Conceivably, the four could 

represent rhyolite magma that had been heated in proximity 

to the intermediate magmas during or before eruption, but 

we have no independent evidence supporting that suggestion. 

Support for the higher temperature range for some 1912 rhyolite pumices comes from the work of Clocchiatti (1972), who 

measured homogenization temperatures of 850±10oC (108 

determinations) for melt inclusions with vapor bubbles trapped 

inside their quartz phenocrysts.

Contact heating may also have taken place in the rhyolite 

magma that was later extruded as the Novarupta dome, which 

has yielded pairs that give 833oC and 840oC. Several more 

equilibrium pairs in the dome rhyolite, however, gave values 

up in the dacite-andesite temperature range (Hildreth, 1983; 

Coombs and Gardner, 2001), suggesting contamination shortly 

before extrusion. A discrete dacite layer (65.1% SiO2

) within 

the rhyolite dome gave 915oC. A sample from the Phantom 

dome block bed gave 935oC and –10.35 fO2, near the high 

ends of the ranges found for dacite plinian pumice.

Isotope Ratios

Oxygen isotope ratios were measured for plagioclase, 

quartz, orthopyroxene, and titanomagnetite separated from 

1912 rhyolite, dacite, and andesite (fig. 154). Values of 

d18Oplag for rhyolites are +6.0–6.4, for dacites +5.8–6.0, and 

for andesites +5.6–5.9. The plagioclase data should represent 

close approximations to nonhydrated whole-rock values, and 

the slightly heavier values of the rhyolites are what is predicted for a normal fractionation sequence. Fractionations 

of 18O among the coexisting phenocryst species (Hildreth, 

1987) is consistent with the range of Fe-Ti-oxide temperatures 

(800–990oC) determined for the 1912 andesite-to-rhyolite 

array (Hildreth, 1983; and section above titled “Mineralogy 

of 1912 Products”). Regardless of the extent to which crustal 

melting may have contributed to genesis of the rhyolites, the 

d18O data indicate that crustal rocks previously affected by 

hydrothermal alteration or surface weathering were insignificant contributors.

Nd isotope ratios for 1912 eruptive products and for 

the adjacent stratovolcanoes are within the narrow range 

found for the entire Alaska-Aleutian Quaternary arc. Values 

of 143Nd/144Nd for the whole arc range only from 0.51290 to 

0.51310 (George and others, 2003; and many sources cited 

therein), while for products of the 1912 eruption, the range is 
206 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

r

A ASH FLOWS C D G NOVARUPTA

+8 d a d r d

+7

+6

+5

+4

+3

+2

Quartz

Plagioclase

Orthopyroxene

Titanomagnetite

Ο,SNOW in parts per thousand 

FM MC

typical error δ18

Figure 154. Values of d18O for coexisting quartz, plagioclase, orthopyroxene, and titanomagnetite separated from Novarupta 

lava and from individual pumice blocks of 1912 ignimbrite and fallout Layers A, C, D, and G. Symbols at top: r, rhyolite; d, 

dacite; a, andesite. Isotopic determinations for Falling Mountain (FM) and Mount Cerberus (MC) were for whole-rock 

crystalline dacite. Analyses by Hildreth in USGS laboratory of J.R. O’Neil at Menlo Park, California, in 1980. Values are 

deviations in parts per thousand from that of standard mean ocean water (SMOW).

0.512952 to 0.513035 (table 2), a range that also brackets all 

the 143Nd/144Nd values measured for the entire Katmai volcano cluster (Hildreth, 1983; and authors’ unpublished data). 

Because the small ranges determined for 1912 rhyolite, dacite, 

and andesite mutually overlap, no systematic fractionationassimilation sequence is discernible among them on the basis 

of Nd isotopes. The only pre-Quaternary rocks exposed 

nearby for which Nd-isotope values have been determined 

(Lowenstern and Mahood, 1991) are Pliocene intrusions (more 

radiogenic than 1912 products, at 0.513067–0.513089) and 

Jurassic siltstone (less radiogenic, at 0.512725–0.512838), neither of them suitable assimilants to account for the observed 

range of 1912 isotopic diversity (fig. 1 of Lowenstern and 

Mahood, 1991).

Pb-isotope ratios for volcanic-front centers along the 

Alaska Peninsula have quite limited ranges (George and others, 2003): 206Pb/204Pb values determined extend from 18.73 

to 18.88, 207Pb/204Pb from 15.52 to 15.58, and 208Pb/204Pb 

from 38.18 to 38.42. Only a few Pb-isotope ratios have been 

measured for the Katmai cluster. An andesitic enclave in the 

Novarupta dome gave values (18.88, 15.58, and 38.39) at the 

radiogenic ends of the ranges cited, and values for dacite and 

andesite of the 1953–74 eruption of Trident are very similar 

(George and others, 2003). A 1912 rhyolite pumice gave 

values (18.85, 15.57, and 38.375) trivially less radiogenic 

than those for dacite pumice (18.88, 15.57, and 38.38) or the 

Novarupta andesite (Reagan and others, 2003).

Sr-isotope ratios measured for 1912 eruptive products range fairly widely, but (like 143Nd/144Nd) the ratios for 

rhyolite, dacite, and andesite exhibit wholesale overlap (table 

2; fig. 155). Rhyolite pumice clasts (n=3) yield 87Sr/86Sr 

values of 0.70368 to 0.70374, and rhyolite lava (n=2) from 

the Novarupta dome 0.70372. Dacite pumices (n=10) are in 

the range 0.70354 to 0.70362, and andesite scoriae (n=17) 

0.70352 to 0.70374. Two scoriae atop the Turtle, more 

mafic than the continuous array, gave less radiogenic values: 

0.70344 (54.6% SiO2) and 0.70338 (50.4% SiO2, olivine 

accumulative); and a mafic enclave (55.2% SiO2) in Novarupta 

rhyolite gave 0.70348 (George and others, 2003). For comparison, 15 samples from Mount Katmai range from 0.70335 to 

0.70372, and 10 from Trident only from 0.70344 to 0.70359. 

The 1912 rhyolite and andesite thus have in common that they 

extend to Sr-isotope ratios more radiogenic than lavas of the 

adjacent edifices.

Because the rhyolite contains only a third as much Sr 

(58–95 ppm) as the andesite-dacite array (210–330 ppm), it 

should have been more susceptible to contamination (by either 

magma mixing or assimilation), but its Sr is no more radiogenic than that in much of the andesite. We again emphasize 

that the pale-gray dacite and black andesite (fig. 4) are simply 

convenient nametags along a phenocryst-rich compositional 

continuum, that the andesite-dacite distinction at 63 percent 

SiO2 is an arbitrary convention, and that they were coerupted 

throughout much of the 1912 sequence. The mafic outliers 
Chapter 13. 1912 Magma Compositions and Preeruptive Storage 207

have the least radiogenic Sr (0.70338–0.70348), but, within 

the andesite-dacite continuum, ratios for andesites (0.70352 

to 0.70374) wholly encompass those for dacites (0.70354 to 

0.70362). There was therefore clearly no systematic assimilation process, neither within the continuum nor relating the 

continuum to the rhyolite (0.70368 to 0.70374). 

Some have tried in the past to model Sr-isotope variation in 1912 products by assimilation of the exposed Jurassic sandstone-siltstone of the Naknek Formation, which is 

subhorizontal here and extends from the surface to a depth 

of ~1,500 m (Riehle and others, 1993; Detterman and others, 

1996). We see this as a pointless exercise because the magma 

reservoir was probably at least twice that deep and likely to 

have been enclosed by earlier Mesozoic sedimentary strata or 

by Paleozoic basement rocks (see fig. 13 of Hildreth and Fierstein, 2000). Small but varied and unsystematic contamination by feldspar-rich sedimentary rocks comparable to Naknek 

arkoses (267–705 ppm Sr; 0.7042–0.7048) might nonetheless 

help account for some of the 87Sr/86Sr variations in the 1912 

magmas; but so could partial melts of arc-intrusive rocks at 

any depth. 

Numerous Miocene and Pliocene tonalite-granodiorite 

plutons exposed in the Katmai area are reasonable candidates to provide crustal assimilants; about 30 samples of 

such local granitoids give ranges of 59–67 percent SiO2 and 

280–650 ppm Sr (authors’ unpublished data), but the only 

87Sr/86Sr value yet determined for any of them is 0.703288 

(Lowenstern and Mahood, 1991) for one porphyritic pluton, 

far less radiogenic than any 1912 product. A sill of highsilica rhyolite (0.70427; 238 ppm Sr; 3.1 Ma) adjacent to 

that pluton exemplifies a local shallow intrusion presumed 

to be enriched in crustal melt contributions. A mixing line 

between the two intrusions (both intruding Naknek Formation strata near Mount Mageik; Hildreth and Fierstein, 2003) 

passes through high-Sr members of the 1912 andesite-dacite 

array (fig. 155), illustrating potential modes of introducing 

isotopic variability antecedent to continuing crystal-melt 

fractionation. Many other potential modes can be envisaged, 

entailing unexposed pre-Mesozoic basement or the (isotopically unstudied) granitoid plutons nearby, some of which are 

as old as 20 Ma (Hildreth and Fierstein, 2003).

Another general process promoting Sr-isotopic variation 

within the 1912 suite would be upper-crustal coalescence of 

many crystal-rich magma batches, each with a unique history 

of assimilation and fractionation during ascent through 30 km 

of peninsular crust. For example, products of the 1953–74 

eruption of Trident, which was concluded by Coombs and others (2000) to have involved advanced mixing of a new batch 

of andesite with a shallow body of resident dacite, yield a 

range of 87Sr/86Sr values—from 0.703455 at 56 percent SiO2 to 

0.70352 at 57 percent SiO2 through to 0.70357 at 64.2 percent 

SiO2. Intrabatch variations at the 0.0001 level are potentially 

generated at any depth, deep to shallow, by interaction with 

Paleozoic or Mesozoic crustal rocks, and then further complicated by blending of magma batches.

U and Th isotopes have been measured for ~33 samples of 

1912 eruptive products by Reagan and others (2003) and Turner 

and others (2010). Values of (230Th/232Th) are consistently 

high at 1.35 to 1.46, and (238U/232Th) ranges from 1.28 to 1.51, 

yielding a modest range in (230Th/238U) values from 0.95 to 1.05. 

Parentheses indicate activity ratios, not elemental ratios. On a 

U-Th equiline diagram (fig. 156), the three most mafic samples 

have 3–5 percent excess 230Th, while most of the andesite 

samples plot close to the equiline, and most dacite samples plot 

to the right of it at 1–3 percent excess 238U. The 1912 rhyolites 

have the highest values (1.43–1.46) of (230Th/232Th) and plot not 

far from the equiline—slightly to the left of it with Reagan’s 

data, slightly to the right with Turner’s data. 

Any process that fractionates U and Th from each other 

introduces radioactive disequilibrium, thus requiring either 

ingrowth or decay of 230Th to restore secular equilibrium, processes that take about 350,000 years. Their extreme incompatibility in mantle minerals governs the conventional presumption that mantle processes fractionate U from Th only trivially. 

In crustal rocks, however, zircon and apatite are widespread 

and strongly fractionate U and Th relative to host melts. Katmai dacites contain apatite but apparently lack zircon, whereas 

both the 1912 rhyolite and the 22.8-ka plinian rhyodacite from 

Mount Katmai clearly fractionated zircon (fig. 8 of Hildreth 

and Fierstein, 2000).

Fractionation of zircon (with Th/U typically lower than 

the melt) is likely to have contributed to U-Th isotopic variations in the 1912 rhyolite. The effects of zircon fractionation 

are obvious in the suppression of Zr and Hf enrichment in the 

rhyolites (fig. 151) and the reduced Zr/Hf ratios relative to 

the dacites (table 2). Such effects were plotted in figure 6 of 

Hildreth (1987) before zircon was identified in 1912 rhyolites 

and were at the time attributed to residual source-rock zircon. 

A consequence of zircon subtraction (whether refractory or 

fractionated) is, of course, to shift melts with excess 238U 

instantaneously to the left, back toward or across the equiline, 

independent of any secular ingrowth of 230Th (fig. 156). 

Both U-series studies illustrated a 40-k.y. pseudoisochron 

that passes through many of the mafic, andesitic, and dacitic 

samples (fig. 156), but it is not clear what this might actually 

represent. Three andesite-dacite samples from the unrelated 

1953–74 mixed eruption of Trident also fall along that pseudoisochron, as do the dacites of Falling Mountain and Mount 

Cerberus (Reagan and others, 2003), which are 2–3 times 

older than 40 ka (table 1). Far more likely than an expression 

of any time relationship, the trend probably represents a crude 

mixing array that reflects crustal assimilation at various depths 

and blending of successive magma batches; an open-system 

interpretation is strengthened by the fact that the zircon-free 

andesite-dacite array crosses the equiline from 230Th excesses 

to 238U excesses.

Moreover, Mount Katmai had erupted voluminous 

rhyolite and rhyodacite starting around 22.8 ka (Hildreth and 

Fierstein, 2003), which is hard to reconcile with steady U-Th 

maturation of its andesite-dacite magma reservoir since 40 ka.
208 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

0.7038

0.7037

0.7036

0.7035

0.7034

0.7033

0.7032

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 x10-3

87Sr 86Sr ratio

1

Sr content, in parts per million

Rhyolites

1912 rhyolite

1912 dacite

1912 andesite

glass

1953–60 Trident

Jn

both

0.7048

Sill 0.70427

Porphyry

Figure 155. Sr-isotope ratios plotted against reciprocal of Sr concentration (ppm-1), a convention that transforms a mixing 

hyperbola into a straight line. Line connects data (s) for Pinnacle Porphyry (63–65% SiO2

) and high-silica rhyolite sill (77% 

SiO2

), both near West Mageik Lake and both ~3.1 Ma (Lowenstern and Mahood, 1991; Hildreth and Fierstein, 2003). Symbols 

are identified in inset for 1912 ejecta and for 1953–60 lava flows of Southwest Trident. Tie-lines connect data for three wholepumice samples and their matrix glasses, illustrating fractionation trend from andesite-dacite continuum toward rhyolites. 

Percent SiO2

 of the three pumice-glass pairs, respectively, are: sample K-75, 59.3, 66.8; sample K-45, 64.6, 75.2; and sample 

K-1490, 67.7, 76.0. It is not implied that these particular Pliocene intrusions provided assimilants to 1912 or Trident magmas, but, 

instead, that comparable Tertiary intrusive rocks are more likely candidates than the shallowly exposed Naknek Formation (Jn).
Chapter 13. 1912 Magma Compositions and Preeruptive Storage 209

MS

N

N

N

KR

22.5 ka

1.34

1.30 1.34 1.38 1.42 1.46

1.48

1.46

1.44

1.42

1.40

1.38

1.36

40 k.y.

andesite

dacite

rhyolite

equiline

Zircon

U addition

Ageing

fractionation

(230Th 232Th) activity ratio

(

238U 232Th) activity ratio

Figure 156. U-Th equiline diagram, combining Novarupta-Katmai data of Reagan and others (2003) 

and Turner and others (2010) for 33 samples. Equiline represents secular equilibrium. Parentheses 

indicate activity ratios, not elemental ratios. Distinguished by colors are rhyolite (red), dacite 

(green), and andesite (black). N, Novarupta dome lava; all others are 1912 pumice and scoria, 

except KR, Mount Katmai 22.5-ka rhyolite lava on south rim of caldera. MS, 1912 mafic samples 

(as distinguished in table 2 from andesite-dacite continuum). Dashed 40-k.y. pseudoisochron and 

all three rhyolites left of equiline are from Reagan and others (2003). Inset schematically shows 

trends expected to result from instantaneous addition of U, ingrowth of 230Th by ageing, and either 

zircon fractionation or its retention in residue of crustal partial-melt contributions. 

The 22.5-ka rhyolite lava flow at Mount Katmai has lower U/

Th and lower (230Th/232Th) than 1912 rhyolites and plots farther left on an equiline diagram (Reagan and others, 2003), 

with significant excess 230Th: (238U/230Th) = 0.973. Products of a voluminous plinian eruption that accompanied or 

directly preceded the 22.5-ka rhyolite lava had clearly undergone zircon fractionation (fig. 8b of Hildreth and Fierstein, 

2000), thus reducing its U/Th ratio, as likewise inferred for 

the 1912 rhyolite.

The U-Th isotope data thus reinforce the inference from 

the Sr-isotope results that the 1912 compositional range was 

not produced by closed-system fractionation. The array of 

isotope values from excess 230Th to excess 238U, combined 

with a wide range of (226Ra/230Th)—(1.0–2.5; Turner and 

others, 2010)—suggests accumulation and blending of many 

different magma batches with ranges in crustal depth of 

batch coalescence, residence time, and extent of intracrustal 

assimilation. Because basalts are rare, primitive compositions 

absent, and andesites dominant, we assume that most batches 

arose from deep-crustal MASH zones that blended varied 

crustal melts with differentiates of varied basalts, as outlined 

by Hildreth and Moorbath (1988) and modelled by Annen and 

others (2006).

The distinctively higher (230Th/232Th) range of the 1912 

rhyolites (relative to the andesite-dacite array) and their position not far from the equiline can be interpreted in various 

ways: (1) The conventional interpretation would infer a far 

longer residence time (100,000–350,000 years) for the rhyolite 

magma than for the coerupted andesite and dacite, a scenario 

that we find implausible for the 140-k.y.-old, recurrently active, 

predominantly intermediate, Katmai-Trident volcanic group. 

(2) Zircon fractionation from the 1912 rhyolite itself may have 

shifted the melt from originally greater 238U excess back toward 

the equiline. (3) Rhyolitic partial melt contributions from felsic 
210 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

arc plutons old enough to be at secular equilibrium might have 

modified the U-Th budget of the dacite-derived rhyolite melt 

with which it blended. (4) Had such a remelting pluton been 

of late Pleistocene age, refractory zircon might have shifted the 

rhyolitic partial melt extract toward the equiline, away from 

probable bulk-rock excess 238U. (5) The felsic plutonic rock 

remelted might have actually been an early differentiate of 

Mount Katmai andesite, compositionally akin to 1912 magmas, 

young enough to retain some degree of (230Th/238U) disequilibrium, and subject to the same shift promoted by refractory zircon. In view of the hundreds of late Pleistocene and Holocene 

eruptions that built Katmai and Trident, not one of which had 

previously produced high-silica rhyolite, we consider option 

(1) the least plausible, option (5) the most consistent with the 

many other compositional constraints, and options (2), (3), and 

(4) all plausible contributors. We return to this topic as part of 

a comprehensive summation in the section below titled “Origin 

of the 1912 Rhyolite.”

Experimental Petrology

Phase-equilibrium experiments were undertaken on natural samples of 1912 rhyolite by Coombs and Gardner (2001) 

and of 1912 dacite and andesite pumice by Hammer and others 

(2002). The rhyolite study was conducted under water-saturated conditions, in accord with the evidence of Lowenstern 

(1993) for preeruptive gas saturation, and within a temperature range bracketing those indicated by Fe-Ti-oxide pairs 

(800oC–850oC; Hildreth, 1983). It was found that the natural 

phase assemblage was stable at 780oC–860oC at H2O-saturated 

pressures less than 100 MPa (1 kb). The best compositional 

matches for natural plagioclase and orthopyroxene were found 

at 70–100 MPa for 800oC and 40–50 MPa at 840oC. Quartz 

was found in only 4 of 24 experimental runs, and because 

quartz stability increases with pressure, it has been suggested 

that the low pressures are underestimates. Nonetheless, FTIR 

determinations of 4.0–4.5 weight percent H2O and 20–50 ppm 

CO2 in melt inclusions within 1912 quartz, combined with 

experimentally calibrated mixed-vapor-saturation isobars (fig. 

8 of Wallace, 2005; Newman and Lowenstern, 2002) yield 

entrapment pressures of 100–130 MPa, in agreement with 

the upper end of the H2

O-saturated estimates of Coombs and 

Gardner (2001). Assuming densities of 2,550–2,700 kg/m3 

for the local sedimentary section, these results converge on a 

probable depth range of 3–5 km.

The 1912 rhyolite was thus stored in a shallow reservoir where it crystallized its sparse assemblage of unzoned 

euhedral phenocrysts, which are nowhere found to contain 

higher pressure melt inclusions. Amphibole is absent in 1912 

rhyolite pumice, but at water-saturated pressures of 100-150 

MPa Coombs and Gardner (2001) found it to be the liquidus 

phase, thus sustaining the evidence against a higher pressure crystallization history for the rhyolite. No antecrysts 

have been found in 1912 rhyolite pumice, and xenocrysts are 

limited to rare clinopyroxene, typically broken, transferred 

from coerupted dacite or andesite. The sparsity and euhedal 

habit of the unzoned phenocrysts, especially the gem-quality 

quartz dipyramids, suggest weak undercooling, slow growth, 

and stable shallow storage of the rhyolite magma. Thermal 

continuity from rhyolite to dacite (as indicated by Fe-Ti-oxide 

pairs) and the need for a heat source to keep the rhyolite 

crystal-poor suggest preeruptive contiguity.

Hammer and others (2002) experimentally investigated 

1912 pumice blocks from the bulk-compositional extremes 

bracketing the andesite-dacite continuum, a dacite (68% SiO2

) 

that gave Fe-Ti-oxide temperatures of 848oC–876oC and an 

andesite (58.7% SiO2) that gave 952oC–963oC. The dacite was 

one of the rare pumice clasts found to contain small amounts 

of euhedral unrimmed hornblende. Matching of modes, melt 

compositions, and mineral-rim compositions of experimental 

charges and natural samples was best achieved under watersaturated conditions at 930oC–960oC and 75–100 MPa for the 

andesite and 850oC–880oC and only 25–50 MPa for the dacite. 

Lowenstern’s (1993) determination of 2.8±0.5 weight 

percent H2

O in melt inclusions in 1912 dacite phenocrysts is 

consistent with melt entrapment at the low-temperature, highpressure end of these ranges for water-saturated dacite. 

CO2 contents of melt inclusions (MI) in 1912 andesite 

and dacite have never been measured accurately, however, 

owing in part to crystallization and breakage of inclusions in 

the andesite and low CO2 in the dacite. Nonetheless, global 

evidence suggests that CO2 and SO2 should contribute to 

any hydrous vapor phase coexisting with such intermediate arc magmas, and Lowenstern (1993) demonstrated that 

1912 andesite and dacite did indeed contain a free gas phase 

before eruption. Hammer and others (2002) thus undertook numerous additional runs with a CO2

-H2O mixed fluid 

phase, adjusting the mole fraction of water in the fluid (XH2Ofl) 

between 0.34 and 0.85, supplementing their abundant data 

from water-saturated experiments. As they discuss in detail, 

reasonable intermediate values of XH2Ofl yield preferred storage 

depths between 4 and 5 km for the dacite and 4.5–5.7 km for 

the andesite, consistent with overlapping to slightly shallower 

estimates for the rhyolite (fig. 157).

Hornblende similar in composition to the trace amphiboles in the dacite pumice block selected for experimental 

work was produced experimentally only at slightly higher 

PH2O and in somewhat less evolved melt than under equilibrium conditions determined for the dacite sample itself (fig. 6 

of Hammer and others, 2002). It was suggested that the natural hornblende could have been drawn up from a deeper level 

of the voluminous zoned dacite and added syneruptively to 

the highly evolved dacite in which it was found. Most 1912 

dacite and virtually all 1912 andesite, however, lack amphibole. Hammer and others (2002) also showed that amphiboles grown experimentally in 1912 rhyolite and andesite are 

compositionally unlike any natural 1912 hornblendes (their 

fig. 8). The euhedral unrimmed hornblende found in Novarupta dome rhyolite has the composition of those in the natural 

and experimental dacites, not that of hornblende grown experimentally from the rhyolite. Moreover, plagioclase included 
Chapter 13. 1912 Magma Compositions and Preeruptive Storage 211

1

2 50

75

100

800 850 900 950 1000 0 1 2 3 4 5

125

150

25

3

4

5

6

1

2

3

4

5

6

Temperature, in ̊C

Depth, in kilometers

lithostatic load

ρ=2,700 kgm-3

Pressure, in megapascals

Depth, in kilometers

Distance, in kilometers

rhyolite

dacite

andesite

rhyolite

dacite

andesite

unerupted

cumulate mush

XH2Ofl=1

XH2Ofl=0.88

XH2Ofl=0.5

XH2Ofl

=0.72

Mt. Katmai

Figure 157. Summary of constraints on 1912 magma-storage conditions inferred from phase-equilibrium experiments of Coombs 

and Gardner (2001) and Hammer and others (2002), conducted on 1912 rhyolite and on end-member samples of the andesite-dacite 

continuum (ADC). Experimentally bracketed temperature ranges for all three compositions were in good agreement with those inferred 

from equilibration of FeTi-oxide pairs (Hildreth, 1983). Upper quadrilaterals represent P-T ranges determined under water-saturated 

conditions (XH2Ofluid = 1). Hammer and others (2002) also made runs for andesite and dacite samples under fluid-saturated conditions 

with ranges of CO2

 and H2O proportions in a mixed volatile phase. Lowenstern (1993) had earlier provided independent evidence for 

preeruptive vapor saturation in all three 1912 compositions; and Wallace (2005) subsequently showed melt inclusions in rhyolite quartz 

to contain 20–50 ppm CO2 as well as 4.0–4.5 weight percent H2O, indicating minimum entrapment pressures of 100–130 MPa. As yet 

uncertain CO2 contents of andesite and dacite magma were probably greater. Accordingly, P-T estimates are illustrated here for 

XH2Ofluid = 0.5—a probable minimum value for ADC. Also illustrated are P-T estimates for intermediate values of 0.88 for dacite and 0.72 

for andesite, which correspond to chamber-model depths portrayed in cartoon at right, as proposed by Hildreth and Fierstein (2000).

in and attached to dome hornblende crystals are more calcic 

than those of 1912 rhyolite but within the compositional 

range of plagioclase in the dacite (Coombs, 2001). The 

hornblende was evidently transferred from dacite to rhyolite 

magma during the intraconduit mingling made manifest by 

the dacite layers in the rhyolite dome. Ascent and transfer 

of the amphibole from its higher PH2O site of origin into 

a small fraction of the erupting dacite and thence into the 

dome rhyolite must have required only a few days in order 

to avoid development of dehydrated reaction rims (Hammer 

and others, 2002). This suggests that Novarupta extruded less 

than a week, not months or years, after the plinian eruptions. 

Prompt extrusion of the dome rhyolite is likewise suggested 

by preservation within the dome of subordinate Fe-Ti-oxide 

pairs characteristic of the andesite-dacite contaminants that 

had failed to reequilibrate to the lower temperature of their 

new rhyolitic host.

Preeruptive Magma Storage and Syneruptive 

Transport

Here we summarize the data, constraints, and inferences 

that bear upon the distribution of magma storage at the onset 

of the 1912 eruption (fig. 158). Any distribution model needs 

to account for arrival of rhyolite, dacite, and andesite at 

Novarupta on 6 June, caldera collapse at Mount Katmai on 7 

June, initiation of the plinian sequence by unadulterated rhyolite for several hours, and subsequent mingling of the confluent magmas for two more days.
212 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Plausible Storage Sites of 1912 Magmas

In contrast to most earlier products of Mageik and Trident, 

the Holocene eruptive products of East Mageik, Southwest 

Trident, and Mount Martin are not easily distinguishable chemically from the intermediate suites of Novarupta and Katmai 

(Hildreth and Fierstein, 2000). Because so many Holocene 

products of Novarupta, Katmai, Trident, Mageik, and Martin 

are similar pyroxene-plagioclase andesites and dacites, it is 

useful to summarize here the volcanological evidence capable 

of supplementing the chemical distinctions as means to sharpen 

understanding of magma storage and transport in 1912.

Viewed toward 335o

2 km

-10 km

-8 km

-6 km

-4 km

-2 km

+1 km

5 km4321 1

sea level S.L.

Base of Naknek Fm.

Base of P-J sedimentary rocks

Pre-Permian basement

Mid-crustal magma reservoir

Unerupted

cumulate mush

Martin Mageik Trident Katmai Alagogshak

MC FM

N

TW

Tsw Jn Jn

SW NE

Jn Jn

H.I.

Jn

7100 6115 6010 6128

6715

4000

3260

5605

1912 R sill R

D

1953-74 0.7 km3 A

Agglut.

Katmai Pass

?

5.5 km3

collapse

From Novarupta, Mount Katmai is 10 km east, the Holocene vent of East Mageik is 8 km southwest, that of Mount 

Martin 15 km southwest, and the 1953–74 vent of Southwest 

Trident only 4 km south (fig. 5). There is no evidence (observational, stratigraphic, or morphologic) that Mount Martin has 

erupted historically, and there has been no obvious change in 

the configuration of its crater or fumarolic discharge since it 

was first photographed in 1913 (Griggs, 1922, p. 85). Separated from Novarupta by the massive Mageik volcano, Mount 

Martin’s distance and its small but consistent differences in K 

and Sr contents seem sufficient to exclude its plumbing system 

as a plausible contributor to the 1912 eruption. 

Figure 158. Katmai volcanic cluster magmatic plumbing system; schematic illustration drawn to scale along N65oE volcanic axis, 

looking N25oW with no vertical exaggeration. Elevations on profile are in feet (1 m = 3.28 feet). Wavy vertical lines indicate presentday fumarolic emissions. Jn, marine sedimentary rocks of Jurassic Naknek Formation. Novarupta (N), Falling Mountain (FM), Mount 

Cerberus (MC), and West Trident (TW) are not actually along section, but their relative positions (see fig. 5) are indicated above 

profile, respectively 4.5 km, 4 km, 4 km, and 1.5 km northwest of line of section. G indicates direction toward Mount Griggs, 12 km 

northwest of the profile. Precollapse profile of Mount Katmai is adapted from figure 102; volume displaced in 1912 was about 5.5 km3

and surface subsidence was 1.2±0.1 km vertically. Displaced volume is modelled alternatively as conical funnel and cylindroid, each 

having top surface area (4 km2

) that of caldera floor. H.I., Horseshoe Island dacite dome; Agglut., remnant of pre-1912 agglutinated 

dacite fallout that mantles west rim (fig. 145) and Peak 6128 and thickens into a pre-1912 crater. Magma reservoir of 1912 is depicted 

(just before eruption) as a unitary chamber zoned from andesite (A) to dacite (D) to rhyolite (R) in the proportions (1/4.5/7.5) erupted. 

Because the magma volume erupted was 2.3 times greater than the volume collapsed, the 13-km3

 chamber is depicted as elongate 

along the volcanic axis, 1.3 km thick, 2 km across axis (into the profile), and 5 km along axis, thus extending well beyond caldera 

footprint. Rhyolite sill penetrates subhorizontal sedimentary strata, extending an additional 6 km toward Novarupta or Trident, whence 

the magma presumably diked its way toward surface, ultimately through the Naknek Formation (Jn). Chamber would have been 

larger to extent that additional magma failed to erupt. Depth of reservoir is constrained loosely by experimental work (fig. 157) but is 

represented arbitrarily at an upper-crustal discontinuity and beneath but (for clarity) clear of the caldera-collapse models. The 0.7 km3

of magma that erupted at Southwest Trident (Tsw) in 1953–74 is shown stored as a circular sill 100 m thick; as a vertical dike, it would 

presumably have had an aspect ratio even thinner.
Chapter 13. 1912 Magma Compositions and Preeruptive Storage 213

For more than 140 k.y., Trident has produced andesites 

and dacites that are clearly distinguished chemically from 

those of Novarupta, and our extensive fieldwork has turned 

up no record that its magmas ever evolved as far as rhyodacite or rhyolite. Moreover, except for Southwest Trident, all 

component cones and domes of Trident appear to be older than 

44±12 ka (Hildreth and others, 2003a, b). The magmas that 

built Southwest Trident in 1953–74 are compositionally closer 

to the Novarupta andesite-dacite array than any previous 

products of Trident, but they appear to represent independent 

andesite and dacite batches uncontaminated by leftovers from 

the 1912 reservoir (Coombs and others, 2000; Hildreth and 

Fierstein, 2000). The small but significant differences in K, 

Fe, and Sr and—despite proximity to Novarupta—the lack of 

quartz xenocrysts or chemical evidence for rhyolite contamination of the 1953–74 magmas appear to exclude participation 

of any Trident precursors in 1912. 

East Mageik (the Holocene component of Mount Mageik) 

is actually closer to the 1912 vent than is Mount Katmai, but it 

has not erupted historically and its dozen Holocene lava flows 

are limited to the range 60–64 percent SiO2 (Hildreth and others, 2000a). Rich in plagioclase and pyroxenes, some of its 

lavas are compositionally so similar to the 1912 andesites and 

dacites that it would not be radical to entertain a 1912 scenario 

that involved magma stored beneath East Mageik. There is 

no evidence, however, for eruption or structural disturbance 

of Mount Mageik, in 1912 or subsequently. And many other 

Holocene dacites of Mount Mageik are richer in K, Fe, and Zr 

than the 1912 dacites (Hildreth and Fierstein, 2000).

Southwest Katmai is most plausible of the clustered 

centers to have had some or all of the 1912 magma stored 

beneath it before the off-axis eruption took place at Novarupta. Katmai caldera collapsed during the sequence of 

plinian eruptions at Novarupta, and the only postclimactic 

extrusions were at Novarupta and on the Katmai caldera floor. 

Of the entire Katmai cluster, only Southwest Katmai had 

previously erupted rhyodacite and rhyolite, and nearly all of 

its younger products have been dacite or rhyodacite (63–72% 

SiO2). Although they are not identical, the 1912 andesitedacite suite is compositionally closer to many products of 

Southwest Katmai than to those of any of the other centers 

(Hildreth and Fierstein, 2000). 

A model envisaging storage of all the 1912 magma 

beneath Southwest Katmai needs, however, to account for the 

following observations: (1) The 5.0–5.5-km3

 caldera compensates for no more than 40–45 percent of the 13.5 km3

 of 

magma erupted. (2) The complex 60-hour eruptive sequence 

issued from a new vent that broke out through flat-lying 

Mesozoic sedimentary rocks at the foot of West Trident, 10 km 

from Mount Katmai. (3) No magma erupted at Mount Katmai 

in 1912 until the Horseshoe Island dacitic lava dome was 

emplaced on the caldera floor sometime following collapse of 

the edifice. (4) Although rhyolite dominated the 1912 eruption, only one true rhyolite (72.1% SiO2

; 22.5 ka) is exposed 

at Mount Katmai, and no rhyolitic lithics are recognized 

among the basaltic-to-rhyodacitic lithic ejecta thrown out by 

hydrothermal explosions during the caldera collapse (Hildreth and Fierstein, 1992). (5) Compositions of the numerous 

Katmai rhyodacite lavas do not exhibit the influence of zircon 

fractionation so conspicuous for the 1912 rhyolite array; only 

the voluminous 22.8-ka rhyolitic plinian pumice fall and 

ignimbrite (LPFI; 71–72.3% SiO2

) from Mount Katmai does 

show such zircon control (Hildreth and Fierstein, 2000). If 

the distinction principally reflects the influence of enhanced 

magmatic water content in promoting both zircon fractionation 

(by lowering viscosity) and plinian eruption, then it would not 

be implausible that the LPFI and 1912 rhyolite magmas were 

produced at different times in the same evolving reservoir. 

(6) Novarupta dome rhyolite is locally contaminated with 

streaks and blobs of contemporaneous andesite and dacite. If 

comparably commingled rhyolite were visible in Horseshoe 

Island dacite (66.4% SiO2), Fenner (the only geologist who 

ever laid hands on it) would probably have noticed it, because 

magmatic assimilation was one of his foremost preoccupations (Fenner, 1923, 1926, 1930, 1950; Wright, 1952). Unless 

Fenner missed it, withdrawal of the (more buoyant) rhyolite 

layer must have been effectively complete from the part of the 

Katmai reservoir that later leaked dacite to the caldera floor. 

Nonetheless, analogously, postclimactic blocks of the ephemeral Phantom dome strewn around Novarupta basin are also 

dacite (62.2 to 66.7% SiO2) that is not visibly contaminated 

by the rhyolite that earlier and later issued from the same vent. 

The evidence from Fenner’s hurried 1923 visit to the Horseshoe Island dome thus remains tantalizingly inconclusive.

No Preeruptive Magma Storage Beneath 

Novarupta

In addition to the rapid decline of magmatic gas contributions and temperatures of fumaroles in Novarupta basin, 

several other lines of evidence support the inference that the 

1912 magma reservoir did not directly underlie the vent at 

Novarupta. Falling Mountain dome adjacent to the 1912 

vent (fig. 96) is not as young as previously thought; it yields 

a K–Ar age of 70±8 ka and consists of dacite compositionally 

similar to West Trident, thus providing no support for recent 

magma storage beneath the Novarupta depression. Lithic 

ejecta from Novarupta are limited to lithologies exposed at 

the surface, suggesting a shallowly flaring vent funnel (as 

elaborated in chapter 7) rather than subsidence into a subjacent chamber. Moreover, the 1912 vent region underwent 

no structural resurgence, visible uplift, or eruptive activity of 

any kind after the Novarupta lava dome plugged the Episode 

III conduit. Although the asymmetrical ejecta ring surrounding Novarupta is cut by numerous extensional faults (figs. 70, 

97), they reflect spreading of the 225-m-high pile in response 

to compaction and welding, as described in chapter 7, above. 

Because the pumice-fall layers are locally downfaulted several 

meters but nowhere uplifted relative to continuously exposed 

unfaulted parts of the ring, the faulting provides no evidence 

for postclimactic, areally distributed, magma pressure beneath 
214 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

the 1912 vent depression. Causing no significant deformation 

of the basin floor, the Phantom and Novarupta lava domes 

simply squeezed up the same conduit to the same restricted 

point-source vent that had earlier fed the ejecta ring and plinian Layers C through G (fig. 96).

Data Bearing Upon Models of the 1912 Plumbing 

System 

The 1912 ejecta themselves provide several constraints 

for envisaging a model of the 1912 plumbing system. The 

~13 km3 of magma released in 1912 consisted of ~4.5 km3 

of dacite and ~1 km3 of andesite (both having 25–42 weight 

percent phenocrysts) and 7–8 km3 of crystal-poor high-silica 

rhyolite (with only 0.5–3 weight percent phenocrysts) (fig. 

147). Homogeneous pumice with 68.7–77.0 percent SiO2 

has not been found, so a broad compositional gap separates 

the slightly zoned rhyolite from the strongly and continuously zoned andesite-dacite (fig. 148). The only rhyodacites 

(68–72% SiO2) identified in the whole region are some of the 

youngest eruptive products at Mount Katmai, but such compositions are absent in the 1912 suite.

In spite of the gap in bulk composition, Fe-Ti-oxide 

geothermometry demonstrates continuity in both magma 

temperature and oxygen fugacity (Hildreth, 1983) between 

the nearly aphyric rhyolite (800oC–857 ̊C) and the extensively 

crystallized dacite (848oC–950oC)-to-andesite (952oC–990 ̊C) 

continuum. Thermal and redox continuity suggests physical 

contiguity, supporting the inference that the andesite-dacite 

magma was the proximate heat source that kept the rhyolite 

nearly aphyric. The phenocryst-rich intermediate magma may 

have graded down into a mushy cumulate substrate that served 

not only as thermal buffer but, by compaction and upward 

percolation of its evolved interstitial melt, as a contributor of 

rhyolitic liquid (see Bacon and Druitt, 1988; Philpotts and others, 1998; Sisson and Bacon, 1999). 

About 3 km3 of rhyolite magma erupted before being 

joined by any coerupting andesite and dacite (figs. 34, 60), 

indicating that the conduit that fed the Novarupta vent tapped 

the rhyolitic part of the reservoir first. It took 3–4 hours 

before the first andesite-dacite arrived at the vent, as recorded 

by Layer B1.

Despite fluctuations and pulses in the proportions of 

andesite and dacite that coerupted during each of the subsequent episodes (fig. 60), no compositional or textural evidence 

has been found for more than one batch of (continuously 

zoned) intermediate magma. Ranges in phenocryst zoning 

overlap extensively for the andesites and dacites (Hildreth, 

1983; Avery, 1992) irrespective of position in the eruptive 

sequence, supporting collinearity of bulk compositions (figs. 

59, 148, 151) as evidence that all the andesite and dacite are 

comagmatic. One might be tempted to speculate (1) that some 

or all of the andesite could have represented a new batch that 

had just arrived from depth and “triggered” the 1912 outburst 

or (2) that the andesite and dacite magmas came from separate 

chambers, but neither idea is easy to reconcile with the bulk 

compositional and thermal continuity of the andesite-dacite 

suite nor with the modal and compositional overlap of their 

abundant phenocrysts. Fluctuations in the proportions of 

andesite and dacite that erupted together are more likely to 

reflect the dynamics of magma withdrawal from a single unitary chamber (Spera and others, 1986; Blake and Ivey, 1986) 

and of transport in a complex conduit system (Carrigan and 

others, 1992) rather than confluence from separate chambers. 

The unusually long horizontal component of 1912 magma 

transport may be implicated in producing the complicated 

plumbing that favored andesite-dacite fluctuations and permitted those magmas to bypass the small fraction (<0.1 percent) 

of the rhyolite that was detained and contaminated somewhere 

along the distal conduit system and left to extrude postclimactically as the terminal lava dome.

If two or more chambers had contributed to the 1912 

eruption, it might be expected that lithic fragments of breached 

wall-rock septa between them (Curtis, 1968; Hildreth, 1983) 

would appear among the ejecta, but neither hornfelsed siltstone nor alternative candidates have been recognized. The 

suite of nonjuvenile lithic fragments in 1912 ignimbrite and 

fallout layers (Hildreth, 1987) is derived predominantly from 

the Jurassic marine sedimentary Naknek Formation, which 

extends from the surface to a depth of about 1,500 m (fig. 96). 

Sparse fragments of Falling Mountain dacites and Trident 

andesites, both truncated by the 1912 vent, are also present, 

but no lithics from the roughly 3,500 m of Mesozoic strata that 

regionally underlie the subhorizontal Naknek Formation (Detterman and others, 1996) have been recognized.

Sparsity of rhyolitic pumice blocks and lapilli in Layers 

G, F, D, and all but the lowermost part of C suggests that, after 

dominating Episode I, the rhyolite magma was either largely 

exhausted or was excluded from access to the conduit by the 

flux of dacite. Complete withdrawal of the rhyolite layer from 

the magma chamber is consistent with postcaldera eruption 

of the Horseshoe Island dacite on the Katmai caldera floor. 

Pulses of andesite magma, on the other hand, were able to gain 

sporadic access to the Novarupta vent until virtually the end of 

the eruption, leading to ultraproximal emplacement of numerous andesite-dacite pyroclastic fall and flow deposits (Fierstein 

and others, 1997; Houghton and others, 2004) intercalated 

within the voluminous sequence of dacite-dominated regional 

plinian fall deposits (Layers C, D, F, and G).

Compositionally banded pumice (fig. 61) was common 

throughout the 1912 eruptive sequence following deposition of 

all-rhyolitic Layer A. In total, such banded pumice makes up 

3–5 percent of the trillions of pumice lumps deposited, but its 

fraction fluctuated greatly during the 60-hour eruption, ranging erratically from 0 to 37 percent in the numerous subunits 

emplaced (Fierstein and Hildreth, 1992). Banded pumice is 

especially abundant in Layer B2 and in the middle part of the 

main VTTS-filling ignimbrite sequence, in both of which it 

consists principally of mingled rhyolite and andesite. Banded 

pumice is also abundant in ignimbrite Packages 8 and 9 that 

ended Episode I and in the thin proximal PDC and scoria-fall 
Chapter 13. 1912 Magma Compositions and Preeruptive Storage 215

units of Episodes II and III, but in these units the mingling 

is between andesite and dacite. The mingling combinations 

generally reflect proportions of the magmas coerupting, so the 

only unit where rhyolite-dacite banded pumice is common is 

Package 7, which is andesite-poor (figs. 27, 34). The extreme 

sparsity of rhyolite-dacite banded pumice elsewhere during 

Episode I, when all three magmas coerupted for many hours, 

may tell less about the plumbing system than about the physical difficulty of mingling between the high-silica rhyolite and 

crystal-rich dacite on a syneruptive timescale. The lower viscosity of the hotter andesite may have been the key to unstable 

conduit flow promoting entrainment of its highly viscous 

companion magmas.

The compositional ranges of plagioclase and orthopyroxene in the rhyolite are outside the corresponding (wide) ranges 

of zoning in the dacite and andesite (fig. 12 of Hildreth, 1983). 

Neither these nor the quartz phenocrysts present in 1912 rhyolite occur in noncontaminated 1912 dacite or andesite. The ZrSiO2 relations (fig. 151) also illustrate clearly that 1912 dacite 

is closely related to the coerupted andesite and is not a hybrid 

mixture of rhyolite and andesite (though a few dacite samples 

may contain traces of rhyolite contaminant). Microprobe 

analyses generally distinguish matrix glass compositions of 

1912 rhyolite, dacite, and andesite (Avery, 1992; Fierstein and 

Hildreth, 1992), but the dacite and rhyolite glass arrays are 

continuous and overlap slightly (fig. 149). 

Plagioclase and orthopyroxene phenocrysts are broadly 

similar in the andesite and dacite, each exhibiting comparably 

broad, overlapping ranges of zoning, with normal and reverse 

zoning coexisting within individual scoria and pumice blocks 

(Hildreth, 1983; Shearer and others, 1991; Avery, 1992). Zoning ranges of feldspar and pyroxenes in the dacite extend to 

only slightly more evolved compositions than in the andesite 

(Hildreth, 1983). The shared complexity suggests intimate 

preeruptive association of the andesite and dacite and some 

mixing of their phenocrysts. We envisage such heterogeneities 

to result from limited convective stirring within a graded or 

layered body of crystal-rich magma, differentiating by upward 

percolative loss of interstitial melt and perhaps disturbed on 

a century or decadal timescale by injection of new andesitic 

batches from below.

In contrast to the extensive and complex zoning of phenocrysts in the andesite and dacite, the oligoclase and orthopyroxene phenocrysts in the rhyolite are almost unzoned. Unlike 

the rounded quartz in many pyroclastic rhyolites worldwide, 

quartz in the 1912 rhyolite consists of dipyramidal euhedra. 

These features and its nearly aphyric condition (0.5–3 weight 

percent phenocrysts) suggest that the rhyolite had undergone 

little cooling and had experienced a simple and probably short 

history since separating from a crystal-rich residue (or, alternatively, after some strong reheating encounter had resorbed all 

previous phenocrysts). Once separated, the greater buoyancy 

and viscosity of the rhyolite may have suppressed stirring at 

the interface and entrainment of phenocrysts from the crystalrich residue (plausibly the underlying dacite magma, as 

discussed below). Such apparently sharp interfaces between 

density-stratified magmatic layers in reservoirs that fed large, 

strongly zoned eruptions have been discussed by Fridrich and 

Mahood (1987), Bacon and Druitt (1988), and Johnson and 

Fridrich (1990).

We don’t know what fraction of the magma stored in the 

1912 reservoir actually erupted, but the 13 km3 of magma that 

did erupt (if initially all stored jointly) could have been held 

in a spherical chamber about 3 km in diameter. Alternatively, 

a squat cylindrical 13-km3 chamber with height and diameter 

both 2.55 km would underlie an area only slightly larger than 

that of the Katmai caldera floor. Because the magma volume 

erupted was about 2.3 times greater than the volume collapsed, however, it is more likely that the magma reservoir 

was irregular, perhaps with an elongate protrusion extending 

from beneath the caldera some unknown distance toward 

Novarupta or Trident (fig. 158). This might have eventually 

advanced into a dike or sill along joints or bedding planes in 

the horizontal Mesozoic sedimentary section. A sill extending 

to Novarupta from a chamber beneath Mount Katmai (if 10 

km long and 1 km in cross width) would at rest contain only 

0.1 km3 of magma if 10 m thick (or 1 km3 if 100 m thick). 

During propagation of such a sheet, most of the magma 

would clearly remain in the main reservoir until the eruption was underway (fig. 158). But a sheet of rhyolite magma 

should have cooled and crystallized significantly during an 

advance of 10 km through cold sedimentary wall rocks unless 

its propagation was rapid.

Dissolved H2O concentrations measured for rhyolitic 

melt inclusions trapped in 1912 quartz phenocrysts range 

from 3.5 to 4.7 weight percent, averaging about 4.3 weight 

percent (Westrich and others, 1991; Lowenstern, 1993; Wallace, 2005). Such values pertain to rhyolite samples from 

Layer A, early all-rhyolite ignimbrite, later mixed ignimbrite, 

and the plug dome, suggesting a limited range in preeruptive 

rhyolitic water content comparable to the rhyolite’s limited 

ranges in major and trace elements. The very few FTIR 

measurements of H2O dissolved in melt inclusions in 1912 

dacite are in the range 2.2 to 3.1 weight percent, all three 

determinations having been for plagioclase phenocrysts from 

a single lump of plinian Layer C pumice. No reliable values 

have been measured for 1912 andesite, in which the melt 

inclusions have generally broken, leaked, or partially crystallized (Lowenstern, 1993). Evidence of Cu-rich bubbles in 

melt inclusions and of progressive partitioning of S, Cu, and 

Cl into a preeruptive vapor phase during magmatic evolution 

suggests fluid saturation of all 1912 magma prior to the eruption (Lowenstern, 1993). Because 4.3 weight percent H2

O 

is sufficient for water saturation of rhyolite melt at 100–130 

MPa, saturation thus implies a reservoir depth of 3–5 km. 

Embracing the analytical uncertainties and allowing for small 

contributions of CO2 and SO2 in the aqueous fluid phase 

(Wallace, 2005), these estimates could be expanded to about 

80–150 MPa or 3–6 km depth (for rhyolite, dacite, and andesite alike), in acceptable agreement with the phase-equilbrium 

experiments (fig. 157) recounted above (Coombs and Gardner, 2001; Hammer and others, 2002). 
216 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

There is little doubt that 1912 andesite and dacite were 

part of a continuously zoned magma body that underlay 

Mount Katmai. Large fluctuations in the andesite/dacite 

proportions that erupted during the 60-hour sequence (figs. 

34, 60) may have been governed by their viscosity contrast, 

by viscous segregation during 10 km of subterranean sheet 

flow, and by convective dynamics of withdrawal from the 

main reservoir. Although we clearly favor the model of a 

zoned reservoir where the rhyolite overlay the andesite-dacite 

continuum, preeruptive location of the rhyolite is less firmly 

established. Favoring contiguity and petrogenetic kinship 

are thermal continuity, Sr-Nd-Pb-O isotopic overlap, concurrent eruption throughout Phase B and part of C (altogether for 

>24 hours), and phase-equilibrium experiments permissive 

of preeruptive storage at similar depth. Because of the wide 

bulk-compositional gap and differences in short-lived isotope 

ratios, (230Th/232Th) and (226Ra/230Th), however, it may be useful to summarize and again scrutinize the varied evidence for 

origin of the rhyolite.

Origin of the Rhyolite Magma

We discuss here the evidence bearing upon the preeruptive site of the 7–8 km3

 of rhyolite magma released in 1912, 

how it may or may not have been intimately situated along 

with the andesite-dacite continuum, and when and by what 

processes it may have been generated. It seems to be generally underappreciated that high-silica rhyolite (75–78% SiO2

), 

although common enough intracontinentally, is uncommon in 

island arcs and continental margin arcs. No other late Quaternary example has been reported on the Alaska Peninsula, 

and we know of only three older remnants there. For most arc 

volcanoes, the most evolved product is dacite (63–68% SiO2) 

or rhyodacite (68–72% SiO2). Therefore, generation of highsilica rhyolite must entail materials or processes that are otherwise seldom involved or effective in arc magma evolution. 

Possibilities to consider include partial remelting of silicic 

plutonic rocks, expulsion of highly evolved interstitial liquid 

from crystal-rich dacitic mush in a chamber (or a migmatitized 

domain at any crustal depth), buoyant ascent of such liquid 

from crystallizing rinds at chamber sidewalls, or protracted 

settling of a phenocryst suite rich in low-silica phases. In each 

case, efficient isolation of high-silica rhyolitic melt from abundant complementary crystals and suppression of convective 

reentrainment would be critical to the process. Considerable 

time might be required to purge a viscous partial-melt extract 

of its restite or antecrysts.

Isotopic and chemical affinities of the 7–8 km3

 of highsilica rhyolite to the coerupted dacite and andesite were 

outlined above. The rhyolite and the intermediate magmas 

appear all to have assimilated melt from wall rocks that had 

only modest Sr-isotopic contrast and minimal Pb, Nd, and 

O isotopic effects. Oxygen-isotope data for 1912 ejecta 

suggest a normal magmatic fractional-crystallization progression with no detectable contribution from sedimentary 

or hydrothermally altered rocks (Hildreth, 1987). Likewise, 

for both matrix glass and whole-rock samples, parallelism 

of rare-earth patterns, with increasing REE abundance (and 

Eu deficiency) from andesite to dacite to rhyolite (fig. 153) 

suggests a simple fractionation sequence with no extraneous 

contribution to the rhyolite large enough to be chemically 

identifiable. Very low concentrations of Ni and Cr, each as 

low as 0–3 ppm, in the nearly aphyric rhyolite demand that 

crystal-melt fractionation have continued subsequent to any 

contributions of extraneous partial melt. Although the Srisotope data indicate small wall-rock contributions to all the 

1912 magmas, the combined Nd, Sr, and O isotope results 

show unequivocally that the rhyolite magma was not substantially a partial melt of the Mesozoic and older stratified rocks 

constituting the Alaska Peninsula basement. The Jurassic 

sandstone and siltstone of the exposed Naknek Formation is 

not a geochemically viable assimilant, even had the magma 

been stored that shallowly. Taken altogether, the isotope data 

favor fresh arc-intrusive rocks as the most likely source of 

minor partial-melt contributions.

Sr-isotope ratios for the 1912 rhyolite (0.70368–0.70374) 

are slightly more radiogenic than for coerupted dacite 

(0.70354–0.70362), but they are wholly overlapped by those 

for andesite (0.70338–0.70374). The modest Sr content of the 

rhyolite (58–95 ppm) rendered it sensitive enough to contamination that derivation of only 5–7 percent of its Sr from a 

source like the Tertiary rhyolite sills exposed nearby (0.7043; 

235 ppm Sr; fig. 155; Lowenstern and Mahood, 1991) would 

suffice to produce a shift of 0.0001 in 87Sr/86Sr. Because 1912 

dacite matrix glass also has low Sr contents (80–101 ppm) like 

the bulk rhyolite, comparably modest proportions of assimilated Sr would have been required had the contamination process operated on the rhyolitic interstitial melt phase of a dacite 

mush before its expulsion to form the proximate progenitor of 

the crystal-poor 1912 rhyolite.

Because the andesite-dacite continuum likewise spanned 

a significant range (0.00036) in 87Sr/86Sr, the intermediate 

magma had apparently also been affected by assimilation 

comparable to that evident in the rhyolite. Less assimilant 

is thus required to go from 1912 dacite to 1912 rhyolite than 

to produce the Sr-isotopic range within the andesite-dacite 

continuum (fig. 155). The isotopic coherence of the entire 

1912 suite, in O, Nd, and Sr, makes it doubtful that the rhyolite could be predominantly a partial melt of any extraneous 

source rock.

The glass (melt) phase interstitial to the crystal-rich 1912 

dacite is itself high-silica rhyolite only slightly less evolved 

than the nearly aphyric 1912 rhyolite (as determined by 

microprobe). For example, the average dacite-glass versus 

bulk-rhyolite compositions (normalized volatile-free) compare 

as follows (all figures in percent): 1.1 vs 0.9 CaO; 0.25 vs 0.15 

MgO; 0.27 vs 0.15 TiO2

; 1.6 vs 1.3 Fe2O3; 2.9 vs 3.2 K2O; 

and 77.6 vs 78.2 SiO2. In fact, the ranges overlap for most elements (fig. 149). If most of the melt constituting the rhyolite 

had once been interstitial liquid that escaped upward from a 

compacting (and gas-saturated) volume of intermediate 
Chapter 13. 1912 Magma Compositions and Preeruptive Storage 217

crystal mush, such modest compositional differences could 

have resulted from (1) limited subsequent crystal fractionation 

of the rhyolite, (2) additions of small wall-rock partial-melt 

increments to both, as inferred from the Sr-isotope data, (3) 

internal crystal-liquid reequilibration of the melt-depleted 

dacite mush, and (4) contamination of the dacite mush by melt 

and crystals from the contiguous andesite. Note that glass in 

the dacite pumice would represent, by such a mechanism, the 

melt phase left behind in the dacite mush after escape of the 

melt fraction that became the rhyolite.

Whatever proportion originated by upward escape of 

interstitial melt from crystal mush (whether or not augmented 

by sidewall ascent of fractionating liquid), and irrespective of 

the fraction contributed by wall-rock partial melting, the 1912 

rhyolite was chemically and isotopically closely related to the 

zoned crystal-rich dacite magma that erupted behind it (figs. 

149, 152–155). Thermally continuous and virtually continuous in melt composition, they were probably physically 

contiguous as well. Rare quartz phenocrysts found in mineral 

separates from two dacite samples, the most silicic dacites 

crushed (Hammer and others, 2002), might be cognate but are 

more likely to be contaminants, transferred syneruptively or 

across an intrachamber interface.

As for the phenocryst-poor rhyolite and the 69–77 percent SiO2

 compositional gap, discontinuities in composition 

and mineralogy are common in caldera-forming pyroclastic 

eruptions large and small (Hildreth, 1981). They have been 

explained in terms of density-stratified layered chambers that 

accumulated incrementally and differentiated internally (Fridrich and Mahood, 1987; Bacon and Druitt, 1988; Johnson and 

Fridrich, 1990). Derivation of rhyolitic melt from a crystalrich intermediate parent magma was modelled by Grove and 

Donnelly-Nolan (1986) in terms of extensive low-pressure 

crystallization over a small cooling interval—rapid multiphase crystallization along a gently sloping cotectic having 

shallow thermal curvature in temperature-composition space. 

Maintaining a compositional gap so established would require 

efficient expulsion of interstitial rhyolitic melt and subsequent 

isolation from its intermediate parent, which would then be 

left behind as a mushy quasi-cumulate. Mechanisms for incremental upward separation of buoyant residual liquid, when 

successively intercepted new magma batches crystallize within 

or atop cumulate zones, were proposed by Bacon and Druitt 

(1988), Grove and others (1997), Philpotts and others (1998), 

and Sisson and Bacon (1999). Vesiculation caused by rapid 

crystallization of lenses of andesite-dacite recharge magma 

could repeatedly hasten upward segregation of gas-saturated 

residual liquid, thereby intermittently augmenting the overlying zone of thermally buffered, water-saturated, phenocrystpoor rhyolite. Minor assimilation of partial melt from wall 

rocks need induce little or no crystallization of such doubly 

buffered rhyolite; moreover, the Sr-isotope data suggest that 

most assimilation took place before the rhyolite separated 

from the intermediate mush. We are persuaded that such a 

model fits best the 1912 reservoir because of the isotopic and 

chemical affinities among all the 1912 ejecta, their continuity 

in magmatic temperature and oxygen fugacity, and the need 

for a huge proximate residue of hot crystal mush from which 

to have extracted (and maintained aphyric) at least 8 km3

 of 

high-silica rhyolite.

It was previously suggested that the magmatic focussing 

implicit in the unusual clustering of several stratovolcanoes 

might somehow be implicated in generating the unusual 

high-silica rhyolite at Katmai (Hildreth, 1983, 1987). Among 

the centers here, however, we now know that only Southwest 

Katmai has produced magma more evolved than dacite, that 

Northeast Katmai and the Trident cones and domes have long 

been dead, and that comparable Quaternary clusters and calderas along the Alaska Peninsula (Miller and others, 1998) lack 

high-silica rhyolite. Mount Katmai is the only center in the 

cluster where basalt has ascended to eruptible levels, thereby 

investing crustal melting with a heat source significantly 

intensified relative to the flux of crystal-rich andesite typical 

of the other centers. If thermal “focussing” was indeed a factor in producing the rhyolite, the focus is better thought of as 

beneath Mount Katmai rather than the cluster as a whole.

Alternatives to a Zoned Reservoir? 

Although our earliest data already favored a zoned 

chamber, the two-chamber idea of Curtis (1968) was initially 

left open as a possible alternative (Hildreth, 1983, p. 49-50). 

Subsequently it was stated (Hildreth, 1987) that “for every 

complexly zoned eruption, it needs to be asked afresh whether 

the syneruptively mingled compositions reflected (1) addition 

of a new batch of relatively primitive magma from depth, (2) 

a single zoned or layered chamber, or (3) mixing of magmas 

from two or more discrete pods, dikes, or sills in a complex 

reservoir. Although the continuity in Fe-Ti-oxide temperatures 

argues in favor of the second scenario for 1912 (Hildreth, 

1983), the existing data do not really permit one to exclude a 

chance encounter of the third kind (Curtis, 1968).” 

Two Chambers?

By 1987, the rapid thermal decline of the 1912 vent 

region had raised doubts that any chamber had ever underlain Novarupta basin, and new work led to the suggestion 

that structural trends parallel to the local direction of plate 

convergence might have permitted lateral magma transport 

from a reservoir beneath Trident (Hildreth, 1987; Wallmann 

and others, 1990). Having by now established, however, that 

Falling Mountain and Mount Cerberus are older than 60 ka 

and compositionally related to Trident (not to Novarupta), that 

the three cones of Trident existing in 1912 had long been dead 

(since at least 40 ka), and that magmatic precursors of Southwest Trident were not involved in 1912, there is no longer any 

basis for supposing that any 1912 magma had been resident 

under Trident, either. This does not, of course, preclude a 

transport path of 1912 magma from Mount Katmai to Novarupta beneath long-crystallized parts of the Trident complex. 
218 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Sill transport from Katmai to Trident, thence dike transport 

toward Novarupta (parallel to the plate-motion vector and to 

vertical jointing in the Naknek Formation) is not unreasonable 

(Hildreth, 1987; Wallmann and others, 1990).

A New Magma Batch from Depth?

As for the possibility of introducing a new magma batch 

not already part of the zoned system, a newly arrived “triggering” batch of andesite might be expected to be conspicuous 

among the ejecta evacuated from a reservoir of this (intermediate) size. Despite persistent search and many analyses, 

however, no mafic or intermediate 1912 ejecta have been 

found that do not belong chemically and mineralogically to 

the very phenocryst-rich andesite-dacite zoned continuum. 

No phenocryst-poor or decidedly more primitive mafic ejecta 

have been identified. (The five andesites more mafic than the 

continuum are comparably crystal-rich, and at least one is 

certainly olivine-accumulative.)

It was speculated by Eichelberger and Izbekov (2000) 

that an aphyric rhyolite dike arose from depth (the middle 

crust?) and “simultaneously” intersected the surface at Novarupta and the andesite-dacite chamber beneath Mount Katmai. 

Such a deus ex machina would need to have approached the 

surface without causing surface deformation anywhere along 

the 10-km-long reach separating the two vents. We can verify 

none of the surface features attributed by those authors to dike 

emplacement between Novarupta and Katmai caldera, where 

the connecting reach is covered by tens of meters of glacial 

ice and 1912 ejecta. Its strike would have been east-west, at a 

high angle to vertical jointing in the basement (330o±20o) and 

to the plate-convergence vector (320o), which closely coincide 

in this area (Hildreth, 1987). It would be extraordinary for a 

dike to propagate 10 km in a direction at 50o–60o to the maximum horizontal stress and to the plane of preferred anisotropy 

in the wall rocks (Wallmann and others, 1990). 

For the rhyolite to be an extraneous intruder, the thermal, 

isotopic, and glass-compositional continuity of the rhyolite 

with the coerupted dacite would have to be purely coincidental. The phase-equilibrium experimental data and meltinclusion volatile evidence indicating shallow storage of 1912 

rhyolite, dacite, and andesite all at similar depths need not, of 

course, require differentiation of the aphyric rhyolite within 

the upper-crustal reservoir where the phase assemblages last 

equilibrated; but if the rhyolite had risen from some deeper 

extraneous source, all restite, phenocrysts, or entrained crystal 

mush would need to have been completely resorbed during 

rapid ascent. 

The Mount Katmai-Trident chain had been magmatically 

active for at least 140,000 years (Hildreth and others, 2003b) 

and had erupted ~80 km3

 of magma that ranged from basalt 

to rhyodacite, predominantly andesite-dacite. It is hard to 

envisage how a deep-crustal processing domain (MASH zone 

of Hildreth and Moorbath, 1988; or hot zone of Annen and 

others, 2006) that had been releasing intermediate magmas for 

so long and so currently could abruptly generate a large batch 

of minimum-melt high-silica rhyolite. Because basalt-induced 

partial melting of amphibole-bearing mafic meta-igneous 

deep-crustal rocks generally yields intermediate melts (Rapp 

and Watson, 1995; Sisson and others, 2005; Annen and others, 

2006), not high-silica rhyolites, the best candidates for nearprimary arc-crustal melts are the uncommon high-temperature 

crystal-poor dacites and rhyodacites. Moreover, a large volume of rhyolite magma from the deep crust would require an 

enormous source domain, raising problems of source-rock heterogeneity, hybridization, and source depletion and dehydration over a span of 140,000 years. If a deep felsic pluton were 

indeed to have been partially remelted, yielding a large batch 

of rhyolitic magma, it is hard to envisage how such a batch 

could run the 20–30 km crustal gauntlet of mushy pods and 

trailings left by the many forerunning basalts and andesites 

without entrainment or mixing. It appears far more feasible to 

separate the high-silica rhyolite in the upper crust.

Roof-Zone Remelting?

Extraction of rhyolitic melt from the underlying andesitedacite reservoir need not have been a one-stage process. During a magmatic history longer than 100,000 years, tonalitic to 

granodioritic plutons could have crystallized in the upper crust 

beneath Mount Katmai. Had the 1912 vapor-saturated andesite-dacite chamber developed within or adjacent to such a late 

Pleistocene pluton, rhyolitic partial melts from it could have 

augmented the rhyolite melt expelled from the dacite mush. 

Difficulties with such a model include the apparent absence of 

inherited zircon or other refractory xenocrysts and the chemical and O-Sr-Nd-Pb isotopic affinities of the 1912 rhyolitic 

and intermediate magmas. Such affinities appear to limit any 

excess pluton-derived partial melt in the rhyolite to a modest 

contribution, as implicit in figure 155. On the other hand, contributions from a Tertiary or early Quaternary arc pluton could 

have high (230Th/232Th) and equilibrium (230Th/238U), consistent 

with the near-equilibrium U-Th data for the 1912 rhyolite (fig. 

156). Or, if the pluton were of late Pleistocene age like most 

of Mount Katmai, its partial melts in the presence of refractory zircon could be expected to shift toward the equiline from 

bulk-rock 238U excesses.

Still closer similarity of partial melts of plutonic wall 

rock and rhyolitic melt extracted from resident dacitic mush 

would result if the “granodiorite” had been a crystalline roof 

zone in the Mount Katmai system itself. Thermal waxing 

and waning during an intrusive and eruptive history longer 

than 100,000 years could have produced broadly dacitic (or 

more silicic) differentiates many times and lodged some 

of them beneath the edifice as substantial bodies, mushy 

or solidified. Partial remelting of such forerunner material 

(Mahood, 1990) during the thermally waxing buildup of the 

1912 andesite-dacite chamber might have generated rhyolite 

melt not unlike that expelled from the dacite itself, reflecting 

essential “consanguinity” within a broadly comagmatic longlived system. If it was ~100,000 years old, 230Th ingrowth 

would have driven such a fossilized zone closer to the 
Chapter 13. 1912 Magma Compositions and Preeruptive Storage 219

230Th/238U equiline, helping to resolve the U-series uncertainties concerning the 1912 rhyolite.

The process of extracting high-silica-rhyolite partial 

melts from quartz-bearing granitoid has the added appeal 

of being consistent with the rarity of such compositions in 

immature arcs and their abundance in continental interiors. Tertiary plutons sampled in the Katmai area (n=22) are 

mostly tonalitic (57–65% SiO2), but a few are more evolved 

(67–71% SiO2). Remelting of intrusive remainders of the 

22.5-ka rhyolitic eruption (71–72% SiO2) of Mount Katmai 

might well have yielded a high-silica melt extract. Nevertheless, the mushy crystal-rich 1912 dacite had done so, too, 

even without participation of quartz, as its interstitial glass 

phase contains 76–79 percent SiO2.

1912 Magma Storage Model 

Figure 158 portrays a preeruptive magma-storage model 

consistent with all the many constraints discussed. The evidence weighs heavily against participation of preexisting Trident magma, and nothing favors more than one magma chamber. The chamber could well have been larger than the 13 km3

erupted and depicted, and it could have been a bit shallower 

than shown, but, if the rhyolite had indeed been water-saturated at 4.0–4.5 weight percent, its roof is not likely to have 

been much deeper. Vertical displacement of Mount Katmai by 

1.2±0.1 km demands that the magma body have been at least 

that thick (in addition to cumulates of unknown but probably 

significant thickness). Compensation by collapse of only 5.5 

km3 for the 13 km3 erupted requires that the reservoir have 

been areally more extensive than the caldera. Magma chambers considerably more extensive than superjacent calderas 

would appear to be a common pattern, considering the areal 

spectra of batholiths and calderas (Lipman, 1984). A simple 

model for 1912 would be a storage zone elongate along the 

volcanic axis, above the axial zone long subject to distributed 

magma ascent from deep below. Elongation of the chamber 

along axis lessens the distance required for sill propagation 

toward Trident or Novarupta. 

Sill injection is favored by the shallow overburden and 

by the horizontal bedding planes of the Mesozoic marine 

section (Fenner, 1923; Lowenstern and others, 1991). 

Advance of a horizontal sill from beneath the volcanic chain 

toward the off-axis Novarupta depression lessens the local 

overburden by at least 700 m, not insignificant for magma 

initially only 3–6 km deep; progressive reduction in vertical 

stress would favor sill propagation away from the highland 

edifice. Ultimately, of course, the rhyolitic magma had to 

crosscut strata to reach the 1912 vent site, but the terminal 

dike segment could have been short—breaking away from 

the hypothetical sill either right under lowland Novarupta or 

somewhere beneath Trident where the plate-motion vector, 

inferred regional stress field, and jointing in the basement 

rocks should have favored a north-northwesterly direction 

of dike propagation (Hildreth, 1987; Wallmann and others, 1990). In this setting, dike transport directly east-west 

between Mount Katmai and Novarupta would be unlikely, 

still less so to the extent that outbreak depth influenced vent 

location, because much of that 10-km path runs beneath terrain that was lower in elevation than the 1912 vent site.

It can be inferred that present-day upper crustal seismicity largely reflects response to hydrothermal processes 

and not shallow magma storage. The modest batches of 

andesite-dacite magma typical of the Katmai cluster volcanoes probably ascend from midcrustal reservoirs or deeper, 

from well below the brittle-ductile transition (at a depth of 

~10 km). The only evidence for late Quaternary reservoirs 

sufficiently large, shallow, and sustained to produce rhyolite, 

rhyodacite, large-magnitude eruptions, and caldera collapse 

points exclusively to Mount Katmai. The model depicted 

(fig. 158) is consistent with the volume and displacement 

requirements, compositional integrity of the zonation, and 

eruption of ~3 km3 of unaccompanied rhyolite magma first. 

To the extent that the reservoir was elongate toward Trident, the path required for sill propagation shortens. For the 

rhyolite to have remained phenocryst-poor on departing from 

the reservoir into cold wall rocks, sill injection had to be fast. 

Might it have been accomplished during the five days (1–5 

June 1912) of preeruptive seismicity? Shallow earthquake 

swarms that migrate along rift zones in Iceland and Hawaii 

(from central volcanoes to remote eruption sites) track the 

propagation of basaltic dikes at rates of 0.1 to 6 km per hour 

(Brandsdóttir and Einarsson, 1979; Klein and others, 1987). 

Comparable data are lacking for silicic dikes and sills, but 

even rhyolite might reasonably be expected to propagate the 

10 km to Novarupta in 120 hours (5 days).
220 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Campsite of Geophysical Expedition of 1989 in arcuate graben 1.5 km 

northeast of Novarupta dome. Typically 8–14 participants at a time (and as 

many as 29 altogether) used WeatherPort structures and smaller, backpacking 

tents during 6 weeks of geophysical surveys of the 1912 vent region. West 

Trident Volcano in background, heavily mantled with 1912 fall deposits. Photo 

by John Eichelberger.
Chapter 14

Comparisons with Other Historic Eruptions 

Every great explosive eruption is unique in some 

respects. The Novarupta outbreak was extreme in its compositional range and extraordinary in its separation of vent 

and subsidence sites, but it had much in common with other 

plinian eruptions. Data compiled in table 3 are provided 

to compare aspects of the 1912 eruption with those of several other well-characterized explosive eruptions—larger or 

smaller, mostly historical, some notorious. Many others might 

have been chosen, but the examples tabulated were selected 

for variety and because most of the parameters listed are fairly 

well constrained by data. Significant fractions of ejecta were 

lost at sea for about half the eruptions listed, and several other 

well-characterized island eruptions were ignored because the 

lost fraction is too great.

Of the 24 eruptions listed in table 3, 18 were from arc 

volcanoes, reflecting principally the rarity of explosive intracontinental activity in the Holocene. That four are from Iceland 

is a tribute to the detailed work of Sigurdur Thorarinsson. All 

24 eruptions were plinian except for Pelée, which is included 

here for its historical importance in volcanology; several also 

had phreatomagmatic phases.

Although all the magmas were rich in dissolved volatile components, there is no obvious correlation of plinian 

explosivity with major-element composition, which ranges 

from rhyolite to andesite, and even rarely to basalt or phonolite. The range provides a corrective reminder to those of us 

who have taken for granted the abundance of rhyolites among 

the ignimbrite-forming eruptions of the intracontinental North 

American Tertiary and Quaternary. From arc volcanoes generally, high-silica rhyolites like that of 1912 are uncommon, 

though not rare. The apparent exception, New Zealand (for 

which Taupo is an example in the table), owes its voluminous 

Quaternary rhyolites more to quasi-continental rifting than to 

arc volcanism. 

Many of the examples listed in table 3 produced small 

quantities of ejecta more mafic than the predominant eruptive volume, but only Novarupta, Hekla, and Mazama erupted 

large subordinate fractions of andesite or basalt. Relatively 

mafic enclaves were scattered within the dome lavas of Pelée, 

preclimactic Pinatubo, and postclimactic Novarupta. Among 

the eruptions listed, fairly homogeneous magma batches 

include the trachyandesites of Tambora and El Chichón, 

the andesite of St. Vincent, the dacites of Santa María and 

Huaynaputina-I, and the rhyolites of Öraefajökull and Taupo. 

Although they were parts of zoned eruptive sequences, the 

~40 km3

 of climactic Mazama rhyodacite (~70.5% SiO2), 

the 8 km3 of Novarupta rhyolite (~77.5% SiO2), and the 5.5 

km3 of climactic Pinatubo dacite (~64.5% SiO2) were fairly 

homogeneous.

Caldera subsidence attended all the eruptions listed 

that released more than 10 km3

 of magma. Somewhat less 

voluminous eruptions at Krakatau (9 km3), Pinatubo (5.5 km3), 

and Apoyo (4–5 km3) also produced calderas, but comparably voluminous eruptions at Huaynaputina (9 km3

), Santa 

María (4–8 km3), Quizapu (4 km3), and Vesuvius (4 km3) did 

not. Initiation of subsidence of the 2-km3 Öskjuvatn caldera 

in 1875 is attributed to withdrawal of basaltic magma along 

the rift zone and its eruption 70 km north of Askja, not to the 

0.34-km3 plinian rhyolite eruption at what became the caldera 

site (Sigurdsson and Sparks, 1981). Despite differences in 

volume and composition, the withdrawal and collapse at Askja 

in 1875 are hydraulically the closest analogue we know of for 

the Katmai-Novarupta connection of 1912.

The climactic episodes of most of these plinian eruptions 

lasted less than a day, and even some of the largest historical events may have lasted little more than two days. At the 

extreme, we think the great Bishop Tuff eruption lasted less 

than six days, based on an uninterrupted plinian pumice fall 

(of varying intensity) and accumulation rates calculated for the 

comparably dispersed ejecta of well-studied historical plinian 

deposits (Wilson and Hildreth, 1997; Hildreth and Wilson, 

2007). Several of the eruptions listed in table 3, however, 

consisted of more than one plinian episode, separated by lulls 

of hours or days, including Tambora, El Chichón, Taupo, and 

Novarupta. The 1912 sequence at Novarupta spanned 60 

hours because it actually consisted of three successive plinian 

episodes with multihour lulls between. 

Many great eruptions commence with a vent-opening 

outburst, commonly phreatomagmatic, that deposits a small 

volume of initial ash. The lack of evidence for such a deposit 

at Novarupta is anomalous and might simply mean that it was 

scoured from the region around the vent by the blast-like allrhyolite pyroclastic density currents that accompanied initiation of the main plinian Episode I.

In all or most of the prehistoric, enormous (100–1,000 

km3

), caldera-forming, intracontinental ignimbrite eruptions, 

the volume of ignimbrite exceeds that of its companion fallout, 

more so where intracaldera tuff can be taken into account. 
222 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Table 3. Comparison of some explosive eruptions.

 [For the nine eruptions below the line, there is little or no historical record, so the data are based principally on geological investigations. Composition abbreviations: A, andesite; B, basalt; C, comendite; D, dacite; Ph, phonolite; R, rhyolite; Rd, rhyodacite; Tp, tephriphonolite; Ta, trachyandesite; Tr, trachyte. Duration of eruption climactic episode includes neither precursors nor sporadic postclimactic activity; lulls of hours to days between plinian episodes are inferred for 

Novarupta, El Chichón, Tambora, and Kuwae. Pyroclastic density currents (pdc) include flows, surges, and coignimbrite ashfall (as identified in each report); 

fall (F) is fallout from column and umbrella cloud, mostly plinian.]

Eruption and year/age Magma km3 Composition Duration 

hours Syneruptive deaths Fall vs pdc Referencesa

Novarupta 1912 13.5 R>D>A <60 1 F~pdc 8, 9, 15

St. Helens 18 May 1980 0.3 D 9 57 F>pdc 7, 19

Pinatubo 1991 5.5 D>>A>B 9 350 pdc>F 21

El Chichón 1982 0.5 Ta ~155 >1800 F>pdc 29, 35

Quizapu 1932 4 Rd>A 18 0 F>>>pdc 14

Santa María 1902 4–8 D 20 >1500 F 9, 10, 37

St. Vincent 1902 0.8 A 10 >1600 F>pdc 13

Pelée 8 May1902 <0.2 A>D <1 28,000 pdc>F 11, 12

Tarawera 1886 0.8 B 4 153 F 3, 36

Krakatau 1883 9 D 23–30 36,400 pdc~F 25, 30

Askja 1875 0.34 R>>A>B 17 0 F>>pdc 4, 20, 31, 32

Tambora 1815 33 Ta ~24 >10,000 F>pdc 24, 26, 27

Huaynaputina-I 1600 9 D 20 ~1400 F>pdc 1

Öraefajökull 1362 2 Rd ? >220 F>pdc 34

Vesuvius 79 4 Tp>Ph 19 >3,500 F>pdc 5, 6, 28

Kuwae ~1452 >35 D>>A~B ? many pdc>F 23, 40

Baitoushan ~969 ~25 C>Tr ? many F>pdc 17

Taupo 232 35 R 24–48 0 pdc>F 39

Apoyo-A 2.3 ka 4–5 D ? ? F~pdc 33

Hekla H3 2.9 ka 2.2 R>D~A ? 0 F 18

Minoan 3.5 ka 28 D>A 24–48 many pdc>F 22

Hekla H4 4.5 ka ~2 R>D>A 24–30 0 F 18

Mazama 7.7 ka 46 Rd>A 24–30 some pdc~F 2, 41

Bishop Tuff 760 ka 650 R ~130 0 pdc>F 16, 38

a

References:1. Adams and others, 2001; 2. Bacon and Druitt, 1988; 3. Carey, R.J., and others, 2007; 4. Carey, R.J., and others, 2009; 5. Carey, S., and 

Sigurdsson, 1987; 6. Cioni and others, 1995; 7. Criswell, 1987; 8. Fierstein and Hildreth, 1992; 9. Fierstein and Nathenson, 1992; 10. Fierstein and Nathenson, 

1993; 11. Fisher and Heiken, 1982; 12. Gourgaud and others, 1989; 13. Hay, 1959; 14. Hildreth and Drake, 1992; 15. Hildreth and Fierstein, 2000; 16. Hildreth 

and Wilson, 2007; 17. Horn and Schmincke, 2000; 18. Larsen and Thorarinsson, 1978; 19. Lipman and Mullineaux, 1981; 20. Macdonald and others, 1987; 21. 

Newhall and Punongbayan, 1996; 22. Pyle, 1990; 23. Robin and others, 1994; 24. Self and others, 2004; 25. Self and Rampino, 1981; 26. Self and others, 1984; 

27. Sigurdsson and Carey, 1989; 28. Sigurdsson and others, 1985; 29. Sigurdsson and others, 1984; 30. Sigurdsson and others, 1991; 31. Sigurdsson and Sparks, 

1981; 32. Sparks and others, 1981; 33. Sussman, 1985; 34. Thorarinsson, 1958; 35. Varekamp and others, 1984; 36. Walker and others, 1984; 37. Williams and 

Self, 1983; 38. Wilson and Hildreth, 1997; 39. Wilson and Walker, 1985; 40. Witter and Self, 2007; 41. Young, 1990.
Chapter 14. Comparisons with Other Historic Eruptions 223

Among the modest to medium-size historical plinian eruptions 

tabulated in table 3, however, no such systematic partitioning 

of the ejecta is apparent. In 14 of the eruptions listed, fallout 

was volumetrically dominant and, among these, flow deposits 

were trivial or absent in 6. In 6 of the eruptions listed, deposits 

of pyroclastic density currents predominated and, among these, 

massive involvement of seawater or lakewater played a role in 

3 (as it did also at Krakatau). In 4 of the 24 listed (Novarupta, 

Krakatau, Apoyo-A, and Mazama), volumes of fall and flow 

deposits were roughly equal. As these 4 represent ranges of 

volume, composition, and eruptive behavior, we recognize no 

shared pattern that accounts for such partitioning equality. It 

needs to be recognized, however, that relative proportions of 

coignimbrite and coplinian ash in many distal fine-ash deposits 

are poorly known, because such distal ash is seldom scrutinized 

by microprobe shard-counting like that undertaken by Fierstein 

on the compositionally heterogeneous ash of 1912.

Deaths caused directly by the eruptions are listed in 

table 3. Neither direct injuries nor indirect deaths (owing to 

starvation, debris flows, or forced migration) are included. 

The death toll clearly correlates more with demography than 

volcanology. The absence of casualties at Quizapu and Askja 

reflects their remoteness, as it does for Novarupta, where 

the only known death attributable to the 1912 eruption was 

an elderly refugee already suffering from tuberculosis and 

nephritis who died aboard the Manning in Kodiak harbor on 

the evening of 9 June, after the ashfall had ceased. The list 

shows that agricultural communities on tropical volcanoes are 

at elevated risk, as are settlements on or near island volcanoes 

where tsunami generation can cause widespread devastation. 

Limitation of death tolls to a tenth of what they might have 

been during the latter-day eruptions of St. Helens and Pinatubo reflects the wisdom of volcanologists and their influence 

with the authorities.
224 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

The Griggs expedition of 1917, spiffy and dry at Kodiak, just before shipping 

out to Katmai Bay on 15 June for 10 weeks in the Valley of Ten Thousand 

Smokes (VTTS). Shown is the entire party, from left to right: Sayre, Maynard, 

Church, Folsom, Griggs, Hine, Shipley, (Paul) Hagelbarger, Yagashof, and 

Metroken. Photo courtesy of the National Geographic Society. Folsom and 

Griggs had together ascended Katmai Pass from the south and discovered 

the VTTS on 31 July 1916, last full day of that season’s explorations.
Chapter 15

Retrospective: Evolution of Ideas about the 1912 Eruption 

In the final year of his long life, Fenner (1950) reflected: 

“A geologist coming into the Katmai country in the years 

following the eruption found himself faced with phenomena 

for which no text-book descriptions, or even experience in 

volcanic regions that had been less recently and less violently 

active, would have prepared him. He would be surrounded by 

factual evidence of volcanic processes for which text-books 

either gave no explanation or gave explanations obviously 

out of accord with what he saw.” Fenner clung too long to 

imaginative misinterpretations of what he saw, but one can 

still empathize with his 1919–1923 predicament. Previous 

pyroclastic eruptions investigated in detail had been few. The 

leading model at the time was the directed blast of 8 May 

1902 from Pelée, but the analogy was misleading for the 1912 

ignimbrite, which had no recognizable source vent on any 

volcanic edifice. The column-collapse scoria flows of 7 May 

1902 at St. Vincent would have provided a better model, but 

their early interpretation was confused with the nuées ardentes of Pelée. A still better model would have been the CE 79 

eruption of Vesuvius, but in Fenner’s time its interpretation 

had advanced little since Pliny’s eyewitness account. The best 

model might have been the 1883 eruption of Krakatau, but its 

vent and most of its ignimbrite were beneath the sea (Simkin 

and Fiske, 1983).

In retrospect, it seems remarkable that a great eruption 

that generated international press coverage attracted so few 

early investigators. Rugged frontiersmen, suitably equipped, 

were resident in Kodiak, Kanatak, Cold Bay, and Naknek, 

but none had sufficient curiosity to leave their summertime 

subsistence pursuits to approach the volcano. Martin sailed 

to Katmai village in 1912, and Hesse and Horner hiked to 

Martin Creek in 1913, but clouds, creeks, and the ash blanket kept them from Mount Katmai and the VTTS. In 1915, 

Griggs, Folsom, and Fulton were stopped by Katmai River 

from approaching Mount Katmai, but they became the first to 

view and photograph its beheaded edifice (fig. 100). Only on 

a second expedition, in 1916, did Griggs climb to the caldera 

rim and cross Katmai Pass into what he then named the Valley 

of Ten Thousand Smokes.

Griggs was a respected botanical scholar and an adventurous outdoorsman, whose 1913 studies of revegetation of 

the ash blanket on both sides of Shelikof Strait prompted the 

National Geographic Society to select him to lead a 1915 expedition. His Katmai years coincided with a career shift from 

cytology and taxonomy to colonization dynamics of various 

marginal environments. Griggs also had a talent for evoking 

public fascination with nature, helping to strengthen mutually 

beneficial relations with directors of the National Geographic 

Society and eventuating in establishment of one of the world’s 

most magnificent and unspoiled wilderness parklands. 

Although Griggs was a good field observer, he had little 

geological training and no previous experience with volcanic 

phenomena. He was personally in charge of the explorations 

and was called Professor Griggs or the Director by expedition 

members. Only in 1919 were geologists invited to participate, and his relations with them that summer were neither 

close nor smooth. Griggs’ geological inexperience is evident 

in his presumption that Mount Martin was “a new volcano 

(that) sprung into being at the time of the great explosion” of 

Mount Katmai (Griggs, 1917; 1922, p. 86). After two seasons 

of trudging around in the pumice-fall deposits surrounding 

Katmai River, he first encountered ignimbrite in Mageik 

Creek and called it “the largest and most striking accumulation of ash observed anywhere.”

It is also remarkable that he termed the main VTTS 

ignimbrite a “great hot mud flow,” despite observing that 

it burned the trees it engulfed (Griggs, 1918c). Griggs had 

earlier examined the Katmai River debris-flow deposit (figs. 

120–122), in which he recognized uncharred trees and bushes; 

later finding that the main VTTS deposit was rather similar 

looking may have influenced his “hot mud flow” misinterpretation. From his observations that the “high sand mark” wraps 

much of the upper VTTS, diminishes gradually downvalley, 

and left no remnant of a counterpart deposit higher upslope, 

Griggs (1918c) inferred that the material had “welled quietly up out of the bowels of the earth,” nonexplosively. He 

did observe, however, that the “high sand mark” vanishes in 

Novarupta basin and that pumice is coarser around Novarupta 

than elsewhere. Impressed by the fissure fumaroles and hightemperature acid gases, Griggs took the fissures to be magmatic vents, and he inferred existence of a batholithic magma 

body beneath and coextensive with the VTTS, a notion likely 

to have come from a geology textbook.

Having viewed Katmai beheaded on his first visit in 

1915 and having climbed to its caldera rim in 1916, before 

he had any inkling of the VTTS and Novarupta, Griggs ever 

remained attached to his first impression that the pumice falls 

had issued from Mount Katmai. He rationalized the coarse 
226 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

pumice around Novarupta and the plug dome itself as manifestations of one of many (supposedly fissural) vents distributed throughout the VTTS that had released the ignimbrite. 

Griggs nonetheless expressed his puzzlement about why the 

VTTS should extend perpendicular to the volcanic line and 

why the VTTS and Mount Katmai should have erupted more 

or less sequentially.

Fenner and Zies recognized that the high-temperature 

particulate mass had carried no liquid water, leading them 

to characterize the deposit as an ash flow, sand avalanche, 

or usually sand flow (Fenner, 1920, 1923). They concurred 

with Griggs that the ignimbrite did not descend from Mount 

Katmai, that its source lay somewhere in the VTTS, and that it 

was overlain by stratified pumice falls (which they all misattributed to Mount Katmai). None of them recognized that the 

Layer A pumice fall underlies the ignimbrite in Mageik Creek, 

is ubiquitous on and south of Mount Katmai, but is missing 

in the VTTS. Failure to distinguish among the several layers 

of fall deposits (A–H) prevented them from realizing that 

the ignimbrite was synplinian, emplaced during the fallout 

sequence, not before it as they inferred from stratigraphic relations in the VTTS alone. The misunderstanding is attributable 

in part to the fact that (before 1923) all ascents to the caldera 

rim had been from the south, where one cannot observe either 

ignimbrite-fallout age relations or the decline in coarseness 

of the fallout layers away from Novarupta (fig. 105). Locked 

into convictions that the ignimbrite erupted in the VTTS and 

most of the fallout at Mount Katmai, they never arrived at a 

single-vent column-collapse model for the contrasting but concurrent modes of pyroclastic emplacement. Griggs and Fenner 

acknowledged the coarse pumice falls close to Novarupta, and 

they granted that Novarupta had been one of many vents, but 

they never mentioned any attempt to distinguish Novarupta 

fallout from that attributed to Mount Katmai.

Agreeing with Griggs’ interpretation of fissure vents all 

over the VTTS, Fenner (1920, p. 581) wrote that, concerning 

the origin of the sand flow, “we suppose that rhyolitic magma, 

charged with dissolved gases, rose to the surface in the newly 

formed vents. According to general observation, the usual 

course for such a magma is either to retain its gases and form 

a flow of obsidian, or to evolve them with explosive violence 

and scatter the disrupted particles to a great distance. In this 

instance, however, it apparently pursued an intermediate 

course, and produced, by moderately forcible disruption, an 

outward-spreading and forward-moving torrent of incandescent sand and pumice, each particle of which was surrounded 

by and partially suspended in gases which it continued to give 

forth during its impetuous flow.” Despite Fenner’s idiosyncratic view that magma might reach the surface nonexplosively and evolve most of its gases only subsequently, this 

is nonetheless one of the first clear formulations of ash-flow 

emplacement and the cause of its mobility. 

When Marshall (1935) introduced the term “ignimbrite” 

for such deposits, specifically for the many sheets of variably welded rhyolitic tuff in New Zealand, he cited Fenner’s 

VTTS work for both mode of emplacement and manner of 

cohesion and induration of hot viscous glass shards (sintering, welding), which Fenner had learned in the glass industry. 

Gilbert’s (1938) description of the Bishop Tuff seconded both 

Fenner and Marshall in citing the importance of continued gas 

emission during outflow for mobility, welding, cooling, and 

crystallization of the deposit. Smith (1960) summarized the 

evolution of ideas about pyroclastic flows, from the abrupt 

directed blast at Pelée to the extended outpouring at Novarupta. He emphasized the distinction between basal pyroclastic avalanches and overriding billowing ash clouds, and he 

credited Fenner with recognizing that initial momentum and 

gravity were supplemented by prolonged internal gas production in accounting for pyroclastic-flow mobility. The columncollapse model for the origin and momentum of pyroclastic 

flows was implicit in the St. Vincent eruption of 1902, but its 

appropriateness was not appreciated until Hay’s (1959) study, 

perhaps because it was andesitic, subplinian, and widely conflated with the dome-sourced blasts and block-and-ash flows at 

Pelée. The first unequivocal description of pumice-rich silicic 

ignimbrite being generated by collapse of a plinian eruption 

column was that of Kozu (1934) concerning the 1929 eruption 

of Komagatake in Hokkaido (Tsuya, 1930).

Neither Marshall nor Gilbert was able to identify vents 

for their ignimbrite sheets, and, like Fenner, they appealed 

generally to fissures in the tuff and to burial of vents by the 

deposits themselves. Citing varied lithic suites in the ignimbrite, Gilbert had inferred “scattered vents,” as had Fenner on 

the basis of fumarolic emissions along the entire VTTS. MacGregor (1952) interpreted extracts from Fenner’s many papers 

to infer that he had really meant to give primacy to Novarupta, 

but Fenner always referred also to fissure vents throughout the 

valley, and he always assigned the fallout sequence to Mount 

Katmai. As late as 1953, many still inferred fissure vents to 

be distributed across much of the upper VTTS (Williams and 

others, 1953). Only after Curtis (1968) had isopached the 

individual fallout layers was it settled that both the plinian 

phase and the ignimbrite had issued from Novarupta basin.

Fenner’s family home was just west of New York City, 

in eastern New Jersey, where he did his Ph.D. dissertation on 

basalts of the Watchung Mountains and became intimately 

familiar with the Mesozoic sills of the Newark Basin (Fenner, 

1926, 1929). His dissertation emphasized secondary replacement minerals in the basalt, and he had previously spent 

15 years internationally investigating hydrothermal fluids, 

secondary minerals, and ore deposits. At the Geophysical 

Laboratory, not long before his first Katmai trip, he had conducted supercritical hydrous experimental work that demonstrated major increases in mineral solubility with temperature 

(Morey and Fenner, 1917). It seems easy (if perhaps facile) to 

view Fenner’s ideas at Katmai as outgrowths of these previous 

experiences. Impressed by the horizontal Jurassic strata that 

extend across the whole VTTS from Mount Katmai, Fenner 

proposed that (instead of Griggs’ batholith) a rhyolite sill had 

propagated 20 km northwestward from Mount Katmai and, 
coextensive with the VTTS, had released both the ignimbrite 

and the fumarolic gases.

More puzzling is why Fenner never even discussed mingling of separate magmas as an alternative for producing the 

ubiquitous banded pumice, especially as he acknowledged that 

the adjacent volcanoes were largely andesitic and the juvenile 

1912 magma was predominantly rhyolitic. In illustrating a 

strikingly banded black-and-white pumice clast, he even wrote 

that it was “formed by the partial mingling of two chemically 

diverse fluids” (Fenner, 1923, p. 38–39). But he insisted that 

the black andesitic fluid was not a new magma but a product 

of fusion by the rhyolite magma of older previously solid 

lavas and morainal debris. He never mentioned the apparent 

contradiction between the extended time required for remelting 

solid andesite and the limited (syneruptive) time indicated by 

the razor-sharp contacts between black and white pumice bands 

(fig. 61). The thermal requirements and necessarily inferred 

physical location of such fusion and mingling lured him into 

advocating his most imaginative and outrageous hypothesis.

Fenner recognized that lithic ejecta in 1912 fall deposits 

were far from adequate to account for the Katmai caldera by 

explosive origin, and he dismissed subsidence as subordinate 

or speculative (Fenner, 1920, p. 594). He proposed instead 

that the mountaintop had been assimilated by the new rhyolitic 

magma and that the andesitic component of the banded pumice represented remelted lavas of the Katmai edifice. Because 

he presumed separate vents for the ignimbrite down in the 

VTTS, its abundant banded pumice required a different source 

of andesitic assimilant, which he assigned to morainal debris 

in the valley. Such a scenario forced him to envision that the 

rhyolitic magma had reached the surface nonexplosively, in 

both the VTTS and the crater of Mount Katmai, and that it 

had reposed there quiescently long enough to remelt, partially 

assimilate, and mingle with the surficial andesites before 

their joint vesiculation and violently explosive fragmentation 

and dispersal. In dismissing explosivity before the magma 

had reached the surface, he cited sparsity of lithic ejecta and 

absence of structural disruption of the basement strata; what 

he appears to have been dismissing was a magma-chamber 

explosion, and he evidently had no vision of fragmentation in 

a conduit that feeds a plume. Fenner made many astute observations, but the principal flaws that drew him into his radical 

scenario were the two-vent presumption, dismissal of caldera 

subsidence by magma withdrawal, and ignoring the possibility 

of simple mingling of coexisting confluent magmas.

Fenner never revealed how he imagined a rhyolitic 

magma that had decompressed to the surface might have 

delayed volatile exsolution and plinian dispersal until after it 

had remelted several cubic kilometers of andesite. He often 

invoked an intracrater lava lake as an element of his quiescent 

assimilation process, and he cited fallout clasts of obsidian and 

revesiculated agglutinate as crusts and “scum” from such a 

lake; both are actually Episode I welded vent fill that was later 

reejected (figs. 62, 63). Fenner also cited breadcrusted blocks 

near Novarupta as evidence of delayed vesiculation, but such 

blocks are recycled vent-filling agglutinate and fragments of 

the Episode IV Phantom dome (fig. 54).

Although never quite conceding that rhyolitic magma 

is generally of lower temperature than andesitic magma 

(Fenner, 1931, p. 542), Fenner acknowledged repeatedly 

that a large excess heat supply was required for phenocrystpoor rhyolite to remelt voluminous andesite. For this he 

appealed to hypothetical and unspecified exothermic reactions 

within the volatile-rich rhyolite magma while it was supposedly reequilibrating to greatly reduced pressure. “Magmas 

should not be regarded as inert mixtures, such as are worked 

with in experimental laboratory melts....During their ascent 

from great depths, changes of internal equilibrium lead to 

exothermal reactions, somewhat analogous to the development of the latent heat of crystallization” (Fenner, 1944). He 

proposed that “the rhyolite liquid was so highly mobile that 

it soaked into xenoliths and permeated and softened them so 

thoroughly that they became inflated at the same time as the 

liquid magma....The view that rhyolitic magmas are essentially 

highly viscous seems to persist in spite of much evidence 

to the contrary” (Fenner, 1950, p. 613). He was probably 

predisposed to favor such nebulous ideas by his experimental 

work with supercritical fluids (Morey and Fenner, 1917), his 

studies of hydrothermal and “pneumatolitic” (Fenner, 1933) 

ore deposits, and contemporary buzz about exothermic reactions (Day and Shepherd, 1913, p. 600). Fenner advocated 

his model, sometimes aggressively, for the rest of his life 

(Fenner, 1920, 1923, 1926, 1929, 1931, 1934, 1937, 1938a, 

1938b, 1944, 1950). His final statement read: “When relief 

of pressure gives opportunity for volatiles to escape, they 

may not be able to take advantage of it immediately. Relief 

of pressure favors the escape of gases, and therefore reactions 

proceed in the direction that leads to the formation of gases, 

but the rearrangements may require time for their development. In a chain of chemical reactions, a bottle-neck may 

occur which slows the whole series down; but...the speed of 

reactions increases rapidly with rise of temperature, and, if 

the net effect in a magma is exothermic, reactions that have 

begun very slowly proceed more and more rapidly, at a high 

compound interest rate, as the temperature rises, and finally 

reach a cataclysmic stage” (Fenner, 1950, p. 609). A century 

of experimental petrology has proven his radical hypotheses 

untenable, and a half century of stratigraphic studies at Katmai 

has proven them unnecessary.

Advances in Volcanology and Progress in 

Understanding the 1912 Eruption

Understanding of volcanic processes has advanced greatly 

since Fenner’s day, through a combination of observational, 

theoretical, analytical, experimental, stratigraphic, and granulometric studies. The breakthrough in clarifying the events of 

1912 started with the 1953–54 stratigraphic study by Curtis 

(1968), which demonstrated that virtually all the juvenile 

eruptive products had issued at Novarupta, not Mount Katmai. 

Chapter 15. Retrospective: Evolution of Ideas about the 1912 Eruption 227
228 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Relationships among conduit flow, magma fragmentation, eruption columns, ignimbrites, and plinian dispersal were progressively clarified in studies by Smith (1960), Walker (1971, 1973), 

Sparks (1976), Wilson (1976), and hundreds more, culminating 

in overview volumes by Sparks and others (1997), Gilbert and 

Sparks (1998), and Freundt and Rosi (1998).

 Successive advances in understanding 1912 eruptive processes have included the following: 

 1. Fundamental was stratigraphic documentation that 

plinian fallout and ignimbrite emplacement were synchronous and sustained together for more than half a 

day. We observed as early as 1976 that part of rhyolitic 

Layer A underlies the ignimbrite and dacitic Layers 

C-H overlie it, but it required years of detailed regional 

work to appreciate the synchroneity of zoned Layer B 

and most of the zoned ignimbrite. Challenges included 

the rugged glacial terrain and the limited area of overlap 

between fall and flow distributions, but we were also 

confronted by the then-reigning supposition that such 

synchroneity should not exist, based on oversimplified 

interpretations of the column-collapse model.

 2. Progressive compositional changes permitted establishment that various facies in the ignimbrite were deposited contemporaneously, reflecting differences in initial 

momentum, vertical position in stratified (densitygraded) currents, and outflow distance. Cross-stratified 

bedsets on the ridgecrests, massive flow units in the 

valleys, and a few thin blast deposits are compositional 

and temporal counterparts.

 3. Compositional zonation of the ignimbrite permitted mapping of nine distinguishable packages, each 

consisting of a few or several flow units, successively 

emplaced over an interval of ~16 hours.

 4. Progressive downvalley deflation, densification, and 

increasing intergranular friction caused ignimbritedepositing currents to change from turbulent to fluidized 

to sluggish grainflows distally. Laminated ignimbrite 

and many distal flow units represent not vent-derived 

currents but features emerging from massive ignimbrite 

that was shearing to a halt, stalling, and locally remobilizing in pulses.

 5. Welding was immediate where ignimbrite was thick, 

creating valley-axial swales that channelled flow units 

only hours younger. But crystallization of glassy 

ignimbrite, which contributed acid gases to the steamdominated fumaroles, continued for a decade or more.

 6. Fine ash settled more slowly than the bulk of each plinian deposit, some of it drifting widely, even westward, 

in directions independent of the main southeasterly 

umbrella cloud. Such fines were intrinsic to the primary 

plinian plume, and some fraction were probably swept 

back up into the column from the deflation zone around 

the vent, but only a minor contribution of coignimbrite 

fines was elutriated from the VTTS-filling ignimbrite 

sheet. Because there were three plinian episodes, a significant fraction of the slow-settling fine ash of Episode 

I was deposited with the fallout of Episode II and III.

 7. The effectiveness of 1912 dust and acid aerosol on 

cooling the atmosphere was modest compared to that of 

many lesser eruptions because the predominant rhyolite, 

though rich in halogens, was poor in sulfur.

 8. Caldera collapse began in the 11th hour of the eruption 

and may have been largely over by the 38th hour (fig. 

60). Seismicity and ejection of phreatic mud layers near 

the end of Episode III indicate a short resumption of 

subsidence around the 58th hour; and after the eruption 

ended, earthquakes of M6.0 in the 66th hour and M6.9 

in the 89th hour are hard to explain other than by further 

wall slumps or caldera-floor settling.

 9. The “ten thousand” fumaroles were mostly rooted in the 

ignimbrite, from which acid gases liberated from the 

tuff itself leached metals for a decade; soluble surface 

sublimates were weathered away within subsequent 

decades. Fumaroles lasted longest on the floor of 

Katmai caldera and in the arcuately fissured vent area of 

Novarupta basin, where only wispy subboiling emissions persist today.

 10. Magma mingling was syneruptive. Sharp contacts in 

banded pumice reflect at most hours to minutes of contiguity before vesiculation, fragmentation, and eruptive 

quench. Some xenoliths were oxidized, but none were 

partially melted, not even siltstones and granitoids, let 

alone andesite lavas and boulders.

 11. Chemical and petrographic characterization of most 

lavas from all the nearby volcanoes confirmed the affinity of 1912 andesite and dacite with products of Mount 

Katmai, not of Trident, Mageik, or even the Southwest 

Trident lavas and ejecta of 1953–74.

 12. The high-silica rhyolite that dominated the 1912 eruption 

remains a regional rarity of unproven affinity. Its chemical and isotopic similarity to the melt (glass) phase of the 

coerupted dacite, its thermal and redox continuity with 

the dacite as shown by Fe-Ti-oxide pairs, and the similar 

preeruptive storage depths inferred from phase-equilibrium experiments are all consistent with a comagmatic 

zoned system. If the rhyolite originated elsewhere, the 

chain of coincidences is remarkable.

 13. Cutting the nearly horizontal sedimentary basement 

strata that form the walls of the VTTS and Katmai 
Canyon, there are many dikes and sills, probably all 

of Miocene or Pliocene age. Magma transport may 

usually be vertical or nearly so, but sills demonstrate 

alternatives. From a magma body 3–6 km beneath 

Katmai caldera, magma transport by a 10-km-long sill 

to a position beneath Novarupta is more feasible than a 

dike, which (like many before it; fig. 135) could have 

ascended through the Katmai edifice itself. Transport 

from a sill to the surface in Novarupta basin would 

finally require a dike or pipe-like conduit.

 14. Within ~2 km of Novarupta dome, sector-confined fall 

deposits of local dispersal and thin pyroclastic-densitycurrent deposits are intercalated with the regionally 

dispersed plinian layers of Episodes II and III. They 

contribute to overthickened sections of proximal 

ejecta and reflect preferential partitioning of andesitic 

and lithic fragments into an annular collar around the 

emerging jet, producing transient asymmetrical fountaining and column-margin collapse pulses.

 15. Geophysical investigations at Novarupta and the VTTS 

have been bedeviled by shallow crustal heterogeneities. Arrays of seismometers in 1965–67 yielded 

data believed to indicate magma storage beneath the 

volcanic axis, but a new deployment in 1987–91 failed 

to identify the S-wave screening interpreted earlier. 

P-wave delays were found to be greatest near Katmai 

Pass, where poorly welded thick ignimbrite fills the 

former defile. Seismic-refraction and gravity profiles 

across the central VTTS in 1966–69 were misinterpreted to indicate thin ignimbrite because no account 

was taken of concealed welded zones. Heat-flow 

measurements in Novarupta basin showed order-ofmagnitude variations in conductive and convective 

heat flux on a meter scale, owing to vapor transport 

along faults and fractures, and yielded nothing useful 

about the deeper thermal regime. A gravity survey of 

Novarupta basin failed to outline the vent area, owing 

to limited density contrast between basement siltstone 

and welded vent fill. An aeromagnetic survey of 

Novarupta basin was overinterpreted without taking 

into account great local variations in vent-fill welding, thickness, andesite-dacite-rhyolite proportions, or 

fumarolic leaching and magnetite deposition.

Can another great eruption occur on the Alaska Peninsula 

(Fierstein and others, 1998)? Of course. And what might be 

different next time? The Katmai region is not greatly more 

populous today than in 1912, but Kodiak and Cook Inlet 

certainly are. The first airplane in Alaska was a demonstration flight at Fairbanks in 1913; there are thousands of aircraft 

today. Alaska Volcano Observatory has numerous instruments 

at Katmai and elsewhere along the peninsula, and satellite 

surveillance is now routine. Many volcanoes are closely 

monitored for signs of unrest, and timely warnings would be 

issued if an eruption were pending. Many Alaskan communities have experienced recent Cook Inlet ashfalls and would be 

better stockpiled with supplies and better prepared to protect 

life, lodging, and equipment than in 1912. The 1912 eruption 

at Novarupta, so unusual in so many ways, has also left us with 

two exceptional warnings. Don’t count your plinian outbursts. 

Who would have expected three separate plinian eruptions on 

successive days? And don’t count on your next rhyolite to 

erupt from a volcano at all. It might break out through a ridge 

of siltstone.

Chapter 15. Retrospective: Evolution of Ideas about the 1912 Eruption 229
230 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Dave Johnston, USGS volcanologist, who worked with 

Hildreth and Anita Grunder in the VTTS in 1979 but was 

fatally swept away by the 18 May 1980 eruption of Mount 

St. Helens, Washington. Photo taken by Dan Kosco in 1978 

at southwest base of Novarupta dome. On the fallen block 

of flow-banded rhyolite are the initials, carved in 1923, of 

Clarence Norman Fenner (C.N.F.) and Charles Yori (C.Y.).
Acknowledgments 231

 Acknowledgments

Our principal sources were field observations during 20 summer expeditions to Katmai, as well as the many 

earlier publications cited. The National Geographic Society 

granted access to its photo archives of the Griggs expeditions and provided prints of numerous historical images 

selected by the authors. The National Park Service made 

available the field diaries of Jasper Sayre and E.T. Allen, 

as well as a photo collection by Charles Yori. Our initial 

fieldwork in 1976 was encouraged by Garniss Curtis and 

supported by National Science Foundation grants to Ian 

Carmichael. A dozen seasons on foot were supported by the 

Geothermal Research and Volcano Hazards Programs of the 

U.S. Geological Survey, as were Fierstein’s two excursions 

along Shelikof Strait in the good ship Ten Bears, piloted by 

Eric Stirrup and Hank Pennington. Starting in 1996, seven 

helicopter-based seasons to investigate the eruptive history of the wider Katmai volcanic cluster were supported 

by the Alaska Volcano Observatory, under the leadership of 

Terry Keith and Tom Murray. We are especially grateful to 

Michelle Coombs and Terry Keith, both of that observatory 

and both old Katmai hands, for detailed and constructive 

reviews of this lengthy contribution. 

Helicopter pilots Paul Walters, Bill Springer, Jim Sink, 

and Sam Egli ably handled the challenges of howling winds 

and socked-in passes to bring us back safely (though often 

green). Equally expert were the fixed-wing pilots of KatmaiAir, led by legendary bush pilot Sonny Peterson. Between 

stormy sorties, the U.S. Fish and Wildlife Service bunkhouse 

in King Salmon provided many amenities, thanks to Susan 

Savage and Donna Dewhurst.

Collaboration with Bruce Houghton and Colin Wilson 

extended our reach, broadened our perspectives, advanced 

our understanding of the 1912 eruption, and brightened our 

morale in wind and rain. The geophysical expeditions of 

1989 and 1990, spearheaded by John Eichelberger, brought 

new dimensions to investigation of the Novarupta vent region 

and introduced us to the mixed blessings of helicopters. 

Radioisotopic age determinations by Marvin Lanphere and 

Andrew Calvert were critical for calibrating the pre-1912 

eruptive history of the region. For collaboration, logistical 

support, field assistance, and comradeship, we are grateful to many colleagues (in roughly chronological order): 

Larry Jager, Dan Kosco, Tom Miller, Dave Johnston, Anita 

Grunder, Terry Keith, Tina Neal, Gail Mahood, Jim Riehle, 

Buck Detterman, Pete Ward, Betsy Yount, John Eichelberger, 

Jim Papike, Vicki McConnell, John Power, Maura Hanning, 

Paul Wallace, Bob Symonds, Bea Ritchey, Michelle Coombs, 

Dave Tucker, Julia Hammer, Nancy Adams, and (perennially) 

John Paskievitch. Hildreth is especially grateful that Ian Carmichael sent him off to Katmai on the hunch that something 

might come of it; and he is more than pleased that his own 

hunch that Fierstein might eventually fill the boots once worn 

by Dave Johnston was so amply rewarded.

Numerous personnel of the National Park Service were 

logistically helpful, notably Gil Blinn, Lynn Fuller, George 

Stroud, Penny and Dennis Knuckles, Bruce Kaye, Bud Rice, 

Karen Jettmar, Eric Schmidt, Ron Squib, Jim Gavin, Dave 

Morris, Ralph Furbush, Ray Bane, Hal Grovert, Susan Savage, Janis Meldrum Kozlowski, Rick Potts, Karen Gustin, 

John Bundy, and Roy Wood. Their service in preserving one 

of the world’s most pristine wilderness parklands is seldom 

adequately acknowledged. We salute them.
232 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Ian Carmichael (left) and Garniss Curtis, geology professors at the 

University of California, Berkeley, visiting Three Forks Overlook above the 

lower Valley of Ten Thousand Smokes in August 2003. Together, they had 

inspired and supported Hildreth’s first expedition to the area in 1976, when 

he was a Berkeley graduate student.
References 233

References

Abbot, C.G., 1913, Do volcanic explosions affect our climate?: National Geographic Magazine, v. 24, p. 181–198.

Abe, K., 1992, Seismicity of the caldera-making eruption of 

Mount Katmai, Alaska, in 1912: Bulletin of the Seismological Society of America, v. 82, p. 175–191.

Adams, N.K., de Silva, S.L., Self, S., Salas, G., Schubring, 

S., Permenter, J.L., and Arbesman, K., 2001, The physical 

volcanology of the 1600 eruption of Huaynaputina, southern 

Peru: Bulletin of Volcanology, v. 62, p. 493–518.

Adams, N.K., Houghton, B.F., Fagents, S.A., and Hildreth, 

W., 2006a, The transition from explosive to effusive eruptive regime; the example of the 1912 Novarupta eruption, 

Alaska: Geological Society of America Bulletin, v. 118, p. 

620–634.

Adams, N.K., Houghton, B.F., and Hildreth, W., 2006b, 

Abrupt transitions during sustained explosive eruptions; 

examples from the 1912 eruption of Novarupta, Alaska: 

Bulletin of Volcanology, v. 69, p. 189–206.

Allen, E.T., and Zies, E.G., 1923, A chemical study of the 

fumaroles of the Katmai region: National Geographic 

Society, Contributed Technical Papers, Katmai Series, No. 

2, p. 75–155.

Andersen, D.J., Lindsley, D.H., and Davidson, P.M., 1993, 

QUILF—A Pascal program to assess equilibria among FeMg-Mn-Ti oxides, pyroxenes, olivine, and quartz: Computers & Geosciences, v. 19, p. 1333–1350.

Anderson, T., and Flett, J.S., 1903, Report on the eruptions of 

the Soufrière, in St. Vincent, in 1902, and on a visit to Montagne Pelée, in Martinique—Part I: Philosophical Transactions of the Royal Society of London, Series A, v. 200, p. 

353–553.

Annen, C., Blundy, J.D., and Sparks, R.S.J., 2006, The genesis 

of intermediate and silicic magmas in deep crustal hot 

zones: Journal of Petrology, v. 47, p. 505–539.

Arculus, R.J., 2003, Use and abuse of the terms calcalkaline 

and calcalkalic: Journal of Petrology, v. 44, p. 929–935.

Avery, V.F., 1992, A petrogenetic study of the dacite from the 

1912 eruption of Novarupta, Katmai National Park, Alaska; 

implications for magma storage locations: Fairbanks, University of Alaska, M.S. thesis, 177 p.

Bacon, C.R., and Druitt, T.H., 1988, Compositional evolution of the zoned calcalkaline magma chamber of Mount 

Mazama, Crater Lake, Oregon: Contributions to Mineralogy 

and Petrology, v. 98, p. 224–256.

Bacon, C.R., and Hirschmann, M.M., 1988, Mg/Mn partitioning as a test for equilibrium between coexisting Fe-Ti 

oxides: American Mineralogist, v. 73, p. 57–61.

Baedecker, P.A., ed., 1987, Methods for geochemical analysis: U.S. Geological Survey Bulletin 1770. (Paginated by 

chapter.)

Ballard, S., Carrigan, C.R., and McConnell, V.S., 1991, Shallow conductive-component of heat flow near Novarupta 

Dome, Katmai, Alaska: Geophysical Research Letters, v. 

18, p. 1529–1532.

Berg, E., Kubota, S., and Kienle, J., 1967, Preliminary 

determination of crustal structure in the Katmai National 

Monument, Alaska: Bulletin of the Seismological Society 

of America, v. 57, p. 1367–1392.

Blake, S., and Ivey, G.N., 1986, Magma mixing and the 

dynamics of withdrawal from stratified reservoirs: Journal of Volcanology and Geothermal Research, v. 27, p. 

153–178.

Bordet, P., Marinelli, G., Mittempergher, M., and Tazieff, H., 

1963, Contribution à l’étude volcanologique du Katmai et 

de la Vallée des Dix Mille Fumées: Mémoires de la Société 

Belge de Géologie, de Paléontologie et d’Hydrologie, No. 

7, p. 1–114.

Bowen, N.L., 1913, The melting phenomena of the plagioclase 

feldspars: American Journal of Science, v. 35, p. 577–599.

Bowen, N.L., 1915, The later stages of the evolution of the 

igneous rocks: Journal of Geology, v. 23, Supplement, 

p. 1–89.

Brandsdóttir, B., and Einarsson, P., 1979, Seismic activity 

associated with the September 1977 deflation of Krafla 

Volcano in northeastern Iceland: Journal of Volcanology and 

Geothermal Research, v. 6, p. 197–212.

Branney, M.J., and Kokelaar, P., 2002, Pyroclastic density 

currents and the sedimentation of ignimbrites: Geological 

Society of London Memoir 27, 152 p.

Buddington, A.F., and Lindsley, D.F., 1964, Iron-titanium 

oxide minerals and synthetic equivalents: Journal of Petrology, v. 5, p. 310–357.

Cahalane, V.H., 1959, A biological survey of Katmai National 

Monument: Smithsonian Institution Publication 4376, 231 p.

Cameron, R.E., 1970, Soil microbial ecology of Valley of 

10,000 Smokes, Alaska: Journal of the Arizona Academy 

of Science, v. 6, no. 1, p. 11–40.

Cameron, W.A., and Larson, G.L., 1992, Baseline inventory 

of the aquatic resources of Aniakchak National Monument, 

Alaska: Seattle, National Park Service, Technical Report 

NPS/PNROSU/NRTR-92/03, 215 p.

Carey, R.J., Houghton, B.F., Sable, J.E., and Wilson, C.J.N., 

2007, Contrasting grain size and componentry in complex 

proximal deposits of the 1886 Tarawera basaltic Plinian 

eruption: Bulletin of Volcanology, v. 69, p. 903–926. 
234 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Carey, R.J., Houghton, B.F., and Thordarson, T., 2009, Abrupt 

shifts between wet and dry phases of the 1875 eruption of Askja Volcano; microscopic evidence for macroscopic dynamics: Journal of Volcanology and Geothermal 

Research, v. 184, p. 256–270.

Carey, S., and Sigurdsson, H., 1987, Temporal variations in 

column height and magma discharge rate during the 79 A.D. 

eruption of Vesuvius: Geological Society of America Bulletin, v. 99, p. 303–314.

Carey, S., and Sparks, R.S.J., 1986, Quantitative models of 

the fallout and dispersal of tephra from volcanic eruption 

columns: Bulletin of Volcanology, v. 48, p. 109–125.

Carrigan, C.R., Schubert, G., and Eichelberger, J.C., 1992, 

Thermal and dynamical regimes of single- and two-phase 

magmatic flow in dikes: Journal of Geophysical Research, v. 

97, p. 17377–17392.

Choux, C., Druitt, T., and Thomas, N., 2004, Stratification 

and particle segregation in flowing polydisperse suspensions, with applications to the transport and sedimentation 

of pyroclastic density currents: Journal of Volcanology and 

Geothermal Research, v. 138, p. 223–241.

Cioni, R., Civetta, L., Marianelli, P., Metrich, N., Santacroce, R., and Sbrana, A., 1995, Compositional layering and 

syneruptive mixing of a periodically refilled shallow magma 

chamber; the AD 79 plinian eruption of Vesuvius: Journal of 

Petrology, v. 36, no. 3, p. 739–776.

Clocchiatti, R., 1972, Les cristaux de quartz des ponces 

de la Vallée des Dix Mille Fumées (Katmai, Alaska): 

Comptes Rendus, Academie des Sciences de Paris, t. 274, 

p. 3037–3040.

Clocchiatti, R., 1975, Les inclusions vitreuses des cristaux de 

quartz: Mémoires de la Société Géologique de France, no. 

122, 96 p.

Clough, C.T., Maufe, H.B., and Bailey, E.B., 1909, The 

cauldron-subsidence of Glen Coe and the associated igneous phenomena: Quarterly Journal of the Geological Society of London, v. 65, p. 611–678.

Coombs, M.L., 2001, Experimental and petrologic constraints 

on magma storage, movement, and interactions at two volcanoes in Katmai National Park, Alaska: Fairbanks, University of Alaska, Ph.D. dissertation, 218 p.

Coombs, M.L., and Gardner, J.E., 2001, Shallow-storage conditions for the rhyolite of the 1912 eruption at Novarupta, 

Alaska: Geology, v. 29, p. 775–778.

Coombs, M.L., Eichelberger, J.C., and Rutherford, M.J., 2000, 

Magma storage and mixing conditions for the 1953-1968 

eruption of Southwest Trident Volcano, Katmai National 

Park, Alaska: Contributions to Mineralogy and Petrology, v. 

140, p. 99–118.

Cowee, C., Faust Larsen, J., Guetschow, H., Eichelberger, J., 

Kent, A., and Hutcheon, I., 1999, Melt inclusion textures 

and volatile compositions from Novarupta dome, Katmai 

National Park, Alaska: Eos, American Geophysical Union 

Transactions, v. 80, no. 17, p. S352.

Criswell, C.W., 1987, Chronology and pyroclastic stratigraphy of the May 18, 1980, eruption of Mount St. Helens, 

Washington: Journal of Geophysical Research, v. 92, p. 

10237–10266.

Curtis, G.H., 1968, The stratigraphy of the ejecta from the 

1912 eruption of Mount Katmai and Novarupta, Alaska, in 

Coats, R.R., Hay, R.L., and Anderson, C.A., eds., Studies in 

Volcanology: Geological Society of America Memoir 116, 

p. 153–210.

Curtis, G., Williams, H., and Juhle, W., 1954, Evidence against 

assimilation of andesite by rhyolite in the Valley of 10,000 

Smokes, Alaska: American Geophysical Union Transactions, v. 35, no. 2, p. 378.

Daly, R.A., 1914, Igneous rocks and their origin: New York, 

McGraw-Hill, 563 p.

Day, A.L., 1931, Melting temperatures of granite and basalt: 

Carnegie Institution of Washington Year Book No. 30, p. 

75–78.

Day, A.L., and Shepherd, E.S., 1913, Water and volcanic 

activity: Geological Society of America Bulletin, v. 24, p. 

573–606.

Day, R.H., 1995, New information on Kittlitz’s murrelet nests: 

The Condor, v. 97, p. 271–273.

Decker, R.W., 1963, Proposed volcano observatory at Katmai 

National Monument; a preliminary study: Hanover N.H., 

Dartmouth College, unpublished report, 54 p. [Katmai 

National Park archives].

Decker, R.W., 1964, Geophysical investigations in Katmai 

National Monument, Alaska: American Geophysical Union 

Transactions, v. 45, p. 124.

Detterman, R.L., Case, J.E., Wilson, F.H., and Yount, M.E., 

1987, Geologic map of the Ugashik, Bristol Bay, and 

western part of Karluk quadrangle, Alaska: U.S. Geological 

Survey Map I-1685; scale 1:250,000.

Detterman, R.L., Case, J.E., Miller, J.W., Wilson, F.H., and 

Yount, M.E., 1996, Stratigraphic framework of the Alaska 

Peninsula: U.S. Geological Survey Bulletin 1969-A, 74 p.

Devine, J.D., Sigurdsson, H., Davis, A.N., and Self, S., 1984, 

Estimates of sulfur and chlorine yield to the atmosphere 

from volcanic eruptions and potential climatic effects: Journal of Geophysical Research, v. 89, p. 6309–6325.

Dixon, J.P., and Power, J.A., 2009, The January 2006 volcanic-tectonic earthquake swarm at Mount Martin, Alaska, in
References 235

Haeussler, P.J., and Galloway, J.P., eds., Studies by the U.S. 

Geological Survey in Alaska, 2007: U.S. Geological Survey 

Professional Paper 1760-D, 17 p.

Donnay, J.D.H., 1956, The geological studies of Rolf Werner 

Juhle (1929-1953)—in memoriam: Journal of Geological 

Education, v. 4, p. 47–51.

Doukas, M.P., and McGee, K.A., 2007, A compilation of gasemission data from volcanoes of Cook Inlet (Spurr, Crater 

Peak, Redoubt, Iliamna, and Augustine) and Alaska Peninsula (Douglas, Fourpeaked, Griggs, Mageik, Martin, Peulik, 

Ukinrek Maars, and Veniaminof), Alaska, from 1995–2006: 

U.S. Geological Survey Open-File Report 2007–1400, 13 p.

Druitt, T.H., 1998, Pyroclastic density currents, in Gilbert, 

J.S., and Sparks, R.S.J., eds., The physics of explosive 

volcanic eruptions: Geological Society of London Special 

Publication 145, p. 145–182.

Druitt, T.H., Bruni, G., Lettieri, P., and Yates, J.G., 2004, The 

fluidization behaviour of ignimbrite at high temperature and 

with mechanical agitation: Geophysical Research Letters, v. 

31, L02604, doi: 10.1029/2003GL018593.

Druitt, T.H., Avard, G., Bruni, G., Lettieri, P., and Maez, F., 

2007, Gas retention in fine-grained pyroclastic flow materials at high temperatures: Bulletin of Volcanology, v. 69, p. 

881–901.

Dumond, D.E., 2005, A Naknek chronicle: Washington, 

National Park Service, 111 p.

Eichelberger, J., and Hildreth, W., 1986, Research drilling at 

Katmai, Alaska: Eos (American Geophysical Union Transactions), v. 67, p. 778–780.

Eichelberger, J.C., and Izbekov, P.E., 2000, Eruption of andesite triggered by dyke injection; contrasting cases of Karymsky Volcano, Kamchatka, and Mount Katmai, Alaska: 

Philosophical Transactions of the Royal Society of London, 

series A, v. 358, p. 1465–1485.

Eichelberger, J.C., Hildreth, W., and Papike, J.J., 1987, Direct 

observation of a young igneous system; a proposal for 

research drilling at Katmai, Alaska: Continental Scientific 

Drilling Program, 174 p.

Eichelberger, J.C., Hildreth, W., and Papike, J.J., 1989, Direct 

observation of a young igneous system; a science plan for 

research drilling at Katmai National Park, Alaska: Continental Scientific Drilling Program, 218 p.

Eichelberger, J.C., Ballard, S., Carrigan, C.R., Goodliffe, A., 

Hildreth, W., Iwatsubo, E., Kasameyer, P.W., Keith, T.E.C., 

Kienle, J., Papike, J.J., Pollard, D.D., Stone, D.E., Wallmann, P.C., Ward, P.C., Wilt, M., and Yount, M.E., 1990, 

Geophysics at Katmai; geophysical expedition to Novarupta 

Volcano, Katmai National Park, Alaska: Eos (American 

Geophysical Union Transactions), v. 71, p. 733–735.

Eichelberger, J.C., Hildreth, W., and Papike, J.J., 1991, The 

Katmai Scientific Drilling Project, surface phase; investigation of an exceptional igneous system: Geophysical 

Research Letters, v. 18, p. 1513–1516.

Eicher, G.J., Jr., and Rounsefell, G.A., 1957, Effects of lake 

fertilization by volcanic activity on abundance of salmon: 

Oceanography, v. 2, no. 2, p. 70–78.

Evermann, B.W., 1914, Alaska fisheries and fur industries in 

1913: Washington, Department of Commerce, Bureau of 

Fisheries Document 797.

Fenner, C.N., 1920, The Katmai region, Alaska, and the great 

eruption of 1912: Journal of Geology, v. 28, p. 569–606.

Fenner, C.N., 1923, The origin and mode of emplacement 

of the great tuff deposit of the Valley of Ten Thousand 

Smokes: National Geographic Society, Contributed Technical Papers, Katmai Series, no.1, p. 1–74.

Fenner, C.N., 1925, Earth movements accompanying the 

Katmai eruption: Journal of Geology, v. 33, p. 116–139 and 

193–223.

Fenner, C.N., 1926, The Katmai magmatic province: Journal 

of Geology, v. 34, p. 673–772.

Fenner, C.N., 1929, The crystallization of basalts: American 

Journal of Science, v. 18, p. 225–253.

Fenner, C.N., 1930, Mount Katmai and Mount Mageik: 

Zeitschrift für Vulkanologie, Band 13, p. 1–24.

Fenner, C.N., 1931, The residual liquids of crystallizing magmas: Mineralogical Magazine, v. 22, p. 539–560.

Fenner, C.N., 1933, Pneumatolytic processes in the formation 

of minerals and ores, in Finch, J.W., and others, eds., The 

Committee on the Lindgren Volume, Ore deposits of the 

Western States: American Institute of Mining and Metallurgical Engineers, p. 58–106.

Fenner, C.N., 1934, Some magmatic problems: Journal of the 

Washington Academy of Sciences, v. 24, p. 113–124.

Fenner, C.N., 1937, A view of magmatic differentiation: Journal of Geology, v. 45, p. 158–168.

Fenner, C.N., 1938a, The phenomena of Falling Mountain: 

American Journal of Science, v. 35-A, p. 35–48.

Fenner, C.N., 1938b, Contact relations between rhyolite and 

basalt on Gardiner River, Yellowstone Park: Geological 

Society of America Bulletin, v. 49, p. 1441–1483.

Fenner, C.N., 1944, Rhyolite-basalt complex on Gardiner 

River, Yellowstone Park, Wyoming— a discussion: Geological Society of America Bulletin, v. 55, p. 1081–1096.

Fenner, C.N., 1950, The chemical kinetics of the Katmai eruption: American Journal of Science, v. 248, p. 593–627 and 

697–725.
236 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Fierstein, J., 2007, Explosive eruptive record in the Katmai 

region, Alaska Peninsula; an overview: Bulletin of Volcanology, v. 69, p. 469–509.

Fierstein, J., and Hildreth, W., 1992, The plinian eruptions of 

1912 at Novarupta, Katmai National Park, Alaska: Bulletin 

of Volcanology, v. 54, p. 646–684.

Fierstein, J., and Hildreth, W., 2001, Preliminary volcanohazard assessment for the Katmai Volcanic Cluster, Alaska: 

U.S. Geological Survey Open-File Report 00–489, 50 p., 

oversize plate in pocket.

Fierstein, J., and Hildreth, W., 2008, Kaguyak dome field and 

its Holocene caldera, Alaska Peninsula: Journal of Volcanology and Geothermal Research, v. 177, p. 340–366.

Fierstein, J., and Nathenson, M., 1992, Another look at the 

calculation of fallout tephra volumes: Bulletin of Volcanology, v. 54, p. 156–167.

Fierstein, J., and Nathenson, M., 1993, Reply to Comment by 

W.I. Rose: Bulletin of Volcanology, v. 55, p. 375–378.

Fierstein, J., and Wilson, C.J.N., 2005, Assembling an ignimbrite; compositionally defined eruptive packages in the 1912 

Valley of Ten Thousand Smokes ignimbrite, Alaska: Geological Society of America Bulletin, v. 117, p. 1094–1107. 

Fierstein, J., Houghton, B.F., Wilson, C.J.N., and Hildreth, 

W., 1997, Complexities of plinian fall deposition at vent; 

an example from the 1912 Novarupta eruption: Journal of 

Volcanology and Geothermal Research, v. 76, p. 215–227.

Fierstein, J., Hildreth, W., Hendley, J.W.II, and Stauffer, 

P.H., 1998, Can another great volcanic eruption happen in 

Alaska?: U.S. Geological Survey Fact Sheet 075-98, 2 p.

Filson, J., Simkin, T., and Leu, L., 1973, Seismicity of a caldera collapse; Galápagos Islands 1968: Journal of Geophysical Research, v. 78, p. 8591–8622.

Fisher, R.V., 1966, Mechanism of deposition from pyroclastic 

flows: American Journal of Science, v. 264, p. 350–363.

Fisher, R.V., and Heiken, G., 1982, Mt. Pelée, Martinique; 

May 8 and 20, 1902, pyroclastic flows and surges: Journal of Volcanology and Geothermal Research, v. 13, p. 

339–371.

Fliedner, M.M., and Klemperer, S.L., 2000, Crustal structure transition from oceanic arc to continental arc, eastern 

Aleutian Islands and Alaska Peninsula: Earth and Planetary 

Science Letters, v. 179, p. 567–579.

Fouqué, F., 1879, Santorin et ses eruptions: Paris, Masson, 

479 p.

Freundt, A., and Bursik, M., 1998, Pyroclastic flow transport mechanisms, in Freundt, A., and Rosi, M., eds., From 

magma to tephra: Elsevier, p. 173–245.

Freundt, A., and Rosi, M., eds., 1998, From magma to tephra: 

Elsevier, 318 p.

Fridrich, C.J., and Mahood, G.A., 1987, Compositional layers 

in the zoned magma chamber of the Grizzly Peak Tuff: 

Geology, v. 15, p. 299–303.

Gedney, L., Matteson, C., and Forbes, R.B., 1970, Seismic 

refraction profiles of the ash flow in the Valley of Ten Thousand Smokes, Katmai National Monument, Alaska: Journal 

of Geophysical Research, v. 75, p. 2619–2624.

George, R., Turner, S., Hawkesworth, C., Morris, J., Nye, 

C., Ryan, J., and Zheng, S.-H., 2003, Melting processes 

and fluid and sediment transport rates along the AlaskaAleutian arc from an integrated U-Th-Ra-Be isotope study: 

Journal of Geophysical Research, v. 108, no. B5, 2252, 

doi:10.102/2002JB001916; ECV, p. 6–1 to 6–25.

Gilbert, C.M., 1938, Welded tuff in eastern California: Geological Society of America Bulletin, v. 49, p. 1829–1862.

Gilbert, J.S., and Sparks, R.S.J., eds., 1998, The physics of 

explosive volcanic eruptions: Geological Society of London 

Special Publication 145, 186 p. 

Girolami, L., Druitt, T.H., Roche, O., and Khrabrykh, Z., 

2008, Propagation and hindered settling of laboratory ash 

flows: Journal of Geophysical Research, v. 113, B02202, 

doi: 10.1029/2007JB005074.

Goodliffe, A.M., Stone, D.B., Kienle, J., and Kasameyer, P., 

1991, The vent of the 1912 Katmai eruption; gravity and 

magnetic measurements: Geophysical Research Letters, v. 

18, p. 1521–1524.

Gourgaud, A., Fichaut, M., and Joron, J.-L., 1989, Magmatology of Mt. Pelée (Martinique, F.W.I.); I. Magma mixing 

and triggering of the 1902 and 1929 Pelean nuées ardentes: 

Journal of Volcanology and Geothermal Research, v. 38, p. 

143–169.

Griggs, R.F., 1917, The Valley of Ten Thousand Smokes; 

National Geographic Society explorations in the Katmai 

district of Alaska: National Geographic Magazine, v. 31, no. 

1, p. 12–68.

Griggs, R.F., 1918a, The recovery of vegetation at Kodiak: 

Ohio Journal of Science, v. 19, p. 1–57.

Griggs, R.F., 1918b, Are the Ten Thousand Smokes real volcanoes?: Ohio Journal of Science, v. 19, p. 97–116.

Griggs, R.F., 1918c, The great hot mud flow of the Valley of 

Ten Thousand Smokes: Ohio Journal of Science, v. 19, p. 

117–142.

Griggs, R.F., 1918d, The character of the eruption as indicated 

by its effects on vegetation: Ohio Journal of Science, v. 19, 

p. 173–209.
References 237

Griggs, R.F., 1918e, The eruption of Katmai: Nature, v. 101, 

no. 2547, p. 497–499.

Griggs, R.F., 1918f, The Valley of Ten Thousand Smokes: 

National Geographic Magazine, v. 33, no. 2, p. 115–169.

Griggs, R.F., 1920, The great Mageik landslide: Ohio Journal 

of Science, v. 20, p. 325–354.

Griggs, R.F., 1921, Our greatest National Monument: National 

Geographic Magazine, v. 40, p. 219–292.

Griggs, R.F., 1922, The Valley of Ten Thousand Smokes: 

Washington, D.C., National Geographic Society, 340 p.

Griggs, R.F., 1933, The colonization of the Katmai ash, a new 

and inorganic “soil”: American Journal of Botany, v. 20, p. 

92–113.

Griggs, R.F., 1961, We Two Together: Pacific Grove, California, The Boxwood Press, 320 p.

Grove, T.L., and Donnelly-Nolan, J.M., 1986, The evolution 

of young silicic lavas at Medicine Lake Volcano, California; implications for the origin of compositional gaps in 

calc-alkaline series lavas: Contributions to Mineralogy and 

Petrology, v. 92, p. 281–302.

Grove, T.L., Donnelly-Nolan, J.M., and Housh, T, 1997, Magmatic processes that generated the rhyolite of Glass Mountain, Medicine Lake volcano, California: Contributions to 

Mineralogy and Petrology, v. 127, p. 205–223.

Grunder, A.L., Laporte, D., and Druitt, T.H., 2005, Experimental and textural investigation of welding; effects of 

compaction, sintering, and vapor-phase crystallization in 

the rhyolitic Rattlesnake Tuff: Journal of Volcanology and 

Geothermal Research, v. 142, p. 89–104.

Hammer, C.U., 1977, Past volcanism revealed by Greenland 

Ice Sheet impurities: Nature, v. 270, p. 482–486.

Hammer, C.U., Clausen, H.B., and Dansgaard, W., 1980, 

Greenland ice sheet evidence of post-glacial volcanism and 

its climatic impact: Nature, v. 288, p. 230–235.

Hammer, J.E., Rutherford, M.J., and Hildreth, W., 2002, 

Magma storage prior to the 1912 eruption at Novarupta, 

Alaska: Contributions to Mineralogy and Petrology, v. 144, 

p. 144–162.

Harker, A., 1909, The natural history of igneous rocks: New 

York, MacMillan, 384 p.

Hay, R.L., 1959, Formation of the crystal-rich glowing avalanche deposits of St. Vincent, B.W.I.: Journal of Geology, 

v. 67, p. 540–562.

Hildreth, W., 1981, Gradients in silicic magma chambers—

implications for lithospheric magmatism: Journal of Geophysical Research, v. 86, p. 10153–10192.

Hildreth, W., 1983, The compositionally zoned eruption 

of 1912 in the Valley of Ten Thousand Smokes, Katmai 

National Park, Alaska: Journal of Volcanology and Geothermal Research, v. 18, p. 1–55.

Hildreth, W., 1987, New perspectives on the eruption of 1912 

in the Valley of Ten Thousand Smokes, Katmai National 

Park, Alaska: Bulletin of Volcanology, v. 49, p. 680–693.

Hildreth, W., 1991, The timing of caldera collapse at Mount 

Katmai in response to magma withdrawal toward Novarupta: Geophysical Research Letters, v. 18, p. 1541–1544.

Hildreth, W., and Drake, R.E., 1992, Volcan Quizapu, Chilean 

Andes: Bulletin of Volcanology, v. 54, p. 93–125.

Hildreth, W., and Fierstein, J., 1992, Hydrothermal explosion 

breccia emplaced during caldera collapse of Mount Katmai, 

Alaska, on 6 June 1912: Eos, American Geophysical Union 

Transactions, v. 73, no. 43, p. 635–636.

Hildreth, W., and Fierstein, J., 2000, Katmai volcanic cluster and the great eruption of 1912: Geological Society 

of America Bulletin [GSA Overview Paper], v. 112, p. 

1594–1620.

Hildreth, W., and Fierstein, J., 2003, Geologic map of the Katmai Volcanic Cluster, Katmai National Park, Alaska: U.S. 

Geological Survey Map I-2778, scale 1:63,360. Includes six 

15-minute quadrangles and 43-page pamphlet. 

Hildreth, W., and Moorbath, S., 1988, Crustal contributions to 

arc magmatism in the Andes of central Chile: Contributions 

to Mineralogy and Petrology, v. 98, p. 455–489.

Hildreth, W., and Wilson, C.J.N., 2007, Compositional zoning 

of the Bishop Tuff: Journal of Petrology, v. 48, p. 951–999.

Hildreth, W., Fierstein, J., Lanphere, M.A., and Siems, D.F., 

1999, Alagogshak volcano; a Pleistocene andesite-dacite 

stratovolcano in Katmai National Park, in Geologic Studies 

in Alaska by the U.S. Geological Survey 1997: U.S. Geological Survey Professional Paper 1614, p. 105–113.

Hildreth, W., Fierstein, J., Lanphere, M.A., and Siems, D.F., 

2000, Mount Mageik, a compound stratovolcano in Katmai 

National Park, in Geologic Studies in Alaska by the U.S. 

Geological Survey 1998: U.S. Geological Survey Professional Paper 1615, p. 23–34.

Hildreth, W., Fierstein, J., Lanphere, M.A., and Siems, D.F., 

2001, Snowy Mountain; a pair of small andesite-dacite stratovolcanoes in Katmai National Park, in Geologic Studies in 

Alaska by the U.S. Geological Survey 1999: U.S. Geological Survey Professional Paper 1633, p. 13–34.

Hildreth, W., Fierstein, J., Lanphere, M.A., and Siems, D.F., 

2002, Mount Griggs; a compositionally distinctive Quaternary stratovolcano behind the main volcanic line in Katmai 
238 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

National Park, in Studies by the U.S. Geological Survey in 

Alaska, 2000: U.S. Geological Survey Professional Paper 

1662, p. 87–112.

Hildreth, W., Fierstein, J., Lanphere, M.A., and Siems, D.F., 

2003a, Trident Volcano; four contiguous stratocones adjacent to Katmai Pass, Alaska Peninsula, in Studies by the 

U.S. Geological Survey in Alaska, 2001: U.S. Geological 

Survey Professional Paper 1678, p. 1–28. 

Hildreth, W., Lanphere, M.A., and Fierstein, J., 2003b, Geochronology and eruptive history of the Katmai Volcanic 

Cluster, Alaska Peninsula: Earth and Planetary Science Letters, v. 214, p. 93–114.

Hildreth, W., Fierstein, J., Siems, D.F., Budahn, J.R., and Ruíz, 

J., 2004, Rear-arc vs arc-front volcanoes in the Katmai 

reach of the Alaska Peninsula; a critical appraisal of acrossarc compositional variation: Contributions to Mineralogy 

and Petrology, v. 147, p. 243–275.

Hildreth, W., Fierstein, J., and Calvert, A.T., 2007, Blue 

Mountain and The Gas Rocks; rear-arc dome clusters on 

the Alaska Peninsula: U.S. Geological Survey Professional 

Paper 1739-A, p. 1–27.

Holmes, A., 1916, The origin of igneous rocks [Essay-review 

on The later stages of the evolution of the igneous rocks, by 

N.L. Bowen]: Science Progress, v. 11, p. 67–73.

Horn, S., and Schmincke, H.-U., 2000, Volatile emission 

during the eruption of Baitoushan Volcano (China/North 

Korea) ca. 969 AD: Bulletin of Volcanology, v. 61, p. 

537–555.

Houghton, B.F., Wilson, C.J.N., Fierstein, J., and Hildreth, 

W., 2004, Complex proximal deposition during the plinian 

eruptions of 1912 at Novarupta, Alaska: Bulletin of Volcanology, v. 66, p. 95–133.

Hubbard, B.R., 1932, Mush You Malemutes!: New York, The 

America Press, 179 p.

Hubbard, B.R., 1935, Cradle of the Storms: New York, Dodd, 

Mead and Co., 285 p.

Humphreys, W.J., 1913, Volcanic dust and other factors in the 

production of climatic changes and their possible relation 

to ice ages: Mount Weather Observatory Bulletin, v. 6, p. 

1–34.

Hussey, J.A., 1971, Embattled Katmai—a history of Katmai 

National Monument: San Francisco, National Park Service, 

457 p.

Iddings, J.P., 1892, The origin of igneous rocks: Bulletin of 

the Philosophical Society of Washington, v. 12, p. 89–213.

Iddings, J.P., 1909, 1913, Igneous rocks: New York, John 

Wiley, 2 volumes, 454 p, 685 p.

Iddings, J.P., 1914, The problem of volcanism: New Haven, 

Yale University Press, 273 p.

Iverson, R.M., and Vallance, J.W., 2001, New views of granular mass flows: Geology, v. 29, p. 115–118.

Jaggar, T.A., 1927, Eruption of Mageik in Alaska: The 

Volcano Letter, no. 147, Hawaiian Volcano Observatory 

[Implausible eruption report; see Hildreth and others, 2000]

Johnson, C.M., and Fridrich, C.J., 1990, Non-monotonic 

chemical and O, Sr, Nd, and Pb isotope zonations and 

heterogeneity in the mafic-to-silicic-composition magma 

chamber of the Grizzly Peak Tuff, Colorado: Contributions 

to Mineralogy and Petrology, v. 105, p. 677–690.

Jolly, A.D., and McNutt, S.R., 1999, Seismicity at the volcanoes of Katmai National Park, Alaska, July 1995-December 

1997: Journal of Volcanology and Geothermal Research, v. 

93, p. 173–190.

Jolly, A.D., Moran, S.C., McNutt, S.R., and Stone, D.B., 2007, 

Three-dimensional P-wave velocity structure derived from 

local earthquakes at the Katmai group of volcanoes, Alaska: 

Journal of Volcanology and Geothermal Research, v. 159, p. 

326–342.

Jones, P.D., Wigley, T.M.L., and Kelly, P.M., 1982, Variations 

in surface air temperatures, Part 1. Northern Hemisphere, 

1881-1980: Monthly Weather Review, v. 110, p. 59–70.

Kanamori, H., Mori, J., Hauksson, E., Heaton, T.H., Hutton, 

L.K., and Jones, L.M., 1993, Determination of earthquake 

energy release and ML using TERRAscope: Bulletin of the 

Seismological Society of America, v. 83, p. 330–346.

Keith, T.E.C., 1991a, Fossil and active fumaroles in the 1912 

eruptive deposits, Valley of Ten Thousand Smokes, Alaska: 

Journal of Volcanology and Geothermal Research, v. 45, p. 

227–254.

Keith, T.E.C., 1991b, Argillic alteration in the Novarupta 

vent region, Katmai National Park, Alaska: Geophysical 

Research Letters, v. 18, p. 1549–1552.

Keith, T.E.C., Thompson, J.M., Hutchinson, R.A., and White, 

L.D., 1992, Geochemistry of waters in the Valley of Ten 

Thousand Smokes region, Alaska: Journal of Volcanology 

and Geothermal Research, v. 49, p. 209–231.

Keller, A.S., and Reiser, H.N., 1959, Geology of the Mount 

Katmai area, Alaska: U.S. Geological Survey Bulletin 1058-

G, p. 261–298.

Kienle, J., 1970, Gravity traverses in the Valley of Ten Thousand Smokes, Katmai National Monument, Alaska: Journal 

of Geophysical Research, v. 75, p. 6641–6649.

Kienle, J., 1991, Depth of the ash flow deposit in the Valley 
References 239

of Ten Thousand Smokes, Katmai National Park, Alaska: 

Geophysical Research Letters, v. 18, p. 1533–1536.

Kienle, J., Swanson, S.E., and Pulpan, H., 1983, Magmatism 

and subduction in the eastern Aleutian arc, in Shimozuru, 

D., and Yokoyama, I., eds., Arc volcanism; physics and 

tectonics: Tokyo, Terra Scientific Publishing Company, p. 

191–224.

Kimball, H.H., 1913, The effect upon atmospheric transparency of the eruption of Katmai volcano: Monthly Weather 

Review (Weather Bureau, U.S. Dept. of Agriculture), v. 41, 

p. 153–159.

Klein, F.W., Koyanagi, R.Y., Nakata, J.S., and Tanigawa, 

W.R., 1987, The seismicity of Kilauea’s magma system, in

Decker, R.W., Wright, T.L., and Stauffer, P.H., eds., Volcanism in Hawaii: U.S. Geological Survey Professional Paper 

1350, p. 1019–1185.

Kleinman, J.W., and Iwatsubo, E.Y., 1991, A geodetic network 

in the Novarupta area, Katmai National Park, Alaska: Geophysical Research Letters, v. 18, p. 1517–1519.

Kleinman, J.W., Iwatsubo, E.Y., Power, J.A., and Endo, E.T., 

1997, Geodetic studies in the Novarupta area, Katmai 

National Park, Alaska, 1990 to 1995, in Dumoulin, J.A., and 

Gray, J.E., eds., Geologic studies in Alaska by the U.S. Geological Survey, 1995: U.S. Geological Survey Professional 

Paper 1574, p. 83–92.

Kodosky, L.G., 1989, Surface mercury geochemistry as a 

guide to volcanic vent structure and zones of high heat flow 

in the Valley of Ten Thousand Smokes, Katmai National 

Park, Alaska: Journal of Volcanology and Geothermal 

Research, v. 38, p. 227–242.

Kosco, D.G., 1981, Characteristics of andesitic to dacitic volcanism at Katmai National Park, Alaska: Berkeley, University of California, Ph.D. dissertation, 249 p.

Kozu, S., 1934, The great activity of Komagatake (Japan) in 

1929: Tschermaks Mineralogische und Petrographische Mitteilungen, v. 45, p. 133–174.

Kubota, S., and Berg, E., 1967, Evidence for magma in the 

Katmai volcanic range: Bulletin Volcanologique, v. 31, p. 

175–214.

Lacis, A., Hansen, J., and Sato, M., 1992, Climate forcing by 

stratospheric aerosols: Geophysical Research Letters, v. 19, 

no. 15, p. 1607–1610.

Lacroix, A., 1904, La Montagne Pelée et ses eruptions: Paris, 

Masson, 662 p., 30 plates.

Larsen, G., and Thorarinsson, S., 1978, H4

 and other acid 

Hekla tephras: Jökull, v. 27, p. 28–46.

LeBas, M.J., LeMaitre, R.W., Streckeisen, A., and Zanettin, 

B., 1986, A chemical classification of volcanic rocks based 

on the total alkali–silica diagram: Journal of Petrology, v. 

27, p. 745–750.

Lindgren, W., 1913, Mineral Deposits: New York, McGrawHill, 883 p.

Lipman, P.W., 1984, The roots of ash flow calderas in western 

North America; windows into the tops of granitic batholiths: 

Journal of Geophysical Research, v. 89, p. 8801–8841.

Lipman, P.W., and Mullineaux, D.R., eds., 1981, The 1980 

eruptions of Mount St. Helens, Washington: U.S. Geological Survey Professional Paper 1250, 844 p.

Lovering, T.S., 1957, Halogen-acid alteration of ash at Fumarole No. 1, Valley of Ten Thousand Smokes, Alaska: Geological Society of America Bulletin, v. 68, p. 1585–1604.

Lowenstern, J.B., 1993, Evidence for a copper-bearing fluid 

in magma erupted at the Valley of Ten Thousand Smokes, 

Alaska: Contributions to Mineralogy and Petrology, v. 114, 

p. 409–421.

Lowenstern, J.B., and Mahood, G.A., 1991, Petrogenesis of 

high-silica rhyolite on the Alaska Peninsula: Geophysical 

Research Letters, v. 18, p. 1565–1568.

Lowenstern, J.B., Wallmann, P.C., and Pollard, D.D., 1991, 

The West Mageik Lake sill complex as an analogue for 

magma transport during the 1912 eruption at the Valley of 

Ten Thousand Smokes, Alaska: Geophysical Research Letters, v. 18. p. 1569–1572.

Lu, Z., Fatland, R., Wyss, M., Li, S., Eichelberger, J., Dean, 

K., and Freymueller, J., 1997, Deformation of New Trident 

volcano measured by ERS-1 SAR interferometry, Katmai 

National Park, Alaska: Geophysical Research Letters, v. 24, 

no. 6, p. 695–698.

Lyons, W.B., Mayewski, P.A., Spencer, M.J., and Twickler, 

M.S., 1990, A northern hemisphere volcanic chemistry 

record (1869-1984) and climatic implications using a 

South Greenland ice core: Annals of Glaciology, v. 14, p. 

176–182.

Macdonald, R., Sparks, R.S.J., Sigurdsson, H., Mattey, D.P., 

McGarvie, D.W., and Smith, R.L., 1987, The 1875 eruption 

of Askja volcano, Iceland; combined fractional crystallization and selective contamination in the generation of rhyolitic magma: Mineralogical Magazine, v. 51, p. 183–202.

MacGregor, A,G., 1952, Eruptive mechanisms—Mt. Pelée, the 

Soufrière of St. Vincent (West Indies) and the Valley of Ten 

Thousand Smokes (Alaska): Bulletin of Volcanology, series 

2, v. 12, p. 49–74.

Mahood, G.A., 1990, Second reply to comment on “Evidence 

for long residence times of rhyolite magma in the Long 

Valley magma system; the isotopic record in the precaldera 

rhyolite lavas of Glass Mountain”: Earth and Planetary Science Letters, v. 99, p. 395–399.
240 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Marshall, P., 1935, Acid rocks of the Taupo-Rotorua volcanic 

district: Royal Society of New Zealand Transactions, v. 64, 

part 3, p. 323–366.

Martin, G.C., 1913, The recent eruption of Katmai volcano in 

Alaska: National Geographic Magazine, v. 24, p. 131–181.

Martin, G.C., 1921, Preliminary report on petroleum in 

Alaska: U.S. Geological Survey Bulletin 719, 83 p.

Martin, G.C., 1926, The Mesozoic stratigraphy of Alaska: U.S. 

Geological Survey Bulletin 776, 493 p.

Matumoto, T., 1971, Seismic body waves observed in the 

vicinity of Mount Katmai, Alaska, and evidence for the 

existence of molten chambers: Geological Society of 

America Bulletin, v. 82, p. 2905–2920.

Matumoto, T., and Ward, P.L., 1967, Microearthquake study of 

Mount Katmai and vicinity, Alaska: Journal of Geophysical 

Research, v. 72, p. 2557–2568.

 Miller, T.P., McGimsey, R.G., Richter, D.H., Riehle, J.R., 

Nye, C.J., Yount, M.E., and Dumoulin, J.A., 1998, Catalog 

of the historically active volcanoes of Alaska: U.S. Geological Survey Open File Report 98–582, 104 p.

Miyashiro, A., 1974, Volcanic rock series in island arcs and 

active continental margins:American Journal of Science, v. 

274, p. 321–355.

Moore, J.C., and 11 others, 1991, EDGE deep seismic reflection transect of the eastern Aleutian arc-trench layered lower 

crust reveals underplating and continental growth: Geology, 

v. 19, p. 420–424.

Moran, S.C., 2003, Multiple seismogenic processes for highfrequency earthquakes at Katmai National Park, Alaska; 

evidence from stress tensor inversions of fault-plane solutions: Bulletin of the Seismological Society of America, v. 

93, p. 94–108.

Morey, G.W., and Fenner, C.N., 1917, The ternary system 

H2O-K2SiO3-SiO2: Journal of the American Chemical Society, v. 39, no. 6, p. 1173–1229.

Mori, J., White, R.A., Harlow, D.H., Okubo, P., Power, J.A., 

Hoblitt, R.P., Laguerta, E.P., Lanuza, A., and Bautista, B.C., 

1996, Volcanic earthquakes following the 1991 climactic 

eruption of Mount Pinatubo; strong seismicity during a 

waning eruption, in Newhall, C.G., and Punongbayan, R.S., 

eds., 1996, Fire and Mud—eruptions and lahars of Mount 

Pinatubo, Philippines: Seattle, University of Washington 

Press, p. 339–350.

Motyka, R.J., 1977, Katmai caldera; glacier growth, lake rise, 

and geothermal activity, in Short Notes on Alaskan Geology—1977: Alaska Division of Geological and Geophysical 

Surveys, Geologic Report 55, p. 17–21.

Motyka, R.J., 1978, Surveillance of Katmai caldera and crater 

lake, Alaska: 1977: Final report on U.S. National Park 

Service purchase order PX 9100-7-1009: Geophysical 

Institute,University of Alaska, Fairbanks, 19 p.

Mullen, M.W., 1987, Petrology and provenance of sandstones 

of the Naknek Formation, Alaska Peninsula, in Hamilton, 

T.D., and Galloway, J.P., eds., Geological studies in Alaska 

by the U.S. Geological Survey during 1986: U.S. Geological Survey Circular 998, p. 86–90.

Muller, E.H., and Coulter, H.W., 1957a, Incipient glacier 

development within Katmai caldera, Alaska: Journal of 

Glaciology, v. 3, p. 13–17.

Muller, E.H., and Coulter, H.W., 1957b, The Knife Creek 

Glaciers of Katmai National Monument, Alaska: Journal of 

Glaciology, v. 3, p. 116–122.

Muller, E.H., Juhle, W., and Coulter, H.W., 1954, Current 

volcanic activity in Katmai National Monument: Science, v. 

119, p. 319–321.

National Park Service, 1975, Interview with eyewitnesses of 

Katmai eruption; transcript of taped interview with Harry 

and Jennie Kaiakokonok at King Salmon on 29 April 1975 

by Park Ranger Michael J. Tollefson: Katmai National Park 

archives, 28 p.

Newhall, C.G., and Punongbayan, R.S., eds., 1996, Fire and 

mud—eruptions and lahars of Mount Pinatubo, Philippines: 

Seattle, University of Washington Press, 1,126 p.

Newhall, C.G., Daag, A.S., Delfin, F.G., Jr., Hoblitt, R.P., 

McGeehin, J., Pallister, J.S., Regalado, M.T.M., Rubin, M., 

Tubianosa, B.S., Tamayo, R.A., Jr., and Umbal, J.V., 1996, 

Eruptive history of Mount Pinatubo, in Newhall, C.G., and 

Punongbayan, R.S., eds., 1996, Fire and mud—eruptions 

and lahars of Mount Pinatubo, Philippines: Seattle, University of Washington Press, p. 165–195.

Newman, S., and Lowenstern, J.B., 2002, VolatileCalc; a silicate melt-H2O-CO2 solution model written in Visual Basic 

for Excel: Computer Geoscience, v. 28, p. 597–604. 

Page, R. A., Biswas, N. N., Lahr, J. C., and Pulpan, H., 1991, 

Seismicity of continental Alaska, in Slemmons, D. B., 

Engdahl, E. R., Zoback, M. D., and Blackwell, D. D., eds., 

Neotectonics of North America: Boulder, Colorado, Geological Society of America, Decade Map Volume l, chapter 4.

Palais, J.M., and Sigurdsson, H., 1989, Petrologic evidence 

of volatile emissions from major historic and pre-historic 

volcanic eruptions, in Kidson, J.W., ed., Understanding 

climate change: American Geophysical Union Monograph 

52, p. 31–53.
References 241

Papike, J.J., 1992, The Valley of Ten Thousand Smokes, Katmai, Alaska; a unique geochemistry laboratory: Geochimica 

et Cosmochimica Acta, v. 56, p. 1429–1449.

Papike, J.J., Keith, T.E.C., Spilde, M.N., Galbreath, K.C., 

Shearer, C.K., and Laul, J.C., 1991a, Geochemistry and 

mineralogy of fumarolic deposits, Valley of Ten Thousand 

Smokes, Alaska; bulk chemical and mineralogical evolution 

of dacite-rich protolith: American Mineralogist, v. 76, p. 

1662–1673.

Papike, J.J., Keith, T.E.C., Spilde, M.N., Shearer, C.K., 

Galbreath, K.C., and Laul, J.C., 1991b, Major and trace element mass flux in fumarolic deposits, Valley of Ten Thousand Smokes, Alaska; rhyolite-rich protolith: Geophysical 

Research Letters, v. 18, p. 1545–1548.

Payne, A.L., and Eichelberger, J.C., 2009, Ti-in-quartz geothermometry of magmas from Katmai, Alaska; a combined 

cathodoluminescence/electron microprobe study: 6th 

Annual Workshop on Japan-Kamchatka-Alaska Subduction 

Processes, Scientific Program and Abstracts, University of 

Alaska, Fairbanks (June 22-26, 2009), p. 120.

Peacock, M.A., 1931, Classification of igneous rock series: 

Journal of Geology, v. 39, p. 54–67.

Perry, K.W., 1912, Extract from report of Capt. K.W. Perry, 

U.S.R.S., on board the Revenue Cutter “Manning”: 

National Geographic Magazine, v. 23, no. 8 (August 1912), 

p. 824–832.

Philpotts, A.R., Shi, J., and Brustman, C., 1998, Role of 

plagioclase crystal chains in the differentiation of partly 

crystallized basaltic magma: Nature, v. 395, p. 343–346.

Pinney, D.S., and Beget, J.E., 1991, Late Pleistocene volcanic 

deposits near the Valley of Ten Thousand Smokes, Katmai 

National Park, Alaska, in Reger, R.D., ed., Short notes on 

Alaskan geology 1991: Alaska Division of Geological & 

Geophysical Surveys Professional Report 111, p. 45–53.

Plafker, G., Moore, J.C., and Winkler, G.R., 1994, Geology of 

the southern Alaska margin, in Plafker, G., and Berg, H.C., 

eds., The Geology of Alaska: The Geology of North America, v. G-1, Geological Society of America, chapter 12.

Poreda, R.J., and Craig, H., 1989, Helium isotope ratios in 

circum-Pacific volcanic arcs: Nature,v. 338, p. 473–478.

Prejean, S, Haney, M., Pesicek, J., and Thurber, C., 2008, Seismicity and structure of the Katmai volcanic cluster, Alaska, 

revealed: American Geophysical Union, Fall Meeting, 

abstract V54A-07.

Punongbayan, R.S., Newhall, C.G., and Hoblitt, R.P., 1996, 

Photographic record of rapid geomorphic change at Mount 

Pinatubo, 1991-94, in Newhall, C.G., and Punongbayan, 

R.S., eds., Fire and Mud—eruptions and lahars of Mount 

Pinatubo, Philippines: Seattle, University of Washington 

Press, p. 21–66.

Pyle, D.M., 1989, The thickness, volume and grainsize of 

tephra fall deposits: Bulletin of Volcanology, v. 51, p. 

1–15.

Pyle, D.M., 1990, New estimates for the volume of the 

Minoan eruption, in Hardy, D.A., ed., Thera and the Aegean 

World III: London, The Thera Foundation, v. 2, p. 113–121, 

Ramdohr, P., 1962, Erzmikroskopische Untersuchungen 

an Magnetiten der Exhalationen im Valley of the 10000 

Smokes: Neues Jahrbuch fur Mineralogie, Monatshefte 

1962, p. 49–59.

Rampino, M.R., 1988, Volcanic winters: Annual Reviews of 

Earth and Planetary Sciences, v. 16, p. 73–99.

Rampino, M.R., and Self, S., 1984, Sulphur-rich volcanic 

eruptions and stratospheric aerosols: Nature, v. 310, p. 

677–679.

Rapp, R.P., and Watson, E.B., 1995, Dehydration melting of 

metabasalt at 8-32 kbar; implications for continental growth 

and crust-mantle recycling: Journal of Petrology, v. 36, p. 

891–931.

Ray, D.K., 1967, Geochemistry and petrology of the Mt. 

Trident andesites, Katmai National Monument, Alaska: 

Fairbanks, University of Alaska, Ph.D. dissertation, 198 p.

Reagan, M.K., Sims, K.W.W., Erich, J., Thomas, R.B., Cheng, 

H., Edwards, R.L., Layne, G., and Ball, L., 2003, Timescales of differentiation from mafic parents to rhyolite in 

North American continental arcs: Journal of Petrology, v. 

44, p. 1703–1726.

Reck, H., 1928, Deutung der vulkanischen Geschichte und 

der Calderabildung auf der Insel La Palma: Zeitschrift für 

Vulkanologie, Band 11, p. 217-243.

Reck, H., 1936, Santorin—der Werdegang eines Inselvulkans 

und sein Ausbruch 1925–1928: Berlin, Verlag von Dietrich 

Reimer, 3 volumes.

Riehle, J.R., Detterman, R.L., Yount, M.E., and Miller, J.W., 

1993, Geologic map of the Mount Katmai quadrangle 

and adjacent parts of the Naknek and Afognak quadrangles, Alaska: U.S. Geological Survey Map I-2204; scale 

1:250,000.

Rigg, G.B., 1914, The effects of the Katmai eruption on 

marine vegetation: Science, v. 40, no. 1032, p. 509–513.

Robin, C., Monzier, M., and Eissen, J.-P., 1994, Formation of 

the mid-fifteenth century Kuwae caldera (Vanuatu) by an 

initial hydroclastic and subsequent ignimbritic eruption: 

Bulletin of Volcanology, v. 56, p. 170–183.

Sayre, J.D., and Hagelbarger, P.R., 1919, A study of temperatures in the Valley of Ten Thousand Smokes: Ohio Journal 

of Science, v. 19, p. 249–278.
242 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Sbar, M.L., and Matumoto, T., 1972, Refraction profiles in the 

Valley of Ten Thousand Smokes, Katmai, Alaska: Bulletin 

Volcanologique, v. 35, p. 335–349.

Scott, W.E., Hoblitt, R.P., Torres, R.C., Self, S., Martinez, Ma. 

M.L., and Nillos, T., Jr., 1996, Pyroclastic flows of the June 

15, 1991, climactic eruption of Mount Pinatubo, in Newhall, 

C.G., and Punongbayan, R.S., eds., Fire and mud—eruptions and lahars of Mount Pinatubo, Philippines: Seattle, 

University of Washington Press, p. 545–570.

Self, S., and Rampino, M.R., 1981, The 1883 eruption of 

Krakatau: Nature, v. 294, p. 699–704.

Self, S., Rampino, M.R., Newton, M.S., and Wolff, J.A., 1984, 

Volcanological study of the great Tambora eruption of 1815: 

Geology, v. 12, p. 659–663.

Self, S., Gertisser, R., Thordarson, T., Rampino, M.R., and 

Wolff, J.A., 2004, Magma volume, volatile emissions, 

and stratospheric aerosols from the 1815 eruption of 

Tambora: Geophysical Research Letters, v. 31, L20608, 

doi:10.1029/2004GL020925.

Shearer, C.K., Papike, J.J., and Spilde, M.N., 1991, Pyroxene/

melt trace element behavior; a study of pyroxenes from 

the Valley of Ten Thousand Smokes, Alaska: Geophysical 

Research Letters, v. 18, p. 1557–1560.

Sheppard, D.S., Janik, C.J., and Keith, T.E.C., 1992, A comparison of gas geochemistry of fumaroles in the 1912 ashflow sheet and on active stratovolcanoes, Katmai National 

Park, Alaska: Journal of Volcanology and Geothermal 

Research, v. 53, p. 185–197.

Shipley, J.W., 1920, Some chemical observations on the volcanic emanations and incrustations in the Valley of 10,000 

Smokes, Katmai, Alaska: American Journal of Science, v. 

50, p. 141–153.

Sigurdsson, H., 1990, Evidence of volcanic loading of the 

atmosphere and climate response: Paleogeography, Paleoclimatology, and Paleoecology, v. 89, p. 277–289.

Sigurdsson, H., and Carey, S., 1989, Plinian and co-ignimbrite 

tephra fall from the 1815 eruption of Tambora volano: Bulletin of Volcanology, v. 51, p. 243–270.

Sigurdsson, H., and Sparks, R.S.J., 1981, Petrology of rhyolitic and mixed magma ejecta from the 1875 eruption of 

Askja, Iceland: Journal of Petrology, v. 22, p. 41–84.

Sigurdsson, H., Carey, S., and Espindola, J.M., 1984, The 

1982 eruptions of El Chichón volcano, Mexico; stratigraphy 

of pyroclastic deposits: Journal of Volcanology and Geothermal Research, v. 23, p. 11–37.

Sigurdsson, H., Carey, S., Cornell, W., and Pescatore, T., 1985, 

The eruption of Vesuvius in 79 A.D.: National Geographic 

Research, v. 1 (3), p. 332–387.

Sigurdsson, H., Carey, S., and Mandeville, C., 1991, Krakatau: 

National Geographic Research & Exploration, v. 7(3), p. 

310–327.

Simkin, T., and Fiske, R.S., 1983, Krakatau 1883—the volcanic eruption and its effects: Washington, Smithsonian 

Institution Press, 464 p.

Simkin, T., and Howard, K.A., 1970, Caldera collapse in the 

Galápagos Islands, 1968: Science, v. 169, p. 429–437.

Sisson, T.W., and Bacon, C.R., 1999, Gas-driven filter pressing in magmas: Geology, v. 27, p. 613–616.

Sisson, T.W., Ratajeski, K., Hankins, W.B., and Glazner, A.F., 

2005, Voluminous granitic magmas from common basaltic 

sources: Contributions to Mineralogy and Petrology, v. 148, 

p. 635–661.

Smith, N.R., and Griggs, R.F., 1932, The microflora of the ash 

of Katmai volcano with especial reference to nitrogen fixing 

bacteria: Soil Science, v. 34, p. 365–373.

 Smith, R.L., 1960, Ash flows: Geological Society of America 

Bulletin, v. 71, p. 795–842.

Snyder, G.L., 1954, Eruption of Trident volcano, Katmai 

National Monument, Alaska: U.S. Geological Survey Circular 318, 7 p.

Sparks, R.S.J., 1976, Grain size variations in ignimbrites and 

implications for the transport of pyroclastic flows: Sedimentology, v. 3, p. 147–188.

Sparks, R.S.J., Self, S., and Walker, G.P.L., 1973, Products of 

ignimbrite eruptions: Geology, v. 1, p. 115–118.

Sparks, R.S.J., Wilson, L., and Hulme, G., 1978, Theoretical 

modeling of the generation, movement, and emplacement of 

pyroclastic flows by column collapse: Journal of Geophysical Research, v. 83, p. 1727–1739.

Sparks, R.S.J., Wilson, L., and Sigurdsson, H., 1981, The 

pyroclastic deposits of the 1875 eruption of Askja, Iceland: 

Philosophical Transactions of the Royal Society of London, 

Series A, v. 299, p. 241–273.

Sparks, R.S.J., Bursik, M.I., Carey, S.N., Gilbert, J.S., Glaze, 

L.S., Sigurdsson, H., and Woods, A.W., 1997, Volcanic 

plumes: John Wiley and Sons, 574 p.

Sparks, R.S.J., Tait, S.R., and Yanev, Y., 1999, Dense welding 

caused by volatile resorption: Journal of the Geological 

Society, London, v. 156, p. 217–225.

Spera, F.J., Yuen, D.A., Greer, J.C., and Sewell, G., 1986, 

Dynamics of magma withdrawal from stratified magma 

chambers: Geology, v. 14, p. 723–726.
References 243

Sun, S.-s., and McDonough, W.F., 1989, Chemical and isotopic systematics of oceanic basalts; implications for mantle 

composition and processes, in Saunders, A.D., and Norry, 

M.J., eds., Magmatism in the Ocean Basins: Geological 

Society Special Publication 42, p. 313–345.

Sussman, D., 1985, Apoyo caldera, Nicaragua; a major Quaternary silicic eruptive center: Journal of Volcanology and 

Geothermal Research, v. 24, p. 249–282.

Symonds, R.B., Rose, R.I., and Reed, M.H., 1988, Contribution of Cl- and F-bearing gases to the atmosphere by volcanoes: Nature, v. 334, p. 415–418.

Thorarinsson, S., 1958, The Öraefajökull eruption of 1362: 

Reykjavik, Acta Naturalia Islandica, v. II, no. 2, 99 p.

Trop, J.M., Szuch, D.A., Rioux, M., and Blodgett, R.B., 

2005, Sedimentology and provenance of the Upper Jurassic 

Naknek Formation, Talkeetna Mountains, Alaska; bearings on the accretionary tectonic history of the Wrangellia 

composite terrane: Geological Society of America Bulletin, 

v. 117, p. 570–588.

Tsuya, H., 1930, The volcano Komagatake, Hokkaido, its 

geology, activity, and petrography: Bulletin of the Earthquake Research Institute, Tokyo Imperial University, v. 8, p. 

238–270.

Turner, S., Sandiford, M., Reagan, M., Hawkesworth, C., 

and Hildreth, W., 2010, Origins of large-volume, compositionally zoned volcanic eruptions; new constraints from 

U-series isotopes and numerical thermal modeling for the 

1912 Katmai-Novarupta eruption: Journal of Geophysical 

Research, v. 115, B12201, doi:10.1029/2009JB007195. 

Valentine, G., 1987, Stratified flow in pyroclastic surges: Bulletin of Volcanology, v. 49, p. 616–630.

Varekamp, J.C., Luhr, J.F., and Prestegaard, K.L., 1984, The 

1982 eruptions of El Chichón volcano (Chiapas, Mexico); 

character of the eruptions, ash-fall deposits, and gas phase: 

Journal of Volcanology and Geothermal Research, v. 23, p. 

39–68.

Verbeek, R.D.M., 1885, Krakatau: Batavia, 495 p.

Volz, F.E., 1975a, Distribution of turbidity after the 1912 Katmai eruption in Alaska: Journal of Geophysical Research, v. 

80, p. 2643–2648.

Volz, F.E., 1975b, Burden of volcanic dust and nuclear debris 

after injection into the stratosphere at 40o–58oN: Journal of 

Geophysical Research, v. 80, p. 2649–2652.

Walker, G.P.L., 1971, Grain-size characteristics of pyroclastic 

deposits: Journal of Geology, v. 79, p. 696–714.

Walker, G.P.L., 1973, Explosive volcanic eruptions—a new 

classification scheme: Geologische Rundschau, v. 62, p. 

431–446.

Walker, G.P.L., Heming, R.F., and Wilson, C.J.N., 1980, Lowaspect ratio ignimbrites: Nature, v. 283, p. 286–287.

Walker, G.P.L., Self, S., and Froggatt, P.C., 1981, The ground 

layer of the Taupo ignimbrite; a striking example of sedimentation from a pyroclastic flow: Journal of Volcanology 

and Geothermal Research, v. 10, p. 1–11. 

Walker, G.P.L., Self. S., and Wilson, L., 1984, Tarawera 1886, 

New Zealand—a basaltic plinian fissure eruption: Journal of 

Volcanology and Geothermal Research, v. 21, p. 61–78.

Wallace, P.J., 2005, Volatiles in subduction zone magmas; concentrations and fluxes based on melt inclusion and volcanic 

gas data: Journal of Volcanology and Geothermal Research, 

v. 140, p. 217–240.

Wallmann, P.C., Pollard, D.D., Hildreth, W., and Eichelberger, 

J.C., 1990, New structural limits on magma chamber 

locations at the Valley of Ten Thousand Smokes, Katmai 

National Park, Alaska: Geology, v. 18, p. 1240–1243.

Ward, P.L., and Matumoto, T., 1967, A summary of volcanic 

and seismic activity in Katmai National Monument, Alaska: 

Bulletin Volcanologique, v. 31, p. 107–129.

Ward, P.L., Pitt, A.M., and Endo, E., 1991, Seismic evidence 

for magma in the vicinity of Mt. Katmai, Alaska: Geophysical Research Letters, v. 18, p. 1537–1540.

Westrich, H.R., Eichelberger, J.C., and Hervig, R.L., 1991, 

Degassing of the 1912 Katmai magmas: Geophysical 

Research Letters, v. 18, p. 1561–1564.

Wilcox, R.E., 1999, The idea of magma mixing; history of 

a struggle for acceptance: Journal of Geology, v. 107, p. 

421–432.

Williams, H., 1941, Calderas and their origin: University of 

California Publications in Geological Sciences, v. 25, no. 6, 

p. 239–346.

Williams, H., Curtis, G., and Juhle, W., 1953, Mount Katmai 

and the Valley of Ten Thousand Smokes, Alaska (a new 

interpretation of the great eruptions of 1912): Proceedings 

of the 8th Pacific Science Congress (Quezon City, Philippines), v. II, p. 129.

Williams, S.N., and Self, S., 1983, The October 1902 plinian 

eruption of Santa Maria volcano, Guatemala: Journal of 

Volcanology and Geothermal Research, v. 16, p. 33–56.

Wilson, C.J.N., 1980, The role of fluidization in the emplacement of pyroclastic flows; an experimental approach: 

Journal of Volcanology and Geothermal Research, v. 8, p. 

231–249.

Wilson, C.J.N., 1984, The role of fluidization in the emplacement of pyroclastic flows, 2. experimental results and their 
244 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

interpretation: Journal of Volcanology and Geothermal 

Research, v. 20, p. 55–84.

Wilson, C.J.N., and Hildreth, W., 1997, The Bishop Tuff; new 

insights from eruptive stratigraphy: Journal of Geology, v. 

105, p. 407–439.

Wilson, C.J.N., and Walker, G.P.L., 1982, Ignimbrite depositional facies; the anatomy of a pyroclastic flow: Journal of 

the Geological Society of London, v. 139, p. 581–592.

Wilson, C.J.N., and Walker, G.P.L., 1985, The Taupo eruption, 

New Zealand, I. General aspects:Philosphical Transactions of the Royal Society of London, Series A, v. 314, p. 

199–228.

Wilson, L., 1976, Explosive volcanic eruptions III. Plinian 

eruption columns: Geophysical Journal of the Royal Astronomical Society, v. 45, p. 543–556.

Wilson, L., Sparks, R.S.J., and Walker, G.P.L., 1980, Explosive volcanic eruptions IV. The control of magma properties and conduit geometry on eruption column behavior: 

Geophysical Journal of the Royal Astronomical Society, v. 

63, p. 117–148.

Wilson, L., and Walker, G.P.L., 1987, Explosive volcanic eruptions—VI. Ejecta dispersal in plinian eruptions; the control of eruption conditions and atmospheric 

properties:Geophysical Journal of the Royal Astronomical 

Society, v. 89, p. 657–679.

Witter, J.B., and Self, S., 2007, The Kuwae (Vanuatu) eruption 

of AD 1452; potential magnitude and volatile release: Bulletin of Volcanology, v. 69, p. 301–318.

Wright, F.E., 1952, Memorial to Clarence Norman Fenner: 

Proceedings Volume of the Geological Society of America 

for 1951, p. 103–107.

Yoder, H.S., Jr., 1992, Norman L. Bowen (1887-1956), MIT 

Class of 1912, first predoctoral fellow of the Geophysical 

Laboratory: Earth Sciences History, v. 11, no. 1, p. 45–55.

Yoder, H.S., Jr., 1993, Timetable of petrology: Journal of Geological Education, v. 41, p. 447–489.

Yoder, H.S., Jr., 2004, The Geophysical Laboratory: Volume 

III of Centennial History of the Carnegie Institution of 

Washington, Cambridge University Press, 270 p.

Young, S.R., 1990, Physical volcanology of Holocene airfall 

deposits from Mt. Mazama, Crater Lake, Oregon: University of Lancaster (U.K.), Ph.D. dissertation, 299 p.

Zies, E.G., 1924a, The fumarolic incrustations in the Valley 

of Ten Thousand Smokes: National Geographic Society, 

Contributed Technical Papers, Katmai Series, No. 3, p. 

157–179.

Zies, E.G., 1924b, Hot springs of the Valley of Ten Thousand 

Smokes: Journal of Geology, v. 32, p. 303–310.

Zies, E.G., 1929, The Valley of Ten Thousand Smokes; I. The 

fumarolic incrustations and their bearing on ore deposition; 

II. The acid gases contributed to the sea during volcanic 

activity: National Geographic Society, Contributed Technical Papers, Katmai Series, No. 4, p. 1–79.
Chapter 15 Retrospective: Evolution of Ideas about the 1912 Eruption 245

Appendixes A–B–C
246 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Appendix A. Major-element chemical analyses of eruptive products, Novarupta 1912.

[The 10 major oxides (reported in weight percent) are normalized to H2O-free totals of 99.6 weight percent (allowing 0.4 weight percent for trace oxides and halogens); determinations by wavelength-dispersive x-ray fluorescence in U.S. Geological Survey laboratory at Lakewood, Colorado; supervised by J.E. Taggart. 

Precision and accuracy are discussed by Baedecker (1987) and Bacon and Druitt (1988). FeO* is total iron calculated as FeO. “Original total” is the volatilefree sum of the 10 oxides, as analyzed, before normalization, with total iron calculated as Fe2

O3. LOI is weight loss on ignition at 900°C. —, not analyzed.]

Sample SiO2 TiO2 Al2O3 FeO* MnO MgO CaO Na2O K2O P2O5 LOI Original 

total

Layer A

K-88 77.36 0.14 12.32 1.24 0.04 0.10 0.94 4.27 3.15 0.05 1.30 97.84

K-1000-a 77.48 0.14 12.18 1.30 0.04 0.18 0.85 4.21 3.16 0.05 1.69 97.31

K-1001 77.43 0.16 12.16 1.30 0.05 0.14 0.87 4.36 3.12 — 1.45 98.27

K-1065 77.53 0.16 12.16 1.28 0.05 0.13 0.85 4.29 3.14 — 1.64 98.27

K-1079-a 77.46 0.14 12.20 1.26 0.04 0.17 0.86 4.26 3.15 0.05 1.36 97.98

K-1190 77.45 0.17 12.18 1.29 0.05 0.13 0.85 4.33 3.14 — 1.51 98.12

Layer B

K-90-a 77.43 0.16 12.21 1.29 0.05 0.14 0.89 4.29 3.13 — 1.50 97.89

K-90-c 64.50 0.65 15.97 5.23 0.12 2.19 5.07 4.06 1.65 0.15 0.55 99.14

K-827-a 77.44 0.17 12.16 1.32 0.05 0.16 0.86 4.28 3.14 — 1.70 98.26

K-827-c 67.97 0.51 15.06 4.21 0.09 1.67 3.88 3.96 2.16 0.11 0.79 99.21

K-827-d 59.35 0.71 16.88 6.72 0.13 3.64 7.36 3.40 1.26 0.15 0.18 99.69

K-1008-c 63.31 0.66 16.05 5.81 0.12 2.63 5.48 3.77 1.63 0.14 0.50 99.27

K-1061-a 77.31 0.17 12.19 1.38 0.05 0.16 0.88 4.33 3.12 — 1.56 98.04

K-1061-c 60.26 0.70 16.57 6.64 0.13 3.52 6.79 3.50 1.35 0.15 0.35 99.17

K-1068-a 77.24 0.17 12.27 1.35 0.05 0.17 0.91 4.30 3.13 — 1.40 98.25

K-1068-a 77.37 0.14 12.25 1.29 0.04 0.19 0.88 4.25 3.14 0.05 1.62 97.58

K-1073 77.54 0.16 12.14 1.29 0.05 0.12 0.86 4.30 3.14 — 1.39 97.62

K-1074-a 77.38 0.14 12.22 1.29 0.04 0.17 0.92 4.25 3.14 0.05 1.23 97.82

K-1158-c 65.59 0.65 15.59 5.04 0.11 1.97 4.65 4.10 1.75 0.14 0.70 99.02

K-1160-a 77.11 0.16 12.56 1.32 0.05 0.13 0.86 4.28 3.12 — 1.25 98.30

K-1160-c 65.25 0.59 15.68 4.96 0.11 2.18 4.99 3.83 1.88 0.13 0.58 99.07

K-1194-a 77.36 0.17 12.27 1.30 0.05 0.13 0.88 4.31 3.12 — 1.19 98.23

K-1199-c 66.45 0.60 15.43 4.70 0.11 1.85 4.33 4.09 1.91 0.14 0.72 98.78

K-1199-d 60.10 0.70 16.56 6.74 0.13 3.59 6.78 3.52 1.32 0.14 0.25 99.26

K-1200-c 61.36 0.70 16.34 6.41 0.13 3.11 6.31 3.62 1.46 0.15 0.37 99.34

K-2466 59.11 0.71 16.82 6.67 0.13 3.73 7.29 3.63 1.29 0.22 0.34 98.39

K-2466-b 59.64 0.73 16.70 6.76 0.13 3.59 7.16 3.41 1.31 0.17 0.34 98.58

K-2488-a 61.53 0.72 16.22 6.30 0.13 3.12 6.21 3.66 1.50 0.20 1.10 98.62

K-2488-b 60.88 0.70 16.67 6.26 0.13 3.15 6.57 3.62 1.42 0.19 1.05 98.56

K-2488-c 61.49 0.72 16.19 6.32 0.13 3.16 6.19 3.66 1.52 0.22 1.15 98.03

K-2488-d 61.38 0.70 16.59 6.15 0.13 3.00 6.44 3.55 1.49 0.18 1.12 97.51

Layer C

K-45 64.57 0.71 15.65 5.37 0.12 2.14 4.97 4.20 1.74 0.14 — 96.83

K-45-glass 75.24 0.39 12.71 1.94 0.04 0.59 1.57 4.11 2.93 0.06 — 97.40

K-91 65.29 0.64 15.85 5.02 0.11 1.98 4.71 4.14 1.71 0.15 0.57 99.31

K-1270-a 65.81 0.64 15.45 5.08 0.11 1.91 4.57 4.09 1.78 0.14 2.09 97.32

K-1270-b 65.55 0.64 15.65 5.01 0.11 1.96 4.65 4.12 1.76 0.13 2.05 97.39

K-1270-c 65.54 0.65 15.59 5.06 0.11 1.97 4.69 4.09 1.75 0.14 2.32 97.10

K-1270-d 60.14 0.71 16.73 6.61 0.12 3.32 7.03 3.46 1.35 0.14 1.19 98.22

K-1270-e 63.17 0.68 15.92 5.95 0.12 2.62 5.63 3.75 1.60 0.14 1.93 97.59

K-1270-f 65.54 0.62 15.64 5.04 0.11 2.00 4.71 4.04 1.75 0.13 2.39 97.41

K-1271-a 65.51 0.64 15.74 5.03 0.11 1.89 4.68 4.10 1.76 0.14 2.09 97.46

K-1271-b 61.90 0.68 16.47 6.11 0.12 2.92 6.24 3.55 1.49 0.13 1.49 98.00

K-1271-c 65.31 0.65 15.69 5.09 0.11 2.02 4.78 4.08 1.73 0.14 2.04 97.76

K-1271-d 65.66 0.65 15.47 5.12 0.11 1.98 4.63 4.07 1.77 0.14 2.14 97.23
Appendix A 247

Sample SiO2 TiO2 Al2O3 FeO* MnO MgO CaO Na2O K2O P2O5 LOI Original 

total

K-1271-e 65.62 0.64 15.69 5.00 0.11 1.91 4.69 4.07 1.74 0.14 2.01 97.15

K-1271-f 65.12 0.65 15.54 5.34 0.11 2.12 4.86 4.01 1.72 0.14 2.06 97.43

K-1271-g 60.63 0.70 16.76 6.46 0.12 3.13 6.80 3.48 1.38 0.14 1.26 98.08

K-1271-h 65.73 0.68 15.61 5.04 0.11 1.90 4.46 4.11 1.81 0.15 2.09 96.97

K-1271-i 65.58 0.67 15.60 5.07 0.12 1.91 4.61 4.11 1.77 0.18 2.13 96.77

K-2002-a 61.53 0.72 16.37 6.28 0.12 3.00 6.22 3.71 1.46 0.17 1.43 97.93

K-2002-b 63.78 0.63 15.92 5.46 0.11 2.47 5.45 3.97 1.63 0.16 0.57 98.84

K-2620-a 65.28 0.65 15.83 5.10 0.11 1.97 4.69 3.99 1.75 0.21 1.95 97.50

K-2620-b 65.57 0.69 15.72 5.01 0.11 1.98 4.56 3.93 1.81 0.22 2.04 96.92

Layer D

K-39-r 64.94 0.68 15.84 5.31 0.12 1.92 4.85 3.98 1.82 0.12 — 96.27

K-55 64.83 0.70 15.90 5.26 0.12 2.16 5.11 3.66 1.71 0.14 — 96.51

K-94-a 77.48 0.16 12.22 1.26 0.05 0.13 0.84 4.30 3.14 — 1.36 98.59

K-94-b 65.10 0.65 15.77 5.14 0.12 2.03 4.76 4.19 1.68 0.15 0.67 99.14

K-94-c 65.47 0.64 15.77 4.92 0.11 1.93 4.68 4.20 1.73 0.15 0.61 99.18

K-1083-a 77.45 0.17 12.18 1.30 0.05 0.13 0.85 4.31 3.15 0.00 1.43 98.12

K-1083-c 65.57 0.65 15.69 4.99 0.11 1.92 4.62 4.16 1.74 0.15 0.52 99.04

K-1268-a 65.29 0.66 15.78 5.16 0.11 1.97 4.78 3.99 1.72 0.14 2.09 97.17

K-1268-b 59.92 0.72 16.55 6.84 0.13 3.45 7.11 3.42 1.30 0.14 1.26 98.07

K-1268-c 62.45 0.67 16.25 6.01 0.12 2.78 6.04 3.58 1.55 0.14 1.66 97.45

K-1268-d 65.27 0.62 15.88 5.06 0.11 1.97 4.85 3.99 1.71 0.14 2.06 97.21

K-1268-e 65.06 0.66 15.75 5.30 0.11 2.02 4.84 4.03 1.69 0.14 1.96 97.37

K-1268-f 62.04 0.70 16.13 6.37 0.12 3.00 6.17 3.41 1.52 0.14 2.11 96.97

K-1269-a 65.25 0.66 15.70 5.14 0.11 2.02 4.84 4.01 1.72 0.14 2.07 97.09

K-1269-b 65.59 0.64 15.60 5.08 0.11 1.96 4.72 3.98 1.79 0.13 2.23 97.04

K-1269-c 66.54 0.59 15.40 4.69 0.10 1.84 4.46 3.96 1.90 0.12 2.26 97.00

K-1269-d 65.16 0.64 15.75 5.14 0.11 2.06 4.86 4.02 1.73 0.13 2.27 97.37

K-1269-e 65.64 0.64 15.64 4.99 0.10 1.91 4.71 4.05 1.77 0.14 2.10 97.42

K-1269-f 65.79 0.64 15.50 5.03 0.11 1.92 4.64 4.07 1.77 0.13 2.12 97.04

Layer F

K-53 64.47 0.71 15.61 5.40 0.12 2.26 5.15 3.99 1.72 0.16 — 96.80

K-631-b 64.74 0.68 15.88 5.29 0.12 2.09 4.81 4.18 1.65 0.16 1.17 98.46

K-631-c 66.41 0.60 15.44 4.74 0.11 1.84 4.40 4.06 1.86 0.14 1.44 98.08

K-1267-a 63.10 0.67 16.13 5.83 0.12 2.63 5.73 3.65 1.59 0.13 1.65 97.54

K-1267-b 65.43 0.64 15.74 5.09 0.11 1.96 4.71 4.02 1.74 0.14 1.85 97.42

K-1267-c 62.95 0.67 16.04 5.91 0.12 2.74 5.84 3.63 1.56 0.13 1.63 97.46

K-1267-d 64.02 0.67 15.98 5.55 0.11 2.34 5.37 3.81 1.61 0.14 2.04 97.23

K-1267-e 63.91 0.66 15.88 5.66 0.11 2.47 5.46 3.65 1.68 0.13 1.77 97.24

K-1267-f 63.73 0.67 16.01 5.66 0.11 2.46 5.44 3.72 1.66 0.13 1.57 97.68

K-1267-g 65.52 0.67 15.69 5.07 0.11 1.95 4.56 4.08 1.78 0.16 1.94 97.13

Layer G

K-23 65.32 0.65 15.80 5.04 0.11 1.73 4.62 4.32 1.87 0.14 — 97.71

K-54 65.59 0.67 15.58 5.11 0.12 1.99 4.67 3.98 1.74 0.16 2.27 96.94

K-101 62.82 0.72 16.16 5.74 0.13 2.65 5.68 4.00 1.57 0.13 — 98.28

K-107-d 61.01 0.73 16.60 6.53 0.13 3.19 6.43 3.42 1.40 0.15 3.49 95.98

K-1266-a 63.64 0.62 15.78 5.66 0.11 2.57 5.62 3.75 1.71 0.13 0.30 99.07

K-1266-b 65.62 0.64 15.60 5.02 0.11 1.94 4.67 4.12 1.73 0.14 0.49 98.35

K-1266-c 65.13 0.64 15.78 5.10 0.11 1.99 4.86 4.15 1.70 0.14 0.39 99.10

K-1266-d 64.09 0.66 15.54 5.70 0.12 2.54 5.26 3.87 1.68 0.14 0.36 98.68

K-1266-e 63.77 0.66 15.99 5.50 0.11 2.28 5.40 4.13 1.60 0.14 0.34 99.02

Appendix A. Major-element chemical analyses of eruptive products, Novarupta 1912.—Continued
248 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Sample SiO2 TiO2 Al2O3 FeO* MnO MgO CaO Na2O K2O P2O5 LOI Original 

total

K-1266-f 63.42 0.65 15.75 5.76 0.11 2.69 5.71 3.71 1.69 0.13 0.38 98.63

Novarupta lava dome

K-16 76.86 0.17 12.53 1.43 0.05 0.02 0.95 4.35 3.21 0.02 — 97.68

K-17 56.54 0.81 17.37 8.34 0.15 4.13 8.06 3.19 0.90 0.10 0.05 99.19

K-18 65.06 0.71 15.50 5.37 0.12 1.95 4.85 4.22 1.68 0.15 — 99.76

K-22 76.54 0.23 12.52 1.52 0.06 0.08 1.14 4.38 3.10 0.04 — 99.02

K-622 77.44 0.15 12.13 1.28 0.04 0.18 0.89 4.29 3.14 0.05 0.36 98.52

K-623 55.55 0.75 17.88 7.72 0.14 4.31 9.22 2.97 0.92 0.13 0.40 99.15

K-2004 57.14 0.72 16.87 7.69 0.15 4.61 7.62 3.71 0.92 0.16 0.05 99.18

RLS-214 76.52 0.21 12.50 1.53 0.07 0.34 1.16 4.32 2.94 0.02 — 99.70

Pyroclastic flows

K-7A-r 77.66 0.13 12.34 1.24 0.04 0.12 0.83 4.00 3.20 0.03 2.55 96.07

K-7A-s 77.83 0.20 11.97 1.36 0.05 0.10 0.84 4.03 3.19 0.03 — 97.20

K-11-a-r 77.42 0.14 12.30 1.25 0.04 0.12 0.86 4.27 3.16 0.03 2.69 96.36

K-11-a-s 77.47 0.21 11.90 1.41 0.05 0.10 0.92 4.34 3.17 0.03 — 96.60

K-12-c 66.57 0.64 15.38 4.68 0.11 1.72 4.21 4.24 1.87 0.18 1.54 97.79

K-13-c 66.13 0.65 15.43 4.87 0.11 1.77 4.38 4.27 1.81 0.17 1.39 97.30

K-14-c 65.92 0.61 15.53 4.84 0.11 2.03 4.63 3.79 1.96 0.17 1.70 97.33

K-15-c 67.18 0.60 15.14 4.54 0.10 1.72 4.28 3.90 2.00 0.13 1.35 97.98

K-37-c 67.22 0.61 14.92 4.55 0.10 1.77 4.33 3.90 2.06 0.12 — 97.30

K-42-r 77.41 0.15 12.35 1.23 0.04 0.11 0.83 4.24 3.21 0.03 2.60 95.99

K-42-s 77.19 0.21 12.44 1.26 0.06 0.10 0.88 4.26 3.17 0.03 — 96.37

K-44-r 77.49 0.13 12.30 1.24 0.04 0.12 0.85 4.22 3.17 0.03 3.23 97.17

K-44-s 77.14 0.21 12.48 1.28 0.05 0.11 0.94 4.16 3.19 0.03 — 95.75

K-57 64.85 0.70 15.61 5.17 0.12 2.04 4.97 4.26 1.76 0.13 — 97.37

K-60 61.35 0.74 16.24 6.34 0.13 2.97 6.26 3.91 1.53 0.15 — 99.93

K-63-c 65.37 0.63 15.64 5.04 0.11 2.20 4.70 3.87 1.88 0.17 1.55 97.44

K-64-c 65.27 0.68 15.75 5.12 0.11 2.09 4.83 3.71 1.87 0.16 2.24 97.36

K-66-c 64.94 0.67 15.57 5.43 0.12 2.26 4.96 3.79 1.72 0.13 1.10 98.30

K-66-d 61.97 0.70 16.24 6.21 0.13 2.93 6.18 3.60 1.49 0.15 0.74 98.85

K-74-c 68.62 0.54 14.76 4.08 0.10 1.48 3.85 3.88 2.18 0.12 1.15 98.27

K-75-c 65.89 0.65 15.53 4.95 0.11 1.86 4.57 4.13 1.75 0.16 1.45 98.10

K-75-d 59.27 0.75 16.31 6.88 0.14 3.88 7.30 3.63 1.32 0.12 — 97.89

K-75-d-glass 66.81 0.72 15.61 4.40 0.10 1.56 3.91 4.17 2.15 0.17 — 98.72

K-75-e 66.56 0.64 15.31 4.80 0.11 1.72 4.31 4.19 1.80 0.15 1.39 97.90

K-76 65.35 0.66 15.62 5.16 0.12 1.93 4.77 4.12 1.71 0.15 1.62 97.84

K-78 65.52 0.70 15.40 5.32 0.12 2.07 4.70 3.89 1.72 0.15 1.65 97.68

K-82-c 65.61 0.65 15.24 5.24 0.12 2.16 4.73 3.87 1.83 0.14 1.44 97.83

K-82-d 60.44 0.73 16.41 6.72 0.14 3.40 6.82 3.44 1.37 0.15 1.10 98.21

K-100-a 77.72 0.18 11.95 1.30 0.05 0.11 0.85 4.25 3.16 0.03 2.53 96.91

K-100-c 64.02 0.68 15.69 5.57 0.12 2.51 5.31 3.93 1.61 0.15 1.24 98.08

K-100-d 57.93 0.72 16.59 7.27 0.14 4.62 7.80 3.22 1.17 0.14 0.49 99.04

K-108-c 65.86 0.66 15.39 5.06 0.12 1.94 4.60 4.06 1.76 0.15 1.30 97.99

K-108-d 64.93 0.67 15.62 5.29 0.12 2.09 5.03 4.02 1.68 0.15 1.41 97.87

K-113-c 65.35 0.67 15.54 5.22 0.12 2.06 4.77 4.00 1.73 0.15 1.02 98.21

K-113-d 60.00 0.74 16.61 6.77 0.14 3.40 6.94 3.55 1.29 0.15 — 99.23

K-119D-r 59.00 0.73 17.09 7.01 0.14 3.50 7.40 3.30 1.31 0.12 — 97.99

K-121 77.70 0.13 12.11 1.25 0.04 0.16 0.86 4.11 3.20 0.05 2.80 96.27

K-122 77.64 0.13 12.11 1.28 0.04 0.17 0.85 4.17 3.16 0.05 2.57 96.21

K-122-d 58.69 0.72 17.02 6.97 0.14 3.65 7.35 3.64 1.30 0.13 — 98.62

Appendix A. Major-element chemical analyses of eruptive products, Novarupta 1912.—Continued
Appendix A 249

Sample SiO2 TiO2 Al2O3 FeO* MnO MgO CaO Na2O K2O P2O5 LOI Original 

total

K-123-d-r 58.69 0.71 16.92 7.05 0.15 3.80 7.31 3.55 1.29 0.13 — 97.99

K-131-d-r 58.72 0.72 16.86 7.08 0.14 3.71 7.44 3.49 1.31 0.12 — 97.63

K-135-c 66.04 0.67 15.38 5.00 0.12 1.83 4.48 4.17 1.77 0.15 1.52 97.59

K-135-d 59.85 0.73 16.73 6.76 0.13 3.54 7.14 3.27 1.30 0.15 0.73 98.44

K-138-r 77.30 0.15 12.41 1.25 0.04 0.13 0.86 4.29 3.16 0.02 3.21 95.48

K-138-s 77.05 0.21 12.41 1.25 0.06 0.13 0.96 4.28 3.24 0.02 — 95.39

K-138-glass 77.25 0.17 12.34 1.27 0.05 0.36 0.81 4.08 3.24 0.03 — 97.65

K-139-r 77.37 0.15 12.34 1.20 0.04 0.11 0.86 4.29 3.19 0.03 3.04 96.03

K-139-s 77.22 0.21 12.33 1.25 0.06 0.09 0.93 4.20 3.28 0.03 — 95.56

K-162 64.52 0.66 16.11 5.16 0.10 2.27 4.79 4.08 1.78 0.13 — 98.24

K-182 65.52 0.67 15.77 5.03 0.09 2.11 4.56 3.91 1.80 0.13 — 97.70

K-184 59.47 0.72 16.77 6.81 0.12 3.56 7.03 3.63 1.35 0.15 — 99.70

K-200 62.52 0.70 16.06 5.98 0.12 2.79 5.90 3.86 1.52 0.14 1.29 97.98

K-202 64.78 0.67 15.86 5.23 0.11 2.08 4.75 4.20 1.77 0.14 — 98.09

K-203 60.63 0.73 16.57 6.63 0.13 3.25 6.64 3.49 1.39 0.14 1.22 98.57

K-581 59.69 0.72 16.56 6.84 0.13 3.46 7.13 3.61 1.31 0.14 0.43 98.62

K-1363 77.39 0.14 12.21 1.30 0.04 0.18 0.87 4.25 3.15 0.05 2.16 97.04

K-1364 77.46 0.14 12.21 1.27 0.04 0.16 0.86 4.25 3.15 0.05 2.16 97.08

K-1365 77.54 0.14 12.22 1.26 0.04 0.19 0.86 4.12 3.19 0.05 3.02 96.21

K-1365-r 77.55 0.18 12.11 1.28 0.05 0.12 0.83 4.30 3.15 0.02 2.60 96.96

K-1365-s 77.49 0.18 12.09 1.28 0.05 0.14 0.84 4.36 3.17 — 2.75 96.40

K-1365-t 77.61 0.18 11.99 1.28 0.05 0.11 0.84 4.35 3.16 0.03 2.59 96.58

K-1365-u 77.37 0.17 12.24 1.26 0.05 0.12 0.85 4.32 3.16 0.06 2.76 96.17

K-1490 67.72 0.57 15.10 4.37 0.10 1.59 3.91 4.08 2.03 0.13 1.61 97.65

K-1495 65.73 0.65 15.67 5.01 0.11 1.88 4.53 4.05 1.81 0.16 1.00 97.89

K-1511-c 60.08 0.74 16.77 6.78 0.13 3.28 6.76 3.53 1.36 0.16 0.86 97.98

K-1518-a 67.45 0.59 14.92 4.54 0.10 1.81 4.05 3.90 2.10 0.14 1.39 97.46

K-1518-b 59.20 0.72 16.73 6.90 0.13 3.90 7.23 3.36 1.29 0.15 0.87 98.25

K-1518-c 60.04 0.73 16.91 6.65 0.13 3.31 6.85 3.46 1.36 0.15 0.66 98.37

K-1518-d 59.99 0.74 16.55 6.91 0.13 3.58 6.75 3.41 1.38 0.15 0.78 98.11

K-1518-e 59.24 0.73 16.84 6.95 0.14 3.71 7.20 3.37 1.27 0.15 0.60 98.19

K-1519-b 59.23 0.70 16.46 6.96 0.14 4.36 6.99 3.32 1.29 0.14 0.95 98.03

K-1525 77.19 0.18 12.28 1.30 0.05 0.19 0.87 4.32 3.17 0.05 2.52 96.51

K-2582-a 66.09 0.59 15.44 4.71 0.11 2.03 4.60 3.91 1.94 0.19 1.60 97.99

K-2582-b 65.49 0.66 15.57 5.01 0.11 1.98 4.62 4.20 1.76 0.20 1.29 97.91

K-2582-c 66.73 0.61 15.16 4.67 0.11 1.78 4.15 4.21 1.97 0.20 1.54 97.19

K-2584-b 77.27 0.17 12.35 1.35 0.06 0.15 0.92 4.16 3.11 0.05 2.14 96.76

K-2588-c 77.18 0.18 12.45 1.36 0.05 0.14 0.94 4.15 3.10 0.05 2.14 96.89

K-2614-a 59.19 0.73 16.75 6.95 0.14 3.61 7.22 3.45 1.35 0.20 1.15 98.11

K-2614-b 59.47 0.70 16.44 7.03 0.14 3.81 6.96 3.45 1.40 0.20 1.46 98.14

K-2614-c 59.31 0.72 16.58 7.21 0.15 3.46 6.97 3.48 1.52 0.19 1.54 97.90

K-2614-d 58.80 0.71 16.20 7.34 0.15 4.16 7.26 3.38 1.40 0.19 1.45 97.73

K-2616-a 59.69 0.73 16.62 6.89 0.14 3.61 6.85 3.54 1.33 0.20 1.33 98.27

K-2616-b 59.50 0.73 16.57 6.88 0.14 3.66 7.07 3.53 1.33 0.20 1.11 98.60

K-2617-a 63.85 0.67 16.17 5.54 0.12 2.46 5.36 3.61 1.61 0.21 1.76 97.33

K-2617-b 77.60 0.17 12.27 1.28 0.05 0.12 0.80 4.03 3.18 0.09 3.00 95.75

K-2618-a 65.12 0.67 15.57 5.20 0.12 2.09 4.71 4.19 1.73 0.20 1.60 97.89

K-2618-b 64.28 0.68 15.76 5.43 0.12 2.24 5.06 4.19 1.63 0.20 1.54 97.93

K-2618-c 66.28 0.59 15.40 4.72 0.10 1.88 4.42 4.04 1.99 0.19 1.51 97.68

K-2618-d 59.57 0.73 16.75 6.84 0.13 3.49 7.02 3.53 1.33 0.20 1.02 98.14

K-2619 60.65 0.73 16.58 6.46 0.13 3.14 6.71 3.61 1.38 0.21 0.91 98.54

Appendix A. Major-element chemical analyses of eruptive products, Novarupta 1912.—Continued
250 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Sample SiO2 TiO2 Al2O3 FeO* MnO MgO CaO Na2O K2O P2O5 LOI Original 

total

K-2621-a 61.08 0.72 16.43 6.50 0.13 3.19 6.31 3.60 1.43 0.21 0.99 98.82

K-2621-b 65.94 0.63 15.67 4.81 0.11 1.84 4.46 4.14 1.78 0.20 2.24 97.27

K-2621-c 60.52 0.71 16.79 6.46 0.13 3.26 6.63 3.54 1.37 0.19 1.39 97.26

K-2622-a 65.52 0.66 15.62 5.03 0.11 1.88 4.54 4.28 1.75 0.20 1.34 98.20

K-2622-b 63.41 0.68 16.03 5.62 0.12 2.41 5.47 4.08 1.56 0.21 1.41 98.16

K-2623 65.20 0.64 15.86 5.15 0.11 2.19 4.84 3.60 1.80 0.19 1.86 97.31

K-2624 60.42 0.70 16.37 6.45 0.13 3.55 6.81 3.60 1.38 0.19 0.94 98.58

K-2625 67.11 0.56 15.13 4.33 0.10 1.76 4.26 4.09 2.08 0.18 1.08 98.10

K-2626-a 65.12 0.68 15.79 5.27 0.11 2.16 4.75 3.78 1.71 0.22 2.01 97.12

K-2626-b 60.86 0.75 16.49 6.72 0.13 3.30 6.42 3.31 1.41 0.21 1.25 97.87

K-2626-c 59.92 0.72 17.15 6.66 0.13 3.36 6.91 3.23 1.32 0.20 1.41 97.58

K-2626-d 64.06 0.70 15.99 5.59 0.12 2.35 5.16 3.80 1.62 0.22 1.60 97.17

K-2627-a 60.88 0.72 16.49 6.48 0.13 3.17 6.62 3.49 1.40 0.21 1.50 97.84

K-2627-b 59.34 0.74 16.53 6.94 0.14 3.73 7.17 3.52 1.28 0.20 0.94 98.19

K-2649-a 60.30 0.71 16.72 6.53 0.13 3.21 6.77 3.63 1.39 0.21 1.26 98.28

K-2649-b 61.22 0.71 16.37 6.34 0.13 3.10 6.39 3.70 1.44 0.20 0.87 98.59

K-2649-c 59.68 0.74 16.76 6.86 0.14 3.39 6.97 3.52 1.31 0.21 0.33 98.62

K-2650-a 67.44 0.58 14.60 4.67 0.10 1.93 4.17 3.81 2.11 0.19 1.60 98.22

K-2650-b 66.02 0.63 15.46 4.87 0.11 1.87 4.44 4.15 1.84 0.20 1.50 97.90

K-2651-a 66.31 0.65 15.48 4.82 0.11 1.81 4.39 3.89 1.94 0.20 1.90 97.18

K-2651-b 66.23 0.62 15.33 4.91 0.10 1.93 4.38 3.79 2.12 0.18 1.74 97.45

K-2651-c 60.25 0.72 16.78 6.61 0.13 3.29 6.76 3.49 1.37 0.20 1.41 97.37

K-2651-d 65.10 0.66 15.71 5.24 0.11 2.10 4.82 3.81 1.86 0.20 2.09 97.00

K-2651-e 61.05 0.72 16.49 6.36 0.13 3.16 6.46 3.56 1.47 0.18 1.57 97.24

K-2652-a 60.00 0.73 16.77 6.55 0.13 3.38 6.93 3.59 1.32 0.20 0.79 98.61

K-2652-b 59.68 0.72 16.58 6.78 0.14 3.56 7.10 3.57 1.28 0.20 0.34 99.14

K-2652-c 65.98 0.64 15.65 4.74 0.11 1.86 4.49 4.07 1.84 0.20 1.92 97.37

K-2652-d 65.70 0.65 15.56 5.01 0.11 1.93 4.56 4.07 1.79 0.20 1.99 97.32

K-2653-a 59.61 0.73 16.74 6.83 0.13 3.52 7.16 3.40 1.26 0.21 0.44 98.75

K-2653-b 59.47 0.74 16.70 6.90 0.14 3.65 7.12 3.38 1.27 0.21 0.21 98.98

K-2653-c 59.57 0.74 16.72 6.71 0.13 3.66 7.19 3.37 1.30 0.21 0.38 98.31

K-2653-d 60.72 0.73 16.41 6.61 0.13 3.32 6.61 3.45 1.40 0.21 0.33 98.90

K-2654-a 64.96 0.68 15.78 5.23 0.11 2.06 4.81 4.06 1.69 0.21 1.53 97.82

K-2654-b 64.87 0.66 15.93 5.20 0.11 2.10 4.86 3.99 1.66 0.22 3.20 96.27

K-2654-c 60.53 0.73 16.72 6.41 0.13 3.14 6.66 3.71 1.38 0.20 0.45 98.90

K-2654-d 59.96 0.72 16.77 6.65 0.13 3.36 6.97 3.51 1.33 0.20 0.45 99.17

K-2654-e 59.22 0.73 16.92 6.81 0.13 3.56 7.27 3.49 1.27 0.20 0.47 98.89

K-2654-f 64.99 0.66 15.88 5.13 0.12 2.05 4.80 4.09 1.67 0.21 4.36 94.71

Novarupta scoria falls

K-542 63.72 0.69 15.88 5.73 0.12 2.51 5.45 3.76 1.60 0.14 1.13 98.47

K-543 50.41 0.69 14.03 10.13 0.17 11.43 10.12 2.02 0.50 0.09 0.20 99.37

K-721 59.98 0.70 17.00 6.53 0.12 3.11 7.15 3.53 1.34 0.14 0.43 99.63

K-851 54.63 0.77 17.05 8.24 0.14 5.39 9.44 2.94 0.87 0.13 0.30 99.91

K-1594-a 61.63 0.71 16.47 6.13 0.12 2.96 6.25 3.69 1.48 0.17 0.87 98.58

K-1594-b 61.62 0.71 16.16 6.37 0.13 3.10 6.16 3.70 1.48 0.17 0.81 98.60

K-1595-a 62.28 0.70 16.33 6.03 0.12 2.84 5.96 3.62 1.53 0.18 1.05 98.19

K-1595-b 62.32 0.69 16.21 5.99 0.12 2.95 6.02 3.58 1.54 0.17 1.17 98.28

K-1595-c 61.44 0.70 16.70 6.11 0.12 2.99 6.40 3.52 1.44 0.18 1.19 98.39

K-1596-a 65.08 0.68 15.79 5.18 0.11 1.94 4.75 4.19 1.71 0.17 0.95 98.41

K-1596-b 61.73 0.75 15.96 6.57 0.13 3.11 6.04 3.61 1.52 0.18 1.02 98.58

K-1596-c 63.64 0.66 16.21 5.41 0.11 2.40 5.42 3.92 1.64 0.17 0.87 98.28

Appendix A. Major-element chemical analyses of eruptive products, Novarupta 1912.—Continued
Appendix A 251

Sample SiO2 TiO2 Al2O3 FeO* MnO MgO CaO Na2O K2O P2O5 LOI Original 

total

K-1596-d 61.19 0.72 16.33 6.29 0.13 3.20 6.50 3.63 1.45 0.17 0.61 98.81

K-1597-a 65.67 0.64 15.83 4.85 0.11 1.81 4.50 4.29 1.74 0.16 1.21 98.12

K-1597-b 65.77 0.67 15.65 4.92 0.11 1.86 4.46 4.21 1.77 0.17 1.35 97.98

K-1597-c 65.19 0.64 15.92 4.95 0.11 1.93 4.72 4.27 1.71 0.16 1.23 98.25

K-1597-d 65.11 0.65 15.82 5.10 0.11 2.05 4.77 4.08 1.75 0.17 1.09 98.21

K-2005 61.82 0.71 16.14 6.23 0.13 3.01 6.16 3.75 1.49 0.17 0.52 98.76

K-2012-a 61.81 0.69 16.56 5.98 0.12 2.87 6.16 3.75 1.49 0.17 0.80 98.62

K-2012-b 65.41 0.66 15.82 4.95 0.11 1.90 4.62 4.25 1.70 0.17 0.99 98.22

K-2013-a 61.65 0.72 16.37 6.21 0.12 2.98 6.16 3.72 1.49 0.18 0.91 98.55

K-2013-b 61.14 0.71 16.65 6.22 0.12 2.93 6.53 3.70 1.43 0.17 0.74 98.71

K-2013-c 61.84 0.71 16.22 6.36 0.13 3.08 6.03 3.56 1.48 0.18 0.99 98.25

K-2013-d 65.66 0.63 15.80 4.87 0.10 1.87 4.68 4.07 1.76 0.16 1.32 97.69

K-2013-e 65.37 0.65 15.69 5.01 0.11 1.92 4.67 4.29 1.72 0.17 1.08 98.42

K-2015-a 61.76 0.72 16.25 6.28 0.13 2.95 6.17 3.68 1.49 0.17 0.99 98.05

K-2015-b 65.32 0.65 15.82 5.00 0.11 1.93 4.68 4.21 1.70 0.17 1.21 98.19

K-2015-c 65.60 0.64 15.64 4.97 0.11 1.93 4.54 4.26 1.75 0.16 1.10 98.07

Blocks from Phantom Dome

K-20V 64.76 0.66 15.89 5.29 0.11 2.09 4.96 4.06 1.64 0.14 0.24 99.05

K-513-v 64.34 0.56 15.66 5.30 0.11 2.58 5.43 3.82 1.69 0.10 0.29 99.22

K-2022-a 65.57 0.65 15.61 5.00 0.11 1.95 4.62 4.17 1.75 0.15 0.66 98.89

K-2022-b 64.94 0.65 15.78 5.31 0.11 2.17 4.87 3.88 1.74 0.15 2.10 97.23

K-2022-c 66.65 0.69 15.40 4.38 0.11 1.99 4.37 4.15 1.78 0.09 0.79 98.33

K-2023-a 62.24 0.72 16.16 6.03 0.13 2.89 5.89 3.89 1.49 0.15 < 0.01 99.22

K-2023-b 64.05 0.66 15.86 5.50 0.12 2.36 5.24 3.98 1.69 0.14 0.20 99.21

K-2023-c 63.89 0.69 15.82 5.64 0.12 2.42 5.20 4.02 1.64 0.16 0.26 98.84

Appendix A. Major-element chemical analyses of eruptive products, Novarupta 1912.—Continued
252 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Sample Rb Sr Y Zr Ba Ni Cu Zn Cr

Layer A

K-1000-a 58 70 45 155 906 1 — 56 —

K-1001 65 64 42 153 877 2 <2 44 11

K-1065 67 64 44 155 863 <2 <2 42 10

K-1079-a 56 71 44 151 915 1 — 58 —

K-1190 64 62 42 153 938 3 <2 43 9

Layer B

K-90-a 65 64 42 153 915 4 3 41 11

K-90-c 34 261 36 154 538 4 9 64 12

K-827-a 66 64 43 151 842 4 3 42 11

K-827-c 48 207 30 152 613 5 10 57 13

K-827-d 27 307 24 114 348 7 13 73 30

K-1008-c 36 272 29 140 371 0 9 74 17

K-1061-a 67 66 44 155 814 2 2 43 11

K-1061-c 28 301 30 121 326 4 16 78 27

K-1068-a 59 73 44 156 909 1 — 63 —

K-1073 68 64 44 155 821 3 2 42 13

K-1074-a 59 73 44 151 882 1 — 61 —

K-1158-c 37 242 31 166 482 4 6 64 11

K-1160-c 43 247 30 150 519 5 7 60 18

K-1194-a 64 64 43 155 982 3 <2 41 9

K-1199-c 42 234 32 168 487 4 6 64 15

K-1199-d 28 301 30 123 350 6 13 79 37

K-1200-c 34 285 27 135 401 4 14 73 23

K-2466 27 301 23 117 446 — — — —

K-2466-b 25 304 24 117 445 — — — —

K-2488-a 31 276 26 136 508 — — — —

K-2488-b 29 290 26 133 485 — — — —

K-2488-c 24 269 27 138 487 — — — —

K-2488-d 29 280 23 126 505 — — — —

Layer C

K-91 36 248 31 165 508 4 7 59 10

K-1270-a 42 238 37 166 598 2 21 68 —

K-1270-b 38 246 35 171 582 2 15 65 —

K-1270-c 38 252 34 167 559 4 25 73 —

K-1270-d 33 309 31 130 452 4 29 80 13

K-1270-e 42 271 33 155 520 3 23 79 —

K-1270-f 36 244 37 161 586 1 23 72 —

K-1271-a 38 251 33 164 583 4 14 72 —

K-1271-b 34 284 30 143 489 6 32 79 —

K-1271-c 38 256 36 166 567 4 18 74 —

Appendix B. Trace-element chemical analyses of eruptive products, Novarupta 1912.

[Determinations (in parts per million) by energy-dispersive x-ray fluorescence in U.S. Geological Survey laboratory at Lakewood, Colorado; D.F. Siems, 

analyst. Precision and accuracy are discussed by Baedecker (1987) and Bacon and Druitt (1988). —, not analyzed. Additional data are given by Turner and 

others (2010).]
Appendix B 253

Sample Rb Sr Y Zr Ba Ni Cu Zn Cr

K-1271-d 36 249 36 170 567 8 23 77 —

K-1271-e 40 250 35 166 564 5 20 66 —

K-1271-f 35 251 36 159 549 6 22 75 —

K-1271-g 30 299 29 130 473 8 31 84 3

K-1271-h 31 229 33 167 — — — — —

K-1271-i 35 236 30 163 571 — — — —

K-2002-a 32 273 29 134 — — — — —

K-2002-b 29 254 32 139 — — — — —

K-2620-a 36 244 31 161 568 3 22 82 8

K-2620-b 37 236 32 167 481 4 14 90 8

Layer D

K-39-r 36 243 30 161 578 2 12 54 5

K-55 38 238 30 166 574 4 18 70 15

K-94-a 66 63 44 155 1040 3 3 40 9

K-94-b 36 253 32 160 543 2 5 64 8

K-94-c 37 243 30 160 608 4 8 59 9

K-1083-a 67 64 45 155 675 3 <2 47 10

K-1083-c 38 245 31 162 526 5 7 63 8

K-1268-a 37 249 36 162 565 1 58 64 —

K-1268-b 31 313 31 125 440 2 64 72 1

K-1268-c 38 274 34 145 484 1 66 74 3

K-1268-d 38 254 38 165 571 1 50 69 0

K-1268-e 36 253 37 162 560 2 47 75 0

K-1268-f 36 280 33 138 487 1 69 80 10

K-1269-a 39 249 34 159 545 4 23 71 —

K-1269-b 42 251 36 167 581 4 16 72 —

K-1269-c 40 238 34 158 605 5 23 75 —

K-1269-d 36 256 34 163 564 9 23 76 —

K-1269-e 37 251 38 167 572 3 23 71 —

K-1269-f 38 243 37 170 577 4 21 74 —

Layer F

K-53 35 251 29 154 526 8 29 64 9

K-631-b 34 254 36 153 432 <2 8 72 10

K-631-c 39 227 32 151 467 5 9 65 10

K-1267-a 40 278 35 152 525 2 25 74 —

K-1267-b 38 250 34 163 569 1 28 69 —

K-1267-c 34 274 33 148 543 1 25 79 —

K-1267-d 36 263 33 154 529 2 34 75 —

K-1267-e 42 265 32 157 534 2 25 74 —

K-1267-f 38 260 32 155 533 3 29 75 —

K-1267-g 33 234 31 164 — — — — —

Layer G

K-23 38 259 32 161 554 10 14 61 11

Appendix B. Trace-element chemical analyses of eruptive products, Novarupta 1912.—Continued
254 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Sample Rb Sr Y Zr Ba Ni Cu Zn Cr

K-54 35 252 29 161 537 8 15 61 5

K-101 33 273 28 151 514 — — — —

K-107-d 29 279 32 137 535 16 13 74 18

K-1266-a 42 273 34 151 587 1 7 68 —

K-1266-b 36 245 36 168 582 2 2 73 —

K-1266-c 35 257 34 164 563 1 3 73 —

K-1266-d 36 254 33 158 555 2 5 76 1

K-1266-e 36 270 35 160 546 1 3 74 —

K-1266-f 42 266 34 151 562 3 9 73 —

Novarupta lava dome

K-16 60 75 43 158 964 — — — —

K-17 18 315 22 102 339 — — — —

K-18 33 257 32 164 558 14 14 51 —

K-18-s 39 262 33 163 568 6 16 58 12

K-22 69 96 42 160 917 — 4 41 9

K-622 60 76 43 159 971 — — — —

K-623 19 359 21 101 311 — — — —

K-623-r 17 369 19 93 — — — — —

K-2004 16 333 22 86 — — — — —

RLS-214 66 86 48 157 952 — — 31 —

Pyroclastic flows

K-7A-r 79 91 48 165 925 2 3 44 6

K-11-a-r 69 84 48 162 924 1 1 37 6

K-12-c 31 217 29 158 608 — — — —

K-13-c 33 230 33 174 625 — — — —

K-14-c 38 239 30 160 649 — — — —

K-15-c 50 245 36 176 648 6 11 50 7

K-37-c 50 218 32 183 691 4 22 56 5

K-42-r 63 75 41 156 915 — 8 44 4

K-44-r 63 76 42 158 944 — — — —

K-57 36 258 30 160 548 4 10 55 6

K-60 31 290 25 141 523 13 26 55 —

K-63-c 34 238 30 156 625 — — — —

K-64-c 37 229 31 157 511 7 18 139 11

K-66-c 40 255 30 161 562 5 2 60 12

K-66-d 32 282 27 142 499 7 9 65 21

K-74-c 47 213 29 165 694 3 6 49 4

K-75-c 34 249 32 165 580 8 16 60 7

K-75-d 25 306 25 124 431 — — — —

K-75-e 38 248 32 170 573 2 16 53 5

K-76 35 258 32 164 569 6 17 64 8

K-78 33 246 34 162 565 6 14 61 18

K-82-c 37 246 30 165 615 6 20 53 6

Appendix B. Trace-element chemical analyses of eruptive products, Novarupta 1912.—Continued
Appendix B 255

Sample Rb Sr Y Zr Ba Ni Cu Zn Cr

K-82-d 35 299 27 127 462 11 26 84 24

K-100-a 64 77 41 154 903 — 1 43 4

K-100-c 34 267 30 152 506 4 15 60 14

K-100-d 24 307 23 104 319 27 33 74 54

K-108-c 40 250 30 165 577 7 22 61 7

K-108-d 32 261 29 156 520 8 17 66 8

K-113-c 42 246 32 167 572 4 9 63 11

K-113-d 26 290 25 128 454 18 18 63 —

K-119D-r 25 308 25 119 420 — — — —

K-121 62 66 42 150 861 1 — 45 —

K-122 54 64 39 146 866 1 — 61 —

K-122-d 22 308 25 124 436 — — — —

K-122-d-r 27 315 25 119 — — — — —

K-123-d-r 30 299 26 131 447 — — — —

K-131-d-r 26 322 25 120 425 — — — —

K-135-c 38 243 34 164 585 5 16 61 10

K-135-d 29 307 27 120 417 9 35 71 32

K-139-r 65 73 39 158 914 2 5 28 4

K-162 41 252 36 170 597 5 24 55 6

K-182 28 242 29 166 592 12 14 41 —

K-184 28 301 26 138 500 12 10 54 —

K-200 29 272 29 148 511 — — — —

K-202 33 242 30 164 581 13 14 54 —

K-203 29 294 27 138 477 — — — —

K-581 24 308 24 128 454 — — — —

K-1363 56 66 44 150 917 1 — 61 —

K-1364 52 68 39 141 878 1 — 70 —

K-1365 54 67 41 147 900 1 — 58 —

K-1365-r 63 70 39 155 919 2 3 40 7

K-1365-u 58 66 39 154 952 — — — —

K-1490 35 205 33 161 — — — — —

K-1495 35 247 36 167 — — — — —

K-1518-a 42 213 35 176 — — — — —

K-1525 58 69 46 156 — — — — —

K-2582-a 38 234 30 166 661 — — — —

K-2582-b 31 242 31 163 602 — — — —

K-2582-c 36 216 34 171 642 — — — —

K-2584-b 63 78 39 157 946 — — — —

K-2588-c 59 77 43 159 952 — — — —

K-2614-a 29 303 24 118 382 6 23 109 29

K-2614-b 29 292 25 120 436 9 24 93 35

K-2614-c 29 298 30 119 452 8 27 113 26

K-2614-d 28 292 23 115 394 7 26 96 55

Appendix B. Trace-element chemical analyses of eruptive products, Novarupta 1912.—Continued
256 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Sample Rb Sr Y Zr Ba Ni Cu Zn Cr

K-2616-a 28 300 29 121 514 12 27 84 23

K-2616-b 28 304 29 121 446 11 25 87 28

K-2617-a 32 259 34 146 464 5 15 67 13

K-2617-b 65 61 43 154 846 3 3 44 9

K-2618-a 38 247 32 165 541 5 17 63 11

K-2618-b 33 254 35 153 665 2 21 62 10

K-2618-c 44 232 30 166 656 3 18 58 11

K-2618-d 28 307 30 122 445 5 30 76 22

K-2619 29 297 31 128 464 3 28 70 22

K-2621-a 31 287 32 134 580 7 26 72 16

K-2621-b 39 253 30 164 797 4 19 47 8

K-2621-c 29 293 30 126 497 6 37 75 24

K-2622-a 37 240 32 165 611 3 20 60 9

K-2622-b 32 270 34 148 637 2 10 61 13

K-2623 40 232 30 160 631 8 11 61 12

K-2624 28 294 29 127 520 11 23 76 30

K-2625 46 223 31 171 621 <2 5 56 12

K-2626-a 36 241 31 159 525 2 19 74 12

K-2626-b 29 289 31 129 456 7 25 77 20

K-2626-c 28 302 24 120 442 8 29 76 22

K-2626-d 32 260 35 149 469 2 19 64 14

K-2627-a 30 287 25 127 497 6 24 91 21

K-2627-b 27 300 24 117 431 6 26 77 32

K-2649-a 30 300 26 123 385 4 25 90 20

K-2649-b 31 286 31 132 498 7 29 75 20

K-2649-c 28 307 29 121 429 5 24 74 19

K-2650-a 50 214 32 171 541 3 15 59 14

K-2650-b 42 232 31 172 727 3 17 45 9

K-2651-a 39 235 33 173 501 4 13 61 11

K-2651-b 43 223 31 164 522 5 8 69 11

K-2651-c 29 298 30 126 406 7 12 92 26

K-2651-d 38 242 31 159 509 4 7 77 11

K-2651-e 29 285 30 130 406 7 9 96 19

K-2652-a 29 302 26 126 401 5 7 73 25

K-2652-b 28 303 25 121 455 7 8 79 25

K-2652-c 37 233 31 162 440 2 5 64 9

K-2652-d 38 235 32 164 493 5 8 63 10

K-2653-a 28 313 25 123 506 7 13 80 26

K-2653-b 27 308 30 124 500 7 8 76 29

K-2653-c 27 305 30 121 425 5 6 77 32

K-2653-d 31 296 31 131 542 4 14 74 22

K-2654-a 36 245 31 159 503 5 19 64 10

Appendix B. Trace-element chemical analyses of eruptive products, Novarupta 1912.—Continued
Appendix B 257

Sample Rb Sr Y Zr Ba Ni Cu Zn Cr

K-2654-b 37 254 31 156 532 3 14 51 9

K-2654-c 29 301 31 130 537 6 21 74 19

K-2654-d 28 310 32 127 508 6 21 70 23

K-2654-e 27 315 25 118 458 8 26 75 28

K-2654-f 37 253 31 162 607 5 15 50 8

Novarupta scoria falls

K-542 31 263 31 155 525 — — — —

K-543 13 299 16 66 186 — — — —

K-721 29 309 31 125 445 3 61 75 5

K-851 23 341 25 88 268 11 9 73 61

K-851-r 16 349 21 87 — — — — —

K-1594-a 27 286 29 133 — — — — —

K-1594-b 31 271 30 136 — — — — —

K-1595-a 32 273 30 142 — — — — —

K-1595-c 28 289 27 132 — — — — —

K-1596-a 30 245 33 157 — — — — —

K-1596-c 33 258 29 152 — — — — —

K-1596-d 31 286 29 137 — — — — —

K-1597-a 33 242 31 160 — — — — —

K-1597-b 35 236 31 161 — — — — —

K-1597-c 30 249 33 147 — — — — —

K-1597-d 36 242 35 160 — — — — —

K-2005 29 270 29 133 — — — — —

K-2012-a 31 276 30 137 — — — — —

K-2012-b 29 250 30 161 — — — — —

K-2013-a 27 279 30 132 — — — — —

K-2013-b 26 278 24 131 — — — — —

K-2013-c 29 277 27 135 — — — — —

K-2013-d 31 242 31 155 — — — — —

K-2013-e 32 242 33 160 — — — — —

K-2015-a 30 271 27 131 — — — — —

K-2015-b 28 240 30 159 — — — — —

K-2015-c 32 231 32 157 — — — — —

Blocks from Phantom dome

K-20V 29 263 29 162 569 — — — —

K-513-v 33 256 29 133 577 — — — —

K-2022-a 30 233 31 163 — — — — —

K-2022-b 34 246 32 150 — — — — —

K-2022-c 30 233 31 166 — — — — —

K-2023-a 25 279 26 143 — — — — —

K-2023-b 31 256 32 157 — — — — —

K-2023-c 33 254 30 150 — — — — —

Appendix B. Trace-element chemical analyses of eruptive products, Novarupta 1912.—Continued
Sample Ba Co Cr Cs Hf Rb Sb Ta Th U Zn Zr Sc La Ce Nd Sm Eu Gd 

Layer A K-88-r 897 0.6 0.6 2.40 4.80 62 — 0.40 5.1 2.30 42 185 7.2 19.0 40.0 24 4.90 0.780 5.9 

K-88-s 984 0.7 1.4 2.60 5.00 65 — 0.49 5.6 2.10 45 248 7.4 19.0 41.0 21 5.30 0.780 5.7 

Layer D K-39-r 508 10.6 7.9 1.50 4.20 37 — 0.27 2.9 1.40 72 170 15.9 13.0 26.0 19 3.50 0.980 4.9 

K-39-s 600 11.3 8.2 1.60 4.40 41 — 0.35 3.3 1.80 75 200 16.7 13.0 27.0 18 3.80 1.000 4.5 

K-55 634 116.0 8.2 1.53 4.90 38.9 0.47 0.71 3.4 1.52 77.3 154 17.3 13.2 31.5 18.5 5.04 1.100 5.5 

Layer F K-53 566 68.6 12.2 1.36 4.49 49.1 0.52 0.48 3.1 1.40 79.0 — 20.4 12.6 29.9 16.6 4.84 1.120 4.7 

Layer G K-23 570 10.5 7.5 1.40 4.10 36 — 0.41 3.1 1.50 72.0 120 16.5 13.0 27.0 16 3.60 1.020 3.1 

Novarupta lava dome K-16-r 914 0.6 0.9 2.60 4.90 64 — 0.42 5.4 2.30 46 161 7.4 19.0 40.0 22.0 4.90 0.790 6.8 

K-16-s 995 0.6 2.5 2.60 5.00 69 — 0.49 5.6 3.00 44 155 7.3 19.0 40.0 22.0 5.30 0.800 6.2 

K-17 360 23.6 27.9 0.72 2.50 23 0.32 0.16 1.4 0.63 84 140 29.3 6.9 14.0 8.6 2.92 0.903 — 

K-622 991 0.7 3.5 2.57 5.12 59.9 0.89 0.41 5.2 2.29 40.4 141 7.6 18.2 41.4 23.3 5.56 0.855 6.5 

K-623 354 22.5 43.5 0.68 2.41 19.9 0.36 0.19 1.9 0.79 83.0 115 31.3 7.6 16.7 11.0 3.05 0.932 3.5 

RLS-214 940 1.6 1.6 2.30 4.90 64 1.20 0.44 5.0 2.10 37 178 8.4 19.0 39.0 20 5.60 0.780 6.1 

Pyroclastic flows K-60 505 35.0 16.7 2.00 3.48 36 2.15 0.33 2.9 1.20 88.8 110 21.0 10.8 23.2 14 3.98 0.970 — 

K-113-d 470 92.1 27.0 1.10 3.10 27 0.36 0.56 2.8 1.30 72 120 23.6 10.2 21.7 14 3.76 0.915 — 

K-119D-r 469 18.1 36.0 1.10 3.20 28 — 0.30 2.8 1.20 80 180 23.8 10.0 21.0 14 3.20 0.890 3.6 

K-119D-s 467 17.8 35.2 1.00 3.10 30 — 0.27 2.9 1.50 84 170 24.1 10.0 20.0 16 3.20 0.910 4.2 

K-122-d 462 19.3 33.2 1.10 3.20 34 — 0.26 3.0 1.40 86 220 24.3 11.0 22.0 16 3.20 0.930 4.1 

K-123-d-r 522 17.8 28.3 1.10 3.40 28 — 0.30 3.0 1.50 85 180 23.6 11.0 23.0 18 3.20 0.910 4.0 

K-123-d-s 501 18.0 27.6 1.40 3.50 20 — 0.40 2.9 1.30 90 110 25.0 11.0 24.0 14 3.80 0.970 4.1 

K-123-d-t 487 16.6 24.4 1.00 3.20 30 0.70 0.20 2.8 1.40 83 120 22.3 11.0 23.0 17 3.70 0.890 3.9 

K-131-d-r 483 18.7 36.8 1.10 3.00 29 — 0.22 2.7 1.30 106 100 24.2 10.0 21.0 15 3.10 0.900 3.5 

K-131-d-s 483 18.5 35.6 1.20 3.00 36 — 0.28 2.7 2.00 102 140 24.1 10.0 21.0 21 3.30 0.920 4.3 

K-162 618 11.0 10.2 1.50 4.30 39 — 0.42 3.2 1.80 74 160 16.1 13.0 26.0 17 3.60 1.020 5.1 

K-182 562 10.2 6.5 1.40 4.30 37 — 0.31 3.1 1.70 67.0 150 16.1 12.0 25.0 22 3.60 0.920 5.0 

K-184 492 18.6 36.2 1.20 3.30 34 — 0.30 2.9 1.50 85.0 110 24.8 11.0 23.0 19 3.30 0.950 3.9 

Appendix C. Trace-element analyses of 1912 eruptive products by Instrumental neutron activation analysis (INAA).[Determinations (in parts per million) by INAA in U.S. Geological Survey laboratories. —, not analyzed. Methods and precision discussed by Baedecker (1987).]
Sample Ba Co Cr Cs Hf Rb Sb Ta Th U Zn Zr Sc La Ce Nd Sm Eu Gd 

K-200 522 14.0 22.0 1.20 3.72 33 0.46 0.25 3.0 1.40 71.7 140 21.1 11.2 24.3 15 4.13 0.978 — 

K-202 565 11.8 6.5 1.40 4.20 39 — 0.36 3.1 1.60 79.0 160 17.2 13.0 27.0 19 3.90 1.030 5.1 

K-203 460 18.0 28.0 1.10 3.40 31 0.39 0.22 3.1 1.20 80 190 22.3 11.0 22.6 14 3.86 0.920 — 

K-581 482 18.1 30.0 1.10 3.34 27.0 0.34 0.20 2.7 1.26 86.5 99.5 25.4 9.9 23.3 13.9 3.77 1.020 4.1 

K-1365 878 0.5 <0.29 2.45 4.94 60.9 0.93 0.41 5.1 2.44 39 156 7.1 18.1 41.3 23.9 5.94 0.800 6.1 

K-1490 711 9.45 6.59 1.64 4.75 43.10 0.62 0.32 3.78 2.01 66.1 172 15.8 14.3 32.8 19.9 5.10 1.05 5.46 

K-1490-glass 904 3.40 3.27 2.35 6.49 61.10 0.76 0.43 5.45 2.77 36.5 229 8.52 17.5 40.9 23.4 6.11 0.86 6.35 

Novarupta scoria falls

K-542 599 13.8 10.5 1.38 4.43 35.0 0.47 0.29 3.3 1.52 77.5 145 21.0 12.3 30.1 18.5 4.77 1.120 5.0 

K-543 197 54.3 230.0 0.36 1.57 10.1 — 0.08 1.0 0.39 68.9 54.7 45.5 4.9 11.2 7.47 2.35 0.787 2.8 

K-721 440 17.9 25.6 1.10 3.26 31 0.39 0.24 2.9 1.20 72 120 23.2 10.5 22.0 12 3.78 0.942 — 

K-851 270 28.0 93.6 0.69 2.29 24 <0.40 0.19 1.9 0.73 79 89 33.5 7.2 16.1 10 2.96 0.844 — 

Blocks from Phantom Dome

K-20V 580 11.4 9.8 1.20 4.14 34 0.53 0.27 3.1 1.50 73.0 140 17.9 12.0 26.2 15 4.52 1.070 — 

K-513-v 610 14.0 23.0 1.40 3.62 40 0.57 0.26 3.2 1.50 73 230 20.7 12.0 26.0 18 4.34 0.990 — 

Appendix C. Trace-element analyses of 1912 eruptive products by Instrumental neutron activation analysis (INAA).—Continued
260 The Novarupta-Katmai Eruption of 1912—Largest Eruption of the Twentieth Century: Centennial Perspectives

Produced in the Menlo Park Publishing Service Center, California

Manuscript approved for publication March 22, 2012

 Text edited by Peter H. Stauffer

Layout and design by Judy Weathers

Mid-evening sunlight bathes the Late Pleistocene dacite domes Falling Mountain 

and Mount Cerberus, both draped by 1912 pumice falls. The sun-lit domes frame 

the entrance to Katmai Pass. View southeastward toward snow-streaked West 

Trident (peak 5605) in cloud. In fair weather, fieldwork often extended as late as 

11 p.m. during Alaskan summers. Photo taken in August 1982.

Hildreth and Fierstein—The Novarupta-Katmai Eruption of 1912—Professional Paper 1791