U.S. Department of the Interior

U.S. Geological Survey

Open File Report 2020–1002

Preliminary Analyses of Volcanic Hazards at Kīlauea Volcano, 

Hawai‘i, 2017–2018
Cover.  Photograph of the upper part of the fissure 8 channel during the 2018 eruption of the lower East Rift Zone of Kīlauea Volcano. The view is to the

northeast. Lava is flowing from lower right to upper center of the image. U.S. Geological Survey photograph taken on June 22, 2018.
Preliminary Analyses of Volcanic Hazards at 

Kīlauea Volcano, Hawai‘i, 2017–2018

By Christina A. Neal and Kyle R. Anderson

Chapter A

Preliminary Analysis of Hazards at the Kamokuna Ocean Entry

By the Hawaiian Volcano Observatory

Chapter B

Preliminary Analysis of Current Explosion Hazards at the Summit of 

Kīlauea Volcano

By Kyle R. Anderson, Donald A. Swanson, Larry Mastin, Christina A. Neal, and Bruce F. Houghton

Chapter C

Volcanic Hazard at the Summit of Kīlauea; June 29, 2018, Update

By the Hawaiian Volcano Observatory

Chapter D

Preliminary Analysis of the Ongoing Lower East Rift Zone Eruption of 

Kīlauea Volcano—Fissure 8 Prognosis and Ongoing Hazards

By the Hawaiian Volcano Observatory

Open File Report 2020–1002

U.S. Department of the Interior

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

DAVID BERNHARDT, Secretary

U.S. Geological Survey

James F. Reilly II, Director

U.S. Geological Survey, Reston, Virginia: 2020

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Suggested citation:

Neal, C.A., and Anderson, K.R., 2020, Preliminary analyses of volcanic hazards at Kīlauea Volcano, Hawai‘i, 2017–2018:

U.S. Geological Survey Open-File Report 2020–1002, 34 p., https://doi.org/10.3133/ofr20201002.

ISSN 2331-1258 (online)
iii

Acknowledgments

Many colleagues at the Hawaiian Volcano Observatory, other U.S. Geological Survey Volcano

Science Center offices, and university collaborators contributed their insights and expertise

to the content of these reports. Partner agencies were often the impetus for preparation of

the reports and assisted us in dissemination to the public and we gratefully acknowledge the

support and assistance of the National Park Service (specifically Hawai‘i Volcanoes National

Park), the Hawai‘i County Civil Defense Agency, the U.S. Coast Guard Honolulu Sector, and

the National Oceanic and Atmospheric Administration. We also thank technical reviewers, both

internal and external, for rapid turnaround.

Contents

Acknowledgments ........................................................................................................................................iii

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

Chapter A. Preliminary Analysis of Hazards at the Kamokuna Ocean Entry................................................3

Chapter B. Preliminary Analysis of Current Explosion Hazards at the Summit of Kīlauea Volcano...........13

Chapter C. Volcanic Hazard at the Summit of Kīlauea; June 29, 2018, Update ........................................17

Chapter D. Preliminary Analysis of the Ongoing Lower East Rift Zone Eruption of Kīlauea Volcano—

Fissure 8 Prognosis and Ongoing Hazards..............................................................................25
iv

cm centimeters

ERZ East Rift Zone

ft feet

GPS Global Positioning System

HCCDA Hawai‘i County Civil Defense Agency

HVO Hawaiian Volcano Observatory

in. inches

km kilometers

LERZ lower East Rift Zone

m meters

m3 cubic meters

m3/s cubic meters per second

m/h meters per hour

mi miles

NPS National Park Service

ppm parts per million

UAS Unoccupied Aircraft Systems

USGS U.S. Geological Survey

Abbreviations
Introduction

From 2017 to 2018, the U.S. Geological Survey (USGS) 

Hawaiian Volcano Observatory (HVO) responded to ongoing 

and changing eruptions at Kīlauea Volcano as part of its 

mission to monitor volcanic processes, issue warnings of 

dangerous activity, and assess volcanic hazards. To formalize 

short-term hazards assessments—and, in some cases, issue 

prognoses for future activity—and make results discoverable 

to both the public and the authorities, HVO released reports 

online. These reports were published rapidly, received peer 

review under the USGS’s Fundamental Science Practice 

guidelines, and were intended to address a focused question 

posed by one or more cooperating agencies—for this reason, 

they were called “cooperator reports.” This Open-File Report 

concatenates four such products issued in 2017 and 2018 into 

a single publication. These reports have been reformatted and 

lightly edited for clarity, but the content has not otherwise 

been changed from the versions first publicly released.

Report Issued During the Pu‘u ‘Ō‘ō Eruption, 

Middle East Rift Zone

Kīlauea Ocean-Entry Hazards Analysis for the U.S.

Coast Guard (March 2017)

Lava intermittently flowing into the ocean on the south 

coast of Kīlauea since 1986 posed a variety of hazards that 

have been described in both formal and informal publications 

(for example, Mattox and Mangan, 1997; Poland and Orr, 

2014; Johnson, 2000; and status reports issued daily by 

HVO). Most of the land at the ocean-entry sites was managed 

by Hawaiʻi Volcanoes National Park, which communicated 

warning information to visitors. In 2017, during a period 

of activity at the Kamokuna Ocean Entry inside Hawaiʻi 

Volcanoes National Park, HVO was asked by the U.S. Coast 

Guard Honolulu Sector to inform management decisions about 

tour boat access to the ocean entries. To assist the Coast Guard 

in its rule-making process, HVO assembled the best available 

information to describe what was known about the extent of 

ocean-entry hazards. This report (chapter A) was delivered to 

the Coast Guard on March 29, 2017, and posted on the Coast 

Guard’s public website related to the rule-making process. 

It was also later posted to HVO’s website on June 27, 2018, 

during the 2018 activity.

Reports Issued During the 2018 Lower East Rift 

Zone Eruption and Summit Collapse

Kīlauea Volcano began a dramatic change in activity in 

late April 2018, culminating in a historically unprecedented 

eruption in the lower East Rift Zone and simultaneous 

episodic summit collapse that closed Hawaiʻi Volcanoes 

National Park and forced the evacuation of thousands of 

people from lower Puna, a district in eastern Hawaiʻi (Neal 

and others, 2019). During the eruption, which lasted more 

than three months, local authorities with responsibility for 

public safety and access management were in need of constant 

updates on the status of the activity, extent of the hazards, and 

prognosis for its progression. HVO provided this information 

during day-to-day interactions with officials and in writing in 

the form of three separate cooperator reports.

Kīlauea Summit Hazards Analysis for the National

Park Service (May 2018)

As magma drained from Kīlauea’s summit into the East 

Rift Zone, HVO recognized that the receding lava lake within 

Halemaʻumaʻu Crater might lead to explosive activity—

analogous to events believed to have occurred in 1924. This 

possibility became a key concern of Hawaiʻi Volcanoes 

National Park management and Hawaiʻi County Civil Defense 

Agency. To evaluate the potential for increasingly hazardous 

activity, K.R. Anderson and others prepared a report during the 

first week of May, only days after the onset of activity. Owing 

to the rapidly evolving situation, this report was constructed 

by a small group in 2–3 days and necessarily relied heavily on 

analogy with previous explosive activity at Kīlauea’s summit. 

This report (chapter B) was delivered to Hawaiʻi Volcanoes 

National Park on May 8, 2018, and formed the basis of a 

public meeting inside Hawaiʻi Volcanoes National Park on 

May 9 at which USGS scientists described volcanic activity, 

the current assessment of hazards, and likely outcomes.

Preliminary Analyses of Volcanic Hazards at Kīlauea 

Volcano, Hawai‘i, 2017–2018

By Christina A. Neal and Kyle R. Anderson
2

Preliminary Analyses of Volcanic Hazards at Kīlauea Volcano, Hawai‘i, 2017–2018

Updated Kīlauea Summit Hazards Analysis for the

National Park Service (June 2018)

As the 2018 eruption and summit collapse activity 

continued, HVO re-evaluated future outcomes and the 

possibility of a transition to more hazardous behavior at 

Kīlauea’s summit. This work formed the basis for a hazards 

analysis delivered to Hawaiʻi Volcanoes National Park on 

June 29, 2018, in response to the park’s request for input into 

their ongoing management decisions regarding park closure 

and the safety of employees and assets. The report (chapter C) 

addressed the possibility of larger and more dangerous activity 

that would involve response by the Hawai‘i County Civil 

Defense Agency.

This second summit report was constructed during a 

period of semi-steady eruptive activity. This allowed more 

time for HVO to solicit input from a broad group of experts 

within the USGS as well as colleagues in Iceland, Japan, and 

U.S. academic institutions. Expert opinion was evaluated, in 

part, in the context of an event-tree analysis (for example, 

Hoblitt and Newhall, 2002) led by colleagues from the 

Volcano Disaster Assistance Program of the U.S. Geological 

Survey and the U.S. Agency of International Development. 

The final report was shared with Hawaiʻi Volcanoes National 

Park, discussed with the public at community meetings, and 

posted on the HVO website on July 5. 

Kīlauea East Rift Zone Hazards Analysis for Hawai‘i

County Civil Defense Agency (July 2018)

As the eruption continued and thousands were displaced 

from their homes, responding agencies grappled with 

planning for a severely impactful event of unknown duration. 

A recurring question for USGS scientists from both the 

public and responsible officials was how long would the 

effusion of lava likely continue? To address this concern and 

review ongoing hazards relevant to local, State, and Federal 

authorities, HVO scientists prepared a report (chapter D) for 

the Hawai‘i County Civil Defense Agency that was delivered 

on July 15, 2018. The product was developed by scientists 

most familiar with lower East Rift Zone geologic history and 

volcanic processes active at that time. In addition to being 

shared directly with the Civil Defense Agency, the report was 

posted on HVO’s website.

References Cited

Hoblitt, R., and Newhall, C., 2002, Constructing event trees 

for volcanic crises: Bulletin of Volcanology, v. 64, p. 3–20.

Johnson, J., 2000, Viewing Lava Safely—Common Sense is 

Not Enough: U.S. Geological Survey Fact Sheet 152-00, 

https://pubs.usgs.gov/fs/2000/fs152-00/.

Mattox, T.N., and Mangan, M.T., 1997, Littoral hydrovolcanic 

explosions; a case study of lava-seawater interaction at 

Kīlauea Volcano: Journal of Volcanology and Geothermal 

Research, v. 75, p. 1–17.

Neal, C.A., Brantley, S.R., Antolik, L., Babb, J.L., Burgess, 

M., Calles, K., Cappos, M., Change, J.C., Conway, S., 

Desmither, L., Dotray, P., Elias, T., Fukunaga, P., Fuke, 

S., Johanson, I.A., Kamibayashi, K., Kauahikaua, J., Lee, 

R.L., Pekalib, S., Miklius, A., Million, W., Moniz, C.J., 

Nadeau, P.A., Okubo, P., Parcheta, C., Patrick, M.R., Shiro, 

B., Swanson, D.A., Tollett, W., Trusdell, F., Younger, E.F., 

Zoeller, M.H., Montgomery-Brown, E.K., Anderson, K.R., 

Poland, M.P., Ball, J.L., Bard, J., Coombs, M., Dietterich, 

H.R., Kern, C., Thelen, W.A., Cervelli, P.F., Orr, T., 

Houghton, B.F., Gansecki, C., Hazlett, R., Lundgren, P., 

Diefenbach, A.K., Lerner, A.H., Waite, G., Kelly, P., Clor, 

P., Werner, C., Mulliken, K., Fisher, G., Damby, D., 2019, 

The 2018 rift eruption and summit collapse of Kīlauea 

Volcano: Science, v. 363, no. 6425, p. 367–374.

Poland, M.P., and Orr, T.R., 2014, Identifying hazards 

associated with lava deltas: Bulletin of Volcanology, v. 76, 

p. 10.
Background

Since the onset of the Puʻu ʻŌʻō eruption in January1983, 

lava has entered the Pacific Ocean for about half the time (as 

of March 2017), constructing dozens of lava deltas and adding 

about 440 acres of new land to the Island of Hawaiʻi. Above 

water, these deltas have ranged in size from tiny surfaces 

measured in tens or hundreds of square meters (similar 

dimensions in square yards) up to massive shelves tens of acres 

in size. The largest delta documented was 64 acres.

The lava deltas have usually begun to form as soon as a 

lava flow reaches the water (fig. 1). The size of the subsequent 

delta is likely determined, in part, by the length of time that 

the lava flow feeding it remains active, and presumably also 

by the size and (or) angle of the near-shore coastal slope upon 

which the delta forms. Most of the delta is composed of lava 

rubble that accumulates on this slope, fragmented during the 

interaction between the active lava flow and the cold sea water. 

When this fan of material builds up to sea level, lava that no 

longer interacts with sea water, and is therefore not fragmented, 

is emplaced on top, producing the relatively smooth flow 

surface that characterizes the visible lava delta. Thus, the lava 

deltas that we see are built upon a naturally unstable base.

Over time, most (if not all) deltas experience collapses 

where portions of the deltas fall into the water, probably in 

response to submarine landslides or slumps caused by (1) 

compaction of the rubble underlying the delta surface, (2) 

oversteepening of the underlying fan of rubble at the front 

of the delta, (3) erosion of the submarine delta by strong 

ocean currents or surf, (4) shaking caused by strong surf or 

earthquakes, or (5) perhaps by some other process not yet 

identified. These causes are in addition to normal erosion 

from ocean wave action. Most collapses are small and go 

unreported, and even those as large as several acres in size 

might be missed or only identified days later during aerial 

reconnaissance missions. Typically, the continued influx of 

lava causes the collapsed part of the delta to rebuild, or at least 

begin to rebuild, within a few days, often obscuring evidence 

that a collapse took place.

Observations have shown that at least some larger 

delta collapses—those ranging in size from several to tens 

of acres—occurred in piecemeal fashion, as the collapse 

of a series of smaller slices from the front of the delta. We 

infer that these scenarios are caused by considerably larger 

submarine landslides that develop progressively, often lasting 

several hours.

On rare occasions, delta collapses trigger small 

explosions—steam blasts—that can hurl both molten and solid 

fragments of the delta hundreds of meters (similar distances 

in yards) away, both inland and out to sea. Even collapses of 

about 1 acre have triggered explosions. Delta collapses can 

also cause local tsunami capable of flooding the adjacent delta, 

or even the land above the adjacent sea cliff. Hot, acidic steam 

can also engulf the immediate area, posing yet another hazard.

Chapter A. Preliminary Analysis of Hazards at the Kamokuna 

Ocean Entry

By the Hawaiian Volcano Observatory

Figure 1.  Schematic drawing that shows (a) development, (b) growth, and (c) collapse of a lava delta. Images also available at https://hvo.wr.usgs.

gov/hazards/oceanentry/deltacollapse.
4

Preliminary Analyses of Volcanic Hazards at Kīlauea Volcano, Hawai‘i, 2017–2018

Summary of Current Conditions

The episode 61g lava flow reached the ocean along the 

south coast of Hawaiʻi in late July 2016, at a location known 

as Kamokuna, and quickly began to build a lava delta. Many 

small collapses were reported by National Park Service (NPS) 

personnel over the following months, as the delta grew, but 

by the end of the year it had a surface area of about 23 acres. 

Starting mid-afternoon on December 31, 2016, the lava delta 

abruptly began to collapse piecemeal into the ocean (fig. 2). 

Most of the delta slid into the water over the next several hours, 

leaving behind narrow remnant ledges at the base of the sea cliff 

that totaled about 2.5 acres (fig. 3).

As the collapse progressed, it began to eat into the older sea 

cliff behind and adjacent to the east end of the delta, sequentially 

removing another 4 acres of land, possibly caused by undercutting 

promoted by the delta collapse. This portion of the older sea cliff 

included part of the Hawaiʻi Volcanoes National Park viewing 

area. The collapse of the older sea cliff, in some instances, 

produced large waves that splashed back onto the sea cliff. The 

total area that collapsed, including the Kamokuna delta and the 

older sea cliff, was approximately 25 acres.

Lava continued to enter the ocean following the delta 

collapse, but did so as a large firehose-like stream of lava that 

emerged from a lava tube exposed at a height of approximately 

21 meters (m; ~70 feet [ft]) above the ocean in the face of a sea 

cliff that is 28 m (~90 ft) high. This entry point is located at: 

19.32056° N., 155.04015° W.

Unlike previously documented collapses at this delta and 

others, the delta did not immediately begin to re-form after the 

New Year’s Eve collapse in 2016. We suspect that the collapse 

formed an extremely steep slope descending underwater from 

the base of the sea cliff. Until the offshore region shallows 

enough (or the debris fan likely forming below water becomes 

less steep) to allow net accumulation of lava above sea level, 

construction of a new delta will not occur. Note that, at the time 

of this writing, observations at the coastline indicate that a small 

delta may have begun to form starting around March 20, 2017.

Figure 2.  Map of the southeast shore of Kīlauea showing the area of the episode 61g lava flow near the coast and the Kamokuna lava

delta on January 3, 2017.
Figure 3.  Photographs of the Kamokuna lava delta before and after the December 31, 2016, collapse. Left, View of the delta on October 14, 2016,

when its size was ~15 acres. U.S. Geological Survey photograph by L. DeSmither. Right, View on January 1, 2017, after the delta collapse, showing

two remnants of the delta. U.S. Geological Survey photograph by M. Patrick.

Ongoing Hazards

Sea Cliff Collapse

Vertical sea cliffs in the vicinity of the lava entry point 

have proven to be unstable, producing collapses of various 

sizes. These collapses were preceded by the development of 

shore-parallel cracks inland of the cliff edge. For instance, on 

January 25, Hawaiian Volcano Observatory (HVO) geologists 

noted an arcuate crack running parallel to the 28-m-high 

(~90-ft-high) sea cliff about 15 m (~50 ft) inland of the stream 

of lava at the Kamokuna ocean entry. Ground inspection of this 

crack on Saturday January 28 showed 30 centimeters (cm; or 

~12 inches [in.]) of separation across the crack. On Wednesday 

February 1, four days later, this crack had widened to about 

70cm (~28 in.), and the seaward block was visibly oscillating 

by as much as ~2 cm (~1 in.), possibly in response to explosions 

below as hot lava mixed with cool ocean water (fig. 4). In 

addition, the ground in the immediate vicinity was shaking.

Part of the block, estimated to be about 80 m long (~260 ft), 

collapsed into the ocean on February 2. HVO geologists in the 

field at the time observed a wave propagating outward from the sea 

cliff but noted the wave was no larger than a typical ocean swell. 

Photographs of the collapse by visitors at the national park viewing 

area show a large rebound splash that also threw dense blocks from 

the collapsed sea cliff roughly 100 m (~330 ft) out to sea.

The collapse of small parts of this cliff continued for some 

days after, some observed and filmed by tourists aboard tour boats. 

The few collapses for which good observations exist showed that 

the cliff crumbled to pieces as it fell. Whereas the collapses that 

were observed occurred as single events, it is difficult to know if 

other events might progress inland in piecemeal fashion, taking off 

additional slices of the sea cliff. It is also not known if all sea cliff 

collapses include only that part of the sea cliff above water, or if, 

during larger collapses, part of the submarine cliff also fails.

Figure 4.  Photographs of the sea cliff crack

inland from the Kamokuna ocean entry on January

28, 2017, when the crack was ~30 centimeters

(cm) wide (left), and on February 1, 2017,

when the crack was ~70 cm wide (right). U.S.

Geological Survey photographs; also available

at https://hvo.wr.usgs.gov/multimedia/uploads/

multimediaFile-1627.jpg.

Chapter A. Preliminary Analysis of Hazards at the Kamokuna Ocean Entry5
6

Preliminary Analyses of Volcanic Hazards at Kīlauea Volcano, Hawai‘i, 2017–2018

Tephra Jets

The stream of lava entering the ocean produces intermittent 

explosions of spatter and fine fragments, including Pele’s hair 

(fig. 5). Based on HVO’s limited observations of the current 

entry, large fragments of molten lava are being thrown vertically 

at least 30–40 m (about 100–130 ft), with some landing on the 

adjacent 28-m-high (~90-ft-high) sea cliff and building a small 

tephra cone. Most fragments, however, are raining offshore. 

Without a continuous record of activity, we cannot state precisely 

how far this hot spatter can be thrown, but past experience 

suggests that small pieces of material can be lofted as high and 

as far as 100 m (~330 ft). Large explosions with even greater 

throw distance are possible. Visit https://pubs.usgs.gov/fs/2000/

fs152-00 for more information.

Delta and Submarine Slope Collapse

As long as lava enters the ocean, further delta construction 

and collapse events could occur at some point. These collapses 

can be small or large and occur with little or no warning. 

Whereas submarine slope failures are probably closely 

associated with delta collapses, some might occur in the absence 

of delta collapses. We have no way of presently detecting or 

monitoring this phenomenon, nor do we know if it presents 

any perceivable hazard. However, the failure of the steep 

fan of rubble that develops offshore probably will displace 

water, potentially creating surface waves, though we have no 

information on how large the resulting waves (if any) might be.

For a schematic diagram illustrating the delta collapse process, 

see the fact sheet at https://pubs.usgs.gov/fs/2000/fs152-00.

Ballistics

Large, dense fragments ejected during some delta collapses 

can be thrown in all directions from the point of collapse, 

including out to sea, in response to the explosive interaction of the 

hot delta with cold sea water (fig. 6). Based on a review of nearly 

30 years of delta collapse and ejecta distance observations mined 

from the HVO records (discussed in next section), we consider a 

radius of 300 m, or about 1,000 ft, to be a reasonable minimum 

high-hazard zone around a lava delta, where one is present (for 

example, see event of January 30, 1996, below).

Explosions are less likely for collapses of older, cooler 

material. However, observations of recent sea cliff collapses have 

shown that ballistics can be thrown as far as 100 m (~330 ft) out to 

sea owing to the dynamics of the rebounding splash following the 

impact of the sea cliff in the water.

There is no obvious relation between the size of the delta 

and the extent of ballistic hazard. Both large and small lava deltas 

(or large and small parts of deltas) have collapsed and triggered 

explosions. Why some collapses lead to explosions and some do 

not is not known, but likely depends on how hot the collapsing 

rock is, and possibly the size, style, and abruptness of the collapse, 

as well as the nature of the submarine slope.

Figure 5.  Photograph showing a typical tephra jet at the Kamokuna ocean

entry. U.S. Geological Survey photograph taken on January 30, 2017.

Figure 6.  Photograph of a ballistic block thrown inland during an explosion

triggered by a lava delta collapse. U.S. Geological Survey photograph.
Waves and Surges

During collapse events, water is displaced impulsively and 

one or more waves can be produced that travel radially away 

from the point of collapse or explosion. During the December 31, 

2016, collapse event, NPS eyewitnesses noted waves or splashes, 

probably related to the collapse of the older sea cliff, crashing atop 

the ~15-m-high (~50-ft-high) sea cliff near the public viewing area. 

Additionally, a visitor’s video clip shows a small fishing boat taking 

on water when a small collapse event occurred nearby (unrelated to 

the December 31 collapse), which sent a wave out to sea.

An analysis by National Oceanic and Atmospheric 

Administration scientists that evaluates wave heights generated by 

sea cliff collapses indicates that, for a reasonable range of collapse 

sizes from the current sea cliff, waves of between about 1.5 and 

5 m (5 and 16 ft) in height could travel as far as 100 m (~330 ft) 

from shore. With the exception of the splash in the immediate 

impact zone, these waves are not steep and breaking. Rather, 

they are more like those of typical ocean swells and will diminish 

rapidly in size with distance from the impact zone. 

Scalding Water

Lava entry into the ocean produces a plume of hot, acidic 

water that travels offshore or along shore, depending on ocean 

currents. Recent HVO thermal imaging documented surface 

water temperatures of 60 °C (142 °F) as far as about 50 m 

offshore, and temperatures as high as 44 °C (111 °F) extending 

more than 300m seaward (fig. 7). Past evaluation of this plume of 

hot water suggests it may be limited to the upper 1–2 m (3–7 ft) 

of the water column.

Laze

The interaction of hot lava and seawater produces “laze”, 

a cloud of steam, hydrochloric acid droplets, and volcanic glass 

Figure 7.  Thermal infrared image (left) and oblique aerial photograph (right) of the plume of hot water at the Kamokuna ocean entry that extends

several hundred meters offshore. Boats for scale. U.S. Geological Survey photographs taken on March 16, 2017.

particles that can be harmful to breathe (fig. 8). Laze drifts 

downwind, making this hazard strongly dependent on wind 

conditions, which can change throughout the day. The plume is 

typically visible in an HVO webcam accessible at https://hvo.

wr.usgs.gov/cams/panorama.php?cam=HPcam. Altitudes of 

the laze plume have not been rigorously tracked, but anecdotal 

evidence suggests that near the ocean entry, it remains typically 

below about 300 m (~1,000ft) above ground level. No data exist 

on how often the laze plume drifts offshore into areas that could 

impact boat traffic.

The size of the laze plume can increase significantly 

during delta collapses. This hot, acidic plume can envelop 

nearby areas, causing scalding and potentially pulmonary 

edema and death, if inhaled.

Figure 8.  Photograph of a laze plume as it drifts offshore from the

ocean entry at Kamokuna on January 3, 2017. The edge of the lava

“firehose” is visible as red incandescence. U.S. Geological Survey

photograph; also available at https://hvo.wr.usgs.gov/multimedia/

uploads/multimediaFile-1588.jpg.

Chapter A. Preliminary Analysis of Hazards at the Kamokuna Ocean Entry7
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Preliminary Analyses of Volcanic Hazards at Kīlauea Volcano, Hawai‘i, 2017–2018

Summary of Hazardous Delta Collapses 

During the Pu‘u ‘Ō‘ō Eruption

Not all delta collapse events from 1988 to present are 

included. This list includes collapse events that did one or more of 

the following: (1) triggered explosions that threw molten spatter 

or dense rocks onto the adjacent sea cliff; (2) caused localized 

tsunami; (3) caused the collapse of slices of the adjacent, older sea 

cliff; or (4) prompted incidents where people nearby had to run for 

safety. Information presented here was gleaned from HVO internal 

reports, with some additions from HVO field logbook entries.

March 26, 1988

Lava delta location/name: Kupapaʻu

Collapse size: No apparent collapse

Summary: NPS personnel living at the Wahaʻula Visitor Center, 

1 km (~0.6 mi) west of the entry were awakened at 1:25 a.m. 

by a roar “like a jet engine” and reported large hydromagmatic 

explosions that lasted for about an hour, ejecting material 

as high as ~100 m (~330 ft) vertically and 100–150 m 

(~330–490 ft) laterally from two tephra cones at the front of 

the delta. Observations the next day found that both cones 

were heavily mantled with spatter, but the eastern tephra cone 

had a conspicuous deposit of dense spatter bombs, as large as 

footballs, that littered the area as far as 60 m (~195 ft) inland 

of the cone. Blocks of dense rock were also abundant in the 

deposit around the eastern cone. The event was inferred to be 

the result of a large underwater landslide or slumping event that 

opened cracks in the delta, which channeled water to the lava 

tube; no actual delta collapse was identified. The size of the 

delta was not reported, so it could not be determined if blocks 

and debris reached the adjacent sea cliff.

May 30, 1988

Lava delta location/name: Kupapaʻu

Collapse size: Not reported

Summary: Catastrophic slumping of the underlying submarine 

debris fan left the Kupapaʻu lava delta unsupported, causing a 

large delta collapse at 7:59 p.m. that resulted in large explosions. 

The blasts tossed blocks of dense pāhoehoe more than 100 m 

(~330 ft) inland, but it was not reported if this reflects the distance 

inland from the edge of the collapse scar or the sea cliff.

July 12, 1988

Lava delta location/name: Kupapaʻu

Collapse size: ~1 acre

Summary: The entire delta broke off into the ocean without 

warning at 8:42 a.m. Two large explosions occurred 10–20 

seconds apart, throwing spatter about 100 m vertically and 

sending spectators running. Spatter was deposited within a 

radius of 50 m inland from the sea cliff, but most of the deposit 

fell 30 m (~100ft) inland from the cliff where it covered 

10–20 percent of the ground surface. Fallout included 10- to 

30-cm-long (4- to 12-inch-long) ribbons and cow-dung bombs. 

This was the first collapse witnessed by an HVO scientist, who 

stated that “The collapses...permit no possible means of escape 

for anyone on the delta at the time of collapse.”

August 15, 1988

Lava delta location/name: Kupapaʻu

Collapse size: ~4 acres

Summary: Almost the entire delta collapsed at 6:14 a.m. and 

NPS employees living at Wahaʻula Visitor Center felt the shock. 

Later in the day, a small deposit of spatter was discovered that 

covered an area about 10 m (~33 ft) wide and 20 m (~66 ft) 

long. Because the entire delta collapsed, we infer the deposit to 

be on the sea cliff.

September 15, 1988

Lava delta location/name: Kupapaʻu

Collapse size: ~1 acre

Summary: A major collapse at 11:07 p.m. removed the entire 

delta, triggering explosions that produced a tephra cone and hurled 

dense, fist-sized fragments of the sea cliff onshore.

January 23, 1989

Lava delta location/name: Kupapaʻu

Collapse size: Not reported

Summary: A major delta collapse occurred at 8:44 a.m., claiming 

50 percent of the delta. Subsequent explosions threw dense blocks 

of lava 10–50 cm (~4–20 in.) in diameter as far as 40–50 m 

(~130–165 ft) inland from the edge of the collapse.

April 19, 1993

Lava delta location/name: Laeʻapuki

Collapse size: ~1 acre

Summary: A major collapse event that started at 9:43 p.m. was 

followed by an explosion containing incandescent rocks. These 
fragments were directed to the northwest and thrown as far as 

200 m (~660 ft) inland from the source of the explosion (which 

was located ~120 m, or ~400 ft, inland from the sea cliff). 

Several meter-sized (yard-sized) blocks were found within 20 m 

(~65 ft) of the ocean and did not reach the sea cliff; beyond this 

area, fragments were generally <25 cm (<10 in.). One person 

disappeared into the ocean when the part of the delta they were 

standing on collapsed and 22 visitors were treated for injuries 

sustained from falls or from getting hit by rocks.

May 15, 1993

Lava delta location/name: Kamoamoa

Collapse size: Not reported

Summary: A deposit of mostly baseball- to football-sized rocks 

was discovered on May 17 scattered to the north and west as 

far as 100 m (~330 ft) inland from the ocean entry, with smaller 

debris extending 150 m (~490 ft) inland. The date of the event 

that produced this deposit is inferred from seismic data to be 

May 15.

November 26, 1993

Lava delta location/name: Kamoamoa

Collapse size: ~5 acres

Summary: Cracks formed on the delta in mid-November. On 

the afternoon of November 26, vigorous tephra jets started. In 

the evening, a large surface flow emerged from a crack on the 

delta, as the delta appeared to tilt seaward, sending spectators 

running. This was followed by a major delta collapse and large 

explosion at 9:28 p.m. A localized tsunami washed onshore 

right afterward.

February 22, 1994

Lava delta location/name: Kamoamoa

Collapse size: ~2.5 acres

Summary: Part of the delta collapsed on February 22, depositing 

a carpet of ribbon spatter and cow-dung bombs as far as 80 m 

(~260ft) inland from the resulting scarp. Finer grained tephra 

and lava fragments were found hundreds of meters from the 

entry.

July 8, 1994

Lava delta location/name: Kamoamoa

Collapse size: ~2 acres

Summary: An inactive part of the delta collapsed at 12:36a.m. 

Dense blocks as large as 0.5 m (20 in.) in diameter were 

deposited 30–40 m (~100–130 ft) inland on the surface of the 

remaining delta by the resulting localized tsunami.

January 30, 1996

Lava delta location/name: Kamokuna

Collapse size: ~4 acres

Summary: Part of the Kamokuna delta collapsed progressively, 

in piecemeal fashion, over a period of about 6 hours. Multiple 

explosions occurred, throwing blocks as large as 75 cm (~30 in.) 

across as far as 250 m (~820 ft) inland from the original coastline. 

A separate report stated than dense rocks were ejected to a height 

of nearly 100 m (~330 ft) and thrown more than 300 m (~985 ft) 

inland but does not specify if this is from the point of the explosion 

or the sea cliff. The final collapse in the sequence created a 

small, hot local tsunami that deposited 50-cm-diameter (20-inchdiameter) blocks as far as 30 m (~100 ft) inland from edge of the 

collapse scar on the delta.

July 12, 1996

Lava delta location/name: Laeʻapuki

Collapse size: ~3 acres

Summary: A collapse on July 12 cut back into older sea cliff 

and triggered explosions that deposited spatter and small blocks 

5–30 cm (2–12 in.) in diameter as far as 30 m (~100 ft) inland 

of the sea cliff.

December 2, 1996

Lava delta location/name: Laeʻapuki

Collapse size: ~34 acres

Summary: The delta began to collapse in piecemeal fashion 

starting at 7:50 a.m. and continued over the next 2.5 hours, until 

the entire 26-acre delta was gone. In addition, another 8 acres of 

older sea cliff collapsed as well, bringing the total collapse area 

to 34 acres. Dense rock fragments were thrown 100 m (~330ft) 

inland, and finer debris as far as 320 m (1,050 ft) inland, from 

the sea cliff. Blocks more than 30 cm (12 in.) across were 

thrown 50 m (~165 ft) inland.

December 10 or 11, 1998

Lava delta location/name: Kamokuna

Collapse size: ~14 acres

Chapter A. Preliminary Analysis of Hazards at the Kamokuna Ocean Entry9
10

Preliminary Analyses of Volcanic Hazards at Kīlauea Volcano, Hawai‘i, 2017–2018

Summary: A large delta collapse, sometime on December 10 

or 11, removed about 14 acres, including 6 acres of the older 

adjacent sea cliff.

March 8, 1999

Lava delta location/name: Kamokuna

Collapse size: ~20 acres

Summary: Nearly the entire Kamokuna delta collapsed on 

March8. The collapse was preceded by an explosion that rocked 

the ground and threw spatter 60–75 m (~195–245 ft) into the air. 

Seven people on the delta, who had walked past warning signs, ran 

and made a narrow escape. The delta collapsed shortly afterward.

April 13, 1999

Lava delta location/name: Kamokuna

Collapse size: Not reported

Summary: The outer margin of the delta apparently collapsed, 

which triggered spattering that ejected ribbon spatter as long as 

1m (~1 yard) and flattened bombs the size of dinner plates, as well 

as dense rocks as large as 20 cm (~8 in.) in diameter. The deposit 

formed a continuous ground cover 30–35 m (~100–115 ft) inland 

from the sea cliff.

August 18, 1999

Lava delta location/name: Kamokuna

Collapse size: ~15 acres

Summary: A collapse in the morning removed about 15 acres of 

land, including 11.5 acres of the active delta and ~3.5 acres of 

older sea cliff.

August 27, 2005

Lava delta location/name: East Laeʻapuki

Collapse size: ~11 acres

Summary: A localized tsunami, triggered when part of the 

delta collapsed, swept blocks as large as 1 m (~1 yard) onto 

adjacent parts of the delta.

November 28, 2005

Lava delta location/name: East Laeʻapuki

Collapse size: ~44 acres

Summary: Starting at 11:10 a.m., and lasting for about 5 hours, 

the East Laeʻapuki delta collapsed in piecemeal fashion. Almost 

the entire 34-acre delta collapsed as well as an additional 10 acres 

of the older sea cliff behind the delta, bringing the total size of 

the collapse to 44 acres. Lithic blocks as large as 15 cm (~6 in.) 

across were thrown 150 m (~490 ft) inland from the pre-collapse 

cliff. Spatter was thrown 100 m (~330 ft) inland, and finer debris 

was deposited as far as 550 m (~1,800 ft) inland, with almost total 

ground coverage as far as 230 m (~755 ft) inland.

May 10, 2007

Lava delta location/name: East Laeʻapuki

Collapse size: ~23 acres

Summary: The East Laeʻapuki lava delta began to collapse in 

piecemeal fashion starting around 2:25 p.m. and continued for 

at least the next 4 hours, removing part of the delta and adjacent 

older sea cliff. Fist-sized dense rocks were thrown as far as 

140m (~460 ft) inland from the resulting collapse scar in the 

delta. The largest dense block, found 40 m (~130 ft) inland, was 

~90 cm (~35 in.) across. A 35-cm-diameter (~14-inch-diameter) 

rock was thrown 120 m (~400 ft) inland. Surprisingly, the 

collapse occurred 2 months after the ocean entry stopped.

July 30, 2008

Lava delta location/name: Waikupanaha

Collapse size: ~2 acres

Summary: A small delta collapse occurred between 5:00 and 

6:00 a.m., based on anomalous seismicity. Blocks of dense lava 

as large as 80 cm (~32 in.) across, but on average about 10 cm 

(~4 in.) across, were thrown as far as 110 m (~360 ft) inland.

August 27, 2008

Lava delta location/name: Waikupanaha

Collapse size: 1–2 acres

Summary: A small delta collapse occurred between 10:00 and 

11:00 p.m., based on seismicity. Dense rocks were thrown as far 

as 180 m (~590 ft) inland from the sea cliff. The average block 

size was 5–10 cm (~2–4 in.), but many blocks were 25 cm 

(~10in.) across.

December 7, 2008

Lava delta location/name: Waikupanaha

Collapse size: 3–4 acres
Summary: A delta collapse occurred on the morning of 

December 7, possibly between 2:40 and 5:23 a.m., based on 

seismicity. Fist-sized rocks and smaller fragments fell as far as 

215 m (~705 ft) inland. Several dense rocks were found 375m 

(1,230 ft) inland, but we cannot unequivocally say that they 

were deposited by this explosion.

January 18, 2009

Lava delta location/name: Waikupanaha

Collapse size: Not reported

Summary: Dense blocks of lava, thought to be recent, were 

found impacted into the tephra cone on top of the sea cliff on 

January 22, 2009. We infer that these are from a collapse that 

reportedly occurred on January 18.

February 17, 2009

Lava delta location/name: Waikupanaha

Collapse size: Not reported

Summary: A crack across the delta was observed on February 16 

and was observed to be wider the next day. At about 1:30 p.m., 

the delta collapsed, throwing dense, angular fragments as far as 

275 m (~900 ft) inland from edge of the collapse scar, or 240 m 

(~785 ft) inland from the older sea cliff. The deposit included 

pebble- to football-sized rocks as well as cow-dung bombs.

December 31, 2016

Lava delta location/name: Kamokuna

Collapse size: ~25 acres

Summary: A piecemeal collapse of the delta began in the 

mid-afternoon and continued into the evening. In addition 

to the collapse of about 21 acres of the delta, about 4 acres 

of the older sea cliff behind and to the east of the delta also 

collapsed, taking with it part of the NPS public viewing area. 

Little explosive debris was produced.

Chapter A. Preliminary Analysis of Hazards at the Kamokuna Ocean Entry11

Introduction

We examine here the possibility and potential impacts 

of future explosive events from within Halemaʻumaʻu. In 

particular, the potential for the summit lava lake surface to drop 

to or below the elevation of the groundwater table, estimated to 

be 460 meters (m; 1,500 feet, ft) below the caldera floor, raises 

the strong possibility of explosions caused by interactions of 

groundwater and hot rock which would impact the summit area. 

This document reviews current activity, describes a credible set 

of circumstances that could produce such explosions, examines 

hazards and their extent, and discusses uncertainties. It is meant 

as a guide for managing risk in the Kīlauea summit region.

Background

Kīlauea Volcano’s summit lava lake is directly connected 

to its summit magma reservoir. As pressure in the reservoir 

decreases, the surface height of the lava lake also decreases, and 

vice versa. The elevation of the lava lake surface is measured by 

laser rangefinder, thermal camera, and other methods.

Current Activity

After repeatedly overflowing onto the floor of 

Halemaʻumaʻu in late April, the surface of Kīlauea’s lava lake 

began to drop on May 2, 2018. Around the same time, deflation 

of Kīlauea’s magma reservoir was detected by the summit 

tiltmeter network. The rate of lava lake subsidence increased 

slowly but over the last three days of available data has remained 

relatively constant at about 2 meters per hour (m/h; ~7 feet per 

hour). From its height at 1,025 m above sea level on May 2 to 

the most recent estimate at 9:00 p.m. on May6, the lava lake 

surface dropped more than 200 m (660ft). Measurements have 

become more difficult to make as the surface has dropped farther 

from monitoring instruments, but thermal camera imagery 

indicates continued lowering of the lake surface since that 

time, and tiltmeters at Kīlauea’s summit also indicate a steady 

depressurization of the summit magma reservoir.

Outcome of Concern

Assuming the lake surface continues to drop at its current 

rate, we can extrapolate forward in time. Such an extrapolation is 

associated with very large uncertainty, as the system may change 

in unexpected ways, but it guides our thinking about potential 

outcomes. At the current rate of decline, the lava lake may drop 

below the water table near the end of this week (fig. 1).

Such a condition has been associated with explosive 

activity at the summit of Kīlauea Volcano in the past. In 

February 1924, for example, lava drained from Halemaʻumaʻu 

Crater and, by early May 1924, dropped below the water table. 

Collapse of the crater walls, and influx of groundwater into the 

conduit to Halemaʻumaʻu, caused repeated explosions between 

May 11 and 27, 1924. These explosions threw rocks larger than 

25 centimeters (cm; 10 inches [in.]) in diameter—maximum 

size about 2 m (~7 ft)—as far as 1 kilometer (km; 0.6 miles 

[mi]) or more from the vent. Ash from the explosions fell from 

North Hilo to beyond Pāhala, pea-size rocks were reported to 

have fallen at the Volcano House, and gravel-size rocks were 

deposited 3 km (2 mi) southwest of Halemaʻumaʻu.

Potential Hazards

For management purposes, we can define two types of 

hazard zones for future Halemaʻumaʻu explosions:

1. Ballistic projectile zone.—This is a zone of extreme risk, 

in which large projectile-like rocks travel on cannonballlike paths outwards from the vent in all directions. The 

chance of fatality and severe injury within this zone is 

high. For practical purposes, a projectile size limit of 

10 cm (4 in.) can be taken as the outer edge of this zone.

2. Ashfall zone.—This zone is located primarily 

downwind from the vent where smaller particles 

(ash to centimeter in size) fall. Debris falling in this 

Chapter B. Preliminary Analysis of Current Explosion Hazards at 

the Summit of Kīlauea Volcano

By Kyle R. Anderson,1 Donald A. Swanson,1 Larry Mastin,1 Christina A. Neal,1 and Bruce F. Houghton2

1

U.S. Geological Survey.

2

University of Hawaiʻi at Mānoa.
14

Preliminary Analyses of Volcanic Hazards at Kīlauea Volcano, Hawai‘i, 2017–2018

region is unlikely to threaten human life, but it can 

heavily impact transportation, infrastructure, and 

utilities. Visibility can be low, cars can lose traction 

on roadways, water supplies can be contaminated, 

machinery can be damaged by abrasion and corrosion, 

power transformers can short out, and prolonged 

exposure can result in respiratory problems. Some 

of these problems can persist for days or longer after 

an eruption stops, as wind re-suspends ash. A more 

complete discussion of ash impacts can be found at 

https://volcanoes.usgs.gov/volcanic_ash.

In the ballistic projectile zone, risk depends on the size 

of the projectiles, so we typically plot contours of rock size 

to make hazard projections (fig. 2). In the ashfall zone, the 

risk increases with ash thickness and with meteorological 

conditions. For example, wind affects visibility and ash 

infiltration into mechanical and electronic components, 

and wetness affects road traction and weight of ashfall on 

structures. Therefore, we typically plot ash thickness for 

scenarios or past events on a map (fig. 3).

Two eruptions—the March 19, 2008, and the 1924 

explosions—provide information about the scale of hazards 

for (1) small and (2) moderate Halema‘uma‘u explosions.

1. Small event.—March 19, 2008. This small event began the 

current 2008–2018 summit eruption. The ballistic projectile 

zone extended radially outwards for a distance of 300 m 

Figure 1.  Plot of the elevation of Kīlauea’s lava lake surface (in meters, m) versus

time, with extrapolation into the future at a subsidence rate of 2.2 meters per hour (m/h).

This subsidence rate is approximately its rate from the time following the magnitude 6.9

earthquake that occurred on May 4, 2018, to the present (May 8, 2018). The water table at

roughly 600 m above sea level is indicated by the black horizontal line. At 2.2 m/h, the lava

lake surface could reach the water table within the next several days, although such an

outcome is far from certain. The water table around the lava lake is also likely complex, and

its elevation there is only approximately known.

(1,000 ft). The ashfall zone extended at least 1.5 km (1 mi) 

downwind (to the southwest).

2. Moderate event.—1924 explosions. The ballistic projectile 

zone extended 1 km (0.6 mi) to the north and south of the 

Halemaʻumaʻu Crater rim, and less to the east and west. 

The ashfall zone extended at least 30 km (20 mi) from 

Halema’uma’u, in a variable pattern indicating complex 

winds over an extended period of time. Dispersal toward 

the southwest would be expected during normal trade 

winds, but winds can vary with daily meteorology. The 

U.S. Geological Survey is running twice-daily simulations 

of ashfall dispersal under current conditions for hazard 

planning (fig. 4).3

Less likely but more hazardous scenarios do exist. If the 

pressure in Kīlauea’s shallow magma reservoir greatly decreases, 

it is possible that the ground surface in a broader area above the 

reservoir would begin to collapse along faults into the evacuated 

space. This process is distinct from the reduction in lava lake 

surface height described above and would require a greater degree 

of depressurization. This scenario does not seem likely at the 

present. In 1924, the ground above the reservoir subsided several 

meters without inducing a collapse—far more subsidence than has 

been recorded during the current activity. Larger eruptions are also 

known to have occurred in the late 18th century. However, there is 

no evidence at present that would suggest an eruption as large as 

those in the late 18th century is likely in the short term.

3

Simulations are done using the Ash3D volcanic ash dispersion model at https://vsc-ash.wr.usgs.gov/ashgui/#/publicresults/MNL-1025775/DEP. [Editor’s note: This link 

was actively updated during the eruption event.]
Figure 2.  Map of the ballistic projectile zone for the 1924 eruption at Kīlauea’s summit. Colored dots

show individual projectiles from <25 to >150 centimeters in diameter. Collectively, they define a hazard

zone of extreme risk with a radius of approximately 1 kilometer (0.6 miles). The orange color maps post1924 lava flows, which buried any older ballistic rocks. Ballistic rocks fell in the white area just southeast

of the crater but cannot be distinguished today from older rocks owing to human activity after 1924.

Figure 3.  Map of the ashfall zone for the 1924 eruption of Kīlauea. The red line encloses the large

and complex region of ashfall. Numbers show ash thicknesses (in centimeters, cm) measured by

Thomas Jaggar soon after the 1924 eruption. We know that, in fact, the ashfall zone was much larger

than shown here as reports indicate that ash was dispersed northward as far as North Hilo. An isopach

is a line of equal ash thickness.

Chapter B. Preliminary Analysis of Current Explosion Hazards 15
16

Preliminary Analyses of Volcanic Hazards at Kīlauea Volcano, Hawai‘i, 2017–2018

Uncertainties

Many aspects of this analysis have a high degree of 

uncertainty, which are discussed here.

1. Time when the lava column reaches the water table.—The 

current rate of lava subsidence (~2 m/h) is derived from only 

five days of observations. We do not fully understand why 

the magma reservoir is steadily draining, or how long it will 

continue to drain. The subsidence rate will likely change in 

coming days, but when, how much, and whether the rate 

will increase or decrease are all unknown. The rate may or 

may not be directly impacted by changes in the ongoing 

lower East Rift Zone eruption. The depth of the water table 

is also known only from observations in a research well 

located 1.5 km (0.9 mi) south of the lava lake. Details of the 

water table in the immediate vicinity of the lava lake are not 

well known.

2. How long until water begins to interact with hot rock.—As 

rock around the conduit cools, water will migrate towards 

the conduit; the duration of this process is not known.

3. Whether or not conditions will produce explosions.—

Explosions are believed to require pressurization as water 

is heated to steam by magma. Crater walls may collapse 

and block the conduit, causing pressurization of steam. 

Alternatively, rapid mixing could produce steam and increase 

pressure even when confinement is poor. These processes 

are not well understood globally, and the timing of their 

occurrence (if they do occur) may be impossible to predict.

Figure 4.  Map showing the model output of

possible ash extent and thickness for a plausible

explosive event from the Kīlauea summit should

phreatic explosions commence. Contours show

expected ash deposit thickness (in centimeters, cm)

under the wind conditions of May 7, 2018, at 12:00

p.m. Coordinated Universal Time. The assumed

plume height (in kilometers, km), duration, and

erupted volume (in cubic kilometers of dense rock

equivalent) used in the simulation are listed in the

upper left. In this scenario, the maximum thickness

is predicted to be less than 1 cm (<0.5 inches) at a

distance of less than 5 km (3 miles) from the vent.

4. How large explosions will be.—Above we have outlined the 

two most credible scales for future explosions, that is, small 

and moderate events.

5. How long such explosions will continue.—Individual 

explosions may last minutes to tens of minutes. Episodes 

of historical explosive activity have lasted days (in 2008) to 

weeks (in 1924). Repeated episodes have persisted for longer 

only when the caldera floor was below the water table. 

Conclusions

Interaction of magma, hot rock, and groundwater as the 

Halemaʻumaʻu lava lake recedes deeper into the volcano is 

likely and has the potential to produce sudden and largely 

unpredictable explosions. Individual explosions may be brief 

(minutes) but may occur in sequences or clusters lasting weeks 

or longer. This process could begin as early as mid-May 2018 

and may result in intermittently hazardous conditions in and 

around the summit of Kīlauea Volcano.

The onset of such activity will likely be abrupt and 

follow quickly after some triggering event; for example, 

collapse and blockage of the deepening crater. It is not certain 

that the Hawaiian Volcano Observatory will receive signals in 

monitoring data (earthquakes or tremor) that suggest the onset 

of this activity. Once the lava level reaches the groundwater 

elevation, the onset of continuous ashy plumes or a sequence 

of violent steam-driven blasts may be the first sign that activity 

of concern has commenced.
More powerful explosions accompanied by ground 

slumping and ash emission began on May 16. The most notable 

explosions—and the type discussed here—have produced 

relatively high levels of ground shaking, are apparently associated 

with abrupt pressurization of the magma reservoir, and through 

late May emitted relatively vigorous ash plumes. We here refer to 

these as collapse/explosion events.

Early collapse/explosion events (before late May) ejected 

ash and gas to heights above 25,000 ft and large (ballistic) 

fragments tens of centimeters in size to the area immediately 

surrounding the vent (fig. 1). Observations and preliminary 

models suggest that these explosions may have been caused 

not by interaction of magma with groundwater, as previously 

believed to have occurred at Kīlauea in 1924, but rather by 

Introduction

This document is a guide for understanding current 

activity and hazards at and around the summit of Kīlauea 

Volcano. Here, we summarize activity from late April through 

the present (June 29, 2018), detail possible future outcomes, 

and review hazards associated with these outcomes. Few 

processes outlined below are known sufficiently well for us to 

be able to assign quantitative probabilities to possible future 

events. Instead, we rank future possibilities in qualitative 

terms of likelihood based on our understanding of current data. 

We stress that our understanding of Kīlauea and the current 

eruption is continually evolving as we obtain new information 

and that our analyses may change in response.

Current Activity

In a general model of the 1983–present eruptions of Kīlauea, 

magma from the mantle rises beneath the summit, passes through 

the magma storage system, and ultimately exits the summit 

towards the East Rift Zone (ERZ). If the rate of magma evacuation 

towards the ERZ exceeds the rate of magma supply to the summit, 

the reservoir depressurizes (“deflates”), and vice versa. This causes 

subsidence of rock in and around Kīlauea Caldera.

Deflation of Kīlauea’s shallow summit magma reservoir 

began in early May and continued at a near-constant rate through 

the middle of the month. Deflation was triggered by the intrusion 

of magma into Kīlauea’s lower ERZ, and also possibly changing 

conditions in the rift itself, which have enabled increased rates 

of magma storage (for instance, owing to rift opening associated 

with the magnitude 6.9 earthquake on May 4, 2018). Reservoir 

deflation caused the floor of the caldera to subside at a rate of 

6–8 centimeters per day (2–3 inches per day) near the overlook 

vent within Halemaʻumaʻu, and the lava lake to drop out of sight 

around May 10—more than 320 meters (m; 1,000 feet [ft]) below 

its high point in late April. Deflation and subsidence stressed the 

rock in and around the caldera, causing more than 800 earthquakes 

during the first two weeks of May, and withdrawal of the lava lake 

destabilized the Halemaʻumaʻu Overlook vent, causing rockfalls 

that produced short-lived ash emissions.

Chapter C. Volcanic Hazard at the Summit of Kīlauea; 

June 29, 2018, Update

By the Hawaiian Volcano Observatory

Figure 1.  Photograph of the parking lot of the former Halema‘uma‘u

Overlook (closed since 2008) taken on June 8, 2018, showing

disturbances caused by 2018 explosive eruptions. The rocks were

ejected from the vent as ballistic projectiles—those in the median

(center) were ejected in either 1924 or 2018, and those in the parking

bays (left and right) were ejected in 2018. The gray color reflects that of

2018 ash, which coats the parking lot and surrounding areas to a depth

of 2–4 centimeters (less than 1.5 inches). Large cracks and uplifted

blocks form by stresses and slumping associated with widening of

Halema‘uma‘u crater.
18

Preliminary Analyses of Volcanic Hazards at Kīlauea Volcano, Hawai‘i, 2017–2018

exsolution, expansion, and release of gases that were dissolved 

in the magma. Collapse/explosion events have occurred 

semiregularly with repose periods (time between events) of 

about 0.5 to 2 days. Seismicity increases in the hours preceding 

explosions, leading to cycles of earthquakes that are felt in the 

summit area (fig. 2).

The mechanism producing collapse/explosion events is not 

well understood. We infer that withdrawal of magma towards 

the ERZ continually works to reduce pressure in the shallow 

reservoir. When the reduction in pressure becomes too great, 

the rock that forms the floor of Halemaʻumaʻu and parts of the 

surrounding Kīlauea Caldera4 slump down into the shallow 

magma reservoir in a collapse/explosion event. The rock 

that slumps down into the reservoir replaces magma that has 

migrated into the ERZ, and abruptly increases reservoir pressure 

(as measured by ground deformation instruments). Similar 

processes have been observed during caldera formation at other 

volcanoes (see section on historical analogs).

In this way, magma evacuation is accompanied by 

relatively nonhazardous slumping and enlargement of 

Halemaʻumaʻu, rather than sudden large-scale collapses and 

more powerful explosions. Since the beginning of May, the 

crater’s volume has more than quadrupled (figs. 1 and 3), and, 

since May 29, a Global Positioning System (GPS) station near 

the north rim of Halemaʻumaʻu crater dropped more than 100 m 

(330 ft) during collapse/explosion events.

At the end of May, collapse of rock from surrounding 

crater walls blocked the Halemaʻumaʻu Overlook vent (which 

formerly contained the lava lake) and changed the character 

of summit activity. Since then, background gas emissions at 

the summit have greatly decreased, collapse/explosion events 

generally have produced only weak ash plumes that do not 

rise higher than 6,000 ft above the crater rim, and no ballistic 

fragments are known to have been ejected. Although the 

plumes have become less vigorous, these more recent events 

have been preceded and accompanied by larger amounts of 

seismic shaking, and reservoir pressurization (as measured 

by ground deformation instruments) during the events has 

increased. The character of subsidence at the summit has also 

changed; deformation has become more localized around 

Halemaʻumaʻu crater and occurs at a higher rate. At the 

current time, subsidence of the caldera continues at a high rate 

owing to magma withdrawal from the Halemaʻumaʻu magma 

reservoir.

Possible Outcomes

Ground subsidence will continue for as long as magma 

is withdrawn from the summit reservoir(s) at a rate that 

exceeds the rate of magma supply, but the rate, style, and 

geographical extent of the subsidence—along with associated 

hazards—may vary. The scenarios below are considered under 

the condition of continued net magma withdrawal. For a 

discussion on how long this might occur for, see the section on 

time frames.

Most Likely Outcome for the Immediate Future 

(up to Two Months)

The most likely activity for the immediate future is 

continued subsidence of Kīlauea Caldera, episodic slumping 

into a widening Halemaʻumaʻu crater, felt earthquakes (some 

large enough to be damaging), and small to intermediate 

ash plumes that remain below 10,000 ft above sea level. As 

the reservoir deflates, cracking and slumping is gradually 

engulfing a broader extent of Kīlauea Caldera (as observed 

Figure 2.  Plot of the number of earthquakes recorded per hour at the summit of Kīlauea from June 10 to June 26, 2018. A clear pattern of

high and low seismicity rates is evident. Most of these earthquakes are far too small to be felt by nearby residents.

4

For the purposes of this document, Kīlauea Caldera refers to the obvious pre-existing topographic depression at the volcano’s summit, which has about half the diameter of 

the complete caldera. The larger Kīlauea caldera formed about 500 years ago. To date, all evidence suggests that the current activity is confined to the topographic depression 

and is not activating the larger structure.
Figure 3.  Comparison of the topography of Halema‘uma‘u Crater in 2009 (left) and on June 21, 2018 (right). The 2018 data are from a

photogrammetric survey of Kīlauea’s summit by the U.S. Department of Interior Unoccupied Aircraft Systems’ (UAS) Kīlauea response team. Since

April, extensive cracking and faulting has occurred around the crater, which has enlarged through collapses of wallrock. The depth of the crater floor

has increased by more than 350 meters (1,100 feet) since early May. Limited UAS flights into the summit area are conducted with permission and in

coordination with Hawai‘i Volcanoes National Park to collect quantitative and qualitative data needed for updated hazard assessments, all of which

are shared with emergency managers. Image courtesy of the U.S. Geological Survey and Office of Aviation Services, Department of the Interior, with

support from the Hawaiian Volcano Observatory and Hawai‘i Volcanoes National Park.

Lava lake

Rubble and 

collapse debris

June 27, 2009

Kīlauea Caldera

Halema`uma`u

Crater

June 21, 2018

Faults and

new scarps

Down-dropped crater floor

in high rates of ground deformation and propagating cracks 

around Halemaʻumaʻu); this process will likely continue to 

enlarge Halemaʻumaʻu and may involve larger slump blocks 

than previously. This activity is impressive in scale—and may 

ultimately involve much or even all of the current Kīlauea 

Caldera—but it need not necessarily involve new or more 

hazardous explosive activity.

Hazardous explosive activity cannot be ruled out, 

however. It is possible that a large section of the Halemaʻumaʻu 

wall could abruptly collapse into the crater. Because a broad 

region east and northeast of Halemaʻumaʻu is currently 

deforming, it is difficult to predict how large such a collapse 

might be or its impact on explosion hazards. Most likely, such 

an event would generate strong seismic shaking and a robust 

ash plume.

Should activity continue as described, primary hazards of 

concern are:

• Damaging earthquakes—potentially exceeding 

magnitude 5 (hazards discussed more fully in the section 

on potential hazards),

• Ash plumes and ashfall (associated with collapse/

explosion events and large rockfalls),

• Large and sudden collapses into the expanding 

Halemaʻumaʻu crater,

• Ground cracking and continued rockfall activity along 

steep caldera walls, and

• Vog (although sulfur dioxide output is approaching low 

pre-2008 levels).

Less Likely Outcomes for the Immediate Future 

(up to Two Months)

Several mechanisms could change the nature of activity and 

associated hazards. These are considered less likely but cannot be 

ruled out. The likelihood of some of these processes may increase 

if the net rate of magma outflux from the summit increases.

Below we consider the possibility of (1) more hazardous 

explosions during ongoing subsidence and enlargement of 

Halemaʻumaʻu, and (2) sudden collapse of the larger caldera system. 

This list may not include all possible future outcomes and hazards.

1. Larger explosions during ongoing subsidence.—Activity in 

and around Halemaʻumaʻu could become more hazardous 

over short time scales. This could be triggered in one of 

several ways, including (a) rapid pressure change or other 

perturbation of the reservoir, (b) opening of new pathways 

between the reservoir and the surface, or (c) interaction of 

magma with groundwater. Rapid pressure change could be 

caused by a large, sudden landslide from the crater’s steep, 

faulted rim. Alternatively, sudden larger scale collapse of 

rock into the reservoir could perturb reservoir pressure 

above levels seen during previous collapse/explosion events. 

New pathways could be formed by explosive ejection of 

rubble in the vent or downward propagation of cracks. 

Groundwater could enter the magmatic system at sufficient 

rates to produce steam-driven explosive eruptions. Some 

of these mechanisms could be preceded by detectable 

changes in monitoring data, but others could happen with 

no warning. If larger explosions do occur, their style and 

magnitude cannot be predicted; it is possible that they 

could produce more ballistics and ash, and possibly also 

pyroclastic surges (defined below).

Chapter C. Volcanic Hazard at the Summit of Kīlauea; June 29, 2018, Update19
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Preliminary Analyses of Volcanic Hazards at Kīlauea Volcano, Hawai‘i, 2017–2018

2. Sudden collapse of the broader caldera system and 

catastrophic failure of high caldera walls.—Even less 

likely but more hazardous scenarios exist. Large explosive 

eruptions have occurred in Kīlauea’s past after caldera 

formation or during the last stage of its formation. It is 

possible that these eruptions were triggered by rapid 

collapse of broad regions of the caldera along calderabounding faults owing to withdrawal of large quantities 

of magma from the summit storage system. Based on 

our understanding of the magmatic system, this activity 

should be preceded by significant changes in earthquake 

activity and ground deformation. At this time, satellite 

radar data show that high rates of deformation are 

concentrated in a well-defined area bordered by calderaboundary faults on the west and south and on the east and 

northeast along a line about 600–900 m (similar distance 

in yards) from the caldera walls. These data do not 

suggest that extensive deformation is occurring outside 

of the caldera. Additionally, we currently see no evidence 

that major caldera-bounding faults are moving, although 

some cracks have been detected that probably formed 

from ground shaking. Additional hazards associated with 

rapid, broad-scale caldera collapse could include high lava 

fountains and larger and more dangerous explosions that 

produce pyroclastic surges (defined below). However, we 

emphasize that current data do not suggest that a larger, 

sudden collapse scenario is likely at present.

Historical Analogs

For additional insight into possible outcomes, we can 

examine past scenarios at other basaltic volcanoes. Though every 

eruption is unique, these events can help inform our thinking 

about the current activity at Kīlauea. Collapses of summit 

calderas—caused by lateral subsurface removal of magma from 

the underlying storage reservoir rather than the explosive removal 

of magma into the atmosphere—have been observed in human 

history only a handful of times. Examples include eruptions at 

Fernandina (Galapagos Islands, 1968), Plosky Tolbachik (Russia, 

1975–1976), Miyakejima (Japan, 2000), Piton de la Fournaise 

(Réunion Island, 2006–2007), and Bárdarbunga (Iceland, 

2014–2015).

Each of these historical collapses were preceded by flank 

eruptions and (or) intrusions similar to what is occurring in the 

lower ERZ at Kīlauea. Moderate to large summit explosions at 

Miyakejima and Fernandina produced widespread ashfall and 

ballistics as far as 2 kilometers (km; 1.2 miles [mi]) from the vent, 

as well as cool, slow-moving pyroclastic surges at Miyakejima 

(this unusual type of flow was not hazardous) and potentially 

deadly high-velocity surges at Fernandina.

As at Kīlauea, various combinations of summit explosions, 

deformation, and earthquake activity often occurred in repeated 

cycles during these episodes at other volcanoes; these observations 

have been interpreted as indicative of piecemeal caldera 

subsidence over a period of days to months. Collapse volumes 

ranged widely from 0.1 to 2 cubic kilometers (0.02–0.5 cubic 

miles), compared to a collapse volume of approximately 0.3 cubic 

kilometers (as of June 21) at Kīlauea. These caldera collapses were 

all largely controlled by pre-existing caldera-bounding faults and 

did not significantly enlarge pre-existing caldera structures.

Potential Hazards

For both scenarios, primary hazards are caused by 

earthquakes and explosions. These hazards are closely related 

but here we address them separately.

Earthquakes and Ground Cracking

During recent weeks, earthquakes at Kīlauea’s summit have 

occurred in swarms associated with collapse/explosion events.

• Earthquake swarms.—As many as 40 earthquakes 

per hour have been recorded during earthquake 

swarms preceding collapse/explosion events (fig. 2). 

Most of these are small and cannot be felt by people, 

but magnitude 3 and larger earthquakes do occur 

at increasing rates through the course of individual 

swarms (fig. 4). Overall, more than 500 earthquakes 

per day have been recorded in the Kīlauea summit 

region during recent weeks. Felt earthquake event rates 

have exceeded 30 earthquakes per day at and around 

the summit.

• Collapse/explosion events.—Energy released during 

collapse/explosion events is equivalent to earthquake 

magnitudes of low- to mid-magnitude 5. These types 

of events emit most of their energy at low frequencies 

and so are not felt as strongly as typical non-volcanic 

magnitude-5 earthquakes. Regardless, shaking can be 

strong and possibly damaging near the summit.

• Other tectonic earthquakes.—Strong earthquakes can 

occur at any time, and the risk of these events is larger 

now owing to ongoing stress changes in and around the 

caldera. These earthquakes will not necessarily occur 

during swarm seismicity or in association with collapse/

explosion events, may be large, and may happen outside 

of the caldera.

The exact location and timing of earthquakes cannot be 

predicted, but if recent patterns continue, earthquake activity 

will increase gradually over the course of an individual swarm 

and culminate in a collapse/explosion event. After these 

events, earthquake activity will drop rapidly before gradually 

increasing again. However, earthquakes can occur at any time.

Historically, high rates of earthquake activity were observed 

during the 1924 summit subsidence and explosions. However, 

based on known historical records, no earthquakes related to 

summit subsidence caused significant damage in 1924. In 1960, 
Figure 4.  Map of the location of earthquakes that are magnitude 3 and greater at the Kīlauea summit region from June 1 to June 15, 2018.

earthquakes occurring in the summit area during subsidence 

caused some minor damage in Volcano, Hawaiʻi.

Residents should continue to be prepared for strong seismic 

shaking and, in the vicinity of the caldera, ground cracks (see 

https://www.shakeout.org/hawaii/ for more information). During 

earthquakes, it is wise to drop, cover, and hold on. With more than 

six weeks of heightened seismic activity, structures are, in some 

cases, already weakened from strong shaking. Ongoing earthquake 

activity can damage these further, especially close to the summit 

in Hawaiʻi Volcanoes National Park and the Volcano Golf Course 

areas. Ground cracks, rockfalls, and damage to roads, trails, rock 

walls, buildings, utilities, and water pipes may also occur.

Gas Emissions

Emissions of sulfur dioxide (SO2) from Kīlauea’s summit 

are currently relatively low. This may possibly be due to 

collapses into the vent in late May, which have likely inhibited 

gas escape and discouraged the exsolution of gases from 

shallow magma; currently, most of Kīlauea’s SO2 is emitted at 

the lower ERZ eruption site. Gas emissions remain a hazard 

at the summit, however. If larger explosions occur that tap 

magmatic gases, surges in SO2 emissions may occur. SO2

emissions may also increase as subsidence progresses and may 

remain elevated after the end of the eruption. These emissions 

can produce volcanic air pollution (or vog), which is carried to 

downwind communities.

Explosions and High Lava Fountains

Explosions at Kīlauea’s summit during 2018 have 

produced only minor ashfall and limited ballistic deposits. 

As previously described, based on our current understanding, 

explosive activity that is larger and more dangerous than what 

has already occurred in 2018 is not considered likely at this 

time. However, it is impossible to rule out such activity, so 

here we detail some of the associated hazards as currently 

understood. These hazards can currently be grouped into four 

types that occur in distinct geographical zones: (1) ballistic 

projectiles, (2) ashfall, (3) fallout from high lava fountains, 

Chapter C. Volcanic Hazard at the Summit of Kīlauea; June 29, 2018, Update21
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Preliminary Analyses of Volcanic Hazards at Kīlauea Volcano, Hawai‘i, 2017–2018

and (4) pyroclastic surges. Hazards associated with ballistic 

projectiles and ashfall were detailed in a previous document5 

so are reviewed only briefly here. Pyroclastic surge and high 

lava fountain hazards were not previously described because 

of their very low probability of occurrence.

1. Ballistic projectiles.—Near the vent, large projectile-like 

rocks travel on cannonball-like paths outwards in all 

directions. This is a zone of extreme hazard. Ballistics 

were produced during earlier collapse/explosion events 

but are not currently being ejected from the vent.

2. Ashfall.—Small ash particles are carried primarily 

downwind from the vent, where they can affect 

transportation, infrastructure, and utilities. Ashfall is 

unlikely to directly threaten human life. Very little ash is 

currently produced during collapse/explosion events, but 

emissions are possible at any time. Graphical forecasts 

of where ash would fall during a significant emission 

can be found at https://volcanoes.usgs.gov/observatories/

hvo/ash_information.html.

3. Fallout from high lava fountains.—The fallout from 

large lava fountains several hundred meters high can 

impact neighboring communities. The fall of reticulite 

from several contemporaneous fountains about 500 years 

ago fell throughout the golf course and Volcano village 

areas, burning vegetation and accumulating a thickness 

of 10centimeters (4 inches) or more. Numerous fires 

could result today from such an event, particularly 

during a dry period. The fountains about 500 years ago 

erupted from steeply inclined circumferential fissures 

within Kīlauea Caldera. Wholesale downdropping of the 

present caldera floor could produce a situation similar to 

that 500 years ago.

4. Pyroclastic surges.—Pyroclastic surges and density 

currents are highly destructive, generally fast-moving 

clouds of volcanic gases and fragments of magma and 

older rocks. They are generally hot and form when 

eruption columns become unstable and collapse back 

around the vent. Surges typically travel tens of meters per 

second, but certain types can move as rapidly as 100–

300 meters per second (200–700 miles per hour). Surges 

usually extend radially from the vent in all directions, 

but can be influenced by topography, thickening in 

valleys and thinning over topographic highs. Owing to 

their high heat and speed, pyroclastic surges are among 

the most dangerous and destructive of volcanic hazards. 

There are very few survivors among those caught in 

the path of a hot surge, and property damage is severe. 

In the past, surges have been produced at Kīlauea by 

sustained eruption columns. For example, pyroclastic 

surges were produced at Kīlauea between the mid-1500s 

and 1790A.D. Surges in and just before 1790 extended 

3–5km (1.8–3 mi) west and south of the caldera and 

form the basis for a surge hazard map shown in figure 5. 

The direction that surges may travel is difficult to predict, 

and the entire summit area of Kīlauea out to about 5 km 

(3mi) from the center of the caldera is susceptible to 

surges if they were to occur (fig. 5). At present, Kīlauea 

is not producing any sustained eruption columns even 

during the largest collapse/explosion events. 

Time Frames of Activity—How Long 

Might This Last?

Deflation of Kīlauea’s summit storage system is occurring 

in response to the removal of magma at a higher rate than the 

reservoir is being resupplied from its deep mantle source. If 

summit magma is predominantly feeding eruptive activity in 

the lower East Rift Zone (LERZ) rather than filling storage 

space (independent of the LERZ eruption), then summit activity 

should cease soon after the LERZ eruption ends. The duration 

of the ongoing LERZ eruption cannot be predicted and, at this 

time, output appears steady. Historical eruptions in Kīlauea’s 

LERZ in 1955 and 1960 lasted 88 and 38 days, respectively.

It is also possible that magma will continue to fill 

storage space in the rift zone, so that summit subsidence will 

continue even after the LERZ eruption ends. Alternatively, 

summit subsidence may greatly slow or even stop if the LERZ 

eruption decreases in vigor, or a new pressure equilibrium is 

obtained between the summit and LERZ. For these reasons, it 

is not possible to forecast the duration of summit subsidence. 

It is most likely that it will continue for weeks to months, and 

it is possible, although less likely, that it will continue longer.

How Will We Know When the Hazard Has 

Passed?

Hazards may remain present at the summit for months 

or longer even after subsidence and related strong seismicity 

stops. Earthquakes will likely occur at elevated but decaying 

rates, ground cracks may worsen, and rockfalls continue. 

Also, based on historical patterns, the summit will eventually 

re-inflate; this process will be associated with its own set of 

hazards, not specifically addressed here.

Conclusions

At present, the most likely course of activity for the 

immediate future at the summit of Kīlauea Volcano is 

5

Chapter B of this report by K. Anderson and others.
Figure 5.  Map of the approximate boundary of the pyroclastic surge zone at the summit of Kīlauea (white dashed line). For simplicity, we assume

a source near the center of the caldera. The boundary shows only the maximum reasonable distance a surge would travel from the caldera as

inferred from past eruptions; it does not indicate that such behavior is likely at this time (it is not), nor that surges would fill the entire area within the

circle (surge deposits would likely travel within narrow regions). Base map image from Google Earth © 2018.

Golf Course Volcano

Village

Chapter C. Volcanic Hazard at the Summit of Kīlauea; June 29, 2018, Update23
24

Preliminary Analyses of Volcanic Hazards at Kīlauea Volcano, Hawai‘i, 2017–2018

continued subsidence of the caldera floor, episodic slumping 

into Halemaʻumaʻu, felt moderate-sized earthquakes, and 

small ash plumes. The duration of this activity may be related 

to the duration of the lower East Rift Zone eruption but cannot 

be confidently predicted. More hazardous explosive eruptions 

related to the ongoing subsidence are unlikely but possible. 

It is important not to underestimate the ability of volcanoes 

to evolve rapidly in unanticipated ways. More hazardous 

behavior is therefore possible at any time, and large-scale 

hazardous caldera collapse is a possible future outcome, 

although it is considered to be very unlikely and should 

be preceded by detectable warning signals. The Hawaiian 

Volcano Observatory should recognize these warning signs by 

direct observation and instrumental monitoring and, should 

they be detected, will alert authorities and the public.

Message from Hawaiʻi County Civil 

Defense Agency

Hawaii County Civil Defense Agency (HCCDA) has 

committed to the preparation, response and recovery of the 

unfolding events with Kilauea. HCCDA is supported by law and 

proclamation by all the departments within the County, State 

of Hawaii and Federal Government to help the people cope 

with impacts caused by the volcano. USGS-Hawaiian Volcano 

Observatory (HVO) is the lead scientific agency in this disaster 

and provides the bulk of information used to identify hazards. The 

HVO is monitoring the situation 24 hours a day and maintains 

constant contact with your HCCDA to provide timely accurate 

information for your safety.
Introduction

In late April 2018, the long-lived Puʻu ʻŌʻō vent collapsed, 

setting off a chain of events that would result in a vigorous 

eruption in the lower East Rift Zone (LERZ) of Kīlauea Volcano, 

as well as the draining of the summit lava lake and magmatic 

system and the subsequent collapse of much of the Kīlauea caldera 

floor. Both events originated in Lava Flow Hazard Zone 1 (Wright 

and others, 1992), which encompasses the part of the volcano that 

is most frequently affected by volcanic activity.

We examine here the possible and potential impacts of the 

ongoing eruptive activity in the LERZ of Kīlauea Volcano, and 

specifically activity at fissure 8 (fig. 1). Fissure 8 has been the 

dominant lava producer during the 2018 LERZ eruption, which 

began on May 3, 2018, in Leilani Estates, following intrusion 

of magma from the middle and upper East Rift Zone, as well 

as the volcano’s summit, into the LERZ. The onset of downrift 

intrusion was accompanied by collapse of the Puʻu ʻŌʻō vent, 

which started on April 30 and lasted several days. Kīlauea 

Volcano’s shallow summit magma reservoir began deflating on 

about May 2, illustrating the magmatic connection between the 

LERZ and the summit. Early LERZ fissures erupted cooler lava 

that had likely been stored within the East Rift Zone, but was 

pushed out in front of hotter magma arriving from farther uprift. 

This hotter magma, similar in composition to lava that had been 

erupting at Puʻu ʻŌʻō, arrived in mid-May, coincident with an 

increase in discharge from the fissures.

The volume of lava erupted during the current activity 

exceeds that of many past eruptions. Given this volume and 

the sustained withdrawal of magma from the summit reservoir 

without appreciable deformation in the LERZ, it is most likely 

that the LERZ eruption may continue for months to years. 

Whereas additional fissures may form either uprift or downrift 

of the current activity at fissure 8, the continued focus of activity 

within the current fissure system after 10 weeks of activity (as 

of July 15, 2018) makes this scenario increasingly unlikely. 

This document reviews current activity, focusing on the fissure 

8 vent, channel, and ocean entry. It describes a credible set of 

future scenarios for fissure 8 and discusses uncertainties. This 

document is meant as a guide for managing hazards and risks in 

Kīlauea’s East Rift Zone.

Summary of Activity for April 30–July 15, 

2018

In early 2018, the lava lake in a small pit crater within 

Halemaʻumaʻu crater rose to high levels, overflowing a few 

times. On April 30, the Puʻu ʻŌʻō vent in the middle East Rift 

Zone began to collapse, and seismicity and deformation migrated 

downrift, signifying an intrusion of magma into the LERZ beneath 

the Leilani Estates subdivision. Cracks began to form within the 

subdivision during the next few days.

An eruption started on May 3 with brief spattering from a 

fissure in the southeastern portion of the subdivision. Additional 

short-lived fissures opened along a 6.7-kilometer (4.2-mile) 

stretch of the LERZ and erupted sporadically, both uprift and 

downrift, over the following week, and produced only small, 

viscous flows.

There was a marked increase in the vigor of the eruption 

starting on May 18, coincident with the production of more 

fluid lava. Activity became longer lived, and large, fast-moving 

channelized flows were produced that first reached the ocean 

along Kīlauea’s southeast coast on May 20, but remained active 

for only a few days. Activity eventually coalesced at fissure 8 and 

the other fissures became inactive or sporadically weakly active 

through June.

Fissure 8 was first active May 5 but reactivated during the 

third week of May with episodic spattering and began to erupt 

with a vigorous fountain late in the day on May 27, producing a 

relatively fast-moving channelized flow that travelled northeast. 

The fountain abruptly stopped the following morning (May28), 

and the flow it fed stalled after crossing Pohoiki Road. The 

fissure 8 fountain restarted later the same day, however, and 

began feeding a new fast-moving, channelized flow northeast 

and depositing tephra downwind. This new flow crossed Pohoiki 

Road early the next morning (May 29) and Highway 132 in the 

afternoon, isolating Puna Geothermal Venture.

The fissure 8 channelized flow continued to advance rapidly 

downslope over the following days, reaching the ocean at Kapoho 

Bay late in the day on June 3. The flow filled the bay and spread 

along the coast quickly, destroying hundreds of homes and the tide 

pools south of Kapoho Bay.

Chapter D. Preliminary Analysis of the Ongoing Lower East Rift 

Zone Eruption of Kīlauea Volcano—Fissure 8 Prognosis and 

Ongoing Hazards

By the Hawaiian Volcano Observatory
26

Preliminary Analyses of Volcanic Hazards at Kīlauea Volcano, Hawai‘i, 2017–2018

Fountaining and spattering from fissure 8 began 

constructing a spatter cone (fig. 2), which by the end of 

June was about 55 meters (m; or 180 feet, ft) high and open 

to the northeast. Discharge from the vent continues to feed 

directly into the relatively stable channel, which carries lava 

13kilometers (km) to the ocean. Although difficult to measure, 

the most plausible estimates of the eruption rate from fissure 8 

range from 50 to 150 cubic meters per second.

After several blockages and subsequent clearing or channel 

rerouting around the blockage to keep the channel flowing to 

the north and east of Kapoho Crater, the channel overflowed just 

northwest of Kapoho Crater and a new lobe advanced southward 

along the west margin of the previous flow and entered the ocean 

on July 12. This diversion of the channel flow was the first major 

change in the fissure 8 channel. Even though the channel no longer 

directly fed the massive lava delta to the southeast of Kapoho 

Crater, lava continues to ooze out of the flow front into the ocean 

in many locations.

Figure 1.  Example map of the 2018 eruption of Kīlauea’s lower East Rift Zone updated on July 12, 2018. Lava flows from the current eruption are shown

in pink (flows from May 3–July 10) and red (July 11–12) and lava flows from the 1840, 1955, 1960, and 2014–2015 eruptions are in purple.

Ongoing Fissure 8 Hazards

The upper 4 km of the channel (fig. 3) stand 16–22 m above 

ground level and are as much as 400 m wide. The middle section 

of the channel is braided and fairly narrow, whereas the lower 

section merges again into a single channel feeding a gradually 

thickening and spreading ‘a‘ā flow at the coast. The main hazard 

from the source cone and the channel system is failure of the cone 

or channel walls or blockage of the channel where it divides into 

narrower braids. Either could divert most, if not all, of the lava to a 

new course depending on where the breach occurs.

Areas Potentially Threatened by Fissure 8 

Channel Blockages or Failures

Estimates of future potential flow paths are made here for 

three areas along the north edge of the fissure 8 channel system 
Figure 2.  Photograph of fissure 8 lava fountains within the cinder and spatter cone feeding a wide channelized flow. U.S. Geological Survey

photograph taken on June 22, 2018.

Figure 3.  Photograph of the upper part of the fissure 8 channel. The view is

to the northeast. Lava is flowing from lower right to upper center of the image.

U.S. Geological Survey photograph taken on June 22, 2018.

using drainage areas and the steepest descent lines calculated from 

a 10-m resolution digital elevation model. The drainage areas, here 

called lavasheds (fig. 4; Kauahikaua and others, 2003), define the 

areas in which fluids flow toward a steepest descent line (fig. 4; 

Kauahikaua and others, 2016).

Only flows to the north of the existing channel system will be 

considered because, as of the writing of this report, residents to the 

south have been evacuated whereas residents to the north have not.

Upper Channel

Any major flow caused by a breach of the west wall of the 

channel between the vent (location A in fig. 4) and the intersection 

of Pohoiki Road and Highway 132 (location B in fig. 4) is likely 

to advance northeast into lavashed 1, hugging the northeast 

edge of the existing flow. Beyond Highway 132, the flow may 

enter lavashed 2 and become captured by steepest descent lines 

that pass along the eastern boundary of the Nānāwale Estates 

subdivision (along Road A and possibly Seaview Road). If the 

flow continues to advance, it will ultimately cross Railroad Avenue 

and Government Beach Road, enter lavashed 3, and reach the 

ocean between 1.3 and 2.3 km southeast of Kahakai Boulevard 

(Hawaiian Beaches). If the flow enters lavashed 2 and stalls, 

subsequent lava flows advancing along the west side of the stalled 

Chapter D. The Ongoing Lower East Rift Zone Eruption of Kīlauea Volcano27
28

Preliminary Analyses of Volcanic Hazards at Kīlauea Volcano, Hawai‘i, 2017–2018

Figure 4.  Map of lavasheds—lava drainage areas—that drain through steepest descent lines (light blue lines). The numbered

lavasheds are described in the text. The gray area shows the erupted lava from all fissures of the 2018 eruption as of July 12, 2018,

and the red line within represents the fissure 8 channel system on that same date.

Railroad Ave.

Pohoiki Rd.

Hawaiian Beaches/Shores

Gov’t Beach

Leilani 

Estates

Nanawale

Estates

A

B

C

1

2

4 5

6

7

8

3

flow could enter lavashed 4 in Nānāwale Estates subdivision and 

ultimately reach the coast slightly closer to the Hawaiian Beaches 

and Hawaiian Shores subdivisions.

Middle Channel

The fissure 8 channel becomes braided northeast of 

locationB (in fig. 4), with narrower sections that could form choke 

points. If one of the narrower sections becomes blocked by large 

collapse fragments from the channel wall or spatter cone, lava 

could be diverted out of the channel. If, in this scenario, part of the 

channel is redirected to the north, lava could feed into lavasheds 

5 or 6 and threaten homes and infrastructure in the Noni Farms 

area, as well as cross Railroad Avenue, Papaya Farms Road, and 

Government Beach Road before entering the ocean between 

Kalamanu and the northern edge of the 1960 lava flow.

Lower Channel

The ʻaʻā channel has been unstable in the area of Kapoho 

Crater (location C in fig. 4) and beyond to the ocean. Most 

recently, on July 9–10, a channel overflow in the area northwest 

of Kapoho Crater created a new lobe that advanced south along 

the west margin of the existing flow and entered the ocean on 

July 12, destroying a school and a beach park; however, the 

previous flow to the northeast continued to ooze lava into the 

ocean along its entire front. Although not fed by any surface 

flow, the earlier flow north and east of Kapoho Crater to the 

ocean is still oozing lava into the ocean from its front and could 

potentially thicken and widen beyond the current flow margins—

as it has in the past several weeks. Flows advancing from a 

breach in the northeast side of the channel near Kapoho Crater 

may enter lavasheds 7 or 8 and again threaten the handful of 

remaining structures in the Kapoho Agricultural and Beach Lots, 

structures built on the eastern section of the 1960 lava flow, and 

the Cape Kumukahi Lighthouse.

Gas and Tephra Hazards

Vog

Volcanic gas emissions (or vog) from the fissure 8 vent 

(fig.5) have continued to be unusually high since mid-May 

(over 30,000 metric tons per day—more than 4 times the 

average daily amount from Kīlauea’s summit lava lake prior to 
Figure 5.  Example map of the SO2 forecast for the Island of Hawai‘i on June 24, 2018, posted at http://weather.

hawaii.edu/vmap/hysplit/. The warm colors show elevated SO2 levels (in parts per million, ppm) and the blue lines show

topographic relief.

May 3, 2018), coincident with the increase in eruptive vigor. 

This has caused a significant increase of vog in downwind 

areas, including the Kailua Kona coast. When trade winds 

slacken, easterly and southeasterly winds can blow gases into 

areas on the east side of the Island of Hawaiʻi. Fissure 8 is 

now the dominant producer of volcanic gas on the Island of 

Hawaiʻi and will remain so as long as current rates of eruption 

continue.

Increased Distribution of Tephra Fall

At the moment, lava from fissure 8 erupts from a 60- to 

80-m-long fissure segment. Discharge from the fissure was initially 

characterized by relatively steady low fountaining but has evolved 

into more chaotic Strombolian activity (large bubble bursts). If the 

eruption begins to coalesce into a single point along the fissure, 

higher fountains (100–300 m) could be produced, which would 

result in more widespread deposition of Pele’s hair and cinder. 

Pele’s hair has already been reported several times in Pāhoa (about 

5 km [3 miles, mi] northwest of fissure 8 lava fountains) during 

slack or southerly winds. Both the 1955 and 1960 eruptions in the 

same general area produced lava fountains much higher than what 

has yet occurred during the current eruption.

Tephra fall from 100- to 300-m-tall fountains could 

produce a 30-centimeter (1-ft) deposit several hundred meters 

(similar distance in yards) downwind. This deposit may be 

thinner if the wind is variable and spreads the tephra laterally. 

Previous eruptions produced a 30-centimeter (1-ft) thick 

deposit as far as 625 m (2,000 ft) downwind from the vent at 

Kīlauea Iki Crater, 1.6 km (1 mi) downwind from the vent at 

Mauna Ulu, and 900 m (3,000 ft) from the vent at Puʻu ʻŌʻō.

Ocean Entry Hazards

See chapter A of this report on the Kamokuna ocean entry 

for more detailed information. 

Delta Collapse

The entry of lava into the ocean at Kapoho Bay (fig. 6) has 

built a 6-km-wide lava delta that now extends as far as 800 m 

(0.5 mi) from the pre-eruption coastline of Kapoho Bay. As with 

any lava delta, there is the potential for collapse without warning, 

which could lead to explosions caused by the interaction of 

seawater with hot rock exposed by the collapse.

Chapter D. The Ongoing Lower East Rift Zone Eruption of Kīlauea Volcano29
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Preliminary Analyses of Volcanic Hazards at Kīlauea Volcano, Hawai‘i, 2017–2018

Hydrovolcanic Explosions

Boat tours, as well as observers in the air, have reported 

hydrovolcanic explosions occurring without warning as far 

as 100 m offshore. These events, which last 10–15 seconds, 

have been observed rarely, but may occur several times per 

day. They burst through the water, sending fragments of lava 

and hot water 25 to 100s of meters high. It is likely they are 

caused by the underwater emplacement of ‘a‘ā lava, where 

large amounts of molten lava suddenly come in contact with 

seawater during collapse of a lava conduit.

Both delta collapse and hydrovolcanic explosions are 

primarily hazardous only to boats and other watercraft because 

this area is currently closed to foot traffic. Based on an extensive 

study of these coastal hazards during the 35-year eruption of 

the Puʻu ʻŌʻō vent, a zone with a radius of 300 m is considered 

Figure 6.  Photograph of the lava delta at

Kapoho Bay (looking south) built by lavas

traveling 8 miles from fissure 8, which can be

seen erupting in the distance (orange spot in

upper right). U.S. Geological Survey photograph

taken on June 18, 2018.

Figure 7.  Photograph of the laze (lava haze)

plume from the fissure 8 ocean entry (leftmost

incandescence) lit by the source fountain

(rightmost incandescence) and lava channel. White

lights to the far right are from Pāhoa. Photograph

taken on the evening of June 20, 2018, by Klaus

Hodapp (University of Hawai‘i at Mānoa).

a minimum high-hazard area around pāhoehoe lava deltas 

(Mattox and Mangan, 1997; chapter A of this report). The 2018 

Kapoho Bay lava delta is composed of ʻaʻā lava and more study 

will be required to determine whether this high-hazard margin 

should be modified.

Laze Plume

The large lava haze (or laze) plume (fig. 7) produced at 

the ocean entry poses a health risk to those exposed to it. It will 

continue as long as lava enters the ocean. The composition of the 

plume is the result of the interaction between molten basaltic lava 

and sea water and includes hydrochloric acid, hydrofluoric acid, 

and halide precipitate. It is not known how far downwind harmful 

constituents drift in a laze plume of this size. At times, onshore 

winds carry the laze plume an unknown distance inland.
How Long Will This Eruption Last?

The current eruption started with 23 days of sporadic 

eruption from 24 different fissures that covered a distance of 

6.7 km (4.2 mi), some composed of multiple segments, before 

focusing at fissure 8, which has been erupting continuously 

since May 27. More than 430×106 cubic meters (m3) of lava has 

erupted so far (as of July 15). Most of this volume has come 

from fissure 8, which is discharging lava at an estimated rate 

of about 100 cubic meters per second (m3/s). This exceeds the 

duration (38 days), erupted volume (122×106 m3 of lava), and 

peak time-averaged eruption rate (38 m3/s for the first 2 weeks) 

of the 1960 eruption. Whereas the current eruption has not yet 

lasted as long as the 1955 eruption (88 days, including pauses), 

it has erupted far more lava at a higher rate; the 1955 eruption 

produced 81×106 m3 of lava at a peak time-averaged discharge 

rate of 31 m3/s (for the first phase of the 1955 eruption). In 

this regard, the current eruption may be more similar to the 

1840 eruption, which, though only lasting for 26 days, erupted 

210×106 m3 of lava at a time-averaged discharge rate (for the 

entire eruption) of 94 m3/s. See appendix for brief overviews 

of the 1840, 1955, and 1960 eruptions, as well as the 1924 

intrusion event.

A glance around the LERZ reveals numerous large 

pyroclastic cones, indicating repeated volcanic activity in this area. 

Pu‘u Kaliʻu, which borders the southern edge of Leilani Estates, 

and a younger vent complex that overlies it, are both very close to 

the location of the current fissures. Both of these older eruptions 

are thought to have produced about 200×106 m3 of lava (Moore, 

1992). Other eruptions in the area, including flows erupted in the 

late 1700s, may have produced similar volumes. Perhaps eruptions 

in the LERZ only continue until pressure in the magmatic system, 

partly controlled by vent elevation, becomes too low to sustain the 

eruption. The volume of the current eruption has exceeded that of 

these older nearby eruptions. The steady discharge from fissure 

8 shows no sign of waning supply, suggesting relatively constant 

magma pressure; the lack of significant ground deformation in this 

area shows that there is neither storage nor withdrawal from the 

May intrusion since its initial emplacement.

If the ongoing eruption maintains its current style of activity 

at a high eruption rate, then it may take months to a year or two 

to wind down. Whereas this seems to be the most likely outcome, 

a pause in the eruption, followed by additional activity, cannot 

be ruled out, nor can an abrupt cessation or a transition to steady, 

longer lived activity at a lower effusion rate.

The shield complex of Heiheiahulu, located 9.5 km (6 mi) 

upslope of fissure 8, represents a more voluminous eruption that 

could have lasted several years (Moore, 1992), similar to the 

35-year-long eruption of Puʻu ʻŌʻō. Both of these eruptions started 

with several short ʻaʻā flows erupted along a 3.5 km (2.2 mi) and 

7 km (4.3 mi) long fissure system, respectively, before centralizing 

to a single vent (Moore, 1992; Wolfe and others, 1988) and 

eventually erupting tube-fed pāhoehoe flows. The 2018 LERZ 

eruption has erupted only ʻaʻā flows so far but the eruption rate 

is high, and a stable channel system is being elevated by frequent 

spillovers of pāhoehoe flows above Kapoho Crater. The flow 

maintains its ʻaʻā character below that point to the ocean, where a 

pastier lava oozes from its interior along its edges. A change in the 

character of the channel toward pāhoehoe, if it occurs, could signal 

a gradual change of eruption style and a potentially longer eruption 

with more destruction of infrastructure.

Acknowledgments

Many people contributed ideas and comments to early 

drafts of this manuscript. Christina Neal, Margaret Mangan, 

Matt Patrick, Carolyn Parcheta, and Steve Brantley of the U.S. 

Geological Survey Hawaiian Volcano Observatory provided 

helpful comments on an earlier version of the manuscript and 

we thank them profusely.

References Cited

Coan, T., 1841, Letter from Mr. Coan, dated at Hilo, 25th 

Sept. 1840: The Missionary Herald, v. XXXVII, no. 7, 

p. 281–285.

Kauahikaua, J., Orr, T., Patrick, M., and Trusdell, F., 2016, 

Steepest-descent lines for Kīlauea, Mauna Loa, Hualālai, 

and Mauna Kea volcanoes, Hawaiʻi: U.S. Geological 

Survey data release, https://doi.org/10.5066/F7FJ2DX0.

Kauahikaua, J., Sherrod, D.R., Cashman, K.V., Heliker, C., 

Hon, K., Mattox, T.N., and Johnson, J.A., 2003, Hawaiian 

lava-flow dynamics during the Pu‘u ‘Ō‘ō-Kūpaianaha 

eruption—A tale of two decades, in Heliker, C., Swanson, 

D.A., and Takahashi, T.J., eds., The Pu‘u ‘Ō‘ō-Kūpaianaha 

eruption of Kīlauea Volcano, Hawai‘i—The first 20 years: 

U.S. Geological Survey Professional Paper 1676, p. 63–87. 

[Available at https://pubs.usgs.gov/pp/pp1676/.]

Macdonald, G.A., and Eaton, J.P., 1964, Hawaiian volcanoes 

during 1955: U.S. Geological Survey Bulletin 1171, 170 p., 

5 plates. [Available at https://pubs.er.usgs.gov/publication/

b1171.]

Mattox, T.N., and Mangan, M.T., 1997, Littoral hydrovolcanic 

explosions—A case study of lava-seawater interaction at 

Kilauea Volcano: Journal of Volcanology and Geothermal 

Research, v. 75, p. 1–17.

Moore, R.B., 1992, Volcanic geology and eruption frequency, 

lower east rift zone of Kilauea volcano, Hawaii: Bulletin of 

Volcanology, v. 54, no. 6, p. 475–483.

Richter, D.H., Eaton, J.P., Murata, K.J., Ault, W.U., and 

Krivoy, H.L., 1970, Chronological narrative of the 1959–60 

eruption of Kilauea Volcano, Hawaii: U.S. Geological 

Survey Professional Paper 537–E, 73 p., https://doi.

org/10.3133/pp537E.

Chapter D. The Ongoing Lower East Rift Zone Eruption of Kīlauea Volcano31
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Preliminary Analyses of Volcanic Hazards at Kīlauea Volcano, Hawai‘i, 2017–2018

Wolfe, E.W., Neal, C.A., Banks, N.G., and Duggan, T.J., 1988, 

Geologic observations and chronology of eruptive events, in

Wolfe, E.W., ed., The Puu Oo Eruption of Kilauea Volcano, 

Hawaii—Episodes 1 through 20, January 3, 1983, through June 

8, 1984: U.S. Geological Survey Professional Paper 1463, p. 

1–97, https://doi.org/10.3133/pp1463.

Wright, T.L., Chun, J.Y.F., Exposo, J., Heliker, C., Hodge, J., 

Lockwood, J.P., and Vogt, S.M., 1992, Map showing lavaflow hazard zones, Island of Hawaii: U.S. Geological Survey 

Miscellaneous Field Studies Map MF–2193, scale 1:250,000.
The ongoing 2018 lower East Rift Zone (LERZ) eruption 

is occurring in a similar location to the 1840, 1955, and 1960 

LERZ eruptions, as well as the location of intrusive activity 

in 1924. Discharge or effusion rates during the peak phases of 

the 1955 and 1960 eruptions are very similar to that occurring 

now. The onset of the current activity, with fissures opening 

both uprift and downrift from the initial outbreak, shifting back 

and forth amongst these fissures, and starting and stopping 

erratically, was similar to the 1955 and the 1960 eruptions, 

although the 1960 fissure system was considerably shorter, so 

the effects of the eruption were more focused. The start of the 

current eruption prior to the continuous eruption of fissure 8 

that started on May 27, resembles the beginning of the 1955 

eruption, but ramped up more slowly and was more chaotic. 

The current eruption has not yet produced high (>50 meter) 

fountains similar to those of the 1955 and 1960 eruptions, and 

instead has evolved into a relatively steady eruption at fissure 8 

characterized by low fountaining and Strombolian activity that 

feeds a large-volume channelized flow.

1840 Eruption, May 30–June 24

Observations of the 1840 lower East Rift Zone eruption 

are described by Coan (1841) and are repeated here. The 

1840 eruption started in the upper East Rift Zone and quickly 

migrated to a fissure just west of present-day Pāhoa. T. Coan 

writes, “On Monday, June 1st, the stream began to flow off 

in a northeasterly direction and on the following Wednesday, 

June 3d, at evening, the burning river reached the sea having 

averaged about half a mile an hour in its progress...Sometimes 

it is supposed to have moved five miles an hour, and at other 

times...make no apparent progress...For three weeks this terrific 

river disgorged itself into the sea with little abatement.”

The fissure sources extended about 6.1 kilometers (km) 

(3.8 miles, mi) along a northeast-southwest trend parallel to, 

and 2.6 km (1.6 mi) northwest of, the 2018 fissure system. The 

volume of the 1840 flow was more recently estimated to be 

210×106 cubic meters (m3) at an average rate of 94 cubic meters 

per second (m3/s) over 26 days of the eruption. The distance 

from fissure vent to coast is about 11 km (7 mi) for an average 

initial advance rate of 150–230 meters per hour (170–250 yards 

per hour).

Also of interest were the changes at Kīlauea summit just 

before the 1840 eruption started. Coan describes it vividly,

For several years past the great crater of Kilauea 

has been rapidly filling up, by the rising of the 

superincumbent crust, and by the frequent gushing 

forth of the molten sea below. In this manner the great 

basin below the black ledge, which has been computed 

from three to five hundred feet deep, was long since 

filled up by the ejection and cooling of successive 

masses of the fiery fluid. These silent eruptions 

continued to occur at intervals, until the black ledge 

was repeatedly overflowed, each cooling, and forming 

a new layer from two feet thick and upwards, until 

the whole area of the crater was filled up, at least fifty 

feet above the original black ledge, and thus reducing 

the whole depth of the crater to less than nine hundred 

feet. This process of filling up continued till the latter 

part of May, 1840, when...the whole area of the crater 

became one entire sea of ignifluous matter, raging 

like old ocean when lashed into fury by a tempest. 

For several days the fires raged with fearful intensity, 

exhibiting a scene awfully terrific. For several days...

The infuriated waves sent up infernal sounds, and 

dashed with such maddening energy against the sides 

of the awful caldron, as to shake the solid earth above, 

and to detach huge masses of overhanging rocks, 

which, leaving their ancient beds, plunged into the 

fiery gulf below. So terrific was the scene that no one 

dared to approach near it, and travellers [sic] on the 

main road, which lay along the verge of the crater, 

feeling the ground tremble beneath their feet, fled and 

passed by at a distance...Every thing [sic] within the 

caldron is new. Not a particle of lava remains as it was 

when I last visited it. All has been melted down and 

re-cast. All is new.

Although the summit and rift zone activities bear some 

similarities to 2018 events, the chronological order is reversed. 

The summit’s apparent collapse preceded the LERZ eruption 

in 1840 whereas the 2018 summit collapse started after the 

LERZ eruption began.

1924 Intrusion

Observations of the 1924 intrusion event are described on 

the Hawaiian Volcano Observatory website (https://volcanoes.

usgs.gov/volcanoes/kilauea/geo_hist_1924_halemaumau.html) 

and repeated here. After years of rising lava levels within, and 

overflows from, Halemaʻumaʻu Crater, the lava lake dropped 

out of sight in February 1924. It was followed by an earthquake 

swarm that began in early April, reaching a peak on April 23 with 

ground cracking, faulting, at least 3.6 meters (m) (12 feet, ft) of 

coastal subsidence, and hundreds of felt earthquakes indicating the 

intrusion of magma from the summit into the LERZ. Ultimately, 

no lava was erupted.

Appendix. Comparisons to Other Eruptions Along the Lower East Rift Zone

Chapter D. The Ongoing Lower East Rift Zone Eruption of Kīlauea Volcano33
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Preliminary Analyses of Volcanic Hazards at Kīlauea Volcano, Hawai‘i, 2017–2018

The Hawaiian Volcano Observatory website states, 

“Halema‘uma‘u Crater was 115 m (377 ft) deep following the 

draining of the lake. As seismicity waned in lower Puna, the crater 

floor began to collapse on April 29, deepening to more than 150 m 

(490 ft) on May 1 and nearly 210 m (690 ft) on May 7. Frequent 

dust clouds indicated continuing collapse in the following days.”

The website describes observations of “...more than 50 

explosive events during a 2.5-week period in May 1924. The 

explosions were then, and remain today, the most powerful at 

Kīlauea since the early 19th century, throwing blocks weighing 

as much as 14 tons from the crater. Halema‘uma‘u doubled in 

diameter, deepened to about 400 m (1300 ft), and drastically 

changed in behavior—for the next 85 [sic; 84] years it no longer 

hosted a long-lived lava lake, until one returned in 2008.”

Although there was no LERZ eruption during this activity, 

the subsidence and plentiful earthquakes suggested an intrusion 

similar to the 2018 intrusion and it was followed by summit 

collapse and explosive events. No evidence of an offshore eruption 

has been found after several submarine expeditions in the area.

1955 Eruption, February 28–May 26

The 1955 LERZ eruption lasted for a total of 88 days 

but consisted of three eruptive periods separated by pauses in 

activity. Descriptions of the 1955 eruption here are primarily 

from Macdonald and Eaton (1964).

The first period of the eruption lasted from February 28 

to March 7 (8 days) and consisted of fissures that extended 

5.7km (3.5 mi) from Puʻuhonuaʻula to Kapoho Crater, along 

a trend overlapping the eastern part of the 2018 fissure system, 

but north of it. The 1955 fissures generally propagated to the 

northeast, but chaotically, with activity starting and stopping 

and shifting back and forth along the rift zone. This behavior 

was similar to that displayed during the early part of the current 

2018 activity, but ramped up more quickly, with longer lived 

fissures, higher fountains and spattering, and more voluminous 

lava flows. There was also considerable steam and ash venting, 

which has only been a very minor part of the current activity 

so far. The lavas erupted in 1955 were among the most 

differentiated lavas on Kīlauea.

The first eruptive period in 1955 ended abruptly on 

March7, but seismicity continued southwest of the initial 

breakout point near the current site of the Puna Geothermal 

Venture facility. The second period of the eruption began March 

12 in the area where the continued seismicity was occurring. 

This area is south of Puʻu Kaliʻu, which is on the southern edge 

of Leilani Estates. The second set of 1955 fissures overlaps with 

the western part of the current fissure system, but is south of it. 

This lava was less evolved (fresher) than the magma erupted 

during the first eruptive period that had been stored underground 

for at least decades.

Activity associated with the second period of the eruption 

(34 days) along a 7 km (4.3 mi) long fissure system to the 

southwest of the first eruption period fissure system, also ramped 

up quickly, producing fountains within a few days that were 

higher than any that have occurred during the current activity, 

and sending lava to the ocean. Outbreaks continued to occur 

progressively farther southwest, with some exceptions, producing 

fast-moving flows. Fountaining exceeded 250 m (820 ft) by the 

end of the first week. Most of the fissures were short-lived (hours 

to a few days), and a few vents started and stopped repeatedly. 

The activity stopped on April 7.

After a pause of 16 days, during which seismicity continued, 

the third period of the eruption started unexpectedly on April24 

with a resumption of activity at the western fissures. The eruption 

was episodic and relatively weak initially, but its vigor gradually 

increased through mid-May. On May 16, there was a sudden 

increase in lava output near the west end of the western fissure 

system, with fountaining and new fast-moving flows. After 

32 days of activity, fountaining ended abruptly on May 26, 

accompanied by a marked decrease of notable seismicity.

About 81×106 m3 of lava erupted (dense rock equivalent with 

25 percent void space). The time-averaged dense rock equivalent 

discharge rate is 14 m3/s over the 66 days of actual eruption. 

Considered separately, the three eruptive periods equate to timeaveraged dense rock equivalent discharge rates of 31, 18, and 

7 m3/s for periods 1–3, respectively.

1960 Eruption, January 13–February 19

The following descriptions of the 1960 eruption comes from 

Richter and others (1970). The 1960 eruption, which lasted about 

5 weeks, opened along nearly the entire 1.4 km (0.9 mi) length of 

its fissure system at the onset of eruption. These fissures behaved 

erratically for the first few days, often starting and stopping, but 

coalesced around a few points and began feeding fountains more 

than 400 m high by the end of the first week of activity. Early 

activity often included phreatic steam and ash venting. The high 

fountaining was accompanied by heavy tephra fall, and a large 

tephra cone built up.

A few weeks later, after a substantial edifice, filled with 

ponded lava, had grown around the dominant vents, two new 

fissures opened to the east of, and along the same trend as, the 

initial line of fissures. This may have been caused by an increase in 

head pressure in the magmatic system in response to construction 

of the tephra cone complex and ponded lava.

The lava chemistry changed from more evolved (stored 

magma) to fresher (directly from the summit reservoir) about 

half way through the eruption. This did not seem to cause a 

change in eruptive behavior. The dying phase of the eruption 

lasted from February 7 to 20, with a marked reduction in 

discharge. Whereas slow deflation at the summit began about 

4 days after the eruption started, summit collapse really began 

in earnest on about February7, coincident with the start of the 

dying phase of the eruption.

About 122×106 m3 of lava erupted in total. The timeaveraged discharge rate was about 38 m3

/s during the first two 

weeks of the eruption.
Menlo Park Publishing Service Center

Manuscript approved January 6, 2020

Edited by Monica Erdman

Layout by Cory Hurd
Neal and Anderson—Preliminary Analyses of Volcanic Hazards at Kīlauea Volcano, Hawai‘i, 2017–2018—Open-File Report 2020–1002

ISSN 2331-1258 (online)

https://doi.org/10.3133/ofr20201002