U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2018–5008

Lava Lake Activity at the Summit of Kīlauea Volcano in 2016
Cover.  Photograph of the lava lake at Kīlauea Volcano’s summit, taken from the southeast rim of Halema‘uma‘u Crater. The view is towards the northwest,

with the broad summit of Mauna Loa visible on the skyline. The lake is about 250 meters wide, across its longest axis. Matt Patrick, U.S. Geological Survey,

September 28, 2016.
Lava Lake Activity at the Summit of Kīlauea 

Volcano in 2016

By Matthew R. Patrick, Tim R. Orr, Donald A. Swanson, Tamar Elias, and Brian Shiro

Scientific Investigations Report 2018–5008

U.S. Department of the Interior

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

RYAN K. ZINKE, Secretary

U.S. Geological Survey

William H. Werkheiser, Deputy Director

 exercising the authority of the Director

U.S. Geological Survey, Reston, Virginia: 2018

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Suggested citation:

Patrick, M.R., Orr, T.R., Swanson, D.A., Elias, T., and Shiro, B., 2018, Lava lake activity at the summit of Kīlauea 

Volcano in 2016: U.S. Geological Survey Scientific Investigations Report 2018–5008, 58 p., https://doi.org/10.3133/

sir20185008.

ISSN 2328-0328 (online)
iii

Contents

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

Introduction ..........................................................................................................................................................1

Background..........................................................................................................................................................3

Overview and Setting..................................................................................................................................3

Early Summit Lava Lake Activity ................................................................................................................4

Current Eruption..........................................................................................................................................4

Monitoring Methods .............................................................................................................................................5

The Overlook Crater in Halema‘uma‘u Crater.....................................................................................................7

Basic Geometry ..........................................................................................................................................7

Crater Veneer and Inner Ledges................................................................................................................8

Lake Surface......................................................................................................................................................11

Crustal Plates............................................................................................................................................11

Plate Margins............................................................................................................................................18

Surface Relief ...........................................................................................................................................21

Surface Texture.........................................................................................................................................22

Lake Surface Motion..........................................................................................................................................25

Spattering...........................................................................................................................................................26

Spattering and Nonspattering Phases .....................................................................................................26

The SE Sink..............................................................................................................................................27

Other Spatter Locations............................................................................................................................29

Migrating Spatter.......................................................................................................................................29

Northern Bubble Bursts ............................................................................................................................31

Post-explosion Spattering.........................................................................................................................31

Lava Level Changes ..........................................................................................................................................31

Rockfalls and Explosions...................................................................................................................................36

Crater Wall Cracking.................................................................................................................................36

Veneer and Inner Ledge Collapse............................................................................................................37

Crater Wall Collapses ...............................................................................................................................37

Explosive Events ......................................................................................................................................37

Tephra.............................................................................................................................................................41

Outgassing Plume..............................................................................................................................................43

Volcanic Air Pollution..........................................................................................................................................48

Miscellaneous Observations..............................................................................................................................48

Sounds......................................................................................................................................................48

Heat...........................................................................................................................................................48

Effects of Heavy Rains .............................................................................................................................48

Public Engagement............................................................................................................................................49

2016 Lake Activity in Context.............................................................................................................................49

Relation to the East Rift Zone Eruption at Pu‘u ‘Ō‘ō .........................................................................................50

Comparison with Other Lava Lakes on Earth ...................................................................................................51

Conclusions........................................................................................................................................................51

Acknowledgments..............................................................................................................................................52

References Cited ...............................................................................................................................................52

Glossary .............................................................................................................................................................58
iv

Figures

1. Map showing the location of Kīlauea Volcano and its summit vent ...........................................................2

2. DigitalGlobe WorldView satellite image showing the Overlook crater in Halema‘uma‘u Crater...............3

3. Photographs showing measurements and observations at Halema‘uma‘u..............................................6

4. Observations from the Hawaiian Volcano Observatory (HVO)..................................................................7

5. Photographs showing the webcams on the rim of Halema‘uma‘u Crater near the Overlook crater........7

6. Oblique aerial view of Halema‘uma‘u Crater, viewed from the east...........................................................7

7. Oblique aerial views of the Overlook crater.................................................................................................8

8. Vertical aerial view of the Overlook crater....................................................................................................8

9. Photographs showing a cross section of the Overlook crater....................................................................9

10. Photographs showing the lava veneer on the Overlook crater walls.........................................................9

11. Photograph of bathtub rings on the Overlook crater wall veneer...............................................................9

12. Photograph showing inner ledges at the lake margin.............................................................................. 10

13. Photograph showing the southern ledge.................................................................................................. 10

14. HTcam thermal image showing hot cracks developing on the southern ledge in the hours prior to 

large collapses of the ledge into the lake.................................................................................................. 10

15. Typical view of the lava lake in 2016 .........................................................................................................11

16. Monthly views of the lava lake during 2016.............................................................................................. 12

17. Satellite images of the lake in 2016........................................................................................................... 13

18. Drawings of crustal plate outlines based on five high-resolution satellite images in 2016 .................... 14

19. Histograms of crustal plate measurements taken from WorldView images........................................... 14

20. Image showing spreading zone replication and the formation of new plates......................................... 14

21. A sequence of HMcam images taken on December 18, 2016, showing new plates forming by 

spreading zone replication......................................................................................................................... 15

22. A sequence of HMcam images taken on December 18, 2016, showing new plates forming from 

existing plates in two ways......................................................................................................................... 16

23. Images taken from HMcam and HTcam at roughly the same time showing the formation of a 

megaplate................................................................................................................................................... 16

24. Sequence of HMcam images from December 21, 2016, showing a rockfall that triggered waves and 

sloshing of the lake surface and created many small plates................................................................... 17

25. HMcam image from December 11, 2016, at 10:22 HST, showing a static plate at the lake margin..... 17

26. Photographs showing the most common type of plate margin, simple spreading................................. 18

27. Photograph showing a pulled margin near the SE sink on December 12, 2016 ................................... 19

28. Photograph showing an example of strike-slip motion on a crustal plate margin, where only a minor 

amount of incandescent lava was exposed.............................................................................................. 19

29. Time-lapse images from December 12, 2016, at 17:11 HST, of a propagating crack in the crust........ 19

30. Time-lapse images showing crustal foundering, which normally occurred near the lake margins, 

particularly in the southern portion of the lake, as it is in this example from December 22, 2016......... 20

31. Photograph of quiescent downwelling at the lake margin, taken December 12, 2016, at 17:13 HST.. 20

32. Photograph showing small blisters on the lake surface........................................................................... 21

33. Photographs showing small folds on the lake surface............................................................................. 21

34. Photograph taken October 26, 2016, at 15:16 HST, showing the patchwork appearance of the lake 

surface ........................................................................................................................................................ 22

35. Photographs taken December 8, 2016, showing the provenance of crustal plate areas...................... 22

36. Photographs showing striations on the lake surface................................................................................ 23

37. Photographs showing alternating bands of darkness parallel to the spreading zones.......................... 23
v

38. HMcam image from December 1, 2016, at 01:00 HST, showing pinholes on the lake surface............ 23

39. Sequence of images from December 22, 2016, showing proto-plates and their origin......................... 24

40. Thermal images showing lake surface motion regimes........................................................................... 25

41. Photographs showing typical spattering in 2016...................................................................................... 26

42. Relation between seismic tremor and spattering intensity....................................................................... 27

43. Photographs of the Southeast sink (SE)................................................................................................... 28

44. Photograph of a grotto surrounding the spattering in the SE sink........................................................... 28

45. Photograph of stalactites at the spatter grotto along the eastern lake margin on October 3, 2016...... 28

46. Photographs showing spattering outside of the SE sink area................................................................. 29

47. Sequence of images taken from the HMcam on December 20, 2016, showing spattering that 

appears along the northern lake margin split, with the eastern spatter site gradually migrating 

southeast along the eastern lake margin.................................................................................................. 30

48. Photographs showing sporadic slug bursts in the upwelling zone.......................................................... 31

49. Photographic sequence of a slug burst on December 22, 2016............................................................. 32

50. HMcam images of post-explosion spattering ........................................................................................... 32

51. Thermal images from the HTcam showing the difference in lake level and appearance at the highest 

and lowest levels through the year............................................................................................................ 33

52. Plot of lava lake elevation, summit ground tilt, and seismicity................................................................. 33

53. Monthly thermal camera images of the lava lake, showing level changes............................................. 34

54. Views of the lava lake from the Hawaiian Volcano Observatory............................................................. 35

55. Images from the HMcam show the differing lake level and appearance in September 2016............... 35

56. K2cam webcam image showing a small overflow of lava onto the floor of Halema‘uma‘u Crater, 

taken on October 15, 2016, at 13:34 HST from the Hawaiian Volcano Observatory tower.................. 35

57. Graphs showing increase in small earthquakes during periods of inflation and high lava level............ 36

58. Images of the January 2, 2016, explosion................................................................................................ 37

59. Images of the January 8, 2016, explosion................................................................................................ 38

60. Images of the August 6, 2016, explosion.................................................................................................. 39

61. Images of the October 20, 2016, explosion.............................................................................................. 40

62. Images of the November 28, 2016, explosion.......................................................................................... 41

63. Composite seismic events associated with selected explosive events of 2016..................................... 42

64. Photographs of tephra produced by continuous outgassing................................................................... 42

65. Photograph of egg-shaped hollow glass spherule collected near the Halema‘uma‘u Overlook on 

January 8, 2016.......................................................................................................................................... 42

66. Photographs of Pele’s hair......................................................................................................................... 43

67. Photographs of carpet of Pele’s hair downwind of lake........................................................................... 43

68. Photograph of a typical outgassing plume, taken from Uēkahuna Bluff, near the Hawaiian Volcano 

Observatory, March 20, 2016.................................................................................................................... 44

69. Monthly views of the outgassing plume.................................................................................................... 45

70. Photographs showing alternating trade wind and Kona wind effects on the plume............................... 46

71. Photographs showing a vertical plume rise in slack winds...................................................................... 46

72. View of the plume from a distance ............................................................................................................ 47

73. Photographs showing plume vigor changes in spattering and nonspattering phases........................... 47

74. Photographs showing the robust portion of plume related to spattering................................................. 47

75. Images of the lake surface immediately following unusually heavy rains............................................... 49

76. Photograph showing park visitors enjoying the view of the lake at the Jaggar Museum overlook, 

October 26, 2016........................................................................................................................................ 50

77. Photograph of the small lava lake in Pu‘u ‘Ō‘ō crater, on Kīlauea’s East Rift Zone June 23, 2016...... 50
vi

Table

1. Summary of statistics for crustal plates in the lava lake at Overlook crater, Kīlauea Volcano, 

measured from high-resolution satellite data on five days in 2016 .................................................13
Abstract

The ongoing summit eruption at Kīlauea Volcano, 

Hawai‘i, began in March 2008 with the formation of the 

Overlook crater, within Halema‘uma‘u Crater. As of late 

2016, the Overlook crater contained a large, persistently active 

lava lake (250 × 190 meters). The accessibility of the lake 

allows frequent direct observations, and a robust geophysical 

monitoring network closely tracks subtle changes at the 

summit. These conditions present one of the best opportunities 

worldwide for understanding persistent lava lake behavior 

and the geophysical signals associated with open-vent basaltic 

eruptions. In this report, we provide a descriptive and visual 

summary of lava lake activity during 2016, a year consisting of 

continuous lava lake activity. The lake surface was composed 

of large black crustal plates separated by narrow incandescent 

spreading zones. The dominant motion of the surface was 

normally from north to south, but spattering produced 

transient disruptions to this steady motion. Spattering in the 

lake was common, consisting of one or more sites on the lake 

margin. The Overlook crater was continuously modified by 

the deposition of spatter (often as a thin veneer) on the crater 

walls, with frequent collapses of this adhered lava into the 

lake. Larger collapses, involving lithic material from the crater 

walls, triggered several small explosive events that deposited 

bombs and lapilli around the Halema‘uma‘u Crater rim, but 

these did not threaten public areas. The lava lake level varied 

over several tens of meters, controlled primarily by changes in 

summit magma reservoir pressure (in part driven by magma 

supply rates) and secondarily by fluctuations in spattering and 

gas release from the lake (commonly involving gas pistoning). 

The lake emitted a persistent gas plume, normally averaging 

1,000–8,000 metric tons per day (t/d) of sulfur dioxide (SO2), 

as well as a constant fallout of small juvenile and lithic 

particles, including Pele’s hair and tears. The gas emissions 

created volcanic air pollution (vog) that affected large areas of 

the Island of Hawai‘i. The summit eruption has been a major 

attraction for visitors in Hawai‘i Volcanoes National Park. 

During 2016, the rising lake levels allowed the lake and its 

spattering to be more consistently visible from public viewing 

areas, enhancing the visitor experience. The U.S. Geological 

Survey’s Hawaiian Volcano Observatory (HVO) closely 

monitors the summit eruption and keeps emergency managers 

and the public informed of activity.

Lava Lake Activity at the Summit of Kīlauea Volcano in 2016

By Matthew R. Patrick, Tim R. Orr, Donald A. Swanson, Tamar Elias, and Brian Shiro

Introduction

Lava lakes present a valuable opportunity for studying 

basaltic volcanism. The exposed lava surface provides a clear view 

of the uppermost magmatic system that, even at most open-vent 

volcanoes, is not normally available for direct observation. Lake 

activity may offer insights into the deeper magmatic system, providing important constraints on conduit dynamics, outgassing, and 

magmatic convection (Harris and others, 2005; Oppenheimer and 

others, 2009; Patrick and others, 2015). Despite the advantages of 

lava lakes as a research venue, relatively few long-term continuous observations exist in the modern record owing to the limited 

accessibility of most persistent lava lakes.

The first routine observations and measurements 

of lava lake activity anywhere on Earth were made at 

Kīlauea Volcano’s summit, when a lava lake was present in 

Halema‘uma‘u Crater (fig. 1) during the early 1900s (Jaggar, 

1947; Tilling and others, 2014). The Mauna Ulu eruption 

(1969–74) on Kīlauea’s East Rift Zone provided another 

opportunity for detailed lava lake and lava pond observations, 

with descriptions of gas pistoning (Swanson and others, 1979) 

and the characterization of lake surface crust dynamics as 

an analogue to global plate tectonics (Duffield, 1972). More 

recently, studies performed in brief field campaigns have 

provided new details on activity at the Erta Ale (Ethiopia) 

and Nyiragongo (Democratic Republic of the Congo) lava 

lakes, aided by video, thermal camera imagery, and seismic 

data (Harris and others, 2005; Spampinato and others, 2008, 

2013; Burgi and others, 2014; Lev and others, 2015). The 

emission rates and chemistry of gases emitted from lava lakes 

have also been studied in short field campaigns (Sawyer and 

others, 2008; Allard and others, 2016). Research performed 

on Erebus lava lake (Antarctica) has provided new insights 

into lake motion and pulsatory magma supply into the lake 

(Oppenheimer and others, 2009; Peters and others, 2014). 

Recent studies of lava ponds on Kīlauea’s East Rift Zone have 

clarified the mechanism driving the gas pistoning process 

(Patrick and others, 2011b; Orr and Rea, 2012).

The ongoing summit eruption at Kīlauea Volcano, 

Hawai‘i, began in 2008 and has evolved into a state of 

continuous lava lake activity (Patrick and others, 2013). The 

current lava lake in Halema‘uma‘u Crater (figs. 1 and 2) is 

the most accessible lava lake on Earth, providing a venue 

for regular and detailed direct observations of lava lake 
2

Lava Lake Activity at the Summit of Kīlauea Volcano in 2016

HVO +

Jaggar Museum

UWE

Uēkahuna

Bluff

Kīlauea Caldera

(floor of caldera closed)

KMC

Park 

 visitor 

center

Volcano

House

Volcano

village

Golf course

subdivision

Halema‘uma‘u

Crater

Overlook crater

(lava lake)

Kīlauea

Iki NPT

Mauna Loa

fig. 1B

Kīlauea

caldera

(summit) Pu‘u ‘Ō‘ō

Pu‘u ‘Ō‘ō flow field

(1983-present)

A

B

Southwest Rift Zone

East Rift Zone

Island of Hawai‘i

© 2016 DigitalGlobe

NextView License

Pāhala

0

0

10

5

20 KILOMETERS

10 MILES

0

0

1

0.5

2 KILOMETERS

1 MILE

PPāāhoa hoa

Volcano

village

Area of 

map

CRATER RIM DRIVE

CHA NI OF CRATERS ROAD

155.25° 155°

155.30° 155.25°

19.4°

19.42°

19.44°

155.5°

19.5°

19.25°

Figure 1. Maps showing the 

location of Kīlauea Volcano and its 

summit vent. A, Kīlauea Volcano 

forms the southeast portion of 

the Island of Hawai‘i (see inset). 

Two rift zones extend down the 

flanks of the volcano. The Pu‘u 

‘Ō‘ō eruption, on the East Rift 

Zone, has been ongoing since 

1983 and has produced a 144 

square kilometer lava flow field 

(pink). The summit eruption, the 

focus of this report, is present 

in Kīlauea Caldera. White 

dotted line is the approximate 

boundary between Mauna Loa 

and Kilauea volcanoes. The 

basemap is derived from a 2005 

digital elevation model. B, Map 

of Kīlauea Caldera. The summit 

lava lake is contained in Overlook 

crater, in Halema‘uma‘u Crater 

which is in the southwest portion 

of Kīlauea Caldera. Roads are 

marked by black lines, with the red 

line showing the portion of Crater 

Rim Drive closed to the public 

owing to the summit eruption. NPT 

is a broadband seismic station 

and UWE is an electronic tiltmeter. 

Many other instruments are 

present at the summit but are not 

shown because their data were 

not included in this report. HVO, 

Hawaiian Volcano Observatory; 

KMC, Kīlauea Military Camp.

behavior over a prolonged time period (years)— and the 

first opportunity of this kind worldwide in recent years. The 

robust monitoring network already in place on the volcano 

has allowed for some of the most thorough monitoring of a 

lava lake anywhere in the world (Guffanti and others, 2010), 

providing a valuable opportunity to link direct observations 

with geophysical data, in order to both better understand 

the lava lake and interpret the myriad geophysical signals 

originating from open-vent basaltic eruptions. Beyond its 

role in research, the lake has been both a visitor attraction—

viewing the lake is a major draw in Hawai‘i Volcanoes 

National Park—and a public hazard, as the continuous 
Background

3

0 125 250 METERS

Halema‘uma‘u 

Crater floor

April–May 2015 overflows

Halema‘uma‘u

Crater rim

Halema‘uma‘u

overlook

HTcam

HMcam

Halema‘uma‘u

parking lot

Crater Rim Drive

(closed)

SE sink

Overlook

crater rim

lava lake

Halema‘uma‘u

Crater wall

A4

NPT seismic station

© 2016 DigitalGlobe

NextView License

tephra collection

buckets (red dots)

Figure 2. DigitalGlobe WorldView satellite image taken October 13, 2016, showing the Overlook crater in Halema‘uma‘u Crater. 

The lava lake was contained within the Overlook crater (about 250 x 190 meters) during 2016. Visual observations occurred 

primarily from the Halema‘uma‘u Overlook. Another common location for visual observations was station A4, which provided good 

views of the southeast (SE) sink (the SE sink was not normally visible from the Halema‘uma‘u Overlook as it was obscured by the 

Halema‘uma‘u Crater wall). A visual webcam (HMcam) and thermal camera (HTcam), on the rim of Halema‘uma‘u Crater, provided 

continuous observations of lake activity. In April-May 2015 the lava level rose to the Overlook crater rim and covered a portion 

(dark region) of the floor of Halema‘uma‘u Crater. The SE sink is an area of the lake where spattering is common, with vigorous 

downwelling. Red dots show the location of tephra collection buckets (Swanson and others, 2009).

outgassing creates widespread volcanic air pollution on 

the Island of Hawai‘i. Detailed documentation of its recent 

activity is therefore essential both for fundamental research 

and assessing hazards.

This manuscript is intended to provide an overall summary of activity and context for more in-depth study. During 

2016 the activity in the lava lake was relatively steady and this 

year presented a good opportunity to thematically describe 

the recent nature of lava lake activity at Kīlauea’s summit. In 

this paper, we use the term “lithic” to refer to material erupted 

prior to the current summit eruption, and the term “juvenile” 

to refer to material erupted during the current summit eruption.

Background

Overview and Setting

Kīlauea Volcano forms the southeast portion of the Island 

of Hawai‘i (fig. 1). Eruptions at Kīlauea normally occur either 

at the summit, where Kīlauea Caldera is situated, or along one 

of two rift zones (the East Rift Zone and Southwest Rift Zone). 

The East Rift Zone eruption at Pu‘u ‘Ō‘ō began in 1983 and 

continues at the time of writing (late 2017). This eruption has 

consisted of lava flows, primarily tube-fed pāhoehoe, that have 
4

Lava Lake Activity at the Summit of Kīlauea Volcano in 2016

formed a flow field covering 144 square kilometers (km2) as of 

2017 (Orr and others, 2015; Hawaiian Volcano Observatory, 

written commun., 2016). The ongoing summit eruption began 

in March 2008 and has been concurrent with the East Rift 

Zone eruption. These two ongoing eruptions at Kīlauea mark 

the first time in more than 200 years that long-lived (>1 year) 

concurrent eruptions have occurred at the summit and along 

a rift zone. The summit eruption consists of a large lava lake 

contained within the Overlook crater, which formed at the onset 

of the eruption (Patrick and others, 2013). The Overlook crater 

is within Halema‘uma‘u, a 1-km-diameter crater that resides 

in the southwest portion of Kīlauea Caldera. The caldera floor 

is contained entirely within Hawai‘i Volcanoes National Park, 

which is managed by the U.S. National Park Service. The U.S. 

Geological Survey’s Hawaiian Volcano Observatory (HVO) is 

situated on the north rim of Kīlauea Caldera, 1.9 km from the 

Overlook crater, and is charged with monitoring and hazard 

assessment of the eruption (Tilling and others, 2014).

Early Summit Lava Lake Activity

Lava lakes were observed in Kīlauea’s summit caldera 

in the first written record of Kīlauea’s activity in 1823, when 

missionary William Ellis and his companions travelled over 

the volcano during a tour of the Island of Hawai‘i (Ellis, 1825). 

Lava lake activity was present for much of the next 100 years 

(Macdonald and others, 1983). Much of this lake activity 

was focused in the southwestern portion of Kīlauea Caldera, 

in Halema‘uma‘u Crater, and the persistent lava lake was a 

primary impetus for the establishment of the Hawaiian Volcano 

Observatory in 1912 (Apple, 1987; Tilling and others, 2014; 

Dvorak, 2011, 2016). The year before, in 1911, Frank Perret 

arrived in Hawai‘i and began regular, detailed observations 

of lava lake activity at Halema‘uma‘u (Perret, 1913a,b,c). 

Regular lava lake observations consisted of monitoring seismic 

activity and ground tilt, lava level measurements, and basic 

visual observations (Jaggar, 1947; Tilling and others, 2014). 

Continuous lava lake activity ceased in early 1924 with 

withdrawal of the magma column during an intrusion on the 

lower East Rift Zone, triggering a series of collapses and phreatic 

explosions in Halema‘uma‘u during May of that year (Jaggar 

and Finch, 1924). Sporadic, and generally brief, eruptive activity 

occurred at the summit through the rest of the 1900s, with the 

longest eruption consisting of nine months of lava lake activity 

in Halema‘uma‘u during 1967–68 (Kinoshita and others, 1969). 

The most recent summit eruption before the current one was in 

1982, and consisted of a brief fissure eruption on the floor of the 

caldera (Macdonald and others, 1983).

Current Eruption

In late 2007, seismic tremor and sulfur dioxide (SO2) 

emissions began escalating well above normal background levels 

(Wilson and others, 2008; Johnson and Poland, 2013; Patrick and 

others, 2013). The increasing tremor and SO2 emissions continued 

into early 2008 despite ongoing deflation, providing conflicting 

indicators of eruption potential considering that previous summit 

eruptions were consistently preceded by significant inflation. By 

late February 2008, SO2 emissions were sufficiently high that 

visitor health was impacted and Hawai‘i Volcanoes National 

Park closed the western portion of Crater Rim Drive to the public 

(fig. 1B). On March 12, a fumarolic area was observed on the 

south wall of Halema‘uma‘u Crater, directly beneath the closed 

Halema‘uma‘u Overlook (fig. 2), producing a robust outgassing 

plume. In the early morning hours of March 19, a collapse of the 

fumarolic area was associated with several small earthquakes and 

a small explosive event which ejected lithic blocks around the 

Halema‘uma‘u Overlook (Wilson and others, 2008; Houghton and 

others, 2011). The collapse formed a new crater, informally called 

the “Overlook crater”, which was initially 35-meters (m) wide. 

The new crater continued to produce an outgassing plume that 

persists to this day. Several crater collapses occurred over the next 

few months, enlarging the Overlook crater and triggering small 

explosive events that deposited a mixture of juvenile and lithic 

ejecta around the Halema‘uma‘u Overlook (Wooten and others, 

2009; Houghton and others, 2013; Carey and others, 2015). 

Lava was not visible in the new crater until September 

2008, when a roiling lava lake was observed by helicopter. The 

lake was gas pistoning and was visible during a brief phase of 

inflation associated with a deflation-inflation cycle (Patrick and 

others, 2008), suggesting that the level may have risen into view 

with the inflation. The lake was only sporadically visible over 

the next eight months, and views were obscured by thick fumes. 

A handheld thermal camera provided improved views into the 

crater, and revealed that the lava lake was not continuously present 

in the crater. During summit inflation the lake would often rise 

to cover the bottom of the crater, but at other times (particularly 

deflation phases) lava drained out of sight below the deep floor of 

the Overlook crater, exposing a surface covered by rubble and (or) 

small outgassing vents. A month of continuous lava lake activity 

in June 2009 was the most persistent phase of activity until that 

time (Patrick and others, 2011a), and light detection and ranging 

(lidar) determined that the lake surface was 205 m below the rim 

of the Overlook crater at that time (T. Ericksen, University of 

Hawai‘i Mānoa, personal commun., 2009). Sporadic lava lake 

activity, deep in the Overlook crater, continued into early 2010 

and alternated with periods of spattering at vents on the Overlook 

crater floor. In general, inflation phases corresponded with the lake 

rising and covering the floor of the Overlook crater, while during 

deflation phases the lava lake would drain to leave the rubbly 

crater floor visible.

In February 2010, deflation associated with a collapse of the 

floor of the Overlook crater was followed by inflation associated 

with the lava lake rising and subsequently establishing a more 

continuous presence. The lake level generally rose through 2010, 

and experienced frequent gas pistoning; it reached its highest 

levels (at that time) in February and March 2011, when the lake 

level was 60 m below the Overlook crater rim (Orr and others, 

2015). During this period, rock cracking sounds were common 

and several explosive events occurred, triggered by large collapses 

of the Overlook crater wall into the lava lake (Orr and others, 
 Monitoring Methods

5

2013). The March 2011 Kamoamoa eruption, near Pu‘u ‘Ō‘ō on 

Kīlauea’s East Rift Zone, caused the summit lake to drain out of 

view over the course of a day, dropping roughly 140 m (Orr and 

others, 2015; Carbone and others, 2013; Patrick and others, 2015). 

The lake reappeared about a week later and gradually rose to its 

previous level, but dropped again when new vents opened on Pu‘u 

‘Ō‘ō in August 2011. The lake level recovered again in late 2011, 

and slowly rose to even higher levels over the next year (Patrick 

and others, 2015).

Inflation during October 2012 was associated with the 

lake rising to about 20 m below the Overlook crater rim, but 

the lake dropped several tens of meters with a small intrusion in 

the summit region near the end of that month. Lake levels were 

generally high in 2013 and 2014, normally 30–60 m below the 

Overlook crater rim, but fluctuated on a daily basis with frequent 

deflation-inflation (DI) events (Anderson and others, 2015; Patrick 

and others, 2015). Sharp inflation in April 2015 drove rapid 

lava level rise for several weeks, culminating in the lake spilling 

onto the floor of Halema‘uma‘u Crater for the first time during 

this eruption (fig. 2). These overflows occurred several times 

over the next two weeks, covering about a quarter of the floor of 

Halema‘uma‘u Crater with shelly pāhoehoe (a type of pāhoehoe 

described in Swanson [1973]), and building up the rim of the 

Overlook crater by about 8 m. A small intrusion in the summit 

region triggered a drop in the lake to its more typical levels, which 

persisted through the remainder of 2015.

 Monitoring Methods

The accessibility of the summit lava lake allowed daily 

direct observations of lake behavior from the Halema‘uma‘u 

Overlook (figs. 2 and 3A). These visits often corresponded 

with daily tephra collection and (or) lava level measurements 

described below. HVO scientists normally stood at the 

Halema‘uma‘u Overlook for 10–20 minutes, noting the 

location and intensity of spattering, grotto development, 

general lava level, surface flow direction, sounds, and other 

observations. Although webcams were stationed at the same 

spot, the direct observations were valuable for identifying 

several things that the cameras did not always register clearly. 

This includes rockfalls that were too small to be clearly 

identified in the webcam images but could be sufficiently large 

to trigger spattering. Rock popping and cracking sounds were 

also best recorded through direct observations. High-quality 

photographs taken by HVO scientists tended to have better 

resolution and clarity than webcam images.

Observations from HVO and the Jaggar Museum overlook 

were also useful. The HVO observation tower was built to provide 

commanding views of Kīlauea Caldera, including Halema‘uma‘u 

(fig. 4). When lake levels were high there were good views of 

the lake surface and spattering from the tower. Rock cracking 

and popping sounds were often audible from the Jaggar Museum 

overlook, particularly on slack wind days.

Tephra, which normally included Pele’s hair and tears 

as well as small lithic particles, was normally collected each 

workday from a network of 10 buckets distributed downwind of 

the Overlook crater (Swanson and others, 2009; figs. 2, 3C). Total 

tephra accumulation rates were inferred from the distribution 

across the network, and the proportion of juvenile and lithic 

material in the tephra assemblage was also tracked (Swanson and 

others, 2009). Geochemical analysis of tephra has included spatter 

samples from sporadic explosive events as well as Pele’s tears 

and hair collected daily during normal activity (Rowe and others, 

2015; Thornber and others, 2015).

Starting in 2013, measurements of lava lake level were 

generally made once per day using a handheld laser rangefinder 

from the Halema‘uma‘u Overlook (fig. 3B). One of two laser 

rangefinder models was used: a Safran Vectronix Vector23 or a 

TruPulse 360R. The TruPulse has a stated accuracy of <1 m. The 

Vector23 only states its accuracy (±5 m) over long distances (500–

12,000 m), however, our line of sight distances were <200 m and 

we found that the Vector23 consistently agreed with the TruPulse 

within 1 meter when measuring the lake level. We also performed a 

test over a distance of 160 m, and compared the results with a tape 

measure, and both rangefinders agreed with the measured distance 

to within 1 meter. Therefore, we infer that both the Vector23 and 

TruPulse had an accuracy of ±1 m for our measurements. Real-time 

estimates of lake level were made using an automated analysis of 

thermal camera images (Patrick and others, 2016b) but this method 

was not useful when the lake rose above the top of the thermal 

image field of view in mid-2015 and late 2016.

Cameras provided a means of observing the lake activity 

on a continuous basis. Two visible-wavelength cameras were 

in the HVO observation tower (fig. 4B), with one providing a 

wide view of Halema‘uma‘u at a rate of one image every two 

minutes, and a second camera providing a close-up view of the 

Overlook crater at a higher rate (several frames per second). The 

Halema‘uma‘u Overlook webcam (HMcam) provided a closer 

view of the lake activity (figs. 2 and 5B). The camera recorded 

continuously on a near-infrared (IR) setting, which allowed 

improved views through the fume compared to views in visible 

wavelengths. This camera acquired images at a rate of one frame 

per second in 2016, and observations of the lake improved 

when the live stream from this camera became accessible on 

a large-screen monitor in the HVO lobby during 2016. The 

live stream allowed HVO scientists to see more activity and 

identify patterns, as well as to react rapidly to events like 

collapses. A thermal camera (HTcam) roughly 80 m southwest 

of the Halema‘uma‘u Overlook has been in operation since late 

2010, and acquires an image every five seconds (figs.2 and 

5A) (Patrick and others, 2014). The thermal camera can “see” 

through the thick fume that commonly obscures views in the 

Overlook crater, providing a nearly continuous record of lake 

activity. An automated routine at HVO uses the thermal images 

to track the lake surface speed and flow direction, as well as the 

abundance of spattering, on a near-real-time basis (Patrick and 

Orr, 2018). In addition to the real-time webcams and thermal 

camera, we also deployed two time-lapse cameras on the rim of 

Halema‘uma‘u. These systems used high-quality digital single 

lens reflex (DSLR) cameras, which were an improvement over 

the models described in Orr and Hoblitt (2008). 
6

Lava Lake Activity at the Summit of Kīlauea Volcano in 2016

A B

C D

E

Figure 3. Photographs showing 

measurements and observations 

at Halema‘uma‘u. A, Making visual 

observations of the lake from 

A4 on May 16, 2016. B, Using a 

laser rangefinder to make a daily 

measurement of lake level on 

December 19, 2016. The HMcam 

is in the foreground. C, Daily 

tephra collection from a network 

of buckets provides estimates 

of tephra output on December 

21, 2016. D, Collecting Pele’s 

hair for geochemical analysis in 

the Halema‘uma‘u parking lot on 

November 9, 2016. E, Hawaiian 

Volcano Observatory geologist at 

the margin of the 2015 overflows 

on the floor of Halema‘uma‘u 

Crater on November 29, 2016.

A robust geophysical monitoring network has been in 

place at the summit of Kīlauea for decades (Guffanti and others, 

2010). Seismic monitoring includes a broadband network within 

Kīlauea Caldera (Dawson and others, 1998; Okubo and others, 

2014), as well as several short-period and strong motion stations 

on the volcano. For summit activity, we commonly analyzed 

data from broadband station NPT, on the rim of Halema‘uma‘u 

Crater (fig. 1B). Deformation monitoring includes a network 

of borehole tiltmeters (Cervelli and Miklius, 2003) as well as 

global positioning system (GPS) stations (Miklius and others, 

2005). Data from these ground-based deformation instruments 

are analyzed along with interferometric synthetic aperture radar 

imagery collected by spaceborne instruments (for example, 

Poland and others, 2012). Tiltmeter station UWE, located near 

the Hawaiian Volcano Observatory on the north rim of Kīlauea 

Caldera, was a common station used to monitor the summit 

eruption (fig. 1B).

Routine gas monitoring has occurred for decades at the 

summit of Kīlauea, consisting primarily of SO2 emission rates 

estimated using a correlation spectrometer (COSPEC) and 

other ultraviolet spectrometers (Sutton and others, 2003; Elias 

and Sutton, 2012; Sutton and Elias, 2014). This traditional 

method for SO2 emission rate estimation is performed in 

brief field visits, generally no more than once per day. Other 

techniques have been developed for estimating SO2 emission 

rate on a more continuous basis, although they are still 

limited to daylight hours (Sutton and others, 2013). These 

techniques include (1) an array of upward-looking ultraviolet 

spectrometers downwind of the Overlook crater that can 

estimate SO2 emissions every 10 seconds during normal trade 

wind conditions (Horton and others, 2012; Elias and others, 

2016); and (2) an ultraviolet camera (Kern and others, 2015) 

that also provides high-rate estimates of SO2 emission. In 

addition to SO2 emission rates, gas chemistry is measured 
The Overlook Crater in Halema‘uma‘u Crater

7

Figure 4. Observations from the Hawaiian Volcano Observatory 

(HVO). A, Aerial view, looking south, showing the Hawaiian Volcano 

Observatory and Jaggar Museum (foreground) with Halema‘uma‘u 

Crater and the lava lake in the distance. HVO and the museum are 

1.9 kilometers from the lava lake. Photograph taken July 27, 2016. B, 

Making observations of the lava lake from the HVO observation tower on 

December 20, 2016.

AAXXXX_fig 01

A

B

HVO

A

B

Figure 5. Photographs showing the webcams on the rim of 

Halema‘uma‘u Crater near the Overlook crater (see fig. 2 for locations). A, 

The HTcam thermal camera on July 29, 2016. B, The HMcam near-infrared 

camera on September 9, 2016. 

with a Fourier Transform Infrared spectrometer (FTIR) during 

sporadic field campaigns (Sutton and others, 2013). Ground 

level SO2 concentrations downwind of Halema‘uma‘u were 

measured continuously at three stations in 2016, at varying 

distances from the vent.

The Overlook Crater in Halema‘uma‘u Crater

Basic Geometry

The lava lake was contained within the Overlook crater 

(~250 m diameter), which was itself contained within the larger 

Halema‘uma‘u Crater (~1 km diameter) (figs. 2 and 6). The 

northern portion of the Overlook crater rim coincided with the 

floor of Halema‘uma‘u Crater, and the southern portion of the rim 

ran along the south wall of Halema‘uma‘u (figs. 6 and 7). The 

wall consisted of a talus slope at the base of near-vertical walls, 

Figure 6. Oblique aerial view of Halema‘uma‘u Crater, viewed from the 

east. The Overlook crater and lava lake are located to the south (left). The 

dark portion of the Halema‘uma‘u Crater floor represents overflows from 

the lava lake in mid-2015. Photograph taken November 3, 2016.
8

Lava Lake Activity at the Summit of Kīlauea Volcano in 2016

Figure 7. Oblique aerial views of the Overlook crater. A, The lava 

lake on September 12, 2016, during a nonspattering phase. Note the 

lack of a robust gas plume. B, The lake on November 3, 2016. Note 

the robust portion of the plume that originates directly from spattering 

along the southeastern margin of the lake. C, The lake on July 29, 2016. 

The robust portions of the plume originate from spattering along the 

southeastern and western margins of the lake.

Halema‘uma‘u Crater floor

2015 overflows

Overlook

crater rim

SE sink

southern

ledge

Halema‘uma‘u Crater wall

Halema‘uma‘u Crater rim

HTcam

spattering

~250 m

Overlook

crater rim

Figure 8. Vertical aerial view of the Overlook crater. Photograph was 

taken on November 29, 2016, and at this time spattering was present in 

several locations, including the SE sink.

A

B

C

Halema‘uma‘u Overlook

HTcam

southern 

ledge

SE sink

with extensive chemical alteration of the Halema‘uma‘u Crater 

wall (fig. 7). The Overlook crater was elliptical in map view, with 

dimensions of 250 m (northwest-southeast) × 190 m (southwestnortheast) in November 2016 (fig. 8). In 2016, the Overlook crater 

rim was roughly 77 m below the Halema‘uma‘u Overlook.

The planimetric area of the Overlook crater enlarged during 

2016 owing to collapses of lithic rock that forms the Overlook 

crater walls. Based on high-resolution WorldView satellite images, 

the area of the Overlook crater on December 18, 2015, was 

about 37,000 m2. On November 16, 2016, the area was roughly 

43,500m2, which represents roughly an 18 percent increase.

The Overlook crater walls normally consisted of several 

morphologic zones (fig. 9). The lowest point on the wall, where 

the lake surface contacted the crater wall, sometimes had a small 

ledge built of solidified lava. Above this, extending upwards a 

variable distance, was a deposit of juvenile veneer left attached to 

the wall during higher stands of the lake. Above and behind the 

veneer, the wall of the Overlook crater exposed a cross section of 

the 1974 and the 1967–68 solidified lava fill of Halema‘uma‘u. 

In 2016, the upper 8 m of the wall exposed overflows of lava 

that occurred in 2015. Overflows during 2016 were minor and 

added slightly to the existing overflow thickness only along some 

portions of the Overlook crater rim.

Crater Veneer and Inner Ledges

When the lava lake level dropped, a thin veneer of lava 

(probably less than a meter or two thick) would often remain 

attached to the Overlook crater walls, extending up to the high 

stand of the lake (fig. 10). The veneer often had numerous 

horizontal ribs, which were “bathtub rings” that presumably 

represented incremental lake level changes (and possibly gas 

piston events) (fig. 11). The veneer was an ephemeral feature 

in the crater, often collapsing piecemeal—as large slabs or 

sheets—when the lake surface dropped during summit deflation. 

These collapses would impact the lake surface and often trigger 

spattering; this process is described in more detail in the rockfall 

section of this manuscript.
The Overlook Crater in Halema‘uma‘u Crater

9

2015 overflow (8 m thick)

lithic wall

juvenile veneer

juvenile ledge

pre-2015 Overlook crater rim

post-2015 Overlook crater rim

lake surface

Halema‘uma‘u

Crater floor

Halema‘uma‘u

Crater floor

Halema‘uma‘u

Crater rim

Overlook

crater rim

A B

Halema‘uma‘u

Crater wall

(talus slope)

Figure 9. Photographs showing a cross section of the Overlook crater. A, Wide view of the Overlook crater from station A4 on the rim of Halema‘uma‘u Crater 

(see fig. 2 for location). Spattering is active in the typical SE sink. Photograph taken March 19, 2016. B, Close-up of same photograph, showing detailed structure 

of the Overlook crater wall on a typical day. From bottom to top, the wall consisted of several zones: (1) a ledge of solidified juvenile lava, extending out from the 

wall by as much as a few meters, (2) an unstable veneer of juvenile lava deposited by the lake during higher lake levels, (3) the exposed lithic wall of the crater, 

formed by lava erupted prior to 2008 on the floor of Halema‘uma‘u Crater, and (4) a layer of juvenile lava, roughly 8 meters (m) thick, formed by successive 

overflows during April and May of 2015. The base of this 8-m-thick layer marks the rim of the Overlook crater prior to mid-2015.

Figure 10. Photographs showing the lava veneer on the Overlook crater walls. A, View of the northern Overlook crater wall from the HTcam site. The far wall 

has a light-colored red patch that indicates a recently collapsed portion of the lava veneer. The skyline marks the rim of Kīlauea Caldera, with the Hawaiian 

Volcano Observatory and Jaggar Museum visible as a small bump on the crest. Photograph taken December 13, 2016. B, Close-up of the northern Overlook 

crater wall on the same day. The black veneer extends from the lake surface to the Overlook crater rim, but the red area shows where a large patch of the 

veneer has fallen away. The lake surface was roughly 30 meters below the rim at this time.

A B

Figure 11. Photograph of bathtub rings on the Overlook crater wall 

veneer. The lava veneer, which often extended the entire height of 

the Overlook crater wall, as it does here, sometimes had a ribbed 

appearance that presumably represents lava deposition associated with 

incremental changes in lake level. Photograph is taken from station A4 

on December 4, 2016, with the SE sink on the right side of the photo 

(see fig. 2 for locations). For scale, the lake surface is 30 meters below 

the Overlook crater rim (the crater rim is marked by the horizontal line of 

fume near the top of the image). 
10

Lava Lake Activity at the Summit of Kīlauea Volcano in 2016

If the lake level remained steady, a small inner ledge would 

be built out from the wall by as much as a few meters (fig. 12). 

These small inner ledges were often built from solidified spatter 

deposits and, like the veneer, were ephemeral and prone to 

collapse with drops in the lake level during summit deflation. 

The collapses of the small inner ledges would often trigger brief 

spattering at the point of impact into the lake.

A large inner ledge of solidified lava formed in the 

southern corner of the crater and was present through 2016, 

changing in size and shape with lake level changes (figs. 8 

and 13). We call this the “southern ledge”. It was triangular 

in plan view (triangular because it filled the southern corner 

of the Overlook crater) with dimensions of roughly 80 m 

by 20 m (area about 1,600 m2) in October 2016, based on 

high-resolution satellite imagery. During high lava stands the 

lake would spill onto this ledge and add additional layers of 

lava (appearing to be shelly pāhoehoe), building it higher. 

Collapses of the highly altered Halema‘uma‘u Crater wall 

above the ledge often deposited large, white lithic blocks on 

the ledge. These lithic blocks were subsequently inundated by 

juvenile overflows when the lake level rose above the level 

of the ledge. When the lake level dropped during summit 

deflation, the front of the ledge would often slough off in 

a piecemeal fashion, reducing the size of the ledge. The 

collapses were presumably triggered by the removal of lateral 

support as the lake level dropped. They were sometimes 

preceded by hours or days of enlargement of hot cracks near 

the front of the ledge, as observed by the HTcam (fig. 14). 

Collapses of the southern ledge allowed the lake to fill a larger 

volume, increasing the lake’s surface area.

On September 16–17, 2016, much of the north face of 

the ledge collapsed into the lake in several episodes, leaving a 

Figure 12. Photograph showing inner ledges at the lake margin. Small 

ledges (example marked by arrow) developed where the lake margin 

contacted the Overlook crater wall, extending as much as a few meters 

towards the lake center and modifying the shape of the lake margin. 

Spattering in the SE sink is visible at the right side of the photo. The lightcolored areas consist of altered lava originating from flows from the 1960s 

and 1970s that filled Halema‘uma‘u Crater. Photo by Kirsten Stephens, U.S. 

Geological Survey, May 16, 2016.

Overlook crater rim

southern ledge

Halema‘uma‘u Crater wall

Figure 13. Photograph showing the southern ledge. Lava deposited by 

the lake along the southern margin of the Overlook crater developed a ledge 

that was triangular in plan view and about 80 meters long. Several large, 

white lithic blocks have collapsed from the Halema‘uma‘u Crater wall onto the 

ledge— a common phenomenon. At the time of this photograph (December 

22, 2016) the southern ledge was roughly 5 meters below the rim of the 

Overlook crater. The southern ledge was built upwards by overflows during 

high lava lake levels, but would often collapse into the lake when the lake level 

dropped a significant distance (tens of meters). 

Figure 14. HTcam thermal image showing hot cracks developing on 

the southern ledge in the hours prior to large collapses of the ledge into 

the lake. Image taken September 17, 2016. Scale is in degrees Celsius.

cracks widening southern ledge

prior to collapse

350

300

250

200

150

100

50

fresh, near-vertical north-facing scarp perched above the lake 

surface. Shortly after one of the collapses on September 16, 

HVO scientists at the Halema‘uma‘u Overlook observed that 

incandescent rubbly material (resembling clinker on an active ‘a‘ā 

flow) was occasionally sloughing from the face of the north scarp, 

suggesting that the interior of the southern ledge was “mushy” 

and semifluid owing to incomplete cooling. Jaggar (1917) noted 
Lake Surface

11

similar observations during collapses of inner ledges in the early 

Halema‘uma‘u lava lake, describing “an outflow which also is like 

crumbled cheese, and incandescent, but starting out like a liquid 

and falling like gravel or sand. It trickles out from fresh vertical 

breaks in falling benches.”

Lake Surface

The lava lake was present continuously throughout 2016, 

and most of the surface was easily visible from the Halema‘uma‘u 

Overlook. The lava lake measured roughly 250 m (northwestsoutheast) × 190 m (southwest-northeast) in November 2016, with 

a surface area of approximately 39,000 m2. This is comparable to, 

if not exceeding, the surface area of the lava lake in Nyiragongo 

(Spampinato and others, 2013; Burgi and others, 2014; Patrick and 

others, 2016c), and indicates that the Halema‘uma‘u lava lake was 

one of the two largest lava lakes on Earth (if not the largest) during 

2016. The lake dimensions on January 25, 2016, were 240 m 

(northwest-southeast) × 175 m (southwest-northeast), with an area 

of roughly 35,000 m2. Therefore, during 2016, the lake surface 

area increased by roughly 10 percent. The lake was bound on all 

sides by the steep walls of the Overlook crater, and the lake area 

enlargement was a result of the widening of the Overlook crater 

through collapses of the crater walls.

Crustal Plates

The lake surface consisted of numerous large crustal plates 

separated by narrow incandescent spreading zones (fig. 15). 

Depending on the surface texture and solar illumination, the 

plate appearance could range from dull black to lustrous silver. 

The overall appearance of the lake was roughly similar to the 

descriptions of lava lake activity at Mauna Ulu in 1971 by Duffield 

(1972). This basic geometry was maintained throughout 2016 (see 

section below on crustal plate dimensions), despite changes in lake 

level and spattering activity (fig. 16).

The crustal plates appeared to be thin and flexible. Where 

crust was consumed at spattering sites, the crust was often 

violently ripped and torn—sometimes thrown a few meters in 

the air—revealing that the black crustal plates formed a thin 

(probably no more than several centimeters thick) flexible skin 

over the underlying incandescent lava. As described below, 

approximate surface velocities on the lake were 0.1–0.2 m/s. Over 

a distance of 250 m (see below), this implies that the crust was 

generally less than 20–40 minutes old. At this age, according to 

equation 1 in Hon and others (1994), the uppermost crust would 

be 4–7 centimeters (cm) thick. Based on direct observations, 

Jaggar (1917) states that the surface crust was normally 8–10 cm 

thick for the Halema‘uma‘u lava lake in the early 1900s. This 

meager thickness presumably contributes to the flexibility of 

the crust, which was evident when it would momentarily bend, 

without cracking, as small waves emanated from spatter sites. 

Small folds, described below, also indicate a flexible nature to the 

crust. Brittle behavior was exhibited at the limits of the crust’s 

Figure 15. Typical view of the lava lake in 2016. Photograph taken from 

the rim of Halema‘uma‘u Crater, about 100 meters east of the Halema‘uma‘u 

Overlook on September 7. The lake surface consists of large (tens of meters 

across) black crustal plates separated by narrow incandescent spreading 

zones. The robust portion of the gas plume originates from spattering in the 

SE sink, which is just out of view on the near margin of the lake. 

tensile strength, when tension ripped the surface and produced 

tears that propagated through the black crust.

Crustal plates were irregular in size, ranging from small 

(a few meters wide) to large plates that could span most of 

the lake surface (in other words, nearly 200 m across). We 

analyzed five high-resolution WorldView satellite images 

during 2016 that provided clear views of the lake surface 

during typical activity, and made measurements of a total of 

96 crustal plates (table 1, figs. 17–19). At a given time the lake 

surface consisted of 16–22 plates (mean=19). The plates had 

an average longest dimension of 64 m (standard deviation of 

35 m), with a maximum of 182 m. The average area of the 

individual plates was 1,949 m2 (table 1, fig. 17). The plate 

boundaries were often angular and jagged, but could also be 

arcuate (fig. 18).

The geometry of the plates was constantly changing during 

the course of plate migration from the upwelling zone in the 

north towards the south. Plate geometry changed as a result of (1) 

spreading zone migration from lake margins, (2) spreading zone 

replication, (3) plate splitting by way of crack propagation across 

a plate, and (4) plate fusing by way of spreading zone cessation. 

New plates formed near the upwelling area in the northern section 

of the lake in one of two ways. First, a plate might grow from the 

lake margin as a spreading zone migrated from the lake margin 

toward the lake center. Second, a plate might grow from a spot 

away from the lake margin (for example, in the upwelling zone 

in the north part of the lake) when a spreading zone replicated, 

forming two parallel spreading zones, with the new plate forming 

in the intervening gap as the two spreading zones migrated 

apart (figs. 20 and 21). New plates also formed from existing 

plates in two ways. First, a new plate might form as a result of 

a crack propagating across a plate, splitting it into two plates as 
12

Lava Lake Activity at the Summit of Kīlauea Volcano in 2016

A B C

D E F

G H I

J K L

January 17 February 28 March 19

April 15 May 16 June 26

July 29 August 6 September 3

October 8 November 20 December 4

SE sink

Figure 16. Monthly views of the lava lake during 2016. The shifting plume results in varying views of the lake. Lake activity was relatively steady 

throughout the year, but minor changes occurred. Lake level varied over several tens of meters (evident in this montage). Spattering was highly variable, 

but most commonly present in the SE sink. All 12 images in this figure show active spattering in the SE sink, but this does not imply that spattering was 

always present— in fact, spattering in the SE sink sometimes ceased for several hours at a time.
Lake Surface

13

Table 1. Summary of statistics for crustal plates in the lava lake at Overlook crater, Kīlauea Volcano, measured from high-resolution satellite data 

on five days in 2016.

[m, meters; Std Dev, standard deviation]

Date January 25 June 25 August 1 October 13 November 16 Total

Total lake surface area, m2 34,860 35,759 38,092 39,610 38,809

Number of plates 20 22 18 20 16 96

Area, m2

Minimum 10 223 48 31 14 10

Maximum 5,740 4,582 9,831 8,017 5,906 9,831

Mean 1,743 1,625 2,116 1,981 2,426 1,949

Median 945 1,157 736 1,242 2,216 1,078

Std Dev 1,703 1,245 2,785 2,085 1,994 1,971

Longest dimension, m

Minimum 5 25 14 11 6 5

Maximum 118 104 182 151 150 182

Mean 60 63 63 63 74 64

Median 55 59 48 63 76 58

Std Dev 32 23 47 34 38 35

Perimeter, m

Minimum 13 66 35 29 16 13

Maximum 359 331 526 480 425 526

Mean 176 174 181 182 214 184

Median 139 169 125 176 213 164

Std Dev 108 71 145 112 115 109

100 m

A B C D E

F G H I J

January 25, 2016 June 25, 2016 August 1, 2016 October 13, 2016 November 16, 2016

© 2016 

DigitalGlobe

NextView 

License

Figure 17. Satellite images of the lake in 2016. A–E, High-resolution WorldView satellite images of the lake through the year. F–J, Manually outlined drawings of 

crustal plates based on the satellite images. When the boundaries were not clear in the satellite images we used HTcam and HMcam images from the same time as 

the satellite acquisition to help identify plate boundaries.
14

Lava Lake Activity at the Summit of Kīlauea Volcano in 2016

100 m

January 25, 2016

June 25, 2016

August 1, 2016

October 13, 2016

A.

B.

C.

D.

E.

F.

G.

H.

I.

J.

November 16, 2016

Figure 18. Drawings of crustal plate outlines based on five highresolution satellite images in 2016 (fig. 17). The crustal plates at each 

time are arranged by size to illustrate their varying geometries.

0 2,000 4,000 6,000 8,000 10,000

Plate area, in square meters

0

10

20

30

40

Number of plates

0 200 400 600

Plate perimeter, in meters

0

5

10

15

20

50 100 150 200

Plate length, in meters

0

5

10

15

20

0

A

B

C

Figure 19. Histograms of crustal plate measurements taken 

from WorldView images (see figs. 17 and 18).

spreading zone being replicated

new plate forming

new plate forming

Figure 20. Image showing spreading zone replication and the formation 

of new plates. A spreading zone could replicate, forming two parallel 

spreading zones and a new, growing crustal plate in the intervening space. 

Photograph taken December 15, 2016.
Lake Surface

15

A. 16:06 B. 16:10

C. 16:12 D. 16:14

E. 16:16 F. 16:18

Figure 21. A sequence 

of HMcam images taken on 

December 18, 2016 (times are 

HH:MM HST), showing new 

plates forming by spreading 

zone replication. The yellow 

arrow tracks the formation and 

growth of a new plate, formed 

where a single spreading zone 

split into two parallel spreading 

zones, with the plate forming 

in the intervening gap. The 

plate is formed in the upwelling 

zone (north portion of lake) 

and grows steadily in area as it 

migrates south (towards bottom 

of image).

a spreading zone developed along the crack (fig. 22). Second, 

spreading zones sometimes became inactive, allowing adjacent 

plates to fuse together into a composite plate (fig. 22).

Unusually large plates, sometimes covering nearly 

the entire visible lake surface as viewed from the HTcam, 

occasionally formed (fig. 23). These “megaplates” grew from 

fusing of individual plates as the lake surface velocity dropped 

substantially, which was normally associated with spattering 

in the northern margin of the lake that initiated a flow reversal 

towards the north (Patrick and others, 2016c). Further work 

has shown that the average plate size across the lake at a 

given time is inversely related to the overall surface velocity 

(and therefore plate number scales with surface velocity). In 

other words, a rapid surface flow produced smaller plates, of 

a greater number, while a slowed surface flow produced larger 

plates, of lesser number.

Occasional large rockfalls impacting the lake surface 

triggered sloshing across the entire lake that abruptly pulled and 

split plates into smaller units, creating many small plates. This 

process created a greater number of plates than was usual at any 

one time, and was a conspicuous indicator of a recent collapse 

(fig. 24). Once the waves on the lake surface subsided, within 

several minutes small plates fused into larger ones and the lake 

surface returned to having a typical number of plates.

In some cases a static plate formed near the northern margin 

and remained attached to the crater wall, providing a cap on the 

upwelling zone (fig. 25). When this occurred long crustal plates 

radiated out from the margins of the static plate, extending into 

and migrating towards the southern portion of the lake. Sometimes 

portions of the static plate would detach from the leading edge and 

be shed into the current while the rest of the static plate remained 

attached to the crater wall.
16

Lava Lake Activity at the Summit of Kīlauea Volcano in 2016

1

1a

1b

1c

1

2

3

1

2

1a

1b

1

A. 16:24

B. 16:26

C. 16:28

Figure 22. A sequence of HMcam images taken on December 18, 

2016 (times are HH:MM HST), showing new plates forming from existing 

plates in two ways, First, as marked by the yellow labels, a single plate 

could develop a propagating spreading zone that split the plate into 

two or more new plates. In this example, one plate (1) is split into three 

plates (1a,b,c). Second, as marked by the red labels (1a,b), multiple 

plates could fuse together to form a composite plate (1). In this example, 

the spreading zone separating two plates gradually becomes inactive, 

solidifying and fusing the two plates into one.

A

B

megaplate

megaplate

Figure 23. Images taken from HMcam (A) and HTcam (B) at roughly 

the same time (October 4, 2016 at 07:40 HST) showing the formation of a 

megaplate. When the lake surface velocity dropped to very low levels, often 

associated with spattering in the northern part of the lake which would trigger 

a reversal of the typical southward flow, adjacent plates could fuse together 

as spreading zones became inactive, forming a megaplate that covered the 

majority of the lake surface (Patrick and others 2016c). The yellow arrows in 

A give a sense of the general motion of the megaplate at this time, which was 

towards the two spatter sites at the northern lake margin.
Lake Surface

17

A. 22:30 B. 22:32

C. 22:34 D. 22:36

E. 22:38 F. 22:50

rockfall

into lake

Figure 24. Sequence 

of HMcam images from 

December 21, 2016, 

showing a rockfall 

(occurs around 22:32 

HST) that triggered 

waves and sloshing of 

the lake surface and 

created many small 

plates. Plate size 

returned to normal within 

about 20 minutes. Times 

are shown as HH:MM 

HST.

static (attached) 

plate

Figure 25. HMcam image from December 11, 2016, at 10:22 HST, 

showing a static plate at the lake margin. At times, a plate could remain 

attached to the northern lake margin, providing a cap over the upwelling 

zone. When this happened, long crustal plates radiated out from the 

static plate, spanning the majority of the length of the lake surface. The 

yellow arrows show the general motion of these radiating plates. 
18

Lava Lake Activity at the Summit of Kīlauea Volcano in 2016

A B

parent plate

Figure 26. Photographs showing the most common type of plate margin, simple spreading. A, Symmetric spreading involves adjacent plates moving at 

roughly the same rate. Photograph taken December 8, 2016. B, Asymmetric spreading involves one plate moving more rapidly away from a more slowly 

moving plate. In this case, fresh lava had the appearance of flowing out from under a parent plate. For scale, the image spans roughly 25 meters from left to 

right. Photograph taken November 26, 2016. Dashed white arrows indicate general direction of plate movement.

Plate Margins

We describe a number of different types of plate margins, 

including (1) simple spreading (both symmetric and asymmetric), 

(2) pulled, (3) transform, (4) unzipping, and (5) foundering. In the 

sections below we discuss the relative motion of adjacent plates, 

but it is important to note that, in most circumstances, the plates 

and margins were together migrating with the overall southward 

lake motion.

The most common type of margin was simple spreading, 

which could range from symmetric to asymmetric (fig. 26). 

Spreading margins consisted of a narrow (<1 m wide) linear zone 

of incandescent lava where crust was formed and slowly moved 

away from the spreading zone. Often the narrow incandescent zone 

formed a jagged, zig-zag line. In other places the spreading zone 

was offset in steps with transform (strike-slip) margins in between. 

Symmetric spreading zones consisted of a bright incandescent 

centerline that transitioned evenly on both sides to dull 

incandescence, and then black crust, suggesting similar spreading 

rates on either side of the margin. In asymmetric spreading zones, 

new crust formed only on one side of the incandescent zone. In 

this case the incandescent zone had an abrupt boundary with welldeveloped black crust on one side, with the other side having the 

gradual transition into dull incandescence and then black crust. In 

asymmetric spreading zones, incandescent lava flowed out from 

underneath the more slowly moving black crust of the parent plate.

Pulled margins were zones of enhanced spreading owing 

to proximity to a spatter site, where surrounding crust is pulled 

more rapidly than it would move passively elsewhere in the lake 

(fig. 27). The crust was “pulled” downward into the volume 

evacuated by gas escaping from the lava. The pulled margins 

produced larger zones of fresh, incandescent lava, which tended 

to have enhanced bursting of small (decimeter size) bubbles, 

perhaps as a result of the larger span of fluid, uncrusted lava.

Transform margins consisted of strike-slip motion between 

plates, and sometimes exposed little to no incandescent lava 

(fig. 28). Instead, the margins had small transpressional folds 

resulting from slight compression, and the folds on each side 

of the margin were in contact, or nearly so, masking any 

incandescence between the plates. Transform margins often 

occurred in steps between offset zones of spreading.

Often an intact plate would be pulled apart, creating a rapidly 

propagating incandescent crack in the black crust, sometimes 

consisting of small, discontinuous en echelon cracks at the leading 

edge (fig. 29). As the crack tip propagated, the crack behind the tip 

would spread open, creating a triangular wedge of incandescent 

lava cutting through the plate. We call this an unzipping margin. 

As fluid lava in the wedge cooled slightly, towards the dullest level 

of incandescence, it would develop a classic zig-zag incandescent 

spreading line. The propagating crack tip would eventually 

intersect another spreading zone (sometimes at right angles) over 

the course of tens of seconds, and the unzipping margin would 

transition to a simple spreading zone.

Crustal foundering was a process whereby slabs of crust 

would detach, slide, and sink into the lake, exposing patches 

of fluid incandescent lava that often experienced minor 

bubbling. Slabs from both sides of the margin were often 

dragged down together. Foundering rarely happened near 

the center of the lake and was much more common around 

the lake margins and in the very southern portion of the lake 

near the southern ledge (fig. 30). One exception was during 

times of megaplates, described above, in which a single large 

plate covered much of the lake surface. At these times, the 

megaplate was susceptible to foundering that could occur near 

the center of the lake. Crustal foundering is common in static 

lava lakes, such as Kīlauea Iki in 1959 (Stovall and others, 

2009); the nearly constant movement within the Overlook 

crater lava lake probably inhibited the conditions required for 

foundering.

At the lake margins the downwelling process often 

involved a narrow zone of foundering, extending out from the 

crater walls by a few meters (fig. 31). In other cases, the lava 

simply subducted against the crater wall at the immediate lake 

margin without any foundering.
Lake Surface

19

Figure 27. Photograph showing a pulled margin near the SE sink on 

December 12, 2016. White arrows show the approximate motion of the 

lake surface. Crustal plates near spattering sites are “pulled” towards the 

spattering at a higher velocity than they would normally experience on the 

lake. When these plates rapidly migrate towards the spatter, a detachment 

zone forms, which we call a pulled margin. At this margin, a broader area 

of incandescent lava was exposed compared to normal spreading zones. 

Often, enhanced bubbling was present in this incandescent zone. 

asymmetric spreading margin

transform margin

asymmetric spreading margin

asymmetric 

spreading 

margin

quasi-transform margin

Figure 28. Photograph showing an example of strike-slip motion on 

a crustal plate margin, where only a minor amount of incandescent lava 

was exposed (bottom of photograph). Quasi-transform margins, where 

the spreading direction was highly oblique to the trend of the plate margin, 

could also occur (upper right area of photo). Photograph taken December 

12, 2016.

A B

C D

0 seconds 4 seconds

8 seconds 22 seconds

Figure 29. Time-lapse images from December 12, 2016, at 17:11 HST, of a propagating crack in the crust. New spreading zones could appear when a plate 

“unzipped”, with the propagating, discontinuous crack and spreading zone migrating across the plate, and intersecting another spreading zone. In this example, 

the crack traverses approximately 9 meters, about half the plate span, in roughly 8 seconds.
20

Lava Lake Activity at the Summit of Kīlauea Volcano in 2016

A 0 seconds B 5 seconds

C 8 seconds D 11 seconds

E 15 seconds F 18 seconds

quiescent downwelling

Figure 30. Time-lapse images showing crustal foundering, which normally occurred near the lake margins, particularly in the southern 

portion of the lake, as it is in this example from December 22, 2016 (at 12:17 HST). In A, the arrows show the convergent motion of the two 

plates, which eventually subduct against one another and disappear into the lake. The southern ledge is visible at the left side of the images.

Figure 31. Photograph of quiescent downwelling at the lake 

margin, taken December 12, 2016, at 17:13 HST. The majority 

of the lake margin had lava quietly downwelling against the 

crater wall, in a zone of foundering that extended out from the 

crater wall by a meter or two. 
Lake Surface

21

Surface Relief

The crustal plates were commonly covered by scattered small 

(1–2 m diameter) domes that resembled blisters (fig. 32). The 

formation of these blisters has been observed clearly by the naked 

eye and video, and consisted of a thin, semi-flexible surface crust 

abruptly doming up within a second or two—suggesting that a 

bubble of gas rose and was trapped beneath the crust. Occasionally 

these blisters would burst as they formed, and eject a small bit of 

spatter, reinforcing the interpretation that the blisters are discrete 

bubbles rising to the surface that fail to break the crust.

Although most of the lake surface was relatively smooth, 

folds did occur (fig. 33). Small folds, with wavelengths less than 

a meter, could occur anywhere on the lake and were associated 

with localized compression of the thin semi-flexible crustal plates, 

particularly near spreading zones. Larger folds, with wavelengths 

of several meters, tended to occur near the lake margins where 

lava was downwelling. Large folds were particularly common in 

the southern portion of the lake near the southern ledge, perhaps 

because the crust was thicker in the section of the lake farthest 

from the upwelling area.

Figure 32. Photograph showing small blisters on the lake surface. 

These blisters were several meters in diameter, and formed abruptly, 

a result of gas bubbles rising to the surface and doming up the thin, 

flexible crust, without breaking it. Photograph taken December 14, 2016, 

at 17:00 HST.

Figure 33. Photographs showing small folds on the lake surface. Small folds, attesting to the thin and semi-flexible nature of the surface crust, were common 

near the lake margins where lava downwelled. Most folds appeared to have amplitudes less than 1–2 meters. A, A series of folds along the southern lake 

margin on January 12, 2016. B, Folds in front of a spattering site, along the southern lake margin on November 26, 2016. C, Larger folds along the eastern lake 

margin on December 8, 2016. D, Small folds made visible by the incandescence from spattering in the SE sink, on December 12, 2016.

A B

C D
22

Lava Lake Activity at the Summit of Kīlauea Volcano in 2016

Small waves were another surface relief feature but were 

limited strictly to the immediate area surrounding a spatter site. 

The waves appeared to have an amplitude of 1–2 m, and extended 

roughly 5–10 m out from the spatter site. The black crust rolled 

atop the waves as they passed, without being torn or broken, 

consistent with a thin and flexible crust.

No lidar data were collected during 2016, so we do not 

have precise information on the variations in surface elevation 

across the lake. Data from 2013 indicated that the upwelling 

zone was 0.6 m higher than the southern part of the lake 

(Anderson and others, 2014).

Surface Texture

Crustal plates often had a variety of surface textures 

(fig.34). Surface texture could be used for tracking the 

provenance of different portions of a given plate, sometimes 

allowing us to link a given area of the plate to the particular 

spreading zone where it formed (fig. 35). The surface textures 

across the lake were best observed at dawn or dusk when 

oblique sunlight highlighted the surface relief.

A uniformly rough texture, on the scale of centimeters, was 

commonly observed and was associated with symmetric spreading 

zones (fig. 26). Striations were a common feature on the crustal 

plates (Duffield, 1972), often extending the entire length of plates, 

and were associated with asymmetric spreading zones. Close-up 

photographs showed that the striations corresponded with small 

jagged points along the front of the asymmetric spreading zone 

where the striated crust formed (fig. 36). The lava extruding from 

the embayments between the jagged points seemed to form narrow 

ridges, whereas the lava extruding out from the tips of the jagged 

points formed subtle valleys. This small-scale relief appears to 

correspond to the striations. Striations were oriented parallel to the 

direction of spreading and thus indicated the direction of flow as 

the crust moved away from the spreading zone where it formed, 

which was useful in determining plate provenance (fig. 35).

At times, alternating bands of light and dark crust 

developed parallel to the spreading zones, and probably 

represented variations in the surface texture highlighted by 

the sun angle (fig. 37). These surface texture differences 

presumably were produced by changes at the spreading zone, 

perhaps in the spreading rate, but we do not know for sure.

The crustal plates commonly had many small, centimetersized scattered holes that exposed incandescent lava beneath the 

crust. These holes were easily visible at night, and resembled 

stars in the night sky (fig. 38). The holes seemed to be produced 

at spreading zones when small bubbles burst through the nascent, 

solidifying crust, with the hole preserved as the crust migrated 

away from the spreading zone. The holes were more abundant 

in certain zones of a given plate, suggesting that they were more 

likely to be formed at some spreading zones than others.

When plates were split apart by unzipping margins, new 

spreading zones appeared and supplied fresh lava to the surface. 

The newer lava commonly had a different surface texture than the 

original plate that was split apart, and the original “proto-plate” 

Figure 34. Photograph taken October 26, 2016, at 15:16 HST, showing 

the patchwork appearance of the lake surface. A given plate could have 

several areas of differing textures, including striations oriented at different 

angles (Duffield, 1972). At low sun angles, these texture differences 

produced strong differences in the brightness of the lake surface. 

S

S

S

C

C

C

A

B

S

S

S

C

C

C

S

C

C

C

Figure 35. Photographs taken December 8, 2016, showing the provenance 

of crustal plate areas. In many cases the surface texture could be used to link 

a given portion of a crustal plate to the spreading zone where the crust formed. 

In these examples, the area of crust (labeled “C”) can be linked to its parent 

spreading zone (“S” of the same color). 
Lake Surface

23

A B

Figure 36. Photographs showing striations on the lake surface. A, Long parallel striations on the lake surface were common, and best visible 

in low-angle sunlight. Image taken October 26, 2016, at 15:15 HST. B, These striations appeared to represent small ridges and valleys formed by 

jagged boundaries of the parent plate at asymmetric spreading zones. Image taken December 10, 2016, at 17:53 HST.

A B

Figure 37. Photographs showing alternating bands of darkness parallel to the spreading zones. The bands probably relate to variations in surface 

texture, and presumably reflect changes in the spreading zone. Photographs taken December 22, 2016.

Figure 38. HMcam image from December 1, 2016, at 01:00 HST, 

showing pinholes on the lake surface. Small (centimeter size) holes 

were common in crustal plates, resulting in tiny spots of incandescence 

scattered across the plate surface. The holes appeared to form from 

tiny bubble bursts in the region of fluid (or semi-fluid) lava at spreading 

zones, with the hole preserved as the crust solidified.
24

Lava Lake Activity at the Summit of Kīlauea Volcano in 2016

was sometimes surrounded by this differing surface texture, 

appearing as an island of older crust that was often distinct to the 

naked eye (fig. 39). Thermal camera images provided an even 

clearer distinction between the proto-plates and the newer lava, 

with the proto-plates having a much lower apparent temperature 

(about 45 degrees Celsius [°C] lower in the example in figure39) 

than the newer lava owing to the greater exposure time of the 

proto-plate. Proto-plates were often portions of static plates 

(attached to the northern lake margin) that broke off and were shed 

into the southward current, as in the example shown in figure 39.

A 11:48 B 11:49 C 11:50

D 11:51 E 11:52 F 11:53

G 11:54

Figure 39. Sequence of images from December 22, 2016, showing proto-plates and their origin. Proto-plates are areas 

of older crust often entirely surrounded by newer crust, which form when new spreading zones split an existing plate. In this 

example, a sequence of thermal camera (HTcam, fig. 2) images (times are HH:MM HST) show a spreading zone form in a static 

plate along the northern lake margin, essentially breaking off a piece (black arrow) of the static plate and causing it to flow south. 

The original piece of static plate is evident in the thermal images owing to its cooler temperature (in other words, greater age), 

and is also obvious to the naked eye (G) because of its different surface texture. 
Lake Surface Motion

25

Lake Surface Motion

For the majority of the time, the lake surface motion was 

stable and consisted of lava flowing radially from its upwelling 

zone near the northern lake margin (fig. 40). Because the 

upwelling zone was often situated 10–30 m out from the northern 

lake margin, most of the lake surface flowed to the south and only 

a small portion flowed west, east or north during periods of normal 

flow behavior.

During this normal mode of lake behavior, crust reaching the 

lake margins quietly subducted in a foundering zone that extended 

out from the lake margin by a few meters. When spattering in 

the southeast (SE) sink was active (see below), which was very 

common, this downwelling was enhanced at the SE sink and 

a large portion of the southward flow was directed towards the 

spattering in the sink, where crust was torn and consumed.

 Normal north-south surface flow (stable regime) Stable regime with slight disruption due to spattering 

Unstable surface flow regime due to vigorous spattering

September 30, 2016 9:30 a.m. September 30, 2016 10:30 a.m.

September 24, 2016 3:30 a.m.

A B

C

Figure 40. Thermal images showing lake surface motion regimes. 

A, Normal surface flow consisted of upwelling in the northern part of 

the lake (top of image), with surface crust radiating out and dominantly 

flowing south. This is called a stable surface flow regime (Patrick and 

others 2016c). B, Slight disruptions to this surface flow regime occurred 

when spattering created a sink and a localized shift in the surface flow 

field. C, Large scale spattering could trigger a complete change in the 

surface flow over the lake surface, often with the surface flowing north. 

Changing flow directions occurred as spattering sites migrated along the 

lake margins. This behavior is called an unstable surface flow regime 

(Patrick and others 2016c).

Localized disruptions to this stable, primarily southward 

surface flow were triggered by the appearance of new spattering 

sites. Spattering sites were areas of lava downwelling (never 

upwelling). Small rockfalls could trigger spattering and create 

a new downwelling area that locally pulled nearby crust into it. 

This downwelling processes was described by Perret (1913b) 

as the “siphon” effect, whereby the large bursting bubbles at 

spattering sites create void space and a localized depression 

that surrounding lava plunges into (Patrick and others, 2016c). 

Jaggar (1917) referred to the same process as “downsucking” 

in the early 1900s lava lake, and noted “a continuous fountain 

is always a place of rapid downsucking and engulfment.” The 

resulting effect on surface motion is that moderate spattering 

could produce a very localized velocity field directed towards the 

spattering, and superimposed on the larger, southward oriented 

velocity field of the majority of the lake surface (fig. 40).
26

Lava Lake Activity at the Summit of Kīlauea Volcano in 2016

Occasionally, significant spattering that appeared along the 

northern lake margin was associated with wholesale reversal of 

the majority of the lake surface flow direction towards the north 

(fig. 40). This flow reversal resulted in a significant drop in surface 

velocity and the fusing of plates to create a megaplate (fig. 23). 

The spattering was mobile, migrating along the lake margin and 

changing the surface vector field, resulting in an unstable surface 

flow regime that could persist for several hours at a time. Patrick 

and others (2016c) contrast this unstable surface flow with the 

normal, stable north-south surface in a quantitative manner.

Large rockfalls into the lake—sometimes creating explosive 

events (Orr and others, 2013)— could produce an abrupt increase 

in the overall velocity of the lake surface. The lake motion was 

directed towards the vigorous spattering at the point of impact, 

with the crust seeming to pour into the spattering at the impact 

site. Presumably, this is an extreme example of the siphon effect 

described by Perret (1913b) and mentioned above. The unusually 

high velocities likely relate to the unusually vigorous spattering 

associated with large collapses into the lake. Once the spattering 

returned to normal, over tens of minutes, the lake surface velocity 

rapidly dropped to more typical levels.

Spattering

Spattering and Nonspattering Phases

Spattering was common in the lake, and was normally 

focused at one or more sites at a given time, with each site 

commonly 10–20 m wide. Spattering appeared to consist of 

pulsating bursts of large spherical bubbles, each decimeters in 

size, with doming and bubble bursts overlapping in both time and 

space at the spatter site (Houghton and others, 2014). Observations 

show that some bursts are from bubbles and others are rebounds 

of lava from the base of the bubbles. The bursts ejected a lattice 

work that extended to 5–10 m height above the lake, with small 

pieces of spatter thrown much higher (>15 m) (fig. 41). Smaller 

bits of spatter are carried by the rising gas plume to the rim of 

Halema‘uma‘u.

Other than direct observations or webcam imagery, seismic 

tremor was the best means of tracking the intensity of spattering in 

the lake (fig. 42). The high-pass (>1 hertz [Hz]) filtered component 

of nearby broadband station NPT (figs. 1B and 2) provided a 

good proxy for spattering intensity and gas emission rates (Kern 

and others, 2015; Nadeau and others, 2015; Patrick and others, 

2016a,c). Infrasonic tremor has shown a similar relation with 

spattering intensity (Patrick and others, 2011a; 2016a).

Spattering was present most of the time, but occasional 

periods of nonspattering could persist for spans of several hours. 

These nonspattering phases often correspond to a slight (<5 m) 

rise in the lake surface in a process of “gas pistoning” (Swanson 

and others, 1979; Patrick and others, 2016a). Gas pistoning in the 

lake at Halema‘uma‘u has been explained as the accumulation 

of bubbles, perhaps as a foam, near the upper surface of the lake 

(Patrick and others, 2016a), following the explanation for similar 

activity at Pu‘u ‘Ō‘ō by Orr and Rea (2012). Nonspattering phases 

A

B

39 meters

Figure 41. Photographs showing typical spattering in 2016. Spattering sites 

were normally at the lake margin, and were several tens of meters wide. The main 

body of the spattering site extended 5–10 meters (m)above the lake, throwing 

small bits of spatter to heights of more than 20 meters. A, Wide view of spattering 

at the northern lake margin. The Overlook crater wall, 39-m high, is shown for 

scale. B, Close-up of spattering in the same location. Photographs taken by Hans 

Schwaiger, U.S. Geological Survey, from station A4 on May 26, 2016.

were conspicuous in seismic tremor data owing to their unusually 

low tremor amplitudes, termed “tremor stagnation” (Patrick and 

others, 2016a) (fig. 42).

Using the high-pass filtered (>1 Hz) component at station 

NPT, we computed 1 minute real-time seismic amplitude 

measurement (RSAM) values (Endo and Murray, 1991) and 

applied a threshold of 100 counts (Patrick and others, 2016c) 

to discriminate between spattering and nonspattering phases. 

We estimate that spattering was active 96 percent of the time 

during 2016, while nonspatter phases accounted for 4 percent. 

This percentage marks a dramatic reduction in the frequency 

of nonspattering phases in 2016 compared to previous years. 

Using the same method, Patrick and others (2016c) estimated 

that nonspattering phases occurred 24 percent of the time 

between January 2013 and September 2015. Just focusing on 

2015 for comparison, this approach yields a nonspattering 

frequency of 23 percent. The much lower frequency of 

nonspattering phases in 2016 may relate to the higher overall 

lava lake levels of 2016.
Spattering

27

30 minutes

12:00

00:00

12:00

19:00 HST 

moderate spattering

(moderate tremor)

01:00 HST 

intense spattering

(high tremor)

05:00 HST 

no spattering (gas piston)

(tremor stagnation)

18:00

06:00

A

B

C

D

The SE Sink

The most common area of spattering was at a site 

called the southeast (SE) sink, which is in the east corner 

of the lake directly below where the Overlook crater rim 

intersects the Halema‘uma‘u Crater wall (figs. 2 and 43). 

This area is referred to as a sink because there is enhanced 

downwelling of the surface crust at the site of the spattering, 

with the surface around the SE sink being pulled towards the 

spattering by way of the siphon effect described by Perret 

(1913b). Note this was not the only area of downwelling; 

there was concurrent quiescent downwelling of lava along the 

lake margins elsewhere, whether or not the SE sink spattering 

was active.

The SE sink spattering was the most consistent spattering 

site in the lake, often persisting for days at a time. Spattering 

in the SE sink was often nestled in a small grotto built of 

solidified spatter attached to the crater walls (fig. 44). The 

overhanging roof and walls of the grotto often had unstable 

Figure 42. Relation between seismic tremor and spattering intensity. A, A helicorder plot showing the seismic trace from 

station NPT (fig. 1B) over 24 hours (December 15, 2016 12:00 HST to December 16, 2016 12:00 HST). These data have 

been high-pass filtered (>1 hertz). Each horizontal trace spans 30 minutes. B, Moderate tremor corresponds with moderate 

spattering in the lake. C, High tremor corresponds with intense spattering in the lake. D, Very weak tremor, also called tremor 

stagnation, is associated with nonspatter phases, which corresponds with a gas pistoning phase (Patrick and others 2016a).

bulbous protrusions that commonly collapsed, changing the 

shape and geometry of the grotto on a daily or hourly basis. 

Sometimes these protrusions on the grotto roof and walls had 

dangling lava stalactites, which were semi-flexible and would 

swing back and forth in the turbulent air around the spattering 

(fig. 45).

It is not clear why spattering in the SE sink was so 

persistent. One possibility is that the subsurface geometry 

of the Overlook crater focuses a disproportionate amount of 

the southward flow into the southeast corner of the lake, and 

this focused downwelling may facilitate bubble coalescence 

and spattering, which then drives enhanced downwelling in a 

kind of feedback loop. Another possibility is that a submerged 

minor conduit exists below the SE sink, with downwelling 

into the conduit. In either case, spattering at the SE sink is 

not the driving force for the normal north-south surface flow 

direction. Patrick and others (2016c) showed that the northsouth surface flow direction is maintained, with little to no 

change, when spattering in the SE sink ceases.
28

Lava Lake Activity at the Summit of Kīlauea Volcano in 2016

A B

C D

Figure 43. Photographs of the Southeast (SE) sink. The SE sink, an area of spattering in the southeast corner of the lava lake, was the 

most common area of spattering. A, View of the SE sink spattering, partly recessed within a grotto formed from overhanging spatter deposits. 

Photograph taken from station A4 on January 7, 2016. B, A close-up of spattering in the SE sink on June 27, 2016. C, Spattering in the SE 

sink. Photograph taken from station A4 on October 5, 2016. D, Spattering in the SE sink was visible from the Hawaiian Volcano Observatory 

(HVO) and Jaggar Museum when the lake level was high. Photograph taken from HVO on September 20, 2016.

Figure 44. Photograph of a grotto surrounding the spattering in the 

SE sink. Note the overhanging bulbous features on the grotto roof. 

Photo by Hans Schwaiger, U.S. Geological Survey, on May 26, 2016.

Figure 45. Photograph of stalactites at the spatter grotto along 

the eastern lake margin on October 3, 2016. Spattering sites were 

commonly set within a grotto, formed from solidified spatter deposits 

with an overhanging roof. Lava dripping down the overhang could 

form stalactites ~2 meters long. These stalactites were semi-flexible, 

and swayed back and forth in the turbulent air around the spattering. 
Spattering

29

Other Spatter Locations

Although spattering was most frequently present in the SE 

sink, it was not uncommon in other portions of the lake (fig. 46). 

However, nearly all of the spattering sites outside of the SE sink 

were relatively transient, generally not persisting for more than 

a few hours. These additional spatter sites were nearly always 

at the lake margins, which could be the result of two factors. 

First, the spattering is often triggered by small rockfalls from the 

crater walls, which necessarily leads to spattering at the margins. 

Second, the downwelling at the lake margin might be a zone of 

weakness that allows gas escape to occasionally trigger larger 

scale spattering.

Less commonly, spattering was present well away from the 

lake margins, sometimes near the center of the lake. These spatter 

sites clearly were not triggered by rockfalls and must have been 

caused by other processes. Normally, spatter sites near the center 

of the lake were slowly carried south towards the southern margin 

and ledge by the prevailing current. This spattering sometimes 

occurred as a series of events.

Migrating Spatter

The spattering sites that occurred outside of the SE sink 

were also often mobile and tended to migrate slowly along 

the lake margins, normally towards the southern portion of 

the lake (fig.47). Presumably the spattering sites were carried 

by the prevailing current, and this is one piece of evidence 

suggesting that the spattering in the lake is generally shallowly 

rooted (Patrick and others, 2016a,c). In the example shown 

in figure47, a spattering site migrated roughly 120 m along 

the east lake margin over a span of 20 minutes, equivalent to 

a velocity of 0.1 m/s. This migration velocity of the spatter 

site is similar to measured surface crust velocities in the lake 

(Patrick and others, 2016c), supporting the idea that spatter 

A B

C D

Figure 46. Photographs showing spattering outside of the SE sink area. A, Spattering along the northern lake margin. Photograph by Hans Schwaiger, U.S. 

Geological Survey, May 26, 2016. B, Close-up of spattering along the northern lake margin. Photograph by Hans Schwaiger, May 26, 2016. C, Spattering in the 

southern portion of the lake, about 20 meters (m) from the lake margin. Photograph taken from a spot about 100 m east of the Halema‘uma‘u Overlook on September 

10, 2016. D, Spattering at the base of the southern ledge. Photograph taken from a spot about 100 m east of the Halema‘uma‘u Overlook on November 26, 2016.
30

Lava Lake Activity at the Summit of Kīlauea Volcano in 2016

15:52

A

15:56

B

16:02

C

16:06

D

16:10

E

16:12

F

Figure 47. Sequence of images taken from the HMcam on December 20, 2016, showing spattering that appears along the northern 

lake margin split, with the eastern spatter site (yellow arrow) gradually migrating southeast along the eastern lake margin. This eastern 

spatter site covers roughly 120 meters in 20 minutes, equivalent to a velocity of about 0.1 meter per second. Spattering that appeared in 

areas outside of the SE sink was normally carried towards the south, presumably by the current in the lake.

is carried by the lake current. However, more detailed work 

could investigate how closely the spatter migration velocity 

compares to the adjacent crust velocity. Migrating spatter sites 

have been observed many times before, and were a common 

phenomenon in the early 1900s lava lake in Halema‘uma‘u. 

The reports from that time refer to this phenomenon as 

“traveling fountains” (Brigham, 1909; Perret, 1913a; and 

many HVO weekly bulletins compiled in Bevens and others, 

1988; see also Patrick and others, 2016c). It is also likely 

similar to the migrating spatter observed at an elongate lava 

pond on the East Rift Zone in late 2007 (Patrick and others, 

2011b).
Lava Level Changes

31

Northern Bubble Bursts

A common feature observed in the lake was sporadic bubble 

bursting in the upwelling zone (Orr and others, 2014) (fig. 48). 

These bursts seem to be quasi-periodic, separated by tens of 

seconds to minutes, and appeared to be individual decimetersize bubbles (slugs) or bubble clusters that abruptly burst at the 

surface, creating a circular exposure of fresh incandescent lava 

a few meters in diameter (fig. 49). Because these bubble bursts 

have been consistently clustered in the north section of the lake, 

coinciding with the zone of lava upwelling, we presume that they 

represent gas bubbles traveling directly upwards from the conduit 

that feeds lava into the base of the lake (Patrick and others, 2016c).

Post-explosion Spattering

Large rockfalls into the lake triggered vigorous spattering, 

which could extend well beyond the point of impact and persist 

long after the initial explosive event. In the November 28 and 

December 2, 2016, collapses, this spattering persisted at a 

rapidly diminishing intensity for about an hour after the rockfall 

(fig. 50). The increased spattering may be the result of enhanced 

coalescence of smaller bubbles (in other words, previously 

exsolved gas) already accumulated in the upper portions of 

the lake, and some may be the result of triggered nucleation of 

bubbles (in other words, new exsolution) in the lake (Carey and 

others, 2012).

Lava Level Changes

The lake level in 2016 fluctuated constantly, over both 

short (minutes) and long (months) timescales. The lake level 

ranged from about 60 to 0 m below the Overlook crater rim, 

corresponding to an elevation above sea level of 971–1,031 m 

(fig. 51). There was little net change in lake level through the 

first eight months of the year (figs. 52 and 53), with an abrupt 

rise in September. The lake surface was sporadically visible 

from the Jaggar Museum overlook in the first half of the year 

(fig. 54) but became more consistently visible after the rise 

in September (fig. 55). On a day to day basis, the lake level 

fluctuated in concert with summit tilt, as in previous years 

(Patrick and others, 2015), and had the typical cycles associated 

with deflation-inflation (DI) events (Anderson and others, 2015; 

Patrick and others, 2015).

The lake surface reached the rim of the Overlook crater on 

just one day during 2016, when two small lobes spilled over the 

rim and flowed several tens of meters onto the Halema‘uma‘u 

Crater floor on October 15 (fig. 56). On November 29, 2016, HVO 

scientists visited the floor of Halema‘uma‘u Crater and sampled 

these overflows (as well as the 2015 overflows). Both the 2015 

and 2016 overflows consisted of large sheets of shelly pāhoehoe.

Lava level fluctuations were the result of two main processes. 

The primary control on lake level has been summit magma 

reservoir pressure, which is tracked primarily with ground tilt. 

The correlation is sufficiently strong that the plot of lava lake level 

closely resembles the plot of summit tilt as measured at station 

UWE (fig. 57). Patrick and others (2015) showed that, based on 

2012–14 data, the summit lake level changed by 5±0.8 m for 

every microradian of radial (along an azimuth of 327°) tilt change 

at UWE. These pressure-driven changes could result in lava lake 

level changes of tens of meters over timescales of several days. 

The secondary control on lava lake level is outgassing-driven 

changes related to spattering and gas-pistoning, producing more 

rapid changes (over minutes to hours) with a smaller amplitude 

(generally several meters).

Magma supply rate is one of the processes controlling 

summit magma reservoir pressure and lava level. On a scale of 

several months, monthly-averaged lake level rose and fell in 

concert with changing uplift rates at the summit as measured 

A

B

Figure 48. Photographs showing sporadic bubble bursts in the 

upwelling zone. Bubble bursts commonly occurred in the same general 

area in the northern section of the lake. The bursts were normally 

separated by tens of seconds. The correspondence of this area of bubble 

bursting with the upwelling zone suggests that these bubble bursts may 

represent gas bubbles rising upwards directly from the conduit that feeds 

lava into the lake. A, Photograph taken from the HMcam site (fig. 2), on 

September 11, 2016. B, Photograph taken roughly 100 meters east of the 

HMcam site on December 19, 2016.
32

Lava Lake Activity at the Summit of Kīlauea Volcano in 2016

A B C

D E F

G H I

Figure 49. Photographic sequence of a bubble burst on December 22, 2016. A close-up of the bubble burst in the northern section of the lake, the 

sequence spans about 6 seconds. The disrupted area of lava is a few meters in diameter.

2 minutes before explosion (Nov 28) 4 minutes after explosion (Nov 28)

2 minutes before explosion (Dec 2) 4 minutes after explosion (Dec 2)

A B

C D

Figure 50. HMcam images 

of post-explosion spattering. 

Prolonged intense spattering 

was often present in the lake in 

the minutes following a rockfalltriggered explosive event. In 

both of these cases, the rockfall 

impacted the southern lake margin, 

which is at the bottom of the 

image. The spattering could occur 

well away from the rockfall’s point 

of impact. 
A B

Lowest level of 2016 Highest level of 2016

60 meters below

Overlook crater rim

February 21, 1:32 a.m.

0 meters below

Overlook crater rim

(lava at rim)

October 15, 1:34 p.m.

20 °C

500

Figure 51. Thermal images from the HTcam showing the difference in lake level and appearance at the highest and lowest levels through the year. A, 

The lowest lake level was approximately 60 meters below the Overlook crater rim, on February 21. B, The highest lake level occurred on October 15, 

when lava slightly overflowed the Overlook crater rim.

980

1,000

1,020

-10

-5

0

5

10

0

20

40

Jan Feb Mar Apr May Jun Aug Sep Oct Nov Dec 0

100

200

300

400

Lava lake elevation, in 

meters above sea level

UWE radial tilt, in

microradians

Located earthquakes 

per day (summit)

Jul

Daily RSAM, in counts

A Overlook crater rim

B

C

D

Months in 2016

Figure 52. Plot of lava lake elevation, summit 

ground tilt, and seismicity. A, Lake surface 

elevation was measured daily using a laser 

rangefinder. The highest measurement, on 

October 15, occurred on the day that lava slightly 

overtopped the Overlook crater rim. B, The 

radial component (along an azimuth of 327°) 

of ground tilt at station UWE (fig. 2). Note the 

frequent deflation-inflation events in the tilt signal, 

which produced daily fluctuations in lava level 

(Anderson and others, 2015; Patrick and others, 

2015). C, Located earthquakes per day in the 

summit region. Spikes in earthquake rates often 

correspond with higher lava levels (see also 

fig. 57). D, Daily average of real-time seismic 

amplitude measurement (RSAM) from station 

NPT, after high-pass filtering (>1 Hz).

Lava Level Changes 33
34

Lava Lake Activity at the Summit of Kīlauea Volcano in 2016

Figure 53. Monthly thermal camera images of the lava lake, showing level changes. Images taken from the HTcam on the 15th of each month at 

midnight. This collection is meant to provide a qualitative sense of lake level and geometry changes from a consistent viewing angle.

A January 15, 12 a.m. B February 15, 12 a.m. C March 15, 12 a.m.

D April 15, 12 a.m. E May 15, 12 a.m. F

I

June 15, 12 a.m.

G July 15, 12 a.m. H

J K L

August 15, 12 a.m. September 15, 12 a.m.

October 15, 12 a.m. November 15, 12 a.m. December 15, 12 a.m.
A B

Figure 54. Views of the lava lake from the Hawaiian Volcano Observatory (HVO). Rising levels in mid-2016 provided the first sustained views of lava from 

HVO and the public viewing area at Jaggar Museum. A, Wide view of Halema‘uma‘u, with spattering visible along the southern lake margin on September 6, 

2016. B, Close-up view of spattering along the southern lake margin. Photograph by Janet Babb, U.S. Geological Survey, July 20, 2016.

A B

September 10 September 24

Figure 55. Images from the HMcam show the differing lake level and appearance in September 2016. The lake reached a high level in early September, but 

deflation-inflation events resulted in a large drop by the end of the month. A, September 10, when the lake level was roughly 8 meters below the Overlook crater 

rim. B, September 24, when the lake was about 37 meters below the Overlook crater rim. Note the Overlook crater walls on September 24 have a covering of 

veneer on the western wall, but the veneer has fallen away on the eastern wall, exposing the light colored lithic wall.

Figure 56. K2cam webcam image showing a small overflow of lava 

onto the floor of Halema‘uma‘u Crater, taken on October 15, 2016, at 

13:34 HST from the Hawaiian Volcano Observatory tower. 

overflow overflow

Lava Level Changes 35
36

Lava Lake Activity at the Summit of Kīlauea Volcano in 2016

-6

-4

-2

0

2

4

995

1,000

1,005

1,010

1,015

1,020

1,025

11/28 12/01 12/05 12/09 12/12 12/16 12/20 12/24 12/27 12/31 01/04 01/08

0

5

10

15

20

25

UWE radial tilt, in 

microradians

Lava lake elevation, in 

meters above sea level

Located earthquakes per day

(upper East Rift Zone)

A

B

Month and day, 2016–2017

Figure 57. Graphs showing increase in small earthquakes during periods of inflation and high lava 

level. A, Plot of radial component (along an azimuth of 327°) of station UWE ground tilt, along with daily 

measurements of lake level. Note the close relation between these two trends (Anderson and others, 2015; 

Patrick and others, 2015). B, Number of located earthquakes per day in the upper East Rift Zone. The 

earthquake count area is defined by these bounds; latitude=19.351 to 19.411, longitude=–155.19 to –155.272.

by GPS. This has occurred throughout the eruption and has 

been ascribed to a slowly pulsing magma supply to the shallow 

storage reservoir under the summit of Kīlauea (Swanson and 

others, 2016).

Periods of unusually high lava levels and summit inflation 

were associated with swarms of shallow (<5 km) earthquakes 

in the summit and upper East Rift Zone (figs. 52 and 57). Most 

of these earthquakes were small, but several were greater than 

magnitude 3 and could be felt by staff at HVO. Sequential peaks 

in summit inflation and lava level during late 2016, owing to 

repeated DI events, produced repeated bursts of small earthquakes 

in this area that diminished when the lake level dropped with 

deflation. The earthquakes are inferred to represent response 

to higher magmastatic pressures in the East Rift Zone conduit 

(Thelen and Patrick, 2012), in a manner analogous to the pattern 

of increasing earthquakes that was observed with inflation and 

unusually high lava levels preceding the opening of new vents on 

the East Rift Zone in 2011 (Thelen and Patrick, 2012; Patrick and 

others, 2015) (fig. 57).

Rockfalls and Explosions

Crater Wall Cracking

Cracking and popping sounds were occasionally heard 

coming from the Overlook crater. These were normally 

associated with unusually high lava levels. The sounds ranged 

from a high-pitch pop or crack to a deep, loud cannon-like 

boom, and could range from occasional to an almost continuous 

cacophony resembling a popcorn popper or fusillade of military 

shelling. Presumably, the popping sounds are due to heating of 

the crater walls resulting in thermal expansion and cracking (Orr 

and others, 2013). Sporadic observations prior to 2015 indicated 

the popping and cracking sounds were commonly related to 

cracking and ejection of rock from the lithic walls (Orr and 

others, 2013). Observations in December 2015 documented this 

process; video shows that small chips of rock frequently burst 

from the lithic wall, with each burst corresponding to a clearly 
Rockfalls and Explosions

37

audible popping or cracking sound. The zone of cracking was 

a few meters above the lake surface, throwing dust and small 

chips onto the crusted lake surface.

Cracking noises were less common in 2016 compared to 

earlier years. In previous years thermal cracking most commonly 

originated from the overhanging wall at the north end of the 

crater. As the lake level rose, it would heat the overhang in an 

oven-like fashion owing to the favorable angle of the crater wall, 

leading to cracking. One reason that thermal cracking sounds 

were less common in 2016 is that the overhang has been reduced, 

minimizing this “reflector oven” effect.

Veneer and Inner Ledge Collapse

As noted earlier, a thin layer of lava was left adhered to 

the Overlook crater wall whenever the lake level dropped. This 

veneer was unstable and frequently broke off in large patches or 

slabs, impacting the lake and commonly triggering spattering. 

The frequency of these veneer collapses seemed to be greater 

during large summit deflation events when the lake level dropped 

significantly, providing both more time for collapses to occur as 

well as more exposed surface area of unstable veneer. The small 

inner ledges built out a few meters from the juvenile veneer at the 

lake margins were also prone to collapse during lava level drops, 

and also triggered spattering. The southern ledge was more stable, 

and tended to collapse only when the lava lake level dropped a 

significant distance.

Crater Wall Collapses

Numerous small collapses occurred on the portion of the 

Overlook crater wall that intersects the floor of Halema‘uma‘u 

Crater. Larger collapses— some triggering explosions— 

originated from the southern Overlook crater wall, which 

corresponded with the steep, highly altered, rubbly wall of 

Halema‘uma‘u Crater. The alteration of this part of the wall took 

place during outgassing around the margin of the 1967–68 lava 

lake; such wall-rock alteration can be traced completely around 

Halema‘uma‘u, extending upwards to the high lava mark of the 

1967–68 lake. These collapses contributed to the enlargement of 

the Overlook crater by about 18 percent during 2016.

Explosive Events

Large rockfalls occasionally triggered explosive events at the 

lava lake (Orr and others, 2013). Although even small rockfalls 

could trigger spattering in the lake, for this discussion we consider 

explosive events to be those which throw juvenile bombs and (or) 

lithic blocks, volcanic ejecta more than about 6 cm in diameter, 

onto the rim of Halema‘uma‘u Crater (Wooten and others, 2009; 

Orr and others, 2013). Based on this criterion, explosive events 

occurred on the following days in 2016—January 2 and 8, August 

6, September 19, October 19, October 20, November 28, and 

December 2. All of these were associated with collapses of wall 

rock from the southern wall of the Overlook crater, where it meets 

the steep, altered wall of Halema‘uma‘u Crater. Each collapse 

deposited juvenile bombs around the Halema‘uma‘u Overlook.

The first explosive event of the year occurred at 14:17 

Hawaii standard time (HST) on January 2 (fig. 58). The initial 

indication of a rockfall was visible in webcam (HMcam) images 

at 14:17:49, and the rockfall impacted the lake at 14:17:54 HST. 

Pyroclasts were visible falling out of the tephra cloud produced 

at the point of impact at 14:18:03 HST, with pyroclasts reaching 

the camera starting around 14:18:08 HST. Falling pyroclasts 

were visible in the webcam images until 14:19:18 HST. The 

main deposit, which consisted mostly of juvenile lapilli and a few 

small bombs, was scattered around the Halema‘uma‘u Overlook, 

extending roughly 30 m from the Halema‘uma‘u Crater rim. 

Sparse, small lapilli reached the Halema‘uma‘u parking lot, 

A B

Figure 58. Images of the January 2, 2016, explosion. A, View of the Overlook crater from the K2cam in the Hawaiian Volcano Observatory 

observation tower, moments after the rockfall. Note the dark, particle-laden plume and incandescence in the area of the SE sink at 14:18:06 HST. B, 

View of the particle-laden plume produced from the rockfall near the SE sink at 14:17:59 HST.
38

Lava Lake Activity at the Summit of Kīlauea Volcano in 2016

approximately 400 m from the explosion point. The juvenile 

pyroclasts were coated in a dusting of lithic ash, with lithic ash 

usually incorporated into the juvenile matrix as well. Additional 

small white flakes of altered lithic rock were deposited around the 

Halema‘uma‘u Overlook and parking lot. Overall, this event was 

one of the smaller explosions to occur at the lava lake.

A larger explosive event occurred a week later on January 8 

at 03:51 HST. The rockfall that triggered the explosion originated 

from the southeast corner of the Overlook crater, near the SE 

sink. The main deposit was again concentrated around the 

Halema‘uma‘u Overlook, and primarily consisted of juvenile 

spatter with sparse Pele’s hair and glassy tears (fig. 59). The largest 

bomb was 25 cm in the long dimension. The lithic component of 

the deposit consisted of thin flakes of a white secondary mineral, 

likely anhydrite.

The next explosive event occurred on August 6 at 22:02 HST 

and was again triggered by a rockfall from the Halema‘uma‘u 

Crater wall, immediately above the SE sink. The main deposit 

began at the Halema‘uma‘u Overlook and extended about 100m 

northeast, reaching about 30–40 m from the Halema‘uma‘u 

Crater rim. The main deposit consisted of a continuous layer of 

scoria, lapilli- to bomb- size (much of it elongate, twisted spatter), 

as much as 20 cm thick (fig. 60). Sparse, small angular blocks 

of wall material were also ejected, and small white lithic flakes 

were abundant throughout the deposit. Spatter slightly damaged 

the housing for a continuously running gravimeter (but did not 

damage the instrument) and completely melted and destroyed the 

large plastic case housing its power system, melting the batteries 

and electronics.

A small explosive event, triggered by a rockfall near the 

SE sink, occurred on September 19 at 21:32 HST, depositing 

ribbons of spatter as much as 15 cm long on the Halema‘uma‘u 

Crater rim. Another small explosive event on October 19 at 

07:45 HST, triggered by a rockfall below the Halema‘uma‘u 

A B

C D

Halema‘uma‘u Crater rim

Figure 59. Images of the January 8, 2016, explosion. A, View of the explosion from the K2cam in the Hawaiian Volcano Observatory observation 

tower, showing hot particles thrown well above the Halema‘uma‘u Crater rim at 03:51:06 HST. B, View of the explosion from the HMcam at 

03:51:06 HST, showing the explosion originating in the southeast portion of the lake. Hot clasts are visible in the air, with a few deposited on the 

crater rim in front of the camera (bottom of image). C, Spatter deposited around the HMcam (top of image), as seen January 8, 2016. D, Close-up 

of a typical bomb. The jackknife is resting against a bomb roughly 20 centimeters in diameter. 
Rockfalls and Explosions

39

A B

C D

Figure 60. Images of the August 6, 2016, explosive E

deposit. A, A continuous layer of spatter, as much as 20 

centimeters thick, deposited about 100 meters east of the 

Halema‘uma‘u Overlook. The Halema‘uma‘u Overlook 

fencing is visible at the top of the photograph. Photograph 

taken August 7, 2016. B, White lithic block deposited on fresh 

spatter. Global positioning system (GPS) unit (16 centimeters 

long) for scale. Lithic clasts were presumably sourced from 

the collapsed portion of the highly altered Halema‘uma‘u 

Crater wall above the SE sink. Photograph taken August 

8, 2016. C, Spatter impacting the ground adhered to small 

particles on the surface, leaving a small area where the 

ground covering was removed when the spatter bounced or 

slid from the impact point. The light colored area to the right 

of the GPS unit is the region lacking the ground cover. D, 

Hawaiian Volcano Observatory geologist points to a pile of 

black melted material that had previously consisted of four 

car batteries and assorted electronics, which powered the 

gravimeter near the Halema‘uma‘u Overlook. Photograph 

taken August 8, 2016. E, Collapsed area. The arrow points to 

a light colored area that is the new scarp created by collapse 

of a portion of the Halema‘uma‘u Crater wall directly above 

the SE sink. Photograph taken August 7, 2016. 
40

Lava Lake Activity at the Summit of Kīlauea Volcano in 2016

Overlook, deposited spatter as much as 30 cm long on the 

Halema‘uma‘u Crater rim. An explosive event on October 20 

at 12:25 HST was triggered by a rockfall from the southern 

Overlook crater wall, directly below the HMcam (fig. 61). The 

talus slope below the HMcam was covered in a continuous 

deposit of spatter, and a sparse tephra deposit extended 

southwest past the Halema‘uma‘u parking lot. The material was 

again dominantly juvenile spatter, as large as bomb size.

Another large slice of the Overlook crater wall directly below 

the HMcam collapsed into the lake, triggering an explosive event 

on November 28 at 11:59 HST. The main deposit, consisting of 

sparse spatter, extended from the Halema‘uma‘u Overlook to a 

A B

C D

E F

Figure 61. Images of 

the October 20, 2016, 

explosion and resulting 

deposit. A, Incandescent 

cloud produced from the 

explosion. View is from the 

K2cam in the Hawaiian 

Volcano Observatory 

observation tower. 

Note a small amount of 

incandescent lava (white 

arrow) has overtopped the 

SE rim of the Overlook 

crater onto the floor of 

Halema‘uma‘u Crater, 

probably from sloshing of 

the lake. B, Airborne clasts 

captured by the HMcam. C, 

Juvenile lapilli and bombs 

on Crater Rim Drive (closed 

to the public), near the 

Halema‘uma‘u parking lot, 

roughly 400 meters from 

the lake (fig. 2). D, Ribbon 

spatter deposited near the 

Halema‘uma‘u Overlook. 

Clast is about 8 centimeters 

long. E, A thick flake of 

white, altered lithic material 

presumably sourced from 

the collapsed portion of the 

Halema‘uma‘u Crater wall. 

F, Small piece of spatter 

(dark clast near tip of pen), 

resting on Pele’s hair and 

lapilli from earlier events. 
Tephra

41

distance of about 100 m southwest (mainly spanning the distance 

between the HMcam and HTcam), reaching 30–40 m southeast of 

the Halema‘uma‘u Crater rim (fig. 62). The largest spatter bombs 

were about 160 cm long, but most were <30 cm. The bombs were 

fluid and stretched upon landing, accounting for their length. 

As with other explosions in 2016, the tephra was dominated 

by juvenile material but had a minor component of small white 

secondary minerals, often coating the juvenile spatter. Spatter 

from this event hit the HTcam enclosure but did not damage it. 

However, spatter also hit the HTcam’s power and ethernet cable, 

partly melting them and interrupting the data stream.

The final explosive event of the year occurred on December 

2 at 06:58 HST and, like the November 28 event, was triggered 

by a large slab of rock below the HMcam collapsing into the lake. 

The tephra deposit on the Halema‘uma‘u Crater rim was smaller 

than that of November 28, and consisted of sparse spatter bombs 

around the HMcam and Halema‘uma‘u Overlook.

Each of these rockfall-induced explosive events was 

associated with a composite seismic event (fig. 63) that consisted 

of a burst of high frequency and long-period energy, followed 

by several minutes of very-long-period oscillations (Chouet 

A B

C D

Figure 62. Images of the November 28, 2016, explosion and resulting deposit. A, Intense spattering and particle-laden plume captured from the K2cam in the 

Hawaiian Volcano Observatory observation tower. B, Dark particle-laden plume rising beneath the HMcam. C, Large spatter bomb near the HTcam (fig. 2). The 

bomb was semi-fluid and was pulled apart like taffy upon impact. D, Dark spatter bombs on the trail near the HTcam. The light-colored lithic blocks are from the 

1924 explosions. 

and others, 2010; Patrick and others, 2011a; Orr and others, 

2013; Chouet and Dawson, 2013). The explosions also triggered 

agitation in the lake (intense bubbling) around the point of impact 

that persisted for tens of minutes, which was associated with an 

increase in the surface flow rate towards the impact site.

Tephra

Tephra was produced from two main processes: explosive 

events and persistent spattering. The explosive tephra—mostly 

spatter bombs and lapilli—are described in the section above.

Persistent spattering produced tephra almost continuously, 

and this was collected and studied on a daily basis through the 

use of a network of 10 plastic buckets placed downwind of the 

vent (fig. 2; Swanson and others, 2009). Typically a total of 5–10 

grams were caught daily by the 10 buckets, at an average daily 

accumulation rate of about 0.4 g/m2. The predominantly ash-size 

pyroclasts were a mixture of juvenile and lithic material; the 

proportion of juvenile material averaged 96.9 percent of the total 

mass collected during 2016, ranging from 64.9 percent (during 
42

Lava Lake Activity at the Summit of Kīlauea Volcano in 2016

-5 -4 -3 -2 -1 10

105 nm/s

02 Dec 2016, 06:58

28 Nov 2016, 11:59

20 Oct 2016, 12:25

06 Aug 2016, 22:02

08 Jan 2016, 03:50

02 Jan 2016, 14:17

very-long-period oscillation

0 1 2 3 4 5 6 7 8 9

Minutes relative to explosion onset

Figure 63. Composite seismic events associated with selected explosive 

events of 2016. Vertical component of broadband station NPT (fig. 1B). 

Composite events at Halema‘uma‘u began with a burst of high-frequency and 

long-period energy followed by several minutes of very-long-period (VLP) 

oscillation (Orr and others, 2013). The VLP signals are easily visible in these 

data. The September 19 and October 19 explosive events are not shown here 

and had very small seismic signals compared to the events shown. nm/s, 

nanometers per second.

A

B

Figure 64. Photographs of tephra produced by spattering. A, Juvenile 

pyroclasts (Pele’s hair and tears, hollow spherules) caught on 0.5-millimeter 

(mm) sieve on November 16, 2016. B, Hollow spherules and Pele’s hair caught 

on 0.5-mm sieve on September 26, 2011.

Figure 65. Photograph 

of egg-shaped hollow glass 

spherule collected near the 

Halema‘uma‘u Overlook on 

January 8, 2016.

the explosive event on January 2) to 100 percent (Swanson and 

others, 2016). Juvenile pyroclasts mainly consisted of Pele’s 

hair and tears, as well as hollow glass spherules (fig. 64), which 

were produced by spattering in the lake and lofted upwards in the 

plume. One glass spherule, collected in January 2016, was eggshaped and roughly 1.5 cm long (fig. 65). There was no significant 

scoriaceous material collected during the normal, persistent 

spattering activity. The nonjuvenile component consisted of ashsize particles of lithic wallrock, often friable and altered, as well 

as secondary sulfates. The lithic component presumably originates 

from small, relatively insignificant, rockfalls from the Overlook 

crater walls. The amount of tephra collected in the buckets is 

generally proportional to lake level. When the level is high, so is 

the tephra accumulation, because the spattering sites are nearer the 

buckets.

Pele’s hair was one of the most abundant types of tephra 

produced by the lava lake. From the Halema‘uma‘u Overlook, 

one could often see clumps of Pele’s hair lofted upwards in the 

plume as it rose above the lake. In the proximal region, near 

the rim of Halema‘uma‘u Crater, the Pele’s hair was coarse and 

commonly had Pele’s tears forming at the ends (fig. 66A). The 

Pele’s hair could be carried many kilometers downwind. In the 

distal region, the Pele’s hair was normally very fine and could 

be decimeters long (fig. 66B), and was often accumulated on the 

lee side of obstacles. 
Outgassing Plume

43

A B

Figure 66. Photographs of Pele’s hair. A, Pele’s hair deposited on the rim of Halema‘uma‘u Crater. Proximal Pele’s hair was commonly coarse and 

often terminated by Pele’s tears. Photograph taken November 9, 2016. B, Pele’s hair deposited 6 kilometers from Halema‘uma‘u Crater. Distal Pele’s 

hair was typically very fine, and could be decimeters long. Photograph taken November 16, 2016.

Pele’s hair

Pele’s hair

A B

Figure 67. Photographs of carpet of Pele’s hair downwind of lake. A, A continuous carpet of Pele’s hair was present as much as several hundred meters 

downwind of the Overlook crater. This photograph was taken December 16, 2016, near station A4 (fig. 2). The trail to A4 is in the center of the photograph and 

the Halema‘uma‘u parking lot is near the top image. B, Discontinuous mats of Pele’s hair in the Halema‘uma‘u parking lot. Photograph by Hannah Dietterich, 

U.S. Geological Survey, September 9, 2016.

As a result of years of persistent spattering and tephra 

production in the Overlook crater, Pele’s hair has accumulated in 

a thick, nearly continuous carpet in the immediate area downwind 

of the crater (fig. 67). On the southwestern rim of Halema‘uma‘u 

Crater, the carpet of Pele’s hair was a few centimeters thick, with 

even greater thicknesses where the hair could accumulate against 

rocks. The accumulation rate increased in 2016, compared to 

earlier years, as a result of high lake levels and tephra production. 

Large mats and clumps of Pele’s hair accumulated in the 

Halema‘uma‘u parking lot, particularly against the curbs. An 

interesting reflective property of the Pele’s hair was observed at 

low sun angles. When looking toward the sun, the carpet of Pele’s 

hair had a lustrous golden appearance, but turning and looking 

away from the sun, the same deposit had a dull olive drab color. 

On Kona (southerly) wind days, Pele’s hair commonly fell at 

HVO and Jaggar Museum, with HVO staff often finding long 

strands of Pele’s hair on their vehicle windshields at the end of the 

workday and trees draped with hair like Christmas tinsel.

Outgassing Plume

Throughout 2016 the lava lake produced a persistent 

outgassing plume (fig. 68), which consisted primarily of H2O, 
44

Lava Lake Activity at the Summit of Kīlauea Volcano in 2016

Figure 68. Photograph of a typical outgassing plume, taken from 

Uēkahuna Bluff (fig. 1A), near the Hawaiian Volcano Observatory, March 

20, 2016. The outgassing plume from the lake was normally white in 

color and semi-transparent, and carried southwest (towards right side of 

photo) by the trade winds. The plume at this time was rising about 500 

meters above the caldera floor. 

CO2, and SO2 with minor amounts of HCL, HF, CO, and other 

trace gases (Sutton and Elias, 2016; HVO unpub. data, 2016). 

Sulfates are an important aerosol component of the plume, and 

plume concentrations of many metallic elements, including gaseous 

elemental mercury, have been elevated above background air levels 

(Mather and others, 2012; Edmonds and others, 2013; Sutton and 

others, 2013; Sutton and Elias, 2016). Typical daily mean values for 

SO2 emission rate during 2016 ranged between 1,000 and 8,000 t/d 

(overall mean=4,600 t/d, standard deviation=1,600 t/d) (Elias and 

Sutton, 2017; HVO unpub. data, 2016).

The outgassing produced a relatively low, bent-over plume, 

resembling those produced by industrial stacks. This would be 

considered a weak volcanic plume, whose motion is determined 

largely by the prevailing winds, as opposed to a strong plume, 

which rises vertically despite local wind conditions (Sparks and 

others, 1997). In Hawai‘i, the normal trade winds blow from the 

northeast, carrying the plume towards the Ka‘ū district. When 

trade winds are absent, Kona (southerly) winds commonly 

prevail, and the plume is carried towards the north, often into 

populated areas of the National Park such as Jaggar Museum, 

Kilauea Military Camp, and Kilauea Visitor Center, as well as 

the populated areas of east Hawai‘i (figs. 69 and 70). On slack 

wind days, the plume would rise vertically more than a kilometer 

(fig. 71). When such weak winds occurred, the nighttime glow 

reflected off of the vertically rising plume could be easily seen 

from nearby communities. Local residents sometimes mistook 

the better visibility of the vertically rising plume at these times 

for an increase in lava lake activity. The vertical glowing plume 

was sometimes visible in nighttime images from webcams at Pu‘u 

‘Ō‘ō, located about 19 km to the east.

The appearance of the plume could range from opaque, white 

and puffy, to a thin, semi-transparent brown haze, presumably 

depending on both gas emission rates (described below) and 

atmospheric conditions. At any given time, the plume commonly 

exhibited this range of color and optical thickness in different 

regions. The plume also showed variations along its length, 

appearing as robust “puffs” separated by gaps of thinner plume 

(fig. 72). These puffs may be caused by fluctuations in outgassing 

at the source (spattering sites), with some contribution by 

turbulence as well. These puffs likely explain the high variability 

of SO2 emission rates over very short (tens of seconds) time spans, 

as recorded by the ultraviolet spectrometer array (Horton and 

others, 2012; Elias and others, 2016).

Another common feature of the plume was a diffuse groundhugging curtain of gas that extended down from the main body 

of the plume (fig. 72). The extent of plume grounding at Kīlauea, 

also referred to as plume fumigation, is controlled by a number of 

factors including wind speed, inversion layer height and strength, 

and atmospheric stability. Plume grounding is an important feature 

of gas release as it has a strong control on gas concentrations 

at ground level (Delmelle and others, 2002). The grounded gas 

curtain at Halema‘uma‘u could be maintained for kilometers, 

frequently producing high SO2 concentrations at ground level in 

downwind areas.

The optical thickness of the plume depended in large part 

on the gas and particle emission rates, which could fluctuate 

dramatically and corresponded with the intensity of spattering. 

Overall, more numerous and (or) intense spatter sites in the 

lake produced higher gas emissions and a more robust gas 

plume. Nonspattering phases, often lasting several hours at a 

time, corresponded with an unusually weak, wispy plume (fig. 

73). Patrick and others (2016a) show that nonspattering phases 

corresponded to SO2 emission rates about one-third of those 

during spattering phases. Therefore, the unusually weak plume 

is mainly a result of a dramatic reduction in gas emission rates. 

Although plume appearance is also controlled by atmospheric 

factors, the link between spattering intensity and plume vigor 

was observed in many different atmospheric conditions and is 

well established both observationally and quantitatively (Patrick 

and others, 2016a,c). The appearance of the plume was also 

related to the particle abundance.

Plume optical thickness was not uniform across the span of 

the lava lake. The most robust portions of the plume originated 

directly from the spatter sites on the lake surface, each site several 

tens of meters across (fig. 74). The remainder of the lake surface 

emitted a diffuse plume. This relation is again consistent with 

previous outgassing estimates, which indicate that the majority 

of outgassing originates directly from the spattering. Patrick and 

others (2016a) showed that spattering accounted for roughly twothirds to three-fourths of the total SO2

 emission rate, while passive 

outgassing from the lake surface produced the remainder.
Outgassing Plume

45

A B C

D E F

G I

J K

H

L

January 26, 4:46 p.m. February 28, 2:51 p.m. March 27, 6:25 p.m.

April 14, 2:12 p.m. May 17, 6:39 p.m.

July 10, 6:51 p.m. September 8, 5:17 p.m.

October 26, 5:39 p.m. November 9, 10:39 a.m. December 16, 8:59 a.m.

July 22 7:12 p.m.

June 27, 4:49 p.m.

Figure 69. Monthly views of the outgassing plume. Photographs of the outgassing plume in varying conditions, all taken from Uēkahuna Bluff. Note 

that in most cases the plume is carried southwest (towards right side of image), but the plume direction could change when the trade winds ceased.
46

Lava Lake Activity at the Summit of Kīlauea Volcano in 2016

A. March 20 (tradewinds) B. March 28 (Kona winds)

C. March 30 (Kona winds) D. April 1 (tradewinds)

Figure 70. Photographs showing alternating trade wind and Kona wind effects on the plume. The 

photographs were taken from Uēkahuna Bluff during 2016.

A B

Figure 71. Photographs showing a vertical plume rise in slack winds. A, The plume 

rising vertically and reaching a neutral buoyancy height of about 1 kilometer above 

the lava lake. Photograph taken from Uēkahuna Bluff on December 2, 2016. B, Park 

visitors at Uēkahuna Bluff watching the vertically rising and expanding plume on a slack 

wind day, March 15, 2016.
Outgassing Plume

47

top of plume

lava lake

ground-hugging curtain

Figure 72. View of the plume from a distance. Photograph taken from the 

Mauna Loa strip road, about 12 kilometers northwest of the lava lake. The 

plume was carried southwest, rising to a height of about 500 meters. The 

plume often had a ground-hugging curtain, as it does here. Photograph taken 

December 28, 2016.

Figure 73. Photographs showing plume vigor changes in 

spattering and nonspattering phases. Spattering intensity controlled 

the rate of gas emission from the lake, which in turn contibuted 

to the optical thickness of the plume. Images are from the K2cam 

in the Hawaiian Volcano Observatory observation tower. A, Thin, 

wispy plume associated with very low gas emission rates during 

a nonspattering (gas pistoning) phase on December 19, 2016. B, 

More robust plume occurring 30 minutes later during a period of 

spattering and higher gas emission rates.

A. Non-spattering (12:10 p.m.)

B. Spattering (12:44 p.m.)

Figure 74. Photographs showing the robust portion of plume related to spattering. The most robust portion of the plume originated directly from 

distinct spattering sites, presumably because of the higher gas emission rates occurring at those sites compared to diffuse gas release from the 

remainder of the lake. A, Robust plume originating from spattering along the southern lake margin. A more diffuse plume comes from the rest of the 

lake surface. Photograph from the Hawaiian Volcano Observatory, December 18, 2016. B, Robust portion of plume originating from spattering along 

the northern margin of the lake. Photograph taken from the Halema‘uma‘u Crater rim on September 10, 2016.

diffuse plume from lake surface

robust plume from spattering

robust plume from spattering

A B
48

Lava Lake Activity at the Summit of Kīlauea Volcano in 2016

Volcanic Air Pollution

The primary hazard of the summit eruption has been 

volcanic air pollution, also known as vog (Elias and Sutton, 

2017). Although potentially lethal explosive events have occurred, 

the ballistic fallout has been limited to the closed area of the 

park (Houghton and others, 2013), posing no threat to publicly 

accessible areas. Furthermore, the lake itself poses no immediate 

threat of inundation by overflows as it has been normally 

contained by the Overlook crater, which is itself confined by 

Halema‘uma‘u Crater. Instead, the outgassing plume is carried 

far from the vent and affects wide areas of Hawai‘i with high 

concentrations of sulfur dioxide and (or) other vog constituents, 

such as solid sulfate and liquid sulfuric acid droplets.

Vog is a respiratory irritant that negatively affects human 

health (Sutton and others, 1997; Longo, 2013; Tam and others, 

2016; Elias and Sutton, 2017), as well as agriculture in areas 

downwind of the vent. The opening of the summit vent in 2008 

increased the effects of vog, which had already been a long-term 

issue on the Island of Hawai‘i owing to the Pu‘u ‘Ō‘ō eruption that 

began in 1983 (Sutton and others, 1997; Elias and others, 1998; 

Longo and others, 2010; Elias and Sutton, 2017). The impact of 

vog on human health and the environment remains an important 

area of ongoing research. SO2 monitoring and vog forecasting 

(Businger and others, 2015; Elias and others, 2016) have been a 

part of island-wide efforts to better respond to vog conditions.

The Ka‘ū district, directly downwind of the summit vent 

during normal trade wind conditions, has been particularly hard 

hit (Longo and others, 2010). Farming and ranching have been 

impacted, which led to a U.S. Department of Agriculture disaster 

declaration in 2008, allowing affected growers to access federal 

assistance programs (Honolulu Advertiser Staff, 2008; Elias 

and Sutton, 2017). The Ka‘ū high school gymnasium, built in 

2013, was designed to incorporate a vog shelter for sensitive 

residents during periods of poor air quality (Jensen, 2013). During 

prevailing trade wind conditions, air quality in this area of the 

island is routinely impacted; during 2016, the U.S. Environmental 

Protection Agency primary health standard for SO2 (hourly 

average of 0.075 parts per million [ppm]) was exceeded in Pāhala 

(fig. 1A) on 246 days of the year (State of Hawaii Department of 

Health, 2016). 

Trade wind interruptions most commonly occur during the 

winter months, producing vog in the heavily trafficked areas of 

Hawaiʻi Volcanoes National Park and surrounding communities. 

Park rangers carry industrial hygiene SO2 monitoring badges, and 

make limited, temporary closures of areas in the park that have 

high gas concentrations. On November 6, 2016, such a closure 

was enacted at Jaggar Museum, owing to hazardous levels of 

SO2 gas. In 2016, the U.S. Environmental Protection Agency 

primary health standard for SO2 was exceeded on 107 and 77 

days, respectively, at Jaggar Museum and Kilauea Visitor Center 

(https://ard-request.air-resource.com/data.aspx).

The Island of Hawai‘i is currently one of several communities worldwide that copes with the effects of persistent volcanic 

outgassing. Similar to Kīlauea, Masaya Volcano in Nicaragua is 

situated within a national park and emits a continuous plume as 

a result of open-vent basaltic activity, affecting vegetation and 

producing poor air quality downwind (Delmelle and others, 2002; 

van Manen, 2014a). Gas emissions at Turrialba volcano in Costa 

Rica have increased since 2007, affecting vegetation and air quality (Martini and others, 2010; van Manen, 2014b). Miyakejima 

volcano in Japan produces persistent outgassing that has required 

significant adaptive measures by local officials and the public 

(Delmelle, 2003; Ishimine, 2007). Continuous gas emissions from 

Ambrym volcano, in Vanuatu, produce environmental and human 

health impacts, including fluorosis (Cronin and Sharp, 2002; 

Allibone and others, 2012). These are just a few examples of other 

communities affected by persistent volcanic outgassing.

Miscellaneous Observations

Sounds

The most common sound from the Overlook crater resembled 

that of breaking waves on a distant seashore, which presumably 

represented unsteady outgassing. When spattering was active this 

sound was combined with the more energetic sounds of gas release 

owing to bubble bursting, resembling a pulsating roaring sound. 

It was also associated with the low percussive sounds and lumpy 

patter noises of large globs of spatter impacting the lake.

Rock cracking and popping sounds were only occasionally 

observed during 2016. These sounds were not as frequent or 

intense as the rock cracking sounds reported in earlier years.

Heat

When standing at the Halema‘uma‘u Overlook in 2016—

generally about 80–120 m above the lake surface—the radiant 

heat from the lake surface on one’s face was obvious, but normally 

not uncomfortable. Only once during 2016, when spattering in 

the lake was intense and the lake level was relatively high, did 

HVO staff report that the radiant heat was almost unbearable. 

Notwithstanding the radiant heat, the near-constant winds at the 

Halema‘uma‘u Overlook maintained a relatively cool ambient 

temperature at the Halema‘uma‘u Crater rim. The ambient 

temperature was felt to warm slightly when HVO staff were 

sporadically enveloped by the outgassing plume. When HVO 

scientists visited the floor of Halema‘uma‘u Crater on November 

29, 2016, they approached to within about 20 m of the northern 

rim of the Overlook crater. At this spot the air was cool and radiant 

heat was minimal, probably because much of the lake surface was 

blocked by the Overlook crater rim.

Effects of Heavy Rains

During normal rains a sizzling sound could be heard, which 

resembled the sound commonly heard on the East Rift Zone flow 

field when rain falls on active pāhoehoe lobes. In very intense 

downpours, which may only happen a few times a year and persist 

for minutes at a time, the HTcam thermal images of the lake 
2016 Lake Activity in Context

49

Figure 75. Images of the lake surface immediately following unusually 

heavy rains. A, HMcam near-infrared image of the lake surface, showing 

white clouds of condensed water vapor over the central portions of the largest 

crustal plates. Image taken at 12:48 HST on December 2, 2016. B, HTcam 

thermal image at the same time, showing greatly reduced temperatures in 

the areas containing mist. Note that the mist may be attenuating the radiance, 

partly contributing to the lower apparent temperatures.

25 °C

310

B

showed greatly depressed temperatures and the normal webcam A

(HMcam) images showed opaque clouds of condensed water vapor 

above the lake surface. Once the rain ceased, this mist would thin, 

but portions of it persisted over the center of large plates, where 

thermal camera images show the lowest surface temperatures on 

the lake (about 40 °C in fig. 75). Although the surface temperatures 

in the thermal images may be suspect owing to attenuation by the 

mist, the vestiges of the mist over the coolest portions of the plates 

might suggest that the surface temperature momentarily dropped 

below 100 °C as a result of the heavy rain, allowing a thin layer 

of water to briefly accumulate. Otherwise, there was no obvious 

change in the lake surface activity, such as increased foundering or 

plate fusing, during intense downpours in 2016.

Public Engagement

HVO provides several regular information products directly 

to the public by way of the HVO website (https://volcanoes.

usgs.gov/hvo). A daily update is posted each morning with a 

short summary of activity at the summit and East Rift Zone. 

Photographs and video are frequently posted to the website 

multimedia page and the USGS Volcanoes social media accounts 

(Twitter and Facebook). These images and videos are often widely 

shared by users on social media, and are sometimes featured on 

local television news. Four near-real-time webcam views of the 

lake are available on the HVO website. These videos and webcam 

views are valuable for the public to gain an understanding of the 

activity in the lava lake, as the immediate area is closed to the 

public. HVO staff write a weekly “Volcano Watch” article for 

the local newspaper (also posted directly on the HVO website) 

on volcano-themed topics, which often includes explanations of 

recent summit activity. In addition, public talks several times per 

year normally involve an update on summit eruptive activity.

The summit eruption has been a popular visitor attraction 

since it began in 2008, with the closest viewing area at the Jaggar 

Museum overlook (fig. 76). For much of the eruption the lake has 

been too deep to be directly visible from this vantage point, but 

the impressive glow and outgassing plume nevertheless provided 

good views. When lava first became directly visible to visitors 

at the Jaggar Museum overlook in April 2015 the popularity of 

this viewing location increased dramatically, with more vehicles 

arriving than the Jaggar parking lot could accommodate. With lava 

frequently visible at the Jaggar Museum overlook in late 2016, this 

viewing area remains popular, with national park rangers managing 

vehicles at the Jaggar parking lot during the busy dusk hours.

2016 Lake Activity in Context

The 2016 lava lake activity we describe here is broadly 

similar to that of the preceding three years in many respects, 

including the lake surface textures and appearance, surface 

motion, explosions, outgassing and most aspects of the spattering 

behavior. There were several differences with previous years, 

however. First, the crater has continued to enlarge over the past 

few years, resulting in a greater surface area in 2016. Second, the 

frequency of nonspattering phases dropped dramatically. Third, 

the overall lake levels in 2016 were higher than those in previous 

years, resulting in an increasing verticality of the Overlook crater 

wall where it cuts the floor of Halemaʻumaʻu. Tephra production 

increased substantially as a result of the increased spattering and 

higher lake level, and the juvenile proportion of the tephra grew 

higher as the crater wall became more stable and the lake level 

rose.

Overall, 2016 is notable for the remarkable consistency in 

the lava lake’s behavior throughout the year. Despite common 

fluctuations in lake level and outgassing, the lake exhibited an 

overall steadiness in most respects. Combined with the higher 

overall lava levels and clearer views of the lake surface, the 

activity in 2016 therefore provides an unprecedented observational 

record of the nature of stable, persistent lava lake activity. Data 

from 2016 should be useful in further refining models concerning 

lake level changes, gas pistoning, and the relation between 

outgassing and seismic tremor.
50

Lava Lake Activity at the Summit of Kīlauea Volcano in 2016

Relation to the East Rift Zone Eruption 

at Pu‘u ‘Ō‘ō

The 2016 summit activity described here was concurrent 

with the Pu‘u ‘Ō‘ō eruption, which began in 1983 (Heliker and 

Mattox, 2003; Orr and others, 2015). For the Pu‘u ‘Ō‘ō eruption, 

the first five months of 2016 consisted of slow-moving pāhoehoe 

flows roughly 5 km northeast of Pu‘u ‘Ō‘ō (Patrick and others, 

2017). This activity marked the final stages of Episode 61e, also 

called the “June 27th flow,” which had threatened the town of 

Pāhoa (fig. 1A) in 2014–2015 (Poland and others, 2016; Patrick 

and others, 2017). Episode 61e ended roughly a week after new 

fissures formed on Pu‘u ‘Ō‘ō on May 24, 2016 (Patrick and others, 

2017). These new fissures eventually focused on a single vent 

east of Pu‘u ‘Ō‘ō, feeding lava to a new flow (the Episode 61g 

flow; Orr and others, 2017). This lava flow moved southeast and 

reached the ocean on July 26, 2016, forming the Kamokuna ocean 

Figure 76. Photograph showing park visitors 

enjoying the view of the lake at the Jaggar Museum 

overlook, October 26, 2016. Photograph taken from 

the Hawaiian Volcano Observatory observation tower 

at dusk, a popular time for visitation. 

entry, which was active for the remainder of the year. Throughout 

these changes on the flow field, a small lava lake remained active 

within the western portion of Pu‘u ‘Ō‘ō crater (fig. 77). This lava 

lake, in what we call the “west pit”, was roughly 50 m in diameter 

and about 20 m below the rim of the west pit. The lake surface had 

an elevation that varied between 843 and 856 m above sea level, 

which was roughly 120–180 m below the level of the lava lake in 

Halema‘uma‘u.

The opening of the Episode 61g vent on May 24, 2016, may 

correspond with an abrupt drop in summit lava lake level of about 

16 m between May 24 and May 26. If so, this relation would 

follow previous patterns in which an East Rift Zone vent opening, 

and subsequent draining of the shallow magma reservoir at Pu‘u 

‘Ō‘ō, triggered a drop in summit lake level (Patrick and others, 

2015). This drop in summit lake level, however, also occurred 

during a phase of deflation associated with a deflation-inflation 

cycle, so it is difficult to isolate what portion of this drop was the 

result of the East Rift Zone vent.

Figure 77. Photograph of the small lava lake in 

Pu‘u ‘Ō‘ō crater, on Kīlauea’s East Rift Zone June 

23, 2016. The lake was active throughout 2016 and 

concurrent with the summit lava lake. The lake is 

roughly 50 meters in diameter.
Conclusions

51

Comparison with Other Lava Lakes 

on Earth

The lava lake in Halema‘uma‘u Crater is one of several 

persistent lava lakes on Earth. Other long-standing lakes include 

those at Erta Ale (Ethiopia; Harris and others, 2005), Nyiragongo 

(Democratic Republic of the Congo; Spampinato and others, 

2013), Erebus (Antarctica; Oppenheimer and others, 2009), 

Ambrym (Vanuatu; Allard and others, 2016), and Villarrica (Chile; 

Moussallam and others, 2016). Recent lava lakes have become 

active at Nyamuragira (Democratic Republic of the Congo; 

Campion, 2014) and Masaya (Nicaragua; Global Volcanism 

Program, 2016) as well.

Of these lakes, only those at Halema‘uma‘u and 

Nyiragongo exceed 30,000 m2 in surface area, to our knowledge. The remainder are generally much smaller (<6,000

m2). 

The Halemaʻumaʻu lake bears the most resemblance to the 

lakes in Nyiragongo and Erta Ale. For instance, Erta Ale has 

many similarities in surface behavior, with large crustal plates 

and varying spreading zones, and sparse spattering sites that 

locally disrupt surface motion (Oppenheimer and Yirgu, 

2002; Spampinato and others, 2008). Recent observations of 

Nyiragongo lava lake indicate a more active surface than the 

lake at Halemaʻumaʻu, with many scattered spattering sites 

active at a given time. Significant lake level changes have 

been recorded at Erta Ale and Nyiragongo (Burgi and others, 

2014; Barnie and others, 2016), but measurements of short 

term lake level changes have been sparse (Spampinato and 

others, 2013; Burgi and others, 2014). With rough similarities 

in appearance, we expect that some of the observed patterns 

and processes in the Halema‘uma‘u lake may be relevant 

for Nyiragongo and Erta Ale. Patrick and others (2016c), 

for instance, suggested that phases of shallowly driven lake 

surface motion, common at Halema‘uma‘u, may also occur at 

Erta Ale.

Conclusions

This report provides a descriptive and visual summary of 

lava lake activity at the summit of Kīlauea Volcano, Hawai‘i, 

during 2016. A synopsis of the activity is as follows:

• The summit eruption in 2016 consisted of continuous 

lava lake activity. The lake was 250 × 190 m in size 

(~39,000 m2), and was one of the largest lava lakes on 

Earth during 2016.

• The lake surface consisted of large crustal plates (on 

average about 60 m in the longest dimension) separated by 

narrow incandescent spreading zones.

• The lake motion was normally from north to south, but 

episodes of spattering could produce transient disruptions 

to the typical motion.

• Spattering took place most of the time but could shut down 

for episodes lasting several hours (driving gas pistoning). 

Seismic tremor at the summit was closely correlated with 

spattering intensity and gas emission rates.

• The Overlook crater was modified by unstable deposits 

of juvenile lava on the crater walls. This lava veneer 

commonly collapsed into the lake, triggering spattering, 

particularly during periods of summit deflation and lava 

level drops.

• Large collapses of the Overlook crater walls triggered 

several small explosive events that deposited spatter on 

the rim of Halema‘uma‘u Crater, but these events did not 

threaten public areas.

• Lake level varied over several tens of meters, controlled 

both by magma reservoir pressure and, to a smaller degree, 

outgassing processes. High lava levels were associated 

with an increase in the frequency of small earthquakes in 

the upper East Rift Zone.

• The lake produced an outgassing plume with typical 

daily average SO2 emission rates of 1,000–8,000 t/d 

(mean=4,600 t/d). The plume was normally carried 

southwest in the trade winds, and produced volcanic air 

pollution (vog) affecting large portions of the island.

• The lake has been a major tourist attraction in Hawai‘i 

Volcanoes National Park, and rising lake levels in 

2016 provided frequent views of the lake from public 

viewing areas.

The summit eruption has provided new insights into lava 

lake dynamics and open-vent basaltic eruptions, including 

(1) the triggering of explosions by rockfalls (Orr and others, 

2013), (2) the low density (and hence high gas content) of the 

lava lake (Carbone and others, 2013; Poland and Carbone, 

2016), (3) the fact that the lake level acts as a piezometer of 

summit magma reservoir pressure (Patrick and others, 2015), 

(4) that gas pistoning in the lake is driven by shallow gas 

accumulation near the top of the lake (Patrick and others, 

2016a), (5) the real-time modeling and forecasting of vog 

hazards (Businger and others, 2015), (6) the strong correlation 

between outgassing rates and seismic tremor (Kern and others, 

2015; Nadeau and others, 2015; Patrick and others, 2016a), 

and (7) the recognition of slowly pulsing magma supply to the 

summit (Swanson and others, 2016).

Much remains to be learned about the summit eruption 

and lava lake. More frequent and precise measurements of 

lava lake level could provide new insights on gas dynamics 

in the lake. Analog and computational modeling may help 

link lake surface motion with convection dynamics within 

the lake. Gas accumulation within the lake has been inferred 

from lava level measurements and other indicators (Patrick 

and others, 2010, 2016a; Carbone and others, 2013), but the 

distribution of bubbles within the lake is still not known. It is 

unclear how bubble distribution changes during gas pistoning 
52

Lava Lake Activity at the Summit of Kīlauea Volcano in 2016

or as a result of changes in spattering and lake motion. Analog 

modeling, such as that performed by Spina and others (2016), 

could provide more insight on gas segregation, accumulation, 

and bubble coalescence in the lake. However, from a hazards 

perspective, the most pressing need for future research is a 

better understanding of the impact of the outgassing and vog 

on human health (Tam and others, 2016).

Two factors should aid in improving our understanding 

of the eruption and its hazards. First, if the eruption persists 

into the coming years, it will provide an even more robust, 

continuous dataset for formulating and testing hypotheses. 

Although the common steadiness of the activity is an 

advantage in many respects, the longer the eruption lasts the 

more likely we are to see additional “extreme” events, such 

as the March 2011 draining of the lake or the May 2015 rise 

and overflows, which are particularly instructive for revealing 

lake processes. Second, improving technology will allow 

the characterization of lake behavior in more detail. Higher 

resolution thermal cameras would provide finer precision in 

lake surface textures and temperatures. Continuous lava level 

measurements, either through a stereo-camera setup or other 

instrument, would allow better study of rapid, gas-driven 

processes in the lake. Overall, the lava lake in Halema‘uma‘u 

provides an ideal venue for testing instruments and techniques 

that could be applied to other lava lakes or open-vent basaltic 

eruptions.

Acknowledgments

The entire HVO staff, along with many volunteers, 

contributed to monitoring the summit eruption, as well as the 

concurrent long-lived eruption on Kīlauea’s East Rift Zone 

at Pu‘u ‘Ō‘ō. We thank the U.S. National Park Service, the 

land manager for the area containing the summit eruption, 

for facilitating HVO work in the restricted areas of Hawai‘i 

Volcanoes National Park. We also thank Heather Wright and 

Ingrid Johanson for reviews, which improved the manuscript. 

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58

Lava Lake Activity at the Summit of Kīlauea Volcano in 2016

Glossary

A4 An ash collection bucket near the rim of 

Halema‘uma‘u Crater about 200 m west of 

the lava lake (fig. 2). This spot is a common 

site for observing the lava lake, and is one of 

the few locations with reliable views of the 

SE sink.

DI event Abbreviation of deflation-inflation 

event. DI events are cycles of magma 

reservoir pressure that commonly occur at 

the summit of Kīlauea Volcano, and are best 

observed in summit tiltmeters (such as at 

station UWE, see below). Increasing values 

of radial tilt (along an azimuth of 327°) at 

UWE correspond to inflation of the magma 

reservoir, and decreasing values correspond 

to deflation. DI events are relevant to the 

summit eruption because they are associated 

with cycles of lava level change. Deflation 

corresponds with a dropping lava level, and 

inflation with lava level rise.

Halema‘uma‘u Overlook Former public 

viewing platform, enclosed by wooden 

fencing, situated on the southeast rim of 

Halema‘uma‘u Crater (fig. 2). The Overlook 

crater formed in 2008 directly below this 

overlook. The Halema‘uma‘u Overlook 

has been struck by blocks and spatter in 

several explosive events since the current 

summit eruption began, and has been closed 

to the public since February 2008. The 

Halema‘uma‘u Overlook is the most common 

location on the Halema‘uma‘u Crater rim for 

Hawaiian Volcano Observatory geologists to 

make visual observations of the lava lake.

HMcam A camera situated at the Halema‘uma‘u 

Overlook that provides one of the best views of 

the lake (fig. 2). The camera acquires in a nearinfrared mode, which provides improved views 

through the volcanic fume. In the near-infrared 

mode the images are shown as grayscale.

HTcam A longwave thermal infrared 

camera situated about 80 m southwest of the 

Halema‘uma‘u Overlook (fig. 2).

Jaggar Museum/overlook Jaggar Museum is 

located on the northern rim of Kīlauea Caldera, 

and is attached to the Hawaiian Volcano 

Observatory buildings (fig. 1). In front of the 

museum is a public viewing area (Jaggar Museum 

overlook) that is currently the best location for the 

public to view the Overlook crater and lava lake.

Overlook crater The informal name given to the 

crater formed on March 19, 2008, at the opening 

of the current summit eruption. The Overlook 

crater is in the southeast portion of Halema‘uma‘u 

Crater directly below the Halema‘uma‘u Overlook 

(fig. 1). The active lava lake is contained within 

the Overlook crater. When the crater formed on 

March 19, 2008, it was 35 m wide. By late 2016 

the crater had enlarged to 250 × 190 m.

SE (southeast) sink An area along the 

southeastern margin of the lava lake that is often 

spattering (fig. 2). This site is the most common 

spattering area in the lake. When spattering is 

present it is also an area of enhanced downwelling 

of surface crust. The spattering in this area often 

builds a grotto of solidified spatter.

Spattering/nonspattering regimes In 2016 the 

lake was spattering most of the time (spattering 

regime), with one or more spattering sites active. 

Occasionally, spattering would shut down and 

the lake would switch to a nonspattering regime. 

These nonspattering regimes could last for several 

hours, and normally corresponded with the lake 

level abruptly rising several meters in a process 

called “gas pistoning”.

UWE A tiltmeter located near the Hawaiian 

Volcano Observatory on the north rim of Kīlauea 

Caldera (fig. 1).
Menlo Park Publishing Service Center, California

Manuscript approved for publication January 11, 2018

Edited by Katherine Jacques

Layout and design by Cory Hurd

Back cover. Asymmetric spreading involves one plate moving 

rapidly away from a more slowly moving plate. Photograph taken 

November 26, 2016
Patrick and others—Lava Lake Activity at the Summit of Kīlauea Volcano in 2016—Scientific Investigations Report 2018–5008

ISSN 2328-0328 (online)

https://doi.org/10.3133/sir20185008