FRONT COVER

Photograph of bluff exposure Nk-11, Noatak National Preserve, Alaska, with water-filled kettle depressions in 

background. Amphitheater-like gully heads have resulted from thaw and flowage of ice-rich permafrost (photo by 

author). Inset photographs on the back cover are (from top to bottom) (1) Ice-wedge cast in gravel at exposure Nk-29A 

(photo by G.M. Ashley, 7/26/83); (2) conifer log exhumed by erosion near river level at exposure Nk-37 (photo by 

M.E. Edwards, 7/13/95); (3) exposure Nk-27, where upper and lower diamicts are separated by remnants of eroded 

floodplain deposit, from point bar on opposite side of Noatak River (photo by author, 7/23/83); (4) exposure Nk-26, 

showing upper and lower diamicts separated by floodplain deposits that overlie alluvial gravel (photo by author, 

7/19/83); and (5) varves with dropstone at exposure Cu-6 (photo by G.M. Ashley, 7/17/83). 
Guide to Surficial Geology and River-Bluff 

Exposures, Noatak National Preserve, 

Northwestern Alaska

Scientific Investigations Report 2008–5125

By Thomas D. Hamilton

U.S. Department of the Interior

U.S. Geological Survey

Prepared in cooperation with the National Park Service
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2009

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.

Suggested citation:

Hamilton, T.D., 2009, Guide to surficial geology and river-bluff exposures, Noatak National Preserve, northwestern 

Alaska: U.S. Geological Survey Scientific Investigations Report 2008-5125, 116 p.

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This report and any updates to it are available online 

at: http://pubs.usgs.gov/sir/2008/5125/
v

Contents

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

Introduction.....................................................................................................................................................2

Upper Noatak River Valley ...........................................................................................................................6

Introduction............................................................................................................................................6

Exposure Nk-3 .......................................................................................................................................7

Exposure Nk-4 .......................................................................................................................................8

Exposure Nk-5 .......................................................................................................................................8

Exposure Nk-6 .......................................................................................................................................8

Exposure Nk-7 .......................................................................................................................................9

Exposure Nk-8 .....................................................................................................................................10

Exposure Nk-9 .....................................................................................................................................10

Exposure Nk-10 ...................................................................................................................................11

Exposure Nk-11 ...................................................................................................................................11

Exposure Nk-12 ...................................................................................................................................12

Exposure Nk-13 ...................................................................................................................................13

Discussion............................................................................................................................................13

Aniuk River Area ..........................................................................................................................................14

Introduction..........................................................................................................................................14

Exposure Nk-14 ...................................................................................................................................15

Exposure Nk-14A (not illustrated) ....................................................................................................16

Exposure Nk-15 ...................................................................................................................................16

Exposure Nk-16 ...................................................................................................................................16

Exposure Nk-17 ...................................................................................................................................17

Exposure Nk-18 ...................................................................................................................................17

Exposure Nk-19 ...................................................................................................................................17

Exposure Nk-20 ...................................................................................................................................18

Exposure Nk-21 ...................................................................................................................................18

Exposure An-1 .....................................................................................................................................19

Exposure An-2 .....................................................................................................................................20

Exposure An-3 .....................................................................................................................................20

Exposure An-4 (not illustrated).........................................................................................................20

Exposure An-5 .....................................................................................................................................21

Exposure An-6 .....................................................................................................................................21

Exposure An-7 .....................................................................................................................................21

Discussion............................................................................................................................................22

Cutler River Area..........................................................................................................................................23

Noatak River Bluffs.............................................................................................................................23

Introduction.................................................................................................................................23

Bluff Exposures (Nk-22 through Nk-25 and Cu-1).................................................................24

Discussion...................................................................................................................................26

Lower Cutler River..............................................................................................................................26
vi

Introduction.................................................................................................................................26

Exposure Cu-4.............................................................................................................................26

Exposures Cu-5 and Cu-6 .........................................................................................................26

Exposures Cu-2 and Cu-3 .........................................................................................................26

Discussion...................................................................................................................................28

Upper Cutler River Valley...................................................................................................................29

Exposures Cu-7 through Cu-12 ................................................................................................29

Discussion...................................................................................................................................31

 Imelyak River Valley ...........................................................................................................................32

Exposures Im-1 through Im-4...................................................................................................32

 Discussion...................................................................................................................................33

Aniuk Lowland Below Cutler River—Noatak River Bluffs ....................................................................34

Introduction..........................................................................................................................................34

Exposure Nk-26 ...................................................................................................................................35

Exposure Nk-27 ...................................................................................................................................37

Exposure Nk-28 ...................................................................................................................................38

Exposure Nk-29A.................................................................................................................................39

Exposure Nk-29B.................................................................................................................................40

Exposure Nk-30 ...................................................................................................................................40

Exposure Nk-31 ...................................................................................................................................41

Exposure Nk-32 ...................................................................................................................................42

Exposure Nk-33 ...................................................................................................................................44

Exposure Nk-34 ...................................................................................................................................45

Exposure Nk-35 ...................................................................................................................................45

Exposure Nk-36 ...................................................................................................................................47

Exposure Nk-37 ...................................................................................................................................47

Exposure Nk-38 ...................................................................................................................................50

Exposure Nk-39 ...................................................................................................................................50

Discussion............................................................................................................................................51

Aniuk Lowland Below Cutler River— Tributary Drainages...................................................................52

Introduction..........................................................................................................................................52

Exposure Makpik-1.............................................................................................................................52

Exposure Anisak-1..............................................................................................................................53

Exposure Itim-1....................................................................................................................................53

Exposure Ctn-1 (New Cottonwood Creek)......................................................................................54

Exposure Ctn-2 ....................................................................................................................................54

Exposure Nm-1 (Nimiuktuk River) ....................................................................................................55

Exposure Nm-2....................................................................................................................................55

Exposure Nm-3....................................................................................................................................55

Exposure Nm-4....................................................................................................................................56

Exposure Ak-1 (Aklumayuak Creek) ................................................................................................56

Discussion............................................................................................................................................56

Nimiuktuk River to Aklumayuak Creek .....................................................................................................57

Introduction..........................................................................................................................................57

Exposure Nk-40 ...................................................................................................................................57
vii

Exposure Nk-41 ...................................................................................................................................58

Exposure Nk-42 ...................................................................................................................................59

Exposure Nk-43 ...................................................................................................................................59

Exposure Nk-44 ...................................................................................................................................59

Exposure Nk-45 ...................................................................................................................................59

Exposure Nk-46 ...................................................................................................................................60

Exposure Nk-47 ...................................................................................................................................60

Exposure Nk-48 ...................................................................................................................................61

Discussion............................................................................................................................................61

Sapun Creek..................................................................................................................................................62

Exposure Sp-1......................................................................................................................................62

Exposure Sp-2......................................................................................................................................63

Discussion............................................................................................................................................63

Sapun Creek to Kaluktavik River...............................................................................................................64

Exposure Nk-49 ...................................................................................................................................64

Exposures Nk-50A and Nk-50B.........................................................................................................65

Exposures Nk-51A and Nk-51B.........................................................................................................65

Exposure Nk-52 ...................................................................................................................................66

Exposure Nk-53 ...................................................................................................................................67

Discussion............................................................................................................................................67

Lower Kaluktavik River Valley....................................................................................................................68

Exposure Kl-1.......................................................................................................................................68

Exposure Kl-2.......................................................................................................................................68

Exposure Kl-3.......................................................................................................................................69

Discussion............................................................................................................................................69

Kaluktavik River to Noatak Canyon...........................................................................................................70

Exposure Nk-54 ...................................................................................................................................70

Exposure Nk-55 (not illustrated).......................................................................................................71

Exposure Nk-56 ...................................................................................................................................71

Exposure Nk-57 ...................................................................................................................................71

Exposure Nk-58 ...................................................................................................................................72

Exposure Nk-59 ...................................................................................................................................72

Eastern Sector............................................................................................................................72

Western Sector .........................................................................................................................75

Exposure Nk-60 ...................................................................................................................................76

Discussion............................................................................................................................................77

Noatak Canyon to Kugururok River ..........................................................................................................77

Exposure Nk-61 ...................................................................................................................................78

Exposure Nk-62 ...................................................................................................................................79

Discussion............................................................................................................................................79

Kugururok River Valley................................................................................................................................79

Exposure Ku-1......................................................................................................................................80

Exposure Ku-2......................................................................................................................................80

Exposure Ku-3......................................................................................................................................81

Exposure Trail-1 (Trail Creek)............................................................................................................81
viii

Discussion............................................................................................................................................81

Kugururok River to Eli River........................................................................................................................82

Introduction..........................................................................................................................................82

Exposure Nk-63 ...................................................................................................................................83

Exposure Nk-64 ...................................................................................................................................83

Exposure Nk-65 ...................................................................................................................................84

Exposure Nk-66 ...................................................................................................................................85

Exposure Nk-67 ...................................................................................................................................85

Discussion............................................................................................................................................85

Kelly-Avan Drainage System .....................................................................................................................86

Introduction..........................................................................................................................................86

Exposure Avan-1 .................................................................................................................................86

Exposure Avan-2 .................................................................................................................................86

Exposures Kly-1 through Kly-5..........................................................................................................87

Exposure Kly-6.....................................................................................................................................87

Discussion............................................................................................................................................88

Eli-Uvgoon Drainage System .....................................................................................................................88

Exposure Eli-1......................................................................................................................................88

Exposure Eli-2......................................................................................................................................88

Exposure Uv-1......................................................................................................................................89

Exposure Uv-2......................................................................................................................................89

Discussion............................................................................................................................................90

Summary and Regional Relations .............................................................................................................90

Acknowledgments.......................................................................................................................................92

References Cited..........................................................................................................................................92

Appendix 1—Radiocarbon age determinations from river bluffs within 

Noatak National Preserve ............................................................................................................95

Appendix 2—Clast Lithologies of Tills and Glaciolacustrine Deposits, Central 

and Western Aniuk Lowland ........................................................................................................99

Introduction..........................................................................................................................................99

Stone Counts......................................................................................................................................100

Discussion..........................................................................................................................................102

Conclusions........................................................................................................................................103

Glossary.......................................................................................................................................................104

Figures

1. Noatak River region, northwest Alaska, showing boundaries of Noatak National Preserve 

and mapped extents of glacial lakes ........................................................................................2

2. Upper Noatak basin (Aniuk Lowland), showing major drainages and locations of measured 

sections ..........................................................................................................................................3

3. Middle Noatak River valley and lower Noatak basin (Mission Lowland), showing major 

drainages and locations of measured sections ......................................................................4

4. Typical vertical succession in till contrasted with vertical succession in glaciolacustrine 

deposits, as observed in upper Noatak basin..........................................................................6

5. Generalized geologic map, Douglas Creek area, upper Noatak River valley...............................7
ix

 6. Exposure Nk-3.......................................................................................................................................8

 7. Exposure Nk-4.......................................................................................................................................8

 8. Exposure Nk-5.......................................................................................................................................9

 9. Exposure Nk-6.......................................................................................................................................9

10. Exposure Nk-7.....................................................................................................................................10

11. Exposure Nk-8.....................................................................................................................................10

12. Exposure Nk-9.....................................................................................................................................11

13. Exposure Nk-10...................................................................................................................................11

14. Exposure Nk-11...................................................................................................................................12

15. Exposure Nk-12...................................................................................................................................12

16. Exposure Nk-13...................................................................................................................................13

17. Section through Itkillik II (late Wisconsin) moraine belt, upper Noatak River valley, 

showing interrelations of exposures Nk-8 through Nk-13...................................................14

18. Generalized geologic map, Aniuk River area, north-central upper Noatak basin ..................15

19. Exposure Nk-14...................................................................................................................................15

20. Exposure Nk-15...................................................................................................................................16

21. Exposure Nk-16...................................................................................................................................16

22. Exposure Nk-17...................................................................................................................................17

23. Exposure Nk-18...................................................................................................................................17

24. Exposure Nk-19...................................................................................................................................17

25. Exposure Nk-20...................................................................................................................................18

26. Exposure Nk-21...................................................................................................................................18

27. Exposure An-1.....................................................................................................................................19

28. Exposure An-2.....................................................................................................................................20

29. Exposure An-3.....................................................................................................................................20

30. Exposure An-5.....................................................................................................................................21

31. Exposure An-6.....................................................................................................................................21

32. Exposure An-7.....................................................................................................................................21

33. Schematic cross-profile of Noatak River valley above Itkillik I (Atongarak Creek) 

moraine belt ................................................................................................................................23

34. Generalized geologic map, Cutler River area, south-central upper Noatak basin .................23

35. Exposure Nk-22...................................................................................................................................24

36. Exposure Nk-23...................................................................................................................................24

37. Exposures Nk-24 and Cu-1................................................................................................................25

38. Exposure Nk-25...................................................................................................................................25

39. Exposure Cu-4.....................................................................................................................................27

40. Exposure Cu-5.....................................................................................................................................27

41. Exposure Cu-6.....................................................................................................................................27

42. Exposure Cu-2.....................................................................................................................................28

43. Exposure Cu-3.....................................................................................................................................28

44. Exposure Cu-7.....................................................................................................................................29

45. Exposure Cu-8.....................................................................................................................................30

46. Exposure Cu-9.....................................................................................................................................30

47. Exposure Cu-10...................................................................................................................................30

48. Exposure Cu-11...................................................................................................................................31

49. Exposure Cu-12...................................................................................................................................31
x

50. Exposure Im-1 .....................................................................................................................................32

51. Exposure Im-2 .....................................................................................................................................32

52. Exposure Im-4 .....................................................................................................................................33

53. Exposures Im-5 and Im-6...................................................................................................................33

54. Generalized geologic map, Noatak River valley between mouth of Cutler River and lower 

Nimiuktuk River (western Aniuk Lowland)............................................................................................34

55. Exposure Nk-26...................................................................................................................................35

56. Exposure Nk-26 (continued) .............................................................................................................36

57. Exposure Nk-27...................................................................................................................................37

58. Exposure Nk-28...................................................................................................................................38

59. Exposure Nk-29A................................................................................................................................39

60. Exposure Nk-29B................................................................................................................................40

61. Exposure Nk-30...................................................................................................................................41

62. Exposure Nk-31...................................................................................................................................42

63. Exposure Nk-32...................................................................................................................................43

64. Exposure Nk-32 (continued) .............................................................................................................44

65. Exposure Nk-33...................................................................................................................................45

66. Exposure Nk-34...................................................................................................................................45

67. Exposure Nk-35...................................................................................................................................46

68. Exposure Nk-36...................................................................................................................................47

69. Exposure Nk-37...................................................................................................................................48

69. Exposure Nk-37 (continued) .............................................................................................................49

70. Exposure Nk-38...................................................................................................................................50

71. Exposure Nk-39...................................................................................................................................50

72. Exposure Makpik-1.............................................................................................................................52

73. Exposure Anisak-1..............................................................................................................................53

74. Exposure Itim-1...................................................................................................................................53

75. Exposure Ctn-1....................................................................................................................................54

76. Exposure Ctn-2....................................................................................................................................54

77. Exposure Nm-1....................................................................................................................................55

78. Exposure Nm-2....................................................................................................................................55

79. Exposure Nm-3....................................................................................................................................55

80. Exposure Nm-4....................................................................................................................................56

81. Exposure Ak-1.....................................................................................................................................56

82. Generalized geologic map, Noatak River valley between Nimiuktuk River and 

Kugururok River...........................................................................................................................57

83. Exposure Nk-40...................................................................................................................................58

84. Exposure Nk-41...................................................................................................................................58

85. Exposure Nk-42...................................................................................................................................59

86. Exposure Nk-43...................................................................................................................................59

87. Exposure Nk-44...................................................................................................................................59

88. Exposure Nk-45...................................................................................................................................60

89. Exposure Nk-46...................................................................................................................................60

90. Exposure Nk-47...................................................................................................................................60

91. Exposure Nk-48...................................................................................................................................61

92. Exposure Sp-1.....................................................................................................................................62
xi

 93. Exposure Sp-2...................................................................................................................................63

 94. Exposure Nk-49.................................................................................................................................64

 95. Exposure Nk-50A..............................................................................................................................65

 96. Exposure Nk-50B..............................................................................................................................65

 97. Exposure Nk-51.................................................................................................................................66

 98. Exposure Nk-52.................................................................................................................................66

 99. Exposure Nk-53.................................................................................................................................67

100. Exposure Kl-1 ....................................................................................................................................68

101. Exposure Kl-2 ....................................................................................................................................69

102. Exposure Kl-3. ...................................................................................................................................69

103. Sketch showing geologic relations of end moraine and outwash train near mouth of 

Kaluktavik River valley ...............................................................................................................70

104. Exposure Nk-54.................................................................................................................................70

105. Exposure Nk-56.................................................................................................................................71

106. Exposure Nk-57.................................................................................................................................71

107. Exposure Nk-58.................................................................................................................................72

108. Exposure Nk-59.................................................................................................................................74

109. Exposure Nk-60.................................................................................................................................77

110. Exposure Nk-61.................................................................................................................................78

111. Exposure Nk-62.................................................................................................................................79

112. Exposure Ku-1...................................................................................................................................80

113. Exposure Ku-2...................................................................................................................................80

114. Exposure Ku-3...................................................................................................................................81

115. Exposure Trail-1 ................................................................................................................................81

116. Generalized geologic map, Noatak River valley, Kugururok River to Eli River.......................82

117. Exposure Nk-63.................................................................................................................................83

118. Exposure Nk-64.................................................................................................................................83

119. Exposure Nk-65.................................................................................................................................84

120. Exposure Nk-66.................................................................................................................................85

121. Exposure Nk-67.................................................................................................................................85

122. Exposure Avan-1...............................................................................................................................86

123. Exposure Avan-2...............................................................................................................................87

124. Exposures Kly-1 through Kly-5 .......................................................................................................87

125. Exposure Kly-6 ..................................................................................................................................88

126. Exposure Eli-1....................................................................................................................................88

127. Exposure Eli-2....................................................................................................................................89

128. Exposure Uv-1...................................................................................................................................89

129. Exposure Uv-2...................................................................................................................................89

Tables

1. Glacial advances recognized in the De Long Mountains and their central Brooks Range 

equivalents.....................................................................................................................................5

2. Characteristics of tills versus glaciolacustrine deposits, upper Noatak basin ...........................6

3. Correlation of depositional units in exposure Nk-37 ......................................................................52
METRIC-ENGLISH EQUIVALENTS

TO CONVERT MULTIPLY BY TO OBTAIN

millimeters (mm) 0.040 inches

centimeters (cm) 0.397 inches

meters (m) 3.281 feet

kilometers (km) 0.621 miles
Guide To Surficial Geology and River-Bluff Exposures, 

Noatak National Preserve, Northwestern Alaska

By Thomas D. Hamilton

Abstract

From its origin in rugged granitic highlands of the central 

Brooks Range, the Noatak River flows westward between the 

De Long Mountains and the Baird Mountains before turning 

south to enter Kotzebue Sound. Glaciers of middle and late 

Pleistocene age entered the Noatak River valley from the east, 

north, and south. Glaciers flowed down the upper Noatak 

River valley from the rugged peaks at its head, merging with 

tributary glaciers that issued from cirque-headed valleys along 

its south flank. Farther downvalley, small glaciers flowed 

northward from the Baird Mountains and much larger glaciers 

issued from the De Long Mountains. The De Long Mountains 

glaciers expanded southward to cover parts of the Noatak 

valley floor; they dammed the Noatak River during successive 

advances, creating a series of glacial lakes. The more extensive 

glacial advances dammed huge lakes that filled the Aniuk 

Lowland to overflowing. At various times, overflow waters 

spilled northward through Howard Pass, southward via Hunt 

River into the Kobuk River system, and westward down a 

series of channelways that skirted south of the glacier margins.

Prominent bluffs along the Noatak River and its principal 

tributaries reveal glacial, glaciolacustrine, fluvial, and eolian 

sediments. More than 120 measured bluff exposures are 

described and illustrated in this report. These are dated by 92 

radiocarbon age determinations and by the presence of the 

old Crow tephra, which was deposited about 130,000-140,000 

years ago. Six geologic base maps, which cover sections of the 

Noatak River valley from east to west, show the locations of 

the river bluffs in relation to the glacial, glaciolacustrine, and 

fluvial deposits that cover the valley floor.

The upper Noatak River valley is dominated by a bulky 

end moraine near Douglas Creek that was deposited during the 

last glacial maximum about 25,000-15,000 14C yr BP (termed 

the Itkillik II phase in the central Brooks Range glacial 

succession). Bluffs along this section of the Noatak River 

reveal thick till that underlies the moraine and interfingers 

downvalley with outwash and upvalley with moraine-dammed 

lake deposits. Remnants of older river gravels that underlie the 

set of glacial deposits contain wood fragments that are dated at 

about 35,000-30,000 14C yr BP.

The Aniuk River area, which includes much of the 

eastern Aniuk Lowland, contains older moraines derived from 

headwaters of the Noatak valley that lie downvalley from the 

Douglas Creek moraine. These older moraines are assigned to 

the Itkillik IA and IB advances of the central Brooks Range 

glacial succession. Their deposits are seldom visible in river 

bluffs, but associated outwash and glaciolacustrine sediments 

are commonly exposed. More ancient end moraines farther 

downvalley are buried beneath lake deposits of the Aniuk 

Lowland, but are traceable as subdued arcuate drainage 

divides and as boulder concentrations in river bluffs or along 

their bases.

The Cutler River area was occupied by glacial lakes 

assignable to three separate glacial phases. The oldest of 

these was probably dammed by the Cutler moraine, which 

crosses the Noatak valley floor near the mouth of Cutler River. 

The younger two are correlated with Itkillik-age deposits 

in the Aniuk Lowland. Glaciers of Itkillik age also flowed 

northwestward down the Cutler and Imelyak valley systems 

from cirques along the Noatak-Kobuk divide, but they did not 

reach the Noatak valley floor. 

The western Aniuk Lowland, which extends westward 

from the Cutler River mouth to the lower course of Nimiuktuk 

River, is dominated by a series of large end moraines 

deposited by glaciers from the De Long Mountains and that 

flowed southeastward down the Nimiuktuk valley system 

and then up the Noatak River valley. The Cutler moraine is 

the most extensive of these deposits. Following the Cutler 

glaciation, less extensive glacial advances built end moraines 

near the present-day mouths of Makpik Creek and Anisak 

River during intervals that may correlate with the Itkillik 

1A and Itkillik 1B phases in the central Brooks Range. The 

Cutler, Makpik, and Anisak glaciers dammed the Noatak 

River, creating the series of glacial lakes that covered the 

Aniuk Lowland. High river bluffs through this sector of the 

Noatak valley expose sequences of massive till and glaciallake deposits that alternate with interglacial river gravels and 

organic-rich floodplain deposits. Floodplain sediments in 

two of the bluffs contain the Old Crow tephra, a stratigraphic 

marker for an early phase of the last interglaciation.

Downvalley from Nimiuktuk River, glaciers in the De 

Long Mountains flowed southward through the Kalaktavik, 

Kugururok, and Kelly drainage systems, deflecting the Noatak 

River into a more southerly position against the north flank 

of the Baird Mountains. These glaciers dammed the Noatak 

drainage near the mouths of their valleys, and glacial lakes 

subsequently expanded northward up each valley when the 
2 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

Brooks Range ALASKA

0 100

0 50 100 MILES

200 KILOMETERS

68o

164o 160o 156o

66o

Kotzebue 

Sound

K o b u k R i v e r

DE LONG MOUNTAINS

N o a t a k

Howard 

Pass

fig. 2

fig. 3

Nimiuktuk River

Douglas 

 Creek

Mt Igikpak

Arrigetch

Peaks

Kelly River

Eli River

R i v e r

Anisak

River

Noatak National Preserve

Gates of 

the Arctic

National Park

Igichuk

Hills

Kotzebue

B A I R D M O U N T A I N S

B R O O K S

C E N T R A L

R A N G E

Aniuk River

AL

ML

Figure 1. Noatak River region, northwest Alaska, showing boundaries of Noatak National Preserve and mapped extents 

of glacial lakes (dark blue). Easternmost lake is centered over Aniuk Lowland (AL), also known as upper Noatak basin. 

Westernmost lake extends southward into Mission Lowland (ML). Tree symbols show northward limit of spruce (from 

Edwards and others, 2003). Figures 2 and 3 show locations of measured sections. Modified from Hamilton, 2001.

glaciers receded. Ice advances of the last glacial maximum 

(locally termed the Avan glaciation) reached the mouth of 

Avan River valley, but elsewhere they were restricted to upper 

valleys and valley heads in the De Long Mountains and to 

cirques in the Baird Mountains. The reduced extent of these 

glaciers contrasts strongly with the much larger correlative 

glaciers of Itkillik II age throughout the central Brooks 

Range. Bluffs along the Noatak River and lower courses of 

its tributaries expose till and glaciolacustrine deposits, as 

well as terraced river gravels and floodplain deposits that 

formed during postglacial downcutting. In several locations, 

the postglacial alluvium contains wood or peat that yield 

radiocarbon ages of 13,000 yr BP and younger.

The sparse river-cut exposures downvalley from Kelly River 

exhibit mainly lake deposits, associated deltas and fan deltas, and 

loess. Heavy loess cover obscures much of the older terrain across 

this sector of the Noatak valley floor. No significant exposures 

were recorded downvalley from the large fan-delta deposit of 

Eli River, possibly because the Noatak River has been aggrading 

through this section of its valley during Holocene time.

Introduction

The Noatak River originates in rugged granitic highlands 

of the west-central Brooks Range and flows westward into 

Kotzebue Sound (fig. 1). Along most of this route, its valley 

parallels the structural grain of the Brooks Range, and 

separates the DeLong Mountains to the north from the Baird 

Mountains to the south. A short distance beyond the Kelly 

River confluence, the Noatak curves southward; it skirts the 

west end of the Baird Mountains, then intersects the coast 

opposite the town of Kotzebue. The valley of the Noatak 

River widens in two places into broad basins that contained 

extensive Pleistocene-age lakes. The upper basin, termed 

the Aniuk Lowland by Wahrhaftig (1965), extends westward 
 Introduction 3

from below Douglas Creek to near Anisak River. The lower 

basin, termed the Mission Lowland by Wahrhaftig (1965) 

extends southward from near Kelly River to the Igichuk Hills, 

a northeast-trending bedrock ridge about 25 km inland from 

the coast. For about 310 km of its course, beginning near 

Douglas Creek and ending below Kelly River, the Noatak and 

its tributaries flow within the Noatak National Preserve.

The upper Noatak basin, or Aniuk Lowland, has a 

maximum width of about 80 km and extends about 90 km 

downvalley (fig. 2). This depression is centered along the 

Noatak River, and it is drained additionally by three principal 

tributaries to the Noatak: the Anisak and Aniuk Rivers, 

which flow southward from the De Long Mountains, and 

the Cutler River system, which drains northern parts of the 

Baird Mountains and the south-central Brooks Range. During 

glacial phases of the middle and late Pleistocene, valley and 

piedmont glaciers flowed southeastward out of the Nimiuktuk 

valley system and dammed the Noatak River, forming glacial 

lake Noatak (Hamilton and Van Etten, 1984; Hamilton, 2001). 

The more extensive advances filled much of the basin with 

glacier ice and with proglacial lakes, which overflowed at 

various times northward via Howard Pass, southward down 

Hunt River into the Kobuk River valley, and westward around 

the ice margin into the lower valley of the Noatak River. A 

large glacier that originated in highlands near the head of the 

Noatak valley system terminated in the lake at those times, as 

did smaller glaciers that flowed from uplands north of Feniak 

Lake and near the heads of Cutler and Imelyak River valleys. 

During the late Pleistocene, less extensive ice advances from 

the Nimiuktuk River area dammed a narrow water body that 

extended up the basin center. Valley glaciers in the upper 

Noatak, near Feniak Lake, and within the Cutler River 

drainage system formed prominent end moraines beyond the 

lake margins at those times.

Below the Nimiuktuk River confluence, the Noatak bends 

sharply southward; it flows south and then west for about 

90 km through a relatively narrow valley that terminates in 

Noatak Canyon, a rock-walled gorge just above the mouth 

of Kugururok River (fig. 3). The river was pushed into this 

position by glaciers that originated in the De Long Mountains 

Ak-1

159o00' 158o00' 157o00'

68o

15'

68o

00'

67o

45'

67o

30'

0

0

25 50 KILOMETERS

30 MILES

Upland above 

600 m asl MOUNTAINS

Lake DE LONG

BAIRD

MOUNTAINS

NOATAK RIVER

Feniak

Lake

Aniuk

River

HOWARD

PASS

Etivluk R

Nigu R

Anisak R

Imelyak

Cutler

River

New

Cottonwood

Creek

Okak Bend

Makpik Cr

Natmotirak Cr

Kaluich Cr

Douglas Cr

River

Lake

Matcharak

Flora Cr

Amakomanak Cr

Aklumayuak Cr

Hunt River

28

29b

29a

30

33 32

31

Makpik-1

34

35b 35a

36 37 38

An-3

20

19

18 17

16

15

14

Im-2

Im-3

Im-1

21

22

23

24

Cu-1

Cu-4

Cu-2

Cu-3

Cu-6 Cu-5

Cu-10

Cu-11

Cu-12

Cu-8

Cu-7

Cu-9

25

26 27

An-7

An-5An-6

An-4 An-1

An-2

1312 11 8

9

10

7 6

5

4

3

Im-6

Im-5

Im-4

Anisak-1

Itim-1

Ctn-1

Ctn-2

Figure 2. Upper Noatak basin (Aniuk Lowland) showing major drainages and locations of measured sections 

(see figs. 5, 18, 34, and 54 for geologic settings). Numbers without prefixes refer to Noatak River bluffs (designated 

Nk in figs. 5, 18, and 34, and in text). Arrows show major Pleistocene glacial-flow directions, with size of arrow 

proportional to glacial discharge.
4 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

Figure 3. Middle Noatak River valley and lower Noatak basin (Mission Lowland), showing major drainages and 

locations of measured sections, (see figs. 82 and 115 for geologic settings). Numbers without prefixes refer to 

Noatak River bluffs (designated Nk in figs. 82 and 115, and in text). Arrows show major Pleistocene glacial-flow 

directions, with size of arrow proportional to glacial discharge. 

162o00' 160o00'

68o

15'

68o

00'

67o

45'

68o

30'

50 KILOMETERS

Upland above 

600 m asl

Lake

0

0

25

30 MILES

DE LONG MOUNTAINS

NOATAK

RIVER

Eli River

Kelly

Nimiuktuk River

Seagull Cr

Kugururok 

Trail Cr

Uvgoon Cr

Sapun Cr

River

River

Kaluktavik River

Avan River

Wrench Cr

Lake Kaiyak

Lake 

Narvakrak

Thunder

Mtn

Ku-1

Ku-2

Ku-3 43

49

48

44

50A

51

47

Nm-4

45

41

46

42

40

39

52

Kl-2

50B

Trail-1

Kly-3

Avan-1

Nm-3

Sp-1

Sp-2

Nm-2

Avan-2

Kly-5

Kly-6

Kly-2

Kly-1

Kly-4

Uv-1

Uv-2

Eli-2

Eli-1

53

54

Kl-1 55 56

57 58 59

60

61

62

63

65 64

66

67

Noatak Canyon

Nm-1

and that flowed southward through the Kelly, Kugururok, and 

Kaluktavik valley systems. Glacial-lake deposits are present 

along the valley floor upstream from the former ice dams 

created by those glaciers.

Much of the lower Noatak basin, or Mission Lowland, 

lies beyond the western boundary of the Noatak National 

Preserve, and is not illustrated in figure 3. A series of broad 

lakes probably filled this basin during middle and late 

Pleistocene time, but poor exposures obscure their record. 

Some of the lake stages may be slackwater deposits (as 

described by Waitt, 1980) that formed when glacial outburst 

floods were dammed for periods of days or perhaps weeks 

where the Noatak River crosses the Igichuk Hills through a 

narrow gorge. Other deposits that may be lacustrine in origin 

are obscured by thick loess that was scoured from exposed 

sediments on the basin floor by strong southerly winds.

This report describes the deposits of Quaternary age 

that are exposed in bluffs along the Noatak River and its 

tributaries through the segment of its valley that lies within 

the Noatak National Preserve (see fig. 1). The bluffs discussed 

and illustrated in this report were examined during traverses 

down the Noatak River at various times between 1979 and 

2000. River bluffs in tributary drainages were accessed by 

foot where close to the Noatak River and by helicopter where 

in more distant locations. The bluff exposures, which stand 

as high as 86 m, provide a basinwide stratigraphic record of 

alternating lake stages and alluvial episodes, and of glacial 

expansions and wastage. This report is divided into six 

geographic sections arranged in a downvalley succession. 

Each section is introduced by a base map that relates every 

individual bluff exposure within that section to its local 

geologic setting. These geologic maps are generalized to make 

relations between bluff stratigraphy and corresponding terrain 

units as clear as possible. See Hamilton (in press) for a more 

detailed surficial geologic map of the Noatak region. 

Although it generally was recognized that lobes of 

glacier ice from the De Long Mountains had flowed south 

across the Noatak River valley (Karlstrom and others, 1964; 
 Introduction 5

Table 1. Glacial advances recognized in the De Long Mountains and their central Brooks Range equivalents.

[Modified from Hamilton, 2003. MIS, marine isotope stage]

Local Glacial Advance Central Brooks Range Equivalent Probable Age

Neoglacial Neoglaciation Late Holocene

Unnamed Late Itkillik II readvance

Late Wisconsin (MIS 2) Avan Itkillik II

Unnamed None recognized Early Wisconsin (MIS 4) Anisak Itkillik IB

Makpik Itkillik IA

Later interglacial (MIS 5d-5a) Okak None recognized

Cutler Sagavanirktok River Middle Pleistocene1

Unnamed older drift Sagavanirktok River or older Middle Pleistocene or older

1

The middle Pleistocene is defined by Richmond and Fullerton (1986) as beginning at the Bruhnes/Matuyama geomagnetic field 

reversal, which has been dated at about 780,000 years ago (Baksi and others, 1992). It ended at the beginning of the last interglacial 

maximum (marine isotope stage 5e) about 130,000 yr B.P. 

2

The late Pleistocene is defined as beginning with the last interglacial maximum (MIS 5e). It ended about 10,000 yr B.P. at the 

beginning of the Holocene postglacial interval.

}

}

}

Late Pleistocene2

Coulter and others, 1965; McCulloch, 1967), the consequent 

formation of large glacier-dammed lakes was seemingly 

not anticipated by those workers. The likely presence of 

such lakes in the upper Noatak basin was first suggested 

by Stephen C. Porter (University of Washington, personal 

commun., 1973). Subsequent geologic mapping in the 

Noatak’s upper basin (Hamilton, 1984a, 1984b) and farther 

west (Hamilton, 2003 and in prep.) documented wavecut notches and beach, deltaic, and other glaciolacustrine 

deposits of multiple lake stages that were associated with 

end moraines of five or more glacial advances of middle 

and late Pleistocene age (Hamilton and Van Etten, 1984; 

Hamilton, 2001).

A consistent set of terms has been employed for 

glacial-geologic mapping through the central Brooks Range 

(Hamilton, 1986, 1994, and references therein; Hamilton and 

Porter, 1975), and use of these terms has been extended into 

upper parts of the Noatak River valley. The Sagavanirktok 

River glaciation is equated broadly with multiple glacial 

advances of middle Pleistocene age, about 780,000 to 125,000 

years before present (yr B.P.) (table 1). Glacial advances 

of presumed late Pleistocene age (about 125,000 to 10,000 

yr B.P.) form a suite of moraines and related deposits that 

collectively are assigned to the Itkillik glaciation (table 1). The 

older deposits of this assemblage (termed Itkillik I) are beyond 

the range of reliable radiocarbon dating (about 38,000 yr in 

northern Alaska according to Hamilton and Ashley, 1993), 

but correlative deposits in the northeastern Brooks Range and 

across central Alaska yield cosmogenic ages up to 60,000 to 

100,000 yr B.P. (Briner and others, 2005). A younger set of 

deposits (termed Itkillik II) is radiocarbon-dated to be between 

about 24,000 and 11,000 14C yr B.P. (Hamilton, 1986).

Glaciers in the De Long Mountains, in contrast, were 

nourished largely from moisture sources west of the Brooks 

Range in the Bering and perhaps Chukchi Seas, and probably 

responded somewhat differently than central Brooks Range 

glaciers during each glacial cycle. For this reason, I employ 

terms used in the central Brooks Range for glacial advances 

within the upper Noatak River valley and as general time 

horizons, but use local names for end moraines generated by 

glaciers issuing from the De Long Mountains. Those features 

are named for tributary drainages that join the Noatak River 

close to where the moraines cross the valley center (Hamilton, 

2001, 2003). Local moraine names and their probable central 

Brooks Range equivalents are listed in table 1. 

The Noatak National Preserve has an arctic climate, 

with long cold winters and short cool summers (Childers and 

Kernodle, 1981). Tundra vegetation, with low shrubs present 

along stream courses, predominates in the upper Noatak River 

valley and in headward parts of its tributaries. Vegetation 

patterns are more complex downvalley from Cutler River, where 

riparian stands of cottonwood (Populus balsamifera) extend 

along the Noatak and lower parts of some triburtaries. Spruce 

(Picea) occurs within the lower Noatak River valley (see fig. 1), 

and extends as riparian stands upvalley to just above Noatak 

Canyon. The Noatak valley floor is underlain by continuous 

permafrost, and permafrost generally also is continuous beneath 

surrounding uplands (Ferrians, 1965; Brown and others, 1997).

Bluff exposures were sampled for radiocarbon age 

determinations where suitable organic material was available. 

The 92 radiocarbon ages discussed on the following 

pages and summarized in appendix 1 are all expressed in 

radiocarbon years, as reported by the dating laboratories. 

They are not converted into calendar years because, for the 

older ages, the conversion values used may be subject to 

future modifications. Where sets of radiocarbon ages are 

discussed, they generally are expressed as thousands of 

years B.P., abbreviated as ka. Wood fragments sampled for 

radiocarbon dating were identified at the U.S. Department 

of Agriculture’s Forest Products Laboratory in Madison, 
6 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

Wis. They are referenced in the text as “USDA-FPL,” 

followed by the date of the written communication in which 

the identification was reported. Color designations of soils and 

sediments are from the Munsell Soil Color Chart (Munsell 

Color Co., Baltimore, Md).

A major problem in interpretation of bluff sediments along 

the Noatak River and its tributaries is determining the origin 

of bouldery diamicts. These unsorted and unstratified deposits 

could have formed either by direct glacial deposition as till or at 

short distances beyond the ice front as proximal glaciolacustrine 

sediment. Although superficially similar, till and glaciolacustrine deposits differ in many characteristics (table 2), and generally have different vertical successions (fig. 4). Till typically is 

massive, strongly jointed, and highly compact; and it supports 

vertical faces on river bluffs. Lower contacts generally are sharp 

and erosional, with underlying sediments commonly deformed 

by the overriding glacier. Proximal glaciolacustrine sediments, 

in contrast, have a more clayey matrix; they tend to have crude 

stratification and basal stone-free facies. Water-washed beds of 

muddy gravel, which are interstratified with unsorted deposits 

or fill erosional channels within them, may represent intervals 

of sudden drainage of the lake due to breaching of its glacial 

dam (as described elsewhere by Waitt, 1980, and Walder and 

Costa, 1996). The stone-free basal sediments, which generally are about a meter thick and commonly include rhythmites, 

may have formed during an initial shallow-lake stage or when 

glacier ice was too distant to contribute dropstones to the site. 

In contrast to the stable and near-vertical faces of till deposits, 

glaciolacustrine sediments tend to flow readily where exposed 

along the faces of river bluffs. The till must have been compacted and partly dewatered by overriding glacier ice, becoming 

“dry” permafrost (permafrost with negligible water content) 

when later frozen. In contrast, the glaciolacustrine sediments 

probably were water-saturated during deposition; they later 

became ice-rich permafrost that is subject to thaw, collapse, and 

flowage on bluff faces.

Although I use the metric system throughout this report, 

former lake heights and other altitude data are presented also in 

feet. This is because the original measurements generally were 

read in feet above sea level from helicopter altimeters and topographic maps, then later converted into meters. Geologic terms 

used in this report are defined in the Glossary section, with 

definitions in some cases tailored to their specific applications to 

the Noatak River valley. 

Upper Noatak River Valley

Introduction

This sector of the Noatak River valley extends from the 

Lake Matcharak area through a prominent moraine belt below 

Figure 4. Typical 

vertical succession 

in till contrasted with 

vertical succession 

in glaciolacustrine 

deposits, as observed 

in upper Noatak 

River basin. Facies 

designations: ff, 

floodplain deposit; 

gl, proximal 

glaciolacustrine 

deposit; gl-d, distal 

glaciolacustrine 

deposit; t, till. From 

Hamilton, 2001.

TILL GLACIOLACUSTRINE

DEPOSIT

gl-d

gl

t

ff

gl-d

gl-d

gl

ff

Table 2. Characteristics of tills versus glaciolacustrine deposits, upper Noatak basin. 

[From Hamilton, 2001]

Till Glaciolacustrine deposits

Underlying deposits commonly truncated by erosion and (or) glacially tectonizedUnderlying deposits generally undisturbed; may be transitional 

upward to marsh or pond deposits

Lower contact sharp; generally erosional Lower contact sharp to gradational; no erosion of underlying beds

Generally massive, with no vertical trends in clasts or matrix except 

at top of unit

Basal sediments commonly are rhythmites. Main body of unit may 

be crudely bedded, with cut-and-fill structures and interbeds of 

water-washed muddy gravel

Matrix commonly sandy silt to silty sand Matrix generally clayey silt to gritty clayey silt

Highly compact; stands in vertical faces Generally uncompacted and ice-rich; flows readily upon thawing

Strongly jointed, with oxides along joint planes No jointing; dark gray color without oxides

Commonly fissile, with platy stones parallel to fissility Fabric generally absent; compressional deformation common beneath dropstones
Upper Noatak River Valley 7

Nk-12

Nk-11

Nk-9 Nk-7

Nk-6

Nk-3

Nk-5

Nk-8

Nk-13

Nk-4

Im-5

Im-6

Nk-10

Noatak

Lake

Matcharak

River

Douglas

Creek

0 20 KILOMETERS

0 10 MILES

Itkillik II

Outwash

Drift

Itkillik I sheets

Bedrock

Meltwater 

channel

Alluvium

Fan-delta

deposit

Terrace 

gravel

Sand deposits

67o

50'

156o 157 30' o

00'

67o

40'

Figure 5.

Generalized 

geologic map, 

Douglas Creek 

area, upper 

Noatak River 

valley. 

Douglas Creek (fig. 5). Bluff exposures along this stretch of 

the river consist of: (1) till, ice-contact deposits, and proximal outwash of the moraine belt, and (2) glaciolacustrine 

sediments, fan-delta deposits, and slackwater deposits that 

aggraded in a depositional basin behind the moraine complex 

as the glacier retreated (Hamilton, 1984 and in press). Eleven 

stratigraphic sections, five of them with radiocarbon dates, 

were measured along this stretch of the Noatak River. Two 

additional exposures (Nk-1 and Nk-2) closer to the valley 

head are low (8-10 m) river cuts into fan deposits that formed 

within the last 1,000 yr (Hamilton and Brubaker, 1983); they 

are not discussed further or illustrated herein.

The easternmost exposures documented in this report 

(Nk-3 through Nk-5) are low (8-17 m) river bluffs near Lake 

Matcharak. The Noatak valley floor here contains ice-stagnation deposits with numerous kettle lakes. Tributary streams 

that enter from the south and southwest have built extensive 

late-Holocene fan deposits that overlie probable fan deltas of 

latest Pleistocene and early Holocene age (Hamilton, 1984a). 

River bluffs expose late-glacial basin-filling deposits overlain 

by Holocene alluvium.

Through the stretch between Lake Matcharak and Douglas 

Creek, the Noatak River occupies a broad Holocene floodplain 

incised within lacustrine terraces and remnants of ice-stagnation deposits. Exposures NK-6 through and Nk-8, measured 

along the Noatak River 11 to 0.5 km upvalley from Douglas 

Creek, stand 17-30 m high. They expose alluvial terrace gravel 

underlain by lacustrine and related deposits that formed behind 

the Itkillik II moraine dam during glacier wastage.

Farther downriver, the Noatak River plunges through the 

moraine belt in a steep, narrow, boulder-filled gorge. Bluff 

exposures standing 30-70 m high (Nk-9 through Nk-13) 

exhibit lacustrine and ice-stagnation deposits upstream from 

the gorge, diamict and alluvium within the gorge, and proximal outwash farther downvalley.

Exposure Nk-3

A south-facing cutbank at the apex of a meander bend of 

the Noatak River 4 km southeast of Lake Matcharak stands 

11 m high, exposing very sandy fine gravel capped by 2.5-

3.5 m of floodplain deposits (fig. 6). Peat from the base of 

the floodplain sequence is dated at 10,000 ±145 yr B.P. The 

frost-churned upper 0.7 m of the exposure marks the active 

layer above a former permafrost table. At one locality along 

the bluff, stony clayey silt extends through an interval 2.6-5.8 

m below the ground surface. Many tabular stones in the silt 

are inclined, as if dumped in from above. The silt probably 

represents an oxbow or kettle lake in the alluvium, which later 

filled with overbank deposits.
8 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

Figure 6. Exposure Nk-3. North 

side Noatak River 4 km southeast 

of Lake Matcharak. Black dot, 

radiocarbon age determination 

(yr B.P.) with laboratory number in 

parentheses (see appendix 1).

Figure 7. Exposure Nk-4. North 

side Noatak River opposite 

south end of Lake Matcharak. 

Black dot, radiocarbon 

age determination (yr B.P.) 

with laboratory number in 

parentheses (see appendix 1).

m

20

10

 0

>40,000

(I-12,512)

2

1

3 Peat and silt. Sod and peat (0.3 m) above

0.5 m frost-mixed olive brown (2.5Y 4/4)

stony sandy silt. Bluff cap.

Gravel. Rounded to subrounded stones up

to large cobble size, with rare very small

boulders, in matrix of medium to coarse

sand with granules. Recessional outwash?

Sand. Light gray, massive to faintly laminated,

fine to medium sand with dispersed pebbles. 

Fluvial slackwater deposit.

3 0.8

2 6.1

1 9.9

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

Exposure Nk-4

A west-facing cutbank 17.6 m high near the south end of 

Lake Matcharak intersects a nearly level alluvial surface that is 

widespread around the lake. The bluff exposes slackwater sand 

deposits with horizontal beds 1-2 cm thick, overlain by gravel 

that contains rounded to subrounded stones up to large cobble 

size with some very small (up to 40 cm diameter) boulders 

also present (fig. 7). Small abraded wood fragments scattered 

0.4 m below the top of the sand unit at one locality are dated 

at >40,000 yr B.P. They probably were redeposited from older 

sediment. The bluff is capped by frost-mixed, slightly oxidized, stony sandy silt that is overlain by peat and modern sod.

Exposure Nk-5

An east-facing river bluff near the north edge of a large 

alluvial fan west of Lake Matcharak stands 16.8 m high, with 

only basal sections exposed. Its terrace-like upper surface 

matches in height the extensive terrace around Lake Matcharak. The measured section (fig. 8) may represent a younger 

terrace remnant inset within the older ice-stagnation and 

basin-filling deposits that cover most of this stretch of the valley floor. Exposed sediments primarily are fine Noatak River 

gravel that includes granule-sized rock chips characteristic of 

local alluvial fans. A gravel-filled burrow is present in the sand 

and silt deposit that separates the gravel units. 

Exposure Nk-6

A southwest-facing cutbank 25.6 m high intersects partly 

eroded remnants of a postglacial valley floor about midway 

between Douglas Creek and Lake Matcharak. The basal unit in 

the exposure (unit 1) consists of coarsening-upward sediments 

that probably were deposited in a broad, shallowing body of 

standing water (fig. 9). Thixotropic, gray, structureless clayey 

silt grades upward into fine sand and silty very fine sand that 

form parallel laminations 1-3 cm thick and ripple-drift sets 6-8 

cm thick with drapes of silty fine sand up to 3.5 cm thick. The 

upper part of the unit consists of well sorted and well bedded 

fine and medium sand. Overlying alluvial gravel (unit 2) is 

capped by frost-churned, stony, peaty silt that thickens and 

thins above the channeled gravel surface.

A 16-m terrace is attached to the downvalley end 

of exposure Nk-6 by a slip-off slope that formed during 

river downcutting. The terrace face exposes alluvium and 

capping deposits similar to those seen farther upvalley at 

exposure Nk-5.

m

15

10

 5

 0

10,000±145

(I-11,423)

4

3

2

1

? ? ? ?

Covered Debris

apron

Note expanded scale

Peat and silt. Peat, silty peat, and gray peaty silt; 

horizontally layered. Contains gastropod shells. 

Floodplain deposit.

Sand and fine gravel. Slightly crossbedded silty 

fine sand with gravel lenses. Overlain by nonbedded, 

silty, sandy, fine gravel that contains many vertical 

stones. Overbank deposit.

Peat. Dark reddish brown (5YR 2.5/2) woody peat. 

Contains scattered pebbles, granules, and sand 

grains; horizons of calcareous algae; beds of silty 

peat; and lens of fine gravel. Floodplain deposit.

Fine gravel. Granules, pebbles, and sparse small 

cobbles, with beds of medium sand 4-6 cm thick. 

Stones in top 15 cm have minor oxide staining and 

vertical fabric, and are intruded into base of unit 2. 

Alluvium.

4 0.5

3 0.6

2 2.1

1 5+

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION
Upper Noatak River Valley 9

Figure 8. Exposure Nk-5. 

South side Noatak River 3.5 km 

northwest of Lake Matcharak.

m

15

10

 5

 0

20

4

3

2

1

Covered

Covered

Note expanded scale

Sod and sandy sod. Bluff cap.

Gravel. Rounded to subrounded pebbles 

and small cobbles in matrix of grayish brown

(10YR 5/2), poorly sorted, fine to coarse sand

with granule-sized rock chips. Alluvium + 

fan deposit.

Sand and silt. Gray (2.5Y 5/5) slightly clayey

silt to silty fine sand, alternating with grayish

brown (10YR 5/2) fine sand to poorly sorted

coarse to fine sand in parallel beds 3-15 cm

thick. Floodplain deposit.

Sand and gravel. Beds 40-50 cm thick of 

subrounded pebbles and small cobbles in matrix 

of poorly sorted fine to coarse sand with granules; 

alternate with parallel beds 10-25 cm thick of 

laminated well-sorted fine sand and clayey silt. 

Fluvial slackwater + fan deposits.

4 0.2

3 0.7

2 0.5

1 6.5+

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

Figure 9. Exposure Nk-6. 

North side Noatak River 11 

km east-southeast of mouth 

of Douglas Creek.

m

30

20

10

 0

3

2

1

Stony, peaty silt. Light gray to light yellowish brown 

(10YR 6/1 to 10YR 6/4) silt with frost-mixed, vertically 

oriented stones and with deformed lenses of reddish

brown peat. Floodplain deposit.

Sandy gravel. Matrix-free granule-pebble-small-cobble 

gravel at base. Coarsens upward into rounded to 

subrounded pebbles, cobbles and sparse very small 

boulders in matrix of poorly sorted medium to coarse sand 

with granules. Channeled upper surface. Alluvium.

Sand and silt. Gray, structureless, clayey silt; grades 

upward into rythmically laminated fine sand and silty fine 

sand cut by cast of syngenetic ice wedge. Capped by fine 

and medium sand in parallel wavy beds 2-8 cm thick. 

Basin-fill deposit.

3 0.4 - 1.3

2 10.2 - 9.3

1 15

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

Exposure Nk-7

A northwest-facing cutbank at the apex of a meander bend 

7 km upvalley from the mouth of Douglas Creek stands 29.7 m 

high; it intersects a kettle-pocked erosion remnant of the former 

Noatak valley floor. The north end of the exposure contains 

sand overlain by thick gravel (fig. 10). Beds within the sand 

(unit 1) dip downvalley at 2°–5°. The gravel (unit 2) consists 

of rounded to subrounded stones up to 55 cm diameter with 

sand interbeds 15-20 cm thick. Frost churning has affected the 

surface cap of sod and silt (unit 3), which contains some stones 

admixed from the underlying gravel. Peat 10 cm above the base 

of the bluff cap at one locality is dated at 2,660 ± 80 yr B.P.

Near the midpoint of the bluff, unit 1 thickens to 26.5 m 

and consists of fine sand with interbeds of medium sand and 

fine gravel. All beds dip downvalley at about 15°, and climbing ripple sequences are common. The unit clearly is deltaic.

Near the downvalley end of the bluff, deltaic sand 

with gravel interbeds overlies 5.4 m of highly deformed 

sand beds. Formerly near-horizontal parallel beds of fine 

to medium sand 5-6 cm thick have been folded, contorted, 

segmented, and rotated, probably by melt of nearby 

glacier ice.

The surface of the erosion remnant contains three pondfilled kettles. Two kettles have water levels about 20 m above 

the river; the third kettle has been breached by the river and 

partly filled with sediments to about the level of the modern 

floodplain. Kettle-like ponds within this sediment fill suggest 

that ice blocks may still have been present after the river 

downcut to about its present level.
10 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

Figure 11. Exposure 

Nk-8. North side Noatak 

River 0.5 km above mouth 

of Douglas Creek. Frontal 

view of exposure. Black 

dot, radiocarbon age 

determination (yr B.P.) 

with laboratory number 

in parentheses (see 

appendix 1).

Exposure Nk-8

A cutbank along the north side of the Noatak River just 

above the mouth of Douglas Creek intersects an 18-m alluvial 

terrace that is inset within the Itkillik II moraine belt. Separate 

sections were measured at the east and west ends of the exposure, as described previously by Hamilton and others (1987).

The eastern (upvalley) section consists dominantly of deltaic foreset beds that dip downvalley at angles as steep as 26° 

near the base of the section, decreasing upward to 6°-8° (fig. 

11). Fine to medium sand, stony sand, and fine gravel alternate 

in beds 10-50 cm thick. A bed of black autochthonous peat 2-8 

cm thick at the contact between the gravel and the underlying 

deltaic beds is dated at 9,280 ±150 yr B.P. The peat extends 

through the eastern part of the bluff, indicating that deltaic 

sediments were exposed subaerially for some time before the 

Noatak River overran the site. 

Near the center of the exposure, the deltaic sediments 

grade downward and westward into gray horizontally bedded, 

well sorted fine sand with some 20-cm interbeds of clayey 

silt to silty fine sand. Small wood fragments and rootlets from 

along bedding planes 1.4 m below the upper contact of this 

unit are dated at 15,030 ±200 yr B.P.

Figure 10. Exposure 

Nk-7. South side Noatak 

River 7 km eastsoutheast of mouth of 

Douglas Creek; north 

end of bluff. Black 

dot, radiocarbon age 

determination (yr B.P.) 

with laboratory number 

in parentheses (see 

appendix 1).

Near the west end of the bluff, dark gray organic silt 

grades upward into sandy fine gravel. Overlying coarser gravel 

(unit 2) consists of rounded to subrounded pebbles, small 

cobbles, and some larger cobbles in a sparse sandy matrix. The 

gravel thickens downvalley, where an inactive fan of Douglas 

Creek is graded to the gravel terrace.

Exposure Nk-9

A prominent bluff on the southeast side of the Noatak 

River 1.5 km below Douglas Creek intersects an eroded remnant of the Itkillik II drift sheet whose irregular upper surface 

rises to a maximum height of 36.7 m. A terrace-like bench 13 

m high is cut into its east flank, and a surface equivalent to the 

17-m terrace of exposure Nk-8 abuts its south flank.

Beds of fine sand at the base of the section (fig. 12) 

show northeastward (upvalley) apparent dips, but associated 

structures indicate an updip flow direction (about 275°). This 

anomaly indicates that the present dip of the beds probably 

developed postdepositionally, perhaps by deformation associated with wastage of stagnant glacial ice. Coarse alluvial gravel 

above the sand contains clasts up to 32 cm diameter. A possible 

deltaic deposit with east-dipping beds caps the section.

m

30

20

10

 0

3

2

1

2,660 ± 80

(I-12,511) Sod and silt. Sod above silty sod and

humic silt. Some nearly vertical stones near

base. Bluff cap.

Gravel. Pebbles, small cobbles, and sparse

larger stones in abundant sand-granule matrix.

Contains sparse beds of fine to medium sand. 

Alluvium.

Sand. Well sorted fine to medium sand, in

parallel sets with some ripple-drift crosslamination. Locally deformed by faulting. 

Upper contact obscured by gravel drape. 

Deltaic deposit.

3 0.7

2 <19

1 >10

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

15,030 ± 200 9,280 ± 150

(I-12,514) (I-13,396)

m

20

10

 0

ca. 200 m

W E

Sod and silt. Surface sod above 

gray to brown stony silt with deformed 

lenses of brown peat. Bluff cap.

Gravel. Pebbles, small cobbles, and

some larger cobbles in sparse sandy

matrix. Some sand interbeds. 

Alluvium.

Sand and silt. Steeply dipping sand,

stony sand, and small-pebble gravel;

alternating in beds 10-50 cm thick.

Capped by bed of black peat 2-8 cm

thick. Grades westward into horizontally

bedded fine sand, silty fine sand, and

clayey silt. Deltaic and lacustrine beds.

3 0.7

2 4.8-2.5

1

3

2

1

12.0-14.3

THICKNESS

(m)

UNIT DESCRIPTION 

and 

INTERPRETATION
Upper Noatak River Valley 11

3

2

1

Sand and fine gravel. Inclined beds of fine sand 

and pebble-small-cobble gravel, with some drapes

of gray clayey silt. Deltaic deposit.

Coarse gravel. Rounded to subrounded clasts up 

to large cobble size, with some very small boulders. 

Alluvium.

Sand. Fine sand and silty fine sand; commonly in 

parallel beds and laminae. Ripple cross-laminae, 

planar and tangential crossbeds, silt drapes, and 

flame structures also present. Ice-contact deposit?

3 ca.10

2 ca.16.5

1 ca.10

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

m

30

 0

20

10

40

Figure 12. Exposure Nk-9. 

Southeast side Noatak River 

1.5 km downstream from 

mouth of Douglas Creek.

Figure 13. Exposure Nk-10. 

North side Noatak River 3.5 

km west of mouth of Douglas 

Creek.

?

? ? ?

1

2 Silt. Poorly exposed. Contains rythmites consisting of 

alternating coarse silt and slightly clayey fine silt, with 

sparse dropstones. Beds are tilted, faulted, and folded, 

with deformation increasing downward. Distal

glaciolacustrine deposit.

Stony silt. No primary exposures. Rounded to 

subrounded stones to 47 cm diameter mantle bluff 

face. Ice-proximal glaciolacustrine deposit.

2 ca.30

1 ca.26

m

60

40

20

 0

Note compressed scale

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

Exposure Nk-10

A weathered bluff on the north side of the Noatak River 

3.5 km west of Douglas Creek has a poorly exposed face 56 

m high, and rises inland at a gentler angle for 7 m more to an 

irregular kame and kettle surface. The bluff intersects the inner 

edge of the Itkillik II end-moraine complex. It exhibits silt 

above stony silt, with stones becoming abundant below 26 m 

height (fig. 13).

The silt (unit 2) contains rhythmites of alternating coarse 

silt and slightly clayey fine silt, with sparse dropstones. Some 

ripple-drift cross-laminations occur within thicker layers, but 

beds generally are parallel. Couplets 0.4-5 cm thick occur in 

packets of 10-40 thin or thick couplets, with thickness being 

fairly constant within each packet. The coarse and fine layers 

of each couplet show equivalent thickness variations, suggesting formation by turbidity currents rather than annual sediment cycles (G.M. Ashley, Rutgers University, oral commun., 

7/5/83). The beds are tilted, folded, and cut by normal faults, 

with intensity of deformation increasing downward. They dip 

southwest at 10°-12°, possibly due to the melt of underlying 

glacier ice.

The silt becomes increasingly stony below 26 m height, 

and rounded to subrounded clasts up to 46 cm diameter mantle 

the face of the bluff. The stones possibly were deposited as 

dropstones or turbidites in an ice-proximal lake.

Exposure Nk-11

A south-facing 70-m bluff 5.5 km below the mouth of 

Douglas Creek is situated within the moraine belt of Itkillik 

II age. The bluff intersects an irregular surface that contains 

numerous kettles and several river-terrace remnants that 

formed as drainage became reestablished during glacier retreat 

from the Itkillik II end moraine (Hamilton and others, 1987). 

The lowest stratigraphic unit (unit 1), which forms verticalsided buttresses near the base of the section, consists of compact pebble-small cobble gravel in a silty sand matrix (fig. 14). 

The upper part of the deposit is structureless, but overturned 

folds and one near-vertical 30-cm bed of deformed peaty silt 

are present at greater depth. The peaty silt bed has an apparent 

age of 34,990 ± 230 yr B.P. Unit 1 probably is stream gravel 

with associated floodplain deposits that subsequently was 

deformed by overriding glacier ice.

Overlying alluvium (unit 2) consists of parallel-bedded 

to crossbedded sand, pebbly sand, and pebble-small-cobble 

gravel. Beds of oxidized organic silt with rootlets in growth 

position 4 m and 2 m below the top of the alluvium are dated 
12 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

at 34,840 ±950 yr B.P. and 30,070 ±470 yr B.P., respectively. 

Gravel beds at greater depth dip upvalley at angles up to 12°-

34°, then level out and fine laterally to form a paleobasin floor 

composed of muddy sand. This closed depression within the 

gravel may have resulted from continued melt of buried glacier 

ice during deposition of unit 2. 

The upper diamict (unit 3) is interpreted as massive till 

with basal sediments consisting largely of redeposited river 

gravel. Unsorted, rounded to subrounded, striated clasts up to 

boulder size dispersed in a compact, gray, silty matrix grade 

downward at about 3.5 m depth into compact rounded pebbles 

and small cobbles that resemble the diamict of unit 1. Like 

unit 1, this deposit exhibits faint, highly deformed size stratification. Clasts of peaty silt incorporated in the diamict 70 cm 

above its base are dated at 34,010 ± 350 yr B.P.; they must 

have been redeposited from unit 2.

Unit 4 consists of rounded to subrounded alluvial pebbles 

and cobbles in a poorly sorted matrix of sand with phyllite 

chips. The alluvium contains several near-horizontal sand beds 

10-30 cm thick that are continuous laterally for at least 20 m. 

A lag concentration of boulders up to 60 cm diameter occurs 

at the base of the alluvium and on the upper surface of the 

underlying diamict.

Exposure Nk-12

An unusually unstable bluff extends along the north bank 

of the Noatak River at the head of the Itkillik II outwash train 

(see fig. 5). The moraine front here is irregular and has been 

eroded by both glacial meltwater and by ice-marginal drainage derived from Douglas Creek. The outwash head is kettled, 

indicating that outwash overlapped the stagnating glacier 

terminus. Much of the basal unit in the bluff has deformed 

plastically, extruding toward the river edge and causing grabens and other tension features to form in the overlying gravel. 

The bluff’s irregular upper surface contains many steep (up to 

34°), unstable, unvegetated fault scarps indicative of continued 

tensional deformation.

Figure 15. Exposure 

Nk-12. North side Noatak 

River 10 km west of 

mouth of Douglas Creek. 

Upvalley (east) end.

m

30

 0

20

10

40

3

2

1 Diamict. Stones to very small boulder size (40 cm

diameter) in matrix of dark greenish gray stony silt to 

clayey silt. Wedges out downvalley. Till or 

glaciolacustrine deposit.

Gravel. Stones up to large cobbles, with some very 

small boulders, in matrix of course sand and granules. 

Outwash.

Sand and soil. Silty fine sand with some frost-mixed 

pebbles and cobbles. Bears Arctic Brown Soil profile, 

with solum 19 cm thick. Bluff cap.

1 16

2 15

3 0.3

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

m

60

 0

40

20

80

Covered

34,010 ± 350

(USGS-2453)

30,070 ± 470

(USGS-1835)

34,840 ± 950

(USGS-1836)

34,990 ± 230

(USGS-2454)

4

5

3

2

1

Note compressed scale

Upper diamict. Clasts up to boulder size dispersed 

in compact gray silt. Grades downward into compact, 

deformed, pebbles and small cobbles in silty matrix. 

Till and tectonized proglacial deposit.

Sand and fine gravel. Fine to medium sand, pebbly 

sand, and pebble-small-cobble gravel. Contains beds 

of oxidized organic silt near upper contact. Alluvium.

Lower diamict. Rounded pebbles and small cobbles 

in matrix of compact silty sand to sandy silt. 

Structureless near top; faintly bedded and deformed 

near base. Till and tectonized alluvium.

Coarse gravel. Pebbles and cobbles in matrix of 

poorly sorted sand with phyllite chips. Some sand 

interbeds. Alluvium.

Peat and silt. Peat above frost-mixed silty peat; 

grades downward into silty gravel. Bluff cap.

Debris apron.

3 10.1

4 22

5 0.7

2 18

-- 9.7

1 10.5

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

Figure 14. Exposure 

Nk-11. North side Noatak 

River 5.5 km west of 

mouth of Douglas Creek. 

Black dot, radiocarbon 

age determination (yr 

B.P.) with laboratory 

number in parentheses 

(see appendix 1).
Upper Noatak River Valley 13

Figure 16. Exposure Nk-13. North 

side Noatak River 13 km west of 

mouth of Douglas Creek. Black dot, 

radiocarbon age determination 

(yr B.P.) with laboratory number in 

parentheses (see appendix 1). 

m

30

20

10

 0

30,160 ± 410

(USGS-1837)

2

1

Covered

Debris apron.

Gravel. Interbedded sand and pebble-smallcobble gravel at base. Grades upward into 

pebble-small-cobble gravel with some sand and 

pebble beds, then into weakly stratified pebbles 

and cobbles in matrix of medium to coarse sand 

and granules. Alluvium, grading upward into 

outwash.

Sod, peat, and silt. Sod and brown peat

above stony silt. Many stones vertical. 

Bluff cap.

-- 6.0

1 24.5

2 1.1

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

Diamict comprises the basal half of the bluff (unit 1) at 

its upvalley end (fig. 15) but it wedges out downvalley, and 

overlying outwash gravel thickens correspondingly. Diamict 

and gravel have been mixed together through much of the 

lower part of the bluff, and the original character of the basal 

diamict has been obscured. 

The outwash (unit 2) consists dominantly of rounded to 

subrounded stones to large cobble size with some very small 

boulders (30-35 cm diameter) in a matrix of coarse sand and 

granules. The underlying diamict consists of clasts of similar 

size, shape, and lithologies in a matrix of dark gray stony 

clayey sandy silt. Clasts on the exposed face of the diamict 

may largely be derived from overlying outwash, but the high 

clay content (about 5-10 percent) and extreme instability of the 

diamict suggest a separate, possibly glaciolacustrine, origin.

Exposure Nk-13

An exposure into the Itkillik II outwash terrace 3 km 

downvalley from the moraine front stands about 31.5 m high. 

The terrace surface is planar for about 1 km upvalley from that 

exposure, then it degenerates into kame-and-kettle topography 

that probably marks the downvalley limit of Itkillik II glacier 

ice. Other kettle fields downvalley from the exposure probably 

developed from melting of older glacial ice of Itkillik I age 

after overriding by the Itkillik II outwash train.

The section at exposure Nk-13 consists of alluvium 

which coarsens progressively upward into outwash, with no 

evident erosion surfaces or unconformities (fig. 16). In the 

basal 8 m of the exposure, beds of medium to coarse sand up 

to 25 cm thick alternate with thicker beds of sandy pebblesmall-cobble gravel. The central 8 m of the section consists 

of faintly bedded rounded pebbles, small cobbles, and sparse 

medium cobbles with some 10-cm interbeds of coarse sand 

and pebbles. Pebbles, small to medium cobbles, and sparse 

larger cobbles in a matrix of nonoxidized medium to coarse 

sand and granules dominate the upper 8 m of the deposit. A 

bed of dark gray clayey silt and gray silty fine sand 8.5 m 

above river level contains sparse rootlets and organic detritus 

that are dated at 30,160 ±410 yr B.P.

Progressive changes in clast lithology reflect increasing dominance of upvalley sources as sediment size increases 

upward through the section. The percentage of locally derived 

carbonate rocks decreases upward from 30 to about 10; 

whereas granitic rocks from glacial source areas near the valley head increase upward from less than 1 percent of all clasts 

to about 10 percent.

Discussion

The 11 exposures from the upper Noatak River valley provide a complete cross section through the Itkillik 

II moraine belt and through the lacustrine and slackwater 

deposits that formed during glacier retreat (fig. 17). Radiocarbon ages from five of the bluffs (appendix 1) provide a direct 

age bracket for the advance and retreat of the Itkillik II glacier 

(Hamilton and others, 1987), and provide limiting ages on the 

subsequent lake stage.

Nk-9 through Nk-13 provide exposures 30-70 m deep 

into the Itkillik II moraine belt and its associated outwash 

apron. Radiocarbon dates show that deposition of fine interstadial alluvium began sometime before 35 ka and continued 

until at least 30 ka. Subsequent glacier expansion is recorded 

by coarsening-upward sediment with increasing upvalley 

lithologies at Nk-13 and by deposition of the upper diamict at 

Nk-11. The glacier initially eroded and redeposited interstadial 

alluvium along the valley center, then later deposited massive, 

bouldery, silt-rich till.

The basal diamicts at exposures Nk-12 and Nk-11 are 

puzzling. Geologic relations at the moraine front indicate that 

the diamict at Nk-12 should be a till, but its unstable, plastic 

character and high silt content suggest that it may be glaciolacustrine in part. Perhaps the Itkillik II glacier advanced past 

the site, retreated, and then readvanced into moraine-dammed 

lake deposits to form the basal diamict. The lower diamict 

of Nk-11 has an apparent radiocarbon age of 34,990 ±230 yr 

B.P., which approaches the limit of accurate radiocarbon dating. The lower diamict most likely is a subglacial deposit that 

consists of till above ice-thrust alluvium, but its radiocarbon 

determination may be a minimum age that does not closely 
14 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

date the glacial advance. However, subsidence features in the 

overlying alluvium indicate that stagnant glacier ice must still 

have been present during deposition of the interstadial alluvium, and kettles in Itkillik II outwash downvalley from Nk-13 

likewise indicate persistence of underlying glacial ice until late 

Wisconsin time (Hamilton and Van Etten, 1984).

Exposures Nk-10 and Nk-9 exhibit glaciolacustrine sediments to heights as great as 56 m above modern river level and 

deformation structures formed by melting of buried glacial ice. 

These deposits may represent an early ice-contact stage of a 

lake that formed behind the moraine dam shortly after deposition of the upper diamict and high-level (48-69 m) recessional 

outwash at Nk-11.

As the Itkillik II glacier continued to retreat upvalley, an 

elongate lake formed within the basin that developed behind 

its moraine belt. The lake extended upvalley at least 11 km, 

as indicated by the basal lacustrine and deltaic units at Nk-8 

through Nk-6, and it filled with dominantly deltaic sediments 

to a height of 11-15 m above modern stream level before probable breaching of the moraine dam allowed reestablishment of 

the Noatak River through this stretch of its valley. Radiocarbon ages from Nk-8 show that the lake was in existence by 15 

ka and that the river had become established across the former 

lake floor by about 9.3 ka.

Exposures Nk-5 and Nk-4 show that the elevated base 

level provided by the moraine-dammed lake caused the Noatak 

River to aggrade by about 10 m farther upvalley, depositing 

slackwater sediments upstream to at least the Lake Matcharak 

area (see fig. 5). Alluviation of fine gravel upvalley from Lake 

Matcharak also may be related to this base-level rise, because 

its minimum age limit of 10.0 ka at Nk-3 is close to the age 

limit of 9.3 ka on lacustrine deposits at Nk-8. 

Subsequent alluviation formed a conspicuous 17- to 18-m 

terrace that is widespread around Lake Matcharak and traceable downvalley through the Douglas Creek area. Alluviation 

of terrace gravel ended sometime between 9.3 and 2.7 ka, 

based on bracketing radiocarbon ages from Nk-8 and Nk-7, 

respectively.

Schist, vein quartz, and granitic rocks dominate the 

lithologies of all diamicts and gravel units in the upper Noatak 

valley. Quartzite and carbonate rocks generally are present 

but less abundant. Granitic rocks commonly are the major 

component of the largest size fractions, and they are particularly abundant in glacial till and outwash. Especially during 

times of aggradation, when little sediment by-passing occurs, 

interstadial deposits derived largely from adjoining tributary 

valleys are distinguished readily from glacial deposits, which 

typically were dominated by sediments eroded from the rugged granitic highlands at the valley head.

Aniuk River Area

Introduction

For about 9 km downvalley from the Itkillik II moraine 

front, the Noatak River occupies a narrow (0.5 km) Holocene 

floodplain flanked by the 30-m terraces of the continuous outwash apron that originates at that moraine. Beyond this point, 

the floodplain abruptly widens to about 3 km and is bordered 

by more fragmentary remnants of the outwash (fig. 18). These 

outwash remnants commonly are flanked by younger terraces 

composed dominantly of sand. Both outwash and sand are heavily kettled, indicating that numerous stagnant ice masses of Itkillik I age must have persisted through the Itkillik II ice advance.

The Itkillik I end-moraine complex crosses the valley center in a 9-km-wide belt 22-32 km downvalley from 

the Itkillik II moraine front. The Holocene floodplain of the 

Noatak River narrows to 1.0-1.5 km through this stretch, and 

is bordered by remnants of Itkillik II outwash incised within 

till and ice-stagnation deposits of the Itkillik I glacial advance.

Downvalley from the Itkillik I moraine front, the Noatak 

basin floor becomes a broad plain of low relief that is underlain by glaciolacustrine deposits of Itkillik I and Itkillik II 

Figure 17. Section through Itkillik II (late Wisconsin) moraine belt, upper Noatak River valley, showing interrelations of exposures Nk-8 through Nk-13. Vertical scale shows altitude (meters above sea level). Black dot, radiocarbon age determination (yr B.P.) with laboratory number in parentheses (see appendix 1).

0 4 8 km 

425

400

450

475

500

525

550

m asl 

Nk-13 Nk-12

Nk-11 Nk-10

Nk-8

30,160 410

34,840 950

30,070 470

9,280 150

15,030 200

Alluvium

Lacustrine deposits

Distal

Proximal

Till

Outwash

Glaciolacustrine

deposits

34,010 560

?
Aniuk River Area 15

ages (fig. 18) and locally by concealed older deposits. The 

lacustrine plain is incised deeply by the Aniuk River as well 

as the Noatak River, and bluff exposures along both drainages 

provide good stratigraphic records of alternating glacial and 

alluvial episodes.

The upper reaches of Aniuk River were largely fed by 

eastern tributaries that originated as outwash trains of Itkillik 

age (fig. 18; Hamilton, 1984a, 1984b). Exposures generally 

are limited to late Pleistocene and Holocene alluvium.

Exposure Nk-14

A bluff with a severely slumped face extends along the 

south bank of the Noatak River 5 km upvalley from the mouth 

of Atongarak Creek. The exposed part of the bluff face stands 

17 m high and consists of a younger sandy terrace deposit 

that is incised within the outwash terrace of Itkillik II age (see 

fig. 18). A vegetated slope rises inland from the bluff crest to 

the terrace-like surface of the sand deposit that stands 21.5 m 

above river level.

A partial section excavated 11-14 m above the river 

exposed about one meter of bedded sand with willow-cored 

peaty sand mounds above tundra soil (fig. 19). The buried 

tundra soil consists of layers of black humic fine sand up to 

about 20 cm thick alternating with thinner beds of dark gray 

fine sand. The humic sand contains abundant rootlets. Beds are 

deformed by overturned folds of probable solifluction origin 

and by collapse into a wedge-like depression. A thick peaty 

bed at 11.5 m height is dated at 4,220 ±110 yr B.P.

Figure 18. Generalized geologic map, Aniuk River area, north-central upper Noatak basin. Outer and inner Itkillik I 

drifts are correlated with Itkillik IA and IB advances elsewhere in Brooks Range. Unit (sd) designates glacial deposits 

of probable middle Pleistocene age that are concealed beneath glaciolacustrine sediments.

Howard

 Pass

An-2

Nk-19

Nk-18

Nk-20

Nk-17

Nk-16

Nk-15

Nk-21

Nk-14

Nk-14A

Nk-13

An-3

An-1

An-5

An-6 An-7

Aniuk

River

Noatak

Noatak R

River

Atongarak Creek

Flora Cr

Pupik Hills

An-4 

Kettle 

?

?

?

?

?

?

?

Glaciolacustrine

deposits

Itkillik I

Itkillik II

Itkillik I

Older

Bedrock and colluvium,

undifferentiated

Meltwater

channel

Inferred 

subsurface

contact

Terrace gravel

Alluvium

Itkillik II

Itkillik I

Topographic

divide 

Sand deposits Drift

sheets

Outwash

?

?

0 25 KILOMETERS

0 15 MILES

68o

10'

157o 158 00' o

00'

68o

00'

(sd)

(sd)

(sd)

(sd)

(sd)

(sd)

(sd)

(sd)

Figure 19. Exposure Nk-14. South side Noatak River 27 km eastsoutheast of mouth of Aniuk River. Black dot, radiocarbon age determination (yr B.P.) with laboratory number in parentheses (see appendix 1). 

m 20

10

 0

3,710 ± 90

(I-13,448)

3,110 ± 90

(I-12,515)

4,220 ± 110

(I-13,521)

? ? ?

Sand and organic sand. Gray, 

fine to medium sand; grading 

upward into black, organic, silty 

fine sand. Deformed paleosol 

(tundra soil) at 11-13 m above river 

level. Peat beds and willows in 

growth position common. Face 

severely slumped and collapsed. 

Floodplain and marsh deposits.

19.8

THICKNESS

(m)

DESCRIPTION and

INTERPRETATION
16 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

The tundra soil is overlain by brownish gray medium and 

fine sand that alternate in beds 1-2 cm thick. Peaty interbeds 

and abundant rootlets in growth position are present within the 

sand, and willow stems up to 5 cm diameter commonly form 

the cores of peaty lenses. Beds typically are undulating at the 

base of the unit, reflecting the surface of the underlying buried 

soil, and become more planar upward. Willow in growth position at 13 m height is dated at 3,710 ± 90 yr B.P.

Willow in growth position also was sampled 6.4 m above 

the river during an earlier visit to this site. Its radiocarbon age 

of 3,110 ± 90 yr B.P. is too young for its position in the bluff 

face. The willow may have been in a slump block that was not 

recognized during that visit.

Exposure Nk-14A (not illustrated)

A partly vegetated bluff face on the north shore of a 

kettle lake 1.5 km north of the Noatak River opposite Nk-14 

(see fig. 18) intersects probable outwash of Itkillik II age. The 

weathered face of the bluff stands 30 m above river level and 

exhibits rounded pebbles and small to medium cobbles (up to 

16 cm long) in a sandy matrix. The upper 1.1 m of the deposit 

is a light gray (5Y 6/2), frost-churned, silty sandy gravel with 

many stones oriented vertically.

The kettle at the base of the bluff intersects an abandoned channel network of the Noatak River that probably is 

of late Holocene age (Hamilton, 1984a). The kettle clearly 

has enlarged into these deposits, and shows no evidence of 

sediment filling from the river. It evidently has continued to 

develop into late Holocene time, and may still be active today.

Exposure Nk-15

The north-facing cutbank of a large-amplitude meander 

bend of the Noatak River intersects deposits of Itkillik I age 

about 5.5 km south-southeast of the mouth of Atongarak 

Creek (see fig. 18). The valley floor here is a kettled surface 

of low relief that probably formed during or after ice wastage 

from the Itkillik I moraine belt.

The bluff face stands 50 m high and exposes gravel 

overlain by sand (fig. 20). The contact between these units is 

hummocky in profile, with relief up to about 15 m. The gravel 

consists of rounded to subrounded pebbles and cobbles in a 

sandy matrix, and includes some small boulders up to about 

70 cm long. The overlying sand deposit has a planar upper 

surface which masks the relief on the underlying gravel.

Exposure Nk-16

A cutbank on the south side of the Noatak River 3 km 

above the mouth of Atongarak Creek stands 24.8 m high 

and exposes probable outwash gravel (fig. 21). Pebbles and 

cobbles up to about 30 cm diameter, with sparse boulders, 

occur in a sandy matrix. Some sand layers are interbedded 

within the gravel.

From the bluff crest, the surface rises inland 15 m more 

to a flat-topped surface of pebble-cobble gravel with sparse 

small boulders in a matrix of oxidized dark yellowish brown 

(10YR 4/4) sand. The oxidized matrix of this deposit contrasts 

strongly with the virtually unweathered matrix of the younger 

gravel unit in the cutbank.

Figure 21. Exposure Nk-16. South 

side Noatak River 22 km eastsoutheast of mouth of Aniuk River. 

m

30

20

10

 0

Gravel. Stones to cobble size, with sparse

large boulders, in oxidized dark yellowish brown 

sandy matrix. Some sand layers. Outwash.

24.8

THICKNESS

(m)

DESCRIPTION and INTERPRETATION

Figure 20. Exposure Nk-15. South 

side Noatak River 25.5 km eastsoutheast of mouth of Aniuk River.

m

60

40

20

 0

2

1

Note compressed scale

Gravel. Rounded to subrounded pebbles,

cobbles, and some small boulders in sandy

matrix. Irregular (kame-like) upper surface. 

Outwash.

Sand. Very well sorted fine sand to silty

fine sand. Gently undulating upper surface. 

Slackwater or lacustrine deposit.

1 50-35

2 0-15

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION
Aniuk River Area 17

Figure 22. Exposure Nk-17. North side Noatak River 17.5 km east 

of mouth of Aniuk River. 

Exposure Nk-17

A cutbank exposure on the north side of the Noatak River 

5 km northwest of Atongarak Creek intersects a probable 

outwash terrace inset within the outermost end moraine of 

Itkillik I age (see fig. 18). The moraine here is represented by 

hummocky coarse gravel, which stands 35 m above the river. 

Unvegetated scarps and sag ponds suggest lateral flow toward 

the river; they expose poorly sorted stones up to 65 cm long in 

a muddy matrix.

The river-cut face of the moraine is obscured entirely 

by slides and flows (unit 1; fig. 22). Exposed clasts are 

subrounded pebbles, cobbles, and very small boulders of 

upvalley lithologies (granite, gneiss, vein quartz, schist, 

and carbonate rocks). Matrix material is sand and silt, but 

may have been mixed on the bluff face, and original matrix 

composition is uncertain.

A 16.5 m gravel terrace (unit 2) is inset within the 

moraine (fig. 22). Weakly stratified, subrounded, pebble-small 

cobble gravel in a matrix of well washed coarse sand coarsens 

upward slightly into the middle part of the unit, where sparse 

medium cobbles occur. Gravel beds 50 cm thick alternate with 

10-cm beds of pebbly medium sand. Clasts are of upvalley 

lithologies, dominantly schist, vein quartz, and carbonate 

rocks. The gravel is capped by 1.8 m of gray, frost-mixed silty 

sandy gravel (unit 3) that locally overlies fissile gray stony 

clayey silt with sand interbeds.

Exposure Nk-18

A weathered bluff face north of the Noatak River 2 

km downvalley from the outermost Itkillik moraine front 

interesects the outwash apron associated with that moraine 

(fig. 18). The outwash terrace here stands 25 m high; its face 

exposes rounded pebbles and small cobbles up to 15 cm long 

in a sandy matrix (fig. 23). Rock types include granite, vein 

quartz, greenstone, schist, quartzite, and limestone. Many 

stones are carbonate-encrusted and (or) discolored by iron 

and manganese oxides. A trench at the crest of the bluff 

exposes 0.4 m dark grayish brown stony sandy silt above 

yellowish brown sandy gravel.

Figure 23. Exposure Nk-18. North side Noatak River 15.5 km east 

of mouth of Aniuk River. 

m

30

20

10

 0

Gravel. Rounded pebbles and small 

cobbles in sandy matrix, oxidized 

yellowish brown (10YR 5/4) near top. 

Capped by 0.4 m dark grayish brown 

(10YR 4/2) stony sandy silt. 

Outwash.

25

THICKNESS

(m)

DESCRIPTION and

INTERPRETATION

Exposure Nk-19

A cutbank exposure into a Holocene alluvial terrace of 

the Noatak River 3 km downvalley from the Itkillik I moraine 

front (see fig. 18) stands 7.3 m high. The lowest exposed 

deposit (unit 1) is a bed of massive peat 3.3-4.5 m above 

river level (fig. 24). Overlying floodplain deposits (unit 2) 

consist of bedded sand, organic silty fine sand, and sandy 

peat. A sample of the lowest exposed peat is dated at 6050 

±120 yr B.P.

m

 0

20

30

40

10

1 35

2 14.7

3 1.8

THICKNESS

(m)

UNIT DESCRIPTION and

INTERPRETATION

?

1

3

2

Stony silt. Gray, frost-mixed 

stony silt to silty sandy 

gravel; many stones vertical. 

Contains some lenses and 

clots of deformedpeat. 

Locally overlies fissile, gray 

stony clayey silt with sand 

interbeds. Pond deposit.

Gravel. Weakly stratified, 

subrounded pebbles, small 

cobbles, and sparse larger 

cobbles in matrix of coarse 

sand and granules. Some 

10-cm beds of coarse sand 

and pebbly medium sand. 

Outwash.

Diamict. Rounded to 

subroundedpebbles, 

cobbles, and very small 

boulders in sandy to muddy 

matrix. Mixed by slides and 

flows on bluff face. Till and 

ice-contact gravel?

m 9

 6

 3

 0

6,050 ± 120

(I-13,522)

Covered

2

1

Note expanded scale Debris apron.

Peat. Massive peat bed. Bog 

or marsh deposit.

Sand and peat. Sand, sandy 

peat, and organic silty fine sand, 

in parallel near-horizontal beds. 

Base not exposed. Floodplain 

deposit.

-- 3.3

1 1.2

2 2.8

THICKNESS

(m)

UNIT DESCRIPTION and 

INTERPRETATION

Figure 24. Exposure Nk-19. South side Noatak River 13.5 km east 

of mouth of Aniuk River. Black dot, radiocarbon age determination 

(yr B.P.) with laboratory number in parentheses (see appendix 1). 
18 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

Figure 26. Exposure Nk-21. 

Southeast side Noatak River 8 

km south-southwest of mouth 

of Aniuk River. Black dot, 

radiocarbon age determination 

(yr B.P.) with laboratory number 

in parentheses (see appendix 1). 

Exposure Nk-20

A cutbank exposure on the north side of the Noatak River 

6.5 km east-northeast of the mouth of Aniuk River stands 26 m 

high and has a nearly horizontal, planar upper surface. It stands 

near the contact between Itkillik II and Itkillik I glaciolacustrine 

deposits on the Noatak basin floor (see fig. 18). Two silty and 

clayey stony units of probable glaciolacustrine origin are present 

(units 1 and 3; fig. 25). The lower of the two units is a poorly 

sorted stony clay that contains abundant faceted and striated 

clasts of upvalley lithologies. Overlying alluvium (unit 2) was 

deposited on an erosional unconformity that contains lag boulders up to 1.2 m long. In the upper glaciolacustrine unit (unit 3), 

an early shallow-water phase of stone-free fine sediment grades 

upward into clayey silt with dropstones that formed when the 

water deepened and icebergs were able to reach the site. Dropstones dominantly are rounded pebbles and small cobbles, with 

some larger clasts up to small boulder size.

Fragments of a small tree about 13-15 cm diameter occur 

up to 9.4 m height in a gulley on the bluff, but their original 

location on the bluff face could not be determined. The wood 

was identified as probably spruce or possibly larch (USDA/FPL, 

date uncertain).

Exposure Nk-21

A prominent bluff along the southeast side of the Noatak 

River 8 km below the mouth of Aniuk River intersects an unusually high-standing and hummocky part of the Noatak basin floor. 

The bluff face stands as high as 74.5 m, but the ground surface 

rises inland, forming a broad, hummocky, southeast-trending topographic divide about 150 m above river level (see fig. 18).

The basal unit in the bluff is a compact stony silt with scattered striated stones up to 1.2 m diameter (fig. 26). Clasts are 

upvalley lithologies: limestone, dolomite, and marble; with lesser 

granite, gneiss, and a dark aphanitic igneous rock. This glacial 

diamict probably is a till, but its well sorted silt matrix suggests 

that the glacier probably had advanced into a glacial lake and may 

have deposited its load in contact with lake water.

The glacial diamict is transitional upward into interbedded 

sand and sandy fine gravel (unit 2), with maximum clast size about 

7 cm. This unit may be a slackwater deposit that formed when 

the Noatak River was still partly blocked by glacier ice farther 

downvalley. The uppermost unit (unit 3) is best exposed in a promontory at the west end of the bluff, where pebble-small-cobble 

gravel coarsens upward into gravel that contains cobbles and small 

boulders up to about 45 cm diameter.

Figure 25. Exposure Nk-20. 

North side Noatak River 6.5 

km east-northeast of mouth 

of Aniuk River. 

m 30

20

10

 0

4

3

2

1

Peat and organic silt. Bog deposit.

Stony silt. Stones to very small boulder size, commonly 

striated, in matrix of dark gray clayey silt. Stone-free silt, 

sandy silt, and silty clay at base. Upper contact commonly 

channeled, with gravel, peat, and organic silt fillings. 

Upper glaciolacustrine unit.

Gravel. Pebbles, cobbles, and sparse small boulders in 

sandy matrix. Alluvium.

Stony clay. Rounded pebbles, cobbles, and some small 

boulders with random fabric,dispersed in dark greenish 

gray (5GY 4/1)sandy silty clay. Many clasts faceted and 

striated. Erosional upper contact, with lag boulders. 

Lower glaciolacustrine unit.

1 11-13

2 2-6

3 11-6.5

4 0-4.5

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

m

60

40

20

70

50

30

10

 0

3

2

1

Note compressed scale

1 27

2 17

3 30.5

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

Gravel. Pebbles and small cobbles in sandy matrix; 

coarsens upward into cobble-small boulder gravel. Surface 

is littered with boulders and boulder fragments up to ca. 68 

cm length. Alluvium.

Stony and sandy fine gravel. Interbedded in beds 10-50 

cm thick. Sand is dark grayish brown (10YR 4/2), well 

sorted, fine to medium sand with lenses of gray silty fine 

sand. Gravel is dominantly pebbles with coarse sand 

matrix. Transitional contact with unit 3. Fluvial bar and 

overbank deposits.

Stony silt. Striated stones scattered in matrix of dark olive 

gray (5YR 3/2), well sorted, nonbedded silt. Till?
Aniuk River Area 19

Pebble-small-cobble gravel is dominant along the bluff’s 

crest, with scattered larger cobbles and boulders up to a 

maximum length of 68 cm. Boulder lithologies include typical 

upvalley types—granite, gneiss, quartzite, and vein quartz—

with pyroxenite also present. A test pit exposes subrounded 

pebbles and small cobbles in a matrix of yellowish brown 

(10YR 5/4) silt with granules that probably was mixed into the 

gravel by frost activity.

Exposure An-1

A prominent bluff on the south side of Aniuk River 12 

km above its mouth stands about 80 m high. Although this 

feature is only 13 km northeast of Nk-20, it contains a much 

older stratigraphic record that may correlate more closely 

with that of Nk-21. The bluff is well beyond the limit of Itkillik II glaciolacustrine deposition in the basin (see fig. 18), 

therefore all exposed glaciolacustrine units must be of Itkillik 

I age or older.

The lower glaciolacustrine unit (unit 1) is a thick (43 m)

stony gray clay that contains dispersed pebble and cobble 

dropstones. The clay generally is unstratified, but a gravel bed 

is evident at about 15 m height and a peat bed at 25 m height 

(fig. 27). The dispersed clasts decrease in abundance upward, 

whereas layers and lenses of pebble-cobble gravel become 

more abundant in that direction. One gravel layer near the 

upper contact of unit 1 contains boulders to nearly 1 m length; 

another nearby gravel layer is capped by a 2-cm-thick peat bed.

The overlying alluvium (unit 2) is a coarse (cobble-small 

boulder) gravel that contains highly oxidized sand beds. The 

upper 1.2 m of the alluvium has been subjected to severe frost 

action; it has been mixed with the overlying silt and clay, 

and many stones are oriented vertically. A contorted peat bed 

about 10 cm thick is present at 1 m depth at one locality along 

the bluff face.

The upper glaciolacustrine unit (unit 3) consists of gray 

clay and brown silt, which generally are laminated. Stones 

are rare, and none exceed cobble size. Silty peat 2 m above 

the base of the unit is dated at >39,500 yr B.P. A 1.5-m bed 

of pebble-small- cobble gravel in the middle part of the unit 

is capped by a thin (0.5 cm) peat bed with an apparent age of 

39,700 ±1,600 yr B.P., which is beyond the limit of accurate 

radiocarbon dating at other sites in northern and central 

Alaska (for example, Hamilton and others, 1988; Hamilton 

and Ashley, 1993). A pollen assemblage from this peat is 

typical of low shrub-herb tundra with some alder thickets 

(T.A. Ager and E. Shaw, U.S. Geological Survey, written 

commun., 2/8/83). The bluff is capped by about 8 m of 

alluvial gravel (unit 4).

m

80

60

40

20

 0

39,700 ± 1,600

(USGS-1665)

>39,500

(USGS-1666)

4

3

2

1

Note compressed scale

Gravel. Rounded pebbles and cobbles in 

sandy matrix. Alluvium.

Slightly stony clay and silt. Gray clay 

and brown silt, generally laminated. 

Contains sparse pebbles and cobbles. 

Layer of pebble-small-cobble gravel 

capped by thin peat bed occurs 7.5-9.0 m 

above base. Upper glaciolacustrine 

unit.

Gravel. Pebbles, cobbles, and small 

boulders, with interbeds of highly oxidixed 

brown (7.5Y 5/4) sand. Upper 1.2 m 

mixed with gray silty clay and contorted 

peat beds, with many stones vertical. 

Alluvium.

Stony clay. Rounded to subrounded 

pebbles and cobbles in matrix of 

nonstratified gray clay. Stones lack fabric 

and many are steeply inclined. Lenses 

and layers of pebble-cobble gravel 

increase upward. Contains peat beds at 

25 m height and within gravel near upper 

contact. Lower glaciolacustrine unit.

3 20

4 8.2

2 8

431

THICKNESS

(m)

UNIT DESCRIPTION and

INTERPRETATION

Figure 27. Exposure An-1. South side Aniuk River 31 km southwest of Howard Pass. Black dot, 

radiocarbon age determination (yr B.P.) with laboratory number in parentheses (see appendix 1). 
20 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

Exposure An-2

A cutbank on the north side of Aniuk River 5 km west 

of An-1 intersects a 20-m terrace that is widespread along this 

stretch of the river (fig. 18). A probable glaciolacustrine stony 

clay at the base of the exposure (fig. 28) is overlain by oxidized 

sand that grades upward into alluvial gravel. A 5-cm peat bed 

at the top of the gravel, dated at >48,000 yr B.P., contains pollen typical of herbaceous tundra with sparse willows and dwarf 

birch (T.A. Ager and E. Shaw, U.S. Geological Survey, written 

commun., 2/8/83). The topmost unit, which consists of clasts 

dispersed in a brown silty matrix, in part may be a solifluction 

deposit derived from the adjoining valley side.

Exposure An-3

A cutbank on the south side of Aniuk River 4.5 km 

upvalley from exposure An-1 intersects a 20-m terrace that 

contains outwash derived from the Itkillik I moraine front 

overlain by glaciolacustrine deposits (fig. 18). Coarse gravel 

at the base of the section (fig. 29) consists of typical upper 

Noatak drainage lithologies (schist, vein quartz, quartzite, 

and granite). The gravel fines upward into gravelly sand at 

about 7 m height and then into lacustrine sandy silt with 

sparse pebbles at about 12 m. The top 4 m of the bluff face 

is covered largely by peat, which has draped downward over 

ice-rich stony silt.

Exposure An-4 (not illustrated)

A prominent moraine-like ridge along the north side of 

Aniuk River 22 km southwest of Howard Pass (see fig. 18) is 

vegetated, and its poorly exposed face therefore is not illustrated. Remnants of the 20-m outwash terrace are inset along its 

southeast flank, and an apparent kame terrace near its southwest 

end has a probable ice-contact face 25 m high. The ice-contact 

face consists of a mixture of (1) subangular pebbles and small 

cobbles of local sandstone and shale mixed with (2) rounded 

cobbles and small boulders up to 45 cm diameter of granite and 

quartzite. Excavations into the weathered bluff face exposed 

fine sand near river level and, midway up the bluff face, rounded 

pebbles in an abundant matrix of platy coarse sand and granules. 

Cobbles and small boulders are most abundant near the top of 

the bluff. The upper surface of the deposit is continuous with 

paired terrace remnants that are traceable northward along an 

underfit stream channel into the Pupik Hills (see fig. 18).

Figure 28.

Exposure An-2. North 

side Aniuk River 

29.5 km southeast of 

Feniak Lake. Black 

dot, radiocarbon 

age determination 

(yr B.P.) with 

laboratory number 

in parentheses (see 

appendix 1). 

Figure 29. Exposure 

An-3. South side Aniuk 

River 28 km southwest 

of Howard Pass.

m

20

10

 0

>48,000

(USGS-1667)

3

2

1

Stony silt. Pebbles and cobbles dispersed in 

brown sandy silt. Upper 1.5 m frost-deformed

with many stones vertical. Origin uncertain.

Sand and gravel. Fine to medium sand, 

grading upward into pebble-small-cobble

gravel in abundant sandy matrix. Peat bed

at upper contact. Alluvium.

Stony gray clay. No description available. 

Glaciolacustrine deposit?

3 ca.7

2 ca.6

1 ca.7

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

m

20

10

 0

?

4

3

2

1

Stony silt. Sandy silt with sparse pebbles. 

Glaciolacustrine deposit.

Gravelly sand. Transitional contact with

unit 1. Slackwater deposit?

Gravel. Rounded to subrounded pebbles,

cobbles, and sparse very small boulders in

sandy matrix. Outwash.

Largely covered. Probably peat above

stony silt. Bluff cap over glaciolacustrine 

deposit.

3 4

4 4

2 5

1 7

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION
Aniuk River Area 21

Figure 30. Exposure An-5. 

Northwest side Aniuk River 

12 km southwest of Howard 

Pass. Black dot, radiocarbon 

age determination (yr B.P.) 

with laboratory number in 

parentheses (see appendix 1). 

m

5

 0

8,210 ± 130

(I-13,232)

8,530 ± 140

(I-13,231)

2

1

Peat and sand. Massive peat overlain by

silty to sandy peat and fine gravel. Grades

laterally into organic silty fine sand. 

Floodplain deposit.

Gravel. Pebbles and small cobbles of mostly

local lithologies in abundant matrix of gray,

platy granules and medium to coarse sand.

Contains large wood fragments (6 cm diameter)

in lens of organic silty fine sand. Alluvium.

2 2-3

1 3-2

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

Note expanded scale

Exposure An-5

A 5-m cutbank on the northwest side of Aniuk River 

12 km southwest of Howard Pass exposes Holocene alluvial 

gravel and floodplain deposits (fig. 30). Pebbles and small 

cobbles of mostly local platy quartzite and sandstone occur 

in a matrix of gray platy granules and medium to coarse 

sand. Some sandy lenses of similar composition also occur 

within the gravel. At one locality, a channel in the gravel 

surface dips to within 1 m of the river. Large fragments of 

willow (Salix) up to 6 cm diameter in a matrix of organic 

silty fine sand 3.8 m above river level within this channelfilling deposit are dated at 8,210 ± 130 yr B.P.

The gravel elsewhere is overlain by 2-3 m of peat 

that grades upward into silty to sandy peat and fine gravel. 

Fragments of willow (Salix) wood from the base of the peat 

unit are dated at 8,530 ± 140 yr B.P.

Figure 31. Exposure An-6. 

East side Aniuk River 8 km 

southwest of Howard Pass.

m

10

5

 0

2

1

Silty gravel. Gravel clasts mixed with

brown silt. Frost-churned deposit.

Gravel. Rounded pebbles, cobbles, and some

very small boulders in sandy matrix. Outwash.

Note expanded scale

2 1.0

1 7.2

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

Figure 32. Exposure An-7. 

South side Flora Creek 4.5 km 

above its mouth.

m

20

10

 0

Gravel. Pebbles, small cobbles, and some larger

cobbles in very sandy matrix. Sand may underlie

gravel near base of section. Alluvium above 

deltaic(?) deposit.

15

THICKNESS

(m)

DESCRIPTION and INTERPRETATION

?

Exposure An-6

An 8-m cutbank exposure along the east side of Aniuk River 

8 km southwest of Howard Pass exposes mainly alluvial gravel 

(fig. 31). Rounded clasts are up to cobble size, with a few very 

small boulders also present. Quartzite is dominant, but granite 

also is common in the cobble fraction. The uppermost meter of 

the deposit has been frost churned and mixed with brown silt.

Exposure An-7

A cutbank of Flora Creek 4.5 km above its mouth intersects 

a flat-topped gravel deposit 15 m high (fig. 32). Pebbles and small 

cobbles predominate, with small quartz pebbles especially abundant. Sparse larger cobbles of granite, quartzite, and vein quartz 

also are present. The gravel has an unusually sandy matrix, and 

may be underlain by sand. It grades upward into a coarser cobble 

gravel with some very small boulders up to about 45 cm long.
22 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

Discussion

Two unusually high bluffs, Nk-21 and An-1, lie well 

beyond the limit of recognized Itkillik I glaciation (see fig. 

18); they expose very long records that appear to include 

pre-Itkillik glacial and interglacial phases. Nk-21, which 

intersects a possible buried arcuate end moraine, contains an 

apparent basal till that either was water-laid or incorporated 

proglacial lacustrine sediments. Clast lithologies indicate 

that the glacier originated in the upper Noatak River valley. 

An apparent arcuate limit of hummocky drift-like topography 

beneath glaciolacustrine sediments north of the Aniuk River 

(Hamilton, 1984b) may define the corresponding north flank 

of this large glacial lobe. The diamict is overlain by probable 

slackwater deposits that may have formed while the Noatak 

River valley was still partly blocked by wasting glacier ice. 

The basal diamict at An-1 may be a basin-margin equivalent 

of the two lowermost units at Nk-21. It appears to be largely 

of glaciolacustrine origin, but includes gravel beds that 

increase upward in the section, perhaps as the thinning of a 

glacier farther down the Noatak drainage system permitted 

temporary or partial releases of an ice-dammed lake. The 

granite-bearing ice-contact sediments in the bluff at An-4 

may have been deposited by the same large Noatak ice lobe.

At exposure An-1, the strongly oxidized peat-capped 

alluvium at 43-51 m height at An-1 probably was deposited 

during a subsequent interglaciation, and it may correlate 

with the pebble-small-cobble channel gravel of lower unit 

3 that occurs at a comparable height in Nk-21. Terrace 

remnants composed of comparable pebble-small-cobble 

gravel are widely present in this sector of the Noatak River 

valley, and may represent a major interglacial deposit. The 

overlying coarser gravel at Nk-21 may represent lag deposits 

of ice-rafted clasts from younger glaciolacustrine-sediment 

cover that later was eroded by the Noatak River when it 

flowed about 70 m above its present level. The clasts include 

pyroxenite boulders, which are not present in the upper 

Noatak River valley. This eroded deposit may correlate with 

the distal glaciolacustrine deposits (unit 3) at An-1, which 

are overlain by alluvium deposited about 71-79 m above 

modern river level. Two radiocarbon ages on the upper 

glaciolacustrine unit at An-1 are considered to be non-finite 

and indicate an age greater than 39.5 ka. 

Exposure Nk-20, between the moraine belts of the 

Itkillik I and older glaciations, contains two glaciolacustrine 

units separated by alluvium. The lower glaciolacustrine unit 

contains only clasts of upvalley lithologies and probably 

correlates with the Itkillik I ice advance. The upper 

glaciolacustrine unit, which contains stone-free sediments 

at its base, is correlated with deposits of Itkillik II age 

downvalley. Alluvium between the two glaciolacustrine units 

may be the source of the spruce or larch wood found on the 

bluff. If so, it may demonstrate that a full interglacial interval 

separated deposits of Itkillik I and Itkillik II ages.

A terrace of about 20 m height, exposed at sites 

An-2 and An-3, represents the partial filling of a trough 

that was eroded by the Aniuk River, probably during the 

interglaciation that preceded the Itkillik I ice advance. The 

trough later filled with distal glaciolacustrine deposits of 

probable Itkillik I age and with outwash from valley trains 

that extended northwest from the Itkillik I glacial terminus 

(fig. 18). The sediment succession at both exposures seems 

to indicate that glaciolacustrine sedimentation preceded and 

followed outwash deposition from the outermost Itkillik 

I ice advance in the upper Noatak River valley. Exposure 

Nk-7, on Flora Creek, also may contain Itkillik I outwash 

above possible glaciolacustrine sediments. A radiocarbon 

determination from inferred outwash at An-2 is non-finite 

at >48 ka.

Two exposures, Nk-17 and Nk-18, provide information 

on the outermost end moraine of Itkillik I age and its 

associated outwash apron, respectively. The moraine stands 

about 35 m high where cut by the Noatak River at Nk-17, 

and its lithologies are typical of glacial source areas in the 

upper Noatak River valley. The general instability of the 

glacial diamict, its evident muddy matrix, and its geologic 

setting (see fig. 18) indicate that the glacier at its maximum 

extent may have terminated in standing water of glacial lake 

Noatak. Clasts in the outwash apron at Nk-18 are stained by 

oxides and encrusted by carbonates, and matrix material near 

the top of the section is discolored by precipitated oxides. 

These weathering features contrast with the unweathered 

gravel of the 16.5-m terrace of probable Itkillik II age that is 

inset within the moraine at Nk-17.

The depositional basin upvalley from the moraine belt 

is flanked by lateral moraines of Itkillik I age. Closer to 

the valley center, drift with an irregular hummocky surface 

is overlain by a blanket of sand, which masks much of 

the underlying relief. Terrace remnants 25-30 m high of 

unweathered Itkillik II outwash are inset within the drift (fig. 

33). The outwash generally is finer than that exposed close 

to the Itkillik II moraine front, but locally (as at Nk-16) it 

is coarser and probably includes clasts reworked from the 

adjoining drift sheet. A sand deposit inset within the outwash 

stands at least 17 m high, but has Holocene radiocarbon 

ages (as discussed below). Recent alluvial surfaces close 

to modern river level are intersected by kettle lakes, which 

evidently have continued to grow after the alluvium was 

deposited. Relict glacier ice of Itkillik I age may still 

underlie this part of the Aniuk Lowland.

Three measured sections (An-5, Nk-14, and Nk-19) 

provide radiocarbon ages (appendix 1) that are compatible 

with a mid-Holocene warm interval in this part of the 

Noatak drainage system. The base of a massive peat unit at 

An-5 is dated at 8.5 ka, and large willows grew about 8.2 

ka in a channel that evidently was cut into the peat. Massive 

peat at Nk-19 was accumulating by 6.0 ka. Mid-Holocene 

peat accumulation at Nk-14 and perhaps at the other sites 

may have terminated shortly before 3.7 ka, and in each case 

likely was due to renewed river alluviation, increased wind 

activity, decreased vegetation cover, or some combination of 

those factors.
Cutler River Area 23

Cutler River Area

To facilitate discussion of the geology of the large and 

complex Cutler River drainage basin, the bluff exposures in 

this sector of the Noatak River valley are divided into six sets. 

Bluffs along or adjoining the Noatak River near the mouth 

of Cutler River (Nk-22 through Nk-25, Cu-1; fig. 34) are 

discussed first, followed by the set of bluffs that cluster closely 

together along the lower courses of Cutler River and Kaluich 

Creek (Cu-2 through Cu-6; fig. 34). The more diverse and 

widely scattered bluffs along the upper courses of Cutler River 

and Kaluich Creek, and along Natmotirak Creek and Imelyak 

River, are then presented in that sequence.

Noatak River Bluffs

Introduction

In the vicinity of its confluence with the Cutler River, 

the Noatak River intersects the Cutler moraine, an arcuate end 

moraine 3-4 km wide that was deposited by a glacier that flowed 

eastward into the upper Noatak basin (Aniuk Lowland) from 

a source in the DeLong Mountains (see fig. 2 and Hamilton, 

Figure 33. Schematic cross-profile of Noatak River valley 

above Itkillik I (Atongarak Creek) moraine belt. Profile extends 

from modern river channel to crest of lateral moraine. Black dot, 

radiocarbon age determination (yr B.P.) with laboratory number in 

parentheses (see appendix 1). 

m

100

80

60

40

20

 0

ca.4 km

1

2

3

4

5

4220 110

5 Late Holocene floodplain and channel deposits.

4 Holocene floodplain and marsh deposits.

3 Itkillik II outwash.

2 Late Itkillik I sand.

1 Itkillik I till and ice-contact deposits.

Nk-14

Nk-14A

Nk-16

Nk-15

Nk-15

Nk-17

REFERENCE

SECTION

UNIT INTERPRETATION

Figure 34. Generalized geologic map, Cutler River area, south-central upper Noatak basin.

Alluvium

Itkillik II

Itkillik I

Itkillik I

Meltwater

outlet

Itkillik II

Itkillik I

Cutler

Outwash

Glaciolacustrine

and slackwater 

deposits

Colluvial-alluvial fill

Bedrock and colluvium 

Drift 

Cutler/ sheets

Sagavanirktok

Im-2

Im-4

Im-3

Im-1

Cu-3

Cu-4

Cu-5

Cu-10

Cu-11

Cu-6

Cu-2

Cu-7

Cu-8

Cu-9

Cu-12

Nk-25 Nk-22

Nk-24 Cu-1

Nk-23

Cr

Kaluich

Hunt R

Cutler

River

Imelyak

Noatak R

River

Natmotirak Cr

0 25 KILOMETERS

0 15 MILES

67o

45'

157o 158 30' o

30'

67o

30'
24 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

2001). Associated lateral moraines are sharply defined, but 

their extension into the valley center is more diffuse because 

the glacier probably terminated in a lake dammed by its 

advance (Hamilton, 2001 and in press). Lacustrine deposits 

correlated with subsequent glacial advances are enclosed 

within the end moraine and extend beyond it (Hamilton, 

2001); and they probably overlap the moraine as well.

Five very similar bluff exposures occur near the Cutler 

River confluence. Exposures Nk-22 through Nk-25 have been 

cut by the Noatak River; Cu-1 is on the Cutler River 2 km above 

its mouth (fig. 34). Each bluff contains a stony silt unit, generally 

disturbed by flowage, overlain by vegetated sandy sediment.

Bluff Exposures (Nk-22 through Nk-25 and Cu-1)

Exposure Nk-22 is located on the south side of the 

Noatak River 8.5 km above the mouth of Cutler River and 

upvalley from the mapped end-moraine limit; it intersects a 

nearly level surface underlain by glaciolacustrine deposits 

(Hamilton, 1984a). The basal deposit in the bluff is highly 

plastic, stony clayey silt (fig. 35) that is nearly identical to 

the basal deposits of exposures Nk-23, Nk-24, and Cu-1 

(discussed below). However, this deposit is only 26 m thick 

at Nk-22, and the associated lacustrine plain stands only 43 

m above modern river level. Clast lithologies are similar to 

those in the three other exposures, but appear to include a 

larger component of granite and other rock types derived from 

the upper Noatak River valley (listed in appendix 2). Limited 

exposures of the overlying unit (unit 2) show well sorted, horizontally bedded, fine and medium sand that contains rootlets 

dated at 13,160 ± 160 yr B.P.

Three nearly identical bluffs (Nk-23, Nk-24, and Cu-1), 

which span a distance of only 5 km, intersect a gently undulating upland surface 54-59 m high that probably is underlain by 

the Cutler end-moraine complex (see fig. 34). In each bluff, 

38-46 m of clayey silt with abundant striated stones is overlain 

by poorly exposed sandy sediments in which stones are rare or 

absent (figs. 36 and 37). The clayey silt is plastic when moistened, and flows readily on all bluff faces; it contains subangular to subrounded pebbles, cobbles, and sparse small boulders. 

Clast lithologies include rare granites, but are dominated by 

gabbros and quartzites, with abundant cherts in the pebble 

fraction (appendix 2). The overlying stone-free unit is generally poorly exposed; but well sorted, stratified, fine sand with 

some medium sand is evident in one locality.

Exposure Nk-25, 3 km below the mouth of the Cutler 

River, is situated inside the arcuate end-moraine belt. This 

river bluff contains the same basal stony silt and overlying 

sand(?) as the four neighboring exposures, but the stony silt 

is more compact and less subject to flowage than correlative 

units farther upvalley (fig. 38A). Undisturbed exposures are 

strongly jointed. An excavation just above the upper contact of 

the stony silt (fig. 38B) exposed alluvial fine gravel, sand, and 

silt that contains a black humic paleosol.

Figure 35. Exposure Nk-22. South side 

Noatak River 8.5 km east-northeast of 

mouth of Cutler River. Poorly exposed, 

with abundant debris flows. Black dot, 

radiocarbon age determination (yr B.P.) 

with laboratory number in parentheses 

(see appendix 1). 

Figure 36. Exposure Nk-23. North side 

Noatak River 5 km east-northeast of 

mouth of Cutler River.

? ? ?

?

2

1

m

60

40

20

 0

2

1

Note compressed scale

Vegetated. Unstable and poorly drained

deposit, entirely obscured by vegetation. 

Unknown deposit.

Stony silt. Subangular to subrounded,

commonly striated, pebbles, cobbles, and

some small boulders in matrix of very dark

gray (5Y 3/1) clayey silt. Exposed only in

debris flow. Glaciolacustrine deposit.

2 21

1 38

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

m

40

20

 0

13,160 ± 160

(USGS-1838)

2

1

Sand. Poorly exposed sandy deposit with no

stones evident. Limited exposure near middle

of unit shows olive (5Y 5/3) to olive gray (5Y 4/2)

fine and medium sand in beds 5-10 cm thick

containing in situ rootlets. Floodplain deposit?

Stony silt. Dark gray (5Y 4/1) clayey silt with

abundant subrounded to angular clasts; some

clasts striated. Highly plastic, flowing readily

on slopes. Glaciolacustrine deposit.

Note compressed scale

2 17

1 26

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

? ?
Cutler River Area 25

Figure 37. Exposures 

Nk-24 and Cu-1. Nearly 

identical bluff exposures 

near mouth of Cutler 

River. (A) Exposure Nk-24, 

south side Noatak River 

3 km east of mouth of 

Cutler River. (B) Exposure 

Cu-1, east side Cutler 

River 2.4 km above its 

mouth. 

Figure 38. Exposure 

Nk-25. West side Noatak 

River 3 km below mouth 

of Cutler River.(A) Bluff 

profile. (B) Detail of base 

of unit 2, from excavation 

24-29 m above river level. 

Black dot, radiocarbon 

age determination (yr 

B.P.) with laboratory 

number in parentheses 

(see appendix 1). 

 0

60

40

20

m

2

1

A

2

1

B

20

60

40

m

 0

Note compressed scales

Sand. Poorly exposed. Origin uncertain.

Stony silt. Abundant pebbles and cobbles

and very sparse small boulders in matrix of

dark olive gray (5Y 3/2) clayey silt. Stones

commonly striated. Glaciolacustrine deposit.

Sand. Mostly covered. Upper 2 m is

structureless, well sorted, silty very fine

sand that grades downward into weakly

bedded fine sand with thin (ca. 1 cm)

layers and lenses of medium sand. 

Origin uncertain.

Stony silt. Subangular to subrounded,

commonly striated, stones up to boulder

size in matrix of very dark gray (5Y 3/1),

plastic, clayey silt. Exposed only in debris

flow. Glaciolacustrine deposit.

2 12.5

1 42

2 12

1 46

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

m

50

40

30

20

10

 0

2

1

Sand? Well sorted silty very fine sand near

top. Vegetated face with only exposures at

base. Origin uncertain.

Stony silt. Subangular to subrounded, commonly

striated, pebbles, cobbles and sparse very small

boulders in matrix of dark olive gray (5Y 3/2) 

slightly clayey silt. Strongly jointed, with joint

planes passing through stones. 

Glaciolacustrine deposit.

A

B

2 23

1 24

See figure 38B

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

m

 5

 4

 2

 0

 3

 1

Fine gravel. Granules and pebbles in matrix of poorly sorted 

fine to coarse sand. Top not exposed.

Sand with silt. Well sorted olive brown (2.5Y 4/4) silty very 

fine sand. Contains layers 1-4 cm thick of gray clayey silt.

Paleosol. Black, pebbly, humic silt and silty humus, alternating

in layers 1-2 cm thick.

Stony silt. Subangular to subrounded stones up to small 

boulders in matrix of very dark gray (5Y 3/1) slightly clayey silt.

Fine gravel. Subangular to subrounded pebbles and small 

cobbles in abundant matrix of poorly sorted medium to coarse 

sand and granules. Directly overlies unit 1.

0.3+

1.4

0-0.2

1.2

2.1

THICKNESS

(m)

DESCRIPTION and INTERPRETATION
26 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

Discussion

Because of its noncompacted nature and its association 

with a probable water-laid end moraine, the basal stony silt at 

exposures Nk-22, Nk-23, Nk-24, and Cu-1 is considered to be 

an ice-proximal glaciolacustrine deposit. This sediment differs 

from normal basal tills, which generally are compact and form 

resistant units in river bluffs (see fig. 4 and table 2). The basal 

unit in all four bluffs probably lacked primary compaction and 

had a high moisture content that later became frozen into ice-rich 

permafrost. These properties, together with its clayey matrix, 

would account for the ubiquitous flowage of this unit on the 

bluff faces. In contrast, the basal unit at exposure Nk-25, which 

probably was deposited subglacially, is more compact and more 

resistant to flowage. The stony silt unit at all five exposures 

contains abundant chert pebbles and gabbro or pyroxenite clasts 

which were derived from sources to the north and northwest in 

the DeLong Mountains, as discussed in the appendix 2.

 The mostly covered unit that overlies the stony silt appears 

to be primarily sandy alluvium that may have formed as a slackwater deposit when the Aniuk Lowland was blocked by a later, 

less extensive glacial advance that terminated farther downvalley (Hamilton, 2001 and in press). The presence of alluvium 

and peat at the sand-silt contact at Nk-25 demonstrates that a 

nonglacial interval separated those two units, and that the sand 

therefore must have formed during a separate glacial advance. 

A radiocarbon age of about 13.2 ka from the middle of the sand 

unit at exposure Nk-22 would seem to provide a representative 

date for the blockage of the Aniuk Lowland by the younger 

glacial advance. However, the basal stony silt unit at this exposure is 15-20 m thinner than at the three exposures clustered 

around the Cutler River confluence, and the upland surface also 

is 15-20 m lower. Exposure Nk-22 might therefore represent 

a late-glacial readvance and renewed blockage of the Aniuk 

Lowland that could have followed an initial cycle of glaciation, 

ice wastage, and river downcutting.

Lower Cutler River

Introduction

For about 16 km above its mouth, the Cutler River is 

incised within an extensive lacustrine plain about 55 m high 

that extends south and east from the Cutler moraine front 

(see fig. 34). Discontinuous remnants of a younger surface 

that stands about 30 m above the river are inset within the 

lacustrine plain. Five exposures (Cu-2 through Cu-6) are 

clustered closely together along the lower Cutler River and 

Kaluich Creek within 5.5 km of the outer margin of the Cutler 

moraine. The highest exposure (Cu-4) appears to exhibit the 

longest stratigraphic record.

Exposure Cu-4

A west-facing bluff along the Cutler River 5.5 km above 

its mouth stands 45 m high and rounds back to an upland 

surface 53 m above modern river level. The bluff documents at 

least two major episodes of glaciolacustrine deposition separated by an interval of river activity (fig. 39A). Poorly exposed 

organic-rich silt at the base of the section may have developed 

on a poorly drained river floodplain or alternatively may 

represent initial ponding by glacier ice advancing eastward up 

the Noatak River valley (as shown in fig. 2). The channeled 

upper surface of the basal silt unit has been incised to a depth 

of at least 2 m. Overlying stony silt contains deformed peat 

and gyttja lenses near its base. Some lenses dip at angles as 

great as 85° and appear sheared, as if overridden and deformed 

by glacier ice. Alluvium above the stony silt contains a possible floodplain deposit (fig. 39B) dated at >50,000 yr B.P. 

Clay rhythmites, which mark the beginning of a younger 

episode of glaciolacustrine sedimentation, are succeeded 

upward by a thick deposit of silty clay that contains abundant 

striated tillstones. Mafic igneous rocks and several varieties 

of chert are the dominant pebble-sized clasts (appendix 2). 

The uppermost unit is dominantly sand and silt that has been 

severely deformed by slumping and flowage. Permafrost has 

aggraded into the deformed sediment, preventing any excavations through it.

Exposures Cu-5 and Cu-6

Two bluffs along Kaluich Creek near its confluence with 

the Cutler River (see fig. 34) are only 1.5 km apart and of 

comparable height (figs. 40 and 41). They intersect the northeast and west margins of a narrow erosion remnant bounded 

by the floodplains of Cutler River and Kaluich Creek.

Exposure Cu-5 contains flow deposits of clayey silt that 

contain abundant striated clasts up to boulder size. Overlying 

faintly bedded, fine to medium sand contains some organicrich zones. Wood fragments from a slump block that may 

have originated 3-6 m below the top of the bluff are dated as 

>40,000 yr B.P. A mammoth tusk also was found within the 

sand deposit.

In exposure Cu-6, a basal deposit of oxidized fine sand 

is overlain by rhythmically bedded clay with dropstones. The 

clay has an erosional upper contact with up to 2 m relief, and 

is overlain by a 26-m-thick deposit of stony clayey silt that 

contains dispersed clasts up to small boulder size. Pyroxenite 

cobbles are common, and black chert is abundant in the pebble 

fraction.

Exposures Cu-2 and Cu-3

Two east-facing cutbanks of the Cutler River 3 and 4.5 

km above its mouth intersect sloping surfaces that are inset 

within uplands of Itkillik I age (see fig. 34). Both bluffs 

contain a basal stony clay unit with abundant polished and 

striated stones up to small boulder size (figs. 42 and 43). The 

clay has been eroded close to river level, and is overlain by 

alluvial gravel containing clasts up to small cobble size. Cu-2, 

a low bluff about 13 m high, contains only Holocene sand 

and peat above the gravel. Willow wood 0.4 m above the base 

of the sand is dated at 7,280 ±120 yr B.P. Cu-3 stands about 
Cutler River Area 27

Figure 39. Exposure Cu-4. 

East side Cutler River 5.5 km 

south-southeast of its mouth. 

(A) Bluff profile. (B) Detail of 

unit 3. Black dot, radiocarbon 

age determination (yr B.P.) 

with laboratory number in 

parentheses (see appendix 1). 

Figure 40. Exposure 

Cu-5. South side 

Kaluich Creek 1 km 

above its mouth. Black 

dot, radiocarbon age 

determination (yr B.P.) 

with laboratory number 

in parentheses (see 

appendix 1). 

Figure 41. Exposure Cu-6. 

East side Kaluich Creek 2.5 km 

west-southwest of its mouth.

m

30

20

10

 0

2

1

>40,000

I-13,465

Note expanded scale

Sand. Well sorted, pale olive (5Y 6/4), fine to

medium sand. Contains faintly bedded organicrich zones 1-15 cm thick. Slackwater 

(floodplain?) deposit.

Stony silt. Rounded to subrounded, commonly

striated stones up to 1 m diameter in matrix of

very dark gray (5Y 3/4) clayey silt. Subject to

flowage along bluff face. Glaciolacustrine 

deposit.

2 15

1 16.5

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

30

m

20

10

 0

3

2

1

Sand. Well sorted, oxidized fine sand and gray silty very 

fine sand. Contains climbing ripples and silty to clayey 

drapes. Deltaic deposit?

Stony silt. Subangular to subrounded, commonly 

striated, pebbles, cobbles, and sparse small boulders 

in matrix of slightly plastic, dark greenish gray (5G 4/1), 

sandy clayey silt. Erosional basal contact. Procimal

glaciolacustrine deposit.

Clay. Rythmically bedded dark gray clay and silty clay, 

forming couplets 2-6 mm thick. Fines upward, with basal 

layer relatively silty. Sparse dropstones of sand, granules, 

and small pebbles. Lebenspurren along some bedding 

planes. Distal glaciolacustrine deposit

2 3.7

1 3.3

3 26

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

m

50

40

30

20

10

 0

1

>50,000

(USGS-1839)

5

?

2

3

4

?

Gravel. Rounded to subrounded pebbles, small cobbles 

and sparse larger cobbles in sparse matrix of poorly sorted 

sand and granules. Alluvium.

Stony silt. Subrounded to subangular, commonly striated, 

pebbles, small cobbles, and sparse larger cobbles in matrix 

of dark gray (5Y 4/1) clayey silt. No obvious sorting or bedding, 

and stones lack fabric. Contains deformed lenses of woody 

peat and gyttja 4-5 m above river level. Glaciolacustrine 

deposit.

Organic silt. Well-bedded, organic-rich deposit, incised to at 

least 2 m depth at contact with unit 1. Poorly exposed. Pond 

deposit?

Sand and silt. Dark gray (5Y 4/1) humic silt, silty fine 

sand, and stony fine sand. Deformed by slumping and 

flowage; no original bedding evident. Origin uncertain.

Stony clay. Subangular to rounded, commonly striated,

pebbles, cobbles, and sparse boulders up to 1.6 m length 

in matrix of very dark gray (5Y 3/1) silty clay. Proximal 

glaciolacustrine deposit.

Silt and clay. Glaciolacustrine deposits. (See fig. 39B.)

A

B

2 1.3

1 9

-- ?

5 5

4 24

3 2.3

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

m

 2

 1

 0

>50,000

(USGS-1839)

c

b

a

Note expanded scale

Silty clay. Blocky silty clay with sparse pebbles.

Glaciolacustrine deposit.

Clay rythmites. Rhythmically bedded clay and silty clay. 

Couplets thicken downward from 3-5 mm at top to ca. 1 cm 

at base. Distal glaciolacustrine deposit.

Stony silt. Faintly bedded silt and clayey silt with sparse 

dropstones up to large cobbles. Contains contorted thin peat 

beds and sparse wood fragments. Floodplain and initial 

glaciolacustrine deposit(?)

c 1.5

b 0.25

a 0.55

THICKNESS

(m)

SUBUNIT DESCRIPTION and INTERPRETATION
28 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

Figure 43. Exposure Cu-3. 

West side Cutler River 4.5 km 

above its mouth.

10 m higher, with its upper surface rising inland. This bluff 

contains a thicker alluvial deposit that is overlain by sand, silt, 

and clay that may have been deposited during an episode of 

impeded drainage. A thick deposit of organic silt at the top of 

the section is cut by an ice wedge about 3 m high and up to 1.5 

m wide.

Discussion

The upper glaciolacustrine unit at Cu-4 is comparable in 

height and lithology to the basal stony clayey silt of Itkillik 

I age that occurs in the five bluffs (exposures Nk-22 through 

Nk-25 and Cu-1) close to the Noatak-Cutler Rivers confluence. The overlying sand and silt, which is associated with an 

upland surface 53 m high, may be a facies equivalent to the 

poorly exposed, sandy, slackwater deposits along the Noatak 

River that underlie an aggradational surface 54-59 m high 

that formed during Itkillik II time. The basal glaciolacustrine 

deposit at Cu-4 may represent an earlier glacial advance that 

Figure 42. Exposure 

Cu-2. West side Cutler 

River 3 km above its mouth. 

Black dot, radiocarbon 

age determination (yr B.P.) 

with laboratory number in 

parentheses (see appendix 

1). 

possibly overrode that locality before the glacier withdrew sufficiently for an ice-dammed lake to form.

Exposures Cu-5 and Cu-6 intersect an erosion surface 

about 30 m high that extends southeastward up the Cutler 

River. Cu-6, on the Kaluich Creek side of the erosion remnant, 

was freshly undercut by the creek when visited in 1983. A 

basal exposure of strongly oxidized sand probably predates the 

last glaciation. Rhythmically bedded clay above the sand probably marks the onset of glacial damming, as at Cu-4. The overlying diamict resembles the basal stony clayey silt that is widespread around the Noatak-Cutler Rivers confluence, where it 

is associated closely with the ice front of Cutler age. Cu-5, on 

the Cutler River side of the erosion remnant, contains a similar 

stony clayey silt that was truncated erosionally at about 16 m 

height and then buried by a sand deposit that resembles the 

slackwater deposits of inferred Itkillik II age elsewhere around 

the Noatak-Cutler Rivers confluence. Wood was found at only 

one location in the sand, and its non-finite age indicates that it 

may have been redeposited from older sediments. 

m

15

10

 5

 0

UNIT

4

3

2

1

THICKNESS (m)

4

1.5

2.6

4.8

 DESCRIPTION and INTERPRETATION

Sod, peat, and peaty sand. Not examined closely. 

Bluff cap.

Sand. Fine sand with ripples, detrital organic mats, 

ball-and-pillow structures, and silt laminations. Some 

interbeds of medium sand and silty fine sand. 

Near-horizontal bedding. Floodplain deposit.

Sandy gravel. Subrounded to rounded pebbles and 

sparse small cobbles in abundant, poorly sorted matrix 

of medium sand to granules. Channel alluvium.

Stony clay. Dark greenish gray (5GY 4/1) silty clay. 

Contains rounded to subrounded pebbles, cobbles and 

sparse boulders. Glaciolacustrine deposit.

7,280 ± 120

(I-13,449)

4

3

2

1

Note expanded scale

m

20

25

10

15

 0

 5

UNIT

 4

 3

 2

 1

THICKNESS

 (m)

 8.3

 3.1

 7.0

 3.5

 DESCRIPTION and INTERPRETATION

Peat and organic silt. Contains ice wedge. 

Sand and pebble gravel locally present at base. 

Loess with peat?

Sand and clay. Rythmically bedded grayish 

brown to gray silt and clay above well sorted fine 

to medium sand with climbing ripples, drapes, 

and detrital organic mats. Glaciolacustrine?

Sand and gravel. Pebbly sand and sandy fine 

gravel, with local sand-free layers of small 

pebbles and of pebbles to small cobbles. Lag 

deposit of coarse cobbles and very small 

boulders near top. Alluvium.

Stony clay. Dark blue-gray (5B 4/1), stiff, plastic, 

silty clay. Contains abundant polished and 

striated stones. Glaciolacustrine deposit.

4

3

2

1

Note expanded scale
Cutler River Area 29

Exposures Cu-2 and Cu-3 contain identical basal units 

of stony, silty clay that probably correlate with the other basal 

glaciolacustrine deposits around the Cutler River mouth that 

are related to the ice advance of Cutler age. Both glaciolacustrine deposits have been erosionally truncated close to river 

level and are overlain by channel gravel of the Cutler River. A 

Holocene section above the gravel at Cu-2 probably represents floodplain accretion about 7.0-7.5 ka, followed by river 

downcutting that allowed the overlying peat and peaty sand 

to form. The sedimentary section above the gravel at Cu-3 is 

thicker (11.4 m) than corresponding deposits at Cu-2, and it is 

more complex. Rhythmically bedded silt and clay above sand 

with climbing ripples probably represents deltaic deposition 

followed by submergence, perhaps due to rising water levels in 

the upper Noatak basin during the Itkillik II ice advance. The 

thick, overlying organic-rich silt may represent loess, which 

may have been retransported by solifluction to the base of the 

hillslope that overlooks Cu-3. This deposit could represent a 

significant time interval, perhaps during all or part of the late 

Wisconsin glaciation.

Upper Cutler River Valley

The valley floor of the Cutler River broadens into a 

marshy lowland with little relief 3 km above the Imelyak 

River confluence. A relatively undissected deposit that fills 

the valley center within this area appears to have transgressed 

across an erosionally dissected, older lacustrine plain (see fig. 

34). These two landscape units have been mapped as Itkillik II 

and Itkillik I glaciolacustrine deposits, respectively (Hamilton, 

1984a). The younger unit is intersected by exposure Cu-7. Farther up the Cutler River, deposits on the valley floor become 

more varied. At exposures Cu-8 and Cu-9, the river flows past 

the subdued end moraine of a glacier that may have terminated 

in standing water during Itkillik I time. Headward parts of the 

valley are mostly underlain by generally shallow, stony, colluvial and alluvial deposits.

Three additional exposures were measured along or near 

Kaluich and Natmotirak Creeks, two western tributaries to the 

Cutler River (fig. 34). All three exposures are within a poorly 

drained landscape of gentle relief in which a blanket of glaciolacustrine deposits of inferred Cutler age (Hamilton, 2001) 

overlies older glacial deposits and bedrock. 

Exposures Cu-7 through Cu-12

Exposure Cu-7, on the west side of Cutler River 12 km 

above the Imelyak River confluence, stands about 21 m high 

and intersects a marshy planar surface. Two sandy deposits 

with peaty interbeds are separated by alluvial gravel (fig. 44). 

The basal unit (unit 1) consists of subhorizontal beds 3-8 

cm thick of dark gray to olive gray silt, silty fine sand, and 

fine sand. Silty fine sand is dominant in the lower part of the 

unit; interbeds 1-2 cm thick of woody bryophytic peat occur 

through the upper part. Wood and peat 1 m below the upper 

contact is dated at 46,800 ++1,400

-1,200 yr B.P. Overlying alluvium 

(unit 2) contains clasts to about 10 cm length of marble, schist, 

vein quartz, and other lithologies that are common near the 

valley head.

The upper sandy unit (unit 3) of Cu-7 is partly obscured by 

slumping. Basal deposits range from interbedded dark greenish gray sand and clayey silt to interbedded silty very fine sand 

to medium sand; these represent probable overbank alluvial 

facies. These sediments grade upward into laterally continuous 

organic silt and fine sand, and then into silty very fine sand with 

interbedded bryophytic peat. A peat bed 1 m above the base of 

the upper sandy unit is dated at 27,530 ± 350 yr B.P.; peat 1.5 m 

Figure 44.

Exposure Cu-7. 

West side Cutler 

River 27 km above 

its mouth. Black 

dot, radiocarbon 

age determination 

(yr B.P.) with 

laboratory number 

in parentheses 

(see appendix 1). 

m

20

25

10

5

15

 0

17,980 120

(USGS-1452)

27,530 350

(USGS-1453)

3c

3b

3d

4

5

2

1

3a

Note expanded scale

Covered

Poorly

Exposed

46,800

(USGS-1454)

Sand with peat. Silty very fine sand and fine sand in beds 0.5-6 cm 

thick. Very dark gray humic fine sand at 0.4-0.9 m depth. Basal 0.8 m

contains 1-3 cm beds of sandy bryophytic peat and abundant rootlets.

Sandy gravel. Subrounded to rounded pebbles and small cobbles in 

sandy matrix. Generally subhorizontally bedded, with some trough 

crossbedding. Some interbeds up to 20 cm thick of slightly oxidized, 

light brown (7.5YR 6/4) fine to medium sand. Sparse lenticular swale 

fillings of gray silty fine sand. Alluvium.

Sand and silt. Silt, silty fine sand, and fine sand in subhorizontal 

beds 3-8 cm thick. Silty fine sand dominant in lower half of unit; well 

sorted fine sand in topmost 0.7 m. Peaty interbeds 1-2 cm thick

throughout upper half of unit. Slackwater and marsh deposit.

Sand and silt. Faintly bedded very fine sand, grading upward into 

nonbedded silt. Loess.

Sand, silt, and peat (overbank and marsh deposits)

Peat and sand. Silty very fine sand and sandy peat in beds 1-5 cm 

thick. Sedge and grass peat dominant near top; mats of bryophytic 

peat below 60 cm depth.

Sand and silt. Organic silt with vertical stems and rootlets, grading 

upward into silty very fine sand and fine sand in beds 1-3 cm thick.

b 2.0+

(base

covered) Silt and sand. Silty very fine sand and medium sand in beds and 

lenses 4-10 cm thick. Upper 0.6 m is olive gray silt to very fine sand 

with some organic beds.

3

d 2.0+

(base

covered)

c 2.1+

(top

missing)

a 1.1+

(top

covered)

4 0.8

5 0.4 Peat and silt. Holocene bluff cap.

2 3.4

1 6.6

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

+1,400

 -1,200
30 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

Figure 46. Exposure Cu-9. West side Cutler River 41 km above its 

mouth.

Figure 47. Exposure Cu-10. North side unnamed eastern tributary 

to Kaluich Creek 1.5 km above tributary’s mouth.

below the unit’s top is dated at 17,980 ±120 yr B.P. The bluff 

is capped by sandy to silty eolian deposits (unit 4) overlain by 

silty peat (unit 5).

Exposure Cu-8 is situated on the northeast side of the Cutler River near the mouth of a tributary stream and close to the 

severely eroded front of a poorly defined drift sheet (see fig. 

34). The exposure stands about 10 m high, rounding back into 

the base of a hillslope. Despite its low height, Cu-8 contains 

a surprisingly old depositional record. Interbedded sand, fine 

gravel, and organic-rich silty fine sand overlie lacustrine clayey 

silt near the base of the exposure (fig. 45). The sand and gravel 

beds dip southwest at about 20°; they probably were deposited 

on a fan delta that was built into standing water by the tributary 

stream that adjoins the bluff. Two radiocarbon determinations 

on willow wood and peat from the inclined beds indicate a 

non-finite age of >40,000 yr B.P. for the deposit. The channeled upper surface of the fan-delta deposit is overlain by 

alluvial gravel which contains clasts of upvalley lithologies 

(dominantly schist, vein quartz, quartzite, and marble). The 

upper 0.7 m of the gravel is oxidized, and rooted willow from 

a peat lens 0.1 m below the oxidized zone has a non-finite age 

of >38,000 yr B.P. The overlying sandy unit contains deformed 

beds of eolian(?) fine sand and silt that may have been displaced by solifluction. Alternatively, this unit may represent a 

former bluff cap that has slumped into its present position.

Pollen assemblages from two horizons in exposure Cu-8 

have been identified and interpreted by T.A. Ager and Effie 

Shaw (U.S. Geological Survey, written commun., 2/9/83). A 

pollen subsample of USGS-1651 (fig. 45), taken near the base 

of the exposure, is dominated by sedge and willow, with birch, 

grass, and sage (Artemesia) also common. This assemblage 

is characteristic of an herb-shrub tundra that contains abundant willow thickets and wet meadows. A pollen subsample 

of USGS-1652, from near the top of the gravel unit, contains 

very high (91 percent) sedge. This assemblage represents a 

wet sedge meadow within a regional tundra environment.

Exposure Cu-9 intersects the drift sheet in the upper 

bedrock valley of Cutler River (see fig. 34). The river’s bed here 

is choked with boulders up to 2.4 m long of typical upvalley 

lithologies (schist, quartzite, and marble). The entire exposure 

has been disrupted by flowage (fig. 46). Fresh river cuts along 

its base show unsorted, glacially shaped stones to boulder size 

in a muddy sand matrix. The overlying vegetated, hummocky 

flow surface rises inland to a moraine crest at about 25 m height.

Exposure Cu-10 occurs 1.5 km above the mouth of an 

unnamed eastern tributary to Kaluich Creek (see fig. 34). Vegetated flows entirely obscure the bluff face (fig. 47), but boulders 

of schist and marble protrude from the flows and are abundant 

in the stream bed. Quartz dominates the pebble fraction, with 

no black chert or granite evident. Although severely mixed by 

flowage, the sediment matrix appears to be dominantly sandy.

Exposure Cu-11, an east-facing cutbank on the west 

side of Kaluich Creek, stands 9.5 m high. Stiff, plastic, stony 

clay, which protrudes just above river level at the base of the 

Figure 45. Exposure Cu-8. Northeast side Cutler River 36 km above its mouth. Black dot, radiocarbon age 

determination (yr B.P.) with laboratory number in parentheses (see appendix 1). 

m

15

10

 5

 0

UNIT

3

2

1

THICKNESS (m)

1.1+

4.7

3.8

 DESCRIPTION and INTERPRETATION

Sand with silt. Very dark gray (10YR 3/1) silty very fine sand; 

interbedded with dark brown (10YR 4/3) fine sand. Beds are 

deformed, and interpenetrate in places. Contains deformed lenses of 

dark grayish brown (10YR 4/2) silt. Basal 10-12 cm consists of faintly 

bedded medium sand overlain by thin organic horizon. Eolian(?) 

deposit above alluvium with paleosol.

Gravel. Subrounded to rounded pebbles and small cobbles in matrix 

of coarse to medium sand. Upper 0.7 m oxidized yellowish brown

(10YR 5/8); overlies peat lens with rooted willow. Alluvium.

Sand and fine gravel. Interbedded fine to medium sand, sandy 

pebble gravel, and organic-rich silty fine sand. Strikes N75o

E; dips 

20o

SW. Contains matted plant material along bedding planes. 

Grades downward and laterally into dark gray clayey silt with some 

beds of fine sand. Deltaic and lacustrine deposits.

?

?

>40,000

(I-12,516)

42,600 ±1100 

USGS-1651)

3

2

1

>38,000

(USGS-1652)

Note expanded scale

m 30

20

10

 0

THICKNESS

 (m)

 20-30

 DESCRIPTION and INTERPRETATION

Stony sand. Rounded to subangular, faceted 

and striated stones up to boulder size in matrix 

of gray muddy sand. Exposed only in debris 

? flows. Till or glaciolacustrine deposit.

m

40

20

 0

 DESCRIPTION and INTERPRETATION

Diamict. Face obscured by vegetated flows. 

Boulders up to 1.6 m diameter exposed on 

bluff face and in streambed. Till or 

glaciolacustrine deposit.

THICKNESS

 (m)

 39

?

Note compressed scale
Cutler River Area 31

bank (fig. 48), probably is glaciolacustrine. Overlying alluvial 

gravel has a cap of silty fine sand that may be either a channel filling or a floodplain deposit. The topmost unit is poorly 

exposed, interstratified stony silt and peat that may represent a 

shallow, intermittent lake.

Exposure Cu-12 is the headwall of a tundra earthflow 

about a kilometer northwest of Natmotirak Creek near the 

west flank of the Cutler River lowland (see fig. 34). The headwall, which stands about 6 m high, exposes laminated clayey, 

sandy silt with dropstones up to about 30 cm diameter that 

decrease upward in abundance but remain unchanged in size 

(fig. 49). Overlying gray silt contains peat layers and lenses 

that have been deformed by ice-wedge growth. Deformation 

increases upward to the top of the unit, where an unconformity 

separates the peaty silt from about 0.5 m of surface sod. An ice 

wedge 3 m wide at its top extends downward from the base of 

the surface sod to below the base of the headwall.

Peat from the base of the peaty silt unit has a non-finite 

age of >48,500 yr B.P. Its pollen assemblage is dominated by 

sedge (55 percent) and willow (24 percent), indicating a wet 

sedge meadow with willow thickets within treeless herb tundra 

(T.A. Ager and Effie Shaw, U.S. Geological Survey, written 

commun., 2/8/83). Peat from the middle of the unit probably 

also is non-finite in age (>43,600 yr B.P.) despite its reported 

age of 43,600 ±1300 yr B.P. Its pollen is almost entirely 

(94 percent) sedge, with grasses and herbs present in small 

amounts but willow absent (T.A. Ager and Effie Shaw, U.S. 

Geological Survey, written commun., 2/8/83). Ager and Shaw 

conclude that this assemblage probably represents a wet sedge 

meadow within treeless tundra.

Discussion

Six exposures along the upper Cutler River and its western tributaries reveal a complex record of middle(?) and late 

Figure 48. Exposure Cu-11. 

West side Kaluich Creek 7 

km above its confluence with 

Natmotirak Creek.

Pleistocene glacial, glaciolacustrine, and alluvial episodes in 

this part of the upper Noatak basin.

Fan-delta deposits at exposure Cu-8 document standing 

water at the Itkillik I moraine front at some time prior to 40 

ka and probably before 42.6 ka. Because the small tributary 

stream that adjoins this site probably was inadequate to build 

an extensive fan-delta complex, it may have been augmented 

by meltwater and detritus from wasting glacier ice in the 

adjoining drainage of Imelyak River. Detailed mapping of this 

relationship should allow direct correlation of the fan delta 

and its contemporaneous lake with either the Itkillik I glacial 

advance or a preceding more extensive glacial expansion in the 

Imelyak drainage system (see fig. 34). The basal slackwater 

deposit at Cu-7 may be correlative with the fan-delta deposit at 

Cu-8 because both units are overlain by similar fluvial gravel 

deposits that alluviated to about the same height (8.5-9.0 m) 

above the modern river. Laminated lacustrine sediments at 

Cu-12 document a glacial-lake stage that could be correlative 

with the basal deposits at Cu-7 and Cu-8, but the probable 

non-finite radiocarbon ages at all three exposures alternatively 

would permit the overlying silt with peat at Cu-12 to be older 

than the alluvial gravel at the other two sites. Cu-11 also contains a probable succession of glaciolacustrine and slackwater 

deposits separated by alluvial gravel. The basal stony clay 

deposit may be correlative with the clayey silt at Cu-12, and 

alluviation along the valley center at Cu-11 could have been 

synchronous with peat accumulation on the higher-standing 

wet sedge meadow at Cu-12.

Late Wisconsin (Itkillik II) glacial damming of the upper 

Noatak basin is documented by overbank and marsh deposits at 

Cu-7; these underlie a 21-m surface, and are bracketed by radiocarbon ages of about 28 ka and 18 ka. Poorly exposed bluff-top 

deposits at Cu-8 and Cu-11 may be correlative with this stage 

of alluviation in the Cutler River area. At Cu-12, which stands 

higher above the modern floodplain, the Itkillik II phase may be 

Figure 49. Exposure Cu-12. 

North side Natmotirak Creek 12 

km above its mouth. Headwall of 

earthflow. Black dot, radiocarbon 

age determination (yr B.P.) with 

laboratory number in parentheses 

(see appendix 1). 

m

10

5

 0

UNIT

 3

 2

 1

 DESCRIPTION and INTERPRETATION

Stony silt and peat. Dark gray stony silt, interstratified with 

and capped by black to dark reddish brown peat. Severely 

slumped. Glaciolacustrine and postglacial deposits.

Gravel. Rounded to subangular pebbles and small cobbles 

in matrix of poorly sorted fine to coarse sand with some silt 

and platy granules. Capped by 0.3 m dark olive brown silty 

fine sand. Alluvium.

Clay. Stiff, plastic, stony gray clay. Glaciolacustrine 

deposit?

THICKNESS 

(m)

2.5

6.5

0.5

3

2

1

Note expanded scale

m

 0

 2

 4

 6

>48,500

(USGS-1648)

43,600 ±1,300

(USGS-1649) 3

2

1

UNIT

3

2

1

 DESCRIPTION and INTERPRETATION

Surface sod. Unconformably overlies unit 2.

Silt with peat. Gray silt with layers and lenses 

of deformed peat. Deformation increases 

upward. Cut by ice wedges. Loess.

Stony silt. Laminated clayey silt, containing 

dropstones that decrease upward in abundance. 

Cut by ice wedges that extend below base of 

exposure. Glaciolacustrine deposit.

THICKNESS

(m)

0.5

1.5

4

Note expanded scale
32 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

Figure 51. Exposure Im-2. 

West side Imelyak River 9 km 

above its mouth.

Figure 50. Exposure Im-1. 

South side Imelyak River 

5.5 km above its mouth. 

Black dot, radiocarbon 

age determination (yr B.P.) 

with laboratory number in 

parentheses (see appendix 1). 

exposures (Im-1 through Im-3) in the lower Imelyak River valley contain assemblages of deposits that can be correlated with 

sequences of events along the Cutler and Noatak Rivers.

The upper valley of Imelyak River is dominated by drift 

sheets of inferred Itkillik I and Itkillik II age and their associated outwash trains (see figs. 5 and 34). Three exposures (Im-4 

through Im-6) in this sector of the valley consist dominantly of 

glacial deposits.

Exposures Im-1 through Im-7

Exposure Im-1 is a north-facing cutbank on Imelyak River 

just upstream from the moraine at the Imelyak-Cutler Rivers 

confluence (fig. 34) The cutbank intersects an alluvial terrace 

28.5 m high that probably is underlain by outwash from the 

adjoining moraine (Hamilton, 1984a). The basal unit exposed 

here is horizontally bedded sandy sediment that contains 

some clayey silt beds (fig. 50). Detrital wood 2 m below the 

upper contact has a non-finite age of >48,000 yr B.P. Overlying coarse gravel consists of upvalley lithologies (schist, vein 

quartz, and marble). The gravel is capped by peat and peaty silt 

that has a basal radiocarbon age of about 9450 yr B.P.

Exposure Im-2, situated 4.5 km farther up Imelyak River, 

is a bluff face 37 m high that contains two glaciolacustrine 

deposits separated by a thick alluvial sequence (fig. 51). The 

basal glaciolacustrine unit consists of silty clay with dropmarked only by an unconformity that separates Holocene sod 

from underlying deformed silt with peat and large ice wedges.

The bouldery flow deposits at Cu-9 and Cu-10 are 

severely mixed and poorly exposed. Both deposits contain 

assemblages of clasts derived exclusively from the headwaters 

of the Cutler River; they lack Noatak valley lithologies, such as 

chert, gabbro, pyroxenite, and granite, that are common around 

the Cutler River mouth. Because Cu-9 intersects a morainal 

ridge, this flow deposit probably is redeposited till from the 

glacier tongue that appears to have terminated in the glacial 

lake of Itkillik I age. Cu-10, which cuts the base of a long 

hillslope, probably intersects a glacial deposit that predates the 

widespread veneer of Itkillik I glaciolacustrine sediments.

Imelyak River Valley

The lower course of Imelyak River extends through an 

area of moderate relief that is underlain by an arcuate end 

moraine near the Imelyak-Cutler Rivers confluence, by a 

bedrock upland north of the moraine, and by glaciolacustrine 

deposits, outwash, and alluvium farther upstream (see fig. 34). 

About 15 km above its mouth, the Imelyak River approaches 

to within 6 km of the Noatak River, and a low north-northwesttrending trough on the basin floor indicates that the two drainages formerly must have been connected at this locality. Three 

m

30

20

10

 0

UNIT

 3

 2

 1

THICKNESS

 (m)

 2.1

 14.9

 11.5

 DESCRIPTION and INTERPRETATION

Peat and silt. Peat, silty peat, and peaty silt. 

Willow stems up to 3 cm diameter present 

through upper 1.4 m. Floodplain deposit.

Gravel. Subrounded stones to large cobble size, 

with some small boulders, in matrix of coarse 

sand and granules. Some interbeds of sand and 

fine gravel. Outwash.

Sand. Olive gray (5Y 5/2) fine sand, silty fine 

sand, and medium sand to granules; in horizontal 

beds ca. 20 cm thick. Contains sparse beds of 

clayey silt 5-7 cm thick. Basin fill.

9,455 ± 40

(USGS-1455)

3

2

1

>48,000

(USGS-1456)

m

40

30

20

10

 0

4

3

2

1

10+

ca. 8

ca. 23

6

50

Covered

?

4

3

2

1

b

a

d

c

b

a

Uncertain. Generally vegetated, sloping surface. 

Appears to be largely or wholly sand.

Stony silt and silty gravel. Sandy clayey silt 

with striated dropstones (a), overlain by silty 

gravel (b). Glaciolacustrine deposit.

Sand and gravel. Pebbly medium sand (a), 

overlain successively by interbedded medium 

sand and silty fine sand (b), sandy 

pebble-small-cobble gravel (c), and faintly 

bedded sand with partings of micaceous fine 

sand (d). Alluvium.

Stony clay. Gray silty clay with faceted and 

striated dropstones. Glaciolacustrine deposit.

THICKNESS DESCRIPTION and INTERPRETATION

(m)

UNIT
Cutler River Area 33

21 m above the river. Im-6, slightly farther upvalley from the 

moraine front, contains gravel above a till-like diamict that has 

a somewhat water-washed sandy matrix.

Discussion

The strongly oxidized gravel at exposure Im-3 resembles 

the gravel sheet around exposure Nk-21, 8 km to the north 

along the Noatak River. Knolls of similar-appearing gravel 

were noted along the northeast side of Imelyak River between 

Im-3 and the Itkillik I moraine front (Hamilton, 1982, 1992). 

Stratigraphic relations at Nk-21 and regional extent of the 

oxidized gravel indicate that the oxidized gravel probably is a 

widespread interglacial deposit of pre-Itkillik age.

The sediment succession at exposure Im-1 is interpreted 

as largely related to the glacial advance down Cutler River 

valley that formed the end moraine near the Cutler-Imelyak 

Rivers confluence. Although this exposure stands only 28.5 

m high, its upper units may have been eroded by the Imelyak River, which is confined narrowly here between the end 

moraine to the south and bedrock uplands to the north. The 

basal sandy unit is largely a slackwater deposit formed by 

partial damming of the river; clayey silt beds indicate intermittent episodes of more effective local or regional blockage 

of drainage. The overlying gravel compositionally resembles 

other gravel units along the Cutler River and its tributaries, 

stones. It is overlain by an interstadial or interglacial complex 

of fluvial sand and fine gravel. The upper glaciolacustrine unit 

consists of sandy, clayey silt with striated dropstones overlain 

by silty gravel. The bluff rises an additional 10 m inland as a 

vegetated surface that may be underlain entirely by sand.

Exposure Im-3 (not illustrated) is a stabilized and largely 

vegetated bluff face that rises about 30 m above an abandoned 

channel segment of the Imelyak River that is now an oxbow 

lake. Sparse exposures show a “brown gravel” consisting of 

weathered pebbles and small cobbles up to about 16 cm diameter in an oxidized sandy matrix. Clasts include quartzites, vein 

quartz, limestone, and schist, with rare granite. The deposit fines 

upward into an oxidized pebble gravel of the same composition.

Exposure Im-4, a south-facing cutbank within the Itkillik 

I moraine belt on the Imelyak River, stands 22.5 m high and 

exhibits only alluvium (fig. 52). Although diamict and outwash of Itkillik II age occur a short distance upvalley from this 

locality (see figs. 5 and 34), the weathered nature of the gravel 

at Im-3 suggests that it is older. The deposit may represent 

recessional outwash of the Itkillik I glacier.

Exposures Im-5 and Im-6 are two cutbanks near the head 

of Imelyak River that intersect an end moraine of probable 

Itkillik II age (shown in southwest corner of fig. 5). Both 

cutbanks expose abundant striated stones up to boulder size 

(fig. 53). Im-5, which contains unsorted till-like sediment, 

intersects a hummocky morainal surface that stands about 

Figure 52. Exposure Im-4. North side 

Imelyak River 2 km below mouth of 

Amakomanak Creek.

Figure 53. Exposures Im-5 and Im-6 

near head of Imelyak River. (A) Exposure 

Im-5, north side unnamed eastern 

tributary to Imelyak River 21 km above 

Amakomanak Creek confluence. (B) 

Exposure Im-6, east side Imelyak River 

24 km above Amakomanak Creek 

confluence.

m

20

10

 0

THICKNESS

 (m)

 22.5 

 DESCRIPTION and INTERPRETATION

Gravel. Rounded to subrounded stones to small 

boulder size (0.7 m) in weakly oxidized (light 

yellowish brown 10YR 6/4) sandy matrix. 

Stones near top weathered and carbonate 

encrusted. May overlie beds of fine sand. 

Alluvium. ? ? ? ? ?

m

15

10

5

 0

 DESCRIPTION and INTERPRETATION

Diamict. Rounded to subangular, striated stones 

up to boulder size (1.5 m) in unsorted to weakly 

sorted sandy matrix.Overlain by pebble-smallcobble gravel with light yellowish brown (10YR 

6/4) sandy matrix. Till and ice-contact gravel.

THICKNESS

 (m)

 13.2

m

20

10

 0

 DESCRIPTION and INTERPRETATION

Diamict. Unsorted, nonstratified, striated stones 

up to boulder size (0.8 m) in unsorted, calcareous, 

muddy matrix. Till.

THICKNESS

 (m)

 10.8+

?

A

B
34 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

Figure 54. Generalized geologic map, Noatak River valley between mouth of Cutler River and lower Nimiuktuk River. Ctn, 

exposures along New Cottonwood Creek. Numbers without prefixes refer to Noatak River bluffs (designated Nk in text).

0 25 KILOMETERS

0 15 MILES

Nimiuktuk River

Cutler R

Makpik

Anisak R

Creek

River

Noatak

Aniralik

Lake

Lake Kangilipak

Feniak

Lake

Aklumayuak Creek

Itimtikrak Creek

MAP UNITS

Recessional

moraine

ow Outwash

Bedrock and 

colluvium,

undifferentiated

Meltwater

channel

Flow direction 

of glacial 

drainage

68o

15' 159o

00' 158o

30'

159o

30'

68o

00'

39

38

37

36

34

33

32

Makpik-1

29

30

A

B

28 

27 

26 

25 

24 

23 22 

A

B 35 31

Okak Bend

Itim-1

Ctn-1

Ctn-2

Ak-1

Glaciolacustrine

deposits

Anisak

Makpik

Older

Alluvium

Terrace 

gravel

Itkillik II

Itkillik I

Sagavanirktok

Drift

sheets

Nm-4

ow

ow

Cutler/

Sagavanirktok

ANIUK

LOWLAND

Avingyak Hills

but it is much coarser than the pebble-small-cobble gravel that 

predominates at the other exposures and texturally is more 

like the proximal outwash deposits along the Noatak River. It 

is interpreted as outwash derived from the adjoining ice front. 

The outwash gravel is overlain unconformably by a peat cap 

of Holocene age. Any former weathering profile at the top 

of the gravel and any younger Pleistocene-age deposits must 

have been eradicated by erosion.

The poorly exposed sandy capping unit at exposure Im-2 

is comparable in character and height to the slackwater(?) sand 

deposits that overlie glaciolacustrine sediments 11.5-14.5 km 

farther to the northwest near the Cutler River mouth. The succession of sediments beneath the upper sandy unit at Im-2 (see 

fig. 51) represents a complex series of events that may include 

blockage of lower Imelyak River valley by advance of the Cutler 

valley glacier (unit 1), then progressive wastage of the glacier 

(units 2a and 2b?), followed by (3) development of interglacial 

conditions (unit 2c). Subsequent advance of a glacier from the 

DeLong Mountains into the Noatak River valley caused impeded 

drainage (unit 2d) followed by standing-water conditions (unit 

3a). Glacial recession (unit 3b) was followed by the advance during which the inferred capping sand (unit 4) was deposited.

Exposures Im-4 through Im-6 represent local glacial and fluvial events in the upper valley of Imelyak River. All three deposits 

are inorganic and hence undated by radiocarbon. However, the 

extent and physical appearance of the drift sheet that is intersected 

by Im-5 and Im-6 are compatible with those of the drift sheet of 

Itkillik II age in the upper Noatak River valley (see fig. 5), and 

glacial limits can be traced directly through mountain valleys that 

connect the two drift complexes. The drift sheet at Im-5 and Im-6 

therefore is assigned confidently to the Itkillik II glaciation.

Aniuk Lowland Below Cutler River— 

Noatak River Bluffs 

Introduction

Downriver from the Cutler River confluence, the 

Noatak River flows north-northwest for 18 km within a 

trough about 7-10 km wide that is confined between lateral 

moraines of the Cutler moraine complex (fig. 54). Along 

the floor of the trough, a Holocene floodplain 2-3 km wide 

is inset within a planar surface that stands 25-40 m above 

the Holocene deposits. This terrace-like surface is nearly 

level near the valley center, but rises at gentle gradients as it 
Aniuk Lowland Below Cutler River—Noatak River Bluffs 35

approaches the lateral moraines and wedges out against their 

inner flanks. The surface appears continuous with the sandy 

deposits (for example,, exposures Nk-23, Nk-24, and Cu-1, 

discussed previously) that surround and overlap the Cutler 

moraine along the lower Cutler River and around its mouth. 

Three exposures (Nk-26 through Nk-28) intersect the sandy 

unit and underlying glaciolacustrine and alluvial sediments 

along this stretch of the valley.

Near Okak Bend, the Noatak River flows through several 

involuted large meanders, then straightens out into a general 

westward course that begins near Makpik Creek. The meanders probably are controlled by bouldery erosion remnants of 

the Makpik drift sheet (Hamilton, 2001 and in press), which 

extends from the De Long Mountains eastward up the Noatak 

valley, terminating in an end moraine that intersects the valley center just west of Makpik Creek (fig. 54). Four closely 

spaced exposures (Nk-29A through Nk-31) provide information on glacial and alluvial history in the Okak Bend area.

Below Makpik Creek, the Noatak River flows westward 

for about 17 km through a stretch that is confined between 

lateral moraines of the Makpik drift sheet. It then intersects 

the Anisak end moraine (Hamilton, 2001 and in press), the 

eastern terminus of the Anisak drift sheet, near the mouth of 

Anisak River (fig. 54). A prominent line of south-facing river 

bluffs begins at the Anisak moraine front and continues down 

the Noatak River valley for 12 km, yielding exposures Nk-34, 

Nk-36, and Nk-37. Downvalley from Nk-37, the Noatak River 

meanders through a broad basin that is enclosed within the 

Anisak moraine. Only two exposures (Nk-38 and Nk-39) 

within this stretch were informative enough to be measured 

and recorded.

Exposures along the Noatak River downstream from 

the Cutler River differ from those farther upvalley in several 

important respects. The discharge of the Noatak River is significantly larger below the Cutler River confluence owing to 

the water contributed by this large tributary. Meander wavelength along the Noatak below the Cutler confluence consequently is much larger than that farther upvalley, and informative bluff exposures commonly extend for a kilometer or more 

along river bends. Erosive ability of the Noatak also is much 

greater below the Cutler confluence, and the Noatak River 

commonly has cut through late Pleistocene deposits to expose 

older sediments near river level. Deep erosion also has resulted 

in large-scale, fluvial cut-and-fill relations that greatly complicate bluff stratigraphy. In some places, downcutting by the 

Noatak River has intersected plastic clay-rich sediments that 

normally occur below river level. These deposits commonly 

appear as diapiric extrusions near the ends of river bluffs, 

where confining overburden has been removed by Holocene 

river erosion (Hamilton, 1995). Finally, the bluffs along this 

stretch of the Noatak River were examined in 1983 and again 

in 1993. Striking changes occured during the 10-year interval between visits: new exposures were cut by the river, and 

some former exposures were obscured by flowage, vegetation 

growth, and other surface processes.

Exposure Nk-26

A prominent bluff exposure 8 km north of the Cutler 

River confluence extends for 0.5 km along the east bank of 

the Noatak River. The bluff’s exposed face stands 30-35 m 

high, and extends upward into a vegetated slope that rises to a 

nearly level surface at about 37-40 m height. An overview of 

the bluff face (fig. 55) shows two glaciolacustrine (stony mud) 

units separated by river gravel and floodplain deposits that 

fill a deeply scoured surface on the older stony mud. Deposition of the younger stony mud was followed by alluviation of 

sand. Two stratigraphic sections were measured near the south 

Figure 55.

Stratigraphic 

relations along 

face of exposure 

Nk-26. East side 

Noatak River 8 

km north of Cutler 

River mouth. From 

Elias and others, 

1999, fig. 5. Black 

dot, radiocarbon 

age determination 

(yr B.P.) with 

laboratory number 

in parentheses (see 

appendix 1). 

ca. 0.5 km

NORTH

Unit

B A

SOUTH

Fluvial sand

Tephra

COVERED

COVERED

COVERED

m

40

7

20

6

5

3

1

7

6

5

3

4

1

 0

4?

2 4

>49,500 ?

>47,000

Unit

Upper stony mud

Floodplain deposits

above gravel

Pond, bog, and

floodplain deposits

Alluvial gravel

Lower stony mud

Deltaic deposit

Paleosol

EXPLANATION
36 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

Figure 56. Exposure Nk-26 (continued). Measured sections (see fig. 55 for locations). Modified from Elias and others, 1999, fig. 6. (A) 

Section A, measured near south end of bluff face. (B) Section B, measured ca. 120 m from north end of exposure. Black dot, radiocarbon 

age determination (yr B.P.) with laboratory number in parentheses (see appendix 1). 

and north ends of the bluff (figs. 56A and 56B, respectively). 

The depositional sequence in the intervening area was partly 

obscured by widespread flowage of the lower stony mud. 

The basal unit (unit 1) consists of about 2.3 m of finely 

laminated fine sand and organic fine sand that contains climbing 

ripples and probably formed as deltaic foreset beds. The sand is 

underlain by a probable floodplain complex that is dominated 

by fluvial deposits (ripple-bedded sand, oxidized fine sand, and 

oxide-impregnated fine gravel) in one locality and probable 

pond deposits (deformed wavy beds of well sorted fine sand and 

dark-colored sapropel) at another locality. A peat bed near the 

top of the unit is 5 cm thick, but has been deformed through a 

vertical range of 35 cm. An ice-wedge cast that originates at the 

peat horizon penetrates 120 cm into the underlying sand.

The lower stony mud (unit 2) forms an erosion remnant 

just downstream from the middle of the bluff. Flows obscure 

much of the bluff face here, but limited exposures show about 

0.5 m of probable floodplain deposits (sand and silty fine 

sand) about 10 m above river level capping the lower stony 

mud and separating it from a younger glaciolacustrine unit. 

The lower stony mud consists of striated clasts up to cobble 

size, with some small boulders, dispersed in dark gray slightly 

clayey silt. The deposit contains several beds of well sorted 

very fine sand and laminated silty clay that have apparent 

dips downriver of 2-3°. These beds are about 0.5 m thick, but 

they thicken to about 1 m to fill depressions in the underlying stony mud. Cobble lithologies are dominantly quartzite, 

limestone, chert, and ultramafic rock types (appendix 2). One 

unusual rounded clast is conifer wood, which was identified as 

Pinus (white pine group) (USDA-FPL; 11/83). The coarse lag 

deposit that lines the river’s edge along this section of the bluff 

is more heterogeneous and more bouldery than lag deposits 

m

40

30

20

10

 0

>47,000

(USGS-1,840)

>49,500

(USGS-1,457)

7

6

4

3

1

?

Covered

Sand. Crossbedded silty very fine sand to coarse sand with sparse 

granules and small pebbles. Some drapes of clayey silt. Contains wedge 

sets with tangential cross bedding. Alluvium.

Stony mud. Very dark gray clayey silt to silty clay, containing abundant 

striated pebbles and small cobbles and rare coarser stones. Stony mud and 

muddy gravel alternate through upper 9.7 m; basal 6.1 m obscured by 

debris flows. Glaciolacustrine deposit.

Sand and silt. Couplets of fine sand and clayey silt, overlain by horizontally 

bedded silt and very fine sand. Grades upward into horizontally bedded silt 

with wood fragments. Capped by compressed black woody peat. Pond, 

bog, and marsh deposit.

Gravel. Rounded pebbles, small cobbles, and sparse larger stones in 

matrix of poorly sorted sand. Alluvium.

Sand. Finely laminated well sorted fine sand with climbing ripples. 

Deformed peat bed at top of unit. Pebble gravel in middle of unit contains 

ice-wedge cast. Deltaic deposit.

Stony silt. Rounded to subrounded pebbles, small cobbles, and some 

larger cobbles, mixed with subangular clasts to boulder size in clayey silt 

matrix. Some stones faceted and striated. Overlies 0.6 m of gray silty clay 

with some thin (2-10 mm) silt beds. Upper contact obscured. 

Glaciolacustrine deposit.

Gravel. Pebbles, small cobbles, and sparse larger clasts in matrix of poorly 

sorted sand with abundant rock chips. Brown silt and black organic silt with 

sparse pebbles fill channel-like depression at upper contact. Alluvium.

Silt, sand, and fine gravel. Horizontally bedded silt, laminated silt, 

ripple-bedded sand, and fine gravel; overlain by dark gray clayey silt with 

dispersed pebbles and thin beds of oxidized fine sand. Floodplain deposit.

Gravel. Rounded to subrounded pebbles, small cobbles, and sparse larger 

cobbles in sandy matrix. Many clasts iron-stained. Alluvium.

3 3.7

4 4.2

6 15.8

1 4.7+

7 6.5

THICKNESS

(m)

A UNIT DESCRIPTION and INTERPRETATION

B m

40

30

20

10

 0

? ? ? ? ?

COVERED

6

5

4

3

4 6.5

5 4.3+

6 5.7+

3 11.0

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION
Aniuk Lowland Below Cutler River—Noatak River Bluffs 37

elsewhere along the bluff face; and it contains numerous ultramafic rocks derived from sources farther downvalley.

The gravel (unit 3) consists of rounded pebbles, small 

cobbles, and sparse larger clasts in a sandy matrix. Many 

stones through the upper 3 m of the deposit have reddish coatings of iron oxides, and clasts in the most permeable beds have 

oxide coatings through the upper 5 m of unit 3. Through the 

southern part of the bluff (fig. 56A), subangular boulders up 

to 65 cm long occur near the base of the gravel, and several 

“stone lines” of subrounded large cobbles and very small boulders occur at higher levels. These deposits probably resulted 

from downcutting and later lateral erosion by the Noatak River 

into the stony silt of the lower glaciolacustrine unit. Through 

the northern part of the bluff (fig. 56B), the gravel is better 

stratified and sorted, with no boulders and with a matrix generally washed free of clay and silt.

An interglacial floodplain complex is expressed by 

channel-filling deposits (unit 4) and peaty beds at heights 

between 11 and 17 m along the bluff face. Near the south end 

of the bluff (figs. 55 and 56A), a thick sequence of pond, bog, 

and marsh sediments fills a deep channel-like depression. 

Laminated sand, silt, and clayey silt are overlain by beds of 

sandy silt and black humic silt with flattened wood fragments. 

One large piece of wood was identified as Picea or Larix

(USDA-FPL, 11/83). Peaty beds 11.0-11.6 m above river level 

in the central part of the bluff contain wood identified as Salix

(USDA-FPL, 11/93), and wood from peat near this locality was 

dated as >49,500 yr B.P. A second probable channel fillng of 

sand, silt, and fine gravel near the north end of the bluff (fig. 

56B) contains twigs and small wood fragments identified as 

Picea or Larix (USDA-FPL, 10/93). 

Floodplain deposits containing the Old Crow tephra (Elias 

and others, 1999), which was deposited about 140,000 yr ago 

(Berger, 2003), cap a higher alluvial gravel deposit (unit 5; 

fig. 56B) through the north part of the bluff. Pollen and insect 

remains from organic deposits associated with the tephra suggest tundra vegetation with local dominance of sedge (Elias 

and others, 1999) 

The upper stony mud (unit 6) contains unsorted, commonly striated, rounded to subrounded pebbles, small cobbles, 

and sparse larger cobbles, which are mixed with subangular 

clasts up to about 1 m diameter. Lithologies are dominantly 

quartzite and a gabbro-like dark crystalline rock, with other 

fine-grained igneous rocks also present (appendix 2). In at least 

one locality, the deposit consists of five subunits, each 1-3 m 

thick. Stone content remains fairly constant in each subunit, 

but matrix alternates between unsorted clayey silt and waterwashed muddy sand and granules. The water-washed beds may 

represent intervals of sudden drainage of the lake, most likely 

due to breaching of its glacial dam. The basal 0.6 m of unit 6 

consists of silty clay with some thin silt beds. This stone-free 

deposit may have formed during an initial shallow-lake stage in

the upper Noatak basin or when glacier ice was too distant to 

contribute dropstones to the site.

The sandy deposit (unit 7) that caps the section generally is eroded back from the bluff face, and is poorly exposed. 

However, one exposure clearly indicates a fluvial origin for 

the deposit. Cross-bedded sand occurs with sparse fine gravel 

and some drapes of clayey silt, with thin lenses of fine organic 

detritus along some bedding planes. Migrating bedforms and 

ripples indicate paleocurrent directions parallel to the modern 

valley. Detrital wood collected 2.4-2.6 m below the exposed top 

of the unit is dated as >47,000 yr B.P.

Exposure Nk-27

An east-facing river bluff 5.5 km downvalley from 

exposure Nk-26 stands 44.5 m high and exhibits two diamicts 

(fig. 57). The upper one-third of the bluff is covered, but sand 

locally is exposed at the base of the covered unit. The contact 

between the two diamicts rises in height from 5.2 m above the 

river near the south end of the bluff to 10.7 m near the center.

Rhythmically laminated silt and clay above a paleosol 

developed on stony silt (unit 1) occurs along a 10-m stretch 

at river level near the center of the bluff. The paleosol surface 

strikes north and dips 10-12° E; it bears polygons 40-50 cm 

Figure 57. Exposure 

Nk-27. West side Noatak 

River 12.5 km northnorthwest of Cutler River 

mouth.

m

50

40

30

20

10

 0

5

4

3

2

1

2 3.5-9

3 0-3.6

4 ca. 25

1 1.5

5 ca. 14.5 Sand. Well sorted fine sand. Generally slumped and 

vegetated. Alluvium?

Upper diamict. Rounded to subrounded, striated pebbles 

and cobbles in matrix of gray muddy sand. Grades upward 

into rounded to subangular pebbles and cobbles in matrix of 

dark gray slightly clayey silt.Faintly bedded. Glaciolacustrine deposit.

Sand, silt and fine gravel. Variable laterally; intermittently 

present. Floodplain deposit.

Lower diamict. Rounded to subrounded, striated stones 

dispersed in highly compact dark gray sandy clayey silt. 

Platy stones parallel near-horizontal fissility. Cut by nearvertical joint planes. Till.

Silt and clay. Faintly laminated stony sandy silt, capped by 

paleosol. Overlain by rhythmically laminated silt and clay. 

Pond and lake deposits.

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION
38 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

Figure 58.

Exposure Nk-28. 

East side Noatak 

River 16.5 km northnorthwest of mouth 

of Cutler River. 

Section measured 

near downriver 

end of bluff. Black 

dot, radiocarbon 

age determination 

(yr B.P.) with 

laboratory number 

in parentheses (see 

appendix 1). 

diameter with marginal troughs about 5 cm deep. In part, the dip 

could be due to undercutting by the river, but part also appears to 

follow the downvalley dip of the upper contact of unit 1.

The lower diamict (unit 2) consists of striated stones 

dispersed in a well mixed matrix of sandy clayey silt. Clasts 

include downvalley lithologies (appendix 2). This deposit is 

highly compact, and maintains vertical faces along the bluff. 

It has a general fissile structure, with near-horizontal zones 

about 0.5 m thick of intense fissility associated with oriented 

platy stones; these probably represent shear zones. Oxides are 

concentrated along near-vertical joint planes and for 0.7 m 

below the upper contact. The lower diamict probably is a true 

till rather than a glaciolacustrine deposit.

The upper diamict (unit 4) is faintly bedded, with beds of 

stony mud alternating with better-washed layers of stony muddy 

sand and some beds of matrix-free pebbles. Striated pebbles 

and cobbles are common throughout the deposit. Chert, schist, 

and igneous rocks dominate the pebble fraction (appendix 2). 

Like the upper diamict at exposure Nk-26, unit 4 probably is 

glaciolacustrine in origin, and its deposition was interrupted 

periodically by breaching of a glacier dam farther downvalley.

Two localities near the center of the bluff exhibit lenses 

of probable fluvial overbank deposits up to 3.6 m thick (unit 

3) that separate the lower and upper diamicts. Sand and fine 

gravel are overlain by interbedded sand and silt with sparse 

granules and pebbles. No organic remains were recognized in 

this alluvial unit.

The gravel bar on the east side of the Noatak River opposite exposure Nk-27 contains large detrital wood fragments 

of two types. Conifer wood, which is impregnated with iron 

oxides, includes large fragments up to 18 cm width that were 

identified as Pinus (USDA-FPL; 10/93). The source of this 

detritus is unknown. Angiosperm wood, identified in the field 

as Populus on the basis of bark and morphology, is present 

as somewhat smaller but more intact logs and branches. This 

detritus was traced upstream to a low Holocene terrace, where 

buried logs up to 11 cm diameter and dated at 1,570 ±90 yr 

B.P. (USGS-3401) are eroding from a cutbank. The Populus(?) wood has been identified as Salix (willow; USDA-FPL, 

10/93), but this identification is suspect.

Exposure Nk-28

A southwest-facing river bluff 9 km downriver from 

Nk-26 has an exposed face 16 m high but rises inland 10 m 

more at a gentler angle to the edge of the broad undulating 

surface of a former valley floor. Nk-28 contains two wellexposed diamicts, with channel and floodplain alluvium 

separating and locally underlying them (fig. 58).

The lowest alluvial sequence is best exposed near the 

north end of the bluff. It declines in height southward, and can 

be traced upriver for only 120 m along the base of the bluff. 

A limited exposure of pebble-small-cobble gravel (unit 1) at 

the north end of the bluff is oxidized to about 0.5 m depth. 

Through this interval, admixed silt and numerous vertical 

stones attest to vigorous frost churning, probably within an 

active layer above a former permafrost table. Silt and peat 

(unit 2) cap the gravel. Gray silt and black organic silt, which 

form the top and base of the unit, are separated by 20-35 cm 

of black to dark reddish brown peat. Sparse flattened willow twigs up to 1 cm diameter have been identified as Salix

(USDA-FPL, 11/30/93). Both the upper and lower silt beds 

thicken into channel-like depressions in the peat and gravel 

deposits that underlie them.

A younger alluvial gravel unit (unit 3) occurs throughout 

the bluff. Clasts up to large cobble size occur in an unusually 

m

20

10

 0

25

15

 5

?

>57,000

(USGS-1841)

6

5

4

3

2

1

Note expanded scale

Silt and Peat. Gray silt and black organic silt above 

and below black to dark reddish brown peat with 

flattened twigs. Floodplain bog and marsh deposit.

Gravel. Pebble-small-cobble gravel. Upper 0.5 m

oxidized with vertical stones. Alluvium.

Gravel. Pebbles and cobbles in matrix of coarse sand 

and granules. Upper 0.7 m oxidized dark yellowish 

brown. Local caps of black humic silt. Alluvium.

Lower diamict. Pebbles, small cobbles, and sparse 

larger clasts in matrix of very compact, dark gray,

clayey sandy silt. Near-horizontal fissility and stone 

fabric. Upper contact erosional, with slight oxide tint. Till.

Gravel. Pebbles and cobbles in matrix of coarse to 

medium sand. Alternating cobble-and-pebble-rich 

layers, and some beds of stratified sand and granules. 

Upper 0.7 m oxidized. Alluvium.

2 1.0

3 5.4

4 2.6

1 0.7+

5 4.8

Upper diamict. Striated clasts to small boulder size 

in matrix of dark grayish brown sandy silt. Till?

6 3.0

-- 10.0 Covered. Vegetated surface, rising inland. 

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION
Aniuk Lowland Below Cutler River—Noatak River Bluffs 39

coarse-grained matrix of coarse sand and granules. The topmost 1 m of the gravel unit has been oxidized, and the upper 

part of the oxidized zone has been further modified by frost 

churning, downward migration of silt particles, and translocation of carbonates. In the central part of the bluff, the gravel 

locally is capped by 25 cm of stony brown sandy silt and black 

organic silt that has a non-finite age of >57,000 yr B.P. Many 

of the stones in this deposit have vertical orientations, and 

were incorporated within the silt by frost action. 

The lower diamict (unit 4), a strongly jointed, extremely 

compact deposit that stands in near-vertical faces, probably 

formed as till. Rounded to subangular pebbles, small cobbles, 

and sparse larger clasts up to small boulder size (about 55 cm 

diameter) occur in a matrix of dark gray (N4), fissile, slightly 

clayey, sandy silt. The near-horizontal fissility lacks obvious grain-size sorting, but platy stones are aligned generally 

parallel to it. Only a very slight oxide tinge occurs at the upper 

contact of this unit. 

The upper alluvial gravel (unit 5) is a weakly bedded 

deposit of rounded to subrounded clasts to large cobble size in 

a matrix of well sorted coarse to medium sand. It is unoxidized 

except for its upper 0.7 m, which has been altered to a yellowish brown (10YR 5/6) color and commonly has vertically 

oriented clasts. The gravel is capped locally by silty floodplain 

deposits. In the central part of the bluff, black to dark brown 

organic silt is up to 30 cm thick and contains algal (Chara?) 

laminations characteristic of a shallow pond deposit. At the 

upriver end of the bluff, black organic silt is interbedded with 

red (2.5YR 4.6) fine sand.

The upper diamict (unit 6), a possible till, generally is poorly 

exposed. It contains striated clasts up to small boulder size in a 

matrix that may consist of very dark grayish brown sandy silt.

Exposure Nk-29A

A pair of cutbank exposures on opposite sides of the 

narrow neck of Okak Bend stand only 450 m apart and intersect the same nearly level upland surface (see fig. 54). The 

northwest-facing cutbank on the west side of Okak Bend contains excellent exposures. Its face stands 25.5 m high, rounding back to a nearly level upland surface 37 m above the river. 

Two diamicts are separated and underlain by alluvial gravel 

and floodplain deposits (fig. 59).

The basal alluvium (unit 1) is exposed only at the 

downstream end of the bluff and near the bluff center. At the 

downstream exposure, northeast-dipping beds of dark gray 

to olive gray silt predominate. Interbeds of black peat with 

willow wood (Salix; USDA-FPL, 12/13/83) occur through 

the basal 65 cm of the deposit; beds of calcareous algae occur 

through the upper 95 cm. Although the base of the silt is not 

exposed, a concentration of boulders in the river begins at the 

point downriver where the lower contact of this dipping bed 

should emerge at the surface. A trench near the bluff center 

exposed alluvium, peat, and silt below the basal contact of the 

lower diamict, which here occurs 3 m above river level and 

rises toward the northeast. Alluvial fine gravel at the base of 

the trench grades upward into sand with detrital fragments 

of Populus wood (USDA-FPL, 10/93). Overlying floodplain 

deposits consist of oxidized peat, organic silt, sandy silt, and 

silty fine sand; they contain an insect fauna characteristic of 

a mesic tundra with woody shrubs (S.A. Elias, University of 

Colorado, written commun., 4/27/94).

The lower diamict (unit 2) has an exposed thickness of 5 

m, but probably extends close to river level beneath the basal 

debris apron along much of the bluff. Pebbles, small to medium 

Figure 59. Exposure Nk-29A. Southeast side Noatak River on west side of neck of Okak Bend, 21.5 km north-northwest of mouth of 

Cutler River. From Elias and others, 1999. Black dot, radiocarbon age determination (yr B.P.) with laboratory number in parentheses (see 

appendix 1). An additional radiocarbon age on the floodplain deposit in upper unit 3 (>46,400: AA20752) is not shown here.

m

20

10

 0

>51,000

(USGS-1842)

4

5

6

7

3

2

1

30

40

?

 +2,700 52,500 -2,000

(USGS-1843)

Debris

 apron

2 5+

3 4.5

4 ca. 9.2

1 2.2+

5 ca. 2

6 4.6

7 3.1 Structureless silt and organic silt with ice wedges. Loess.

Poorly sorted, weakly bedded, medium to very coarse sand with sparse granules and 

small pebbles. Oxidized brownish yellow. Alluvium.

Plastic, dark gray silty clay. Flows readily. Lacustrine deposit.

Upper diamict. Abundant stones up to 1 m diameter in highly compact very dark 

grayish brown gritty silt. Near-horizontal shear planes and stone fabric. Strongly 

jointed, with yellowish red oxidation along joint planes. Grades upward into clayey silt 

with dispersed pebbles and cobbles. Glaciolacustrine deposit above till.

Sand and gravel. Rounded to subrounded pebbles, small cobbles, and sparse larger 

stones in matrix of poorly sorted,immature, medium to coarse sand. Some sand 

interbeds. Capped by 0.5 m dark gray silt above oxidized gravel with ice-wedge casts. 

Fine gravel, sand, silt, and peat fill channel-like surface depressions. Alluvial and 

floodplain deposit.

Lower diamict. Dark, slightly bluish gray clayey silt, with dispersed clasts to medium 

cobble size and sparse larger stones. Lacks fabric. Base generally covered, but 

sticky, plastic, stone-free, silty clay exposed locally. Glaciolacustrine deposit.

Gravel, sand, silt, and peat. Fine gravel grading upward into fine sand with detrital 

wood and into silt with peat. Floodplain deposits with paleosol.

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION
40 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

m

30

20

10

 0

2

1

?

Silt. Poorly exposed gray silt. Loess?

Covered.

1 21

2 2

-- 9

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

Diamict. Striated stones up to >1 m 

diameter in black (5Y 2.5/2) sandy 

clayey silt. Compact and strongly 

jointed. Most platy stones have horizontal fabric. Contains poorly exposed 

layer of black humic silt. Till with 

interstadial beds.

Figure 60. Exposure Nk-29B. West side 

Noatak River on east side of neck of Okak 

Bend, 21 km north-northwest of mouth of 

Cutler River.

cobbles, and sparse larger stones are dispersed in a dark, 

slightly bluish clayey silt. This unit is less compact than the 

upper diamict, and does not support vertical faces. Where 

exposed by trenching near the center of the bluff, the base of 

the lower diamict consists of a sticky, plastic, fissile, stone-free 

silty clay. Strong brown oxide concentrations occur along the 

fissile partings.

The overlying sand and gravel (unit 3) consists of 

rounded to subrounded pebbles, small cobbles, and sparse 

larger cobbles in a matrix of poorly sorted, angular, lithologically immature, medium to coarse sand. The gravel contains 

interbeds of sand and pebbly sand, and locally exhibits largescale cross-bedding typical of bar foresets (G.M. Ashley, 

Rutgers University, oral commun., 7/27/83). The upper 75 cm 

of the gravel commonly is oxidized yellowish red (5YR 5/6), 

and is capped by 0.5 m of dark gray silt overlain by a thin (1-2 

cm) black humic horizon. Ice-wedge casts up to 1.5 m wide 

and 3.2 m deep originate at the top of the gravel. Deformed 

peat within one ice-wedge cast has a non-finite radiocarbon 

age of >51,000 yr B.P.

Channel-like depressions up to about 1.5 m deep incised 

into gravel near the top of unit 3 are filled by sandy fine 

gravel, sand, silt, and peat. Slightly oxidized sand and fine 

gravel at the base of these deposits typically grades upward 

into peaty and silty floodplain deposits that commonly contain 

lenses of sandy fine gravel or pebbly silt. Shards of volcanic 

glass from the floodplain deposits have been identified as the 

ca. 140,000-year-old Old Crow tephra (Elias and others, 1999; 

Berger, 2003). Humic silt from a buried organic soil (Histosol) 

near the northeast end of the bluff has a radiocarbon age of 

52,500 +2,700

-2,000 yr B.P. This should be considered a minimum age 

limit on the paleosol. Black peat near the base of a channel 

filling near the center of the bluff contains pollen spectra and 

an insect fauna characteristic of a mesic tundra with woody 

shrubs (Elias and others, 1999).

The upper diamict (unit 4) contains abundant pebbles and 

cobbles, together with sparse boulders up to slightly more than 

1 m diameter, in a matrix of extremely compact dark greyish 

brown sandy silt. This unit maintains nearly vertical, strongly 

jointed faces, with yellowish red oxidation along all joint 

planes. Sparse near-horizontal shear planes also are present, 

and platy stones generally parallel the fissility. The top of this 

unit is covered, but a test pit into the vegetated slope above its 

highest exposure uncovered a stony sandy silt that appeared 

identical to the upper diamict.

Exposure Nk-29B

The southeast-facing cutbank on the east side of the 

narrow neck of Okak Bend stands about 23 m high. It rounds 

back to an upland surface at about 29 m height that is identical 

to the 37-m surface measured at exposure Nk-29A. Although 

they are situated less than 0.5 km apart, the Noatak River 

between the two exposures flows 8 km around Okak Bend and 

declines about 6 m in altitude over this distance. The higher 

river surface at Nk-29B accounts for most of the discrepancy 

between the measured heights of the upland.

The face of Nk-29B lacks fresh exposures (fig. 60), but may 

contain the same sequence of diamicts and interstadial beds that 

is displayed at Nk-29A. Because of its proximity to that bluff 

face, the poorly exposed Nk-29B will not be discussed further.

Exposure Nk-30

An extensive bluff at the apex of Okak Bend is situated 

close to the inner flank of the Cutler River moraine (see fig. 

54) and intersects a solifluction slope that extends southward 

from the moraine. The bluff face stands 41 m high, rounding back to a gently inclined upland surface at 48 m height. It 

exhibits two diamicts that are separated by alluvial sand and 

gravel and underlain by silt and clay (fig. 61).

Deposits beneath the lower diamict are poorly exposed. 

Dark gray silty clay (unit 1) is extruding plastically near the 

river’s edge, and a trench near the downstream end of the bluff 

exposed 2.7 m of deformed, slightly oxidized silt and pebbly 

sandy silt that locally form discrete beds up to 30 cm thick. No 

organic matter was evident in any of these deposits.

The lower diamict (unit 2) is a very thick (21 m) deposit 

of probable till. It consists of dark gray, compact clayey silt 

with dispersed rounded to subrounded pebbles, small cobbles, 

and sparse larger stones. Black and green chert, dark green 

igneous rocks, and gray quartzite dominate the pebble fraction 

(appendix 2). This deposit is strongly jointed, and breaks down 
Aniuk Lowland Below Cutler River—Noatak River Bluffs 41

into angular fragments about 4 cm diameter. Oxide concentrations occur along some joint planes. Unit 2 also is cut by sets 

of subhorizontal shear planes that occur in zones 10-12 cm 

thick. Platy stones are aligned parallel to these shear planes.

The alluvium (unit 3) between the two diamicts consists 

of subrounded to subangular pebbles, small cobbles, and 

very sparse larger cobbles in a matrix of dark gray, poorly 

sorted, silty sand and granules. Black chert is abundant in the 

pebble range. The sand grains consist mainly of rock chips. 

Cross-bedded medium sand, silty fine sand, and pebbly fine 

sand occur as lenses 30-40 cm thick within the gravel, and 

cross-bedded sand, granules, and muddy small-pebble gravel 

occurs as a channel filling at least 1.3 m thick near the downriver end of the bluff. Unit 3 is capped by 75 cm of ripple 

cross-bedded, slightly oxidized, well sorted fine sand.

The upper diamict (unit 4), a probable glaciolacustrine 

deposit, has been entirely disturbed by flowage and no primary structures are present. Subangular to rounded pebbles, 

cobbles, and sparse boulders up to 1.5 m diameter, many 

faceted and striated, occur in a matrix of olive gray sandy silt. 

The boulders are predominantly igneous rocks, with quartzites also abundant (appendix 2). The top of this unit is not 

exposed.

Limited exposures above the upper diamict contain 

stone-free, loosely packed, yellowish brown silt that is interpreted as loess. It may be 4 m or more thick, but relations to 

units above and below are unclear.

Exposure Nk-31

This southwest-facing river bluff occurs 1.5 km above 

Makpik Creek about where the Makpik moraine must formerly 

have intersected the center of the Noatak River valley (see fig. 

54). The exposed face of the bluff is 27 m high, and meets the 

planar upper surface of a river-terrace remnant at a sharp angle. 

A single diamict occurs beneath alluvial sand and gravel that is 

capped by a probable floodplain complex (fig. 62A).

The base of the diamict is exposed only at the upstream 

end of the bluff, where it rises eastward from 1.5 m above river 

level to 1.9 m above the river and overlies a possible diapiric 

structure. The diamict is underlain here by strongly oxidized 

pebble gravel capped by 0.8 m of interbedded oxidized silt 

and fine sand. The upper 0.5 m of the silt-sand interbeds has 

especially strong oxide coloration (reddish brown; 5YR 3/2), 

and bedding is involuted through this interval. Detrital wood 

from bedding planes 5 cm above the base of the silt-sand unit 

has been identified as spruce (Picea; USDA-FPL, 10/93) and 

dated at >49,000 yr B.P.

The diamict (unit 1) consists of a dark gray clayey silt 

that contains dispersed, striated pebbles, cobbles, and some 

small boulders. It is moderately compact, but lacks fissility or 

stone fabric. Where exposed at the upstream end of the bluff, 

the basal 6 cm of the diamict is a gray, stone-free, slightly silty 

clay. The upper part of the diamict typically has a sandy silt 

matrix, and it tends to maintain steeper faces than the lower 

part of this deposit. Glaciolacustrine sediment may grade 

upward into basal till. The sharp and nearly horizontal upper 

contact of the diamict can be traced visually along the entire 

face of the bluff.

The overlying alluvium (unit 2) consists of sandy pebblesmall-cobble gravel and pebbly sand that alternate in parallel 

beds about 30 cm thick. Both sand and pebbles are moderately 

mature, containing about 50 percent quartz. The basal 1.1 m of 

unit 2, at least locally, is a pebble gravel that consists dominantly 

Figure 61. Exposure Nk-30. 

Northwest side Noatak River 

at apex of Okak Bend, 24 km 

north-northwest of mouth of 

Cutler River.

m

50

40

30

20

10

 0

3

2

1

?

4

Lower diamict. Dark gray, compact, clayey silt

with dispersed rounded to subrounded, striated

pebbles, small cobbles, and sparse larger stones.

Strongly jointed, with oxides along some joint

planes. Contains subhorizontal shear planes with

aligned platy stones. Till.

Silt and silty clay. Highly deformed. Dark gray

silty clay with rounded pebbles squeezing out

along base of bluff; silt and pebbly sandy silt

near downstream end of bluff. Lacustrine or 

glaciolacustrine deposit.

Sand and gravel. Subrounded to subangular

pebbles and small cobbles in matrix of dark gray

silty sand and granules. Some beds of sand,

pebbly sand, and muddy fine gravel. Alluvium.

Upper diamict. Subangular to rounded pebbles,

cobbles, and sparse boulders in matrix of olive

gray sandy silt. Deformed by flowage. Top not

exposed. Glaciolacustrine deposit.

Covered. Includes at least 4 m of loosely

packed, yellowish brown silt Loess?

2 21

3 12.5

4 4.5+

1 2.7

-- 7

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION
42 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

Exposure Nk-32

A north-facing river bluff 2.8 km downriver from the 

mouth of Makpik Creek was visited in 1983 and examined 

again in 1995. The bluff face is largely obscured by vegetation 

and debris. The bluff is highest (29.5 m) at its east end, where 

it intersects the inner flank of the Makpik Creek end moraine; 

it declines westward to form a 14-m alluvial terrace. The basal 

unit in the bluff, which generally is obscured by flowage, 

appears to be a glaciolacustrine deposit that consists of striated 

(60 percent) of subangular black chert. It contrasts with the 

subrounded pebble-small-cobble gravel deposited by the Noatak 

River, and may have been transported by Makpik Creek. The top 

of unit 2 interfingers with the base of the overlying sand unit.

The uppermost unit (unit 3) in the bluff is exposed only 

locally. It typically is a well sorted fine sand that is cut by ice 

wedges. Where exposed, the basal 1 m of this deposit is horizontally bedded gray to grayish brown fine sand and silty very 

fine sand that contains lenses of well washed medium sand 

up to 7 cm thick and also some thin beds of brown organic 

silt. Some beds exhibit internal sigmoidal cross-bedding. The 

upper part of the sand unit (up to 1.7 m exposed) consists of 

dark grayish brown (2.5Y 4/2), faintly bedded, fine sand, very 

fine sand, and organic fine sand. Strong brown (7.5YR 5/6) 

oxide concentrations occur along former vertical rootlets, and 

some actual rootlet remains also are present. Sod, peat, and 

humic sand cap the deposit, and the upper 0.6 m of the sand 

beneath this cap has been frost churned and oxidized to a 

strong brown (7.5YR 4/6) color.

A 9-m river terrace near the upstream end of exposure 

Nk-31 contains alluvial gravel capped by sandy floodplain 

deposits (fig. 62B). A small log identified as Populus (FPL, 

11/17/95) within the floodplain deposits 47 cm above their 

base has been dated at 5,000 ±60 yr B.P.

Figure 62. Exposure Nk-31. North side Noatak River 1.5 km above Makpik Creek. (A) Bluff 

exposure. (B) River terrace immediately above bluff exposure. Black dot, radiocarbon age 

determination (yr B.P.) with laboratory number in parentheses (see appendix 1). 

m

30

20

10

 0

> 49,000

(USGS-3402) 

Diamict. Dark gray clayey silt with dispersed

pebbles, cobbles, and some small boulders.

Moderately compact, no obvious fissility or

clast fabric. Thin layer of stone-free silty clay

at base. Till above glaciolacustrine deposit?

Silt and fine gravel. Oxidized silt and fine sand

above oxidized pebble gravel. Alluvium.

Sand and gravel. Pebble-small cobble gravel

and pebbly sand in parallel beds 30 cm thick.

Interfingering contact with overlying unit 3. Alluvium.

Sand. Well sorted fine sand with ice wedges.

Medium sand lenses near base. Oxide concentrations

along rootlets through upper 1.7 m. Frost churned

beneath 0.6 m cap of peat and humic sand. 

Floodplain and eolian(?) deposit.

1 16.0

2 5.5

3 5.5

0 <1.9

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

m

10

5

 0

Gravel. Subrounded to rounded pebbles and small

cobbles in abundant sandy matrix. Alluvium.

Sod mat.

Sand. Brownish gray silty fine sand and colorless

fine to medium sand, in subhorizontal beds 0.5-

15 cm thick. Contains sparse detrital wood and

willow(?) roots. Small Populus log occurs along

bedding plane near unit base. Alluvium.

Covered 1 5.7+

3

1.25

0.2

2

2

1

3

5,000 ± 60

(AA20753)

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

Note expanded scale

A

B

2

1

3

? ? ? ?

clasts dispersed in gray clayey silt. The clasts range in size up 

to small boulders, but pebbles and small to medium cobbles 

predominate.

A measured section in the east-central part of the bluff, 

where it stands 23 m high, consists of two alluvial gravel units 

separated by floodplain deposits (fig. 63A). The basal gravel 

(unit 1) consists of pebbles and sparse small cobbles in a matrix 

of poorly sorted sand and granules that are dominantly rock 

fragments. Overlying horizontally layered sand and silt (unit 2) 

is capped by black humic silt with abundant roots, which locally 
Aniuk Lowland Below Cutler River—Noatak River Bluffs 43

Figure 63. Exposure Nk-32. South side Noatak River 2.8 km below Makpik Creek. (A) Section measured in 

1983 at east-central part of bluff. (B) Section measured in same general area during revisit in 1995. Black 

dot, radiocarbon age determination (yr B.P.) with laboratory number in parentheses (see appendix 1). 

thickens to 0.6 m and becomes more peaty At that locality, the 

peat overlies 0.5 m of oxidized yellowish brown (10YR 5/8) 

medium sand with shrub roots. A radiocarbon age of 35,000 ± 

2,300 yr B.P. on the paleosol could be finite, but the large counting error indicates that it may provide only a minimum limiting 

age on the deposit. The upper gravel (unit 3) contains somewhat 

coarser clasts in a matrix similar to that of unit 1. The uppermost 2.4 m of the section is obscured by slumping.

The bluff was revisited in 1995 in an attempt to collect 

additional organic samples for radiocarbon dating. However, 

erosional recession of its face by that time had exposed a 

glaciolacustrine deposit about 16 m thick which was actively 

flowing toward and into the river (fig. 63B). The only remaining undisturbed deposit was a 7-m section of gravel capped 

by floodplain deposits that formed the headwall of the debris 

flow. The gravel appeared identical to the alluvium of unit 3 

that had been examined in 1983 (fig. 63A).

A 14-m terrace near the upstream end of the bluff consists of floodplain deposits and thick peat beds above alluvial 

sand and gravel. The floodplain deposits generally are sandy, 

with near-horizontal bedding, abundant rootlets, and locally 

thick peat deposits. An exposure close to Nk-32 intersects 

a deep channel eroded into the alluvium of unit 1 that later 

filled with peat and sand (fig. 64A). A thick bed of peat near 

the channel base formed between about 10.2 and 10.1 ka, and 

a silty peat higher in the section began forming about 9.6 ka. 

A short distance farther upstream, another terrace exposure 

yielded an age of 11,310 ± 85 yr B.P. near the base of floodplain deposits that overlie alluvial gravel and 4610 ±60 yr B.P. 

for the base of a 2-m peat unit that caps the section (fig. 64B). 

A floodplain surface 4.5 m above river level at the downstream end of the bluff (fig. 64C) may be active only during 

times of infrequent severe flooding. The upper 1.9 m of exposed 

sediment consists of a thin cap of peat and sod above a floodplain sequence of oxidized fine sand and organic silty fine sand 

to sandy silt; some medium sand beds occur below 80 cm depth. 

The floodplain deposit contains abundant vertical stems and 

rootlets which, together with mosses, become concentrated into 

near-horizontal peat-like beds below 155 cm depth. Peaty material from 155 cm depth has a radiocarbon age of 930 ±60 B.P. 

m

30

20

10

 0

2

1

?

3

Obscured

35,000 ± 2,300

(I-13,466)

Gravel. Rounded pebbles and some small

cobbles in matrix of poorly sorted, dark gray,

immature sand and granules. Alluvium.

Sand and silt. Dark gray silt, fine sand, and

some medium sand in near-horizontal layers

1-8 cm thick. Capped by paleosol up to 1.1 m

thick that consists of peat, humic silt, and 

oxidized sand with abundant shrub roots. 

Floodplain deposit.

Gravel. Weakly stratified pebbles and cobbles

in matrix of poorly sorted sand and granules. 

Alluvium.

1 8.8

2 3.7

3 8.0

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

A

B

m

30

20

10

 0

2

1

3

Stony silt. Rounded to subrounded pebbles,

small cobbles, and sparse larger cobbles, many

striated, in matrix of dark gray (10YR 1/4) silt. 

Glaciolacustrine deposit.

Gravel. Pebble-small-cobble gravel, with layer

of larger cobbles near center. Upper 30 cm is

pebble gravel with admixed silt and vertical

stones. Sand beds at base. Alluvium.

Bluff cap. Sod (12 m) above structureless

silt (38 m). Basal 25 cm is oxidized (yellowish)

structureless medium sand with vertical pebbles. 

1 16

2 6.3

3 0.75

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION
44 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

Exposure Nk-33

A north-facing cutbank 7 km east-southeast of the mouth 

of Anisak River intersects the 14-m alluvial terrace where it 

is inset within the inner flank of the Makpik Creek moraine 

(see fig. 54). The terrace is 14 m high near the center of the 

exposure, but rises slightly upriver and may stand 15 m high at 

its eastern end. Most of the terrace face exposes only alluvial 

gravel overlain by floodplain deposits (fig. 65). However, a 

plastic stony gray clay locally is extruded from below river 

Figure 64. Terrace 

exposures adjoining 

Nk-32. (A) Deep bog 

exposed on face 

of 14.5-m terrace 

just upstream from 

Nk-32. (B) Terrace 

face about 150 

m upstream from 

Nk-32. (C) Face of 

4.5-m inactive(?) 

floodplain surface 

just beyond west 

end of Nk-32. Black 

dot, radiocarbon 

age determination 

(yr B.P.) with 

laboratory number 

in parentheses (see 

appendix 1). 

m

15

10

5

 0

Gravel. Rounded to subrounded pebbles and granules

in beds 4-6 cm thick. Foreset beds dip westward. Base

not exposed. Alluvium.

Lag deposit. Along river edge. 

Peat and silt. Black peat and very dark gray organic

silt containing abundant rootlets. Rooted shrubs common.

Bluff cap. Modern vegetation mat above densely

matted plant roots. 

Channel fill.

Sand. Subhorizontally bedded fine to medium sand,

generally oxidized (as in unit 2). Lenses of fine organic

detritus along some bedding planes.

Peat and silt. Black peat and very dark gray (N3) organic

silt in weakly defined beds up to 15 cm thick. Abundant

small (<1 cm diameter) twigs and roots.

Sand. Oxidized (reddish yellow: 7.5 YR 6/6) and gray

(N5) fine sand and some medium sand in subhorizontal

beds 1-5 cm thick.

1 3.3+

0 Covered 2.4

2

2.5d

2.8c

1.7b

1.2a

3 0.6

3

2

d

c

b

a

1

0

9,655 ± 75

(AA20756)

10,085 ± 95

(AA20754)

10,205 ± 80

(AA20755)

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

Note expanded scale

Note expanded scale

Note expanded scale

m 15

10

5

 0

Gravel. Rounded pebbles, granules, and sparse very small

cobbles. Finer and coarser clasts alternate in beds 5-10 cm

thick. Tangential cross-bedding. Base concealed beneath

lag apron. Alluvium.

Floodplain complex.

Peat. Matted grasses and sedges with abundant

wood fragments.

Peaty silt and sand. Bedded silt and fine to medium 

sand with bryophytic peat interbeds that become thicker

and more woody upward.

Sand. Faintly bedded fine sand with some medium sand

and silt beds. Coarser beds are weakly oxidized. Some

cryoturbation. Upper 25 cm contains root mottles.

1 3.3+

Covered

2

1.9c

3.8b

1.1a

2

c

b

a

1

4,610 ± 60

(AA20757)

11,310 ± 85

(AA20758)

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

m

 0

 5

? ? ? ?

Covered

930 ± 60

(USGS-3404) 

Sand and silt. Oxidized fine sand and organic silty fine 

sand to sandy silt; interbedded. Abundant vertical stems 

and rootlets, concentrated into peatlike beds at depth. 

Base not exposed. Floodplain deposit.

Peat and sod. Bluff cap.

1.8+

0.1

1

2

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

1

2

A

B

C

level along the base of the bluff. Abundant striated stones indicate that the clay probably is a glaciolacustrine deposit.

Alluvial gravel (unit 1) consists generally of rounded 

pebbles and small cobbles in parallel beds 10-30 cm thick. 

The thicker beds have a matrix of uncolored, poorly sorted 

silty sand and granules; the thinner beds commonly are 

openwork, with partial filling by sandy silt. Near its upper 

contact, unit 1 contains some beds 10-20 cm thick of matrixfree, silty pea gravel and gray fine sand interbedded with 

silty very fine sand.
Aniuk Lowland Below Cutler River—Noatak River Bluffs 45

Figure 65. Exposure 

Nk-33. Postglacial 

terrace, south side 

Noatak River 7 km 

east-southeast of mouth 

of Anisak River. Black 

dot, radiocarbon age 

determination (yr B.P.) 

with laboratory number 

in parentheses (see 

appendix 1). 

The floodplain deposits (unit 2) dominantly are well 

sorted, olive gray (5Y 5/2) very fine sand. Beds of medium 

sand and pebbly sand 1-5 cm thick occur near base of the 

floodplain sequence, and beds of dark gray organic silty fine 

sand 0.5-1 cm thick are common near its top. Vertical rootlets are common. Peat lenses and detrital twigs 50 cm above 

the base of the unit are dated at 12,890 ±190 and 13,620 ±95 

yr B.P., respectively. The upper 0.5-1 m of the sandy unit is 

mottled brownish yellow (10YR 6/8) to olive brown (2.5Y 

4/4) by oxides.

The bluff is capped by about 1 m of sod, black to very 

dark brown peat, very dark gray silt and very fine sand that 

thickens to as much as 3 m in depressions within the underlying sand. Peat from the base of a 3-m depression filling dates 

12,970 ±280 yr B.P.

Exposure Nk-34

A short distance (1.5 km) below the mouth of Anisak 

River, a prominent bluff along the north side of the Noatak 

River marks the outer limit of the Anisak moraine (see fig. 54). 

River bars and channel margins here contain abundant boulders 

up to 1 m long (50-75 cm intermediate diameter). The bluff face 

stands about 55 m high, but the upper surface of the bluff rises 

inland at a gentler angle into a complex of gravel knolls and terracelike benches as much as 77 m above the river (fig. 66).

Figure 66. Exposure 

Nk-34. North side 

Noatak River 1.5 

km below mouth of 

Anisak River.

m

15

10

 5

 0

12,970 ± 280

(I-12,517)

3

2

1

12,890 ± 190

(I-12,542)

0

Gravel. Rounded pebbles, small cobbles, and

sparse larger cobbles in variable matrix (sandy

silt to poorly sorted silty sand and granules).

Some thin lenses of fine to medium sand near

top. Alluvium.

Stony clay. Dark gray, plastic clay with abundant

striated stones. Extruded locally along base of

bluff. Glaciolacustrine.

Sand. Olive gray (5Y 5/2) very fine sand with

interbeds of dark gray, organic, silty fine sand.

Upper 0.5-1 m oxidized olive brown (2.5Y 44). 

Floodplain deposit.

Peat. Black sedge-grass peat with sparse

interbeds of silt, sand, and sandy fine gravel. 

Depression filling.

13,620 ± 95

(AA20770)

1 8.8-7.3

2 4.5-2

3 1-3

0 1-1.5

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

m

80

60

40

20

 0

1

2

?

?

? ? ? ?

Diamict. Subangular to rounded, commonly

striated, pebbles, cobbles, and small boulders

in matrix of dark gray (5Y 4/1) clayey sandy

silt. Exposed only in debris flows. 

Glaciolacustrine deposit?

Fine gravel. Pebbles in matrix of dark

yellowish brown (10YR 4/6) silty sand.

Exposed on crests of knobs and terracelike benches. Ice-contact deposit?

Note compressed scale

1 54+

2 ?

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

The bluff face is heavily vegetated, with exposures limited to recently active flows of diamict (unit 1). Subangular to 

rounded, commonly striated, pebbles, cobbles, and small boulders (up to 70 cm intermediate diameter) occur in a matrix of 

slightly sticky, dark gray (5Y 4/1), gritty, slightly clayey silt. 

Pebble lithologies are dominantly black chert, with igneous 

rocks and quartzites also common (appendix 2). The diamict 

probably is a proximal glaciolacustrine deposit.

The gravel knolls and benches are underlain by rounded 

to subrounded pebbles up to about 7 cm in an oxidized matrix 

of dark yellowish brown (10YR 4/6) silty sand. They may 

have been formed by meltwater flowing along the north margin of the glacier tongue.

Exposure Nk-35

A complex exposure on the south side of the Noatak 

River 4 km below the mouth of Anisak River is situated within 

the Anisak moraine about 1.5 km from its outer limit (see fig. 

54). Lag boulders along the river edge at this locality include 

several lithologies that are rare or absent upriver. These include 

graywackes, conglomerates, chert breccias, fossiliferous limestone, siltstone, and slate. Exposure Nk-35 has two separate 

components (figs. 54A and 54B) which are separated by a kettle 

depression that has been breached by the river. The northwestern section (bluff A) highest and most complex, but its face is 
46 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

partly obscured by slumps and debris flows. The southeastern 

section (bluff B) is lower and is dominantly alluvium.

Bluff A stands as much as 32 m high. It exposes a diamict 

and alluvium, with organic-rich floodplain deposits at its base 

and crest (fig. 67A). A basal deposit that includes organic silt 

to silty fine sand and peat (unit 1) is exposed only in small 

diapiric extrusions that have been elevated to 3.6-1.6 m above 

river level at the extreme northwest end of the bluff. The 

organic deposits are underlain by alluvial sand and gravel, 

which extends below river level. Peat 55 cm above the base of 

the silt unit was initially dated at 40,180 ±750 yr B.P., but a 

later accelerator mass spectrometer (AMS) age of >44,800 yr 

B.P. on wood fragments is considered more reliable.

The lower part of bluff A generally is obscured by a 

debris apron 6.5 m or more thick. The lowest deposit exposed 

above the debris apron is very sandy pebble-small- cobble 

gravel (upper part of unit 1). The overlying diamict (unit 2) 

consists of pebbles and granules dispersed in a matrix of very 

dark gray silty clay. Partings define near-horizontal beds 5-8 

cm thick. A thin (0.8 m) horizon of rhythmically laminated 

dark gray clay and dark greenish gray silt occurs at the base 

of the diamict. Some bedding planes within the rhythmites 

contain trace fossils (lebensspuren).

Figure 67.

Exposure Nk-35. 

South side 

Noatak River 4 

km below mouth 

of Anisak River. 

(A) Measured 

section at 

downstream 

end of exposure. 

(B) Measured 

section at 

upstream 

(southeast) 

part of bluff. 

Black dot, 

radiocarbon age 

determination 

(yr B.P.) with 

laboratory 

number in 

parentheses (see 

appendix 1). 

Sandy pebble-small-cobble gravel and medium sand with 

dispersed small pebbles (unit 3), which overlie the diamict, 

alternate in subparallel, horizontal to gently dipping beds 5-20 

cm thick. Some thin beds of openwork small pebbles with silt 

coatings are present locally. Steeply dipping deformed beds at 

one locality reflect collapse into a steep-sided depression that 

probably resulted from meltout of a mass of residual glacier 

ice. Wood fragments near the base of this kettle fill are dated 

as >45,200 yr B.P.; they probably were redeposited from older 

sediments. Where exposed by excavating, the uppermost 

part of unit 3 consists of at least 1.6 m of silty very fine sand 

and oxidized (yellowish red: 5YR 5/6) fine sand. The sand is 

faintly laminated, with bryophyte mats along some bedding 

planes. A bryophyte mat 1.4 m below the upper contact of unit 

3 has a radiocarbon age of 13,640 ±80 yr B.P.

The upper part of bluff A has been largely obscured by 

thawing of ice wedges and slumping of large blocks of coherent peat from the bluff crest, but several exposures show a 

thick (4-5 m) accumulation of peat and organic silt (unit 4). 

Radiocarbon ages range from about 10.7 ka near its base to 

9.6 ka near its upper surface. The lower part of unit 4 contains 

lenses of silt, sand, and granule-small-pebble gravel, and probably accumulated on a floodplain.

m

40

30

20

10

 0

4

3

2

1

5

Obscured

m

20

10

 0

1

2

Sandy sod, pebbly silt and sod, and sandy 

peat. Rootlets abundant. Bluff cap.

Gravel. Rounded to subrounded pebbles 

and cobbles in matrix of dark gray, poorly 

sorted, silty sand and granules. Sparse 

beds of medium sand to silty fine sand. 

Alluvium.

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

2 0.7

1 23

40,180 ± 750

(USGS-3405) 

13,640 ± 80

(USGS-3406) 

9,565 ± 90 (AA20762)

9,830 ± 75 (AA20771)

10,720 ± 85 (AA20761)

10,560 ± 80 (AA20786)

>45,200 

(AA20760)

>44,800 

(AA20759)

Diamict. Dark gray gritty clayey silt with abundant

striated and faceted pebbles, small cobbles, and sparse

larger clasts. Severely deformed by flowage. 

Glaciolacustrine deposit.

Sand and gravel. Sandy pebble-small-cobble gravel.

Grades upward into gray, well sorted, faintly bedded

fine sand. Alluvium.

Gravel . Subrounded to rounded clasts in poorly sorted

sand-granule matrix. Generally in subparallel, nearhorizontal beds 5-20 cm thick, but collapse structures

also present. Ice-contace alluvium.

Peat and organic silt. Very dark gray organic silt and 

black silty peat, in beds 5-40 cm thick, with ice wedges. 

Abundant wood fragments up to 3-4 cm diameter in peat 

beds. Basal 24 cm contains vertical stones elevated 

from underlying gravel. Floodplain deposit.

Sod. Overlies brown silt with rootlets. Bluff cap.

Organic silt. Organic matter, including rootlets, abundant 

near top and base. Middle 0.6 m less organic, with well 

sorted fine sand interbeds. Floodplain deposit.

Gravel and sand. Sandy granule-small pebble gravel,

overlain by interbedded fine to medium sand and silty 

fine sand. Base covered. Channel filling?

2 12.6

3 12.2

4 3.7

1 c 0.9

1.6b

a 0.7+

5 0.9

abc

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

A

B
Aniuk Lowland Below Cutler River—Noatak River Bluffs 47

The southeast part of the bluff complex (bluff B) stands 

24 m high and consists almost entirely of alluvium (fig. 67B). 

Rounded to subrounded pebbles and cobbles up to about 20 

cm long occur in a matrix of dark gray (10YR 4/1), poorly 

sorted silty sand and granules. The matrix material is angular to 

subangular, and consists mostly of rock chips. Some thin (5-15 

cm) sets of medium sand to silty fine sand are present within 

the gravel. Steeply dipping beds of silt, pebbly silt and sand, 

and granule-small-pebble gravel fill a steep-sided depression in 

the gravel surface. The steepness and poor sorting of the beds 

suggest that deposition could have been contemporaneous with 

meltout of underlying glacier ice. Bluff B is capped by about 

70 cm of sandy sod above silt, sand, and sandy peat. The alluvium of bluff B is highly deformed at its east end, where beds 

drape over and become nearly vertical. The gravel also may 

have been collapsing above melting glacier ice at this locality.

A low terrace just east of bluff B stands 6.4 m above river 

level. An erosion remnant of diamict forms a resistant bench 

up to 2 m thick at the base of the terrace face. The diamict 

consists of striated pebbles, small cobbles, and sparse larger 

clasts dispersed in a matrix of gray gritty silt. It is overlain by 

3.4 m of pebble-small-cobble gravel which is capped by 0.6 m 

of silt and fine sand.

Exposure Nk-36

About 5.5 km downvalley from the outer limit of the 

Anisak drift belt, a steep-sided (18°), narrow-crested (2-5 m) 

moraine ridge intersects the line of bluffs north of the Noatak 

River. A debris flow on the bluff face at this site is 0.5 km 

distant from the Noatak River at the north edge of its floodplain (see fig. 54). The bluff rises 46.5 m above the floodplain 

at the flow locality, and the debris flow exposes only diamict 

throughout this interval (fig. 68). Clasts in the flow deposit are 

rounded to subangular, and commonly striated; matrix is very 

dark gray, gritty, slightly clayey silt. Pebbles and cobbles are 

abundant, very small boulders (30-50 cm diameter) are moderately common, and larger boulders up to 1.4 m diameter are 

sparse. The boulders dominately are coarse-grained igneous 

rocks, gray quartzites, and carbonate rocks; pebbles primarily are coarse-grained and aphanatic igneous rocks, chert, and 

quartz (appendix 2). The diamict probably was orginally a till 

Figure 68. Exposure Nk-36. North side Noatak River 7 km 

downvalley from mouth of Anisak River.

rather than a glaciolacustrine deposit because (1) it occurs in 

the core of a moraine, (2) its matrix has more sand and less 

clay than in typical glaciolacustrine deposits of the upper 

Noatak basin, (3) boulders are as large as 1.4 m diameter, and 

(4) clast abundance shows a smooth decrease with increasing 

size through the cobble and boulder range. 

Exposure Nk-37

A south-facing bluff that stands as high as 57 m begins 

12.5 km downvalley from the mouth of Anisak River and 

extends for more than a kilometer farther west along the 

Noatak River. An apparent recessional moraine of the Anisak 

drift complex crosses the valley center here (see fig. 54), and 

the Noatak is deflected strongly northward into the glacial 

deposits that comprise the northern flank of its valley. The 

bluff exposes a complex glacial, fluvial, and lacustrine record 

that may span three separate glacial advances (fig. 69A; Hamilton, 2001; Edwards and others, 2003). The eastern part of the 

exposure contains two diamicts overlain by a thick sequence 

of lacustrine sediments. The western part contains a higherstanding pair of diamicts overlain by a thinner cover of silt and 

peat. The central part of the bluff, which is mostly concealed 

by massive slumps and flows, contains a wedge-like sediment 

complex that tapers westward and probably formed as a debris 

apron at the face of an ancient river-cut bluff. 

Through the eastern one-third of the bluff, two diamicts 

are underlain and separated by alluvial gravel and are capped 

by a thick but largely concealed sequence of probable lacustrine 

sediments (fig. 69B). The gravel at the base of the section is 

divisible into two units that differ markedly in oxidation and 

probably are separated by a significant time interval. The lowest 

gravel (unit 1), which is exposed only in the extreme eastern 

and east-central parts of the bluff, is cemented strongly by iron 

oxides and stands in vertical faces. Rounded to subrounded pebbles and some small cobbles occur in a brownish yellow (10YR 

6/8) sandy matrix. The deposit contains some thin sand lenses, 

and locally is capped by horizontally bedded, strongly oxidized 

(strong brown: 7.5YR 5/6) medium sand. Near the central part 

of the bluff, the gravel contains detrital logs up to about 18 cm 

diameter of spruce or larch (Picea or Larix; USDA-FPL, 10/93).

The overlying gravel (unit 2) consists of imbricated 

pebbles, small cobbles, and some larger cobbles in a sandy 

matrix. Some beds of silt, sand, and sandy fine gravel also are 

present. Yellowish brown (10YR 5/8) oxide-stained quartz is 

abundant (30-40percent) in the pebble fraction, and dominates 

the sand fraction. Sparse detrital wood fragments include 

spruce or larch (Picea or Larix; USDA-FPL, 11/83) and have a 

non-finite age of >46,000 yr B.P. The basal contact locally is a 

stone line of large cobbles and very small boulders.

The lower diamict (unit 3), a probable till, consists of striated pebbles, small cobbles, and sparse larger stones dispersed 

in a matrix of dark gray, indurated sandy silt to silty sand. This 

unit stands in vertical faces, with prominent jointing parallel 

to the bluff face. Strong brown to dark brown oxides (10YR 

5/6 to 3/2) are concentrated along joint planes and on stone 

m 60

 0

?

40

20

Diamict. Rounded to subangular, striated,

pebbles, cobbles, and sparse boulders in

matrix of very dark gray (5Y 3/1) gritty,

slightly clayey silt. Exposed only in debris

flows. Till?

Note compressed scale

46.5

THICKNESS

(m)

DESCRIPTION and INTERPRETATION
48 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

some flattened wood fragments. The wood has been identified 

as spruce or larch (Picea or Larix; USDA-FPL, 11/83), and 

was originally dated at 36,610 ± 400 yr B.P. (USGS-3287). 

On a later visit, separate samples of detrital wood and peat 

were taken from this horizon and submitted for AMS radiocarbon dating. Both samples yielded non-finite ages greater 

than about 48,500 yr B.P. 

The upper diamict (unit 5) consists of striated pebbles, 

cobbles, and sparse small boulders dispersed in gray, sandy, 

slightly clayey silt. This deposit is very compact and stands 

in vertical faces. It locally is oxidized strong yellowish red by 

ground-water seepage.

surfaces. The diamict has a sharp basal contact, which lacks 

the laminated clayey layer that commonly occurs at the base of 

glaciolacustrine diamicts in the upper Noatak basin.

The gravel between the diamicts (unit 4) commonly 

consists of subrounded pebbles and some small cobbles that 

transition upward into the overlying diamict through a 70-cm 

zone of compact gravel with a silty matrix in which many 

stones are inclined. Elsewhere in the bluff, the gravel consists 

of rounded pebbles, small cobbles, and some medium cobbles 

in a matrix of dark gray, poorly sorted sand and granules. 

It commonly is oxidized to a depth of 20 cm, and locally is 

capped by 20 cm of black, highly compact stony peat with 

Figure 69. Exposure Nk-37. North side Noatak River 12 km west-northwest of Anisak River. (A) Stratigraphic relations in bluff face 

(from a field sketch). From Edwards and others, 2003, fig. 3. (B) Measured section A, with radiocarbon ages, eastern part of bluff. Black 

dot, radiocarbon age determination (yr B.P.) with laboratory number in parentheses (see appendix 1). 

slumps and flows slump 

flow

EAST m 60

30

 0

>42,000

44,800 

(USGS-3407) 

(USGS-3408) 

EXPLANATION

Vegetated slumps and flows

Structureless silt

Laminated silt Stony silt

Diamict Gravel

Imbricated gravel

Colluvium Stone line

m 60

30

 0

WEST

Peat

ca. 1 km

+3,000

 -2, 200

Paleosol

Ice wedge

Vegetated 

slumps and 

flows

m

40

30

20

10

 0

>46,000

(USGS-1845)

5

6

7

4

3

2

1

UNIT

7

6

5

4

3

2

1

THICKNESS

(m)

13.1

13.4

4.2-11.2

1.6-5.0

1.7-5.0

4.8-7.7

2.9+

DESCRIPTION and INTERPRETATION

Silt. Massive structureless brown silt above dark gray laminated silt and clay. 

Beds flat to slightly undulating. Lacustrine deposit and loess(?) 

Stony silt. Pebbles, small cobbles, and sparse larger stones in dark gray

sandy silt. Capped by 0.7 m bedded sand and pebbly sand. 

Glaciolacustrine deposit.

Upper diamict. Striated pebbles, cobbles, and sparse small boulders in 

compact gritty silt to silty sand. Maintains vertical faces. Till.

Gravel. Pebbles and small cobbles in matrix of poorly sorted sand and 

granules to muddy granules. Locally capped by 0.2 m black peat above 0.7 m 

oxidized horizon. Alluvium.

Lower diamict. Striated pebbles, small cobbles, and sparse larger stones in 

indurated gritty silt to silty sand. Strongly jointed, with oxides along joint 

planes and on stone surfaces. Maintains vertical faces. Till.

Imbricated gravel. Pebbles, small cobbles, and sparse larger cobbles in 

sandy matrix. Bedding generally planar and near-horizontal. Some beds of 

sand and sandy pebble gravel. Sparse detrital wood. Stone line at base. 

Alluvium.

Oxidized gravel. Pebbles and some small cobbles in strongly oxidized sand. 

Some beds and lenses of sand and silty fine sand. Strongly cemented by iron 

oxides. Alluvium.

50

60

?? ? ? ?

Covered

36,610 ± 400

(USGS-3287)

>48,440

(Beta-156895)

>48,740

(Beta-156896)

36,610 ± 400

>46,000

>48,440

>48,740

B A

A

B
Aniuk Lowland Below Cutler River—Noatak River Bluffs 49

Figure 69. Exposure Nk-37 (continued). (C) Measured section B, western part of bluff.(D) Detail of debris 

wedge near river level in central part of bluff. From Edwards and others, 2003.

Silty sediments above the upper diamict generally are 

displaced by flowage and slumping and further obscured by 

revegetation of the disturbed surfaces. Rare exposures show 

about 10-14 m of stony silt overlain by a nearly equal thickness of stone-free silt and clay. The dark gray stony silt (unit 

6) contains clasts up to 40-50 cm diameter and is capped by a 

thin (0.7 m) deposit of fine alluvium. The overlying laminated 

dark gray silt and clay (unit 7) is capped by brown to gray 

loess-like silt that contains abundant ice wedges.

Much of the western part of the bluff is obscured by 

slumps and flows, but limited exposures exhibit two thick 

(11-24 m) diamicts separated by glaciolacustrine deposits (fig. 

69C). The lower diamict (unit 1) contains striated clasts to 

small boulder size dispersed in a matrix of very dark grayish 

brown sandy silt. This deposit is strongly jointed, with dark 

grayish brown oxides concentrated along joint planes. Overlying silt and fine sand (unit 2) is rhythmically laminated in 

places, but elsewhere contains diamicts and turbidite layers. 

It appears to be entirely inorganic, and may represent a brief 

glacial fluctuation with the ice front remaining within the 

upper Noatak basin. The upper diamict (unit 3) is disturbed by 

flowage in all exposures. Clasts similar to those of the lower 

diamict occur in a matrix of dark gray clayey silt to very sandy 

silt. Slumped and vegetated deposits above the upper diamict 

appear to be largely stone-free silt and peat. These deposits 

rise to an upper surface that is accordant with the crests of 

slump headwalls along the eastern part of the bluff.

The upper part of the central segment of the bluff has 

been destroyed entirely by flowage, but a wedge of highly 

indurated gravel provides near-vertical basal exposures about 

5-10 m high (fig. 69D). The sediment wedge is thickest to the 

east; it tapers westward and incorporates increasing amounts 

m

60

40

50

20

30

10

 0

2

1

3

Covered

Debris

apron

? ? ?? Upper diamict. Rounded to subangular, striated, pebbles, cobbles, and 

sparse small boulders in matrix of dark gray very sandy silt. All exposures

disturbed by flowage. Glaciolacustrine deposit?

Laminated silt. Gray to dark grayish brown silt and very fine sand in beds 

20-90 cm thick, with some rhythmic couplets. Basal 5 m contains interbedded 

very dark gray pebble-cobble diamict in beds 25-60 cm thick. Upper 1 m 

contains interbedded turbidites(?) of nonsorted sandy fine gravel 8-10 cm thick. 

Glaciolacustrine deposit.

Lower diamict. Rounded to subangular striated pebbles, cobbles, and sparse 

boulders in matrix of very dark grayish brown sandy silt. Strongly jointed, with 

oxides along joint planes. No apparent fissility or fabric. Till?

Covered. Slumped and vegetated. Stone free peat and silt locally exposed. 

Origin uncertain.

3 11.5

2 7.0

-- 6.1

1 23.5+

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

EXPLANATION

Stony silt

Oxidized gravel Diamict

Sandy gravel Bedded

quartzose gravel

Debris cone

Peat bed

Pollen and

insect section

Channel fill

Covered (flow deposits)

Lag apron River level 7/14/95

Gully

10

15

5

 0

50 25 0

BASE LINE (METERS)

100 75

m

10

15

5

 0

WEST EAST m

C

D
50 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

Figure 70. Exposure Nk-38. 

North side Noatak River 16.5 km 

west-northwest of Aniuk River.

m

30

20

10

 0

1

?

2

?? ?

Covered

Diamict. Rounded to subrounded pebbles, cobbles,

and small boulders in matrix of dark gray, sandy,

slightly clayey silt. Severely disturbed by slump and

flowage. Top not exposed. Glaciolacustrine deposit?

Gravel. Coarse and fine gravel in beds 10-20 cm thick. 

Coarse beds are rounded pebbles and small cobbles in 

matrix of very dark gray poorly sorted sand. Fine beds 

are rounded small pebbles and granules without matrix. 

Stones in some beds are silt-coated. Upper 6 cm 

oxidized yellowish brown (10YR 4/4). Alluvium.

Bedrock. Schist and quartzite.

2 7.8+

1 6.2

-- 9.6

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

Figure 71. Exposure Nk-39. 

North side Noatak River 1.5 km 

above mouth of Nimiuktuk River. 

m

20

10

 0

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

1

1

--

15-13

0-2

Gravel. Sandy pebble-small-cobble gravel with

dispersed pyroxenite erratics up to 57 cm diameter.

Probably capped by silt. Alluvium.

Bedrock. Intermittently exposed near river level.

of fine-grained and organic deposits in that direction. Oxidized 

gravel and diamict, which are identical to units 2 and 3 farther 

east in the bluff (fig. 69B), occur locally beneath the sediment 

wedge. The thickest part of the wedge consists of subangular 

to subrounded pebbles, cobbles, and very small boulders in 

beds up to 1 m thick that are separated by thinner (5-10 cm) 

undulating beds of stony sand, pebbly silty sand, and organic 

silt. The gravel layers are matrix-free in some places, and 

elsewhere have a compact silty sand matrix. The upper 4-4.5 

m of the gravel is oxidized reddish yellow (5YR 6/8). This 

unit appears to be a slightly deformed and mixed variant of 

the imbricated gravel which occurs through the eastern part of 

the bluff. The gravel interfingers westward with unsorted to 

weakly sorted, subrounded, commonly fractured pebbles and 

cobbles in an oxidized and indurated sandy to silty matrix. 

Lenses of pebbles, silt, and peat within the deposit dip westward at 7-10°. This unit thins to the west, where it interfingers 

with peat and organic silt. Except for the absence of boulders, 

this unit resembles deposits that form along the base of this 

bluff today. Peat and organic silt overlie and interfinger with 

gravel through much of the colluvial wedge, but generally 

thicken toward its distal (west) end where woody peat in beds 

10-15 cm thick is interbedded with thicker (10-50 cm) beds 

of stony sand and oxidized pebble-cobble gravel. The peat 

contains logs up to 10 cm diameter of spruce or larch (Picea 

or Larix; USDA-FPL, 11/83) that yield three erratic radiocarbon ages (appendix 1), but probably are non-finite (>42,000 

yr B.P.). Pollen and insect records from the peat beds provide 

supporting evidence for an interglacial spruce forest (Edwards 

and others, 2003). Strongly jointed dark gray silt with pebble 

dropstones overlies the peat in one locality. Sediments overlying the colluvial wedge generally are obscured by flowage, but 

alluvial gravel with a stone line at its base appears to overlap 

the eastern part of the wedge. Diamict overlies stony silt above 

the toe of the wedge, but this deposit could be a flow lobe.

Exposure Nk-38

Near the mouth of Itimtikrak Creek, the Noatak River enters 

an unusually straight reach about 9 km long in which bedrock 

commonly is exposed near river level. At the east end of this reach, 

a south-facing river cutbank (fig. 70) stands 23 m high and rounds 

back to an undulating upland surface at about 40 m height.

Schist and quartzite bedrock at the base of the exposure 

stands about 10 m high and is overlain by alluvial gravel 

(unit 1). The gravel consists of alternating coarser and 

finer beds 10-20 cm thick. The coarser beds have a matrix 

of poorly sorted very dark gray sand; the finer beds lack 

any matrix. The upper 6 cm of the deposit are oxidized 

yellowish brown.

Overlying diamict (unit 2) has been modified by slumping and flowage. Striated and faceted clasts up to 65 cm long 

occur in a matrix of dark gray sandy, slightly clayey silt. The 

upper part of this unit is entirely vegetated, and any overlying 

deposits are not visible. 

Exposure Nk-39

Near the mouth of Nimiuktuk River, a south-facing 

gravel cutbank (fig. 71) forms part of a 15-m terrace remnant 

with a near-level, poorly drained upper surface. Pebbles and 
Aniuk Lowland Below Cutler River—Noatak River Bluffs 51

small cobbles dominantly consist of ferruginous sandstone; 

the dispersed larger stones primarily are pyroxenite. Because 

clast size and composition are similar to local river gravels, 

the deposit is interpreted to be a river deposit formed during 

postglacial downcutting. The larger stones were redeposited 

from local glacial sediments that were eroded by the 

downcutting river.

The height of the deposit is comparable to that of other 

local and regional 15-m terraces mapped previously as unit tg4 

by Hamilton (2003).

Discussion

Direct correlation of stratigraphic units in the set of river 

bluffs between Cutler and Nimiuktuk Rivers is complicated by 

(1) facies changes related to former glacier terminal positions 

along the valley axis, (2) lateral facies changes between valley 

center and valley margins, (3) localized downcutting by the 

Noatak River during interglacial and interstadial phases, (4) 

glacial tectonism where grounded ice tongues advanced over 

deformable beds, (5) sediment input via major tributaries, and 

(6) recycling of older glacial, alluvial, and lacustrine sediments by advancing glaciers and the Noatak River. Assignment of bluff units to individual glacial advances and glaciallake stages was attempted in a previous paper (Hamilton, 

2001) and general relations are shown in figure 54.

Many of the higher bluff exposures contain glacial 

till and ice-contact gravel, glaciolacustrine sediments, and 

ancient river gravels. The till and glaciolacustrine deposits 

were differentiated by using the criteria listed in table 2. The 

alluvial gravel deposits generally are similar in clast size and 

composition to channel alluvium of the present-day Noatak 

River. They commonly fill channel-like or larger depressions 

that were deeply eroded following deglaciation and drainage 

of ice-dammed lakes. Probable interglacial deposition of 

the gravel is further indicated by (1) river downcutting close 

to modern level, (2) deep oxidation, (3) presence of conifer 

wood, (4) gravel clast size comparable to Holocene alluvium 

of the Noatak River, and (5) insect assemblages and pollen 

spectra reflecting climates comparable to or warmer than 

that of the present day (Elias and others, 1999; Edwards and 

others, 2003). 

The Old Crow tephra, which formed during an early 

phase of the last interglaciation (Hamilton and BrighamGrette, 1992) has been identified within floodplain deposits in 

Nk-26 and Nk-29A (Elias and others, 1999). Exposure Nk-26 

exhibits dominantly glaciolacustrine deposits that formed in a 

succession of lakes that were dammed by glacial advances farther down the Noatak River valley. This bluff contains a thick 

glaciolacustrine deposit (unit 6; fig. 56A) that corresponds 

in height and in thickness to glaciolacustrine beds exposed 

at Nk-27. Exposure Nk-29A intersects a deeply buried end 

moraine (not shown in fig. 54) that separates the two arms 

of Okak Bend (Hamilton, 2001). The till assignable to that 

end moraine occurs between successions of river gravel and 

glaciolacustrine deposits.

Exposure Nk-30 is farther from the axis of the late Pleistocene Noatak valley than exposures Nk-26 through Nk-29, 

and consequently may differ stratigraphically from those 

bluffs because of its valley-side location. It also stands higher, 

hence has a probable subaerial capping deposit whereas 

alluvial or lacustrine sediments cap lower-standing bluffs. This 

exposure is near the toe of a conspicuous solifluction slope 

that extends southward from the moraine flank. Solifluction 

debris probably is a significant component of late Holocene 

deposits at this locality, and sediments derived from the valley 

sides may be included within older deposits as well.

At exposures Nk-31 and Nk-32, river gravel and floodplain deposits associated with an alluvial terrace about 23-26 

m high unconformably overlie older till, lake sediments, and 

alluvium. Farther downvalley at Nk-35B, an alluvial terrace 

stands at a corresponding height (23 m). The nearby exposure 

Nk-35A forms a conspicuously higher 30-m terrace that is 

dated by a concordant set of four radiocarbon ages as forming 

between 13.6 ka and 9.5 ka. The early postglacial terraces at 

heights of 20-30 m provide a good analogue for the tephrabearing floodplain deposits that stand about 20 m high at 

Nk-26 and Nk-29A. Those features probably formed early in 

the last interglacial interval based on pollen spectra and insect 

fauna (Elias and others, 1999) and on independent age assignments for the Old Crow tephra by Hamilton and BrighamGrette (1992) and by Berger (2003). 

Exposures Nk-32A, Nk-32B, and Nk-33 exhibit remnants 

of an alluvial terrace about 14-15 m high that also occurs 

widely through this sector of the valley. Radiocarbon ages 

from Nk-32B and Nk-33 indicate an age of about 13.5-11.3 ka 

for this feature. Dates on the channel fill at Nk-32A indicate a 

later episode of downcutting to about 6 m height took place at 

about 10 ka. These sets of radiocarbon ages overlap those at 

Nk-35A, indicating that postglacial downcutting by the Noatak 

River must have taken place very rapidly.

The remaining two exposures (Nk-34 and Nk-36) in this 

stretch of the Noatak River valley intersect portions of the 

Anisak moraine. The active debris flows that dominate Nk-34 

indicate that this part of the moraine was built largely of 

glaciolacustrine deposits and that the Anisak glacier therefore 

terminated in a proglacial lake. The bluff face at Nk-36 is 

highly weathered but remains steep, suggesting that it may be 

underlain by till. The kettle-like collapse structures seen in the 

alluvium at Nk-35A indicate that stagnating ice of the Anisak glacier was still present during construction of the 30-m 

alluvial terrace. 

The complex stratigraphic record of exposure Nk-37 

extends back through the last interglacial and includes older 

glacial and interglacial deposits as well. The colluvial wedge 

in the central part of the exposure provides the key to relations between the glacial sequences of the eastern and western 

segments of the bluff (table 3). The eastern part of the wedge 

is dominated by clasts that probably were redeposited from 

the imbricated gravel and possibly also from the diamict that 

overlies that gravel. The wedge is then overlapped by younger 

alluvial gravel, which is overlain by till assignable to the 
52 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

Figure 72. Exposure Makpik-1. West side of west fork Makpik 

Creek 9.5 km north of its confluence with Noatak River.

Aniuk Lowland Below Cutler River— 

Tributary Drainages

Introduction

Ten additional bluffs were examined along tributaries 

to the Noatak River in this sector of its drainage system (fig. 

54). Most are along south-flowing streams that drain the De 

Long Mountains. Single exposures were measured on Makpik 

Creek, Anisak River, and Itimtikrak Creek, and two exposures 

were measured along New Cottonwood Creek. Four bluffs 

are described along Nimiuktuk River, but three of these are 

beyond the north border of figure 54 and are shown only in 

figure 3. A single bluff measured south of the Noatak River is 

situated on Aklumayuak Creek. 

Most of these tributary streams lack the erosive power 

of the Noatak River, and consequently many of their bluffs 

are relict features that have not been undercut recently. Their 

weathered faces reveal general sediment composition, but finer 

details such as bedding thickness and sediment structures are 

obscured. Some of the following bluff descriptions consequently contain little detail and are very brief. 

Exposure Makpik-1

A gravel terrace remnant about 40 m high occurs on the 

west side of the west fork of Makpik Creek 9.5 km north of 

the Noatak River (see fig. 54). The gravel abuts the outer flank 

of the Cutler moraine, and may be a remnant of a formerly 

more extensive ice-marginal meltwater deposit.

The terrace face exposes subrounded to rounded pebbles 

and cobbles with sparse small boulders (55-75 cm diameter) 

in a matrix of coarse sand and granules (fig. 72). Silt is present 

near the top of the bluff as coatings on grain surfaces, but the 

actual depth to which silt was translocated could not be determined owing to the absence of fresh exposures along the bluff. 

A concentration of boulders up to about 75 cm diameter occurs 

in the upper part of the terrace exposure, and similar boulders 

are present along the inner edge of the terrace where it abuts 

the moraine. The boulders in the terrace face may be a lag 

Anisak glacial advance. The till is covered by glaciolacustrine 

sediments, into which extended a body of till that formed 

during a readvance of the Anisak glacier (see fig. 54). A 

thick loess deposit caps the bluff. If correlations between the 

eastern, central, and western parts of the bluff are correct, the 

overall sediment record probably represents a sequence of 10 

major depositional events (table 3).

The basal gravel at exposure Nk-38 contains fine as well 

as coarse beds and probably formed as interstadial alluvium. Its 

oxidized upper horizon indicates that a substantial interval of subaerial weathering followed deposition of the gravel and preceded 

formation of the glaciolacustrine unit. The glaciolacustrine deposit 

may have formed during the Avan advance, the last significant 

Pleistocene glacial event the western Noatak River valley (table 1).

Table 3. Correlation of depositional units in exposure Nk-37. 

[--------, absent or obscured. From Hamilton, 2001]

Western section Central section Eastern section Glacial event

Massive silt (loess cap)

Laminated silt + silt/clay rhythmites

Upper diamict Stony glaciolacustrine silt Anisak readvance

Laminated silt ---------------------------------------------------------------------------

Lower diamict Upper till Anisak advance

-------------------------- Alluvial gravel

----------------------------------Colluvial and peat wedge-------------------------------------

----------------------------------------------------------------------------Lower (oxidized) till Cutler(?) advance

----------------------------------------------------------------------------Imbricated gravel

-------------------------- Oxidized gravel

m

40

20

 0

DESCRIPTION and

INTERPRETATION

Gravel. Subrounded to rounded 

pebbles and cobbles, with sparse 

small boulders in matrix of coarse 

sand and granules. Concentration 

of boulders up to 75 cm diameter 

near top of exposure. Fan-delta 

deposit with till(?).

THICKNESS

 (m)

 40

Note compressed scale
 Aniuk Lowland Below Cutler River—Tributary Drainages 53

Figure 73. Exposure 

Anisak-1. North side 

unnamed western 

tributary to Anisak 

River 6.5 km above 

its confluence with 

Anisak River.

m

20

 10

0

2

1 Gravel. Pebbles and small cobbles in immature

matrix of black sand and platy granules. Platy

stones imbricated, with westward dips. Larger

cobbles present at base. Alluvium.

Stony silt. Poorly sorted stones up to boulder

size, many faceted, polished, and striated, in

matrix of gritty clayey silt. Glaciolacustrine deposit.

1 11.7

2 2.8

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

deposit that represents a brief advance of the fluctuating glacier 

front to the present position of Makpik Creek’s west fork.

Fan-like deposits of pebble gravel on the east side of the 

west fork opposite the terrace remnant are part of an abandoned lower-level fluvial system that originated in the Avingyak Hills. These deposits may represent a fan-delta system that 

was graded to a proglacial lake that formed during a glacial 

advance that followed the Cutler event.

Exposure Anisak-1

A low bluff on a western tributary to Anisak River about 

50 km above the mouth of that river is beyond the north margin of figure 54, but is shown in figure 2. The bluff is situated 

near the apparent northwestern limit of glacial-lake deposits of 

Makpik age (map-unit id1A in Hamilton, 2003). Thin glaciolacustrine sediments are exposed above stream gravel in an 

exposure that stands 14.5 m high (fig. 73).

The gravel (unit 1), which fines upward, contains an 

immature matrix characteristic of sluggish small tributary 

streams. Imbricated clasts indicate eastward flow direction 

like that of the modern stream. The overlying diamict (unit 2) 

contains glacier-modified stones in a matrix of mixed sand, 

silt, and clay.

The gravel was deposited by an aggrading and increasingly sluggish stream that may have been responding to rising 

base level resulting from glacier blockage and lake-level rise 

farther down the Anisak River. The overlying glaciolacustrine sediments would then have formed as the margin of the 

glacier-dammed lake expanded upvalley across this site.

Exposure Itim-1

A northwest-facing bluff on the east side of Itimtikrak 

Creek stands 23.4 m high. It occurs within drift of the Makpik 

glacial advance (see fig. 54), but may be situated at the outer 

flank of a recessional moraine that formed during a readvance 

or stillstand of the Makpik glacier.

The bluff face has collapsed toward Itimtikrak Creek by 

slumping and flowage. Its highly disturbed surface exhibits 

glacier-modified stones to boulder size in a probably unsorted 

but silt-rich matrix (fig. 74). The largest clasts are pyroxenite 

and gray quartzite that originated in valley heads in the De 

Long Mountains. Black chert is prominent among pebblesized clasts. Flowage of the bluff face suggests the presence of 

glaciolacustrine sediments, but the widespread slump blocks 

indicate that an additional unit such as till or gravel may be 

present also. 

The exposure is capped by stony silt and silty peat that 

probably formed by frost mixing of eolian silt (loess) with sod 

and gravel. Silt-free gray sand below 70 cm depth probably 

reflects the former presence and upper limit of permafrost.

Figure 74.

Exposure Itim-1. 

East side Itimtikrak 

Creek 7 km above 

its mouth.

m

30

10

20

0

2

1

?

? ? Peat, silt, and sand. Peat and silty peat overlie

stony brown silt above gray-brown poorly sorted

stony silty sand. Gray sand appears at 70 cm

depth. Base not exposed. Bluff cap.

Stony silt. Subrounded clasts up to 80 cm length,

many faceted and striated, in probable unsorted

silty matrix. Largely obscured by slumps and

flowage. Glaciolacustrine deposit?

2 >0.7

1 22.7

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION
54 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

m

30

20

10

 0

>47,590

(Beta-156894)

3

2

1c

1b

1a

Sandy gravel. Subrounded pebbles and small cobbles in

matrix of dark gray (7.5YR 4/0) poorly sorted sand and

granules. Some channel-form crossbedding. Contains layers

and lenses of gravelly sand 5-10 cm thick. Alluvium.

Sand and fine gravel. Alluvium.

Clast-supported pebble-small cobble gravel with nearhorizontal bedding.

Sandy pebbles in lenticular (channel-filling) beds up to 0.5 m

thick. Interstratified with sand in near-horizontal laminations a few

millimeters thick that contain sparse granules and small pebbles.

Some 10-cm sets of ripple crossbedded sand also present.

b 2

Near-horizontal to ripple cross-laminated sand with some

lenses of silt and other lenses of detrital wood.

1

c 5

a 3

2 7.7

Sand to clay couplets. Rhythmically laminated dark gray

(7.5YR 4/0) silty clay to very dark grayish brown (10YR 3/2)

well sorted very fine sand in couplets 5-10 cm thick. Bulk of

each couplet is dark gray (10YR 4/1) silt with laminae 1-2 mm

thick. Contains isolated stones to very small cobble size.

Couplets thicker (10-20 cm) near base, with coarse silt to

silty very fine sand dominant but clayey laminae 3-4 mm thick

unchanged from higher in unit. Lacustrine deposit.

3 4.7

9.9

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

Exposure Ctn-1 (New Cottonwood Creek)

A south-facing bluff stands 22.3 m high where eastern and 

western forks of New Cottonwood Creek converge just beyond 

the outer edge of the Makpik drift sheet (see fig. 54). The bluff 

exposes laminated lake sediments above fine alluvium (fig. 75).

In the lower part of the section (unit 1), sand coarsens 

upward into channel-filling deposits of sandy pebbles and then 

into pebble-small-cobble gravel. Sandy gravel continues upward 

into overlying alluvium (unit 2). Both units 1 and 2 exhibit 

lenticular channel-fill structures characteristic of fluvial erosion 

and deposition. A large slab of detrital wood in gravel 6.8 m 

above creek level has a non-finite radiocarbon age of >47,590 yr 

B.P. The wood is similar in appearance to spruce, and a cone of 

Picea glauca (white spruce) was recovered at the same level.

The topmost deposit (unit 3) consists of rhythmically laminated silt, silty clay, and very fine sand that contains isolated 

Figure 76. Exposure 

Ctn-2. West side New 

Cottonwood Creek 5.5 

km above its mouth.

stones up to very small cobble size. Beds and lenses 2-3 cm 

thick of sand with some granules occur near the top of the unit. 

The uppermost 70 cm of these sediments is frost-churned and 

filled with rootlets, indicating a former active layer associated 

with a permafrost table deeper than that of the present day.

Exposure Ctn-2

A high bluff with a terrace-like upper surface rises above 

New Cottonwood Creek where it intersects the northern lateral 

moraine of the Anisak (Itkillik Phase IB) advance (see fig. 54). 

The bluff face is largely stabilized and somewhat weathered. 

It exposes gravel above diamict, and water-washed gravel is 

exposed across the bluff’s near-level upper surface (fig. 76).

A recently active debris flow exposes unsorted, glacierabraded clasts up to medium boulder size in a matrix of mixed 

sand to clay-sized grains (unit 1). Limestone is most abundant 

Figure 75. Exposure Ctn-1. New Cottonwood 

Creek at junction of forks 10 km above 

its mouth. Black dot, radiocarbon age 

determination (yr B.P.) with laboratory number 

in parentheses (see appendix 1). 

m

60

40

20

 0

1

2

? Diamict. Unsorted, subangular to subrounded clasts in dark gray 

muddy matrix. About half of the clasts are striated and/or faceted. 

Pebbles to small cobbles dominant, but larger stones range up to 

110 cm length. Till and/or glaciolacustrine deposit.

Gravel. Subrounded clasts to ca. 30 cm diameter in matrix of poorly 

sorted, dark, medium to coarse sand and granules. Clasts lack facets 

and striations; many have carbonate crusts. Matrix grains angular

to subangular, with rock chips dominant. Alluvium.

Note compressed scale

1 46

2 14.3

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION
 Aniuk Lowland Below Cutler River—Tributary Drainages 55

Figure 77. Exposure Nm-1. Southwest 

side Nimiuktuk River 13 km southeast of 

Thunder Mountain.

among the clasts, with quartzite, greenish conglomerate, diorite, pyroxenite, and ferrugineous sandstone also common. The 

unstable flow activity suggests the presence of glaciolacustrine 

sediments, but the bulky lateral moraine at this site indicates 

that glacial till should be present also. Perhaps flowing glaciolacustrine sediments have masked underlying till. 

The overlying gravel (unit 2) contains subrounded clasts 

up to very small boulder size that lack any glacial overprint. 

Lithologies, which include gray quartzite, diorite, conglomerate, and angular fragments of black chert, are less diverse 

than in the underlying diamict. A test pit into the bluff’s upper 

surface exposes frost-stirred and oxidized (dark yellowish 

brown: 10YR 3/6) silty gravel above very dark brown (10YR 

2/2) unweathered sandy gravel at about 40 cm depth.

Exposure Nm-1 (Nimiuktuk River)

A north-facing bluff near the head of Nimiuktuk River 

lies beyond the north margin of figure 54 but is shown in 

figure 3. The bluff intersects a lateral moraine assigned to an 

unnamed glacial readvance of late Anisak age that is mapped 

as unit id1C in Hamilton (2003). Till overlies a bedrock surface 

that stands about 6 m above river level (fig. 77). Unsorted 

glacier-modified clasts occur in a matrix of unsorted fine 

debris. Lithologies include crinoidal limestone, chert, 

ferruginous quartzite, and chert-rich conglomerate. Black 

chert is abundant in clasts up to very small boulder size; 

some large cobbles of green-gray and brown chert also are 

present. These lithologies crop out widely through local valley 

heads, indicating that the late Anisak readvance was a small, 

localized event.

Exposure Nm-2

A terrace exposure along the west side of Nimiuktuk 

River about 9 km below exposure Nm-1 (see fig. 3) occurs 

within probable outwash that issued from the late Aniuk 

moraine front. Many cobble-sized clasts in the terrace gravel 

(unit 1; fig. 78) are platy in shape; these commonly are 

imbricated, dipping upvalley. Black chert and gray quartzite 

are the dominant lithologies. The upper 80 cm of the exposure has been frost-churned and mixed with brown silt of 

probable eolian origin.

Exposure Nm-3

About 30 m of unsorted and unstratified till (fig. 79) is 

exposed in a north-facing bluff in a valley tributary to Seagull 

Creek, which flows southeastward into Nimiuktuk River (see 

fig. 3). At this site, tillstones range in size only up to small 

boulders and larger glacial boulders are rare in the stream bed. 

The relatively small size of these glacier-shaped clasts indicates that they probably were redeposited from alluvium along 

the center of Seagull Creek valley. Ice from the main valley of 

Seagull Creek probably flowed westward up the unglaciated 

tributary valley for a short distance beyond this site.

Figure 79. Exposure Nm-3. South side 

unnamed western tributary to Seagull 

Creek 3 km above its confluence with 

Seagull Creek.

Figure 78. Exposure Nm-2. West side 

Nimiuktuk River 9 km below Nm-1.

m

20

10

 0

1

Diamict. Clasts up to 80 cm length,

many faceted and striated, in compact

gray matrix. Till.

-- 6.3 Bedrock. Lithology not recorded.

1 10.1

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

m

30

20

10

 0

Diamict. Subrounded pebbles, cobbles, and

sparse small boulders in gray muddy matrix.

Many stones faceted and striated. No sorting

or stratification evident. Till.

29.5

THICKNESS

(m)

DESCRIPTION and INTERPRETATION

m

10

 5

 0

2

1

Note expanded scale

Gravel. Subrounded pebbles and small to 

medium cobbles in subhorizontal beds 0.5-1 m 

thick. Some channel fillings present. Black 

chert and gray quartzite dominant. Alluvium.

Silty sand. Black sand and granules 

frost-mixed with brown silt. Bluff cap.

1 7.7

2 0.8

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION
56 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

Figure 80. Exposure Nm-4. 

West side Nimiuktuk River 6 km 

above its mouth.

m

15

10

 5

 0

Gravel. Pebbles, cobbles, and very small boulders

in matrix of black poorly sorted medium sand to

granules with abundant rock chips. Alluvium.

15

THICKNESS

(m)

DESCRIPTION and INTERPRETATION

Figure 81. Exposure Ak-1. 

North side Aklumayuak Creek 

31 km above its mouth.

Exposure Nm-4

A bluff near the mouth of Nimiuktuk River exposes river 

gravel in an alluvial terrace that stands about 15 m high (fig. 

80). Clasts range up to about 38 cm long in a poorly sorted 

sand-granule mixture. Rock types include pyroxenite, limestone, and gray quartzite. Terraces of comparable height are 

widespread in this part of the Noatak drainage system, and are 

mapped as terrace unit tg3 (Hamilton, 2003; in press). 

Exposure Ak-1 (Aklumayuak Creek)

A high-standing terrace near the head of Aklumayuak 

Creek 13 km southwest of Lake Kangilipak exposes gravel 

across its weathered face (fig. 81). Clasts through the lower 

part of the gravel section primarily are pebbles and small 

cobbles, with quartz abundant and other local lithologies such 

as schist, limestone or marble, and quartzite also common. 

Both clasts and matrix coarsen upward, with clasts ranging 

upward in diameter to about 30 cm. Lithologies change also, 

with ultramafic clasts derived from the DeLong Mountains 

becoming common. The base of the exposure is concealed by 

a lower gravel terrace, which rises 8.5 m above river level. A 

concentration of lag boulders on the creek’s floodplain here 

contains many clasts in the 70-75 cm size range and a broken 

fragment of quartzite 82 cm long.

The coarsening-upward gravel with its increasing content 

of far-traveled lithologies indicates probable transition from a 

nonglacial stream deposit to glacial outwash at exposure Ak-1. 

The unweathered but strongly oxidized near-surface gravel 

supports field relations, which suggest an Anisak age (see fig. 

54) for the outwash and its derivation from a glacier margin 

near the west end of Lake Kangilipak. The concentration of 

large boulders at the base of the bluff indicates that the terrace gravel alleviated following dissection of an older glacial 

deposit. Nearby erosion remnants of an ancient drift support 

this assumption.

Discussion

A highly weathered bluff along Makpik Creek exposes 

ice-contact gravel that may be related to the Cutler glacial 

advance. Bluffs along Anisak River and Itimtikrak and New 

Cottonwood Creeks contain glaciolacustrine deposits related 

to the Makpik and Anisak glacial advances. Together with 

wave-cut notches, beach ridges, and other geomorphic evidence, these bluff deposits demonstrate that extensive proglacial lakes inundated this part of the upper Noatak basin during 

those glacial events. At exposure Ctn-1, interglacial alluvium 

with spruce wood and a non-finite radiocarbon age is exposed 

beneath the glaciolacustrine sediments.

Exposures Nm-1 and Nm-2 contain till and probable 

outwash that were deposited near the head of Nimiuktuk River 

valley during a very late glacial readvance of Anisak age. 

The till at Nm-3 may have been formed at the same time by a 

glacier that issued from the same general highland source area 

and extended into the upper valley of Seagull Creek.

Exposure Nm-4, a 15-m terrace near the mouth of Nimiuktuk River, probably is correlative with Nk-39, an alluvial 

terrace of comparable height on a nearby stretch of the Noatak 

River. These terrace remnants are part of the widespread 15-m 

Noatak valley terrace system discussed previously.

The Aklumayuak Creek exposure (Ak-1) is part of 

an outwash train deposited by meltwater that flowed south 

through a deep rock-walled gorge from an ice margin near 

Lake Kangilipak. The present-day creek is an underfit stream 

that occupies a deeply incised valley eroded by much larger 

meltwater streams associated with at least two separate glacial 

advances into the Lake Kangilipak area (Hamilton, 2003 and 

in press).

m

40

30

20

10

 0

Note compressed scale

Gravel. Subrounded pebbles and small cobbles in sandy 

matrix with platy phyllite granules. Coarsens upward into 

coarse-pebble to medium-cobble gravel, that also contains 

large cobbles and very small boulders in matrix of poorly 

sorted sand to small pebbles. Gravel at bluff crest strongly 

oxidized to >30 cm depth, but clasts are little weathered. 

Alluvium and outwash. ?

41.5

THICKNESS

(m)

DESCRIPTION and INTERPRETATION
Nimiuktuk River to Aklumayuak Creek 57

Nimiuktuk River to Aklumayuak Creek

Introduction

Through the 30-km reach between the mouths of 

Nimiuktuk River and Aklumayuak Creek, the Noatak River 

flows southward through a narrow valley only 5 km wide that 

crosses the topographic grain of the De Long Mountains 

(fig. 82). However, the river’s gradient through this stretch, 

about 1.1 m/km, is nearly identical to gradients farther 

upvalley and downvalley. The end moraine correlated with the 

Anisak glacial advance crosses the Noatak valley floor 7 km 

above the mouth of Aklumayuak Creek, and some of the bluffs 

through this reach expose glacial-lake sediments relating to 

this advance. Drift of the preceding Makpik glaciation occurs 

locally in tributary valleys (Hamilton, 2003), but has been 

eroded or blanketed by glacial-lacustrine sediments along the 

floor and lower flanks of the main valley.

Nine river-bluff exposures (Nk-40 through Nk-48) were 

recorded through this sector of the Noatak River valley. Other 

bluff faces were fully vegetated, and their underlying materials 

could not be measured or identified. 

Exposure Nk-40

A silt and gravel exposure 14 km below the mouth of 

Nimiuktuk River rises to a heavily vegetated terrace-like 

surface 44 m above river level, then steps up to a 52-m surface 

farther inland that has pebble gravel exposed along its outer 

edge (unit 1; fig. 83). The 44-m terrace may be inset within the 

higher surface through a cut-and-fill process.

The younger gravel (unit 2) consists dominantly of 

sedimentary and metamorphic rocks, with ultramafic rock 

types present but uncommon. The size range, rounding, and 

lithology of the clasts are characteristic of normal river gravels 

that include rock types transported from the upper Noatak 

River valley. The overlying stony silt, which may extend 

Avan River

Lake Kaiyak

Lake 

Narvakrak

Noatak River

Kugururok River

Kaluktavik River

Nimiuktuk River

Tumit Creek

Aklumayuak Creek

Sapun Creek

Trail Creek

Noatak 

Canyon Noatak

River

40

39

41 42 43

44 45

46

47 48

49

50A

51 50B

52

53

54

55 56

57 58 59

60

61

62

Nm-4

Trail-1

Ku-1

Ku-2

Ku-3

Avan-1

Avan-2

Kl-1

Kl-2

Sp-1

Sp-2

Kl-3

MAP UNITS

Glaciolacustrine

deposits

Outwash

Anisak

Makpik

Undifferentiated

Bedrock and colluvium,

undifferentiated

Alluvium

Terrace gravel

Itkillik II

Itkillik I Drift of

Itkillik I

age

Cutler drift

Avan (Drift of

Itkillik II age)

Meltwater

channel

Lake Moraine

ow

ow

ow

Misheguk

Mountain

0 25 KILOMETERS

0 15 MILES

68o

15'

160o 161 00' o

30'

68o

00'

Figure 82. Generalized geologic map, Noatak River valley between Nimiuktuk River and Kugururok River. Numbers 

without prefixes refer to Noatak River bluffs (designated Nk in text).
58 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

Figure 83. Exposure 

Nk-40. East side Noatak 

River 14 km below 

Nimiuktuk River mouth. 

Figure 84. Exposure 

Nk-41. West side 

Noatak River 17 km 

below Nimiuktuk 

River mouth.

entirely through the 22-m span of units 3 and 4, contains 

sparse clasts interpreted as dropstones; it is considered to be a 

distal rather than proximal glaciolacustrine deposit.

The inferred history of this deposit is (1) river flow at the 

50-m level (regional terrace tg1 of Hamilton, 2003 and in press), 

shortly after glacier retreat from the Anisak moraine, (2) downcutting through the older gravel, (3) either trimming of the older 

gravel to about 22 m height or renewed alluviation of younger 

gravel as base level rose due to renewed glaciation downvalley, 

(3) deposition of distal glaciolacustrine sediments as growing 

glaciers dammed a downvalley stretch of the Noatak River, and 

(4) downcutting to modern river level following deglaciation.

Exposure Nk-41

A prominent bluff along the west side of the Noatak 

River 17 km downstream from Nimiuktuk River rises 65 

m to a terrace-like surface that is broken by kettle depressions (fig. 84). A hummocky, kettled end-moraine complex 

(see fig. 82) extends into the valley center from both valley 

sides at this locality; it rises upvalley into lateral moraines 

along both valley walls. The river’s edge here is paved with 

medium to large cobbles and boulders up to 1.3 m diameter 

(even larger boulders occur beyond reach farther out in the 

river). Pyroxenites and other ophiolite complex rocks derived 

from the DeLong Mountains dominate boulder lithology.

Poorly exposed diamict (unit 1) comprises the central 

part of the bluff face. It is obscured by flowage, by mixture 

with overlying gravel, and by drapes of that gravel. Because 

of its extreme mobility, it is interpreted to be a glaciolacustrine deposit rather than till.

The overlying gravel (unit 2), which is composed dominantly of ultramafic igneous rocks and slate, forms near-vertical faces that rise to about 62 m above river level. It is capped 

by a probable floodplain deposit of silty very fine sand (unit 3).

Pebble-small-cobble gravel in a matrix of platy granules and coarse sand forms a basal exposure 34 m thick at 

the upstream end of the bluff. This deposit, which is not 

illustrated, probably formed by alluviation following river 

incision from the 65-m level.

m

20

30

40

50

60

10

 0

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

2

1

22

8+

4

3

2

1

4

3

12

10

?

Younger gravel. Pebbles and small cobbles. 

Dominantly quartz, black chert, sandstone, 

quartzite, limestone, and phyllite. Some quartz

clasts have schist adhesions. Ultramafic rock types

present but uncommon. Clasts generally rounded; 

some well rounded. Alluvium.

Older gravel. Poorly exposed pebble gravel. 

Origin uncertain.

Covered. Heavily vegetated sediment, 

probably silt. Glaciolacustrine deposit?

Stony silt. Bedded, dark gray, fairly compact 

silt with sparse stones. Poorly exposed because 

of slumping. Distal glaciolacustrine deposit.

m

40

60

80

20

 0

Note compressed scale

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

1 47

3

2 2

1

3

3

15

?

Diamict. Contains boulders, some striated, up to 

1.5 m diameter. Pyroxene and brown sandstone 

dominate the larger clasts. Poorly exposed.

Glaciolacustrine deposit?

Sand. Grayish brown (2.5Y 5/2) silty very fine sand. 

Becomes increasingly organic and then peaty upward 

through topmost 60 cm. Floodplain deposit.

Gravel. Subrounded pebbles and cobbles in poorly 

sorted matrix of sand with slate chips. Ultramafic 

igneous rocks and slate dominate clast lithologies, 

with quartz, basalt, and sandstone also present.

Alluvium.
Nimiuktuk River to Aklumayuak Creek 59

Figure 85. Exposure Nk-42. East side Noatak River 11 km above 

mouth of Aklumayuak Creek.

Exposure Nk-42

A partly vegetated west-facing bluff greater than 25 m 

high intersects probable glaciolacustrine deposits near the 

inner (north) flank of the Anisak end moraine (shown as 

Anisak Drift in fig. 82). Bedrock exposed close to river level 

is overlain directly by gravel that is mixed with diamict which 

has been severely deformed by slumps and flowage (fig. 85). 

Striated stones in a gritty silt matrix are exposed nearly continuously to about 20 m height, then intermittently up to 25.5 m. 

A dense alder thicket above this level reflects poorly drained, 

unstable sediments that probably are an upward continuation 

of the diamict.

A line of large erratic boulders that crosses the stream channel here may be perched on a bedrock ledge. Erratic boulders also 

are common along the river bank downriver from this locality.

Exposure Nk-44

An east-facing river bluff a short distance below exposure 

Nk-43 stands at about the same height (44 m). From a narrow 

bench at this height, the surface rises inland to 52 m above 

river level, where slightly weathered, oxidized pebble-smallcobble gravel is exposed (unit 1; fig. 87). The 44-m terrace 

therefore is inset within a higher and conspicuously older 

gravel surface.

The lower half of the bluff face exposes gray phyllite bedrock; the upper half is dominantly gravel. The gravel (unit 2) 

consists of cobbles and some very small boulders (up to 40 cm 

diameter) in a matrix dominated by phyllite chips. The upper 

8 m of this deposit (unit 3) stands in a steep face that exposes 

alternating cobbles and pebbly sand and granules in beds 

generally 30-50 cm thick. The overlying 3-4 m is covered, but 

flow amphitheaters suggest the presence of ice-rich silt.

Sand consisting dominantly of phyllite chips forms a 

32-cm-thick deposit at the base of the 8-m bedded gravel unit. 

It contains a brownish gray silt bed 1-4 cm thick that locally is 

crossbedded. Fragments of detrital wood from the base of the 

silt bed have non-finite ages of >45,800 yr B.P.

Figure 86. Exposure Nk-43. West side Noatak River 10 km above 

mouth of Aklumayuak Creek.

Figure 87. Exposure Nk-44. West side Noatak River 7 km 

northeast of mouth of Aklumayuak Creek. Black dot, radiocarbon 

age determination (yr B.P.) with laboratory number in parentheses 

(see appendix 1). 

m

20

30

10

 0

THICKNESS

(m)

UNIT DESCRIPTION and

INTERPRETATION

_ 6-10

_

1

>5

>15

?

Bedrock. Gray phyllite with 

vein quartz.

Covered. Dense alder growth.

Diamict. Striated stones in gritty 

silt matrix. Contains admixed 

gravel at base.

m

20

30

40

50

10

 0

THICKNESS

(m)

UNIT DESCRIPTION and

INTERPRETATION

-- 24.0

1 22.0

Bedrock. Gray phyllite, with wavy 

cleavage planes.

Gravel. Rounded to subrounded 

pebbles, small to medium cobbles, 

and sparse larger cobbles in matrix 

of dark gray poorly sorted sand with 

phyllite chips. Mafic to ultramafic 

igneous rocks dominate cobble size 

range. Alluvium.

Exposure Nk-43

A bluff exposure along the west side of the Noatak River 

10 km above Aklumayuak Creek exposes gravel over phyllite 

bedrock (fig. 86). The gravel consists of pebbles to medium 

cobbles, with some larger cobbles, in an immature sand and 

granule matrix. Mafic to ultramafic igneous rocks are abundant. This gravel forms part of a high-level (46-m) alluvial terrace that is inset within the Anisak end moraine (see fig. 82).

m

40

60

20

 0

Note compressed scale

THICKNESS

(m)

UNIT DESCRIPTION and

INTERPRETATION

1

4

2

1

3

2

?

3 8

2 17

19--

4

Oxidized gravel.

Bedrock. Gray phyllite.

Ice-rich silt? Largely 

covered, with flow 

amphitheaters.

Bedded gravel. Weakly 

bedded cobble to pebbly 

sand-granule beds in 

matrix of platy (phyllite) 

granules and sand. 

Alluvium.

Gravel. Cobbles and 

sparse very small boulders in matrix dominantly 

of phyllite chips. Outwash?

>45,800

(Beta-206893)

>45,800

(Beta-206894)

Exposure Nk-45

A gravel terrace 19 m high extends along the east side of 

the Noatak River just downstream from the outer flank of the 

Anisak moraine (fig. 82). The terrace face exposes less than a 

meter of silty floodplain sediments above unweathered, unoxidized sandy gravel (fig. 88).

The gravel (unit 1) consists of pebbles to medium 

cobbles, with some larger cobbles, in a matrix of poorly sorted 
60 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

Figure 88. Exposure Nk-45. 

East side Noatak River 7.5 km 

above mouth of Aklumayuak 

Creek.

Figure 89. Exposure Nk-46. 

East side Noatak River 6 km 

above of mouth of Aklumayuak 

Creek.

sand with phyllite chips. Sand may predominate at the base of 

the section, but slumps obscure the primary sediments.

In contrast to the large boulders along the river channel 

and banks immediately upstream, the lag deposit along the 

river’s edge at the base of Nk-45 consists of large cobbles 

with some very small boulders (up to about 40 cm diameter). 

Pyroxenites dominate the larger clasts. The absence of large 

boulders confirms that this locality lies beyond the limit of the 

Anisak glacial advance. The contrast between the lag deposit 

and the exposed gravels indicates that the terrace gravels were 

deposited after deposition and subsequent erosion of the outwash train from the Anisak glacier.

Exposure Nk-46

A gravel terrace with a nearly level, extensive upper 

surface 45 m above the river extends along the east side of the 

Noatak River 6 km above the mouth of Aklumayuak Creek 

(fig. 89). Phyllite bedrock along the base of the bluff has 

defended the overlying gravel from river erosion.

The gravel (unit 1) consists of pebbles and cobbles in a 

matrix of platy phyllite sand and granules. Small boulders are 

absent. It is capped by one meter or less of floodplain silt.

Figure 90. Exposure Nk-47. 

South side Noatak River 1.5 km 

above of mouth of Aklumayuak 

Creek. Black dot, radiocarbon 

age determination (yr B.P.) 

with laboratory number in 

parentheses (see appendix 1). 

m

40

20

30

50

10

 0

Note compressed scale

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

1

1

35

-- 10 Bedrock. Phyllite.

Gravel. Pebbles and cobbles in matrix of

platy phyllitic sand and granules. Capped by 

1 m or less of silt. Alluvium.

m

20

10

 0

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

1 18-18.5

2

1

2

<1

Gravel. Rounded to subrounded pebbles and

cobbles in abundant matrix of gray, poorly sorted 

sand mixed with phyllite chips. Alluvium

(reworked outwash?).

Silt. Floodplain deposit.

m

20

10

 0

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION ?

2 7

1 18

2

1

13,310 ± 40

(Beta-156904)

13,370 ± 50

(Beta-156903)

Gravel. Rounded to subrounded pebbles, small

cobbles, and dispersed larger clasts to small

boulder size. Quartz abundant (ca. 50%). 

Alluvium.

Sand. Well sorted, bedded, nonoxidized medium

sand to brownish gray silty fine sand; somewhat

pebbly near base. Basal 4.5 m probable floodplain deposit; upper 2.5 m poorly exposed, and 

may in part be eolian.

Terrace remnants at this height are present west of the 

river here, but they are not extensive. More extensive and continuous terraces are present at two lower levels—about 35 and 

20 m above the river.

Exposure Nk-47

A low (25-m) terrace, along the south side of the Noatak 

River just above the Aklumayuak Creek confluence, lies at 

the west end of an extensive gravel terrace (see fig. 82) that 

separates the river from the creek. The terrace face exposes 18 

m of gravel overlain by 6.5 m of sand that is capped by 0.5 m 

of peaty sand (fig. 90).

The gravel (unit 1) is dominantly pebbles and small 

cobbles, with dispersed larger clasts up to small boulder 

size. Quartz is abundant among the smaller clasts. The 

overlying deposit (unit 2) consists of well sorted, medium 

sand to brownish gray silty fine sand in near-horizontal beds 

that generally are 0.5 to 3 cm thick but locally are up to 12 

cm thick. The sand is somewhat pebbly near its base, and 

contains a thin granule bed 2.3 m above its lower contact. 

Two samples from a small lens of woody detritus 2.0 m 

above the base of the sand had concordant radiocarbon ages 
Nimiuktuk River to Aklumayuak Creek 61

Figure 91.

Exposure Nk-48. 

West side 

Noatak River 

opposite mouth 

of Aklumayuak 

Creek. Black dot, 

radiocarbon age 

determination 

(yr B.P.) with 

laboratory number 

in parentheses 

(see appendix 1). 

20

30

40

50

10

 0

m THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

1 4-6

-- 5-3

2 17-14

3 0-3

4 2.3

1

3

2

4

>57,000

(USGS-2457)

>57,000

(USGS-2456)

Bedrock. Gray phyllite with quartz veins. Irregular upper surface.

Diamict. Subangular to subrounded stones up to usual 

maximum diameter of 30 cm. Very sparse larger blocks up 

to 1 m length. Many clasts faceted and striated. No sorting 

or stratification. Some stones near upper contact oxidized. 

Stands in vertical faces. Till.

Gravel. Rounded to subrounded pebbles and cobbles, with 

some lines of large cobbles and some very small boulders. 

Matrix variable: silty coarse sand with granule chips in some 

beds; only partial silt filling between stones in others. Some 

30-cm-thick beds consist of poorly sorted silty gray sand-sized

rock chips with dispersed pebbles. Interbedded coarse and fine 

sand near upper contact. Irregular base fills depressions in 

underlying bedrock. Alluvium.

Gravel. Pebbles and small cobbles, with quartz about 

10 percent by volume and phyllite fragments abundant. 

About 10 percent of clasts have oxidized surfaces. Alluvium.

Silt. Well sorted brown (10YR 5/3) silt. Faint subhorizontal 

bedding. Face severely slumped. Lacustrine.

of 13,370 ± 50 yr B.P. and 13,310 ± 40 yr B.P. The basal 

two-thirds of the sand unit clearly is a floodplain deposit; the 

upper one-third is poorly exposed, and may in part be eolian.

Large cobbles and very small boulders (up to 30-40 cm 

diameter) dominate the lag deposit along the river edge at the 

terrace base. These clasts may be relict from an eroded outwash train associated with the Anisak end moraine.

Exposure Nk-48

The face of a 49-m terrace remnant directly opposite the 

mouth of Aklumayuak Creek exposes alluvium, till, and lacustrine silt above phyllite bedrock (fig. 91). The bedrock has an 

irregular upper surface with about 2 m relief that probably was 

created by river erosion.

Alluvial gravel (unit 1) is 4-6 m thick, being thickest 

over depressions on the bedrock surface. Near its base, beds 

of pebbly sand to pebble gravel are inclined downvalley at 10° 

to 12°. Higher in the unit, a lens of organic-rich sediment up 

to 33 cm thick contains detrital wood fragments interstratified 

with gray sand that overlie a compact layer of peat 1-2 cm 

thick. The wood fragments and the peat have identical nonfinite radioacarbon ages of >57,000 yr B.P. The wood has been 

identified as Salix (willow; USDA-FPL, 9/15/86). A pollen 

assemblage extracted from the peat is characteristic of “...a 

shrub-herb tundra composed of a mixture of dwarf birch, ericales..., willows, grasses, sedges, and herbs” (T.A. Ager, U.S. 

Geological Survey, written commun., 4/3/87). Interbedded 

coarse and fine sand near the upper contact of the gravel may 

represent a slackwater environment that developed as glaciers 

advanced into downvalley sectors of the Noatak valley.

The diamict (unit 2) has the attributes of a subglacially 

deposited till, as listed in table 2. It lacks sorting and stratification, contains abundant faceted and striated clasts, and 

has a compact matrix that allows it to stand in vertical bluffs. 

Ultramafic rocks like those noted in upvalley exposures are 

abundant among the coarser clasts. Some stones near the upper 

contact of the till are oxidized. 

A second deposit of alluvial gravel (unit 3) is present 

locally above the till, being thickest where it fills a channel 

eroded into the till surface. Some clasts have oxidized surfaces. In most exposures, the gravel has been mixed with silt, 

which has slumped from above.

Well sorted stone-free silt 20-23 m thick forms the upper 

half of the bluff. This deposit has faint subhorizontal beds 

0.5 to 3 cm thick, but all exposures are severely slumped and 

structures cannot be traced laterally.

Discussion

Bluffs along the Noatak River from Nimiuktuk River 

to just above Aklumayuak Creek expose glaciolacustrine 

deposits and postglacial fluvial sediments, but outcrops of 

glacial till and outwash are rare. Extensive erosion by the 

Noatak River through this narrow segment of its valley has 

removed most of the glacial record from the valley center 

and left only fragmentary remnants. Bluff exposures above 

the valley-crossing Anisak end moraine differ greatly from 

those within and below the end-moraine belt.

The three exposures (Nk-40 through Nk-42) above the 

end moraine contain glaciolacustrine sediments in exposures 

up to 45 m high, with higher gravel exposed at two locali-
62 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

ties. No glacial deposits have been preserved in either of the 

bluffs (Nk-43 and Nk-44) within the end-moraine zone; however, both bluffs consist of postglacial river terraces at 40-46 

m height that were inset within the end moraine. The two 

bluffs contain basal bedrock outcrops that have defended the 

terrace remnants from subsequent river erosion. Three bluff 

exposures (Nk-45 through Nk-47) below the Anisak moraine 

also are terrace faces that expose postglacial alluvial gravel 

at 44 m and about 18-22 m heights. The higher terrace level 

is correlative with the terrace remnants preserved within the 

end-moraine zone, and also coincides in height with some of 

the glaciolacustrine sediments exposed upvalley of the end 

moraine. The lower terrace level is part of a set of younger 

alluvial terraces.

The bluff (Nk-48) opposite Aklumayuak Creek intersects a terrace remnant that corresponds in height to highlevel (45-50 m) terraces farther upvalley. The Noatak valley 

is wider here than the sector above Aklumayuak Creek and, 

consequently, a more complete glacial record has been preserved from subsequent river erosion. Compact till exposed 

at Nk-48 probably formed during the older glaciation of 

Makpik age because it lies well beyond the mapped limits of 

Anisak glaciation (Hamilton, 2003 and in press). Abundant 

pyroxenite clasts indicate that ice flowed southward from 

prominent ultramafic highlands in the De Long Mountains. 

Alluvial gravels above and below the till are of interglacial 

or interstadial character, and contain no discernable outwash. 

Oxidized stones within the upper gravel and near the top of 

the till indicate a significant hiatus between deposition of 

the till and the overlying lacustrine silt. This thick silt unit, 

which comprises the upper half of the exposure, represents 

a major episode of damming of the Noatak River. However, 

its well-sorted, stone-free character is unlike that of most 

glaciolacustrine deposits in the Noatak valley. The glacier 

dam must have been some distance downvalley, and the silt 

must have been carried into this locality by rivers rather than 

glaciers or icebergs.

Sapun Creek

Two high bluffs along the lower course of Sapun Creek are 

situated near patches of drift of uncertain age (see fig. 82) that 

probably represent a glacial lobe that extended south into the 

valley of Sapun Creek from the Noatak valley. Glaciolacustrine 

deposits of at least two ages also occur at lower altitudes along the 

creek and the adjoining south flank of the main valley.

Exposure Sp-1

A weathered bluff face along the east side of Sapun Creek 

6 km above its mouth stands 91.5 m high and exposes fluvial 

gravel above glacial and glaciolacustrine deposits (fig. 92).

Unit 1, at the base of the bluff, consists of horizontally 

bedded fine sand, silt, and clayey silt; with lenses of organicrich sediment. Some beds 10-20 cm thick of pebble gravel in a 

matrix of platy granules also are present. Slightly cross-bedded 

sand to pebble-small-cobble gravel in the midpart of the unit 

forms a bed 2.5 m thick. Fine peaty lenses concordant with 

bedding occur 7.8 m above river level. Two separate lenses 

about 3 m apart horizontally along this horizon yield identical limiting ages of >43,300 yr B.P. The upper part of the unit 

consists of laminated silt and clayey silt. Unit 1 is interpreted 

as fluvial slackwater deposits that grade upward into lacustrine 

sediments.

Diamict consisting of unsorted and unstratified stones 

up to small boulder size (unit 2) overlies the laminated silty 

deposits, and is interpreted to be glacial till. Its matrix of platy 

phyllite granules and small pebbles indicates some water washing by Sapun Creek at the ice front. Unit 3, probable deltaic 

deposits that overlie the diamict, consists of phyllitic sand 

with lesser fine sandy gravel in parallel beds that generally dip 

downvalley.

The bluff is capped by a 38.2-m thick deposit of fluvial 

sand and gravel (unit 4). Pebbles and small cobbles, domiFigure 92. Exposure Sp-1. East side Sapun Creek 6 km above its mouth. Black dot, radiocarbon age 

determination (yr B.P.) with laboratory number in parentheses (see appendix 1). 

40

60

80

100

20

 0

Note compressed scale

m THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

1 22.5

132

3 17.8

4 38.2

1

3

2

4

>43,300

(Beta-188261)

>43,300

(Beta-188262)

Diamict. Unsorted and unstratified stones up 

to small boulder size in matrix of platy phyllite 

granules and small pebbles. Till?

Bedded fine sediment. Horizontally bedded fine 

sand, silt, and clayey silt, with organic lenses. 

Slackwater and lacustrine deposits.

Sand with fine gravel. Phyllitic sand with some

fine sandy gravel. Parallel beds, dominantly

dipping downvalley. Deltaic deposit.

Sand and gravel. Pebbles and small cobbles

in matrix of poorly sorted platy phyllite granules

and small pebbles. Alluvium.
Sapun Creek 63

nantly of quartz and phyllite, occur in a matrix of poorly 

sorted platy phyllite granules and small pebbles. Sparse larger 

clasts dominantly are phyllite and quartz; and some rounded 

ultramafic rock types also are present.

Exposure Sp-2

A bluff farther down Sapun Creek near the south flank of 

the Noatak River valley provides excellent exposures of fluvial 

and glaciolacustrine deposits (fig. 93). The bluff face rises 

steeply to 40 m height, where a thaw ampitheater exposes an 

11-m-thick section of stony silt. A vegetated surface above the 

amphitheater rises to a knob of slightly oxidized gravel that 

stands as high as 61 m above river level. The largest stones 

exposed on that feature are a partly buried quartz slab with 

exposed length of 72 cm and a large cobble of gray quartzite 

22 cm in diameter. Both clasts are slightly weathered. Below 

the thaw amphitheater, the bluff face exposes a thick deposit of 

fine sandy gravel overlain by fluvial gravel.

The fine sandy gravel at the base of the exposure (unit 

1) is a probable deltaic deposit. Beds of dark gray sand-size 

phyllite chips alternate with similar beds that contain granules 

and dispersed pebbles of phyllite and quartz. Some beds of 

coarser (pebble-small- cobble) gravel are present at the north 

end of the section. The beds dip southward up Sapun Creek 

at 11° to 18°. In a downdip (southward) direction, the gravel 

beds interfinger with sand, and sand beds thicken into a bed 

of poorly sorted muddy sand with widely dispersed pebbles. 

Flattened detrital twigs from a clayey lens 1 m below the top 

of unit 1 have a non-finite age of >48,280 yr B.P. 

An isolated block (unit 1a) of slumped sediment extends 

from 8 to 11.5 m above river level near the north end of the 

bluff. It contains sand and gravel similar to sediments in units 1 

and 2, but some fluvial cross-beds are present and some stones 

are imbricated. The imbrication suggests northward flow direction parallel to present-day Sapun Creek. Wood fragments and 

clasts of detrital peat are present in the slump block.

The alluvial gravel (unit 2) consists of subrounded 

pebbles and small cobbles in an abundant matrix of phyllite 

chips of granule to coarse sand size. Some large cobbles and 

rare small boulders up to 35 cm diameter are present, mainly 

concentrated in a single stone line. Most clasts are phyllite or 

quartz with phyllite adhesions. A 35-cm-thick bed of muddy 

pebble gravel is present 2 m below the gravel’s upper contact. 

It could represent brief damming of the Noatak valley prior 

to the longer-lasting inundation represented by unit 3. At the 

south end of the bluff, the gravel extends lower; it dips southward at 15° to 18° and interfingers southward with phyllitic 

sand of unit 1. Clast lithology is the same as at the north end 

of the bluff, but some beds have a matrix of muddy phyllite 

chips. A lens of small detrital wood fragments from a probable 

channel-filling deposit 2 m below the top of the gravel near the 

north end of the bluff has a non-finite age of >47,590 yr B.P.

The thaw ampitheater exposes pebbles, small cobbles, 

and sparse larger clasts in a matrix of brown slightly clayey 

silt (unit 3). Larger clasts, up to 38 cm long, are subangular 

quartz with phyllite adhesions. Smaller, more rounded pebbles 

and small cobbles include ultramafic rock types, sandstone, 

and limestone. The stony silt of unit 3 is interpreted as a lateglacial or postglacial lake deposit that received some input 

from river gravels and erosion of local phyllitic bedrock.

The lag deposit at the base of the bluff includes striated 

pyroxenite boulders up to 39 cm diameter from the DeLong 

Mountains and large blocks of quartz with phyllite adhesions, 

which probably are derived locally.

Discussion

The sequence of sediments at exposure Sp-1 records the 

advance of a tongue of the Noatak valley glacier southward up 

Sapun Creek, followed by its recession. The fluvial slackwater 

fluvial deposits that grade upward into laminated lacustrine 

sediments reflect base-level rise as the advancing glacier 

progressively blocked the valley of Sapun Creek. The overlyFigure 93. Exposure Sp-2. East side Sapun Creek 3.3 km above its mouth. Black dot, radiocarbon age determination 

(yr B.P.) with laboratory number in parentheses (see appendix 1). 

40

60

20

 0

Note compressed scale

m THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

?

1 29-33

7-10

11

2

3

1

3

2

Drift knob

Thaw

amiphitheater

1a

>47,590

(Beta-156894)

>48,280

(Beta-156893)

Gravel. Subrounded pebbles and small cobbles,

with sparse larger clasts, in matrix of phyllite chips.

Bed of muddy pebble gravel 2 m below upper

contact. Thickens southward. Alluvium.

Sand and fine gravel. Sand is dark gray, and 

dominantly phyllite chips. Gravel is granules and 

dispersed pebbles in sand matrix. some coarser 

(pebble-small-cobble) gravel present. Block of 

sediment near north end of bluff (unit 1a) contains 

wood fragments. Deltaic deposit.

Stony silt. Pebbles, small cobbles, and sparse

larger clasts in matrix of brown slightly clayey silt. 

Glaciolacustrine deposit.
64 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

ing diamict records glacial advance across the site, with some 

water-washing at its face by the still-flowing Sapun Creek. 

Probable deltaic beds above the diamict were formed in 

standing water by Sapun Creek as the glacier began receding 

from its valley. The overlying alluvium, which contains dominantly local rock types with minor admixture of reworked 

glacial clasts, occurs to the unusual height of 91.5 m above 

river level. It may have been deposited while the receding ice 

tongue was still close enough to form a high local base level 

for Sapun Creek.

Exposure Sp-2, at the south margin of the Noatak River 

valley, has been more severely eroded than Sp-1. It records 

a sequence of fluvial and lacustrine sediments that formed 

after recession of the glacier back into the Noatak valley. The 

basal sand and fine gravel comprises part of a deltaic deposit 

that formed while the receding ice front remained nearby 

and meltwater flowed south into the valley of Sapun Creek. 

The overlying gravel resembles nonglacial alluvium that was 

deposited along the Noatak River and its tributaries during 

interglacial and interstadial intervals (Hamilton, 2001). The 

glaciolacustrine stony silt exposed in the thaw amphitheater 

represents a later glacier advance that blocked the Noatak 

valley. This silt exposure occurs at the same height as the 

deltaic deposit (unit 3) at Sp-1, and very likely is contemporaneous with it.

Exposure Nk-48 is situated only a few kilometers 

north of the Sapun Creek exposures, but its relation to those 

deposits is unclear. If the diamicts at Nk-48 and Sp-1 are 

tills deposited during the same glacial advance, then much 

of the subsequent sediment record has been lost to erosion at 

Nk-48. Two radiocarbon age determinations were made on 

organic samples from each of the three bluffs (Nk-48, Sp-1, 

and Sp-2). All ages are non-finite, and confirm that most of 

the events recorded in the bluffs took place prior to the Avan 

(late Wisconsin) glaciation. However, these minimum age 

limits are of little value in correlating events and deposits 

between the three bluffs.

Sapun Creek to Kaluktavik River

Below Sapun Creek, the Noatak River flows generally 

westward for 28 km to the confluence of Kaluktuvik River. Its 

valley floor is wider here than above Aklumayuak Creek, and 

deposits of late Pleistocene age are more commonly preserved 

in river bluffs. However, deep cut-and-fill relations in some 

bluffs attest to the erosional power of the Noatak River through 

this stretch. Most of the river bluffs are heavily vegetated, but 

five of them (Nk-49 through Nk-53) contained exposures sufficient for at least partial measurement and description.

Exposure Nk-49

The poorly exposed face of a 35-m terrace a short distance below Sapun Creek exhibits bedrock near river level 

overlain by gravel beneath a thick silt deposit (fig. 94). The 

gravel (unit 1) is dominated by pebbles and small cobbles; 

larger cobbles are sparse and boulders are absent. Platy stones 

are faintly imbricated. Major lithologies are vein quartz 

(derived from schist), sandstone, quartzite, black chert, and 

green crystalline rock. Ultramafic rock types are rare. Matrix 

is poorly sorted sand and granules, with quartz grains abundant and few phyllite chips. The unit is faintly bedded into 

pebble- and granule-rich layers that are inclined downvalley. 

Clast size and composition are typical of nonglacial alluvium.

The overlying silt (unit 2) has slumped and flowed, and 

undisturbed exposures are limited to the headwalls of thaw 

amphitheaters. The upper 3 m of the deposit is faintly laminated, with black peaty beds, lenses, and layers parallel to 

bedding. Woody peat from 1.1 m below the surface is dated 

at 13,140 ±40 yr B.P. This part of unit 2 may have formed 

on a floodplain or in a thaw lake. Although lower-lying parts 

of unit 2 are covered or severely disturbed, only stone-free 

silt is exposed. The near-level upper surface of unit 2 and its 

absence from slightly higher bedrock outcrops indicates that it 

Figure 94. Exposure Nk-49. South side Noatak River 4.5 km downvalley from Sapun 

Creek. Black dot, radiocarbon age determination (yr B.P.) with laboratory number in 

parentheses (see appendix 1). 

20

30

40

10

 0

m THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

?

-- 5

10

20

1

2

1

2

13,140 ± 40

(Beta-156900)

Gravel. Rounded to subrounded pebbles, 

small cobbles, and sparse medium cobbles. 

Faintly bedded into pebble- and granule-rich 

layers 10-40 cm thick that dip downvalley at 

10o to 13o. Deltaic deposit?

Bedrock. Gray slate.

Silt. Dark gray (5Y 4/1) silt, with black 

peaty lenses and layers through upper 

3m. Lower 17 m obscured by slump 

blocks, but appears stone free. 

Lacustrine?
Sapun Creek to Kaluktavik River 65

probably is a lacustrine rather than eolian (loess) deposit. The 

absence of stones suggests that the deposit was derived from 

nonglacial sources.

Exposures Nk-50A and Nk-50B

Two exposures, Nk-50A and Nk-50B were measured 

about 1 km apart along a long south-facing bluff that declines 

in height downvalley from about 38 m at Nk-50A to 28 m 

near its west end at Nk-50B.

At Nk-50A, bedrock is overlain by diamict, probably till, 

beneath gravel and capping silt (fig. 95). The diamict (unit 1) 

contains unsorted and unstratified, faceted and striated stones 

up to boulder size (1.2 m diameter) in a compact silty matrix 

that maintains a near-vertical bluff face. The clasts mainly are 

rounded pebbles and small cobbles that probably were derived 

from river gravels entrained and transported by a glacier that 

advanced westward down the Noatak valley. Gravel above 

the till consists of clasts to medium cobble size, with sparse 

larger cobbles, in a sandy matrix. Black chert is abundant in 

the pebble range, but the largest clasts are ultramafic rocks and 

quartzites. The bluff is capped by about 6 m of poorly exposed 

silt with peat lenses and layers visible through its upper 2 m.

Exposure Nk-50B, which is incised into the flank of an alluvial terrace that declines in height downvalley, stood 35 m high at 

the locality where measured in 1986 and 28 m where measured 

nearby in 2000 (only the most recent measured section is shown 

in fig. 96). In both measured sections, river gravel stands 23-24 

m high and is capped by 5-10 m of silt. The alluvial gravel (unit 

1) consists of pebbles to medium cobbles, with sparse large 

cobbles, in a gray sandy matrix. Ultramafic rocks and quartzites 

dominate the larger clasts. The silt (unit 2) is faintly laminated 

near its base, where it contains granules and fragments of detrital 

wood dated at 25,060 ±230 yr B.P. This deposit grades upward 

into an oxidized, structureless, probably eolian silt. It is interpreted as a floodplain deposit overlain by loess.

Exposures Nk-51A and Nk-51B

A heavily wooded bluff about 50 m high extends for 

greater than 2 km along the south side of the Noatak River 

about 7-9 km above the mouth of Kaluktavik River. The bluff 

intersects glaciolacustrine deposits which cover this sector of 

the valley floor (see fig. 82). Separate sections were measured 

in 1986 and 2000 where localized exposures present at those 

times provided some information on bluff composition.

Figure 95. Exposure Nk-50A. 

North side Noatak River 8.5 km 

below mouth of Sapun Creek. 20

30

40

10

 0

m

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

?

-- 5-6

16

6

2

3

1

2

3

1 10-11

Gravel. Rounded to subrounded pebbles, small to

medium cobbles, and sparse larger cobbles; some 

beds extremely sandy. Largest clasts are ultramafic

rocks and quartzites. Alluvium.

Diamict. Rounded pebbles and small cobbles,

with sparse larger stones up to 1.2 m diameter, in

matrix of compact olive gray (5Y 5/2) sandy silt. 

Till.

Bedrock. Gray slate.

Silt. Brown to gray silt; poorly exposed. Peat

layers and lenses through upper 2 m. 

Floodplain deposit?

Figure 96. Exposure Nk-50B. 

North side Noatak River; about 

1 km farther west along face of 

same bluff as Nk-50A. Black dot, 

radiocarbon age determination 

(yr B.P.) with laboratory number 

in parentheses (see appendix 1). 

20

30

10

 0

m

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

23

5

1

2

1

2

Gravel. Rounded to subrounded pebbles and 

small to medium cobbles, with sparse large 

cobbles, in matrix of poorly sorted sand and

slate chips.Ultramafic rocks and quartzites 

dominate larger clasts. Alluvium.

Silt. Grayish brown (10Y 5/2) and faintly 

laminated near base, with lenses of granules 

and detrital wood fragments. Grades upward 

into light yellowish brown structureless silt. 

Capped by about 0.5 m peat. Floodplain 

deposit with loess cap.

25,060 + 230

(Beta-206891)
66 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

Figure 97. Exposure Nk-51. 

South bank Noatak River about 

8 km upvalley from mouth of 

Kaluktavik River. (A) Section 

measured in 1986. (B) Section 

measured in 2000. 

At Nk-51A, thick silt overlies gravel (fig. 97A). The gravel 

appears to be fairly well sorted and mature nonglacial alluvium. Its clasts dominantly are quartz, schist, and sandstone 

transported by southern tributaries, and only a small percentage (about 5 percent) of ultramafic rocks derived from glacial 

source areas in the DeLong Mountains. The overlying silt is 

severely slumped in all exposures, but it appears to contain few 

or no stones. The headwalls of thaw amphitheaters expose 2-3 

m of brown silt containing lenses and layers of peat. 

Exposure Nk-51B is completely covered above 30-35 

m height, but debris flows below that level provide limited 

exposures of stony silt overlain by gravel (fig. 97B). Actively 

moving, unvegetated flow surfaces exhibit abundant stones, 

many of them faceted and striated, in a silt matrix. Ultramafic 

rocks and quartzites, abundant in the larger fractions, are 

derived from glacial source areas in the DeLong Mountains. 

The overlying gravel is nonglacial in character, with abundant 

Figure 98. Exposure Nk-52. 

North side Noatak River 6 

km upvalley from mouth of 

Kaluktavik River.

quartz derived from southern tributaries to the Noatak River. Its 

upper contact is concealed.

Exposure Nk-52

A largely vegetated bluff along the north side of the Noatak 

River is situated at the downstream end of a 86-m-high river-cut 

bedrock face. A partial exposure of the bluff was examined in 

1986, but 14 years later it was almost entirely concealed. Stony 

silt is overlain by probable stone-free brown silt (fig. 98).

The stony silt (unit 1), which flows readily in all exposures, 

contains numerous rounded pebbles and small cobbles and 

larger subrounded stones up to small boulder size in abundant 

dark gray clayey silt. The boulders include mafic igneous rock 

types not noted farther upvalley. The overlying fine-grained 

sediment (unit 2) is slumped and nearly entirely vegetated, but 

stone-free brown silt is present in rare exposures.

20

30

40

50

10

 0

m THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

? 2 12

1

2

1 29 Stony silt. Rounded pebbles and small 

cobbles, with some subrounded stones up 

to small boulder size (70 cm length), in 

matrix of slightly plastic dark gray (10YR 4/1) 

clayey silt. Glaciolacustrine deposit.

Silt? Largely covered. Brown silt visible in 

rare exposures. Lacustrine or 

glaciolacustrine deposit?

20

30

40

50

10

 0

m

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

?

29

20

1

2

1

2

Gravel. Rounded to subrounded pebbles, small 

to medium cobbles, and sparse large cobbles 

in abundant matrix of gray subangular medium

to coarse sand with slate chips. Alluvium.

Silt. Dark reddish brown (5 YR 2.5/2), with 

peat layers and lenses, through upper 2-3 m.

Largely concealed below this level. Lacustrine

or glaciolacustrine deposit?

20

30

40

50

10

 0

m

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

? 13

16+

2

--

1

2 1 21

Gravel. Rounded pebbles and small cobbles

in sandy matrix that includes abundant phyllite

chips. Quartz relatively abundant (30 percent

of clasts). Alluvium.

Stony silt. Clasts to medium cobble size, with

some larger clasts up to 40 cm diameter, in 

matrix of dark gray (7.5YR 4/0) gritty silt. Many 

clasts faceted and striated. Ultramafic rocks 

and quartzites are abundant in larger clast 

sizes. Quartz relatively rare (<5 percent). 

Glaciolacustrine deposit.

Covered.

A

B
Sapun Creek to Kaluktavik River 67

Exposure Nk-53

A vegetated bluff about 4 km above Kaluktavik River 

is covered by stabilized and largely vegetated debris flows. 

Where measured in 1986, a debris flow extended to a height 

of 36.5 m on the bluff face. Where measured in 2000, a flow 

exposed stony silt to a height of only 19 m, where it was overlain by gravel (fig. 99).

The stony silt (unit 1) consists of clasts up to small boulder 

size, commonly striated and faceted, in an abundant matrix of 

gray gritty silt. The lower part of the flow has abundant rounded 

pebbles and small cobbles; it may represent a gravel unit 

beneath the flow that perhaps formed prior to deposition of the 

stony silt. The overlying gravel (unit 2), which is only exposed 

to 2 m or less thickness, appears to be nonglacial alluvium. Lag 

boulders up to 1.6 m long along the river edge include ferrugineous sandstone and diverse ultramafic rock types.

Discussion

The glaciolacustrine deposits that cover most of the 

Noatak valley floor between Sapun Creek and Kaluktavik 

River are draped over arcuate ridges (Hamilton, 2003 and in 

press) that resemble buried end moraines. The orientations 

of these features suggest that a glacier flowed south down 

the valley of Kaluktavik River into the Noatak valley, where 

it spread into a broader lobe that dammed the Noatak drainage. During part of this time, it may have contacted a separate 

glacier that flowed westward down the Noatak valley, or the 

two glacial advances may not have been in phase. Because 

outermost end moraines of probable Anisak age have been 

mapped farther north up Kaluktavik River valley and farther 

east up the Noatak valley, the subsurface moraines around the 

mouth of the Kaluktavik are inferred to date from the preceding Makpik glaciation.

The seven bluff exposures measured along the Noatak 

River between the Sapun and Kaluktavik drainages are 

obscured partly by flows and vegetation, and part of their 

record has been lost to erosion by the Noatak River. However, 

some consistent relations are evident: (1) sediments predominantly are either stone-free lacustrine silt, stony glaciolacustrine silt, or nonglacial river alluvium, (2) stone-free silt 

always occurs above the stony silt, and (3) alluvial gravel is 

never exposed above 34 m height. Compact till is exposed in 

bluffs near Sapun Creek but was not seen farther downvalley. Stony silt occurs to 20-30 m height in all three exposures 

within 8 km of the Kaluktavik River mouth, but was not 

recorded farther upvalley. Stone-free silt, the uppermost unit in 

most bluffs, occurs in deposits as thick as 20 m and to heights 

of 50 m above the river. Its thickness and faint laminations 

suggest lacustrine origin, but absence of dropstones indicates 

that it must have formed in a lake dammed by a glacier at a 

location sufficiently distant downvalley that no debris-carrying 

floating ice reached this sector of the Noatak River valley. 

Exposure Nk-49 has unusual delta-like alluvium near its 

base that resembles the lower gravel at Nk-48. Peaty lenses at 

about 34 m height near the top of the stone-free silt unit are 

dated at 13.1 ka. The river evidently flowed at this level for 

some time after downcutting from the 50-m surface. This age 

is very close to the 13.3 ka and 13.4 ka ages on a probable 

floodplain deposit at about 20 m height at Nk-47, about 8 km 

farther upvalley. Perhaps the Noatak River at this time was 

still partly blocked by glacier ice downvalley and was flowing sluggishly at a gradient gentler than that of the present 

day. The three similar radiocarbon ages also may indicate that 

general revegetation of this sector of the Noatak River valley 

began at this time.

Exposure Nk-50A contains a compact till that may correlate with tills mapped at exposures Nk-48 and Sp-1. Overlying gravel and probable floodplain deposits are close in height 

to the silt deposits at Nk-49, suggesting that the Noatak River 

fluctuated near this level for some time after drainage of the 

lake. Both measured sections of exposure Nk-50B, farther 

along the same bluff, consist of postglacial alluvium inset into 

the older deposits.

Exposure Nk-51B contains glaciolacustrine stony silt 

at its base that is overlain by gravel exposed to a height of 

about 34 m above the river. Although the nearby bluff Nk-51A 

contains comparable gravel that rises to a somewhat similar 

height, no stony silt is evident beneath it. The Noatak River 

must have downcut and eradicated the stony silt here, then 

deposited gravel as it alleviated again. Both bluffs stand about 

50 m high, and both may be capped by stone-free lacustrine 

silt, although exposures are limited.

Exposure Nk-52 rises inland to a near-level surface that 

may be close in height to the 50-m level noted in upvalley 

exposures. Like those other high bluffs, Nk-52 exposes stoneFigure 99. Exposure Nk-53. 

North side Noatak River 4.2 

km upstream from mouth of 

Kaluktavik River.

20

30

10

 0

m

THICKNESS

(m)

? UNIT DESCRIPTION and INTERPRETATION

>2

19

2

1

1

2

Gravel. Rounded pebbles and cobbles in 

sandy matrix. Alluvium.

Stony silt. Subangular to subrounded stones 

up to small boulder size, commonly faceted 

and striated, in matrix of gray (5Y 5/1) gritty silt.

Glaciolacustrine deposit.

Covered
68 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

free silt above silty glaciolacustrine sediment, but any intervening alluvium has been lost to erosion. The glaciolacustrine silt 

contains boulders that are larger than those noted upvalley, and 

also rock types not found upvalley. These clasts indicate probable input of sediments derived from the Kaluktavik glacier.

A lower bluff close to the mouth of Kaluktavik River 

(Nk-53) may have been eroded down to about 30-m height 

during late-glacial downcutting. Large lag boulders at its base 

indicate that the Noatak River could have cut into and eroded 

till deposited directly by the Kaluktavik glacier at this locality.

Lower Kaluktavik River Valley

Two exposures near the mouth of Kaluktavik River 

intersect glacial and proglacial deposits associated with an end 

moraine of the glacier that flowed south down the valley of 

Kaluktavik River (see fig. 82).

Exposure Kl-1

A prominent river bluff about a kilometer above the 

mouth of Kaluktavik River occurs where a probable end 

moraine, largely covered by younger glaciolacustrine deposits, crosses the valley center. The former moraine position 

is marked by a concentration of large boulders up to 1.5 m 

diameter in the river bed, by elongated boulder-littered knobs 

that stand about 60 m above the river, and by thick but poorly 

exposed diamict in the weathered bluff face (fig. 100). Basal 

debris aprons 15-19 m high obscure the lowermost sediments.

Figure 100. Exposure Kl-1. West side Kaluktavik River 0.9 km above its mouth.

The lowest exposed deposit (unit 1) is fine gravel at least 

7 m thick that includes some beds of silt-coated pebbles and 

others of pebble-small-cobble gravel in a silty matrix. These 

sediments may have been deposited in standing water or in 

sluggishly moving, very silty water. The overlying coarse 

gravel (unit 2) has abundant large cobbles and some very small 

boulders. It is crudely bedded, and exhibits some size sorting. 

Diamict up to about 18 m thick (unit 3) dominates the exposure. Where measured in 1986, it had all the attributes of a 

subglacial till—unsorted and unstratified, faceted and striated 

stones up to 1 m diameter in a compact matrix of sandy silt 

that locally maintained near-vertical faces. A section a short 

distance to the south, measured in 2000, contained coarse 

gravel like that seen previously, but the overlying compact 

diamict consisted of unstratified pebbles, small cobbles, and 

sparse larger stones in a muddy matrix. Striations were rare, 

and those few present were shallow and diffuse. The tillstones 

at this locality may have been reworked by meltwater or river 

water, which mixed them with river gravels and then deposited 

them in a muddy environment. 

The gravel above the diamict (unit 4) appears to be nonglacial river alluvium. The section is capped by silt, which is 

up to 3.2 m thick locally but commonly is eroded.

Exposure Kl-2

At the mouth of Kaluktavik River, the poorly exposed 

face of a 33-m river terrace exposes pebble gravel beneath 

silt-capped cobble gravel (fig. 101). The terrace extends up the 

river about a kilometer to exposure Kl-1, where it merges with 

the outer face of the end moraine.

20

30

40

50

10

 0

m THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

?

-- 19

4.0

0.4

4

5 4

5

Covered

1

2

3 3 18

2 6-7

1 >7

?

Gravel. Rounded pebbles and cobbles in sandy

matrix. Alluvium.

Diamict. Unstratified pebbles, small cobbles, and

sparse larger stones up to 1 m diameter in sandy

matrix. Few stones striated; some bear shallow 

and diffuse marks like those formed by scour of 

river ice. Till. 

Coarse gravel. Large cobbles and some very

small boulders. Crudely bedded, with 2 prominent

cobble-rich horizons. Advance outwash?

Fine gravel. Pebble-small-cobble gravel with

silty matrix and openwork silt-coated pebbles.

Poorly exposed, with base covered. Slackwater 

deposit?

Covered. Shallow gullies expose fine sand or silt.

Slackwater or lacustrine deposit?

Bluff cap. Sod and peat above frost-mixed stony

brown silt.
Lower Kaluktavik River Valley 69

The gravel (unit 1) consists of rounded to subrounded 

pebbles, cobbles, and rare very small boulders that commonly are silt-coated. Most of the unit is pebble-rich, with an 

abundant matrix of poorly sorted silty sand with rock chips. 

The upper 3 m is coarser cobble gravel, with large cobbles and 

some small boulders concentrated near the top. Clasts include 

several igneous rock types not seen farther up the Noatak 

River valley that must be derived from the Kaluktavik drainage system. The overlying silt (unit 2) is variable in thickness, 

being deepest where it fills channels on the gravel surface. It 

is faintly bedded, with some sand and peat lenses present, and 

bears a peat cap about 0.2 m thick.

The poorly exposed gravel appears to be deltaic, with 

about 3 m of coarser topset beds above inclined foreset beds. 

The silt coatings on the clasts indicate probable deposition 

in a turbid body of standing water. The overlying silt appears 

water-laid, and may be a floodplain deposit.

Exposure Kl-3

A gravel terrace 7.5 km up Kaluktavik River from exposure K-1 stands 15 m high and consists dominantly of imbricated cobble gravel capped by silt (fig. 102). Layers of pebbles 

and small cobbles alternate with cobble lenses within the 

gravel (unit 1), and a sand layer 15 cm thick occurs 5 m above 

its base. Dip directions of the imbricated stones are identical to 

that in the modern river bed, and the alternating gravel layers 

and lenses are like modern bar and channel deposits.

The gravel is overlain by 70 cm of stony silt that is 

capped by 40 cm of structureless silt (unit 2). Many stones in 

the stony silt stand vertically, indicating that they have been 

frost-heaved upward from the underlying gravel. Deformed 

lenses of brown peat also attest to frost action in the stony silt. 

The overlying structureless silt is stone-free, and probably 

formed as loess. A nearly continuous buried peat at the contact 

between the stony and stone-free silts is radiocarbon dated at 

2760 ±40 yr B.P. It probably represents the ground surface at 

the time that influx of eolian silt began. 

Discussion

Exposures along the lower Kaluktavik River intersect the 

core and outer face of an end moraine at Kl-1 and its associated outwash train at Kl-2 (see fig. 103). Fine gravel beneath 

the till and outwash may be a slackwater deposit that grades 

downvalley into deltaic sediments. It may have been deposited 

as advancing glaciers farther down the Noatak valley crossed 

the valley floor and dammed the river. The till-outwash association represents full-glacial conditions in the Kaluktavik 

drainage. Distinctive clast lithologies confirm that ice flowed 

southward down the Kaluktavik valley and across the north 

part of the Noatak valley floor. The outwash gravel aggraded 

to a height of about 30 m, and may correlate with alluvialterrace remnants of similar height farther up the Noatak River 

valley. Silt and nonglacial alluvium are present locally above 

the glacial deposits.

The 15-m terrace exposed farther upvalley at Kl-3 was 

formed by aggrading channel deposits of Kaluktavik River. 

The terrace surface then was subjected to intense frost mixing 

that was followed in late Holocene time by loess deposition.

Figure 102. Exposure Kl-3. 

West side Kaluktavik River 8.5 

km above its mouth. Black dot, 

radiocarbon age determination 

(yr B.P.) with laboratory number 

in parentheses (see appendix 1). 

Figure 101. Exposure 

Kl-2. West side Kaluktavik 

River at its mouth.

20

30

40

10

 0

m THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

?

26-29

0.6-3.4

1

2

1

2

Gravel. Dominantly pebble-rich, with 

abundant poorly sorted silty sand matrix 

containing numerous rock chips. Clasts 

in some beds are silt coated. Upper 3 m 

is coarser (cobble gravel with very small 

boulders up to 37 cm long), and includes

igneous rock types not seen farther up 

Noatak River valley. Deltaic deposit?

Silt. Dark gray (5Y 4.5/1), faintly bedded; 

contains some sand lenses. 

Floodplain deposit.

m

20

10

 0

2

1

Gravel. Imbricated cobble gravel. Layers of

pebbles and small cobbles alternate with

cobble lenses. Alluvium.

Silt. Structureless, stone-free, tan to gray silt

(40 cm) above stony tan silt with deformed 

peat lenses (70 cm). Loess above floodplain 

deposit.

2,760 ± 40

(Beta-206889)

1 14.4

2 1.1

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION
70 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

Figure 104. Exposure 

Nk-54. Slip-off slope, 

southwest side Noatak 

River 3 km below 

mouth of Kaluktavik 

River. (A) Exposure 

where sloping surface 

is 15.5 m high. (B) 

Exposure a short 

distance upstream 

from A, where surface 

is 20 m high. Black 

dot, radiocarbon age 

determination (yr B.P.) 

with laboratory number 

in parentheses (see 

appendix 1). 

Kaluktavik River to Noatak Canyon

For 18 km downvalley from the Kaluktavik River confluence, the Noatak River meanders through glacial-lake deposits 

into which a series of postglacial river terraces have been 

incised. Beyond this stretch, the river intersects drift sheets and 

associated end moraines deposited by ice lobes that diverged 

from the southwest-trending Kugururok valley glacier; these 

flowed more directly southward across low divides and then 

into the Noatak valley (see fig. 82). Exposures upvalley from 

the end-moraine belt exhibit glaciolacustrine silt and stony silt, 

as well as alluvial gravel and floodplain deposits at multiple 

terrace levels. In the end-moraine zone, a large and complex 

river bluff exposes interfingering till and glaciolacustrine sediments bracketed by deposits of alluvial gravel.

Exposure Nk-54

A short distance below the Kaluktavik River confluence, 

exposure Nk-54 is located along the convex side of a meander 

bend. Because the Noatak River was downcutting as it eroded 

the meander laterally, it created an inclined floodplain surface 

(a “slip-off slope”) that declines in height northward toward 

the margin of the modern floodplain. Similar depositional 

sequences were measured at two localities that differ only 

in height: 15.5 m at Nk-54A and 20 m at Nk-54B (fig. 104). 

Figure 103. Sketch 

showing geologic 

relations of end 

moraine and 

outwash train near 

mouth of Kaluktavik 

River valley.

Note 

compressed vertical scale

40

60

20

 0

m

SOUTH

Covered

Kl-2

Kl-1

(2000)

Kl-1

(1986)

Finer gravel

Coarse gravel (outwash)

Till

Silt

Silt

Alluvium

NORTH

0.9 km

20

10

 0

m

20

10

 0

m

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

?

-- 6.6

3.3

3.5

2

3

1

2

3

1 >2.1

3 4.9

2 2.9

1 11.6

1

2

3

11,910 ± 180

(I-14,680)

>45,800

(Beta-206890)

Oxidized gravel. Rounded pebbles, small cobbles, and rare medium 

cobbles in sparse sandy matrix. Sand grains poorly sorted, subangular to 

subrounded, with quartz abundant (40% of all grains). All clasts oxidecoated. Fluvial bar deposit.

Coarse gravel. Rounded to subrounded pebbles, cobbles, and rare very 

small boulders in sparse sand matrix. Some beds lack matrix, and their 

clasts are silt covered. Base not exposed. Fluvial channel deposit.

Coarse gravel. As described for Nk-54A, unit 1. Contains lenca. 1 m 

thick of bedded sand, silty fine sand, and sandy pebble gravel. Base 

not exposed. Fluvial channel deposit.

Covered. Lag pavement of coarse gravel.

Silt. Gray to dark gray (10YR 5/1 to 4/1); faintly bedded. Contains peat 

layers up to 10 cm thick (most common near top) and detrital wood fragments (most common near base). Sand and gravel lenses through basal 

0.6 m. Floodplain deposit.

Silt. As described for Nk-54A, unit 3. Possibly thickened by slumping. 

Floodplain deposit.

Pebble-small-cobble gravel. As described for Nk-54A, unit 2. Fluvial 

bar deposit.

Covered

A

B
Kaluktavik River to Noatak Canyon 71

Coarse gravel at the base of each section probably is channel 

gravel of the postglacial Noatak River. At Nk-54B, it contains 

detrital wood that has a non-finite age of >45,800 yr B.P. This 

age is much too great for the postglacial gravel; the wood 

therefore must have been redeposited from older sediment. 

The channel gravel is overlain by finer gravel that may have 

been deposited on river bars. The probable floodplain deposit 

that caps the section contains detrital wood and lenses of 

sandy alluvium near its base and peaty layers at higher levels. 

A fragment of detrital willow (Salix) wood near the base of 

the floodplain silt at Nk-53A has a radiocarbon age of 11,910 

±180 yr B.P. At each locality, the sediment succession was 

deposited, and the floodplain later abandoned, as the Noatak 

River continued downcutting toward its modern level.

Exposure Nk-55 (not illustrated)

On the north side of the Noatak River about 4 km 

downstream from the mouth of Kaluktavik River, a prominent 

bedrock bluff rises 110 m above river level. A gravel bench at 

96 m height on the flank of the bedrock (phyllite) bluff contains subrounded pebbles and cobbles with a few very small 

boulders. The stones are somewhat weathered, and some are 

fractured. The gravel can be traced downward to 55 m above 

river level, but part of its apparent thickness may be the result 

of draping over underlying bedrock.

Its geomorphic setting indicates that the gravel is part of 

a meltwater channelway that issued from the end moraine near 

the mouth of Kaluktavik River valley. The weathered state 

of the gravel is consistent with Makpik (Itkillik I) age, which 

is the assumed age of that end moraine based on regional 

mapping (Hamilton, 2003 and in press).

Exposure Nk-56

A fresh debris flow originates in a thaw ampitheater 

(fig. 105) along the east side of the Noatak River about 1.5 km 

below exposure Nk-55. This exposure was recorded for the 

first time in 2000 because no debris flow had yet taken place 

at this locality at the time of the 1986 traverse.

Stony fine-grained glaciolacustrine sediments (unit 1) 

are traceable from the river edge up to 32 m height. Clasts up 

to cobble size, with some small boulders, occur in a matrix 

of silt to clayey silt. Some water-washed beds up to 1 m thick 

within the deposit probably represent brief intervals of flowing 

water that followed drawdown of the glacial lake by breaching 

of its ice dam. Ice-rich gray silt (unit 2) is exposed in the 

amphitheater’s headwall.

Formerly active but now vegetated flow ampitheaters occur 

higher on the valley side here. They indicate that glaciolacustrine 

sediments probably originally stood higher, and that those 

exposed at Nk-56 may have been truncated by river erosion.

Exposure Nk-57

A bluff on the north side of the Noatak River is about 

equidistant between Kaluktavik River and Noatak Canyon, 

being 15 km downvalley from the river’s mouth and 14 km 

upvalley from the canyon (see fig. 82). The bluff intersects an 

alluvial terrace that stands 32 m high (fig. 106).

Figure 105. Exposure Nk-56. 

East side Noatak River 5.5 km 

downvalley from mouth of 

Kaluktavik River.

Figure 106. Exposure Nk-57. 

North side Noatak River 14 km 

upvalley from Noatak Canyon.

20

30

40

10

 0

m THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

?

32

4

1

2

1

2

Stony silt. Dark gray (N4) stony silt to clayey silt. 

Contains pebbles, cobbles, and sparse very small 

boulders up to 70 cm length. Some stones faintly

striated. Contains several beds up to 1 m thick of

faintly bedded, poorly sorted sand and granules

with scattered pebbles and some thin (0.5-1.0 cm)

silt beds. Glaciolacustrine deposit.

Silt. Ice-rich gray (N5) silt. Lake or floodplainpond deposit.

20

30

40

10

 0

m THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

?

27-26

1.8-2.8

2

3

1

2

3

? ? ? ? 1 4+

Gravel. Rounded pebbles, small to medium cobbles, 

and some larger cobbles in sparse sandy matrix. Some 

beds openwork, with small pebbles and granules the 

smallest fraction present. Other beds contain abundant

gray rock chips of coarse sand size. Alluvium.

Stony silt. Dark gray (5Y 4/1) stony, gritty silt. Some 

stones striated. Glaciolacustrine deposit.

Peaty silt. Brown to grayish brown silt, coarsening 

near base to medium to fine sand with faint parallel 

bedding. Peat lenses in upper 1 m; dipping to 1.5 m 

depth in channel fills. Floodplain deposit.
72 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

Figure 107. Exposure Nk-58. North 

side Noatak River 9 km upvalley from 

Noatak Canyon.

Glaciolacustrine stony silt (unit 1) is exposed to 4 m 

above river level, the height to which the base of the bluff has 

been freshly eroded by spring floods. The silt probably rises 

higher, but its upper contact is obscured by gravel that has 

slumped downward. The overlying gravel (unit 2) is nonglacial alluvium consisting of rounded to subrounded clasts to 

medium cobble size, with some larger cobbles and a few very 

small boulders up to 36 cm long. Some beds of finer sediment 

are present. The bluff is capped by silt (unit 3), which is peaty 

in its upper parts and sandy near its base. The silt thickens 

downward where channels have incised the surface of the 

underlying gravel. It is interpreted to be a floodplain deposit.

A lower terrace 14 m high is inset into the 32-m terrace 

and extends downvalley from it. It continues at this level 

nearly to the active point bar that marks the apex of this river 

bend, suggesting that the river may have remained about 

14 m above its present level for a significant period while it 

meandered laterally.

Exposure Nk-58

Exposures Nk-58 and Nk-57, which stand 5 km apart 

along the same bluff line that follows the north side of the 

Noatak River, are similar in composition. However, rather 

than forming part of a river terrace, the bluff at Nk-58 rounds 

back to a somewhat higher, undulating upper surface. Coarse 

alluvial gravel (unit 1; fig. 107) is exposed to about 33 m 

height, but its lower part is obscured by a younger alluvial 

terrace (fig. 107). Its upper contact is obscured by vegetated 

brown silt (unit 2) that drapes down over the upper bluff face.

The lower alluvial terrace, which stands about 15 m 

high, is composed of finer gravel, dominantly pebbles and 

small cobbles, in a matrix of dark gray sand and granules.

Exposure Nk-59

A very large bluff a short distance upvalley from Noatak 

Canyon intersects a complex assemblage of glacial deposits 

that formed when a south-flowing lobe of the Kugururok valley glacier advanced into the center of the Noatak valley (see 

fig. 82). The exposure, which stands 30-40 m high, extends 

about 850 m along the north side of the Noatak River. It was 

mapped during a 1-week period in 1986 by measuring a base 

line along the river edge and then describing stratigraphic 

sections measured vertically at 50-m intervals. The depositional record of the western half of the bluff is complex and 

was partly obscured by debris flows in 1986 (fig. 108A). The 

eastern half of the bluff was better exposed and had more consistent stratigraphy (fig.108B); this part of the bluff therefore 

is described first.

Eastern Sector

Through the eastern part of the exposure, preglacial 

gravel is overlain by till and ice-contact sediments that grade 

upvalley into deltaic and lacustrine sediments. These deposits 

were eroded to various levels by the Noatak River, which then 

deposited alluvial gravel above them. The section is capped by 

silt and peaty silt. 

The basal gravel (unit 1; fig. 108C), which generally 

stands to heights of 15-16 m above the modern river, consists 

dominantly of pebbles and small cobbles in a sandy matrix. 

Some centimeter-scale beds of medium sand, sand with granules, and silt-covered openwork pebbles are present. The base 

of the gravel is obscured by debris aprons that originate 7-13 

m above the river, rising in height eastward. The uppermost 

part of the gravel contains silt introduced from above, and it 

locally is oxidized to about 40 cm depth. The gravel is preglacial alluvium that locally was weathered prior to glaciation 

and later altered by silt penetrating downward from overlying 

glaciolacustrine sediments. Locally it is overlain by 0.1-0.3 m 

of floodplain and pond deposits that consist of compact brown 

to gray silt and clayey silt. At 150 m E (see fig.108B), silt and 

clay couplets form the lower part of a 3-m lacustrine section (unit 2; figs. 108B and 108C). The couplets probably are 

annual varves because the upward transition from silt to clay 

(which takes place during autumn freezeup) is transitional but 

that from clay to silt (spring breakup) is abrupt. 

A highly compact diamict of nonsorted and nonbedded 

clasts in a matrix of silty sand (unit 3a) forms near-vertical 

faces 7-11 m high through the east-central part of the bluff 

20

30

40

10

 0

m

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

?

5.5

15.3

2

3

3

1

2

1 17.8+

? ?

?

Gravel of upper terrace. Subrounded to 

rounded pebbles, cobbles, and sparse very 

small boulders (up to 35 cm length) in matrix 

of immature coarse sand and granules. 

Older alluvium.

Gravel of lower terrace. Rounded to 

subrounded pebbles, small cobbles, and 

some larger cobbles in abundant matrix 

of dark gray immature sand and granules. 

Younger alluvium.

Silt. Brown silt. Mostly covered by vegetation. 

Origin uncertain.
Kaluktavik River to Noatak Canyon 73

between base-line positions of about 25 m W and 150 m E. 

The clasts commonly are striated and faceted. Pebbles and 

cobbles predominate, with some small boulders also present. 

This deposit is interpreted as massive till, derived largely 

by reworking of river gravels, that interfingers eastward 

(upvalley) with probable deltaic deposits.

At 150 m E (fig. 108B), the diamict underlies and 

interfingers with beds of sand and gravel that dip upvalley 

at 11° to 18° (unit 3c; fig. 108C). The diamict, which forms 

vertical faces in the lower half of this unit, generally exhibits 

weakly defined size sorting and bedding; it generally contains 

clasts no larger than medium cobble size in a silty matrix. The 

gravel commonly is openwork pebbles and small cobbles, 

with silt partly filling interstices between the clasts. The 

sand commonly is cross-bedded, with medium to fine sand 

predominant. The basal till-like sediment may represent 

advance outwash that was deposited in a proglacial lake (unit 

3b) and later overridden by advancing glacier ice. The sand 

and gravel beds form part of the proglacial deltaic complex.

The deltaic deposit (unit 2c) extends from about 150 m E 

to 250 m E. It dominantly consists of beds 15-45 cm thick of 

pebble and cobble gravel, and of parallel-bedded sand and silty 

fine sand. These beds dip upvalley and toward the Noatak valley 

center at angles from 15° to 20°. Some gravel beds consist of 

well-sorted silt-covered stones that lack any matrix. In some 

thicker (up to 1 m) structureless beds, pebbles and sparse small 

cobbles occur in an unsorted matrix of silt and sand. A channelfilling deposit of sand to fine gravel at about 200 m E is bordered 

by a diapiric structure in which underlying sand has risen about 

2 m vertically. The steeply dipping beds are interpreted as 

deltaic foreset beds; where thick and structureless, they probably 

formed as mass-flow deposits down the delta front.

At the base of the deltaic complex, lacustrine sediments 

underlie and interfinger with deltaic bottomset beds. The 

lacustrine deposits are laminated dark gray (5Y 4/1) clay to 

fine sand. The bottomset beds are horizontal near their base, 

with silty fine sand dominant. They coarsen and steepen 

progressively upward, and thick (18-20 cm) beds of coarse 

sand with granules dipping upvalley from 5° to 15° are 

common in upper parts of the bottomset sequence. 

The glaciolacustrine sediments (unit 3b), which are 

traceable through the eastern 150 m of the bluff, consist of 

unsorted, unstratified clasts dispersed in a matrix of compact 

gritty silt. The stones, some of which are striated, range up to 

small boulder size but dominantly are pebbles and small cobbles. In the upper and basal parts of the unit, beds 0.5-1.0 m 

thick of rounded small to medium cobbles in a sparse matrix 

of pebbles and granules are interbedded within the stony silt. 

These water-washed sediments probably formed when the proglacial lake filled to overflowing and eroded a channel through 

its ice dam. The lake would have remained drained for a short 

interval, enabling the Noatak River to flow briefly across the 

site; it then would have filled again as continuing flow of the 

glacier sealed its outlet channel.

Highly deformed, cohesive, stone-free clayey silt (see 

fig. 108B) is exposed between about 25 m E and 100 m E. 

This deposit reacted plastically to the weight of the overlying gravel, forming near-vertical squeezeup structures with 

heights as great as 7 m. It locally forms recognizable beds of 

laminated silt with thin (millimeter-scale) wavy laminae of 

gray clay spaced at intervals of 15-20 cm, but in most places 

its original structures have been deformed almost beyond 

recognition. Although lacustrine in origin, this deposit is 

separate from the glaciolacustrine stony silt of unit 3b. It 

may have formed in a moraine-enclosed lake during or after 

glacier recession.

The upper gravel (unit 4; figs. 108B and 108C) is 10-11 

m thick in the east-central part of the bluff, where it rises to 

about 37 m above the modern river. Farther upvalley, it has 

been eroded during postglacial river downcutting, reducing its 

thickness. The gravel is parallel- to cross-bedded, and contains 

rounded (some subrounded) pebbles and small to medium 

cobbles, with sparse larger clasts up to small boulder size. It is 

weakly size-sorted, with some pebble- and cobble-rich layers. 

Clasts commonly have thin silt coatings, as on modern river 

bars. The matrix is sand and granules that consist mostly of 

rock chips and with very little quartz. Unlike most underlying units, the upper gravel is loosely consolidated and generally does not support slopes steeper than 45°. An ice-wedge 

cast bordered by stones with vertical orientations was noted 

at 200 m E. Lower parts of the gravel locally contain diapiric 

squeezeups of dark gray stony mud and fine sand, and a concentration of large cobbles and small boulders lies along its 

lower contact. At 50 m E, silty fine sand near the base of the 

gravel contains organic detritus with a non-finite radiocarbon 

age of >58,000 yr B.P. (fig. 108B) that includes wood identified as Picea (USDA FPL, 3/17/87). The gravel formed as 

postglacial river alluvium, with a lag deposit of coarser clasts 

at its base created by erosional winnowing of fine sediments 

from underlying till and glaciolacustrine deposits. The unexpected great age of the detritus, which includes spruce wood, 

indicates that interglacial sediments probably were eroded by 

the Noatak River and then redeposited at this site. 

The bluff is capped by up to 6.5 m of silt, peaty silt, 

and locally sand (unit 5; fig. 108C). Faintly laminated silt 

predominates. It contains peat layers and lenses as thick as 

10-20 cm, which are most abundant in upper parts of the unit. 

In some places, silt beneath the peat beds exhibits aggregate 

structure produced by repeated freeze-thaw. The ice-wedge 

cast at 200 m E originates near the base of the silt and penetrates 4.4 m downward into the underlying gravel. Near the 

wedge cast, peat 0.8 m above the base of unit 4 is dated at 

7,540 ±130 yr B.P. At 350 m E, the silt is underlain by 0.5-0.7 

m of fine sand. Fine sand also is present locally above the silt 

as cliff-head deposits. The silt formed in part as a floodplain 

deposit, and also may have been deposited in ponds on the 

floodplain surface. Some silt also may have been transported 

as loess to this site. Silt deposition continued into at least 

early Holocene time, as indicated by the radiocarbon age. The 

cliff-head deposits formed more recently where strong winds 

swept up the face of the modern bluff, entraining and redepositing sand. 
74 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

Western Sector 

Much of the western part of the bluff face is obscured 

by debris flows, which originate in an amphitheater whose 

headwall stood as high as 45 m above the river (fig. 108A). 

The headwall was actively receding in 1986 owing to thaw 

of massive ice and ice-rich silt, but had become largely 

stabilized and vegetated when seen again 14 years later. 

Available exposures in 1986 displayed diamicts of several 

types interspersed with lacustrine, fluvial, and colluvial 

sediments in deposits that varied laterally and vertically 

over short distances. This variability has resulted from river 

erosion and from collapse into and around cavities created by 

melting glacier ice.

Figure 108. Exposure Nk-59. North side Noatak River 6 to 7 km upvalley from Noatak Canyon. Sketch of bluff face (1986). (A) West half 

of exposure. (B) East half of exposure. Bottom scales in meters west and east of bluff center. Black dot, radiocarbon age determination 

(yr B.P.) with laboratory number in parentheses (see appendix 1). 

20

30

40

10

 0

400W 300W 200W 100W 0

m

20

30

40

10

 0

m

5,710 ± 120

(I-14,682)

8,805 ± 40

(USGS-2460)

Sand

Diamict

Gravel

Covered

(veneer of

flow deposits)

VEGETATED

AMPHITHEATER

Younger 

flow 

amphitheater

OLDER

AMPHITHEATER

WEST EAST

Silt

Peat

Flow

deposit

Till?

Sand

& silt

Sand

and gravel Gravel

Till

Lower gravel

Stony

mud

Till?

Chaos

DEBRIS APRON

Till

GULLEY

Eroded

Gravel

Sand

Active flow

from enlarging

amphitheater

Debris 

slope

Erosion

surface

Lower 

gravel

20

30

40

10

 0

0 100E 200E 300E 400E

m

20

30

40

10

 0

m

7,540 ± 130

(I-14,682)

>58,000

(USGS-2459)

Diamict

Deformed

clayey silt

WEST EAST

Silt

Deltaic deposit

? Gravel lens

TERRACE SURFACE

(30-32 m height) Upper Gravel

DEBRIS APRON

Till

Vegetation

covered

Glacial-lacustrine

Eroded

Gravel Sand

* Major upvalley-dipping structure 

 dipping ca. 80. Cobble gravel 

 above silt or sand.

?

Lower gravel

Debris 

cone

*

Lacustrine

A

B
Kaluktavik River to Noatak Canyon 75

Figure 108. Exposure Nk-59 (continued). (C) Generalized section, eastern part of exposure. (D) Measured section at 190 m W (see fig. 

108 A).

Basal gravel (unit 1; fig. 108D) forms a deposit that is 

continuous with the basal alluvium of the eastern sector of 

the bluff, and it generally is identical in composition. Its base 

is obscured by debris aprons 6.5-8.5 m high that generally 

are lower than those farther east. In common with the gravel 

farther east, the upper 0.5-1.5 m of this deposit is impregnated with silt introduced from above. Because of overriding 

by glacier ice, however, it typically is structureless and more 

compact than the gravel beneath it, generally standing in nearvertical faces. The gravel commonly is overlain by thin beds of 

compact, strongly laminated to faintly bedded silt to clayey silt 

that contains scattered stones at one locality. These sediments 

probably represent local ponding on the Noatak valley floor as 

the advancing glacier approached the valley center.

Till-like sediments similar to those of unit 3a farther east 

overlie the gravel through much of the bluff between 50 m 

W and 300 m W. These sediments commonly are unsorted 

and compact, with abundant striated stones. At 50 m W, the 

diamict contains a sequence of interbedded sand and pebbly 

mud that probably was generated during an outburst flood. In 

other places, the deposit is less compact and contains steeply 

dipping structures, sand lenses, or other attributes of till that 

was remobilized as mass-flow deposits. At 125 m W, crossbedded fluvial sand and gravel lenses interstratified with the 

diamict contain peat dated at 8,805 ±40 yr B.P. Along much 

of its upper surface, lag boulders, gravel interbeds, and deep 

channeling demonstrate that an episode of river erosion followed deposition of the diamict. The early Holocene radiocarbon age indicates that some of the mass-flow deposits may 

have formed by remobilization of till at that time. 

Stony mud that resembles the glaciolacustrine unit 3b 

in the eastern part of the bluff occurs between about 100 m 

W and 175 m W. Striated and faceted stones occur in a dark 

gray, slightly plastic matrix. Interstratified beds of silt-covered 

pebbles and sand with granules may represent minor outburst events. This glaciolacustrine deposit interfingers with 

till to the west, but may contact the eroded margin of a more 

continuous till body to the east. The glacial lake in which it 

formed probably was created during glacier recession, and it 

likely was a younger body that was separate from the more 

extensive lake farther east in which unit 3b formed. Its relation 

to the deformed clayey silt at 25-100 m E is obscure. 

20

30

10

 0

m

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

?

7.4

2.1

3

4

1

2

3

2 2.6

1 6.8+

-- 6.9

4

Sand and gravel. Rounded to subrounded pebbles and small to medium cobbles in matrix of poorly 

sorted sand and granules. Contains interbeds of brown fine sand and light gray silt with some peaty 

beds; these commonly thicken into closed depressions on surfaces of the gravel beds. Lag boulders 

concentrated at contact with underlying diamict. Alluvium.

Diamict. Subrounded to rounded clasts, many striated, in compact matrix of dark gray, gritty, clayey 

silt. Several thin (ca. 5 cm) beds of openwork pebbles and granules near top. Irregular eroded upper 

surface. Till.

Gravel. Rounded pebbles and small to medium cobbles in poorly sorted sandy matrix. Brown silt 

with scattered stones and faint horizontal bedding locally present at upper contact. Base not exposed. 

Alluvium.

Debris apron.

Silt. Laminated silt and peat, overlain by 0.3 m sod. Floodplain deposit and bluff cap.

D

20

30

40

10

 0

m WEST EAST THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

1 3-9

3-10

1-5

4

5

1

5

4

3a 6-11

2

3c 7-9

3-4

3.3

3b

3b

3a

2

3c

Debris

apron

Upper gravel. Rounded pebbles and cobbles in parallel beds that dip downvalley at low angles. 

Dominantly cobble gravel, but contains some beds of crossbedded pebble gravel 10-30 cm thick. 

Matrix dark gray (N3 to N4), poorly sorted, immature sand and granules. Alluvium.

Diamict. Rounded to subrounded pebbles, cobbles, and sparse small boulders in highly compact 

matrix of dark gray (N4) silty sand. Till.

Sand and gravel. Parallel bedded and well stratified. Forms upvalley-dipping beds interspersed 

with mass-flow deposts. Deltaic deposit.

Stony silt. Pebbles, small cobbles, and sparse larger clasts dispersed in very dark gray (N3) gritty 

silt. Glaciolacustrine deposit.

Sand, silt, and clay. Couplets 0.5-1 cm thick of alternating silt and clay. Transitional upward into 

beds of compact dark gray fine sand and silty fine sand with some dark gray (N3.5) clay interbeds. 

Lacustrine deposit.

Basal gravel. Subrounded to rounded pebbles, small cobbles, and sparse medium cobbles in

poorly sorted sandy matrix. Contains beds of sand and granules 4-5 cm thick and beds of siltcovered openwork pebbles 5-10 cm thick. Alluvium.

Peaty silt. Faintly laminated dark grayish brown (2.5Y 4/2) silt with inter-bedded peat lenses that 

thicken and become more continuous upward. Floodplain deposit.

C
76 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

Alluvial gravel (unit 3; fig. 108D) is preserved above till 

and glaciolacustrine sediments along the bluff between about 

125 m W and 250 m W. Clasts to medium cobble size occur 

in a matrix of poorly sorted sand and granules. Interbeds of 

sand and silt, with gravel lenses, typically are subhorizontal 

and thicken into depressions. However, in some places they 

are contorted, with dips up to 35°. These sediments may have 

been deformed by slumping into gravel-floored river channels or by subsidence into voids created by continued melt of 

nearby glacier ice. Although the gravel appears similar to the 

upper gravel farther east in the bluff, it is significantly lower in 

height than the gravel farther east (17-22 m versus 20-35 m). 

The deformation structures indicate that meltout of glacier ice 

likely was continuing while the downcutting Noatak River was 

flowing at a level about 20 m above that of the present.

Between about 50 m W and 150 m W, the gravel had 

been so highly deformed by slump and collapse that it was 

designated as “chaos.” Many stones in this sector are oriented vertically, and festoons and clasts of brown silt have 

intruded the gravel from above. The “chaos” directly overlies 

the eroded surface of till and stony mud, with a lag deposit of 

striated boulders marking the contact. At one site within the 

“chaos” horizon, bedded sand, silt, and peat containing lenses 

of pebble gravel directly overlie diamict. Peat at the base of 

this succession was radiocarbon-dated at 5,710 ±120 yr B.P. 

The “chaos” probably formed by collapse of river gravel over 

melting glacier ice. The bedded sand and silt with basal peat 

may have formed as a kettle fill that followed collapse of a 

vegetated surface during continued meltout of glacier ice in 

mid-Holocene time.

Between 50 m W and 225 m W, the exposed bluff face 

stands about 23-25 m high, with its crest forming the outer 

edge of the amphitheater floor. This section of the bluff is 

capped by silt and peat (unit 4; fig. 108D), which generally is 

2.0-2.5 m thick. Gravel locally is intermixed with the silt at its 

base. Peat beds thicken and become more continuous upward, 

and peat also thickens into a broad swale that is centered at 

about 150 m W.

Flow deposits of muddy gravel are widespread near the 

western end of the bluff. Where exposed at 300 m W, aggregates of mud adhere to clasts and are incorporated within the 

matrix; and fragments of willow wood locally are present. The 

muddy gravel is structureless to faintly bedded, with beds dipping toward the river at about 10°. Farther west, flow deposits 

containing numerous striated stones are draped over the bluff 

face. Alluvial gravel like that of unit 1 farther east is exposed 

intermittently 11-15 m above the river through the veneer of 

flow deposits, and diamict similar to that of unit 3a in the eastern part of the bluff is exposed intermittently at about 18-21 m 

height.

Dark grayish brown (2.5Y 4/2), well sorted fine sand, 

a deposit found nowhere else in the bluff, occurs at 21-31 

m height at the bluff’s extreme west end. The sand contains 

scattered rounded pebbles and small cobbles, but it is slumped 

severely in all exposures and the clasts may have been derived 

from another deposit when slumping took place. Similar 

deposits of fine sand form wind-built dunes that stand as high 

as 10 m on nearby parts of the present-day river floodplain. 

The dunes are most common on concave river banks (cutbanks) directly west of barren point bars across which strong 

downvalley winds can move freely and entrain sand. Their formation primarily may have been during winter months, when 

downvalley winds are common and the river which separates 

cutbank from point bar is frozen.

The headwall of the ampitheater stands 13 m high, and 

it is set back from the bluff face about 35 m. It was mostly 

vegetated in 1986, but rare exposures revealed peat, silt, ice 

wedges, and gravel above massive buried ice with exposed 

thickness as much as 7 m. Sharply defined foliation planes 

within the massive ice dipped about 21° in a general upvalley direction. Clasts frozen into the ice generally were widely 

dispersed, but were concentrated along the foliation planes. 

The ice was clear, with sparse bubbles and no evident dirt 

inclusions. It was directly overlain by poorly sorted gravel that 

contained boulders up to 70 cm diameter. This diamict may be 

ablation drift, a coarse water-washed deposit that commonly 

accumulates on top of downwasting glacier ice.

An older and completely vegetated thaw ampitheater 

farther back from the river between about 250 m W and 50 m 

E rises to 40-45 m height. No sediments were exposed on its 

headwall or floor.

When revisited in 2000, the bluff face and amphitheater 

headwall were obscured almost completely by flows that had 

become stabilized and vegetated. A conspicuous seepage line at 

about 15 m height along the central part of the bluff marked the 

probable upper surface of the basal gravel. Some gravel mixed 

with silt was extruding from part of the headwall, and striated 

stones were common at this locality and elsewhere across the 

amphitheater. Glacier ice no longer was visible. 

Exposure Nk-60

Sediment deposits perched at high levels on a bedrock 

cliff near the western end of the north wall of Noatak Canyon 

were accessed by helicopter in 2003. The overall bluff profile 

stands 135 m high (fig. 109A); the distribution of the surficial 

deposits along the top of the bluff is sketched in figure 109B. 

The bedrock which forms most of the bluff is black slate with 

quartz veins. Along the bluff’s crest it is overlain by till and 

gravelly sand, and is capped by a loess blanket up to 2 m thick.

The till (unit 1) formed over an irregular bedrock surface. 

Its thickness is 8-12 m, but it follows bedrock topography (fig. 

109B) so that its highest exposed occurrence is 31.5 m above 

its lowest exposed base The till is unsorted and nonstratified, 

and contains boulders up to at least 1.3 m diameter. Ultramafic 

lithologies dominate the larger clasts. Through its highest 

exposed position on the bluff, the upper 60 cm of the till is 

oxidized yellowish brown, and its clasts are oxide-stained and 

slightly weathered. 

The sand (unit 2), which ranges in thickness up to 10 m 

or more, consists of black silty sand with platy granule-sized 

fragments of slate. All exposed faces are slumped, so primary 
Noatak Canyon to Kugururok River 77

bedding is not visible. The sand may have formed as a deltaic 

deposit in standing water. 

The loess cap (unit 3) is sandy silt with slate chips 

and stands in near-vertical faces. It probably is a mixed eolian and 

colluvial deposit that formed during incision of Noatak Canyon. 

Discussion

The stretch of the Noatak River valley from the mouth of 

Kaluktavik River to Noatak Canyon was affected strongly by 

the glacier that flowed southeastward from the DeLong Mountains through the Kugururok valley system to its mouth. The 

source of the high-level till at Sekuiak Bluff (at the west end 

of Noatak Canyon) was a broad glacial lobe that covered the 

floor of Kugururok valley and spread south across the Noatak 

valley floor (see fig. 82). Its near-surface weathered horizon 

indicates that the till probably was deposited during Makpik 

(Itkillik I) time. The till farther upvalley at exposure Nk-59 

was deposited by a distributary glacier, probably of the same 

age, that diverged from the main Kugururok valley glacier 

and flowed directly south across low passes into the Noatak 

valley. When seen in 1986, Nk-59 exposed a complex record 

of preglacial river gravel, glacial-age till and proglacial lake 

sediments, late-glacial ice wastage and ponding, and postglacial river and eolian activity associated with continued meltout 

of glacier ice.

Farther east up the Noatak River valley the glaciolacustrine sediments at the base of Nk-56, as well as those farther 

upvalley at Nk-51B through Nk-53, probably were formerly 

Figure 109. Exposure Nk-60. 

North side Noatak River at 

west end of Sekuiak Bluff, 

Noatak Canyon. (A) Overall 

bluff profile. (B) Upper bluff 

face (from a 2002 field sketch).

continuous with the deposits of stony silt in the eastern sector 

of Nk-59. The glaciolacustrine sediments commonly are overlain by thick ice-rich silt, which probably also is lacustrine, but 

the silt generally is poorly exposed and its origin is uncertain.

Exposures Nk-57 and Nk-58 occupy the same bluff line 

north of the Noatak River. The exposed top of the alluvial 

gravel at each bluff stands 30-33 m above river level, and 

is overlain by silt. The silt clearly is a floodplain deposit at 

Nk-57, but at Nk-58 it is thicker, stands higher, and could be 

lacustrine in origin. These deposits probably are continuous 

with the upper gravel and overlying silt exposed in the eastern 

section of Nk-59, which are similar in height. They document 

a significant interval during which the Noatak River remained 

at a level about 30 m above that of the present day.

At Nk-57 and Nk-58, a lower terrace with measured 

heights of 14-15 m may have formed during a pause in 

regional downcutting. The radiocarbon date farther upriver at 

Nk-54A indicates that the Noatak River was flowing at about 

that height about 12 ka as it eroded downward toward its present level.

Noatak Canyon to Kugururok River

Below Noatak Canyon, the Noatak River flows into a 

broad lowland that widens progressively westward. Thick 

glaciolacustrone deposits cover the valley floor, draping over 

arcuate end moraines that were deposited by south-flowing 

Note compressed scale

100

150

50

 0

m

Bedrock

Exposed 

till

Exposed 

sand ?

Covered

Note compressed scale. Zero point is about 70 meters above river level.

40

60

20

 0

m

40

60

20

 0

m

WEST EAST

Bedrock

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

>10 m

up to 2 m

2

3

1 8-12

3

2

1

Sand. Black (10YR 2/1) poorly sorted silty sand with 

platy slate granules. Base not exposed. Deltaic deposit?

Diamict. Unsorted and unstratified clasts up to boulder

size. Matrix uncertain due to admixture of sand from overlying unit. Oxidized yellowish brown (10YR 5/4) near upper

contact at east end of section. Till.

Silt. Bluff cap. Silt with slate chips. Stands in steep 

faces. Loess with colluvium.

A

B
78 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

glaciers at and beyond the mouth of the Kugururok River (see 

fig. 82). Three bluff exposures were recorded along this stretch 

of the Noatak River.

Exposure Nk-61

An arcuate meander cutbank on the south side of the 

Noatak River forms a bluff line that originates in till bluffs 

at the downstream end of Noatak Canyon and extends west 

and then north for about 2.5 km. The bluff has a planar upper 

surface about 50 m high that extends along the cutbank and 

farther downvalley as a conspicuous alluvial terrace. Intermittent exposures reveal gravel above glaciolacustrine sediments 

except near Noatak Canyon, where gravel overlies till and 

bedrock. Bluff exposures were examined in 1986 and 2000, 

with different sections measured on each visit.

Exposure Nk-61A (fig. 110A) was measured near the 

west end of the bluff line near the mouth of a small unnamed 

tributary that enters the Noatak River from the south. The 

bluff face here stands 44 m high, with slump blocks creating 

a gentler slope that rises inland to a planar upper surface 53 

m above the river. The base of the bluff face is covered with 

flow lobes, and the composition of underlying sediments is 

uncertain. The lowest exposed deposit (unit 1) is a strongly 

Figure 110. Exposure Nk-61. Southwest side Noatak River at and below west end of Noatak Canyon. (A) Exposed 

face at west end of canyon. (B) Exposed face a short distance downstream from exposure A.

weathered diamict that contains rotted clasts in a matrix rich 

in clayey weathering products. The diamict probably was 

originally a till. The overlying gravel (unit 2) consists of platy 

immature gravel that grades downward into coarser gravel that 

contains abundant large cobbles. The clasts in the platy gravel 

are mostly of local derivation, whereas those of the coarser 

gravel contain far-traveled igneous rocks. The gravel unit 

probably represents a fan deposit built by the nearby tributary 

stream that overlaps glacial outwash. The topmost unit (unit 

3) is largely obscured by slump blocks, but basal exposures 

reveal stony silt and silty gravel. The silt may be mostly eolian 

in origin; and the gravel may be an alluvial deposit of the 

tributary stream. These two components may have been intermixed in part by frost action and in part by colluvial activity.

Exposure Nk-61B (fig. 110A) was measured a short distance downvalley from Nk-61A. The bluff face here stands 50 

m high, exposing gravel above glaciolacustrine stony silt. The 

glaciolacustrine deposit (unit 1) consists of clasts that range up 

to small boulder size embedded in a matrix of gritty (sandrich) clayey silt. Much of this deposit is obscured by gravel, 

which drapes down from the overlying unit. Stiff clayey silt 

without stones, which is exposed near river level, may represent a basal facies of the glaciolacustrine deposit that formed 

when glaciers were advancing down tributary valleys but had 

Note: compressed scale

40

60

20

 0

m THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

1 15.3

3 >3.4

2 10.0

-- 6.9

Covered

Covered

1

2

3

Silt and gravel. Stony silt (1.2 m thick) above silty gravel (2.2 m). Gravel 

in part consists of subrounded pebbles in immature silty sand matrix. Silt 

contains stones possibly admixed by frost action. Loess and alluvium?

Gravel. Subrounded pebbles and cobbles, many platy in shape, in poorly 

sorted sand-granule matrix. Clasts largely quartz and quartzite; few igneous 

rocks. Grades downward into coarser gravel containing numerous large 

rounded cobbles; many of igneous rock types. Fan deposit above outwash.

Weathered diamict. Intensely oxidized and weathered.Upper several meters 

oxidized strong brown (7.5YR 5/6). Underlying sediments are greenish to 

brownish and appear clay enriched. Numerous pebbles and cobbles; some

 intact, others entirely rotted. Till?

Debris apron. Largely flow lobes derived from unit 1.

Note: compressed scale

40

60

20

 0

m

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

1 25

3 >10?

2 >15?

1

2

3 ? ? ?

Brown silt. Exposed only in slump blocks. May be draped over gravel. 

Origin uncertain.

Gravel. Pebbles and cobbles, typically subrounded, in immature matrix 

of shale or phyllite chips, other rock chips, and angular quartz fragments. 

Weakly bedded, with some beds having muddy matrix. Outwash?

Stony clayey silt. Pebbles, cobbles, and some small boulders in matrix 

of dark gray (N4) gritty,clayey silt. Stiff clayey silt without stones is 

exposed near river level. Glaciolacustrine deposit.

A

B
Kugururok River Valley 79

not yet reached their maximum size. The overlying gravel 

(unit 2) has an exposed thickness of 15 m, but its upper contact 

is obscured by slump blocks and it may rise higher than illustrated in figure 61B. The capping brown silt (unit 3) is exposed 

only in slump blocks. Its exact thickness, structure, and origin 

are uncertain.

Exposure Nk-62

A west-facing exposure on the east side of the Noatak 

River 2 km downstream from Nk-61 stands 32 m high, with a 

slump-covered slope leading farther upward to a near-horizontal terrace-like surface 45 m above river level (fig. 111). Most 

of the bluff face is debris-covered and vegetated, but limited 

exposures were obtained by trenching and also at places where 

the river is undercutting the base of the bluff.

A river-eroded basal exposure, measured in 2000, revealed 

highly weathered stony clay (unit 1). Clasts include brown 

sandstone and sheared quartz fragments—lithologies that are 

rare in Pleistocene-age glacial and glaciolacustrine deposits 

of the Noatak valley. This deposit could be a very old till, or 

possibly gouge along a fault zone. Overlying gravel (unit 2) 

is oxidized to 1 m depth, and locally to 2 m, but its degree of 

weathering is much less than that of unit 1. Stony silt (unit 3) 

that overlies the gravel is a typical glaciolacustrine deposit, but 

it is highly compacted and supports near-vertical faces.

A debris slope littered with pebbles and cobbles intermixed 

with brown silt rises more than 20 m above the exposed basal 

section. Absence of boulders indicates that fluvial gravel rather 

than till probably underlies the debris slope. The clasts may 

have been derived from outwash. The admixed brown silt may 

have been contributed by loess that formerly capped the gravel.

A few meters upstream from the measured section, reddish yellow (5YR 6/8) to pale yellow (2.5Y 8/4) to grayish 

green (5G 5/2) clayey saprolite is squeezing out near river 

level. This intensely weathered residual soil reflects a degree 

of alteration that is unknown among Pleistocene deposits in 

northern Alaska; it suggests that a relict soil of Tertiary age 

could be present at or below river level.

Discussion

The three exposures close to the west end of Noatak 

Canyon underlie an extensive terracelike surface about 50 

m high that may decline in height downvalley. Each of these 

exposures contains alluvial gravel 10-20 m thick that probably 

formed during alluviation of the Noatak River during waning 

phases of the last regional glaciation. The gravel is overlain 

by a poorly exposed cap of sediment that largely may be 

brown silt of eolian (loess) origin. Where close to the mouth 

of a north-flowing tributary stream, the gravel and silt units 

contain fine gravel and platy fan deposits of local lithologies. 

Beneath the gravel, the section closest to Noatak Canyon 

(Nk-61A) contains a highly weathered diamict, whereas the 

other two exposures exhibit glaciolacustrine stony silt. The 

glaciolacustrine deposits may have formed in a broad lake that 

was dammed behind moraines of the Kugururok, Avan, and 

Kelly valley glaciers. Highly weathered deposits, provisionally identified as till and saprolite, occur at or near the bases of 

two of the bluff sections (exposures 61A and 62). Their high 

degree of chemical alteration indicates a probable Tertiary age 

for these units. With the possible inclusion of a lithified gravel 

at Avan-1 (see Avan River section), these are the oldest known 

surficial deposits in the Noatak River valley.

Kugururok River Valley

Three exposures along the lower course of Kugururok 

River intersect glaciolacustrine sediments of Avan (Itkillik 

Phase II) age that locally are draped over morainal ridges 

assigned to the preceding Anisak glacial advance (see fig. 

82). An additional exposure along Trail Creek, a large eastFigure 111.

Exposure 

Nk-62. East 

side Noatak 

River 6.4 km 

upstream 

from 

Kugururok 

River mouth.

20

30

40

50

10

 0

m THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

? ? ?

? ? ? ? ? 1 >2

>2

20

3

4

1

2

3

2 >2 4

Trench

Covered

Obscured

Covered

Gravel. Rounded to subrounded pebbles and cobbles mixed with brown 

silt. Exposed only on weathered debris slope. Base not exposed.

Outwash.

Stony silt. Unsorted pebbles and cobbles, many striated, in matrix of 

compact, very dark gray, gritty clayey silt. Stands in near-vertical faces. 

Base not exposed. Glaciolacustrine deposit.

Fine gravel. Rounded to subrounded pebbles in sand-granule matrix, 

with some sand beds 10-15 cm thick. Quartz ca. 50 percent in pebble 

fraction and 60-70 percent in sand fraction. Moderately oxidized to 1 m 

depth, with some permeable beds oxidized 1 m deeper. Upper contact 

undeformed; lower contact not exposed. Alluvium.

Oxidized clay. Reddish yellow (7.5YR 6/8) stony clay. Exposed only 

near river edge. Contains fractured and weathered clasts of lithologies 

that differ from those in younger tills and glaciolacus-trine deposits. 

Upper contact not exposed. Till?
80 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

Figure 112.

Exposure Ku-1. East 

side Kugururok 

River opposite 

northwest arm of 

Lake Kaiyak. Black 

dot, radiocarbon 

age determination 

(yr B.P.) with 

laboratory number 

in parentheses (see 

appendix 1). 

ern tributary to Kugururok River, is a short distance from the 

Misheguk Mountain mafic and ultramafic complex (Boak and 

others, 1987). The Trail Creek exposure intersects an outwash 

apron just beyond a moraine front correlated with the Avan ice 

advance and near the upvalley margin of glaciolacustrine sediments of similar age.

Exposure Ku-1

Lake deposits of the last major (Avan) glaciation are 

well exposed along the east bank of Kugururok River 27 km 

above its mouth, where the river approaches Lake Kaiyak 

most closely. This river-cut bluff stands 30.8 m high, exposing a complex of lacustrine sediments (fig. 112). In the lowest 

exposed deposit (unit 1), pebbles, cobbles, and some small 

boulders up to about 40 cm diameter are dispersed in a matrix 

of dark gray sandy silt. Stone orientations range from horizontal to vertical, with no fabric evident. In the midpart of the unit, 

two beds of poorly sorted but water-washed sand and gravel 

are separated by 1.3 m of stony silt. The upper gravel bed is 1 

m thick; the lower bed is 0.5 m thick. In the diamict above the 

gravel beds, boulders up to 40 cm diameter are more common 

than in the basal diamict, and the silt matrix is sandier.

The stone-free silt above the diamict (unit 2) is concealed 

partly by slumping. It is capped by oxidized silt and by peat, 

which locally is deformed downward into wedge-like depressions. Peat sampled 1.0 m below the bluff crest has an early 

Holocene radiocarbon age of 9,440 ±40 yr B.P.

Figure 113.

Exposure Ku-2. 

North side 

Kugururok River 

7.5 km southwest 

of Lake Kaiyak.

The stony glaciolacustrine sediments with interbeds of 

muddy gravel reflect two episodes of lake drainage owing to 

ice-dam failure and probably catastrophic outburst floods. The 

stone-free silt (unit 2) overlies the diamict without any evident 

weathering, soil formation, frost disturbance, or other indications of subaerial exposure. This probably reflects persistence 

of a lake in lower Kugururok valley as glaciers thinned and 

receded. The early Holocene radiocarbon age of the buried 

peat implies that lake recession took place near the close of the 

late Pleistocene, but the wedge-like peat protrusions indicate 

that an episode of subaerial ice-wedge formation probably 

preceded the peat accumulation.

Exposure Ku-2

A south-facing bluff along Kugururok River southwest 

of Lake Kaiyak exposes glacial, alluvial, and possibly lacustrine 

sediments above bedrock. Where visible, the upper surface of 

the steeply dipping bedrock has been abraded by overriding 

glacier ice. The overlying diamict (unit 1; fig. 113) contains 

unsorted glacier-modified stones in a gritty silt and clay matrix. 

Much of the sand may have been washed down from the 

overlying gravel and mixed with the diamict on the bluff face. 

The gravel (unit 2), which is dominated by pebbles and small 

cobbles, appears to be river alluvium. It may extend about 1 

m higher than shown in figure 113, but only 5 m thickness is 

exposed. The upper 15.7 m of the bluff face (unit 3) is vegetated 

and its composition is uncertain. However, no clasts are exposed 

m

30

20

10

 0

3

2

1

9,440 ± 40

(Beta-156898)

?

Silt and peat. 0.8 m slighty oxidized brown silt above 0.4 m 

black peat to very dark grayish brown (10YR 3/2) silt. Bluff cap.

Silt. Dark gray (5Y 4/1), frozen, ice-rich clayey silt. No stones 

evident. Face massively slumped. Lacustrine deposit.

Diamict. Unsorted, nonstratified clasts up to large cobble and 

rarely small boulder size; many faceted and striated. Matrix is 

dark gray (10YR 4/1) gritty silt. Contains 2 beds of poorly sorted 

sand and gravel separated by ca. 1.3 m of diamict. Base not 

exposed. Glaciolacustrine deposit.

Covered. Debris apron.

3 1.2

-- 5.2

2 13.5

1 12.1+

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

m

40

30

20

10

 0

3

2

1

?

? ? ?

Concealed. Stabilized and vegetated slumps and flows. 

Polygon troughs common. No clasts exposed. Lacustrine?

Gravel. Pebbles and small cobbles in very dark gray, poorly 

sorted, sandy matrix. Upper contact concealed. Alluvium.

Diamict. Clasts up to boulder size in gritty, clayey silt matrix. 

Till.

Bedrock. Interbedded shale and sandstone, steeply dipping. 

Upper surface polished, striated, and grooved.

3 15.7

-- 11.5

2 5+

1 6

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION
Kugururok River Valley 81

across its surface, suggesting that it may be a fine-grained 

lacustrine or possibly eolian deposit. Troughs resulting from 

meltout of a polygonal ice-wedge network are common.

Lower river terraces here stand 7.8 m and 3.5 m above the 

modern river. At both terrace levels, alluvial gravel is exposed 

above the truncated surface of dipping bedrock.

Exposure Ku-3

An active thaw amphitheater along the Kugururok River 

near its mouth reveals poorly exposed sediments around its 

unstable headwall and mixed detritus across the flow lobe at 

its base. On the flow surface, faceted and striated stones up to 

small boulder size are dispersed in a matrix of clayey silt that 

contains little or no sand (unit 1; fig. 114).

Sediments with near-horizontal stratification (unit 2) are 

evident on the vertical amphitheater headwall, but access is 

difficult and ice-rich permafrost obscures their composition. 

Fine sand may overlie stony mud, but the position and nature 

of the contact between these two deposits are unclear. Vertical 

ice wedges penetrate the upper part of the amphitheater headwall. Subhorizontal sediments between the wedges contain 

black peaty mats at about 6.5 to 7.5 m depth. Peat taken from 

this interval has an apparent radiocarbon age of 43,480 ±1230 

yr B.P., but its large counting error indicates that this may be a 

minimum rather than finite age. The active layer at the top of 

the headwall is estimated to be 30-60 cm deep and probably 

developed in fine sand.

Exposure Trail-1 (Trail Creek)

A bulky end moraine assigned to the Avan (Itkillik Phase 

II) ice advance (see fig. 82) covers the floor of Trail Creek 

valley about 30 km above its confluence with Kugururok 

River. Outwash that issued from the moraine front formed 

a terrace that declines in height downvalley. At an exposure 

midway along its length, the terrace stands 15 m high and is 

underlain by unweathered gravel (fig. 115). Clasts up to 40 cm 

long occur in a matrix of immature (black; 10YR 2/1) sand 

and granules that contains abundant rock chips. A soil profile 

about 0.5 m thick caps the gravel. Dark grayish brown (10YR 

4/2) structureless silt with abundant rootlets overlies oxidized 

and frost mixed silty gravel. The oxidized horizon is about 

20 cm thick. It is dark yellowish brown (10YR 4/6), grading 

downward into dark brown (10YR 4/3).

Discussion

The three exposures along lower Kugururok River 

exhibit glacial, glaciolacustrine, alluvial, and other sediments 

that span two glacial advances followed by the Holocene 

interval. Exposure Ku-1 contains the youngest and least 

ambiguous record. The basal glaciolacustrine sediments at 

Ku-1 are part of the widespread glacial-lake deposits that 

formed behind an ice dam at the mouth of Avan River during 

the last major glacial advance of the Pleistocene. Interstratified gravel beds indicate that the ice dam failed at least twice, 

probably releasing outburst floods down the Noatak River. 

The overlying stone-free silt probably reflects diminishing 

glacier presence but continuing blockage of the Noatak River 

during late-glacial time. The radiocarbon age of 9.5 ka near 

its base clearly dates the bluff cap as Holocene. Several other 

similar peat dates in this region suggest that early Holocene 

climate may have been milder than at present.

Exposure Ku-2 is situated in line with several subsurface 

moraines of Anisak age that were buried beneath younger glaciolacustrine deposits. The diamict at Ku-2 overlies glacierscoured bedrock, and probably was deposited as glacial till. 

Figure 114. Exposure Ku-3. Thaw 

ampitheater along east side Kugururok 

River 2 km above its mouth. Black dot, 

radiocarbon age determination (yr B.P.) 

with laboratory number in parentheses 

(see appendix 1). 

Figure 115. Exposure Trail-1. North side 

Trail Creek 27 km northeast of Lake Kaiyak.

m

15

10

5

 0

Gravel. Subrounded pebbles, small 

cobbles,and sparse larger clasts to 

small boulder size in black (10YR 2/1) 

sand-granule matrix. Capped by soil 

profile about 0.5 thick. Outwash.

15

THICKNESS

(m)

DESCRIPTION and INTERPRETATION

m 50

40

20

30

10

 0

2

1

43,480 ± 1,230 

(Beta-156901)

Flow lobe

Note compressed scale

?

2 29.5

1 19

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

Obscure. Ice-rich permafrost with 

near-horizontal layering. Composition 

uncertain, but stony mud may be 

overlain by fine sand. Penetrated by 

ice wedges. Lacustrine?

Stony clayey silt. Pebbles and small 

cobbles, with sparse larger cobbles 

and small boulders, in clayey silt 

matrix. Glaciolacustrine deposit.
82 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

The overlying gravel may be interstadial in age, but it shows 

no evidence of weathering. The topmost unit appears stonefree, but its composition is otherwise unknown. It may consist 

wholly or largely of silt and organic deposits comparable to 

units 2 and 3 at exposure Ku-1.

Exposure Ku-3 exhibits a sediment succession similar 

to that of Ku-1, but it differs from that exposure in several 

Kugururok River to Eli River

Introduction

Below the mouth of Kugururok River, the Noatak River 

flows westward for about 40 km to the western boundary of 

the Noatak National Preserve (fig. 116). It then curves southFigure 116. Generalized geologic map, Noatak 

River valley, Kugururok River to Eli River. 

Numbers without prefixes refer to Noatak River 

bluffs (designated Nk in text). West boundary of 

Noatak National Preserve shown by broken line.

0 25 KILOMETERS

0 15 MILES

Avan River

Kelly River

Eli

Wrench Creek

Uvgoon Creek

Noatak River

Maiyumerak

Mountains

Amphitheatre

Mountain

Noatak River

Kelly

"west fork"

River

Kugururok River

De Long River

Mountains

Kly-6

67

Eli-1

Kly-2

Kly-1

Avan-1

Avan-2

Kly-4

Kly-3

Kly-5

64

65

63

66

Eli-2

Uv-1

Uv-2

Kelly River Ranger Station

MAP UNITS

Glaciolacustrine

deposits

Bedrock (includes

colluvial cover)

Alluvium

Terrace deposits

Fan and 

fan-delta deposits

Older glacial deposits

Avan drift

SYMBOLS

Morainal

ridge

Thick loess 

cover above 

other deposits

Lake

67o

45'

68o

00'

68o

15'

162o

30' 162o00'

important aspects. The basal glaciolacustrine 

deposit has a clayey silt matrix, which 

contrasts with the conspicuously gritty silt 

matrix of the youngest glaciolacustrine 

deposit at Ku-1 and other exposures. Much of 

the overlying unit is sandy rather than silty, 

and is penetrated by ice wedges much larger 

than the wedge-like features at Ku-1. Finally, 

airphotos of the lower Kugururok River 

valley clearly show that the valley floor near 

Ku-1 contains undisturbed glaciolacustrine 

sediments whereas the area around Ku-3 has 

been scoured by running water, probably 

when the Noatak River was flowing at the 

50-m terrace level. Deposits dating from the 

last glaciation may have been truncated at 

this time, and the bluff section eroded down 

to a lower and older sediment succession. 

This truncation may explain the very old 

radiocarbon age (ca. 43.5 ka), which is much 

older than that of peat at similar stratigraphic 

positions at Ku-1 and other exposures. 

However, this radiocarbon age determination 

is suspect because of its large counting error, 

and it could be a minimum age limit instead.

The outwash exposure (Trail-1) on Trail 

Creek lies just below end moraines assigned 

to the Avan glacial advance and just above 

the upvalley limit of glaciolacustrine deposits 

of the same apparent age (see fig. 82). A soil 

profile on the outwash is similar to other 

soil profiles measured on glacial deposits 

of Itkillik II (late Wisconsin) age through 

the central Brooks Range (Hamilton, 1986). 

Rather than forming an elongate valley train, 

the outwash forms an apron that is truncated 

a short distance beyond the moraine front. 

Glacial meltwater may have flowed into the 

glacial lake at this location, and much of the 

“fan” deposits mapped there (Hamilton, 2003 

and in press) could have formed as a thin 

veneer over deltaic sediments.
Kugururok River to Eli River 83

ward to flow through a broad lacustrine plain. Through its 

westward course, the river is confined to the south by an end 

moraine that was formed by south-flowing glaciers that issued 

from drainage systems now occupied by the Kugururok, Avan, 

and Kelly Rivers. The Noatak River flows through a single 

channel downstream to the mouth of Kelly River, where it 

becomes highly braided. 

Five bluff exposures (Nk-63 through Nk-67) were 

measured through the west-flowing stretch of the Noatak 

River. These exposures reveal glacial tills, glaciolacustrine 

deposits, and fluvial gravels that are overlain in places by thick 

accumulations of silt.

Only low banks were seen along the Noatak River 

through the lacustrine plain that extends downvalley from 

Nk-67 (fig. 116). These banks lie beyond the western boundary of the Noatak National Preserve, and consequently were 

not examined closely.

Exposure Nk-63

The face of a low terrace along the south side of the 

Noatak River’s active floodplain rises 7 m above the floodplain level (fig. 117). Basal gravel (unit 1) contains abundant 

gray quartzite and vein quartz, with black chert and ultramafic 

lithologies also common. The overlying silt (unit 2) is a typical Holocene floodplain deposit. It bears a sod cap that formed 

after the river cut down and abandoned its former floodplain.

m 20

10

 0

Center

section

(C)

Eastern

section

(E)

3

2

8

THICKNESS

(m)

C E

UNIT DESCRIPTION and INTERPRETATION

Organic silt (center section only). Dark reddish brown (5YR 3/2) peat to peaty 

silt, grading downward to dark grayish brown (2.5Y 4/2) silt with rare peaty lenses 

and wood fragments. Peat mass 4.7 m thick fills local depression in the silt.

Slump and flow deposits (eastern section only). Heavily vegetated surface 

rises inland into thaw amphitheater.

d --

c 3.7 Upper diamict. Subrounded pebbles, sparse small cobbles, and rare large 

cobbles in unstratified matrix of very dark gray (10YR 3/1) muddy sand.

Sand. Nonbedded very fine sand, dark grayish brown (2.5Y 3/2), with thin 

layers and lenses of medium sand near upper contact. 

b 0.35

--

?

3.4

0.25

9,220 ± 40

(Beta-156899)

Lower diamict. Pebbles, small cobbles, and sparse larger clasts in matrix of 

dark gray (10YR 4/1) slightly gritty clayey silt.

a 3.6 <7.1

Gravel. Rounded pebbles and some small cobbles with quartz common 

(5-10 percent of total) in abundant sandy matrix. Sparse beds 4-14 cm thick of 

faintly bedded fine to very fine sand with some medium sand.

1 3.9 >1.5

2c

2b

2a

1

3 2d

2c

2b

2a

1

? ? Glaciolacustrine deposits.

m 20

10

 0

2 14

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

Silt. Well sorted silt. Colors gray (10YR 6/1) to strong brown (7.5 YR 5/6) and 

black (5YR 2.5/1). Upper part deformed by slumping and flowage. Contains 

deformed clots of peat that include abundant rootlets and shrub twigs. Lower 

part contains west-dipping lenses of peat and locally more massive but highly 

contorted peat. 

1 8.2 Gravel. Rounded to subrounded pebbles, with some small cobbles and rare

larger cobbles, in matrix of very dark gray (10YR 3.1) sandy silt. Some clasts 

striated. Generally structureless, but contains some west-dipping beds of

water-washed sandy gravel. 

2

1

9,360 ± 40

(Beta-156902)

A

B

Figure 117. Exposure Nk-63. South side Noatak River floodplain 

8.5 km above mouth of Kelly River. Measured heights are above 

active Noatak River floodplain.

m 8

4

0

2

1

Note expanded scale

Gravel. Subrounded stones up 

to medium cobble size in sandy 

matrix. Sand bed near upper 

contact. Alluvium.

Silt. Dark brown to dark gray 

waterlaid silt. Capped by sod 

20-25 cm thick. Floodplain 

deposit.

1 3.1

2 4

THICKNESS

(m)

UNIT DESCRIPTION and 

INTERPRETATION

Figure 118. Exposure Nk-64. North side Noatak River 5 km upstream from Kelly River mouth (2 km above Kelly River Ranger Station). 

(A) Measured sections at central and eastern parts of bluff. (B) Exposed face at west end of bluff. Black dot, radiocarbon age 

determination (yr B.P.) with laboratory number in parentheses (see appendix 1). 

Exposure Nk-64

A 20-m bluff at the north edge of the Noatak River’s 

floodplain is partly concealed by vegetation but yielded three 

measured sections (figs. 118A and 118B). The easternmost 

section exposes a complex of glaciolacustrine sediments that 

overlies fluvial gravel. The gravel (unit 1; fig. 118A) is a 

mature fluvial deposit with quartz comprising 5-10 percent 
84 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

of all stones and about 40 percent of the sand matrix. This 

unit may be thicker than shown because its upper contact is 

obscured by drapes of glaciolacustrine sediment on the bluff 

face. Striated clasts are common in both diamict deposits of 

unit 2. The lower diamict (unit 2a) appears to be undisturbed 

glaciolacustrine sediment, but the upper diamict (unit 2c) may 

have been remobilized as a flow. It probably extends upward 

through the slump and flow deposits that are obscured by vegetation. The thin sand bed (unit 2b) between the two diamicts 

probably formed during a brief interval of lake drainage. 

Near its center, the bluff rises 19.5 m to a nearly level terrace-like surface. At the upper contact of the basal gravel (unit 

1; fig. 118A), which is exposed here, a 10-cm-thick transition 

zone to the lower diamict contains interpenetrating tongues of 

stony silt and gravel in some places and mixed structureless 

silty sandy gravel elsewhere. The two diamicts and intervening 

thin sand bed (units 2a-2c) are nearly identical to the corresponding units farther east, but the upper of the two diamicts 

may have been truncated by river erosion because it is overlain 

at a height of only 11 m by probable floodplain silt (unit 3). 

Peat that fills a 4.7-m-deep depression in the silt has a basal 

radiocarbon age of 9,220 ±40 yr B.P. The depression may be 

the site of a thaw pond, or possibly a small stream channel, on 

the former floodplain. 

From the downstream (western) flank of the center exposure, the bluff slopes westward from the 20-m level down to a 

late Holocene terrace or floodplain level (fig. 118B). This section is dominated by westward-dipping beds of silty to sandy 

gravel that are overlain by silt, organic silt, and peat. These 

sediments comprised a detrital wedge of flow deposits that 

was shed from the face of the 20-m terrace during river downcutting. Although beds generally dip westward at low angles, 

some dip more steeply (up to 28°) toward the east and may 

have filled depressions created by thaw of ice-rich permafrost 

or relict glacial ice. Near the west end of the detrital wedge, 

silty fluvial gravel of unit 1 containing small boulders appears 

to be interbedded with the silt of unit 2. Twigs, root balls, and 

other wood fragments within unit 2 occur in peat beds and also 

are dispersed within the silt. Wood fragments from a possible 

thaw-lake deposit are dated at 9,360 ±40 yr B.P. 

Exposure Nk-65

Two exposures were measured in different years short 

distances above the Kelly River Ranger Station (see fig. 116). 

Exposure Nk-65A was examined in 1986, but later became 

obscured. Consequently, a nearby partly vegetated exposure 

(Nk-65B) was the best exposure available for study in 1999.

Exposure Nk-65A (fig. 119A), an 18-m bluff with a 

terrace-like surface, exhibited an alluvial sequence above 

diamict. The diamict was compact and supported vertical 

faces; it probably formed as till rather than glaciolacustrine 

sediment. Its highly irregular stream-eroded upper surface had 

about 2 m relief. Above the till, a fining-upward succession of 

gravel, sand, and silt represented river-channel deposition followed by aggradation of organic-rich floodplain deposits.

Exposure Nk-65B (fig. 119B), measured a short distance 

above the Kelly River Ranger Station, yielded 8.5 m of gravel 

and stony silt exposed beneath 10 m or more of vegetated flow 

deposits. The gravel (unit 1) is similar to fluvial deposits of 

the modern Noatak River, with lenses of small boulders probably representing lag deposits on former channel floors. This 

Figure 119. Exposure Nk-65. 

North side Noatak River short 

distances above Kelly River 

Ranger Station (KRRS), 3 km 

above Kelly River mouth. (A) 

Section measured in 1986 a short 

(but unknown) distance above 

KRRS. (B) Section measured in 

1999 about 150 m above KRRS.

m

20

10

 0

4 1.8

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

Silt. Silt and organic silt, becoming increasingly 

peaty near upper surface. Floodplain deposit.

Sand. Well sorted olive (5Y 4/4) silty fine sand. 

Some thin interbeds of organic silt. Floodplain 

deposit.

2 >1.5

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

Stony silt. Mostly covered with dense shrubs. 

Glaciolacustrine deposit.

1 7 Sandy gravel. Pebbles and small cobbles 

with lenses of nested small boulders. Loosely 

packed. Alluvium.

3 1.3

2 2.6 Gravel. Subrounded pebbles and small cobbles 

in sandy matrix. Alluvium.

Diamict. Rounded to subrounded pebbles and 

small cobbles with some less rounded larger 

clasts up to boulder size. Many faceted and 

striated. Matrix is very compact dark grayish 

brown (10Y 4/2) gritty silt. Till.

1 3.5

2

1

?

m

20

10

 0

2

1

4

3

?

?

?

A

B
Kugururok River to Eli River 85

alluvium is loosely packed and unweathered. It may predate 

glaciolacustrine deposition, but its fresh appearance suggests 

that it may be a Holocene-age river deposit that was covered 

by debris flows from a nearby glaciolacustrine exposure. The 

stony silt (unit 2) contains abundant polished and striated 

stones of glacial origin, and ultramafic lithologies from glacial 

source areas in the De Long Mountains dominate the larger 

clasts. This unit mostly is covered by dense shrub vegetation, 

but the headwall of a thaw amphitheater from which the flow 

issued is visible farther upslope.

Exposure Nk-66

A tall bluff with a measured height of about 55 m stands 

along the south side of the Noatak River below the Kelly River 

confluence. The bluff’s face is largely obscured by vegetated slump 

blocks (fig. 120), but a near-vertical exposure at its base exhibits 

diamict in a highly compact matrix that contains little or no clay 

(unit 1). The diamict probably was deposited as till. Slump blocks 

above the till (unit 2a) have remained coherent although displaced 

downward on the bluff face. They expose horizontally bedded fine 

sand and silty fine sand that grades upward into probable loess.

Overlying deposits appear to be entirely silt, but are 

poorly exposed on the slumped and vegetated bluff face. Visible parts of units 2b and 2d appear to be nonbedded, and may 

have been deposited as loess. A possible thaw-pond deposit of 

irregularly bedded silt (unit 2c) is exposed in the upper part of 

the bluff face through a section that is steeper and more stable 

than deposits above and below it.

Exposure Nk-67

A 17-m silt exposure with a nearly level upper surface 

(fig. 121) stands along a northwest-facing cutbank of the 

Noatak River. A basal exposure of faintly bedded water-laid 

silt (unit 1) contains peaty beds and mollusk shells through 

a zone about 3.9-4.4 m above the river’s spring-flood level. 

Some vivianite, a mineral that typically forms under waterlogged conditions, also is present within this horizon. Peaty 

beds at 3.9 m height were dated at >43,100 yr B.P.

Silt-rich sediments (unit 2) that appear similar to those 

in the basal exposure extend upward nearly to the top of the 

bluff. These have slumped and flowed, then become revegetated, and consequently are poorly exposed. The section is 

capped by silty sod about 0.5 m thick.

Discussion

Till deposited directly by glacier ice is exposed at two 

localities along the stretch of the Noatak River near the 

Cutler River confluence. Exposure Nk-65A intersects till that 

probably is assignable to the Avan moraine (Hamilton, 2003 

and in press). Farther downriver, the basal till deposit at Nk-66 

probably is an eroded remnant of the north flank of the much 

larger end moraine that was built south of the present course 

of the Noatak River by south-flowing glaciers that issued from 

the De Long Mountains. 

Glaciolacustrine deposits are common along the north 

side of the Noatak River above Kelly River. At Nk-64, two 

Figure 120. Exposure Nk-66. 

South side Noatak River 4 km 

below mouth of Kelly River.

Figure 121. Exposure Nk-67. 

South bank Noatak River 18 

km below mouth of Kelly River. 

Heights measured above recent 

spring-flood level. Black dot, 

radiocarbon age determination 

(yr B.P.) with laboratory number 

in parentheses (see appendix 1). 

m

60

40

20

 0 Diamict. Unsorted stones, many striated, in 

matrix of unsorted silt to granules. Till. 

Poorly exposed. Heavy vegetation cover.

Silt. Fluvial, eolian, and lacustrine(?).

Irregularly bedded. Pond deposit?

Poorly exposed.

Horizontally bedded fine sand and silty 

fine sand. Loosely packed and unstable, 

with all exposures displaced downward 

by slumping. Grades upward into structureless silt (loess). Basal 3.5 m covered.

1 9.3

Covered

2

?

45.4

d

5c

?b

a 12.5

1

2a

2b

2c

2d

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

Note compressed scale

m

20

10

 0

2

1

> 43,100

(Beta-206892)

Silt. Compact, dark gray, faintly bedded.

Contains mollusk shells, peaty beds, and 

vivianite through zone 0.5 m thick. Pond 

deposit.

Silt. Poorly exposed because of heavy 

vegetation cover. Appears similar to unit 1. 

Origin uncertain.

1 ca. 7

2 ca. 10

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION
86 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

glaciolacustrine units are separated by a thin sand deposit. As 

seen in bluff exposures farther upvalley, such brief interruptions 

in glaciolacustrine sedimentation are common in settings where 

glacier dams are breached and their lakes drain abruptly via 

outburst floods. Continued glacier flow can rapidly repair an 

ice dam, permitting the lake to refill soon after it drains.

A terrace at about 18-20 m height underlain by silty floodplain deposits is present at the center section of Nk-64 and at Nk65A. Two similar radiocarbon ages indicate that downcutting from 

this terrace level was underway by early Holocene time.

The tall bluff at Nk-66 is difficult to interpret owing to 

displaced and vegetated slump blocks, but the 18-20 m river 

terrace may also be present here. The horizontally bedded 

fine sand seen at about 13-16 m height in displaced slump 

blocks resembles the eolian-dominated floodplain deposits 

described at Epiguruk, a bluff on the Kobuk River, by Ashley 

and Hamilton (1993) and Hamilton and Ashley (1993). 

Loess deposition would have commenced when the river 

abandoned this terrace level. If this interpretation is correct, 

then an astonishing body of loess about 37 m thick would have 

accumulated during Holocene time at Nk-66.

The 17-m bluff exposure at Nk-67 has a terrace-like 

surface that probably correlates with the 18- to 20-m terrace 

remnants farther upvalley. Rather than alluvium, however, 

exposed lower parts of the bluff face yielded pond and marsh 

deposits with abundant detrital wood and mollusk shells. A 

non-finite radiocarbon age (>43.1 ka) on the detrital wood 

is ambiguous. The wood may have been eroded from older 

sediments farther upvalley and transported downstream to this 

site. Alternatively, the lower part of the deposit truely may be 

this old, and would be separated from overlying much younger 

floodplain deposits by an unconformity concealed beneath 

vegetated slump and flow debris.

Kelly-Avan Drainage System

Introduction

The Avan River joins the Kelly River just 2 km above the 

Kelly River’s mouth (see fig. 116). The narrow bedrock valley of 

the Avan River, which was scoured during the Avan (Itkillik II) 

ice advance, contrasts markedly with the Kelly River’s broad valley floor, which is covered with glaciolacustrine deposits. Only 

two low exposures of alluvial gravel (Avan-1 and Avan-2) were 

measured along Avan River near the mouth of its bedrock valley.

The Kelly River system above the Avan confluence 

consists of the Kelly River trunk stream, it’s informally named 

“west fork,” and Wrench Creek (fig. 116). During the Avan 

glaciation, only very small glaciers advanced short distances 

from high-level cirques, and most valley floors below about 

290 m (950 ft) altitude were inundated by a glacial lake. Five 

bluff exposures (Kly-1 through Kly-5) along Kelly River and 

the lower courses of its principal tributaries intersect glaciolacustrine deposits assignable to that lake stage. Because these 

deposits are similar in character and in age, their exposures 

are described together as a set. An additional exposure (Kly6), described separately, intersects the outer flank of an end 

moraine in the upper valley of Wrench Creek.

Exposure Avan-1

A terrace exposure along the east side of Avan River 

near the range front intersects possible drift of Avan (Itkillik 

Phase II) age (see fig. 116). Poorly exposed diamict overlies 

an unusual lithified gravel (fig. 122). The gravel (unit 1) is 

weakly bedded and indurated throughout. It locally contains 

veins of crystalline calcite. Resistant lithologies such as 

quartzite are little weathered, but probable mafic or ultramafic 

rock types have been reduced to a fine-grained mudlike substance. The gravel is heavily jointed, with joint planes passing 

through rather than around clasts. A block of sediment 2.5 m 

thick dips eastward at 5° to 6°, but beds elsewhere dip toward 

the northeast at about 12°.

The overlying diamict (unit 2) appears to be a poorly 

sorted, nonstratified, bouldery deposit. Its gray matrix generally is obscured by brown silt that drapes over the terrace face. 

The diamict probably is till, but alternatively it could be gravel 

with lag boulders which became intermixed on the bluff face.

Exposure Avan-2

A short distance upvalley from Avan-1, an isolated elongated knob of gravel on the valley floor is an eroded remnant 

of a formerly more extensive valley-filling deposit. The knob’s 

Figure 122. Exposure Avan-1. East 

side Avan River 33 km above its mouth.

m

20

10

0

2

1

?

Indurated gravel. Rounded to subrounded pebbles and cobbles, with 

some sandy beds and lenses 10-20 cm 

thick and some cobble-rich lenses. 

Locally lithified, with joints and calcite

veins. Some stones completely weathered. 

Dip angles up to 12o. Tertiary(?) alluvium.

Diamict. Poorly exposed. Till or gravel.

1 12.5

2 4.2

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION
Kelly-Avan Drainage System 87

river-cut flank exposes clasts up to cobble size, with no boulders present (fig. 123). All rock types are those common to the 

De Long Mountains.

Exposures Kly-1 through Kly-5

The five glaciolacustrine exposures (figs. 124A through E) 

exhibit stony silt that contains clasts up to small boulder size 

that commonly are striated. Lithologies vary slightly between 

the exposures, but quartzite, ultramafic rocks, and black chert 

Figure 123. Exposure Avan-2. West side Avan River 1.5 km above 

Exposure Avan-1.

m

15

10

 5

 0

Gravel. Pebbles, small 

cobbles, and sparse

larger cobbles in sandy 

matrix. Lithologies include 

black chert, quartzite, and 

pyroxenite. Alluvium.

12.5

THICKNESS

(m)

DESCRIPTION and 

INTERPRETATION

generally are abundant at each site. Matrix material at exposures Kly-1 through Kly-3 is dark gray, gritty, slightly clayey 

silt. At Kly-4 and Kly-5, farther up the Kelly River and its 

“west fork,” the matrix is mixed sand and silt which probably 

reflects sediment influx from tributary drainages into the lake. 

At all exposures, the glaciolacustrine deposits flow readily, 

with flows commonly originating at amphitheater-shaped 

headwalls. At Kly-1 and Kly-3, the glaciolacustrine units 

directly overlie bedrock. At Kly-4, a muddy well sorted gravel 

consisting of pebbles and small cobbles and lacking any larger 

stones underlies the glaciolacustrine unit. This may be deltaic 

sediment deposited by the “west fork” stream into the margin 

of the expanding glacial lake. Further lake rise would have 

overwhelmed the delta and flooded the site.

Exposure Kly-6

The stream-cut outer face of an end moraine at the headward forks of Wrench Creek stands 23 m high (fig. 125), but 

a vegetated slope rises inland an additional 17 m to the crest 

of a prominent boulder-littered morainal ridge. The bluff face 

exposes structureless limestone and chert rubble that reflects 

short transport distances from nearby sources.

m

20

10

 0

m

20

10

 0

m

25

15

10

5

10

5

20

0

?

1 8.5-10?

THICKNESS

(m)

UNIT DESCRIPTION and

 INTERPRETATION

THICKNESS

(m)

UNIT DESCRIPTION and

 INTERPRETATION

THICKNESS

(m)

UNIT DESCRIPTION and

 INTERPRETATION

Stony silt. Stones to small 

boulder size, in matrix of 

clayey silt. Glaciolacustrine 

deposit.

-- 14-15.5? Bedrock. Black shale. 

Upper surface obscured 

by drapes of stony silt, and 

may stand higher than 

exposed height.

1

1 17.5-16.5

THICKNESS

(m)

UNIT DESCRIPTION and 

INTERPRETATION

Stony silt. Striated and 

faceted clasts up to 70 cm 

diameter in matrix of dark 

gray, gritty, slightly clayey 

silt. Glaciolacustrine 

deposit.

16

THICKNESS

(m)

DESCRIPTION and 

INTERPRETATION

Stony silt. Slightly clayey, 

gritty silt, containing clasts 

to small boulder size. 

Glaciolacustrine deposit.

-- 2-3 Bedrock. Black shale. 

Erosional upper surface.

1

A

B

C

m

20

10

 0

2 11.7 Stony mud. Clasts up 

to 70 cm diameter in

matrix of mixed sand

and silt. Glaciolacustrine 

deposit.

1 1.6 Muddy gravel? Pebbles 

and small cobbles in muddy matrix. Deltaic deposit?

0

2

1

0

6.7 Bedrock. Quartzite interbedded with black shale. 

Erosional upper surface.

1 14.5 Stony silt. Generally subangular pebblesand cobbles 

with some very small boulders

in matrix of very gritty silt. 

Capped by 40 cm slightly stony, 

frost-mixed silt beneath thin sod

mat. Glaciolacustrine deposit.

m

15

 0

1

D

E

Figure 124. Exposures Kly-1 through Kly-5. Exposures of 

glaciolaustrine deposits in Kelly River drainage system. All 

bluff faces disturbed by flowage. (A) Exposure Kly-1. South 

bank Wrench Creek 15 km above its mouth. (B) Exposure Kly-2. 

West bank Wrench Creek 4 km above Kly-1. (C) Exposure Kly-3. 

East side Kelly River 3 km above “west fork” confluence. (D) 

Exposure Kly-4. South side “west fork” Kelly River 4 km above its 

mouth. (E) Exposure Kly-5. East side Kelly River 11.5 km upvalley 

from mouth of “west fork,” near mouth of small west-flowing 

tributary stream.
88 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

valleys along the northwest flank of Maiyumerak Mountains. 

Those channels then combine into a single stream that flows 

southwestward to join the Eli River.

Two exposures along Eli River intersect glaciolacustrine 

deposits within the broad basin floor (Eli-1) and at its eastern 

edge (Eli-2). The two exposures measured along Uvgoon 

Creek are more diverse. Exposure Uv-2 is a deltaic deposit 

along the east margin of the glacial lake, whereas Uv-1 is the 

stream-cut southeast flank of a high-standing morainal ridge.

Exposure Eli-1

A 6-m-high exposure along the west shore of an oxbow 

lake near the Eli River-Uvgoon Creek confluence consists of 

an amphitheater-headed flow deposit (fig. 126). Exposed in the 

headwall are unsorted clasts up to about 40 cm diameter in a 

matrix of clayey, sandy silt. Ultramafic rock types are abundant, with quartzite and black chert also common.

Beyond the flow headwall, an irregular surface rises 16 

m higher to a level plain that stands 22 m above the oxbow 

lake. The sediment underlying this surface is silt-rich but 

generally concealed; it may be stone-free. Slumps rather than 

flows are the dominant form of deformation, further indicating 

that the silt could have been deposited as loess rather than 

glaciolacustrine sediment. 

Exposure Eli-2

A south-facing 14-m bluff at the mouth of Eli River’s 

bedrock valley exposes nonsorted clasts dispersed in a silty 

to sandy matrix that only locally contains traces of clay (fig. 

127). Clast lithologies dominantly are ultramafic rock types, 

quartzite, limestone, and black chert derived from the De 

Long Mountains.

A boulder line across the midpart of the bluff contains the 

largest boulders visible along the bluff face, and these clasts 

perhaps were ice-rafted to this locality when the glacial lake 

stood briefly at its highest level. The boulders may have been 

concentrated into a lag deposit by fluvial scour during a subsequent episode of lake drainage.

Figure 125. Exposure Kly-6. At headward forks of Wrench Creek 

7.5 km northwest of Ampitheatre Mountain.

Figure 126. Exposure Eli-1. North side Eli River floodplain near 

mouth of Uvgoon Creek.

Discussion

The gravel exposed at Avan-1 is a highly altered deposit 

with an unusual degree of lithification, weathering, and 

structural deformation; and with crosscutting veins and joints. 

It probably is very old, indicating that the U-shaped trough 

occupied by Avan River may have been eroded by glaciers in 

early Pleistocene or perhaps late Tertiary time. Alternatively, 

its unusual degree of alteration may be due to faulting along 

the range front, which focused deformation here and allowed 

access of mineralizing fluids. The overlying diamict may be 

till dating from the glacial advance of Avan age, but it is poorly 

exposed and therefore both age and origin are uncertain. The 

gravel of exposure Avan-2 is part of an erosion remnant that 

stands to about the same height as the gravel unit at Avan-1. 

However, the two gravel deposits differ in composition and in 

postdepositional alteration, and therefore must have formed 

at different times. The highly indurated gravel at Avan-1 may 

have created a resistant barrier behind which valley-filling 

gravel (of which Avan-2 is a remnant) accumulated.

The glaciolacustrine deposits at exposures Kly-1 through 

Kly-5 probably were formed in a single water body that filled 

the lower valleys of Kelly River, its “west fork,” and Wrench 

Creek. Unsorted clasts to boulder size within the lake deposits 

indicate the presence of a nearby calving glacier; most likely 

the glacier that filled Avan River valley, as indicated in fig. 116. 

Matrix material at the five glaciolacustrine exposures generally is 

similar, but contains more clay at downvalley sites and is sandier 

closer to the mouths of tributary streams farther upvalley.

The till exposed at Kly-6 was deposited by a short valleyhead glacier that issued from relatively high-standing cirques 

along the north flank of Amphitheatre Mountain during Avan 

time. Similar short glaciers formed at this time near the heads of 

Kelly River and its “west fork.” These lie beyond the north margin of fig. 116, but are shown elsewhere (Hamilton, in press).

Eli-Uvgoon Drainage System

The Eli River flows westward past the south flank of 

Maiyumerak Mountains, then crosses a broad lake-dotted 

basin before joining the Noatak River (see fig. 116). Uvgoon 

Creek, a northern tributary to the Eli, issues from several 

m

25

 0

23.1+

THICKNESS

(m)

DESCRIPTION 

and INTERPRETATION

Diamict. Unsorted and 

unstratified, angular to

subangular clasts; some 

striated. Most 8 cm or 

smaller in diameter, but 

some boulders up to 90 cm 

diameter also present. Till.

m

25

15

10

5

20

0

?

Covered

6+

THICKNESS

(m)

DESCRIPTION 

and INTERPRETATION

Stony silt. Subrounded 

to subangular pebbles,

cobbles, and some small 

boulders in matrix of

clayey, gritty silt. Some 

clasts striated. Flows

readily. Glaciolacustrine 

deposit.
Eli-Uvgoon Drainage System 89

Figure 127. Exposure Eli-2. North bank Eli River near south flank 

of Maiyumerak Mountains. 

Exposure Uv-1

The southeast flank of a prominent ridge just north of 

Maiyumerak Mountains was steepened at some time in the past 

by stream erosion, forming a weathered face 31 m high (fig. 128). 

This surface is littered with pebbles, small cobbles, and less abundant larger clasts up to 1.5 m long. Lithologies are typical De Long 

Mountains rock types. Dunite, pyroxenite, and limestone containing black chert predominate, with gray quartzite also present.

m

15

 0

 5

 10

14.2

THICKNESS

(m)

DESCRIPTION 

and INTERPRETATION

Stony silt. Nonsorted and 

nonstratified clasts up to 

cobble and rarely boulder 

size in matrix that fines 

upward from silty sand at 

base to sandy silt near top. 

Some clasts striated. Largest 

boulders, up to 90 cm long, 

form line across midpart of 

exposure. Capped by 60 cm 

brown silt that is stony near 

base and peaty near top. 

Glaciolacustrine deposit.

Two benches at the base of the ridge are apparent terraces 

of river-worked gravel that have an exposed thickness of 6 m. 

Clasts are better sorted and less weathered than those exposed 

along the ridge flank, and limestone is the dominant rock type.

Exposure Uv-2

Deltaic gravel (fig. 129) is exposed along the east side of 

a tributary to Uvgoon Creek just beyond the northwest flank 

of Maiyumerak Mountains. This exposure, which stands 11.3 

m high, is part of a terrace system created by stream incision 

into a fan-delta complex that had formed at the margin of a 

glacial lake (see fig. 116). The exposure consists of a nearly 

uniform set of foreset beds that strike N25°E to N50°E and 

dip northwest at 24°-28°. Pebble-small gravel predominates, 

with some sandy layers and lenses also present. Some layers 

are highly cemented by carbonates and stand in vertical faces. 

Stones, which include ultramafic lithologies, greenstones, 

quartz, limestones, and dark gray sandstone, commonly have 

carbonate crusts on their undersides. The terrace is capped 

by frost-mixed stony brown silt. Its upper surface is entirely 

vegetated, with frost hummocks common.

A set of lower (5- to 8-m) terraces on the opposite side 

of the stream from Uv-2 has gravelly surfaces covered with 

only patchy vegetation. These terraces must be significantly 

younger than the terrace at Uv-2.

Figure 128. Exposure Uv-1. 

Stream-cut flank of morainal 

ridge 0.8 km north of Uvgoon 

Creek 17 km southeast of 

mouth of Kelly River. Measured 

downslope from ridge crest.

Figure 129. Exposure Uv-2. East side of unnamed southern tributary to Uvgoon Creek 21 km south-southeast 

of mouth of Kelly River, near northwest flank of Maiyumerak Mountains. 

m

0

20

10

30

40

1

2

Covered

Diamict. Rounded to subrounded pebblesmall-cobble gravel with dispersed 

boulders up to 1.5 m length. Larger clasts 

poorly sorted to unsorted, rounded to subangular, with ultramafic lithologies common. 

Bears loess cap 1 m or less thick. Base 

covered. Till.

Gravel. Clasts well sorted with cobbles

dominant. Limestone abundant in cobble

range. Clasts retain original surfaces, 

with only minor surface etching. Base

covered. Alluvium.

1 31+

2 6+

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

Channel

m

NORTHWEST SOUTHEAST 15

 0

2 <1

THICKNESS

(m)

UNIT DESCRIPTION and INTERPRETATION

Silt. Frost-mixed stony brown silt. Loess.

1 10.5 Gravel. Pebbles and small cobbles with

some sandy layers and lenses. Beds dip

northwest at 24° to 28°. Carbonate 

cement common. Deltaic deposit.

1

2
90 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

Discussion

Three of the four exposures described from the EliUvgoon drainage system contain glaciolacustrine sediments. 

Exposures Eli-1 and Eli-2 exhibit unweathered sediment that 

must date from the youngest lake stage of probable Avan 

(Itkillik II) age. The clayey gritty silt matrix at Eli-1 is typical 

of offshore glacial-lake deposits, whereas the sandier matrix 

at Eli-2 reflects input of fluvial sediments into the glacial 

lake as part of a fan-delta complex near its margin. The 

altitude of Eli-2, about 90 m (300 ft), may be representative 

of at least part of the youngest lake stage that filed the lower 

Noatak basin and extended north into the Kelly River valley 

system. As at Nk-66, Eli-1 may contain a poorly exposed but 

substantial thickness of loess. Silt may have been scoured by 

strong upvalley (southerly) winds from the lower Noatak basin 

(Hamilton, in press) shortly after lake drainage and before the 

newly exposed fine-grained sediments became covered by 

vegetation. The silt then would have been deposited as loess 

across and beyond the northern part of the basin.

Uv-2 is a typical lake-margin delta deposit that formed 

at an altitude of about 210 m (700 ft) near the northwest 

flank of Maiyumerak Mountains. This lake margin stood 

about 120 m higher than the fan-delta deposits examined at 

Eli-2, and it could represent an older and higher lake stage. 

This inference is supported by the high degree of carbonate 

cementation in the deltaic exposure, and by its silt-covered, 

vegetated, frost-heaved upper surface.

Clasts exposed on the flank of the end moraine at 

Uv-1 are dominantly of De Long Mountains lithologies, 

indicating that the moraine probably was built by glaciers that 

originated in the valleys of Kugururok and Avan Rivers and 

flowed directly south across the Noatak valley floor. Previous 

mapping (Hamilton, 2003 and in press) suggested that the 

moraine probably is of Makpik (Itkillik I) age.

The weathered moraine flank at Uv-1 contrasts with 

the unweathered limestone clasts of the two stream terraces 

at its base, which retain their original depositional surfaces 

and show only minor solutional etching. A similar relation 

exists at Uv-2, where the silt-covered, vegetated, frostheaved surface of the higher terrace contrasts with the 

largely barren gravelly surfaces of a set of lower terraces. 

The little-weathered terraces at these two sites may represent 

an interval of area-wide alluviation and downcutting that 

perhaps is correlative with glaciation and glacial-lake 

formation of Avan age.

Summary and Regional Relations

More than 100 bluffs along the Noatak River and its 

tributaries that were measured and examined during 1979-

2005 have been illustrated and discussed in this report. Forty 

eight of those bluffs were dated by radiocarbon.

In the upper Noatak River valley, river-bluff exposures 

provide a cross-section through an end-moraine complex that 

correlates with the Itkillik II glaciation of the central Brooks 

Range on the basis of surface morphology, soil and weathering 

characteristics, and radiocarbon ages (Hamilton, 1986). Lacustrine and slackwater deposits that formed as the glacier receded 

from its end moraine were laid down between 15 ka and 9.3 ka.

Moraines and outwash correlated with two substages of 

Itkillik I glaciation in the central Brooks Range are exposed 

farther downvalley in the eastern part of the Noatak River’s 

upper basin. These deposits locally are unstable and are being 

displaced laterally toward the river by underlying flows of 

clayey sediment. The terminus of the glacier of Itkillik I age 

must have extended into a lake dammed by contemporaneous ice advances farther downvalley. A large kettle, evident in 

outwash of Itkillik II age where it overlaps Itkillik I deposits, demonstrates that glacier ice persisting from the Itkillik 

I glaciation was still present at the time of the Itkillik II ice 

advance. Multiple terraces in the end-moraine zone reflect 

successive levels at which the Noatak River flowed during late 

Itkillik I time, during deposition of Itkillik II outwash, and 

during subsequent Holocene downcutting. 

Two bluffs (An-1 and Nk-21) in the Aniuk area expose glacial and interglacial deposits of pre-Itkillik age. The 78-m-high 

bluff at An-1 contains multiple alluvial and glaciolacustrine 

units and deeply buried peat beds. This bluff and its organic 

record deserve further examination. Exposure Nk-21, which 

stands to 70 m height, has a water-scoured, terrace-like surface 

that was created by the Noatak River flowing at a very high 

level, probably during glacial recession from the Cutler advance. 

It therefore may record an early post-Cutler interglacial stage.

The Cutler River drainage system, in the south-central 

part of the Noatak River’s upper basin, is the largest southern 

tributary to the Noatak River. The Cutler moraine was formed 

by a very large glacier that flowed southeastward out of the 

De Long Mountains; it covered the Noatak valley floor, and 

expanded eastward to the present mouth of the Cutler River. 

The glacier blocked the lower course of that river, deflecting 

it eastward to its present position. Although of middle Pleistocene age (Sagavanirktok River age in the central Brooks 

Range glacial succession), the Cutler advance has no exact 

equivalent in the central Brooks Range. It may be correlative 

with the very large glacier that built the Baldwin Peninsula 

moraine in the Kotzebue Sound region, perhaps about 500-600 

ka (Huston and others, 1990).

Widespread flow deposits of Cutler age around the mouth 

of Cutler River have exposed thicknesses of about 40 m. They 

demonstrate that the Cutler advance terminated in a deep 

proglacial lake. Much of the Cutler drainage system remained 

unglaciated during Cutler and younger advances, but was filled 

with proglacial lakes assignable to Cutler and succeeding lake 

stages (Hamilton, 2001): 

Makpik and Anisak 300 m asl (1,000 ft)

Okak 365 m asl (1,200 ft)

Cutler and older 520 m asl (1,700 ft)
Summary and Regional Relations 91

Along the Cutler River, exposure Cu-7 exhibits peat 

and sand that span the last glacial maximum (the Itkillik 

II advance), as documented by radiocarbon dating. This 

demonstrates that marshy conditions with restricted 

drainage prevailed during Itkillik II time, probably 

promoted by rising base level due to glacier dams farther 

down the Noatak valley. This part of the Cutler drainage 

must have been a biologically rich environment during the 

last glacial maximum, a condition highly unusual within the 

Brooks Range at that time. An older succession of marsh 

deposits at Cu-7 may have accumulated until shortly after 

46.8 ka, but this age determination needs to be confirmed 

by redating using the AMS method.

Through the western part of the upper Noatak basin 

or Aniuk Lowland (between Cutler River and New 

Cottonwood Creek) many of the higher bluffs along the 

Noatak River record the series of end moraines that were 

deposited by glaciers that flowed southeastward from the 

De Long Mountains subsequent to the Cutler advance. 

Those glaciers crossed the valley center and dammed a 

succession of proglacial lakes. Till of the oldest moraine 

(the Okak moraine) is not evident at the surface across the 

valley center, but forms the core of the prominent Okak 

Bend and is exposed at Nk-29. This till overlies the Old 

Crow tephra at that exposure, and therefore is younger than 

the last interglacial maximum (marine-isotope stage 5e). 

Successively younger moraines are the Makpik (broadly 

eroded in the valley center and not exposed in the bluffs), 

the Anisak (exposed at Nk-34), and Anisak recessional 

moraines (one of which is exposed at Nk-37). The moraines 

and their associated lake levels have been discussed and 

illustrated in a previous publication (Hamilton, 2001), 

which concluded that in the western Aniuk Lowland the 

Cutler water plane was at 425 m (1,400 ft) asl, the Okak at 

325 m (1,100 ft) asl, and the Anisak at 300 m (1,000 ft) asl. 

These surfaces are 50-100 m lower than comparable lake 

stands in the eastern part of this lowland, where greater 

isostatic uplift took place owing to the more extensive 

glacier cover over the central Brooks Range.

Lower bluffs through the western part of the 

upper Noatak basin reflect alluvial-terrace formation 

through a series of downcutting stages beginning about 

13 ka. Downcutting was rapid at first, yielding almost 

indistinguishable radiocarbon ages on successively lower 

terraces between about 30 m and 10 m height.

Downstream from Nimiuktuk River, the Noatak 

River was displaced southward by south-flowing glaciers 

that issued from higher parts of the De Long Mountains. 

Through the stretch between the Nimiuktuk and Kugururok 

Rivers, the Noatak occupies a generally narrow and rockwalled valley that is much more constricted than within the 

upper and lower basins. During Makpik and Anisak times, 

individual glaciers flowed southward out of the De Long 

Mountains through major valley systems. Glacier dams 

formed at the mouths of Kaluktavik, Kugururok, Avan, and 

Cutler River valleys during Makpik time, but only at the 

mouth of Avan River valley during the subsequent much 

more limited Avan (Itkillik II) glaciation. Glacial lakes at 

about 400 m (1,300 ft) asl are associated with the Makpik 

advance; lakes at about 300-350 m (1,000-1,150 ft) asl are 

correlated with the Avan advance. A spectacular exposure 

of relict glacier ice was examined in 1986 at Nk-59, but 

was no longer visible when that bluff was revisited 14 years 

later.

The final stretch of the Noatak River valley along 

which bluffs were examined extends from Kugururok 

River to Eli River and constitutes the northern part of the 

lower Noatak basin or Mission Lowland. An end moraine 

parallels the Noatak River to the south through much of 

this stretch. It probably is of Anisak age, but is buried and 

largely obscured beneath lacustrine sediments and loess 

and could not be examined directly. The Avan moraine, 

equated with the last glacial maximum (LGM) and the 

Itkillik II glaciation of the central Brooks Range, also is 

partly obscured by lake sediments, but is well exposed near 

the south flank of the De Long Mountains and in a bluff 

face (Nk-65A). Most exposures in the Kelly River drainage 

system exhibit glaciolacustrine sediments correlated with 

the LGM, which document filling of lower and middle 

valleys to about 290 m (950 ft) asl by elongate arms of a 

proglacial lake. Moraines of Avan age in the Kelly River 

system were restricted to heads of the larger valleys and to 

the mouths of short cirque-headed tributaries. During this 

and preceding lake stages, flow from the Eli River built 

a large fan-delta complex into standing water bodies that 

filled the Mission Lowland. Thick loess was generated from 

the barren mud-covered floor of this basin each time the 

lake drained. Loess blankets much of the Kugururok-Eli 

Rivers area, and may be as thick as 37 m at Nk-66.

Most of the radiocarbon ages from the higher and older 

bluffs along the Noatak River and its principal tributaries 

are non-finite, indicating that the glacial, glaciolacustrine, 

and interglacial alluvial deposits exposed there are all 

older than about 50 ka. (The few apparently finite ages are 

suspect because of large counting errors, and several of 

them have been demonstrated to be incorrect by later AMS 

radiocarbon dating.) These very old ages support recent 

mapping in the De Long Mountains, which has shown that 

the glacial advances of the LGM (Itkillik II) time were 

very limited in extent (Hamilton, in press). Similar very 

restricted glaciation of LGM age has been reported from 

parts of easternmost Russia by Gualtieri and others (2000) 

and by Brigham-Grette and others (2003). A few non-finite 

ages were obtained on detrital wood, commonly identified 

as spruce, found within terrace deposits that clearly are 

postglacial in age. Those wood pieces must have been 

redeposited from older sediments that date back to the 

maximum of the last interglacial, when spruce expanded 

into parts of the Noatak River valley, or to preceding 

interglacials.
92 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

Acknowledgments

My work in the Noatak River valley spanned more than 

25 years and involved a very large number of colleagues. I 

apologize to any that I might have neglected to include here.

The initial phases of the project (1979-92) were 

supported initially by the USGS Branch of Alaskan Geology 

as part of a regional mapping program; later partial support 

was through the USGS Climate History Program. Pollen 

analyses were provided by Thomas Ager (USGS). Field 

assistance during different years was provided by Kim 

Ashley, Dan Bauer, George Lancaster, Dave Logan, Chuck 

Moore, Doug Van Etten, and Toby Wheeler. Dave Logan, 

Chuck Moore, and Bo Wilmer digitized the maps and 

stratigraphic sections that cover the eastern half of the study 

area (the upper valley and upper basin of the Noatak River). 

Gail M. Ashley, who accompanied our field party on a 

traverse down the western sector of the Noatak River in 1983, 

provided invaluable insights into depositional environments 

and other characteristics of the bluff sediments that we 

measured and examined that year.

The National Science Foundation (NSF), through grants 

OPP-9424279 and OPP-0002362 to Scott A. Elias and 

Mary E. Edwards, supported our sampling and analyses of 

organic deposits in selected bluffs during 1993-2000. Other 

participants in this phase of the project were paleobotanists 

Nancy H. Bigelow and Andrea P. Krumhardt, geochronologist 

Glen W. Berger, and tephra specialist Shari J. Preece. Initial 

identification of the Old Crow tephra in bluffs Nk-26 and 

Nk-29A was provided by James E. Begét.

The National Park Service (NPS) provided logistical 

support for the NSF-funded projects, and later furnished 

funds for completion of my field mapping and bluff recording 

in the western part of the Noatak National Preserve. Robert 

Gal, NPS archeologist, was instrumental in arranging for 

helicopter logistics, field support, and funding during 1992-

2003; and Bruce A. Giffen, NPS geologist, provided funding, 

logistical support, and field assistance during completion 

of the project in 2004-06. Additional support for final 

preparation of the report was provided by the USGS National 

Surveys and Analysis Project (Alaska Section) under the 

direction of F.H. (Ric) Wilson.

During final preparation of this report I relied heavily 

on two very capable associates. Linda-Lee Harris (USGS) 

digitized the base maps and stratigraphic sections that cover 

the western part of the study area, and upgraded all of the 

other illustrations to her uniformly high standard of quality. 

Linda also prepared much of the radiocarbon date list and 

formatted the final text and illustrations. Julie A. Esdale 

(Brown University) provided invaluable editorial assistance. 

She compiled the initial drafts of the glossary and part of the 

radiocarbon date list, searched out references, and checked 

figures and text for inconsistencies.

The report has benefited from careful reviews by Julie 

Esdale and Bruce Giffen. Their helpful comments and 

suggestions are greatly appreciated.

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Richmond, G.M., and Fullerton, D.S., 1986, Introduction to 

Quaternary glaciations in the United States of America, 

in Richmond, G.M., and Fullerton, D.S., eds., Quaternary 

Glaciations in the United States of America: Quaternary 

Science Reviews, v. 5 (Quaternary Glaciations in the Northern Hemisphere), p. 3-10.

Wahrhaftig, Clyde, 1965, Physiographic provinces of Alaska: 

U.S. Geological Survey Professional Paper 482, 52 p., 6 

plates.

Waitt, R.B., Jr., 1980, About forty last-glacial Lake Missoula 

jökulhlaups through southern Washington: Journal of Geology, v. 88, p. 653-679.

Walder, J.S., and Costa, J.E., 1996, Outburst floods from 

glacier-dammed lakes—The effect of lake drainage on flood 

magnitude: Earth Surface Processes and Landforms, v. 21, 

p. 701-723.

Appendix 95

Appendix 1—Radiocarbon age determinations from river 

bluffs within Noatak National Preserve
96 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

Appendix 1. Radiocarbon age determinations from river bluffs within Noatak National Preserve.

[yr B.P., years before present; ht, height]

Bluff exposure no. Age (yr B.P.) Laboratory no. 1 Material dated Stratigraphic position 2

and prior publications 3

Exposures Along Noatak River

Nk-3 10,000 ±145 I-11,423 Peat Base of floodplain deposit above gravel

Nk-4 >40,000 I-12,512 Wood Small abraded detrital fragments; probably

redeposited

Nk-7 2,660 ±80 I-12,511 Peat Near base of bluff cap

Nk-8 9,280 ±150 I-13,396 Peat At alluvial-deltaic contact (1)

Nk-8 15,030 ±200 I-12,514 Wood and rootlets Near top of lacustrine beds (1)

Nk-11 34,010 ±350 USGS-2453 Peaty silt Base of upper diamict; probably redeposited (1)

Nk-11 30,070 ±470 USGS-1835 Organic silt 2 m below top of fine alluvium (1)

Nk-11 34,840 ±950 USGS-1836 Organic silt 4 m below top of fine alluvium (1)

Nk-11 34,990 ±230 USGS-2454 Peaty silt Within lower diamict (1)

Nk-13 30,160 ±410 USGS-1837 Rootlets and organic 

detritus

Alluvium 8.5 m above river (1)

Nk-14 3,710 ±90 I-13,448 Wood (Salix) In growth position 13 m above river

Nk-14 4,220 ±110 I-13,521 Peat Buried tundra soil

Nk-14 3,110 ±90 I-12,515 Wood (Salix) In growth position; in slump block?

Nk-19 6,050 ±120 I-13,522 Peat Near exposed base of massive peat 3.3 m 

above river

Nk-22 13,160 ±160 USGS-1838 Rootlets In poorly exposed sand above glaciolacustrine

deposit

Nk-26 >47,000 USGS-1840 Wood fragments Within capping sand at 32 m ht (2) (3)

Nk-26 >49,500 USGS-1457 Wood fragments Floodplain deposit at 9.5 m ht (2) (3)

Nk-27 1,570 ±90 USGS-3401 Wood (Populus) Log in low terrace opposite exposure Nk-27

Nk-28 >57,000 USGS-1841 Organic silt Floodplain deposit at base of lower diamict (3)

Nk-29A >46,400 AA20752 Peat with wood Floodplain deposit; 17.5 m ht (3)

Nk-29A >51,000 USGS-1842 Peat Ice-wedge cast in alluvium; 16m ht (2) (3)

Nk-29A 52,500 +2,700 /-2,000 USGS-1843 Humic silt Channel fill in floodplain deposit; 17 m ht (2) (3)

Nk-31 >49,000 USGS-3402 Wood (Picea) Floodplain deposit near river level (3)

Nk-31A 5,000 ±60 AA20753 Wood (Populus) 9 m terrace; near base of floodplain unit

Nk-32 35,000 ±2300 I-13,466 Peat Paleosol within alluvium; 12.5 m ht (3)

Nk-32A 9,655 ±75 AA20756 Peat 14 m terrace; peaty channel fill; 3 m depth (3)

Nk-32A 10,085 ±95 AA20754 Woody peat 14 m terrace; peaty channel fill; 6 m depth (3)

Nk-32A 10,205 ±80 AA20755 Peat 14 m terrace; base of peaty channel fill (3)

Nk-32B 4,610 ±60 AA20757 Peat 14 m terrace; base of capping peat unit

Nk-32B 11,310 ±85 AA20758 Peat 12.5 m terrace; within overbank unit; 

5.8 m depth (3)

Nk-32C 930 ±60 USGS-3404 Peat 4.5 m terrace; in floodplain deposit

Nk-33 12,890 ±190 I-12,542 Peat 14.5 m terrace; base of sandy floodplain deposit:

8.5 m ht (3)

Nk-33 12,970 ±280 I-12,517 Peat 14.5 m terrace; base of depression fill in floodplain deposit: 10.5 m ht (3)
Appendix 97

Appendix 1. Radiocarbon age determinations from river bluffs within Noatak National Preserve—Continued.

Bluff exposure no. Age (yr B.P.) Laboratory no.1 Material dated Stratigraphic position 2

and prior publications 3

Nk-33 13,620 ±95 AA20770 Detrital twigs 14.5 terrace; base of sandy floodplain deposit:

8.5 m ht (3)

Nk-35A 9,565 ±90 AA20762 Wood (Salix) Near top of depression fill; 31.8 m ht (3)

Nk-35A 9,830 ±75 AA20771 Wood (Salix) Log near top of silt and peat unit; 2.2 m depth (3)

Nk-35A 10,560 ±80 AA20786 Peat Base of silt and peat unit; 3.9 m depth (3)

Nk-35A 10,720 ±85 AA20761 Wood (Salix) Base of silt and peat unit; 28.1 m ht (3)

Nk-35A 13,640 ±80 USGS-3406 Peat Bryophyte mat in eolian sand at 26 m ht (3)

Nk-35A 40,180 ±750 USGS-3405 Peat Diapiric extrusion near river level at downstream 

end of bluff (3)

Nk-35A >44,800 AA20759 Wood fragments Diapiric extrusion near river level at downstream 

end of bluff (3)

Nk-35A >45,200 AA20760 Wood fragments Peaty layer in postglacial kettle fill at 23 m ht; 

probably redeposited (3)

Nk-37 33,690 ±300 USGS-1846 Wood (Picea/Larix) Distal part of detrital wedge near bluff 

center (3) (4)

Nk-37 36,610 ±400 USGS-3287 Peat Floodplain deposit below upper diamict; 

E sector of bluff (3) (4)

Nk-37 44,800 +3000/-2200 USGS-3408 Silty peat Distal part of debris wedge near bluff 

center (3) (4)

Nk-37 >42,000 USGS-3407 Wood (Salix) Distal part of debris wedge near bluff 

center (3) (4)

Nk-37 >46,000 USGS-1845 Wood (Picea/Larix) Detrital wood in imbricated gravel unit; 

E sector of bluff (3) (4)

Nk-37 >48,440 Beta-156895 Wood Floodplain deposit below upper diamict; 

E section of bluff (4)

Nk-37 >48,740 Beta-156896 Wood fragments

 in peat

Floodplain deposit below upper diamict; 

E section of bluff (4)

Nk-44 >45,800 Beta-206893 Detrital wood Near base of alluvial gravel; 36 m ht

Nk-44 >45,800 Beta-206894 Detrital wood Near base of alluvial gravel; 36 m ht

Nk-47 13,310 ±40 Beta-156904 Detrital wood Near base of floodplain unit above gravel; 

20 m ht (5)

Nk-47 13,370 ±50 Beta-156903 Rodent feces Near base of floodplain unit above gravel; 

20 m ht (5)

Nk-48 >57,000 USGS-2456 Detrital wood Alluvium beneath till; ca. 6 m ht

Nk-48 >57,000 USGS-2457 Peat Alluvium beneath till; ca. 6 m ht

Nk-49 13,140 ±40 Beta-156900 Woody peat Silt with peat lenses near bluff crest (5)

Nk-50B 25,060 ±230 Beta-206891 Detrital wood Near base of floodplain deposit above 

gravel; 24 m ht

Nk-54A 11,910 ±180 I-14,680 Detrital wood (Salix) Near base of floodplain deposit above 

gravel; 3 m depth

Nk-54B >45,800 Beta-206890 Detrital wood Within fluvial gravel; 6 m ht

Nk-59 5,710 ±120 I-14,682 Peat Base of “chaos” unit (kettle fill); 17 m ht

Nk-59 7,540 ±130 I-14,681 Peat Near base of silt cap

Nk-59 8,805 ±40 USGS-2460 Peat Alluvium interstratified with diamict; 12 m ht

Nk-59 >58,000 USGS-2459 Detrital wood (Picea) In upper gravel; 29 m ht
98 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

Appendix 1. Radiocarbon age determinations from river bluffs within Noatak National Preserve—Continued.

Bluff exposure no. Age (yr B.P.) Laboratory no. 1 Material dated Stratigraphic position 2

and prior publications 3

Nk-64 9,220 ±40 Beta-156899 Peat Base of peat-filled depression; about 14 m ht (5)

Nk-64 9,360 ±40 Beta-156902 Wood Organic silt unit in detrital wedge (5)

Nk-67 >43,100 Beta-206892 Peat Pond deposit; 3.9 m ht

Exposures Along Aniuk River

An-1 39,700 ±1600 USGS-1665 Peat Mid part of upper glaciolacustrine unit

An-1 >39,500 USGS-1666 Silty peat 2 m above base of upper glaciolacustrine unit

An-2 >48,000 USGS-1667 Peat Upper contact of alluvial gravel; 13 m ht

An-5 8,210 ±130 I-13,232 Wood (Salix) In channel fill; 3.8 m ht

An-5 8,530 ±140 I-13,231 Wood (Salix) Base of peaty channel fill; about 2.5 m ht

Exposures Along Cutler River

Cu-2 7,280 ±120 I-13,449 Wood (Salix) Near base of sand above gravel and diamict

Cu-4 >50,000 USGS-1839 Wood and plant 

remains

Near base of upper glaciolacustrine unit

Cu-5 >40,000 I-13,465 Wood (Salix) In bedded sand that overlies diamict

Cu-7 17,980 ±120 USGS-1452 Peat Peaty sand in slump block near top of bluff

Cu-7 27,530 ±350 USGS-1453 Peat Near base of sand with peat beds; above gravel

Cu-7 46,800 +1,400 /-1,200 USGS-1454 Wood and peat In fine sand and silt near bluff base

Cu-8 >38,000 USGS-1652 Wood (Salix) Near top of gravel that overlies deltaic unit

Cu-8 >40,000 I-12,516 Peat and bark Near top of deltaic and lacustrine unit

Cu-8 42,600 ±1,100 USGS-1651 Wood (Salix) Near base of deltaic and lacustrine unit

Cu-12 43,600 ±1,300 USGS-1649 Peat Within peaty silt above glaciolacustrine unit

Cu-12 >48,500 USGS-1648 Peat Near base of peaty silt above glaciolacustrine unit

Exposures Along Imelyak River

Im-1 9,455 ±40 USGS-1455 Peat Base of peat cap above outwash gravel

Im-1 >48,000 USGS-1456 Detrital wood Near top of bedded sand below outwash gravel

Exposures Along New Cottonwood Creek

Ctn-1 >47,590 Beta-156894 Detrital wood (Picea?) Alluvial gravel; 6.8 m ht

Exposures Along Kaluktavik River

Kl-3 2,760 ±40 Beta-206889 Peat Floodplain-loess contact; 70 cm depth

Exposures Along Kugururok River

Ku-1 9,440 ±40 Beta-156898 Peat Near base of peat above glaciolacustrine unit; 

1.0 m depth

Ku-3 43,480 ±1,230 Beta-156901 Peat Peat mat in ice-rich deposit; about 7 m depth

Exposures Along Sapun Creek

Sp-1 >43,300 Beta-188261 Peat Lacustrine or slackwater deposit beneath 

till; 7.8 m ht

Sp-1 >43,300 Beta-188262 Peat Lacustrine or slackwater deposit beneath

till; 7.8 m ht

Sp-2 >47,590 Beta-156894 Detrital wood Channel fill near top of gravel; 40 m ht

Sp-2 >48,280 Beta-156893 Detrital wood Near top of deltaic beds; 31 m ht

aRadiocarbon labs: AA, University of Arizona; Beta, Beta Analytic; I, Isotopes, Inc.; USGS, U.S. Geological Survey, Menlo Park, Calif.

b Heights are above river level; depths are below ground surface.

c

 (1) Hamilton and others, 1987; (2) Elias and others, 1999; (3) Hamilton, 2001; (4) Edwards and others, 2003; (5) Hamilton, 2003.
Appendix 99

Appendix 2—Clast Lithologies of Tills and Glaciolacustrine 

Deposits, Central and Western Aniuk Lowland

Introduction

Highland source areas to the east, south, north, and northwest fed glacial sediments into 

the central and western Aniuk Lowland, where they are exposed in bluffs along the Noatak and 

lower Cutler rivers. Granitic rocks were derived from highlands to the east around the Noatak’s 

headwaters; schist with abundant vein quartz and diverse metasedimentary rocks were transported via southern tributaries to the Noatak River, especially down the extensive Cutler River 

drainage system. Distinctive ultramafic rocks such as gabbros and pyroxenites (Nelson and Nelson, 1982) were carried southward from the Siniktanneyak Mountain area, and ultramafic rocks 

as well as chert and other sedimentary lithologies traveled southeastward from sources farther 

west in the De Long Mountains.

To assist in determining source areas for till deposits and glaciolacustrine sediments in this 

part of the Aniuk Lowland, clast lithologies were recorded from nine of the bluffs along the 

Noatak River between Nk-22 and Nk-36 and from two additional bluffs (Cu-1 and Cu-4) near the 

mouth of Cutler River. Although 50 clasts were counted in most cases, as few as 25 or as many 

as 100 were tabulated depending on their abundance and accessibility. These diverse stone counts 

were reduced to percentages to facilitate comparisons between stratigraphic units or between river 

bluffs. In several cases (for example, Nk-22), separate counts were made on clasts of different 

sizes from the same stratigraphic unit to investigate how size influences the rock types represented and their relative proportions.
100 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

Stone Counts

Exposure Nk-22

Clasts exposed on surface of debris flow (unit 1).

Cobbles; 28 counted Percent 

Quartzites 25

Pyroxenite 17

Aphanitic igneous rx 14

Misc. metamorphic rx 14

Granitic rx 11

Chloritized rx 11

Marble 8

Pebbles; 90 counted Percent

Quartzites 28

Schist with vein quartz 22

Black chert 17

Pyroxenites 13

Miscellaneous 20

 

Exposure Nk-23 

Clasts exposed on surface of debris flow (unit 1).

Large cobbles and boulders; 30 counted Percent

Gabbros 30

Gray quartzites 27

Ferruginous quartzites 13

Limestone/marble 7

Granite 7

Chlorite schist 7

Black chert breccia 3

Gneiss 3

Slate 3

Pebbles; 100 counted Percent

Pyroxenites 19

Gray-green quartzites 17

Ferruginous sandstone 15

Red, gray, & brown cherts 15

Black cherts 10

Green aphanitic igneous rx 10

Miscellaneous 6

Quartz and quartz w/ schist 4

Granitic rx 1

Exposure Nk-24

Clasts exposed on surface of debris flow (unit 1).

Boulders; 100 counted Percent

Gabbros-syenites 48

Gray quartzites 24

Gray limestone 16

Ferruginous quartzites 8

Basalt 4

Pebbles; 98 counted Percent

Black chert 44

Gabbro types 18

Ferruginous quartzites 12

Basalt 9

Red chert 9

Schist 4

Granite 2

Quartz 2

Exposure Cu-1

Clasts exposed on surface of debris flow (unit 1).

Large cobbles and small boulders (100) Percent

Quartzites 48

Gabbros 28

Misc. igneous rx 12

Limestone 4

Quartz 4

Leucocratic granite 4

Pebbles; 34 counted Percent

Quartzites 58

Black chert 24

Green chert 12

Gray chert 6

Exposure Cu-4

Pebbles from lower and upper glaciolacustrine units. 

Lower Diamict (unit 1); 50 counted Percent

Green porphyritic igneous rocks 22

Gray quartzites 14

Black chert 12

Gray limestone 10

White quartz 10

Leucocratic granite 6

Black phyllite 6

Green dike rx 6

Gray chert 4

Misc. (5 rx., 2percent each type) 10

Upper diamict (unit 4); 50 counted Percent

Gabbro and gabbro-like rx 32

Black chert 18

Green chert 16

Green dike rx 14

Ferruginous quartzite 6

Gray limestone 4

Quartzite 4
Appendix 101

Leucocratic granite 4

Chloritic schist 2

Exposure Nk-25

Pebbles from glaciolacustrine deposit (unit 1);

50 counted Percent

Quartz and quartz w/ schist 44

Phyllitic schist 18

Limestone-dolomite-marble 16

Sandstone-mudstone 8

Misc. igneous rx 6

Quartzite 4

Gray chert 4

Exposure Nk-26

Stones from lower and upper glaciolacustrine units.

Lower stony mud (unit 2); 50 platy cobbles Percent

Gray quartzite 30

Gray limestone 22

Black and gray chert 16

Dark, coarse crystalline rx 16

Dark, fine crystalline rx 16

Limestone 3

Upper stony mud (unit 6); 34 cobbles? Percent

Gray quartzite 35

Gabbro-like dark crystalline rx 35

Basalts 15

Felsic igneous rx 6

White quartz 3

Chert breccia 3

Exposure Nk-27 

Pebbles from lower and upper diamicts.

Lower diamict (unit 2); 50 counted Percent

Porphyritic dark igneous rx 28

Aphanitic green igneous rx 24

Chert 22

Gray & ferruginous quartzites 22

Quartz and quartzose schist 4

Upper diamict (unit 4); 50 counted Percent

Chert 28

Aphanitic green igneous rx 18

Quartz & quartzose schist 14

Dark porphyritic igneous rx 14

Quartzites 8

Graywackes 6

Chert breccia 2

Miscellaneous 10

Exposure Nk-30

Stones from lower and upper diamicts.

Lower diamict; 50 pebbles counted Percent

Chert (equal amts black 

 and green) 28

Dark green igneous rx 22

Gray quartzite 18

Aphanitic green igneous rx 12

Gray limestone 12

Quartz with schist 4

Siltstone 2

Ferrugineous quartzite 2

Upper diamict; 25 boulders counted Percent

Igneous rx 68

Quartzites 28

Marble 4

Exposure Nk-34

Pebbles from debris flow; 50 counted Percent

Chert (mostly black) 38

Coarse-grained igneous rx 16

Quartzites 16

Aphanitic igneous rx 12

Slates 8

Limestone-dolomite-marble 8

White quartz 2

Exposure Nk-36

Clasts exposed on surface of debris flow.

Boulders; 50 counted Percent

Gray quartzite 30

Carbonate rx 30

Coarse-grained crystalline rx 28

Aphanitic igneous rx 6

Chert breccia 2

Conglomerate 2

Chert 2

Pebbles; 50 counted Percent

Chert 32

Aphanitic igneous rx 22

Coarse-grained igneous rx 20

White quartz 12

Granite 4

Limestone 4

Miscellaneous 6
102 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

Discussion

Exposure Nk-22, about 3 km up the Noatak River 

valley from the Cutler moraine front, intersects a terracelike 

depositional surface 40-45 m high. Its diamict may be either 

a remnant of a Cutler-age proglacial deposit that has been 

truncated by erosion or a glaciolacustrine deposit that postdates 

the Cutler advance. The abundant cherts and quartzites in its 

pebble assemblage are comparable to clasts in deposits farther 

downvalley that were derived from the De Long Mountains. 

However, the assemblage also contains abundant schist derived 

from the southern Brooks Range. The cobble assemblage, which 

includes pyroxenite, granitic rocks, and several metamorphic 

rock types, also indicates derivation from multiple sources 

around the central and western Aniuk Lowland.

Three nearly identical bluff faces (Cu-1, Nk-24, and 

Nk-23) intersect the outer part of the Cutler moraine. Cu-1 

and Nk-24 are situated only 2 km apart near the mouth of 

the Cutler River; Nk-23 stands 2.5 km northeast of Nk-24. 

All three bluffs contain a single basal unit of glaciolacustrine 

sediment about 40-45 m thick that largely is obscured by 

debris flows. Boulder samples from the three exposures are 

very similar, with gabbros and quartzites comprising 70-80 

percent of the assemblage at each bluff. The gabbros were 

derived from Siniktanneyak Mountain (north of Feniak Lake), 

and were transported southward either by ice rafting or within 

a glacier tributary to the Cutler glacier. Granites derived 

from intrusions at the head of the Noatak valley are present 

at two of the localities. In contrast, pebble compositions of 

the three diamicts are very different. For example, quartzites 

are dominant at Cu-1, but much less abundant at Nk-23 and 

Nk-24; those at Nk-24 dominantly are ferruginous, whereas 

those at Nk-23 are a gray-green variety.

Exposure Cu-4, 3.7 km up the Cutler River from Cu-1, 

exposes two glaciolocustrine units. The lower diamict contains abundant limestone, quartz, granite, phyllite, and an 

aphanitic green igneous rock; lithologies derived from the 

southern Brooks Range and from intrusions near the Noatak 

headwaters. This assemblage differs significantly from those 

of the glaciolacustrine deposits around the mouth of the Cutler 

River. The upper diamict, in which cherts and gabbro-like 

rocks predominate, differs in important respects from the 

diamict at Cu-1. Black and green cherts are about equivalent 

in abundance at the two sites, but gabbro-like igneous pebbles 

predominate at Cu-4 whereas quartzites are dominant at Cu-1. 

However, lithologies of the mafic pebbles at Cu-4 resemble 

those of the gabbro boulders at Cu-1, Nk-23, and Nk-24, indicating that the four diamicts indeed could be correlative. 

The thick glaciolacustrine deposits at exposure Nk-25, 

only 2.5 km downvalley from the Cutler River mouth, might 

be expected to correlate with the bluff deposits exposed 

around the Cutler moraine. However, Nk-25 intersects a terracelike surface about 45 m high which appears comparable 

to the surface at Nk-22 and the surfaces farther downriver at 

Nk-26 and Nk-27; its diamict also has a stratigraphic position similar to that of the upper glaciolacustrine deposits at 

Nk-26 and Nk-27. Pebble composition of the diamict at Nk-25 

should be an ideal way to test these correlations, but its pebble 

assemblage is unique. Schist, vein quartz, and sedimentary and 

metasedimentary rock types predominate, indicating southerly 

sources and probable transport into the Noatak River via the 

Cutler River system. The De Long Mountains, primary source 

for the clasts farther downriver (as discussed below), were a 

negligible source for the pebbles at Nk-25.

Exposures Nk-26 and Nk-27, which are about 6 km apart, 

intersect a depositional surface about 40 m high that formed 

within the Cutler moraine following a nonglacial interval. 

Each exposure contains two diamicts separated by nonglacial 

alluvium and paleosols. The lower diamict appears to be a glaciolacustrine deposit at Nk-26 but a true till at Nk-27. These 

two deposits may represent maximum and recessional phases 

of the Cutler ice advance, or they could represent separate 

glaciations. Unfortunately, cobbles were sampled at Nk-26 

(incidental to fabric studies), whereas a standard pebble count 

was carried out at Nk-27. The pebbles from Nk-27 dominantly 

are coarse- and fine-grained igneous rocks, chert, and quartzites, and are close in composition to other diamicts derived 

from the De Long Mountains. The lower diamict at Nk-26 also 

appears to show a characteristic De Long Mountains “signature.” The upper diamict at each exposure, a glaciolacustrine 

deposit that rises to about 30 m height, should be correlative 

between the two sites. It may have formed in front of the 

Makpik moraine, derived from glacier sources in the De Long 

Mountains, which crosses the Noatak valley center a short distance downvalley. At Nk-27, the upper diamict contains abundant chert and igneous-rock pebbles, but schist also is abundant and graywackes are common. This assemblage indicates 

that DeLong Mountains lithologies may have been mixed with 

clasts derived from the southern Brooks Range. The upper 

diamict at Nk-26 should be equivalent to that of Nk-27, but the 

composition of its cobble assemblage is markedly different. 

Differing clast sizes may account for part of this contrast, but 

source areas also may differ between the two deposits.

Exposure Nk-30, at Okak Bend, probably intersects 

the north lateral moraine of the Cutler glacier, which flowed 

southeastward from the DeLong Mountains. Pebbles from 

the basal till unit are dominantly chert, igneous rocks, and 

quartzite, a characteristic DeLong Mountains assemblage that 

is common in exposures farther downvalley (for example, 

Nk-34 and Nk-36). Boulders from the upper diamict, a 

glaciolacustrine deposit probably associated with the Makpik 

moraine, also are primarily igneous rocks and quartzite of De 

Long Mountains derivation.

At exposures Nk-34 and Nk-36, pebble counts were 

taken from debris flows on diamicts interpreted to be proximal 

glaciolacustrine deposits associated with the Anisak moraine. 

Pebble assemblages from the two diamicts are nearly identical. 

Chert is dominant at both sites, followed by aphanitic and 

coarse-grained igneous rocks, which are about equal to each 

other in abundance. However, white quartz also is abundant 

at Nk-36 whereas quartzites are about equally numerous at 

Nk-34. These two similar lithologies possibly were not carefully 
Appendix 103

differentiated during the pebble counts. A boulder count from 

Nk-36 shows some similarities to the pebble count, but also 

striking differences. For example, chert, the dominant pebble, is 

rare in the boulder range. It may occur only in thin beds where 

eroded from outcrop, or it may be so brittle or highly fractured 

that it is unable to survive transport as large clasts. 

Conclusions

Clast lithologies from the westernmost sites, Nk-36, 

Nk-34, and Nk-30, have similar compositions that are compatible with a source area in the De Long Mountains northwest 

of the Aniuk Lowland. The progressive upvalley increase in 

limestone pebbles from Nk-36 (4percent) to Nk-34 (8percent) 

and Nk-30 (12percent), as well as the presence of quartz with 

schist at Nk-30, could reflect increased admixture of upvalley 

lithologies as glaciers advanced eastward up the Noatak valley. 

Diamicts from bluffs farther upvalley show more pronounced 

admixture of lithologies from other sources to the north 

(Siniktanneyak Mountain gabbros and pyroxenites), to the 

east (granitic rocks from the valley head), and south (schists, 

marbles, and other metamorphic rocks from the southern 

Brooks Range).

Near the mouth of the Cutler River the depositional 

record becomes extremely complex. Neighboring exposures 

of almost certainly correlative diamicts contain pebble 

assemblages that are strikingly different. However, boulder 

counts are more consistent. They confirm that the three 

exposures into the Cutler moraine contain correlative diamicts, 

and they indicate that the Cutler ice advance included a 

significant northern component—possibly a tributary glacier 

from Siniktanneyak Mountain.

The younger glaciolacustrine deposits inset within the 

Cutler moraine are more diverse, but they also appear to 

contain a characteristic signature—rock types derived from 

the upper Noatak River and from its southern tributaries. 

Whereas ice-proximal deposits of Cutler age contained 

sediments derived dominantly from the Cutler lobe, the 

younger glaciolacustrine deposits associated with more distant 

ice fronts were not dominated by a single source and therefore 

contain a more mixed assemblage of sediments.

The greater heterogeneity of pebbles relative to bouldersized clasts at most sites probably is due to incorporation of 

interglacial alluvium, which fills the valley center today and 

is conspicuous in Pleistocene deposits exposed in river bluffs 

throughout the upper Noatak basin. This alluvium, generally 

pebble-to-small cobble gravel, must have been incorporated 

into glaciers advancing into the Aniuk Lowland and became 

a major component of their debris load at localities along the 

valley center. Reworked interglacial alluvium was even more 

important where glaciers from the DeLong Mountains flowed 

upvalley into the lowland. Those glaciers would have fronted 

in proglacial lakes, and therefore lacked the extensive outwash 

streams that transport alluvium away from an ice front.

The glaciolacustrine deposits in the Aniuk Lowland clearly 

are mixtures of sediments derived from multiple source areas. 

The dominance of individual source areas may have varied 

with time, being reflected in clast compositions that differ 

vertically within a deposit. Any such changes would be masked 

where sediments have been mixed by flowage down bluff 

faces as, for example, at Nk-22 through Nk-24. Many of these 

sediments also would have been recycled from one glaciation 

to the next rather than being flushed out of the basin through its 

narrow outlet. These complications make the rich Quaternary 

depositional record of the Aniuk Lowland difficult to interpret.
104 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

A

abandoned channel A stream channel along 

which runoff no longer occurs.

ablation The wasting of glaciers by melting 

and evaporation.

active layer A surface layer of ground 

above permafrost that freezes each winter and 

thaws each summer. Its thickness ranges from 

several centimeters to a few meters.

aggradation Building upward of a stream 

bed by accumulation of sediments. 

alluvial Pertaining to or composed of 

alluvium (sediment deposited by a stream or 

running water). 

alluvial fan A low, relatively flat to gently 

sloping mass of loose rock material, shaped 

like an open fan or a segment of a cone, with 

its apex pointing upstream. Deposited by a 

stream (a) where it issues from a narrow mountain valley and enters a plain or broad valley, 

or (b) where a tributary stream approaches or 

enters a main stream. It is steepest near the 

mouth of a mountain valley, and slopes outward with gradually decreasing gradient.

alluvium A general term for clay, silt, sand, 

gravel, or similar unconsolidated detritus that is 

deposited by a stream or other body of running 

water. Forms sorted or semisorted sediment in 

the stream bed or on its flood plain or delta, or 

as a fan at the base of a mountain slope.

angular Having sharp edges and corners. 

Indicates that a sedimentary particle has 

undergone little or no abrasion during 

transport.

aphanitic A fine-textured igneous rock in 

which the crystalline components are too 

small to be distinguishable by the unaided eye.

apparent dip The angle that a bedding 

or fault plane makes with the horizontal, 

measured in any random, vertical section 

rather than perpendicular to the strike. It can 

vary from nearly zero to nearly the true dip, 

depending on whether the vertical section is 

close to the direction of the strike or of the dip.

Arctic Brown soil A soil in which the 

surface organic horizon (A horizon) directly 

overlies a brown oxidized B horizon. 

autochthonous Formed or produced in the 

place where now found. Applied to peat or 

other organic deposits that originated at the 

place where their constituent plants grew and 

died. 

Avan A glacial advance down Avan valley 

in the western De Long Mountains that intersected and dammed the Noatak River Refers 

also to the time that advance took place (as in 

Avan time or Avan age). 

B

ball and pillow structure A sedimentary 

structure that forms where a sandy bed overlies mud. A shock or other disturbance can 

cause the sandy layer to founder into the mud 

and to break up into hemispherical or kidneyshaped masses resembling balls and pillows. 

basin A low-lying area with low relief. 

Also applied to the area drained by a river or 

stream (as in drainage basin or river basin).

bedding plane A planar or nearly planar 

bedding surface that visibly separates each 

successive layer of stratified sediment or 

rock from the preceding or following layer.

It commonly marks a change in the environment or process of deposition, and may show 

a separation, a color difference, or both.

bench A long, narrow, relatively level or 

gently inclined strip or platform on a valley 

side or bluff face that is bounded by steeper 

slopes above and below. Appears as a terrace 

or steplike ledge breaking the continuity of a 

slope. Formed by differential erosion of sediments or rocks of varying resistance, or by a 

change in base level of erosion.

bluff A high bank with a steep face overlooking a river or its floodplain, or bodies of 

water such as lakes and seas. Especially common on the outside of stream meanders.

bottomset beds Horizontal or gently 

inclined layers of sediment deposited in front 

Glossary

Definitions of geologic terms used in this report were compiled by Julie A. Esdale from the 

American Geological Institute’s Glossary of Geology (Jackson, 1997). The definitions were 

then edited to better reflect specific usage of those terms within this report.
Glossary 105

of the advancing foreset beds of a delta or of 

a bed form within a river channel. 

boulder size Refers to rounded rock particles with diameters of 25.6 cm or more.

breccia A coarse-grained clastic rock 

composed of angular broken rock fragments. 

It differs from conglomerate in that the fragments have sharp edges and unworn corners. 

Commonly originates as a result of talus 

accumulation.

bryophyte A nonvascular plant that may 

have differentiated stems and leaves, but that 

has no true roots. Commonly refers to mosses.

C

calcareous algae A group of algae that 

remove calcium carbonate from the shallow 

water in which they live and secrete or deposit 

it as a more or less solid calcareous structure. 

calcite A common rock-forming mineral 

composed of calcium carbonate (CaCO3). 

It usually is white to colorless, but also may 

exhibit pale shades of gray or yellow. It is the 

principal constituent of limestone and speleothems (cave deposits), and also occurs in 

crystalline form in marble. Veins of calcite are 

abundant in metamorphic rocks of the Baird 

Mountains and south-central Brooks Range.

carbonate (a) A mineral compound that 

contains the negative ion CO3

-2. Calcite and 

aragonite, CaCO3, are common examples. (b) 

A sediment or sedimentary rock formed by 

precipitation from aqueous solution of carbonates of calcium, magnesium, or iron (for 

example, limestone and dolomite).

carbonate rock A sedimentary rock composed of more than 50 percent by weight of 

carbonate minerals, as described above.

cement Mineral material, usually chemically precipitated, that occurs in the spaces 

among the individual grains of a consolidated 

sedimentary rock, thereby binding the grains 

together as a rigid, coherent mass. The most 

common cements are silica (quartz, opal, 

chalcedony), carbonates (calcite, dolomite, 

siderite), and various iron oxides. Detrital 

clay minerals and other fine clastic particles 

also may serve as cements.

chert A hard, extremely dense or compact, 

dull to semivitreous microcrystalline or 

cryptocrystalline mineral that consists 

dominantly of interlocking minute crystals 

of quartz or masses of amorphous silica. It 

has a tough, splintery to concoidal fracture, 

and may be white or colored gray, green, 

red, yellow, brown, or black. Chert occurs 

principally as segregations (nodules) and 

less commonly as layered deposits (bedded 

chert) in limestones and dolomites. The 

term flint is sometimes used for the dark 

variety of chert.

clast An individual constituent, grain, or 

fragment of a sediment or rock, produced by 

the mechanical weathering (disintegration) 

of a larger rock mass. Generaly used in this 

report for particles larger than sand size.

clay size A term used in sedimentology for 

particles with diameters of 1/256 (0.004) mm 

or less.

climbing ripples A series of cross-laminae 

produced by superimposed migrating ripples, 

in which the crests of vertically succeeding 

laminae appear to be advancing upslope. 

Common in deltaic deposits.

cobble size Rounded to subangular rock 

particles with diameters between 6.4 cm and 

25.6 cm.

colluvium A general term applied to any 

unconsolidated, heterogeneous mass of soil 

material and/or rock fragments deposited 

by rainwash, sheetwash, solifluction, or 

creep. Usually accumulates on lower parts of 

hillslopes. May include talus where closely 

intermixed with finer-grained deposits.

conglomerate A coarse-grained 

sedimentary rock, composed of rounded to 

subangular particles larger than 2 mm in 

diameter of varied size and composition set 

in a fine-grained matrix of sand or silt, and 

commonly cemented by calcium carbonate, 

iron oxide, silica, or hardened clay. 

Represents the consolidated equivalent of 

gravel both in size range and in the roundness 

and sorting of its constituent particles.

couplets Genetically related paired 

sedimentary laminae, generally occurring 

in repeating series as varves, but applied to 

other laminated sediments that do not form as 

annual paired deposits.

crinoidal limestone A limestone consisting 

almost entirely of the fossil skeletal 

parts of crinoids (cup-shaped organisms 

attached to the sea floor by long segmented 

stalks). The stalks are the component most 

commonly preserved.
106 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

cross bedding Cross-stratification (see 

below) in which the cross-beds are more 

than 1 cm in thickness.

cross-stratification Arrangement of 

strata inclined at an angle to the main 

stratification. Commonly subdivided into 

(a) cross-bedding, in which the cross-strata 

are thicker than 1 cm, and (b) crosslamination, in which they are thinner than 

1 cm. Probably most cross-stratification 

is produced by the migration of bed 

forms, particularly ripples (which form 

small-scale cross-lamination) and dunes 

or megaripples (which form medium- to 

large-scale cross-lamination or crossbedding).

cryoturbation A collective term used to 

describe the stirring, churning, and all other 

disturbances of soil by frost action (for 

example, frost heaving, frost mixing, and 

solifluction). It produces hummocky terrain 

and/or patterned ground.

crystalline Applied to rocks consisting 

wholly of crystals or fragments of crystals, 

generally in the form of closely fitting or 

interlocking particles (many having crystal 

faces and boundaries). Characteristic of 

igneous rocks that developed through 

slow cooling from a molten state or of 

metamorphic rocks that have recrystallized 

as a result of temperature and pressure 

changes. The term also may be applied to 

certain sedimentary rocks (such as quartzite 

and some limestones) that are composed 

entirely of crystals. 

cut and fill (a) A process of leveling 

whereby material eroded from one place 

is deposited nearby until the surfaces of 

erosion and deposition are continuous 

and uniformly graded. (b) A sedimentary 

structure characteristic of fluvial 

environments in which a channel eroded 

in older sediment is filled with younger 

sediment. 

cutbank A steep bare slope formed by 

lateral erosion of a stream. Most commonly 

formed on the outside of meanders.

Cutler A glacial advance of middle 

Pleistocene age that issued from the De 

Long Mountains and filled the Noatak 

valley floor, extending upvalley as far as 

the mouth of the Cutler River (see fig. 54). 

Refers also to the time that advance took 

place (as in Cutler time or Cutler age).

D

debris flow A moving heterogeneous mass 

of rock fragments, soil, and mud, more than 

half of the particles being larger than sand size. 

delta A low-lying, nearly flat, alluvial tract 

of land at or near the mouth of a river. Generally forms a triangular or fan-shaped plain 

that is crossed by multiple distributaries of 

the main river. Extends beyond the general 

trend of the lakeshore or seacoast in cases 

where the sediment supplied by the river 

accumulates faster than it can be removed by 

tides, waves and currents. 

deltaic Pertaining to or characterized by 

a delta.

detritus A collective term for loose rock 

and mineral material that is worn off or 

removed from older rocks by mechanical 

means (for example, disintegration or abrasion) and transported from its place of origin.

diamict A general term for a nonsorted 

or poorly sorted, nonstratified sediment or 

sedimentary rock that contains a wide range 

of particle sizes. Includes diamictite (lithified diamict) and diamicton (its nonlithified 

equivalent).

diapir A domelike upward squeezing of 

plastic core material which ruptures, upfolds, 

or othewise displaces overlying sediments 

or rocks. Common along the Noatak River 

where sand, gravel, or other clastic sediments overlie clay-rich lacustrine and glaciolacustrine deposits. 

diorite A plutonic rock intermediate in 

composition between silicic (for example, 

granite) and mafic (for example, basalt). 

Dominantly composed of dark-colored 

amphibole (esp. hornblende), plagioclase, 

and pyroxene. Mafic minerals typically comprise less than 50 percent of the rock. 

dip The angle that a structural surface such 

as a bedding or fault plane makes with the 

horizontal, measured perpendicular to the 

strike of the structure and in the vertical plane. 

dolomite A carbonate sedimentary rock of 

which more than 50 percent consists of the 

mineral dolomite, or a variety of limestone or 

marble rich in magnesium carbonate. Dolomite is clearly associated and often interbedded with limestone, and usually represents a 

postdepositional replacement of limestone. 

dropstone An oversized stone in laminated sediment that depresses the underlying 
Glossary 107

laminae and may be covered by “draped” 

laminae. Most dropstones originate through 

ice-rafting.

dunite An ultratamafic plutonic rock that 

consists almost entirely of olivine, with 

accessory chromite generally present. 

E 

earthflow A mass-movement landform 

and process characterized by downslope 

translation of soil and weathered rock within 

well defined lateral boundaries. Initiates as 

a series of slump blocks that detach from 

a headwall scarp. The flow then moves 

downslope above a basal shear surface that is 

more or less parallel with the ground surface, 

and terminates as a lobe-like deposit. Common in ice-rich permafrost, where thaw generates abundant meltwater and the residual 

permafrost surface serves as a shear plane. 

Earthflows grade into mudflows through a 

continuous range in morphology associated 

with increasing fluidity. 

end moraine A ridge-like accumulation of 

debris at the lower or outer end of a glacier.

eolian Pertaining to the wind. Can refer to 

(a) erosion and deposition accomplished by 

the wind, (b) wind-generated deposits such 

as loess and dune sand, and (c) sedimentary 

structures such as wind-formed ripple marks.

erosional unconformity A surface that separates older rocks that have been subjected to 

erosion from younger rocks that cover them.

erratic A rock fragment carried by glacial 

ice, or by floating ice, deposited at some 

distance from the outcrop from which it was 

derived, and generally resting on bedrock of 

different lithology. Size ranges from pebbles 

to house-size blocks.

extrusion Plastic sediment forced or 

pressed out from its initial position.

F 

fabric The orientation in space of the 

elements (for example, clasts, crystals) that 

constitute a sediment or a sedimentary rock.

faceted boulder A boulder that has been 

ground flat on one or more sides by the 

action of natural agents, such as glacier ice, 

streams, or wind.

facies (a) The appearance and characteristics of a sediment or rock unit, usually 

reflecting the conditions of its origin and 

differentiating it from adjacent or associated 

rocks or sediments. (b) A mappable, areally restricted part of a deposit that differs 

in lithology or fossil content from adjoining 

beds deposited at the same time. (c) The environment or area in which a rock was formed 

(for example, eolian facies).

fan A gently sloping, fan-shaped mass of 

detritus forming a section of a very low cone, 

commonly at a place where there is a notable 

decrease in gradient. See alluvial fan. 

fan delta A gently sloping alluvial deposit 

produced where a mountain stream flows into 

a lake or other water body. Normal fan sediment interfingers or intergrades downslope 

with deltaic sediments.

fault A fracture or zone of fractures along 

which there has been displacement of the sides 

relative to one another parallel to the fracture.

fault scarp A steep slope or cliff formed 

directly by movement along a fault and representing the exposed surface of the fault before 

modification by erosion and weathering.

ferrugineous Pertaining to or containing iron (for example, a sandstone that is 

cemented with iron oxide). Imparts a reddish 

or rusty color to the rock or sediment. 

fining upward sequence A sediment succession that becomes progressively finer in 

grain size upward.

fissile Capable of being split easily along 

closely spaced planes.

flame structure A sedimentary structure 

consisting of wave- or flame-shaped plumes 

of mud that have been squeezed irregularly 

upward into an overlying layer. It probably is 

formed by overburden load accompanied by 

horizontal slip or drag. 

floodplain (a) The flat or nearly flat lowland that borders a stream and that may be 

covered by its waters at flood stages. Constructed of generally fine-grained alluvium 

that is carried in suspension by the river during floods and deposited in the sluggish water 

beyond the influence of the swiftest current. 

A river has a single floodplain, but may have 

one or more higher-standing terraces representing abandoned floodplains. 

flow A mass movement of unconsolidated 

material that exhibits a continuity of motion 

and a plastic or semifluid behavior resembling that of a viscous fluid (for example, 

creep, solifluction, earthflow, mudflow, 
108 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

debris flow). Water usually is required for 

most types of flow movements.

flow amphitheater A bowl-shaped depression bordered on its upslope side by a crescentic scarp. Forms the headward portion of 

an earthflow or some types of debris flow.

fluvial Of or pertaining to a river or rivers.

fold A curve or bend of planar structures 

such as bedding planes or rock strata. Usually a product of deformation.

foliation A general term for a planar 

arrangement of textural or structural features 

in any type of rock. Most commonly applied 

to the planar structure that results from flattening of the constituent grains of a metamorphic rock.

foreset beds The inclined and systematically arranged layers within a cross-bedded 

unit. Generally refers to the set of inclined 

layers of sandy sediment deposited upon 

or along an advancing and relatively steep 

frontal slope, such as the outer margin of a 

delta or the lee side of a dune. Progressively 

covers the set of bottomset beds and in turn 

is covered or truncated by the topset beds. 

Foreset beds represent the greater part of the 

bulk of a delta.

fracture A general term for any break in a 

rock, whether or not it causes displacement, 

due to mechanical failure by stress. Fracture 

includes cracks, joints, and faults.

frost churning See cryoturbation.

G

gabbro A dark-colored, mafic intrusive 

igneous rock composed principally of plagioclase and clinopyroxene (augite), with apatite 

and magnetite or ilmenite as common accessory minerals. Gabbro is the approximate 

intrusive equivalent of basalt. 

glacial (a) Of or relating to the presence 

and activities of ice or glaciers (for example, 

glacial erosion). (b) Pertaining to the distinctive features and materials produced by or 

derived from glaciers and ice sheets (for 

example, glacial lakes). (c) Pertaining to an 

episode of glaciation.

glacial lake (a) A lake that derives much 

or all of its water from the melting of glacier 

ice (for example, fed by meltwater), or lying 

on glacier ice and due to differential melting. 

(b) A lake occupying a basin produced by 

glacial deposition (for example, held in by a 

morainal dam). (c) A lake occupying a basin 

produced in bedrock by glacial erosion (for 

example, a cirque lake). (d) A lake occupying a basin produced by collapse of debris 

overlying or surrounding masses of stagnant 

ice (for example, a kettle lake). 

glaciolacustrine Pertaining to, derived 

from, or deposited in glacial lakes. Most 

commonly refers to deposits and landforms 

formed by erosion and deposition around the 

margins of glacial lakes and to the sediments 

that accumulate on their floors.

glacier outburst flood A sudden release of 

meltwater from a glacier or glacier-dammed 

lake, sometimes resulting in a catastrophic 

flood. Generally results from melting of a 

drainage channel through the ice or from 

buoyant lifting of the ice by meltwater.

gneiss A foliated metamorphic rock in 

which bands or lenses of granular minerals 

alternate with bands or lenses dominated by 

flaky to elongate minerals. Commonly rich in 

feldspar and quartz, but mineral composition 

is not essential in its definition. Varieties are 

distinguished by texture (for example, augen 

gneiss), characteristic minerals (for example, 

hornblende gneiss), or general composition 

and/or origins (for example, granite gneiss).

gorge A narrow, deep stream incision with 

nearly vertical rocky walls.

gouge Soft, uncemented, clayey or clay-like 

material, commonly a mixture of minerals in 

finely divided form, found along some faults 

or between the walls of a fault. Formed by the 

crushing and grinding of rock material during 

fault movement, and by subsequent alteration 

by fluids that circulate along the fault. 

graben An elongate depression bounded by 

faults along both sides.

granite An intrusive igneous rock in which 

conspicuous grains of quartz and alkali feldspars are dominant. Muscovite (white mica) 

generally is present also.

granitic Pertaining to or composed of granite.

granule size Refers to rock particles larger 

than very coarse sand and smaller than 

pebbles, having a diameter in the range of 2-4 

mm. Grains are somewhat rounded or otherwise modified by abrasion during transport.

greenstone An informal term applied in the 

field to a compact dark green altered or metamorphosed basic igneous rock (for example, 

basalt or gabbro) that owes its color to the 
Glossary 109

presence of green metamorphic minerals 

such as chlorite or epidote.

greywacke A dark gray, coarse-grained 

sandstone composed of poorly sorted angular 

to subangular grains of quartz and feldspar 

that are associated with abundant dark rock 

and mineral fragments. 

gritty A textural term for soil or sediment 

that contains enough sand-sized particles to 

impart a roughness to the touch. The actual 

quantity of sand usually is small enough that 

sand cannot be seen by the unaided eye.

gyttja A dark, pulpy, freshwater mud characterized by abundant organic matter that is 

deposited in a marsh or lake whose waters 

are rich in nutrients and oxygen.

H 

headwall (a) A steep slope at the head of a 

valley. Most commonly applied to the rock 

cliff at the head of a cirque. (b) The scarp 

at the upslope end of an earthflow or some 

debris flows.

Histosol A soil type in which the upper 

80 cm or more of its profile consists of >50 

percent organic materials. Most Histosols are 

saturated or nearly saturated with moisture, 

and are ice-rich when frozen.

Holocene An epoch of the Quaternary 

period, from the end of the Pleistocene, 

approximately 10,000 years ago, to the present time. Also the events and deposits assignable to that interval.

humic Pertaining to or derived from humus 

(finely divided and partly decomposed 

organic material). 

hummock A small vegetated mound of earth 

or turf. Not diagnostic of permafrost, but most 

common in subpolar and alpine regions.

hummocky A landform with abundant 

hummocks.

humus The generally dark, more or less 

stable part of the organic matter of soil; so 

well decomposed that the original sources 

cannot be identified.

I

ice-contact deposit Stratified sediment 

deposited in contact with melting glacier 

ice. Characteristic landforms include eskers, 

kames, kame terraces, and drift surfaces with 

numerous kettles.

ice-dammed lake A lake held in place by 

the damming of natural drainage by a glacier 

(for example, advancing across a valley or 

crossing the mouth of a tributary valley).

ice-rafted Applied to detritus such as boulders or till which are deposited by the melting 

of debris-laden floating ice. A diagnostic 

component of glaciolacustrine sediments.

ice-stagnation deposit Deposited in contact 

with stagnating or stagnant glacier ice. Synonomous with ice-contact deposit.

ice wedge Wedge-shaped foliated ground 

ice produced in permafrost. Occurs as a vertical or inclined body that tapers downward; 

can be as much as 6 m wide and 30 m deep. 

Ice wedges originate by the growth of hoarfrost or by the freezing of water in a narrow 

crack or fissure produced by thermal contraction of permafrost.

igneous A term applied to rock or minerals 

that solidified from molten or partly molten 

material (magma). Also applied to the processes 

associated with the formation of such rocks. 

imbricated Overlapping, as tiles on a roof. 

Common among platy pebbles and cobbles in 

stream sediments, where this feature serves as 

a flow-direction indicator.

in situ Formed in the place where now located 

(that is, not transported from elsewhere).

indurated A term applied to rocks or sediments hardened or consolidated by pressure 

or cementation.

interfingering The lateral termination of 

sedimentary units through splitting into 

many thin tongues, each of which pinches 

out independently. Results in the intergradation of markedly different sediments or rocks 

through a vertical succession of thin interlocking or overlapping wedge-shaped layers.

interglacial Pertaining to or formed during 

the time interval between two successive 

glacial epochs or between two glacial stages. 

The term implies both the melting of glaciers 

to about their present extent, and the maintenance of a warm climate for a sufficient 

length of time to permit revegetation to occur.

interstadial; interstade A warmer substage 

within a glacial stage, marked by a temporary 

retreat of the ice.

involution A highly irregular, aimlessly 

contorted sedimentary structure consisting of 

local folds and interpenetrations within fine-
110 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

grained material. Developed by the formation, growth, and melting of ground ice in the 

active layer overlying permafrost. 

Itkillik A general term used for glacial 

advances of late Pleistocene age in the central Brooks Range. Subdivided into Itkillik 

I, older advances of the late Pleistocene, and 

Itkillik II, advances of the last (late Wisconsin) glaciation. 

J

joint A planar surface of fracture or parting 

in a rock or compact sediment along which 

no displacement has taken place. Commonly 

occurs as sets of parallel joints. 

joint plane The surface of a joint.

K

kame A low mound, knob, hummock, or 

short irregular ridge, composed of stratified sand and gravel. Initially deposited by 

a subglacial stream as a fan or delta at the 

margin of a melting glacier, by a superglacial 

stream in a depression on the surface of the 

glacier; or as a ponded deposit on the surface 

or at the margin of stagnant ice. Its final form 

reflects partial collapse of the deposit as supporting ice walls melt away. 

kame terrace A terracelike deposit consisting of stratified sand and gravel that formed 

between a melting glacier or a stagnant 

ice lobe and a higher valley wall or lateral 

moraine; and subsequently left standing after 

the disappearance of the ice. Commonly 

pitted with kettles and has an irregular icecontact slope due to collapse as the supporting ice margin melts away.

kettle A steep-sided, usually basin- or 

bowl-shaped depression, commonly without 

surface drainage, in glacial deposits. Commonly contains a lake or marsh. Formed 

by the melting of a large, detached block 

of stagnant ice left behind by a retreating 

glacier, and wholly or partly buried in glacial 

drift. Kettles may range in depth up to tens of 

meters, and in diameter to 10 km or more.

L

lacustrine Pertaining to, produced by, or 

formed in a lake or around its margin.

lag A residual accumulation of coarsegrained sediment that remains on a surface 

or in a stream channel after the finer material 

has been blown away by winds or carried 

away by running water.

lag boulder A boulder-sized clast originally 

present within heterogeneous till or ice-rafted 

deposits. Remains at the site of deposition 

after the surrounding finer material has been 

eroded and transported away.

lamina The thinnest recognizable layer of 

original deposition in a sediment or sedimentary rock; differing from other layers in color, 

composition, or particle size. May be parallel 

or oblique to the general stratification. Generally restricted to sedimentary layers less 

than 1 cm in thickness. Several laminae may 

constitute a bed.

lamination Fine-scale stratification or bedding; typically exhibited by lacustrine and 

eolian deposits.

lateral moraine A low ridge-like mass of 

rock fragments carried on, or deposited at or 

near, the side margin of a mountain glacier. 

Composed chiefly of debris loosened from 

the valley walls by glacial abrasion and 

plucking, or fallen onto the ice from the 

bordering slopes. 

lebensspuren Tracks or burrows of former 

living organisms evident on the bedding 

planes of fine-grained sediments.

lens A depositional unit bounded by converging surfaces that is thickest in the middle 

and thins toward the edges. Resembles a 

convex lens.

limestone A sedimentary rock composed 

chiefly of calcium carbonate, primarily in 

the form of the mineral calcite (that is, more 

than 95 percent calcite and less than 5 percent 

dolomite). Formed by either organic or inorganic processes, and may be detrital, chemical, oolitic, earthy, crystalline, or recrystallized. Many are highly fossiliferous, in some 

cases representing ancient shell banks or coral 

reefs. 

lithify To consolidate from a loose sediment 

to a solid rock.

lithologically immature Term applied to 

clastic sediment that has been differentiated 

or evolved from its parent rock by processes 

acting over a short time and/or with a low 

intensity. Characterized by relatively unstable 

minerals (such as feldspar), abundance of 

mobile oxides (such as alumina), presence 

of weatherable material (such as clay), and 

poorly sorted and angular grains.
Glossary 111

lithology The physical character of a rock.

loess A widespread, homogeneous, commonly nonstratified, porous, friable, slightly 

coherent, fine-grained blanket deposit, consisting predominantly of silt with subordinate 

grain sizes ranging from clay to fine sand; 

generally buff to light yellow or yellowish 

brown. The mineral grains are fresh and 

angular, and generally are held together by 

calcareous cement. Traversed by networks of 

small narrow vertical tubes (frequently lined 

with calcium-carbonate concretions) left by 

successive generations of grass roots, which 

allow the loess to stand in steep or nearly 

vertical faces. Originates as windblown dust 

derived from unconsolidated and unvegetated 

alluvium, outwash, or lake beds uncovered 

by recent lake drainage.

M

mafic A term applied to (a) igneous rocks 

composed chiefly of one or more ferromagnesian, dark-colored minerals, (b) those 

constituent minerals. 

marble A metamorphic rock consisting 

predominantly of fine- to coarse-grained 

recrystallized calcite and/or dolomite, usually 

with a crystalline to sugary texture.

matrix The finer-grained material enclosing, or filling the interstices between, the 

larger grains or particles of a sediment or 

sedimentary rock; the natural material in 

which a sedimentary particle is embedded. The term refers to the relative size and 

disposition of the particles, and no particular 

particle size is implied. 

meander One of a series of regular freely 

developing sinuous curves, bends, loops, or 

windings along the course of a stream. Produced by a stream swinging from side to side 

as it flows across its floodplain.

meltwater Water derived from the melting 

of snow or ice. Commonly forms streams 

that flow within, under, or along the margins 

of melting glacier ice. 

metamorphic Pertaining to the process of 

metamorphism or to its products. 

metamorphism The mineralogical, chemical, and structural adjustment of solid rocks 

to physical and chemical conditions which 

generally have been imposed at depth below 

the surface zones of weathering and cementation, and which differ from the conditions 

under which those rocks originated. 

moraine A mound, ridge, or other distinct 

accumulation of unsorted, unstratified glacial 

drift, predominantly till, that is deposited 

chiefly by direct action of glacier ice. Forms a 

variety of topographic landforms that are independent of the surface on which the drift lies.

mottled Applied to soil, sediment, or sedimentary rock that is marked with spots of different colors, usually as a result of oxidation 

of iron compounds. Soils that are irregularly 

mottled with spots or patches of different colors usually have developed under conditions 

of poor aeration or seasonal wetness.

mud A slimy, sticky, or slippery mixture 

of water and silt or clay-sized earth material, 

with a consistency ranging from semifluid to 

soft and plastic.

muddy Pertaining to or characterized by 

mud (for example, water made turbid by sediment or sediment consisting of mud).

N

non-finite radiocarbon age A radiocarbon 

age given as “greater than” a certain number of 

years. Such an age can be used only as a minimum limit on the antiquity of an organic sample. 

O

openwork A term applied to a gravel that 

contains unfilled voids.

ophiolite An assemblage of mafic and 

ultramafic igneous rocks, including gabbro, 

peridotite, basalts, rocks rich in serpentine, 

and deep-marine sediments. Represents former ocean crust.

outburst episode See glacier outburst flood.

outwash Stratified detritus (chiefly sand 

and gravel) transported from a glacier by 

meltwater streams and deposited in front of 

or beyond the glacier’s end moraine or active 

margin. The coarser material is deposited 

nearer to the ice. 

outwash train See valley train.

overbank deposit Fine-grained sediment 

(fine sand, silt, and some clay) deposited from 

suspension on a floodplain by floodwaters that 

cannot be contained within the stream channel.
112 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

piedmont glacier A broad mass of glacier 

ice at the base of a mountain range or mouth 

of a mountain valley. Formed by the spreading 

out and coalescing of valley glaciers that issue 

from higher elevations of the mountains.

plastic Applied to a sediment or other 

material in which strain produces continuous, 

permanent deformation without rupture. 

platy Applied to (a) a sedimentary particle 

whose length is more than three times its 

thickness, (b) sediment or sedimentary rock 

that splits into laminae having thicknesses in 

the range of 2 to 10 mm.

Pleistocene An epoch of the Quaternary 

period, after the Pliocene of the Tertiary and 

before the Holocene; also, the rocks, sediments, and events assignable to that interval. 

The Pleistocene epoch began 2-2.5 million 

years ago and lasted until the start of the 

Holocene some 10,000 years ago.

polygon A form of patterned ground whose 

mesh is tetragonal, pentagonal, or hexagonal. 

Large polygons arctic regions are formed by 

thermal contraction and are associated with 

ice wedges.

poorly sorted Term applied to clastic sediment or a cemented detrital rock that consists 

of particles of many sizes mixed together in 

an unsystematic matter so that no one size 

class strongly predominates.

postglacial Pertaining to the time interval 

since the disappearance of glaciers from a 

particular area.

primary structure; primary sedimentary structure A sedimentary structure determined by 

the conditions of deposition such as current 

velocity and rate of sedimentation; and developed at the time of deposition. 

proglacial lake A lake formed just beyond 

the front of a glacier, generally in direct contact with the ice.

pyroxenite An ultramafic plutonic rock 

chiefly composed of pyroxene, with accessory hornblende, biotite, or olivine.

Q

quartzite A metamorphic rock consisting 

mainly of quartz and formed by recrystallization 

of sandstone or chert by either regional or 

thermal metamorphism. Also applied to very 

hard but unmetamorphosed sandstone, consisting chiefly of quartz grains that have been 

overburden The upper part of a sedimentary deposit, compressing and consolidating 

the material below. Also applied to the loose 

soil or sediment overlying bedrock.

overturned fold Applied to a fold, or the 

limb of a fold, that has tilted beyond the 

perpendicular.

oxbow A closely looping stream meander 

having an extreme curvature such that only a 

narrow neck of land is left between two parts 

of the stream. If the stream breaks through 

that neck of land, it commonly abandons its 

former course, leaving behind an oxbow lake 

that marks its former channel.

oxide A mineral compound characterized 

by the linkage of oxygen with one or more 

metallic elements, such as iron or manganese.

oxidized Applied to a rock or sediment 

modified by exposure to atmospheric oxygen 

or oxygen-rich waters.

P

paired terrace One of two steam terraces 

that face each other at the same elevation 

from opposite sides of the steam valley and 

that represent the remnants of the same flood 

plain or valley floor.

paleobasin A basin that formed in the 

past and is no longer expressed as a surface 

topographic feature. 

paleosol A soil horizon that formed in 

the geologic past. Typically buried beneath 

younger soils and sediments.

peat An unconsolidated deposit of partly 

decayed plant remains in which vegetal 

structures are still evident. The deepest 

deposits accumulate in water-saturated environments such as bogs or fens. 

pebble size Refers to rounded to subangular stones with diameters between 4 and 

64 mm.

permafrost Any soil, subsoil, other surficial 

deposit, or even bedrock, in which a temperature below freezing has existed continuously 

for a long time (2 years or more). Characteristic of arctic, subarctic, and alpine regions. 

phyllite A metamorphosed rock, intermediate in grade between slate and mica schist. 

Minute crystals of sericite and chlorite 

impart a silky sheen to its surfaces. Phyllites 

commonly exhibit corrugated cleavage faces.
Glossary 113

so completely and solidly cemented with secondary silica that the rock breaks across or 

through the grains rather than around them.

quartzose Sediments or sedimentary rocks 

containing quartz as a principal constituent. 

Quaternary The second period of the Cenozoic era, following the Tertiary, that began 2 

to 2.5 million years ago and extends to the 

present. Also the corresponding system of 

rocks, sediments, and events assignable to 

that period. The Quaternary period consists 

of two grossly unequal epochs: the Pleistocene, up to about 10,000 years ago, and the 

Holocene since that time.

R

radiocarbon dating also 14C dating A 

method of determining the age of an organic 

material by measuring the concentration 

of carbon-14 remaining in it. It is based 

on the assumption that assimilation of 

carbon-14 ceased abruptly upon the death of 

an organism and that it thereafter remained 

a closed system. The method is useful in 

determining ages in the range of 500 to 

30,000 years or to 40,000 years, although 

arguably it may be extended to 70,000 years 

by using special techniques.

recessional moraine An end or lateral 

moraine built during a temporary but significant pause or minor readvance during the 

retreat of a glacier.

rhythmites A rhythmic (repetitious) 

succession of beds. The term implies no 

limit as to thickness or complexity of 

bedding and it carries no time or seasonal 

connotation. Commonly applied to varvelike sediments for which annual deposition 

cannot be proven.

ripple A small ridge of sand resembling or 

suggesting a ripple of water and formed on 

the bedding surface of a sediment. Commonly appears as a small sand wave similar 

to a dune in shape. 

ripple bedding A bedding surface characterized by ripple marks.

rounded Round or curving in shape. 

Applied to a sedimentary particle whose 

original edges and corners have been 

reduced to smooth curves and whose 

original faces are almost completely 

removed by abrasion. 

S

sag pond A small body of water occupying an enclosed depression or sag formed 

where active or recent fault movement has 

impounded drainage.

sand size A term used in sedimentology 

for particles with diameters between 1/16 

(0.062) mm and 2 mm.

sandstone A clastic sedimentary rock 

composed wholly or largely of sand-size 

particles set in a matrix of finer grains, and 

more or less firmly cemented. Intermediate 

in texture between conglomerate and shale. 

Sandstone varies in color, may be deposited 

by water or wind, and may contain striking 

sedimentary structures such as large-scale 

cross-bedding. 

sapropel An unconsolidated, jelly-like 

ooze or sludge composed of plant remains, 

most often algae, macerating and putrefying 

in an anaerobic environment on the shallow 

bottoms of lakes and seas.

scarp A line of cliffs of any height produced by faulting or by erosion. 

schist A strongly foliated metamorphic 

rock that can be split readily into thin 

flakes or slabs due to the well developed 

parallelism of most of the minerals present, 

particularly platy or elongate minerals (for 

example, mica and hornblende). Mineral 

composition is not an essential factor in its 

definition, but commonly is included in the 

rock name (for example, quartz-muscovite 

schist, amphibole schist).

scour The powerful and concentrated downward erosive action of flowing air, water, or 

ice (for example, on the outside curve of a 

river bend, or during time of flood). 

shale A fine-grained detrital sedimentary 

rock, formed by the consolidation of clay, 

silt, or mud. It is characterized by finely 

laminated structure, which imparts a fissility approximately parallel to the bedding, 

and along which the rock breaks readily into 

thin layers. Shale is generally soft and easily 

scratched, but sufficiently indurated so that 

it will not fall apart on wetting. Its color may 

be red, brown, black, or gray. 

shear plane A surface along which differential movement has taken place parallel 

to that surface.
114 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

sigmoidal cross-bedding Bedding that 

curves in opposing directions like the letter S. 

Characteristic of point-bar deposits (deposits 

formed on the convex sides of river meanders).

silt size A term applied to sedimentary 

particles larger than 1/256 (0.004) mm in 

diameter and smaller than 1/16 (0.062) mm.

siltstone An indurated silt having the 

texture and composition of shale but lacking its fine lamination or fissility. It contains 

hard, durable, generally thin layers, and often 

shows various primary current structures.

slackwater A quiet part of, or a still body 

of water, in a stream (for example, on the 

inside of a bend, where the current is slight).

slate A compact, fine-grained metamorphic 

rock that possesses closely spaced parallel 

cleavage and hence can be split into slabs and 

thin plates. Generally formed from shale.

slide A mass movement of earth, rock, 

or snow resulting from failure under shear 

stress along one or several surfaces that are 

either visible or may reasonably be inferred. 

The moving mass may or may not be greatly 

deformed, and movement may be rotational 

or planar. Named for the material in motion 

(for example, landslide, snowslide, rockslide). 

slip-off slope The long, relatively gentle 

slope on the inside of a stream meander, produced by downcutting of the stream concurrent with the gradual outward migration of 

the meander.

slump A landslide characterized by shearing and rotary mass movement of a body of 

rock or earth along a curved slip surface that 

is concave upward. The slumped mass tilts 

backward with respect to the slope so that its 

upper surface commonly exhibits a reversed 

slope facing uphill.

sod A compact mass of living and dead 

grassy vegetation with interlaced rootlets that 

extends downward several centimeters or 

more from the ground surface.

solifluction The slow viscous downslope 

flow of waterlogged soil and other unsorted 

and saturated surficial material, normally at 

rates of 0.5-5.0 cm/yr. Especially widespread 

in regions underlain by permafrost that acts 

as a downward barrier to percolation of meltwater generated by seasonal thawing of the 

active layer and its snow cover.

solum The upper part of a soil profile (its 

A and B horizons) in which soil-forming 

processes occur. 

squeezeup structure A diapir-like upward 

extrusion of plastic sediment, generally due to 

differential overburden pressure.

stratified Formed, arranged, or laid down 

in layers or strata. Most commonly applied to 

sediments or sedimentary rocks.

striation One of a set of scratches or minute 

lines, generally parallel, inscribed on a rock 

surface by a geologic agent (that is, glaciers 

or faulting).

subangular Somewhat angular; free from 

sharp angles but not smoothly rounded. 

Applied to a sedimentary particle showing 

definite effects of slight abrasion, retaining its 

original general form, and having faces that 

are virtually untouched and edges and corners 

that are rounded off to some extent. Also 

applied to the roundness class containing 

subangular particles.

subglacial (a) Formed or accumulated in or 

by the bottom parts of a glacier (for example, 

meltwater streams, till, moraine). (b) Pertaining to the area immediately beneath a glacier 

(for example, subglacial erosion, subglacial 

drainage). 

subrounded Term applied to a sedimentary 

particle showing considerable but incomplete 

abrasion and an original general form that is 

still discernible, and having many of its edge 

and corners rounded off to smooth curves. 

Also applied to the roundness class containing subrounded particles.

syngenetic Term applied to a primary 

sedimentary structure, such as a ripple 

mark, formed contemporaneously with the 

deposition of the sediment Also applied to 

ice wedges that grow upward as the ground 

surface accretes (for example, by loess or peat 

accumulation).

T

tangential cross-bedding Cross-bedding in 

which the foreset beds appear in section as a 

smooth arc meeting the underlying surface at 

low angles.

tectonism Displacement of rock or sediment by directed forces, resulting in folds, 

faults, and other deformation structures. 

Glacial tectonism occurs where glaciers flow 

over deformable beds.
Glossary 115

tephra A general term for all pyroclastics of 

a volcano. Restricted in this report to finegrained volcanic ash derived from a distant 

source.

terrace Generally applied here to an aggradational deposit of unconsolidated sediment 

that occurs along the margin and above the 

level of a stream or lake, marking a former 

level of that water body.

Tertiary The first period of the Cenozoic 

era, thought to have covered the span of time 

between 65 and 2 to 2.5 million years ago. It 

followed the Cretaceous period and preceded 

the Quaternary. 

thaw amphitheater A depression with an 

arcuate headwall on its upslope side and an 

earthflow or debris flow issuing from its 

downslope side. Formed by thaw of ice-rich 

permafrost.

thaw lake A shallow body of water whose 

basin is produced by collapse of the ground 

following thawing of ground ice in regions 

underlain by ice-rich permafrost.

thixotropic A clay that weakens when disturbed and behaves as a fluid.

till A primarily unsorted and unstratified 

glacial deposit, generally unconsolidated but 

commonly very compact, that consists of 

a heterogeneous mixture of clay, silt, sand, 

gravel and boulders ranging widely in size 

and shape. Deposited directly by and underneath a glacier without subsequent reworking 

by meltwater.

tillstone A stone of pebble to boulder size 

in a deposit of glacial till. Commonly faceted 

and striated by glacial abrasion.

topset bed One of the nearly horizontal layers of sediments deposited on the top surface 

of an advancing delta. It truncates or covers 

the edges of the underlying foreset beds.

trace fossil A sedimentary structure 

consisting of a fossilized track, trail, burrow, 

tube, boring, or tunnel resulting from the 

activities of an animal (for example, a mark 

made by an invertebrate moving, feeding, 

hiding, or resting on or in soft sediment).

truncated Term applied to a soil profile in 

which upper horizons are missing.

tundra A treeless landscape characteristic 

of arctic and subarctic regions. It commonly 

has a marshy surface, which supports a 

growth of mosses, lichens, sedges, and low 

shrubs, and is underlain by dark, mucky soil 

and permafrost.

turbidite Sediment deposited from, or 

inferred to have been deposited from, a turbidity current. Characterized by graded bedding, moderate sorting, and well-developed 

primary structures in a characteristic upward 

succession (termed a Bouma cycle).

turbidity current A density current in water 

or other fluid, caused by matter in suspension 

that gives the water a density greater than that 

of the surrounding or overlying clear water. 

Used in this report to designate a bottomflowing current, laden with suspended sediment, moving swiftly down a subaqueous 

slope under the influence of gravity; and then 

spreading laterally across the floor of a lake 

or other water body.

U

ultramafic An igneous rock composed 

chiefly of mafic minerals (for example, 

minerals rich in iron and manganese such as 

hornblende, augite, or olivine).

unconformity (a) A substantial break or 

gap in the depositional record where a sediment is overlain by another that formed at 

a much later time. It results from a change 

that caused deposition to be interrupted for a 

considerable span of time. (b) The structural 

relation between rock strata or sediment beds 

in contact, characterized by a lack of continuity in deposition, and corresponding to a 

period of nondeposition, weathering, or erosion prior to deposition of the younger beds. 

Commonly marked by absence of parallelism 

between the strata.

underfit stream A stream that appears to be 

too small to have eroded the valley in which 

it flows. It is a common result of drainage 

changes effected by capture, by glacier fluctuations, or by climatic variations.

unsorted A term applied to clastic sediment 

that contains particles of many sizes mixed 

together so that no one size predominates.

unstratified Lacking sedimentary layering 

(stratification). 

V

valley train A long, narrow body of outwash, deposited by meltwater streams far 

beyond the terminal moraine or the margin 

of an active glacier and confined within the 

walls of a valley below the glacier.
116 Guide to Surficial Geology, Noatak National Preserve, Northwestern Alaska

varve A sedimentary bed or lamina or 

sequence of laminae deposited in a body 

of still water within the span of one year. 

Usually applied to a thin pair of graded 

glaciolacustrine layers seasonally deposited, 

usually by meltwater streams, in a glacial 

lake or other water body in front of a 

glacier. A glacial varve normally includes 

a “summer” layer consisting of relatively 

coarse-grained, light-colored sediment 

(usually sand or silt) produced by rapid 

melting of ice in the warmer months, which 

grades upward into a thinner “winter” layer, 

consisting of very fine-grained (clayey), 

often organic, dark sediment slowly 

deposited from suspension in quiet water 

while the streams that fed the water body 

were ice-bound. 

vein quartz A rock composed chiefly of 

quartz crystals of variable size that grew in a 

fracture within another rock.

vivianite A mineral: Fe3(PO4)2. Characteristically blue or green when unaltered, 

but grows darker on exposure. It occurs as 

crystals, fibrous masses, or earthy forms in 

moist settings associated with clays, peat, and 

bog iron deposits.

W

weathering The destructive process or 

group of processes at or near the Earth’s 

surface by which rocks and sediments are 

changed in color, texture, composition, firmness, or form through exposure to atmospheric agents with little or no transport of 

the loosened or altered material. Physical 

disintegration and chemical decomposition of 

rock produce an in-situ mantle of waste. Most 

weathering occurs at the surface, but it may 

take place at considerable depths in welljointed rocks that permit easy penetration of 

atmospheric oxygen and circulating surface 

waters.

wedge The shape of a body of rock or sediment that thins out downward or laterally.

well sorted A term applied to sediment that 

consists of particles all having approximately 

the same size. 
Produced in the Western Region, Menlo Park, California

Manuscript approved for publication, July 16, 2008

Layout and design by Jeanne S. DiLeo