Eruptions of Hawaiian Volcanoes—

Past, Present, and Future

U.S. Department of the Interior

U.S. Geological Survey

General Information Product 117
Cascades of lava fed by fountains at vent (seen spouting on the skyline) fall more than 75 feet* to fill ‘Ālo‘i Crater during the 

1969–71 Mauna Ulu eruption of Kïlauea Volcano. (USGS photograph by Donald A. Swanson)

*This publication uses English units of measurement. For readers who use metric units, a conversion table is given in 

the back of the booklet.

Cover—Eruption of Kïlauea Volcano, as viewed at dawn on January 30, 

1974. Overflows from an active lava lake spill down the flank of the volcanic 

shield at Mauna Ulu, built by many such overflows since 1969. The height of 

this shield was nearly 400 feet when the Mauna Ulu eruptions ended in July 

1974. (USGS photograph by Robert I. Tilling.)
Eruptions of Hawaiian Volcanoes—

Past, Present, and Future

By Robert I. Tilling, Christina Heliker, and Donald A. Swanson

General Information Product 117

First edition, 1987

Reprinted, 1993

Second revised edition, 2010

U.S. Department of the Interior

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

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Viginia: 2010

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

http://pubs.usgs.gov/gip/117/

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its natural and living resources, natural hazards, and the environment:

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

by the U.S. Government

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

owners to reproduce any copyrighted material contained within this report.

Suggested citation:

Tilling, R.I., Heliker, C., and Swanson D.A., 2010, Eruptions of Hawaiian volcanoes— 

past, present, and future: U.S. Geological Survey

General Information Product 117, 63 p.

Cataloging-in-Publication data are on file with the Library of Congress (URL http://www.loc.gov/).
iii

Contents

Preface ...........................................................................................................................................................1

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

Origin of the Hawaiian Islands ....................................................................................................................4

Hawaiian Legends and Early Scientific Work .................................................................................

5

Plate Tectonics and the Hawaiian "Hot Spot" ..................................................................................9

Hawaiian Eruptions in Recorded History ................................................................................................11

Volcano Monitoring and Research ..........................................................................................................15

Volcano Monitoring ...........................................................................................................................16

Anatomy of an Eruption: The Inflation-Deflation Cycle ...............................................................21

Forecasting Eruptions .......................................................................................................................21

Kïlauea's Volcanic "Plumbing System" ....................................................................................................23

Hawaiian Eruptive Style: Powerful but Usually Benign ........................................................................25

Typical Activity: "Nonexplosive" or Weakly Explosive .................................................................25

Infrequent Explosive Activity ...........................................................................................................33

Hawaiian Volcanic Products, Landforms, and Structures ...................................................................37

Lava Flows ...........................................................................................................................................37

Fragmental Volcanic Products ........................................................................................................40

Volcanic Landforms and Structures ...............................................................................................42

Lō‘ihi: Hawai‘i’s Newest Volcano .............................................................................................................48

Volcanic Hazards and Benefits ................................................................................................................50

Volcanic Hazards ...............................................................................................................................50

Volcanic Air Pollution ........................................................................................................................54

Volcanic Benefits ...............................................................................................................................55

Benefits of Research at the Hawaiian Volcano Observatory .....................................................56

Selected Readings ......................................................................................................................................57

Selected Viewings ......................................................................................................................................59

Videos and (or) DVDs ........................................................................................................................59

Selected Websites ......................................................................................................................................60

Conversion of Units .....................................................................................................................................61

Glossary ........................................................................................................................................................62
iv

Special thanks go to Taeko Jane Takahashi and Steven R. 

Brantley, Hawaiian Volcano Observatory, for assistance 

with selection of photographic images and unwavering 

encouragement over the years.
1

Preface

Viewing an erupting volcano is a memorable experience, one 

that has inspired fear, superstition, worship, curiosity, and fascination since before the dawn of civilization. In modern times, volcanic phenomena have attracted intense scientific interest, because 

they provide the key to understanding processes that have created 

and shaped more than 80 percent of the Earth's surface. The active 

Hawaiian volcanoes have received special attention worldwide 

because of their frequent spectacular eruptions, which often can 

be viewed and studied with relative ease and safety.

In January 1987, the Hawaiian Volcano Observatory (HVO), 

located on the rim of Kïlauea Volcano, celebrated its 75th Anniversary. In honor of HVO's Diamond Jubilee, the U.S. Geological Survey (USGS) published Professional Paper 1350 (see list 

of Selected Readings, page 57), a comprehensive summary of 

the many studies on Hawaiian volcanism by USGS and other 

scientists through the mid-1980s. Drawing from the wealth of 

data contained in that volume, the USGS also published in 1987 

the original edition of this general-interest booklet, focusing 

on selected aspects of the eruptive history, style, and products 

of two of Hawai‘i's active volcanoes, Kïlauea and Mauna Loa. 

This revised edition of the booklet—spurred by the approaching 

Centennial of HVO in January 2012—summarizes new information gained since the January 1983 onset of Kïlauea’s Pu‘u 

‘Ö‘ö-Kupaianaha eruption, which has continued essentially nonstop through 2010 and shows no signs of letup. It also includes 

description of Kïlauea’s summit activity within Halema‘uma‘u 

Crater, which began in mid-March 2008 and continues as of this 

writing (late 2010).

This general-interest booklet is a companion to the one on 

Mount St. Helens Volcano first published in 1984 and revised in 

1990 (see Selected Readings). Together, these publications illustrate the contrast between the two main types of volcanoes: shield 

volcanoes, such as those in Hawai‘i, which generally are nonexplosive; and composite volcanoes, such as Mount St. Helens in the 

Cascade Range, which are renowned for their explosive eruptions.

Lava shoots 1,000 feet into the air in April 1983 during a high-fountaining 

episode of the Pu‘u ‘Ö‘ö-Kupaianaha eruption of Kïlauea Volcano. (USGS 

photograph by J.D. Griggs.)
2

Introduction

“The loveliest fleet of islands that lies anchored in any ocean.”—Mark Twain

Few would quarrel with Mark Twain's vivid description of Hawai‘i, 

written after his 4-month stay in 1866. Archeologists believe that the Hawaiian Islands were discovered and settled around the 9th century C.E. or 

earlier by Polynesians sailing from islands, probably the Marquesas, in the 

southern tropical Pacific. Subsequently, nearly a thousand years of cultural 

isolation passed before the first documented visit to Hawai‘i by non-Polynesians. On January 18, 1778, during his third major voyage in the Pacific, 

the famous British navigator and explorer, Captain James Cook, sighted 

the Polynesians' secluded home. Cook named his discovery the "Sandwich 

Islands," in honor of the Earl of Sandwich, then First Lord of the British 

Admiralty. Mark Twain's fleet of islands is larger than Rhode Island and 

Connecticut combined. The Island of Hawai‘i, commonly called the "Big 

Island," covers more than twice the total area of the other islands.

Hawai‘i, which became our 50th state in 1959, is now home for more 

than 1.2 million people and hosts many times that number of visitors each 

year. Hawai‘i's worldwide image as an idyllic tropical paradise is well 

deserved. What is less well known, however, is that the islands exist only 

because of nearly continuous volcanic activity. Most of the prominent features of the Hawaiian Islands, such as Diamond Head on O‘ahu, Haleakalä 

Crater on Maui, and the huge mountains of Mauna Loa and Mauna Kea on 

the Island of Hawai‘i, are volcanic.

The principal Hawaiian islands, 

stretching about 400 miles from 

Ni'ihau in the northwest to the Island 

of Hawai'i in the southeast, are the 

exposed tops of volcanoes that rise 

tens of thousands of feet above the 

ocean floor. Some islands are made 

up of two or more volcanoes. Areas in 

red on the Island of Hawai‘i indicate 

lava flows erupted during the past two 

centuries. Lö‘ihi Seamount, Hawai‘i’s 

newest (and still submarine) volcano, 

lies about 3,100 feet beneath the 

sea. (Modified from image by Joel E. 

Robinson, USGS, in “This Dynamic 

Planet” map of Simkin and others, 

1996.)
3

Since the early 19th century, frequent eruptions 

have been documented at Mauna Loa and Kïlauea; 

these two volcanoes on the Island of Hawai‘i are 

among the most active in the world. Nearby Lö‘ihi 

Seamount, off the island's south coast, is the newest 

Hawaiian volcano, actively growing on the seafloor 

deep beneath the ocean surface.

Most eruptions of Mauna Loa and Kïlauea are 

nonexplosive, and both volcanoes are readily accessible, such that scientists generally can study them at 

close range in relative safety. As a result, these are two 

of the most intensely observed and best understood 

volcanoes on our planet. Research on these active 

volcanoes provides a basis for understanding the life 

story of older, now inactive Hawaiian volcanoes and 

similar volcanoes worldwide. Because of their frequent 

activity and accessibility, Hawaiian volcanoes serve as 

a superb natural laboratory for scientists from around 

the world to study volcanic eruptions.

Shaded relief map of the southeastern part of the Island of Hawai‘i, showing the principal features and 

localities of Mauna Loa, Kïlauea, and Lö‘ihi Volcanoes discussed in the text.

Lili‘uokalani Park, in the city of Hilo on the Island of Hawai'i, 

typifies the tropical beauty and serenity of the Hawaiian 

Islands. (USGS photograph by Taeko Jane Takahashi.)
4

Map of the Pacific basin showing the location of the Hawaiian Ridge-Emperor Seamount Chain in 

relation to some other features and localities mentioned in the text. (Base map from the third edition of 

“This Dynamic Planet” map, 2006)

Origin of the Hawaiian Islands

The Hawaiian Islands are the tops of gigantic 

volcanic mountains formed by countless eruptions of 

fluid lava* over several million years; some tower more 

than 30,000 feet above the seafloor. These volcanic 

peaks rising above the ocean surface represent only the 

tiny, visible part of an immense submarine ridge, the 

Hawaiian Ridge—Emperor Seamount Chain, composed 

of more than 80 large volcanoes. This range stretches 

across the Pacific Ocean floor from the Hawaiian Islands 

to the Aleutian Trench. The length of the Hawaiian 

Ridge segment alone, between the Island of Hawai‘i and 

Midway Island to the northwest, is about 1,600 miles, 

roughly the distance from Washington, D.C., to Denver, 

Colorado. The amount of lava erupted to form this huge 

ridge, about 186,000 cubic miles, is more than enough to 

cover the State of California with a layer 1 mile thick.

*Most of the italicized terms in the text are defined and 

explained as an integral part of the discussion. However, 

for those terms perhaps not fully explained, a Glossary at 

the back of this booklet (p. 62) provides supplementary 

information or broader context.
5

Hawaiian Legends and Early Scientific Work

The distinctive northwest-southeast alignment of the Hawaiian chain was 

known to early explorers of the Pacific Ocean, including the Polynesians who 

first settled the islands. The ancient Hawaiians were superb sailors, excellent 

navigators, and keen observers of nature, including volcanic eruptions and their 

effects. They noticed the varying extent of erosion from island to island, the 

amount of vegetation on the slopes of the various volcanoes, the freshness of 

lava flows, and other indicators of the relative ages of the islands. Some of the 

legends of the early Hawaiians suggest that they recognized that the islands 

become younger from the northwest to the southeast.

Hawaiian legends tell that eruptions were caused by Pele, the sometimestempestuous Goddess of Fire, during her frequent moments of anger. Pele was 

both revered and feared; her immense power and many adventures figured 

prominently in ancient Hawaiian songs and chants. She could cause earth-

quakes by stamping her feet and volcanic eruptions and fiery devastation by 

digging with the "päoa," her magic stick. One oft-told legend describes the long 

and bitter quarrel between Pele and her older sister Namakaokaha‘i, the God-

dess of the Sea, that drove Pele to migrate—from northwest to southeast along 

the island chain—to her present stopping place on the Island of Hawai‘i.

Pele first used her päoa on Kaua‘i, where she subsequently was attacked 

by Namakaokaha‘i and left for dead. Recovering, she fled to Oah‘u, where she 

dug a number of "fire pits"—including the crater we now call Diamond Head, 

the tourist's landmark of modern Honolulu. Pele then left her mark on the island 

of Moloka‘i before traveling farther southeast to Maui and creating Haleakalä 

Volcano, which forms the eastern half of that island. By then Namakaokaha‘i 

realized that Pele was still alive and went to Maui to do battle with her. After 

Above: Pele, the Goddess of Fire (or Volcanoes), as portrayed by artist D. 

Howard Hitchcock. (USGS photograph by J.D. Griggs, with permission of the 

Volcano House Hotel, owner of the original painting.) Below: Night view (time 

exposure) of Pele's home during the 1967–68 eruption within Halema‘uma‘u 

Crater. (Photograph by Richard S. Fiske.) Similar views can be seen on a 

clear night during the current (2010) eruption at Halema‘uma‘u.
6

a terrific fight, Namakaokaha‘i again believed that she had killed her 

younger sister, only to discover later, however, that Pele was very much 

alive and busily working at Mauna Loa Volcano on the Island of Hawai‘i. 

Namakaokaha‘i then conceded that she could never permanently crush her 

sister's indomitable spirit and gave up the struggle. Pele dug her final and 

eternal fire pit, Halema‘uma‘u Crater, at the summit of Kïlauea Volcano, 

where her spirit is said to reside to this day.

Some interpretations directly link Pele’s epic migration to the actual 

successive creation of the islands. Other—and more accepted—interpretations assume that the islands were already in place and that Pele’s arrival 

at each caused new or rejuvenated volcanism. In any case, the various 

accounts of migration of volcanic activity from Kaua‘i to Hawai‘i in Hawaiian legends are in accord with modern scientific studies.

A painting by renowned Hawaiian artist Herb Kawainui Kane depicting Pele fighting with her older sister and nemesis Namakaokaha‘i 

(the Goddess of the Sea) during the fierce battles between these 

two deities in legends of Pele’s migration along the Hawaiian island 

chain (see text). (Image used with permission of the artist.)
7

The first geologic study of the Hawaiian Islands was conducted during 

six months in 1840–1841, as part of the U.S. Exploring Expedition of 1838–

1842, commanded by Lieutenant Charles Wilkes of the U.S. Navy. The 

expedition's geological investigations were directed by James Dwight Dana. 

Though only 25 years old in 1838, Dana was no stranger to volcanoes. In 

1834 he had studied Vesuvius, the active volcano near Naples, Italy.

Dana and his colleagues recognized that the islands become increasingly younger from northwest to southeast along the Hawaiian volcanic 

chain, largely because of differences in their degree of erosion. The greater 

the length of time since its last eruption, the greater the erosion of the volLeft: The deeply eroded Ko‘olau Volcano on the Island of O‘ahu is 2 to 3 million years older than Mauna Loa Volcano 

on Hawai‘i (skyline, right photograph), whose profile is unscarred by erosion. (Photograph by Richard S. Fiske.) Right:

The Hawaiian Volcano Observatory (circled) can be seen perched on Uwëkahuna Bluff, the highest point on Kïlauea’s 

caldera rim. (USGS photograph by J.D. Griggs.)

cano. He also suggested that some other island chains in the Pacific showed 

a similar general decrease in age from northwest to southeast.

The alignment of the Hawaiian Islands, Dana proposed, reflected 

localized volcanic activity along segments of a major fissure zone slashing 

across the ocean floor. Dana's "great fissure" origin for the islands served 

as a prominent working hypothesis for many subsequent studies until the 

mid-20th century. The monumental work of Dana—considered to be the 

first American volcanologist—resulted in greatly increased awareness of the 

Hawaiian volcanoes, which have continued to attract much scientific attention since.
8

Tectonic Plates and Active Volcanoes of the World. Most active volcanoes are located along or near the boundaries of Earth's shifting tectonic plates. Hawaiian volcanoes, however, occur in the middle of the Pacific Plate and are formed by volcanism over the Hawaiian “Hot Spot” 

(see text). Only some of the Earth's more than 500 active volcanoes are shown here (red triangles). (Sketch map from Kious and Tilling, 1996.)
9

Plate Tectonics and the Hawaiian “Hot 

Spot”

In the early 1960s, the related concepts of 

"seafloor spreading" and "plate tectonics" emerged 

as powerful new hypotheses that geologists used to 

interpret the features and movements of the Earth's 

surface layer. According to the plate tectonic theory, 

the Earth's rigid outer layer, or "lithosphere," con-

sists of about a dozen slabs or plates, each averaging 

50 to 100 miles thick. These plates move relative to 

one another at average speeds of a few inches per 

year—about as fast as human fingernails grow. Sci-

entists recognize three common types of boundaries 

between these moving plates (see diagrams at right):

(1) Divergent or spreading—adjacent plates 

pull apart, such as at the Mid-Atlantic Ridge, which 

separates the North and South America Plates from 

the Eurasia and Africa Plates. This pulling apart 

causes "seafloor spreading" as new material from 

the underlying less rigid layer, or "asthenosphere," 

fills the cracks and adds to these oceanic plates.

(2) Convergent—two plates move towards one 

another and one is dragged down (or "subducted") 

beneath the other. Convergent plate boundar-

ies are also called "subduction zones" and are 

typified by the Aleutian Trench, where the Pacific 

Plate is being subducted under the North America 

Plate. Mount St. Helens (southwest Washington) 

and Mount Fuji (Japan) are excellent examples of 

subduction-zone volcanoes formed along conver-

gent plate boundaries.

(3) Transform fault—one plate slides hori-

zontally past another. The best-known example is 

the earthquake-prone San Andreas Fault Zone of 

California, which marks the boundary between the 

Pacific and North America Plates.

Nearly all of the world's earthquakes and active 

volcanoes occur along or near the boundaries of 

the Earth's shifting plates. Why then are the Hawai-

ian volcanoes located in the middle of the Pacific 

Plate, more than 2,000 miles from the nearest 

boundary with any other tectonic plate? The pro-

ponents of plate tectonics at first had no explana-

tion for the occurrence of volcanoes within plate 

interiors (“intraplate” volcanism). Then in 1963, J. 

Tuzo Wilson, a Canadian geophysicist, provided an 

ingenious explanation within the framework of plate 

tectonics by proposing the "hot spot" hypothesis. 

Wilson's hypothesis has come to be accepted widely, 

because it agrees well with much of the scientific 

data on linear volcanic island chains in the Pacific 

Ocean in general—and the Hawaiian Islands in 

particular.

According to Wilson, the distinctive linear 

shape of the Hawaiian-Emperor Chain reflects the 

progressive movement of the Pacific Plate over a 

“deep” and “fixed” hot spot. In recent years, scien-

tists have been debating about the actual depth(s) 

of the Hawaiian and other Earth hot spots. Do they 

extend only a few hundred miles beneath the litho-

sphere? Or do they extend down thousands of miles, 

perhaps to Earth’s core-mantle boundary? Also, 

while scientists general agree that hot spots are fixed 

in position relative to the faster moving overrid-

ing plates, some recent studies have shown that hot 

spots can migrate slowly over geologic time. In any 

case, the Hawaiian hot spot partly melts the region 

just below the overriding Pacific Plate, producing 

small, isolated blobs of molten rock (magma). Less 

dense than the surrounding solid rock, the magma 

blobs come together and rise buoyantly through 

structurally weak zones and ultimately erupt as lava 

onto the ocean floor to build volcanoes.
10

Over a span of about 70 million years, the combined processes of 

magma formation, eruption, and continuous movement of the Pacific Plate 

over the stationary hot spot have left the trail of volcanoes across the ocean 

floor that we now call the Hawaiian-Emperor Chain. A sharp bend in the 

chain about 2,200 miles northwest of the Island of Hawai‘i was previously 

interpreted as a major change in the direction of plate motion around 43–45 

million years ago (Ma), as suggested by the ages of the volcanoes bracketing the bend. However, recent studies suggest that the northern segment 

(Emperor Chain) formed as the hot spot moved southward until about 45 Ma, 

when it became fixed. Thereafter, northwesterly plate movement prevailed, 

resulting in the formation of the Hawaiian Ridge “downstream” from the 

hotspot.

The Island of Hawai‘i is the southeasternmost and youngest island in the 

chain. The southeasternmost part of the Island of Hawai‘i presently overlies 

the hot spot and still taps the magma source to feed its active volcanoes. The 

active submarine volcano Lö‘ihi, off the Island of Hawai‘i's south coast, may 

mark the beginning of the zone of magma formation at the southeastern edge 

of the hot spot. With the possible exception of Maui, the other Hawaiian 

islands have moved northwestward beyond the hot spot—they were successively cut off from the sustaining magma source and are no longer volcanically active.

The progressive northwesterly drift of the islands from their point of 

origin over the hot spot is well shown by the ages of the principal lava flows 

on the various Hawaiian Islands from northwest (oldest) to southeast (youngest), given in millions of years: Ni‘ihau and Kaua‘i, 5.6 to 3.8; O‘ahu, 3.4 

to 2.2; Moloka‘i, 1.8 to 1.3; Maui, 1.3 to 0.8; and Hawai‘i, less than 0.7 and 

still growing.

Even for the Island of Hawai‘i alone, the relative ages of its five volcanoes are compatible with the hot-spot theory (see map, page 3). Kohala, at 

the northwestern corner of the island, is the oldest, having ceased eruptive 

activity about 120,000 years ago. The second oldest is Mauna Kea, which 

last erupted about 4,000 years ago; next is Hualälai, which has had only 

one eruption (1800–1801) in written history. Lastly, both Mauna Loa and 

Kïlauea have been vigorously and repeatedly active in the past two centuries. 

Because it is growing on the southeastern flank of Mauna Loa, Kïlauea is 

believed to be younger than its huge neighbor.

The size of the Hawaiian hot spot is not well known, but it presumably is large enough to encompass and feed the currently active volcanoes 

of Mauna Loa, Kïlauea, Lö‘ihi and, possibly, also Hualälai and Haleakalä. 

Some scientists have estimated the Hawaiian hot spot to be about 200 miles 

across, with much narrower vertical passageways that feed magma to the 

individual volcanoes.

A cutaway view along the Hawaiian island chain showing the inferred 

mantle plume that has fed the Hawaiian hot spot on the overriding Pacific 

Plate. The geologic ages of the oldest volcano on each island (Ma = millions of years ago) are progressively older to the northwest, consistent with 

the hot spot model for the origin of the Hawaiian Ridge-Emperor Seamount 

Chain. (Modified from image of Joel E. Robinson, USGS, in “This Dynamic 

Planet” map of Simkin and others, 2006.)
11

Hawai‘i has a brief written history, extending back only 

about 200 years, compared to such volcanic regions as Iceland, 

Indonesia, Italy, and Japan. Written accounts exist for most 

Hawaiian eruptions since 1823, when the first American missionaries visited the Island of Hawai‘i. Descriptions of earlier eruptions are sketchier, because they are based only on interpretations 

of ancient Hawaiian chants and stories told to the American missionaries by Hawaiian elders and early European residents.

All the known Hawaiian eruptions since 1778 have been at 

Mauna Loa and Kïlauea Volcanoes, except for the 1800–1801 

eruption of Hualälai Volcano on the west coast of the Island 

of Hawai‘i. In an exception to the overall northwest-southeast 

shift of volcanic activity, a series of minor submarine eruptions 

probably occurred in 1955–56 between the islands of O‘ahu and 

Kaua‘i and near Necker Island, about 350 miles northwest of 

Kaua‘i.

For the past 200 years, Mauna Loa and Kïlauea have tended 

to erupt on average every two or three years, placing them 

among the most frequently active volcanoes of the world. At 

each volcano, some intervals of repose between eruptions at a 

given volcano have been much longer than its long-term average. The individual Kïlauea eruptions recorded since 1778 are in 

addition to the nearly continuous eruptive activity within or near 

Halema‘uma‘u Crater, extending throughout the 19th century 

and into the early 20th century.

On March 30, 1984, Kïlauea and Mauna Loa were in simultaneous eruption, the first time since 1924. Above: Kïlauea's Pu‘u ‘Ö‘ö 

vent during its 17th high-fountaining episode. Below: Aerial view 

of a long lava flow during the Mauna Loa eruption, which began on 

March 25; this eruption fed a major lava flow that advanced toward 

the city of Hilo. (Upper photograph by Edward W. Wolfe, USGS; 

lower photograph by Scott Lopez, National Park Service.)

Hawaiian Eruptions in Recorded History
12

Graph summarizing the eruptions of Mauna Loa and Kïlauea Volcanoes during the past 200 years. The Pu‘u ‘Ö‘ö- Kupaianaha eruption has continued into the 21st 

century. Information is sketchy for eruptions before 1823, when the first missionaries arrived on the Island of Hawai‘i. The total duration of eruptive activity in a given 

year, shown by the length of the vertical bar, may be for a single eruption or a combination of several separate eruptions.
13

The active lava lake within Halema‘uma‘u Crater overflowing its levee, as painted by D. Howard Hitchcock in 

1894. Snow-capped Mauna Loa forms the far horizon. (USGS photograph by J.D. Griggs, with permission of 

the Volcano House Hotel, owner of the original painting.)

Simultaneous eruption of both volcanoes 

has been rare, except at times when Kïlauea was 

continuously active before 1924. The only post1924 occurrence of simultaneous eruption was 

in March 1984, when activity at both volcanoes 

overlapped for one day. Long repose intervals 

for one volcano correlate approximately with 

increased activity at the other. This general relation is imperfect but holds well for post-1924 

eruptive activity. Between 1934 and 1952, only 

Mauna Loa was active; between 1952 and 1974, 

only Kïlauea was.

Since July 1950, Hawaiian eruptive activity 

has been dominated by frequent and sometimes 

prolonged eruptions at Kïlauea, while only two 

short-lived eruptions have occurred at Mauna 

Loa (July 1975 and March–April 1984). As of 

2010, Kïlauea’s Pu‘u ‘Ö‘ö-Kupaianaha eruption, 

which began in January 1983, showed no signs 

of decline. This eruption has been primarily fed 

by the Pu‘u ‘Ö‘ö vent, except for two extended 

periods: (1) July 1986–February 1992 at the 

Kupaianaha vent; and (2) July 2007–present at 

vents about a half mile uprift from Kupaianaha. 

Except for the nearly continuous eruptive activity 

at Halema‘uma‘u for a century before 1924, the 

Pu‘u ‘Ö‘ö-Kupaianaha eruption—still continuing 

through 2010—has now become the longest lasting Hawaiian eruption in recorded history.

In mid-March 2008, a new vent opened 

within Halema‘uma‘u Crater, and a faint glow 

could be seen at night. Early on the morning of 

March 19, a small explosion occurred at this 

vent—the first explosive activity at Kïlauea’s 

summit since 1924. Rock debris from the explosion—with a few blocks as large as a yard 

across—was strewn over about 75 acres, covered 

a stretch of Crater Rim Drive, and damaged 

the Halema‘uma‘u visitor overlook. People in 

Pahala (~ 20 miles downwind) reported a light 

dusting of ash on their cars. In early September 

2008, molten lava was observed bubbling and 

sloshing within the pit, and lava has been present 

intermittently into 2010. As the summit activity 

continued—characterized by heavy fuming with 

elevated sulfur dioxide emissions, nighttime glow, 

and occasional explosions—the vent was enlarged 

by repeated wall collapses, becoming about 450 

feet in diameter and 650 feet deep by April 2010. 

The 2008–present Halema‘uma‘u activity is the 

longest summit eruption at Kïlauea since 1924.

For the first year, the eruption at the new 

summit vent had no appreciable effect on the continuing eruption near Pu‘u ‘Ö‘ö, marking the longest known occurrence of simultaneous summit 

and rift eruptions at Kïlauea. Past simultaneous 

activity, such as in 1971, was rare and of short 

duration, generally lasting only a few days at 

most. The ongoing concurrent summit-rift eruption, now approaching three years in duration, is 

unprecedented for Kïlauea in recorded history.
14

Above: Aerial view in November 2008 of the gas plume from the new vent that opened in Halema‘uma‘u 

Crater in mid-March 2008. This activity has continued into 2010 and can be conveniently seen from the 

Jaggar Museum and the Hawaiian Volcano Observatory (circled) on the rim of Kïlauea Caldera. Left:

Nighttime look (January 2010) through the fume at the molten lava sloshing and bubbling within the 

Halema‘uma‘u vent, about 400 feet in diameter. (USGS photographs by Tim Orr).

A pattern of dominant activity alternating between Mauna Loa and 

Kïlauea could imply that both volcanoes may alternately tap the same deep 

magma source. Whether this is so is a topic of scientific debate and continuing research, because abundant physical evidence indicates that each 

volcano has its own shallow magma reservoir that operates independently of 

the other. Also, available data suggest that the lavas of the two volcanoes are 

chemically and isotopically distinct.

The average volume of lava erupted at Kïlauea Volcano since 1956 is 

between 110 and 130 million cubic yards per year. In contrast, the average rate of lava output along the entire Hawaiian-Emperor Chain during 

its 70-million-year life is only about 20 million cubic yards per year. For 

reasons not yet understood, the rate of eruptive activity associated with the 

Hawaiian hot spot for the past few centuries appears exceptionally high 

relative to its long-term average.
15

The first Hawaiian Volcano Observatory (HVO), 

located near the site of the present Volcano House 

Hotel, as it appeared around 1922. (Photographer 

unknown; courtesy of the Bishop Museum, Honolulu, Hawai‘i.) 

Volcano Monitoring and

Research

Before the 20th century, most scientific 

studies of volcanoes were conducted during 

short-lived expeditions, generally undertaken 

as a response to major eruptions. Thomas A. 

Jaggar, Jr., a geologist at the Massachusetts 

Institute of Technology (MIT), was not satisfied with that approach. He recognized that, to 

understand volcanoes fully, one must study them 

continuously before, during, and after eruptions. 

Jaggar's views were profoundly affected by a 

memorable visit in 1902 to the Island of Martinique (West Indies). He went as a member of the 

international scientific expedition sent to study 

that year's catastrophic eruption of Mont Pelée, 

which devastated the city of St. Pierre and killed 

about 30,000 people.

In 1911, spurred by a stimulating lecture 

delivered by Jaggar, a group of Hawaiian residents founded the Hawaiian Volcano Research 

Association (HVRA). The logo of the HVRA 

included the motto Ne plus haustae aut obrutae 

urbes (loosely translated as “Let no more cities 

be destroyed or buried”), reflecting Jaggar's 

memory of Mont Pelée's destructive force and 

his optimistic belief that better understanding 

of volcanoes could reduce the hazard to life and 

property from eruptions.

In 1912, with support from the HVRA and 

the Whitney Fund of MIT, Jaggar established the 

Hawaiian Volcano Observatory (HVO) to study 

the activity of Mauna Loa and Kïlauea on a permanent, scientific basis. "Volcanology" emerged 

as a modern science with the founding of HVO, 

which between 1912 and 1948 was managed by 

the HVRA, the U.S. Weather Bureau, the U.S. 

Geological Survey (USGS), and the National 

Park Service. Since 1948, it has been operated 

by the USGS.

During the past nearly 100 years of 

research, HVO scientists have developed and 

refined most of the surveillance techniques now 

commonly employed by volcano observatories 

worldwide.

Helicopter view of HVO at its present site on the 

western edge of Kïlauea Caldera, after renovation 

and the addition of a new wing (with observation 

tower) in 1986. In the background, fume rises from 

the active vent within Halema‘uma‘u Crater on 

the caldera floor. (USGS photograph by Tim Orr, 

November 2010.)
16

Volcano Monitoring

The term "volcano monitoring" refers to 

the observations and measurements—visual 

and instrumental—scientists make to document changes in the state a volcano during and 

between eruptions. Such changes are now well 

known for Kïlauea, and a pattern of similar 

changes is becoming apparent for the less studied Mauna Loa. As magma enters the shallow 

summit reservoir, the volcano undergoes swelling or inflation (a process similar to the stretching of a balloon being filled with air). This 

swelling in turn causes changes in the shape of 

the volcano's surface. During inflation, the slope 

or tilt of the volcano increases, and reference 

points (benchmarks) on the volcano are uplifted 

relative to a stable point and move farther apart 

from one another. For Hawaiian volcanoes, preeruption inflation is generally slow and gradual, 

lasting for weeks to years. However, once an 

eruption begins, the shrinking or deflation of 

the volcano typically occurs rapidly as pressure 

on the magma reservoir is suddenly relieved—a 

process not unlike deflating a balloon. During 

deflation, changes in tilt and in vertical and hori-zonzontal distances between benchmarks are opposite 

to those during inflation.

Changes in the shape of the volcano during 

inflation and deflation are determined by 

ground-deformation measurements. Tilt changes 

can be measured continuously and extremely 

precisely by use of instruments called tiltmeters, 

which can detect a change in angle of less than 1 

microradian (about 0.00006 degree). A 1-microradian increase in tilt would be equivalent to 

steepening the slope of a board about 0.8 mile 

long by placing a coin under one end.

Tilt changes and associated relative vertical 

displacements can also be detected by periodic 

remeasurement of arrays of benchmarks by leveling, a high-precision field surveying method. 

Changes in horizontal distances between benchmarks can be monitored in the field by using 

portable electronic-distance-measurement 

(EDM) instruments that use laser or infrared 

beams. Collectively, these commonly used 

ground-deformation monitoring techniques have 

Hypothetical slice through Kïlauea Volcano. Magma 

entering the shallow reservoir exerts pressure on the volcano, causing earthquakes and distorting its shape from 

the dashed-line profile to the solid-line profile. During 

inflation, reference points (benchmarks) on the volcano's 

surface are pushed upward and outward relative to points 

assumed to be stable. Changes in the volcano's shape 

and the occurrence of the earthquakes can be tracked 

precisely by volcano-monitoring techniques.

Above: Hawaiian Volcano Observatory 

(HVO) scientists use a laser-ranging instrument in the mid-1980s to make an electronic 

distance measurement (EDM). Snow-capped 

summit of Mauna Loa can be seen in background. (USGS photograph by J.D. Griggs.) 

Below: An HVO scientist takes notes at a 

global positioning system (GPS) measurement site near the Pu‘u ‘Ö‘ö vent, while an 

antenna receiver (on tripod centered over a 

benchmark) acquires signals emitted from 

several GPS satellites. Mauna Kea Volcano 

is visible in background. Repeated measurements at the same benchmark will reveal 

horizontal and vertical motions of that point 

on the volcano. (USGS photograph by Christina Heliker.)
17

a measurement precision of a few parts per million or less. For distances, the notion of one part 

per million (ppm) can be visualized as about 1 

inch in 16 miles, or one car length in bumper-tobumper traffic from Cleveland to San Francisco.

During the past 15 years, the global positioning system (GPS)—a satellite-based technology—has been increasingly used to monitor 

the ground movements at active volcanoes. 

Originally deployed for military purposes by 

the Department of Defense, the GPS involves 

an array of 24 satellites (orbiting about 12,000 

miles above the Earth) that continuously send 

very accurate time signals, which can be picked 

up by GPS receivers on the ground. Using highresolution GPS receivers (not the inexpensive 

devices used by hikers and drivers) and sophisticated computer processing of signals received 

from four or more satellites, scientists can 

determine both distance (longitude and latitude) 

and elevation changes at a given ground reference point ("benchmark") with parts-per-million 

precision. Repeated measurements of a GPS 

network of many benchmarks make it possible to monitor an entire volcano. In addition 

to monitoring inflation/deflation movements at 

Areas of color bands, or "fringes," in this InSAR image—produced from a pair 

of satellite radar images acquired 35 days apart in 2007 by the European 

Space Agency's ENVISAT satellite—show subsidence at Kïlauea's summit 

caldera and a combination of uplift and subsidence centered near Makaopuhi 

Crater. This pattern of deformation reflects an intrusion of magma from the 

summit reservoir into the east rift zone. Each fringe of color bands (violetblue-green-yellow-red) represents about 1.1 inch of deformation (up or down) 

of the ground surface. In this image, a progression of yellow-to-violet colors 

toward the center of a pattern demonstrates uplift, and the opposite color progression indicates subsidence. (Image courtesy of Michael Poland, USGS.)

the volcano summits, GPS measurements show 

that the south flank of Kïlauea and, at times, 

the southeast flank of Mauna Loa are moving 

seaward (to the southeast) at an average rate of a 

few inches per year. As the costs and computerprocessing time of GPS measurements continue 

to decrease, they will likely replace all other 

types of ground-deformation measurements, 

especially since GPS measurements can be made 

around the clock regardless of the weather and 

do not require one benchmark to be seen from 

another.

In recent years, there has been increasing use of another satellite-based tool to track 

ground deformation at Hawaiian and other 

volcanoes—Interferometric Synthetic Aperture 

Radar (InSAR). This technique involves processing radar signals sent by an orbiting satellite and bounced back from the ground surface. 

Changes in the position of the Earth’s surface 

can be determined by analyzing a pair of radar 

images acquired at two different times. Like 

GPS measurements, InSAR monitoring can 

be done in all weather conditions and can map 

ground deformation over a wide area (typically 

30 x 60 miles). InSAR data cover a large area 

but are obtained and processed periodically, 

whereas GPS measurements refer to specific 

points (benchmarks) but can be made frequently 

or even continuously. Taken together, data from 

these two techniques are complementary and 

give a better picture of the overall ground deformation than measurements obtained through 

either technique by itself.
18

The mainstay of volcano monitoring is the continuous recording of seismic activity. Virtually all Hawaiian eruptions are preceded and accompanied 

by an increase in the number of shallow earthquakes. As magma moves into 

the reservoir during inflation, it must make room for itself by rupturing or 

crowding aside the solidified lava that surrounds the reservoir. Such underground ruptures produce seismic waves that travel through the volcano and 

are recorded by a network of seismometers placed on the volcano's surface. 

Ground motions sensed by seismometer are converted into electronic signals, 

which are transmitted by radio and are recorded on seismographs located at 

the volcano observatory. Seismic data are analyzed to determine the time, 

location, depth, and magnitude of earthquakes. Mapping earthquake activity 

allows HVO scientists to track the subsurface movement of magma.

All Hawaiian eruptions are accompanied by volcanic tremor. Quite distinct from the discrete seismic shocks associated with rupture-caused earthquakes, volcanic tremor is a continuous vibration of the ground caused by 

movement of fluids (magma or gas). Volcanic tremor generally is detectable 

and recorded only by seismic instruments; however, if especially vigorous, 

tremor can be felt by people as far as 5 miles from an eruption site.

Above center: On this seismograph, a sharp-needle pen “writes” the seismic signatures with a hot stylus on heatsensitive paper wrapped around a recording drum. (USGS photograph by J.D. Griggs.) For modern-day precise 

monitoring, however, HVO records and analyzes seismic activity with computer recording and processing systems. 

Left: Examples of common seismic signatures typically recorded before and during eruptions. Above right: An 

example of a computer display of digital traces of seismic signals recorded by the network of broadband seismometers around Kïlauea summit. Here, we see the seismic signals produced by the explosions on the morning of March 

19, 2008, that initiated the eruption within Halemau‘ma‘u Crater, which still continues in 2010. (Modified from image 

of Phillip B. Dawson, USGS.)

Short-period earthquake

distant

nearby

Long-period earthquake

Volcanic tremor
19

Principal volcano-monitoring networks operated by the 

Hawaiian Volcano Observatory. The configurations of the 

networks evolve with time—to adapt to new technologies, to 

upgrade systems, and to meet changing needs dictated by 

eruptive activity.

0

0 10 miles

20 km

156 ̊ 00' 155 ̊ 30' 155 ̊ 00'

19 ̊ 00'

19 ̊ 30'

20 ̊ 00'

156 ̊ 00' 155 ̊ 30' 155 ̊ 00'

156 ̊ 00' 155 ̊ 30' 155 ̊ 00'

19 ̊ 00'

19 ̊ 30'

20 ̊ 00'

19 ̊ 00'

19 ̊ 30'

20 ̊ 00'

Mauna Kea

Kohala

Mauna

 Loa

Hualälai

Kïlauea

HVO

Seismic station

0

0 10 miles

20 km

156 ̊ 00' 155 ̊ 30' 155 ̊ 00'

19 ̊ 00'

19 ̊ 30'

20 ̊ 00'

Mauna Kea

Kohala

Mauna

 Loa

Hualälai

Kïlauea

Level lines

Continuously recording

 GPS site

GPS survey benchmark

GPS network

0

0 10 miles

20 km

0

0 10 miles

20 km

Tilt/strain network

Strainmeter

Electronic tiltmeter

Tilt survey array

Mauna Kea

Kohala

Mauna

 Loa

Hualälai

Kïlauea

Mauna Kea

Kohala

Mauna

 Loa

Hualälai

Kïlauea

Volcano-Monitoring Networks on Hawai‘i
20

30

0

10

20

30

0

0

200

2500

2000

1500

1000

500

0

40 41 42 43 44 45 46 47

400

600

800

1000

10

20

Tilt, in

microradians

Number of volcanic

summit earthquakes

Number of tectonic

summit earthquakes

No data

No data

Pu‘u ‘Ö‘ö - Kupaianaha Eruption, January - June 1986

January February March April May

No

data

June

Summit

tilt

Eruptive

episode

Short-period

(tectonic)

earthquakes

Long-period

(volcanic )

earthquakes

600

800

400

200

600

800

400

200

0

1956 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010

Tilt, in microradians

Summit Tilt of Kïlauea 1956–2009

Yea r

Deflation Inflation

Kïlauea Iki

eruption

Pu‘u ‘Ö‘ö - Kupaianaha eruption

(still continuing in 2010)

Mauna Ulu

eruption

Halema‘uma‘u

eruption

= Eruption

= Intrusion

Above: The common pattern of gradual inflation, followed by abrupt deflation, is well demonstrated by changes in “tilt” of the volcano’s slopes associated with major eruptions and intrusions at Kïlauea. A change in tilt of 1 microradian equals an angle of 0.00006 

degree. With the onset of the Pu‘u ‘Ö‘ö-Kupaianaha eruption in 1983, Kïlauea summit underwent long-term net deflation until late 

2003, when this trend reversed for several years. Summit deflation resumed in 2007 and has continued through 2010. (Tilt data plotted by Asta Miklius, USGS.) Below: A detailed look at a 6-month segment of the tilt record reveals similar inflation-deflation patterns 

for the high-lava-fountaining episodes of the Pu‘u ‘Ö‘ö-Kupaianaha eruption, even though the tilt changes and time intervals involved 

are much smaller (compare scales of the two diagrams). Also shown are variation patterns of the two types of earthquakes that commonly precede and accompany Kïlauea eruptions.
21

Anatomy of an Eruption: The Inflation-Deflation Cycle

Kïlauea's behavior during and between eruptions is remarkably regular. 

Monitoring instruments placed at the volcano's summit can be used to trace 

the cycles of gradual inflation, during which the reservoir fills with magma, 

and abrupt deflation, when the reservoir partially empties to deliver magma 

to an eruption. These recurring inflation-deflation cycles are precisely 

recorded by tiltmeters and seismometers, as is well displayed during the 

1983-to-present Pu‘u ‘Ö‘ö-Kupaianaha eruption.

During inflation, rocks surrounding the magma reservoir become 

stressed. This stress is partly relieved by increasing numbers of earthquakes 

that are too small to be felt but are easily recorded by seismometers at 

Kïlauea’s summit. These earthquakes (called short-period or tectonic) are 

recorded as high-frequency features on a seismograph. During deflation 

the stress is completely relieved. The short-period earthquakes stop, but 

their place is taken by low-frequency earthquakes (called long-period or 

volcanic), which reflect adjustments related to the exit of magma from the 

summit reservoir to feed the eruption. Long-period earthquakes are related 

to harmonic tremor, the continuous vibration of the ground associated with 

underground magma or fluid movement.

Kïlauea’s distinctive inflation-deflation pattern is seen in nearly every 

eruption, regardless of the size of the observed tilt changes. For example, 

the pattern is dramatically apparent for the Kïlauea Iki eruption in 1959, 

which involved the largest tilt change recorded to date (nearly 300 microradians). The same pattern is also well seen in activity involving smaller tilt 

changes (20 microradians or less), as observed during the continuous eruption of the Pu‘u ‘Ö‘ö vent in January–June 1986.

Less commonly observed at Kïlauea in the summit tilt record, and 

sometimes also recorded by a tiltmeter at Pu‘u ‘Ö‘ö, is a deflation-inflation

pattern (called a “DI tilt event”) that typically lasts less than a week. A DI 

event is characterized by an abrupt deflation as large as a few microradians 

lasting several hours to 2–3 days, which is followed by a sharp inflation of 

about equal tilt change over several days. This type of tilt pattern was first 

recognized in August 2000, but it has become increasingly more common 

since 2004, especially after 2008. The eruption dynamics of DI events are 

not yet understood. However, these events tend to correlate with lava pulses 

and (or) pauses during activity at the Pu‘u ‘Ö‘ö vent since July 2007 and are 

thought to reflect variations in magma supply to a shallow storage zone just 

east of Halemau‘uma‘u Crater.

Forecasting Eruptions

A prime objective of volcano monitoring is to detect the early signs of 

possible eruptive activity and to make reliable eruption forecasts. Although 

considerable advances have been made in volcano monitoring in Hawai‘i, 

accurate long-term forecasts (one year or longer) still elude scientists. However, the capability for short-term forecasts (hours to months), especially of 

Kïlauea’s activity, is much better.

Accurate short-term forecasts of Hawaiian eruptions are based primarily on analyses of inflation-deflation patterns, made possible through 

decades of study of ground deformation (tilt) and seismicity (earthquakes 

and volcanic tremor). When the level of inflation and the short-period 

earthquake counts are high, the volcano is ready to erupt. Sometimes there 

is a delay of days or even weeks before eruption occurs, but scientists are 

alerted by the patterns and are ready to study the eventual outbreak when it 

does occur. Eruption is signaled by the beginning of sharp deflation accompanied by either harmonic tremor or earthquakes close to the site of eruptive 

outbreak. These signals are usually seen an hour to several hours before lava 

breaks the surface, allowing scientists enough time to travel to the likely site 

of activity and issue warnings.

The combination of seismic and ground-deformation monitoring has 

proved to be the most useful and reliable method in the short-term forecasting of Kïlauea eruptions. However, some other techniques being developed 

or tested show promise and should increase future forecasting capabilities. 

These newer methods include the monitoring of changes in the composition 

and volume of volcanic gas emissions, such as sulfur dioxide, carbon dioxide, hydrogen, helium, and radon; magnetic and gravitational fields of the 

volcano; and various geoelectrical properties of the volcano. Some of the 

gas-monitoring techniques can make measurements with parts-per-million 

(ppm) precision. For gases and fluids, one ppm can pictured in terms of a 

very dry martini—1 drop of vermouth in 16 gallons of gin!
22

In recent decades, great strides have been made in gas monitoring using 

satellite- and ground-based remote-sensing instrumentation and techniques. 

With various types of field-portable spectrometers, HVO scientists continuously measure the emission of sulfur dioxide and carbon dioxide at 

the summit calderas of Kïlauea and Mauna Loa. They also make repeated, 

though not continuous, measurements of gas output at eruptive vents and 

other specific sites. HVO’s near-real-time monitoring of volcanic-gas emissions from the ongoing eruptions at Pu‘u ‘Ö‘ö and Halema‘uma‘u provides 

key information to the National Park Service and Hawai‘i County for 

assessment of potential hazards to visitors and residents from volcanic air 

pollution (discussed later).

Other monitoring techniques are also proving useful—data from 

magnetic, gravity, and geoelectrical studies provide diagnostic information 

about the subsurface configuration and workings of a volcanic system. So 

far, data from the nonseismic and nongeodetic monitoring techniques have 

not revealed definitive short-term precursors to possible eruptions. However, 

they have identified underground movement of magma from one place to 

another, sometimes unaccompanied by measurable ground deformation or 

earthquakes. Experience on well-studied active volcanoes in Hawai‘i and 

elsewhere has shown that the best volcano monitoring is achieved by using a 

combination of approaches rather than relying on any single method.

At present, HVO scientists generally can identify an increased potential 

for Kïlauea or Mauna Loa eruptions and the likely locations of lava outbreaks, but they cannot make specific forecasts of the exact timing or size of 

an expected eruption. However, for a number of Kïlauea eruptions in recent 

decades, the HVO staff has been able to warn officials of Hawai‘i Volcanoes 

National Park and (or) the County of Hawai‘i, hours to days in advance, to 

take safety measures, if deemed necessary.

A scientist uses a correlation spectrometer (COSPEC) to measure 

the emission of sulfur dioxide gas from the Pu‘u ‘Ö‘ö vent. This 

instrument—originally developed to monitor atmospheric pollution by 

measuring sulfur dioxide discharge from industrial smokestacks—

has largely been replaced by instruments that are more sensitive, 

lighter in weight, less cumbersome, and of lower cost. (USGS photograph by J.D. Griggs.) 

A Fourier Transform InfraRed (FTIR) spectrometer is used to analyze volcanic gases emitted from a glowing vent. This instrument (closeup in inset) is capable of analyzing many 

other species of volcanic gases in addition to sulfur oxide and carbon dioxide. (USGS 

photograph by A.J. Sutton.)
23

Kīlauea’s Volcanic

“Plumbing System” 

From decades of monitoring and research 

at HVO, Kïlauea’s volcanic "plumbing system" 

is now relatively well understood. This system 

links the processes involved in the formation, 

transport, storage, and, ultimately, eruption of 

magma to sustain Hawai‘i's active volcanoes.

Kïlauea’s plumbing system is believed to 

extend deep beneath the Earth's surface, where 

magma is generated by partial melting of material beneath the Pacific Plate as it passes over 

the Hawaiian hot spot. This belief is based on 

the persistent recurrence of earthquakes 30 

miles or more beneath Hawai‘i. Earthquakes 

occurring 20–30 miles beneath the surface 

are probably related to the accumulation and 

upward movement of magma. Seismic data for 

levels shallower than 20 miles can be interpreted to define diffuse zones of continuous 

magma rise, one leading to Kïlauea and another 

to Mauna Loa.

Before Kïlauea erupts, most of the magma 

entering the volcano is stored temporarily within 

a shallow reservoir. Earthquake data and grounddeformation patterns suggest that this reservoir 

is located 1 to 4 miles beneath the summit and 

consists of pockets of magma concentrated 

within a crudely spherical space about 3 miles 

across. Earthquakes do not occur within the reservoir, because liquid magma does not rupture to 

generate seismic waves.

Kïlauea eruptions occur either at its summit 

or within two well-defined swaths (called rift 

zones) that radiate from the summit. During 

summit eruptions, the magma reservoir deflates 

only slightly, if at all. This relation implies 

that the rate at which magma is erupted nearly 

equals that at which the reservoir is refilled by 

new magma from depth. During an eruption in 

a rift zone, called a rift or flank eruption, however, the summit region undergoes a significant 

and abrupt deflation as magma moves quickly 

from the summit reservoir into the rift zone. 

Similar summit deflation occurs during a rift 

intrusion, in which magma injected into the rift 

zone remains stored underground there rather 

than breaking the ground surface in an eruption. 

When the rift eruption or rift intrusion ends, the 

summit region reinflates as the shallow reservoir 

is refilled by magma from depth. Small pockets 

of summit-fed magma may be stored for a while 

within a rift zone and form transient secondary 

reservoirs.

The volcanic plumbing system for Mauna 

Loa is less well known. Analysis of data from 

the well-monitored 1975 and 1984 eruptions, 

however, suggests that the essential features of 

Mauna Loa's plumbing system are similar to 

Kïlauea’s, despite the difference in size between 

the two volcanoes. Mauna Loa's magma reservoir also may be larger than Kïlauea’s, which 

would be consistent with the observations that 

Mauna Loa eruptions tend to be characterized by 

higher lava-output rates, longer eruptive fissures, 

and larger lava flows.
24

Southwest Rift Zone

Shallow Magma

Reservoir

Mauna Ulu

East Rift Zone

Depth (Miles)

0

5

10

15

20

25

Halema‘uma‘u

Kïlauea Caldera

Pu‘u ‘Ö‘ö

Hawaiian Volcano

Observatory

Cut-away view looking deep beneath Kïlauea 

Volcano, showing the shallow magma reservoir and 

the principal magma passageways. Areas in yellow 

are the most favorable zones for magma movement (arrows show direction) and storage. Though 

greatly generalized, this depiction of Kïlauea’s 

“plumbing system” is compatible with all known 

scientific information. (Simplified from technical 

illustration of Michael P. Ryan, USGS.)
25

Above: Mount St. Helens, a typical steep-sided 

composite volcano, shortly before its decapitation 

by the May 18, 1980, eruption. (Photograph courtesy of D.R. Pevear, Western Washington University, Bellingham.) Below: Snow-capped Mauna 

Loa, an excellent example of a shield volcano, 

viewed from the Hawaiian Volcano Observatory. 

(USGS photograph by Robert I. Tilling.)

Hawaiian Eruptive Style—

Powerful but Usually Benign

By definition, the adjective eruptive

describes any object or phenomenon associated 

with processes of "bursting forth," "breaking 

out," or "issuing forth suddenly and violently." 

Strictly speaking, no eruption is truly nonexplosive, but most Hawaiian eruptions closely 

approach being such. Indeed, volcanologists 

worldwide use the term "Hawaiian" to characterize similar, relatively gentle eruptive style at 

other volcanoes.

Typical Activity: “Nonexplosive” or 

Weakly Explosive

With infrequent exceptions, eruptions 

of Hawaiian volcanoes generally are weakly 

explosive or nonexplosive and relatively benign. 

Hawaiian eruptions are typically gentle because 

their lava is highly fluid and thus tends to flow 

freely both beneath the surface and upon eruption. In contrast, lava of volcanoes located along 

plate margins, such as Mount St. Helens, generally is more viscous (less fluid) and tends to 

fragment, often very explosively, during eruption. Highly fluid lava favors the nonviolent 

release of the expanding volcanic gases that 

drive eruptions. In contrast, viscous magma 

suppresses easy escape of volcanic gases, which 

results in pressure buildup underground and 

ultimately in explosive gas release and magma 

fragmentation.

Lava viscosity ("stiffness" or "resistance 

to flow") is largely determined by the chemical composition and temperature of the magma, 

the amount of crystals in the magma, and the 

gas content. The low viscosity (high fluidity) of 

Hawaiian lavas derives mainly from its basaltic

composition, characterized by more iron (Fe), 

magnesium (Mg), calcium (Ca), and titanium 

(Ti), and less silicon (Si), aluminum (Al), sodium 

(Na), and potassium (K), compared to viscous 

lavas, such as the dacite erupted explosively at 

Mount St. Helens in 1980. In the graph (page 

26) showing compositional differences between 

Hawaiian basalt and Mount St. Helens dacite, 

the chemical elements are given as oxides [(for 

example, calcium as calcium oxide (CaO)]. 

Basalt is a dark volcanic rock composed of small 

crystals and glass, whereas dacite, also finegrained or glassy, is generally much lighter in 

color.

Hawaiian eruptions typically begin with 

lava fountains spouting from a series of nearly 

continuous fissures, evoking colorful popular 

descriptions such as “curtains of lava" or “curtains of fire." As most eruptions progress, lavafountain activity becomes localized at a single 

vent (an opening from which lava erupts), generally within hours of the initial outbreak. Depending on the shape of the vent and other eruptive 

conditions, lava fountains can vary widely in 

form, size, and duration.

It should not be forgotten, however, that 

Kïlauea also can be violently explosive. Each 

of the last two periods of significant historical 

explosive activity, in 1790 and 1924, was probably driven by expanding steam from heated 

ground or surface water, and each produced 

fatalities. Three smaller explosive bursts have 

even occurred at Pu‘u ‘Ö‘ö, one in 1987 and 

two in the 1990s, peppering the surface of the 

cone with heavy rocks. Since 2008, several small 

explosive events at Halema‘uma‘u Crater have 

showered the nearby ground with ash and blocky 

debris. In fact, Kïlauea erupts explosively about 

as often as does Mount St. Helens, and in the 

past 1,500 years ash from Kïlauea has risen into 

or above the jet stream at least six times. Should 

such a powerful explosive eruption occur today, 
26

Hawaiian Basalt

Mount St. Helens Dacite

2.4 0.6 1.4

2.0 0.6 1.0 1.3

48.4 13.2 11.2* 9.7 10.3 2.8

63.5 17.6 4.2* 5.2 4.6

Silicon Aluminum Magnesium Calcium Sodium Potassium Titanium Other

elements

Iron *

*Total iron as ferrous oxide (FeO)

Above: This graph illustrates the differences in average chemical compositions 

of lava erupted by Hawaiian volcanoes 

and during the 1980 eruption of Mount 

St. Helens. The number for each chemical element gives the amount (in weight 

percent) of that element (expressed 

as oxide) contained in the lava. Left:

Note the contrast in color and texture 

between Hawaiian basalt and Mount St. 

Helens dacite. (USGS photograph by J.D. 

Griggs).

Hawaiian basalt Mount St. Helens dacite

the resulting ash cloud could severely disrupt 

trans-Pacific air traffic.

An explosive eruption at Mauna Loa never 

has been witnessed in recorded history, but field 

mapping has shown ample geologic evidence 

for prehistoric explosive eruptions. Around its 

summit caldera, Moku‘äweoweo, lie several 

deposits of ancient explosive debris, including a 

few blocks as large as about 7 feet across found 

near the summit. Smaller blocks were thrown 

out to distances as great as 2 miles. Preliminary studies suggest that at least three separate 

explosive events occurred, taking place about a 

thousand years ago or perhaps earlier.
Lava fountains can vary widely 

in size and form. Center: A 

1,500-foot-high fountain jets 

from the Pu‘u ‘Ö‘ö vent in 1984; 

note silhouette of helicopter for 

scale. (Photograph by Mardie 

Lane, National Park Service.) 

Top right: An aerial view of 

a discontinuous row of lava 

fountains 50–100 feet high 

during the August 1971 Kïlauea 

summit eruption. (Photograph 

courtesy of the National Park 

Service.) Bottom right: A 

line of lava fountains during 

the 1984 Mauna Loa eruption; 

two scientists (left center) give 

scale. (USGS photograph by 

Richard B. Moore.)

27
28

Above: Mildly explosive entry of lava into 

the ocean, after traveling about 7 miles from 

the Pu‘u ‘Ö‘ö vent in February 1988. (USGS 

photograph by Taeko Jane Takahashi.) Left 

below: A 40-foot arching "hose" fountain 

spurts from Pu‘u ‘Ö‘ö vent in February 

1983. (USGS photograph by J.D. Griggs.) 

Right below: A "dome" fountain, about 

45 feet high, plays continuously for hours 

during the 1969–71 Mauna Ulu eruption of 

Kïlauea. (USGS photograph by Jeffrey B. 

Judd.)
29

During the 1959 Kïlauea Iki eruption, one lava fountain shot up 1,900 feet, the record 

height for historical Hawaiian eruptions. A fountain in 1969 from Mauna Ulu rose 1,770 feet. 

More recently, some of the vigorous eruptive episodes of the 1983–1986 Pu‘u ‘Ö‘ö vent produced lava fountains at least 1,500 feet high. However, when the rate of gas release is too low 

to cause high fountaining, lava merely wells up nonexplosively and flows quietly or oozes 

from the vent. Though impressive, even these spectacularly high lava fountains are products 

of relatively weak explosive activity. By comparison, the May 1980 explosive eruption of 

Mount St. Helens sent ash more than 64,000 feet up into the atmosphere.

Molten lava falling from fountains and quietly erupting from vents often forms long 

incandescent lava streams or lava flows, giving rise to the popular but misleading term "rivers 

of fire." This colorful term is misleading because the lava flows are molten rock and hence do 

not burn: “fire” is involved only if the flows ignite and burn vegetation and wooden structures 

along their paths. Hawaiian lava flows generally advance at average speeds of a few miles 

per hour—a pace slower than that of a person walking quickly or running. However, if a lava 

flow is confined within a channel or lava tube, it can advance more quickly, especially if the 

ground is steep. For short periods of time during some Mauna Loa and Kïlauea eruptions, 

several lava flows have been clocked rushing down steep slopes at 35 miles per hour! But this 

is unusual.

During long-lived eruptions, lava flows tend to become "channeled" into a few main 

streams. Overflows of lava from these streams solidify quickly and plaster on to the channel 

walls, building natural levees or ramparts that allow the level of the lava to rise. Lava streams 

that flow steadily in a confined channel for many hours to days may develop a solid crust or 

roof and thus change gradually into streams within lava tubes. Because the walls and roofs of 

such tubes are good thermal insulators, lava flowing through them can remain hot and fluid 

much longer than surface flows. Tube-fed lava can be transported for great distances from the 

eruption sites. For example, during both the 1969–74 Mauna Ulu eruption and the 1983–present Pu‘u ‘Ö‘ö-Kupaianaha eruption, many lava flows traveled underground through lava-tube 

systems more than 7 miles long to enter the ocean. In fact, lava transported through tubes has 

entered the ocean 75 percent of the time since 1986, with the longest lived of these entries 

lasting 22 months (May 2005–March 2007) at East Lae‘apuki.

A 1,500-foot-high lava fountain erupts from Pu‘u ‘Ö‘ö in September 1984. Red-hot blobs of liquid 

lava ejected high into the air are rapidly cooled in flight, forming a billowing black cloud of cinders 

and Pele’s hair and Pele’s tears that can be carried many miles downwind from the vent. Low lava 

fountains play from fissures at the base of the cone (foreground). (USGS photograph by Christina 

Heliker.)
30

Center: Aerial view of a braided 

lava flow during the 1984 Mauna 

Loa eruption. With imagination, 

some people see in this flow pattern the figure of Pele, Goddess of 

Volcanoes, with her arms raised. 

(Photograph by Katia Krafft, Centre 

de Volcanologie, Cernay, France.) 

Top right: This view into a “skylight” (collapsed roof) of a lava tube 

during the Pu‘u ‘Ö‘ö eruption shows 

how Thurston Lava Tube might have 

looked when it was "active" a few 

hundred years ago. Here, geologists 

sample molten lava flowing through 

the tube using a sledgehammer 

head attached to a steel cable. The 

lava-coated hammer is dangling 

at the edge of the skylight, above 

the surface of the reddish flowing 

lava stream. (USGS photograph by 

J.D. Griggs.) Bottom right: Inside 

the Thurston Lava Tube (Nähuku), 

Hawai‘i Volcanoes National Park. 

(Photograph by Peter MouginisMark, University of Hawai‘i.)
31

Above: Lava cascades plunge 160 feet into Lua Hou Crater on the upper 

part of Mauna Loa's southwest rift zone during the volcano's July 1975 

eruption. (USGS photograph by Robin T. Holcomb.) Left: A clockwisecirculating lava lake (nearly 500 feet across) formed in the west pit of 

Pauahi Crater, on Kïlauea’s upper east rift zone, during the November 1973 

eruption. Small bright spots seen on the lake surface are caused by floating 

trees bursting into flames. (USGS photograph by Robert I. Tilling.)

Lava streams that plunge over cliffs or the steep walls of craters 

form impressive lava cascades or lava falls. Where cascades spill 

into preexisting craters, lava lakes or lava ponds may form. Such 

lakes are considered inactive and generally form a solid crust within 

hours or a few days. The still-molten lava beneath this crust can take 

weeks to years, depending on the lake size and depth, to cool and 

solidify completely. Lava lakes formed at the site of, and sustained 

by, active eruptive vents are considered active. The crust formed 

on these active lakes is not permanent and repeatedly breaks up in 

response to circulation and sloshing of the underlying still-molten 

lava. Repeated overflows from active lava lakes raise lake level by 

rampart construction similar to overflowing lava streams. By this 

process of levee growth, lakes may become perched many feet above 

their surroundings.
32

Surface movements of active lava lakes on Kïlauea’s east rift zone provide a very small scale analogy to 

movements of Earth's tectonic plates. Upper left: Vigorous currents within the active 1987 Kupaianaha 

lava lake break the crust into separate slabs. (USGS photograph by J.D. Griggs.) Lower left: In the 1971 

Mauna Ulu lava lake, moving slabs, ranging in size from a few feet to several tens of feet across but only a 

few inches thick, are rafted by circulating lava beneath. (USGS photograph by Wendell A. Duffield.) Right:

Close-up views of the Mauna Ulu lava lake surface to show small-scale analogs to the three common types 

of tectonic plate boundaries: convergent boundary between two slabs of crust (upper); divergent or spreading boundaries between three slabs (middle); and transform fault offsetting a spreading boundary between 

two slabs (lower). (USGS photographs by Wendell A. Duffield.)

At Kïlauea’s summit, the century-long 

lava-lake activity in Halema‘uma‘u Crater 

ceased after the 1924 explosive eruption. 

However, a lava lake was active in the 

crater for about 8 months during a 1967–68 

eruption. It was not until the 1969–74 

Mauna Ulu eruptions on Kïlauea’s upper 

east rift zone, however, that scientists had 

an opportunity to observe the development 

and behavior of a long-lived active lava lake 

outside the summit region of a Hawaiian 

volcano. The lava-lake behavior at Mauna 

Ulu, including movement and collision 

of thin plates of surface crust floating on 

circulating molten lava, provided a smallscale version of the Earth's global plate 

tectonics (see images this page). Lava-lake 

flow dynamics have been observed during 

Kïlauea’s 1983–present Pu‘u ‘Ö‘ö-Kupaianaha eruption, mostly recently within the 

pit vent at Halema‘uma‘u.
33

Infrequent Explosive Activity

Explosive eruptions that deposit large volumes of pyroclastic debris over large areas—like 

the May 1980 eruption of Mount St. Helens— 

are relatively rare at Hawaiian volcanoes. The 

term "pyroclastic"—derived from Greek pyro

(fire) and klastos (broken)—is a general term 

to describe all types of fragmented new magma 

or old rock ejected during explosive eruptions. 

Relatively few Hawaiian eruptions have been 

violently explosive, based on the scarcity of 

pyroclastic deposits. In contrast, some volcanic 

chains formed along the convergent boundaries 

of the Earth's tectonic plates contain 90 percent or more pyroclastic material. Nonetheless, 

explosive eruptions occur at Hawaiian volcanoes every few decades to centuries—as often 

as at many “explosive” volcanoes. In Hawai‘i, 

however, explosive events tend to be overlooked, 

because gentle effusive eruptions are by far the 

most common.

In 1790, a series of major explosive eruptions, which probably lasted a few days to a few 

weeks, culminated three centuries of intermittent explosive activity that deposited a blanket 

of pyroclastic debris as much as 35 feet thick in 

and around Kïlauea's summit. At the time of the 

1790 eruptions, a band of Hawaiian warriors, 

led by Keöua, chief of the Ka‘ü district, was 

marching across the summit region of Kïlauea 

to battle the army of a cousin and rival chief, 

Kamehameha. Some of Keöua's warriors were 

caught in a hot, high-velocity explosion cloud, 

composed mainly of volcanic steam and other 

gases and hot ash. This cloud, termed a pyroclastic surge, moved swiftly along the ground 

surface and killed a number of people, estimates 

ranging widely, from about 80 to 5,400. Had the 

Hawaiian Volcano Observatory been at its present location on the summit of Kïlauea in 1790, it 

almost certainly would have been destroyed. An 

eyewitness account indicates that an ash column 

probably rose at least 30,000 feet into the sky, 

as has occurred in five other explosive eruptions in the past 1,500 years. Such high-rising 

This footprint and thousands of others are preserved in two muddy ash deposits of Kïlauea's 

explosive eruptions in the 18th centuries. The prints 

in the younger deposit were left by Hawaiians who 

survived the explosions in 1790 from the summit of 

Kïlauea, several miles away. (Photograph by James 

F. Martin, National Park Service.)

ash columns from Kïlauea could pose a volcanic 

hazard to today’s jet aircraft flying at cruise-level 

altitudes (around 30,000 feet).

A much less energetic explosive eruption 

took place at Halema‘uma‘u Crater in May 

1924. Three months before the eruption, the 

long-lived lava lake in Halema‘uma‘u played 

actively about 150 feet below the crater rim. 

Beginning in February, the lake surface began 

to drop rapidly, and before long the lake drained 

entirely, exposing the crater floor. Throughout 

March and April, the crater floor itself subsided, 

apparently in response to magma moving out of 

the summit reservoir into the east rift zone. By 

May 6, the floor of Halema‘uma‘u had dropped 

more than 600 feet below the crater rim.

A series of steam-blast explosions began 

during the night of May 10–11, 1924, at 

Halema‘uma‘u and continued vigorously for 

more than two weeks. Each explosive pulse 

lasted from a few minutes to 7 hours; the most 

powerful ones sent ash plumes more than a 

mile high and hurled large blocks, some weighing several tons, more than a half mile from 

Halema‘uma‘u. Many of these blocks were red 

hot. A photographer, who ventured too close to 

the crater, was struck by a falling block during 

the largest explosion on May 18 and died that 

evening from his injuries. When the explosions 

ended, Halema‘uma‘u was about twice as wide 

and eight times as deep as 3 months earlier.

The 1790 and 1924 eruptions were explosive because they involved the violent mixing of 

groundwater and magma or hot rocks. During 

both eruptions, as the magma column subsided 
34

Guests at a wedding reception pose in May 

1924 at Kïlauea Volcano as a large explosion cloud rises thousands of feet into the air 

above Halema‘uma‘u Crater. Given the data 

from recent studies, their location would now 

be considered too close for safety. (Photograph courtesy of the Bishop Museum, 

Honolulu.)

in the vent, groundwater circulating around the 

vent came into sudden contact with hot material 

and flashed explosively to steam. Both eruptions ejected mainly chunks of solid, hot older 

rocks—only a few of the fragments were formed 

from new magma. Explosions before 1790 

expelled fragments of solid, older rocks and new 

magmatic material, suggesting that groundwater 

mixed with both. Though impressive, the 1924 

explosions produced only about one-tenth of 1 

percent of the volume of the explosions during 

the period 1500–1790.

Pyroclastic deposits exposed at Kïlauea 

indicate that about two dozen major explosive 

eruptions have occurred during the past 50,000 

years. Mauna Loa apparently has had less 

frequent explosive eruptions during the same 

time interval. Judging by their distribution and 

thickness, Kïlauea’s prehistoric pyroclastic 

deposits had to be produced by explosive eruptions at least as strong as the 1790 eruption. One 

explosion about 1,000–1,300 years ago was even 

several times more powerful.

A special type of explosive activity, called 

a littoral explosion, occasionally results when 

active lava flows enter the ocean. Seawater 

comes into contact with the hot inner parts of 

the lava flow and flashes into steam, triggering 

an explosive spray of fragments derived from 

both the solidified outer part of the lava flow 
35

Center: Molten lava is shredded by littoral explosions upon entry into the ocean during the 1969–71 

Mauna Ulu eruption. (USGS photograph by Donald 

W. Peterson.) Top right: Pu‘u o Mahana, originally 

thought to be a prehistoric littoral cone of Mauna 

Loa (see text), is the site of the Island of Hawai‘i's 

green-sand beach. (USGS photograph by Robert I. 

Tilling.) Bottom right: Closeup of the green sand, 

which obtains its color from wave-concentrated 

grains of the mineral olivine. (USGS photograph by 

Robert I. Tilling.)

as well as its still-molten core. Once formed, 

these chilled fragments quickly begin to disintegrate into smaller bits because of wave action. 

Because of their surf-zone locations, most small 

fragmental deposits from littoral explosions are 

quickly removed by erosive wave action. Larger 

deposits, however, can be more permanent and 

form littoral cones. About 50 such cones, prehistoric and historical, dot the shores of Mauna 

Loa and Kïlauea volcanoes. A well-studied 

example of a littoral cone is the 240-feet-high 

Pu‘u Hou, located 5 miles northwest of the 

southernmost point of the Island of Hawai‘i; 

it formed when lava from the 1868 eruption of 

Mauna Loa entered the ocean.

Fragmental deposits from littoral explosions 

and from surf breaking up streams of flowing 

lava can be reworked and concentrated along 

shorelines by wave action to quickly form blacksand beaches, composed of sand-size grains of 

the shattered black glassy lava. Many of these 

“instant” beaches, particularly if small, are 

ephemeral features, soon to be eroded by surf 

or covered by younger lava flows from ongoing 

eruption. Larger beaches, however, can form 

longer lasting landscapes that become popular 

visitor destinations. One of Hawai‘i’s most beautiful and photographed black-sand beaches was 

at Kaimü Bay, on the Puna coast along Kïlauea 

Volcano’s southeastern flank. Unfortunately, 

Kaimü beach met its demise when it was completely buried by lava erupted from the Kupaianaha vent in mid-1990. 

Pu‘u o Mahana, a small prehistoric cone on 

the coast 3 miles northeast of the island’s south 

tip, is the site of Hawai‘i's famous "green-sand 

beach." This beach obtains its color from the 

shiny green mineral olivine (a magnesium-iron 

silicate) eroded from the cone and concentrated 

by wave action. Peridot, a gem-quality variety 

of olivine, is the birthstone for the month of 

August. Pu‘u o Mahana was believed to have 

originated from littoral explosions, but recent 

studies suggest that it probably formed inland, 

at an elevation more than 300 feet above current 

sea level. This cone’s present-day position at the 

water’s edge reflects the gradual sinking of the 

Island of Hawai‘i after Pu‘u o Mahana formed 

tens of thousands of years ago.
36

Night-time view of the vigorous and spectacular littoral explosions that occurred during July 2008, when lava from the Pu‘u ‘Ö‘ö vent entered the ocean 

at Waikupanaha. The size of the explosions can be appreciated from the silhouettes of the unwary onlookers (bottom left), who are much too close to the 

action for their safety. (USGS photograph by Michael Poland.)
37

Hawaiian Volcanic Products, 

Landforms, and Structures 

The volcanic mountains of Hawai‘i have 

been built by the accumulation of basaltic lava 

flows erupted, mostly nonexplosively, over 

hundreds of thousands of years, as the Pacific 

Plate moved northwestward over the Hawaiian 

hot spot. In contrast, volcanic mountains in the 

zones where tectonic plates converge (subduction zones), such as Mount St. Helens and the 

other Cascade Range volcanoes, have been built 

primarily by pyroclastic debris produced by 

explosive eruptions. Even though they both form 

linear mountain ranges, Hawaiian volcanoes 

differ greatly from Cascade volcanoes in mode 

of origin and types of volcanic rocks.

Molten lava can solidify in a variety of 

ways, depending on eruption dynamics and gas 

content of the erupting magma. Volcanic products of Hawaiian eruptions are mostly dark in 

color but vary widely in form and texture.

Lava Flows

Lava flows form more than 99 percent of the 

above-sea parts of Hawaiian volcanoes. Pähoehoe (pronounced "PAH-hoy-hoy") and ‘a‘ä

(pronounced "ah-AH") are the two main types 

of Hawaiian lava flows, and these two Hawaiian 

names, introduced into the scientific literature in 

the early 19th century, are now used by volcanologists worldwide to describe similar lavaflow types. Pähoehoe is lava that in solidified 

form is characterized by a smooth, billowy, or 

ropy surface, while ‘a‘ä is lava that has a rough, 

jagged, spiny, and generally clinkery surface. 

In thick ‘a‘ä flows, the rubbly surface of loose 

block and clinkers hides a massive, relatively 

dense interior.

The contrast between the surfaces of 

pähoehoe and ‘a‘ä flows is immediately obvious 

to anyone hiking Hawaiian lava fields. Walking on dense pähoehoe can be almost as easy 

as strolling on a paved sidewalk. But walking 

across ‘a‘ä is like scrambling over a buildingdemolition site or battle zone, strewn with 

loose, unstable debris of all shapes and sizes. 

The jagged rubble of ‘a‘ä flows quickly destroys 

field boots and, should the hiker stumble or fall 

(not at all uncommon), it can tear clothing and 

flesh.

An active clinkery ‘a‘ä flow advances over the 

smooth surface of an earlier erupted pähoehoe 

flow in 1993. Both flows originated from the Pu‘u 

‘Ö‘ö eruption. (USGS photograph by Christina 

Heliker.)

Closer views of the surfaces of an ‘a‘ä flow (above) 

and a pähoehoe flow (below). (USGS photographs 

by J.D. Griggs and Taeko Jane Takahashi, respectively.)
38

Many Hawaiian lava flows solidify as pähoehoe 

throughout their length, and a few flows solidify 

completely as ‘a‘ä. Most flows, however, consist of 

both pähoehoe and ‘a‘ä in widely varying proportions. Strictly speaking, the terms pähoehoe and 

‘a‘ä should be used to describe completely solidified 

flows and not to moving lava. Yet, many scientists 

find it convenient to apply these terms to describe 

different parts and aspects of still-moving lava flows. 

In a given active flow, pähoehoe upstream commonly 

changes to ‘a‘ä downstream, but, under certain circumstances, ‘a‘ä-crusted lava flows can also change 

into pähoehoe flows. The explanation for changes in 

flow type depends on the delicate balance between 

the initial gas content of the lava, the changes in lava 

viscosity, the rate of deformation ("shear strain"), 

and increasing amounts of crystals in lava as it flows 

and cools. Once this critical balance is upset, pähoehoe-crusted flows can change to ‘a‘ä, or ‘a‘ä-crusted 

flows can change to pähoehoe.

Hawaiian lava is fluid enough to travel great 

distances, especially if it is transported through lava 

tubes. Excellent thermal insulation provided by tubes 

conserves the heat and fluidity needed for lava to 

flow long distances. The long-distance transport of 

lava through tube systems makes possible the development of the gently sloped volcanic shields. Some 

flows produced during the past 200 years are longer 

than 30 miles; in general, pähoehoe flows tend to be 

longer than ‘a‘ä flows. Lava tubes may be preserved 

when an eruption ends and the lava drains away to 

leave open tunnels. They may be as much as several 

tens of feet in width, and one has been followed 

by spelunkers (cave explorers) for about 18 miles. 

Ancient Hawaiians used lava tubes as places of shelter, burial caves, and water-collection sites (by catching drips through the tube roof). Visitors to Hawai‘i 

Volcanoes National Park can walk through Thurston 

Lava Tube (Nähuku), which formed in a pähoehoe 

flow 500–600 years ago.

Fluid lava erupted or flowing under water can 

produce pillow lava, which forms when molten lava 

breaks through the thin walls of underwater tubes, 

squeezes out like toothpaste, and quickly solidifies 

as irregular, tongue-like lobes or protrusions (similar 

structures can result from the formation of multiple 

pähoehoe toes from tube-fed flows). These processes are repeated countless times, and the resulting protrusions stack one upon another as the lava 

flow advances underwater. The term pillow comes 

from the observation that these stacked protrusions 

are sack- or pillow-shaped in cross section. Typically ranging from less than a foot to several feet in 

diameter, each pillow has a glassy outer skin formed 

by the rapid cooling of lava by water. Much pillow 

lava is erupted under relatively high pressure created by the weight of the overlying water, so there is 

little or no explosive interaction between the hot lava 

and cold water. The bulk of the submarine part of a 

Hawaiian volcano is composed of pillow lavas.

Abundant studies, by remotely controlled deepsea cameras as well as by small, manned research 

submarines, have demonstrated the widespread occurrence of pillow lavas in areas of submarine volcanism. 

It was not until 1970, however, that the underwater 

formation of pillow lava was first directly observed. 

During the 1969–74 Mauna Ulu and the 1983–present 

Pu‘u ‘Ö‘ö-Kupaianaha eruptions of Kïlauea, teams 

of scuba-diving observers watched and filmed lava 

pillows being formed as lava flows entered the sea. 

Well-formed pillows have been studied on the submarine parts of Kïlauea and Mauna Loa, as well as 

the submerged parts of the 1800–1801 lava flows of 

Hualälai Volcano off the west coast of Hawai‘i.

A piece of pillow lava is collected by a 

mechanical arm of a Remotely Operated 

Vehicle (ROV) from great water depths on 

the submerged southern slope of Kïlauea 

Volcano. To collect the sample of choice, the 

mechanical arm is precisely manipulated by 

scientists aboard the ROV’s mother ship on 

the ocean surface. (USGS photograph by 

Peter W. Lipman.)

Scuba divers film an underwater lava flow 

during the Pu‘u ‘Ö‘ö-Kupaianaha eruption. As 

the flow advances, incandescent lava breaks 

through the solidified shell of a pillow-lava 

lobe to form another tongue of lava. (Copyrighted photograph courtesy of Sharkbait 

World Pictures, Kailua-Kona, Hawai‘i.)
39

Another common lava feature is the ponded flow or 

lava lake, the formation of which has been described ear-

lier in connection with the eruptive style of Hawaiian vol-

canoes. Upon solidification, the surface of ponded lava is 

smooth, broken only by polygonal cooling cracks, formed 

in much the same way as shrinkage cracks in mud that has 

been dried by the sun. Many lava lakes have formed and 

been well observed during Kïlauea eruptions, the most 

recent of which were lakes at Kupaianaha (1986–90) and 

Pu‘u ‘Ö‘ö (1988–2006). The now completely solidified 

deep lava lake (443 feet) formed during the November–

December 1959 eruption at Kïlauea Iki Crater is the only 

one of these still visible and easily accessible; most other 

lava lakes have been covered by younger lava flows or are 

not safely accessible.

Hawaiian lava lakes have been investigated in detail 

because they furnish natural crucibles to study the cool-

ing, crystallization, and chemical change of basaltic 

lava. These studies have included drilling holes through 

the solid crust of the lake to measure temperature and 

other properties and to sample the still-molten lava in the 

interior. In physical terms, the formation of the lava lake's 

solid crust by cooling can be compared to the formation 

of a sheet of ice on top of a body of water during a winter 

freeze. Holes drilled in 1988 at Kïlauea Iki indicated that 

parts of the deep interior of the lake still contained some 

molten 1959 lava (as much as 15 percent). The inter-

nal temperatures of the deep, hottest zones of the now 

completely solid lava lake (1,100–1,800°F) will remain 

hundreds of degrees hotter than the surface temperature 

for many more years.

2,140 ̊ F.

1,950 ̊ F.

1,400 ̊ F.

Decreasing temperatures

Left: Three specimens from the 1965 lava lake in 

Makaopuhi Crater (about 5 miles west of Pu‘u ‘Ö‘ö), 

sampled by drilling, as seen under the microscope 

(field of view about 0.05 inch). They were collected at 

three different times during drilling, as the lava-lake 

crust solidified and thickened with cooling. The samples 

represent the still-molten portion of the lava lake at the 

time of sampling and in-hole temperature measure-

ment. The amount and kinds of crystals in these speci-

mens increase with decreasing temperatures as the 

lava lake gradually cools. The fine brownish material 

between the crystals was liquid at the time of sampling 

and chilled to a glass when the sample solidified com-

pletely upon rapid cooling. (USGS photomicrographs 

by Thomas L. Wright.)

Far left: Looking about 400 feet down from the rim of Kïlauea Iki Crater to 

the surface of the lava lake formed in the 1959 eruption and a site of drill-

ing studies in 1975 (oval). Left: Closeup of the Kïlauea Iki drilling opera-

tions. HVO scientists wore asbestos gloves to handle hot drilling steel. 

(USGS photographs by Robin T. Holcomb.)
40

Drilling of lava lakes can be risky. When 

the Mauna Ulu eruption began on May 24, 

1969, lava poured into ‘Alae Crater and 

quickly buried a drill rig and related equip-

ment before they be could be lifted out by 

helicopter! A more common risk during drill-

ing is posed by occasional minor steam explo-

sions in drillholes caused by contact of molten 

lava with the cooling water used in drilling.

Fragmental Volcanic Products

Fragmental volcanic debris is formed 

during mildly explosive activity, such as lava 

fountaining, and, less commonly, during the 

infrequent violently explosive eruptions, such 

as those during 1500–1790 at Kïlauea. Tephra

is the general term now used by volcanolo-

gists for airborne volcanic ejecta of any size. 

Additionally, various terms have been used to 

describe ejecta of different sizes. Fragmental 

volcanic products between 0.1 and about 2.5 

inches in diameter are called lapilli; material 

finer than 0.1 inch is called ash. In a major 

explosive eruption, most of the pyroclastic 

debris would consist of lapilli and ash. Frag-

ments larger than about 2.5 inches are called 

blocks if they were ejected in a solid state and 

volcanic bombs if ejected in semisolid, or 

plastic, condition. Volcanic bombs undergo 

widely varying degrees of aerodynamic 

shaping, depending on their fluidity, during 

the flight through the atmosphere. Based on 

their shapes after they hit the ground, bombs 

are variously described, in graphic terms, as 

"spindle or fusiform," "ribbon," "bread-crust," 

or "cow-dung.”

Some common Hawaiian fragmental volcan-

nic products: (Left, top to bottom): reticu-

lite; Pele's tears; and limu o Pele (see text) 

(USGS photographs by J.D. Griggs); (Right, 

top to bottom): volcanic bombs and accre-

tionary lapilli, spherical accumulations of vol-

canic ash, generally formed during explosive 

eruptions in presence of moisture. (USGS 

photographs by John P. Lockwood.)
41

Top: Shiny strands of volcanic glass, 

called Pele's hair, are commonly found 

downwind from active eruptive vents, skylights of lava tubes, or ocean-entry points 

and form matlike deposits. Below: Volcanic spatter sometimes becomes tightly 

welded to form mounds around active 

vents. (USGS photographs by Margaret 

T. Mangan and Richard B. Moore, respectively.) 

Top: Spattering at a vent, fed by tube-fed lava 

actively flowing beneath it, begins to form a 

hornito during the Pu‘u ‘Ö‘ö eruption in 2002. 

(USGS photograph by Donald A. Swanson.) 

Below: With continued spattering, the same 

hornito grew into an unusually high spire-like 

object before collapsing; a person (circled) 

gives scale. The top of the Pu‘u ‘Ö‘ö cone is 

visible on skyline left of spire. (USGS photograph by James Kauahikaua.)

Another category of ejecta far more common than volcanic 

bombs is scoria or cinder, which refers to lapilli- or bombsize irregular fragments of frothy lava. If the cinder contains 

abundant vesicles (gas-bubble cavities), it is called pumice, 

which can be light enough to float on water if the vesicles are 

closed to rapid filling by water. In Hawai‘i, these fragments 

share a common mode of origin: all result from sudden chilling 

of frothy lava from which gases were escaping during fountaining. During the exceptionally high fountaining episodes of 

some eruptions—such as at Kïlauea Iki in 1959, Mauna Ulu in 

1969, or Pu‘u ‘Ö‘ö during 1983–1986—an extremely vesicular, 

feathery light pumice, called reticulite or thread-lace scoria, 

can form and be carried many miles downwind from the high 

lava fountains. Even though reticulite is the least dense kind of 

tephra, it does not float on water, because its vesicles are open 

and interconnected. Consequently, when it falls on water, it 

becomes easily waterlogged and sinks.

If scoria or pumice clots are sufficiently soft to flatten or 

splash as they strike the ground, they are called spatter. The 

still-molten character of spatter fragments can cause them to 

stick together to form welded spatter or agglutinate. Droplets 

of lava ejected in a very fluid condition and solidified in flight 

can form air-streamlined spherical, dumbbell, and irregular 

shapes. Drop-shaped lapilli are called Pele's tears, after the 

Hawaiian goddess of volcanoes. In streaming through the air, 

Pele's tears usually have trailing behind them thin threads of 

liquid lava, which are quickly chilled to form lustrous filaments 

of golden brown volcanic glass, called Pele's hair. Pele's hair 

can form thick mats downwind from high lava fountains near a 

vent, or it can be blown many miles from the vent. Even in the 

absence of high fountaining, thick mats of Pele’s hair can form 

near lava ponds and long-lived skylights, where swirling thermal air currents pluck strands from lava surfaces and deposit 

them on the walls and rim of the lava tube or pond. On some 

occasions, thin flakes of basaltic glass, called limu o Pele (“Seaweed of Pele”), form during explosive activity when hot lava 

enters the sea. These flakes are fragments of the glassy walls 

of exploding steam-filled bubbles of lava; though extremely 

fragile, the largest flakes can be several inches across.
42

Mauna Loa

Mt. Rainier

Kīlauea

ocean

19,000 feet deep

200 km

(125 miles)

Volcanic Landforms and Structures

Hawaiian volcanoes exemplify a type of volcano known 

as a shield volcano built by countless outpourings of fluid lava 

flows that advance great distances from a central summit vent or 

group of vents. The successive piling up of these flows results in 

a broad, gently sloping, convex-upward landform, whose profile 

resembles that of a Roman warrior's shield.

Hawaiian shield volcanoes are the highest and largest mountains on Earth. For example, Mauna Kea Volcano rises 13,796 

feet above sea level (a.s.l.) but extends tens of thousands of feet 

below sea level to meet the deep ocean floor. Mauna Loa Volcano (13,679 feet a.s.l.) is slightly lower than Mauna Kea, but it 

is much larger in volume, comprising about 19,000 cubic miles. 

Measured from its base resting on the deepest part of the bowed 

seafloor, the total height of Mauna Loa is about 56,000 feet—

almost twice the height of the tallest mountain on land, Mount 

Everest (Chomolungma in Tibetan) in the Himalaya (29,028 

feet a.s.l.). The profile of the Mauna Loa shield appears smooth, 

whereas the shield profile of Mauna Kea has a more uneven 

appearance, reflecting the growth of numerous small cinder 

cones on its upper slopes after shield formation.

Hawaiian and other shield volcanoes characteristically have 

a broad summit, indented with a caldera, a term commonly used 

for a large depression of volcanic origin. Most calderas form 

by collapse because of removal of magma from the volcano's 

reservoir by eruption and/or intrusion. Kïlauea’s summit caldera 

is about 2.5 miles long and 2 miles wide. Moku‘äweoweo, the 

summit caldera complex of Mauna Loa, is more elongate, measuring about 3 by 1.5 miles. The terms crater or pit crater are 

applied to similar but smaller collapse features.

Aerial view in February 1973 of two prominent volcanic shields that 

formed during the 1969–1974 eruption on Kïlauea’s upper east rift 

zone (see text). Both the Mauna Ulu shield (background) and the 

somewhat smaller ‘Alae shield (foreground) were built by repeated 

overflows from active lava lakes. In this view, the active ‘Alae lava 

lake with its silvery crust is brim full and overflowing. (USGS photograph by Robert I. Tilling.)

Profile of Hawaiian shield volcanoes compared with the profile of Mount Rainier, one 

of the larger composite volcanoes of the 

Cascade Range, drawn at the same approximate horizontal and vertical scale. The ocean 

floor beneath Mauna Loa and neighboring 

Kïlauea is downwarped many thousands of 

feet because of their immense weight. In size, 

Hawaiian shield volcanoes dwarf composite 

volcanoes.
43

Aerial view from the south of snow-covered Moku‘äweoweo, Mauna Loa Volcano’s summit caldera, and several 

pit craters along its southwest rift zone. Mauna Kea Volcano, which last erupted about 4,000 years ago, can be 

seen in the distance. (USGS photograph by Donald W. Peterson.)

Aerial view of prominent fissures within the southwest rift zone of Kïlauea Volcano. The shiny dark 

lava was erupted from these fissures in September 

1971. (USGS photograph by J.D. Griggs.)

Rift zones radiate from the summit calderas of both Mauna Loa and Kïlauea and extend 

down the volcanic flanks into the sea. They are 

elongate tapering ridges featuring prominent 

open fissures (see image upper right), pit craters, 

cinder and spatter cones, and small volcanic 

shields. The orientation of rift zones is influenced by the gravitational stresses and buttressing effects of preexisting neighboring volcanoes. 

Most Hawaiian eruptions take place either 

within summit calderas or along rift zones.

Repeated forceful intrusions of magma from 

the summit reservoir into the rift zones, together 

with continuous gravity-driven creep of the 

south side of the volcano, have pushed Kïlauea’s 

south flank toward the sea. This seaward movement is readily measurable at rates as high as 

4 inches per year. Eventually the accumulated 

seaward movement causes the south flank to 

become unstable, ultimately resulting in a large 

earthquake. Such earthquakes occur occasionally 

and are accompanied by substantial and sudden 

movements along faults cutting the south flank 

(the Hilina Fault System), as well as by slip 
44

400

200

600

800

1000

00

100

200

300

Meters above pre-1983 surface

Feet above pre-1983 surface

P

r

e

-

1

9

8

3

g

r

o

u

n

d

s

u

r

f

a

c

e

Dece

m

b

e

r

1

983

August

1

984

June

1

983

May

1

986

July

1

985

February

1985

Growth profiles of Kïlauea’s newest volcanic cone, built 

during the first three years of the Pu‘u ‘Ö‘ö-Kupaianaha 

eruption.

Aerial view of some 

scarps of the Hilina 

Fault System, 

expressed as sharp 

cliffs on the south flank 

of Kïlauea Volcano. 

(USGS photograph by 

Donald A. Swanson.)

along a nearly horizontal fault zone at the base of 

the volcano. For example, in response to a magni-

tude 7.2 earthquake beneath the area on November 

29, 1975, points on Kïlauea’s south flank dropped 

as much as 11 feet and shifted southward as much 

as 24 feet. The scarps (steep slopes) of the Hilina 

faults are observable as pali (Hawaiian for cliffs) on 

Kïlauea's south flank.

Prolonged eruptions on Kïlauea’s east rift zone 

during the past four decades have given scientists 

unprecedented opportunities to observe the growth 

of Hawaiian volcanic landforms. The 1969–74 

eruptions created two prominent volcanic shields: 

a symmetrical 397-foot-high mound at Mauna Ulu 

(Hawaiian for "growing mountain") and, abutting 

it, a more irregular shield, 328 feet high, over the 

site of buried ‘Alae Crater. Another lava pond and 

180-foot-high shield developed during the 4.5 years 

(July 1986–February 1992) when the Kupaianaha 

vent was active.

The highest volcanic landform constructed in 

Hawai‘i during the past two centuries is the cinderand-spatter cone built by eruptions at the Pu‘u ‘Ö‘ö 

vent during 1983–86. By mid-July 1986, it had 

grown to its maximum height of about 835 feet 

above the pre-1983 surface. Since 1987, however, 

the form of this cone has been modified by eruptionrelated collapses, creating a large central crater and 

lowering its height by about 225 feet.
45

Above: Pu‘u ‘Ö‘ö cone is one of the most recently created landforms in the 

United States; it began to grow in January 1983 and attained its maximum size 

in mid-1986 (see text). As seen here, a flank-vent eruption on Pu‘u ‘Ö‘ö’s west 

slope lights up the night sky in February 1992. This activity began the building 

of a new lava shield against the cone (see photographs to right). (Time-exposure photograph by Peter Mouginis-Mark, University of Hawai‘i). Above right:

The Pu‘u ‘Ö‘ö cone in June 1992; within four months, the lava shield (middle 

ground) had become well developed. (USGS photograph by Tari Mattox.) 

Below right: Same view of Pu‘u ‘Ö‘ö in August 1997, after a large collapse of 

its top in January 1997. By then, the lava shield had become even larger by 

additional lava flows from flank vents, marked by spatter cones on top of the 

shield. (USGS photograph by Christina Heliker.)
46

Above: Aerial view in November 1992 of a lava delta, only four days old, formed at Kamoamoa Bay as flows from Pu‘u ‘Ö‘ö entered the sea, producing steam clouds 

and extending the shoreline 600 feet seaward. A much larger delta was active at East Lae‘apuki during 2005–2007 (see text). Right: A scientist looks at a large block 

of solidified lava that was hurled more than 50 feet inland during a littoral explosion. The blast was triggered by collapse of an active lava bench in 1989. (USGS photographs by Christina Heliker.)

The Pu‘u ‘Ö‘ö-Kupaianaha eruption of 

Kïlauea Volcano also has produced to date more 

than 540 acres of surviving new land on the 

south coast of the Island of Hawai‘i. New land 

is created when hot lava—in a surface flow or 

fed by a lava tube—streams into the ocean and is 

shattered by explosive interaction with the cold 

seawater, forming a pile of fragmental volcanic 

products at the ocean edge. With sustained entry 

of lava into the ocean, over time this pile of 

loose debris enlarges and extends the shoreline 

seaward to form lava deltas—analogous to sediment deposition forming deltas at the mouths of 

large rivers. Actively growing lava deltas appear 

to be solid, especially if veneered with a surface 

of smooth lava. However, they in fact are highly 

unstable, because they are constructed on weak 

foundations of unconsolidated volcanic rubble. 

Active lava deltas can collapse unexpectedly—in 

part or completely—with little or no warning. 

Such collapses may occur catastrophically or 

piecemeal over several hours. The collapsecaused scar forms a new sea cliff, and the 

ocean area in front of it can again be filled with 

lava continuing to spill into the ocean, thereby 

sustaining the rebuilding of the delta. Some 

scientists call this newest extension of the active 

lava delta a lava bench. The development of lava 

benches shows that lava deltas have already collapsed and may do so again in the future.
47

Left: Aerial view (on December 2, 2005) of the newly exposed sea cliff at the ocean lava entry at East Lae‘apuki, four days after the 

major collapse of the actively growing lava delta at the site (see text) (USGS photograph by James Kauahikaua.) Right: With continued lava entry into the ocean, by late-April 2006 the lava delta had grown back to more than its precollapse size. By mid-2007, this 

delta reached its maximum size to become the largest one observed to date. (USGS photograph by Tim Orr.)

The 1983–present eruption at Kïlauea has 

provided unparalleled opportunities to study 

the evolution of lava deltas, the largest of which 

to date was constructed at the East Lae‘apuki 

ocean lava entry during 2005–2007. This delta 

had grown to about 34 acres in area by midNovember 2005 before suddenly collapsing on 

November 28 to produce the largest collapse 

observed to date. A time-lapse camera onshore 

(see http://gallery.usgs.gov/videos/136) captured 

the piecemeal collapse, which removed the 

entire delta as well as 10 acres of land behind it 

in less than 5 hours. With continued lava entry 

into the ocean at the same site, this delta quickly 

rebuilt and, by March 2007, had developed 

into the largest one observed to date—covering about 64 acres in area (48 football fields!). 

Then, the lava delta became inactive and was 

mostly removed several months later by two 

huge collapses, one in May and another in 

August 2007. Its final few remaining acres collapsed over the next three years. Today, none 

of the originally huge East Lae‘apuki lava delta 

remains.

Collapses involving lava deltas can trigger 

strong steam-blast explosions that hurl lava and 

large rock fragments more than 300 feet inland 

and send waves of scalding water onshore, 

thereby posing serious hazards to too-close 

observers of lava entry into the ocean. Since the 

early 1990s, one person has been killed during a 

lava-bench collapse, and three others have died 

in accidents related to bench or delta collapse.
48

If the hot-spot theory is correct, the next volcano 

in the Hawaiian chain should form east or south of the 

Island of Hawai‘i. Abundant evidence indicates that such 

a new volcano exists at Lö‘ihi, a seamount (or submarine 

peak) located about 20 miles off the south coast. Lö‘ihi 

rises 10,100 feet above the ocean floor to within 3,100 

feet of the water surface. Recent detailed mapping shows 

Lö‘ihi to be similar in form to Kïlauea and Mauna Loa. 

Its relatively flat summit apparently contains a caldera 

about 3 miles across; two distinct ridges radiating from 

the summit are probably rift zones.

Photographs taken by deep-sea cameras show that 

Lö‘ihi's summit area has fresh-appearing, coherent 

pillow-lava flows and talus blocks. Pillow-lava fragments 

dredged from Lö‘ihi have fresh glassy crusts, indicative 

of their recent formation. The exact ages of the sampled 

Lö‘ihi flows are not yet known, but certainly some cannot 

be more than a few hundred years old. In fact, since 1959 

the HVO seismic network has recorded large earthquake 

swarms at Lö‘ihi during 1971–1972, 1975, 1984–1985, 

1990–1991, and 1996, suggesting major submarine erup-

tions or magma intrusions into the upper part of Lö‘ihi. 

The July–August 1996 swarm was by far the most ener-

getic seismic activity at Lö‘ihi recorded to date, involving 

more than 4,200 earthquakes. Ninety-five of these earth-

quakes had magnitudes of 4.0 or larger, and three of these 

were felt onshore by residents of Hawai‘i’s Ka’ü District.

The intense 1996 earthquake activity at Lö‘ihi 

launched two “rapid-response” expeditions in August–

September by University of Hawai‘i scientists to conduct 

onsite observations of the activity. This included surfaceship bathymetric surveys and a series of manned-submersible dives to make closeup observations and collect 

lava samples. These rapid-response and followup studies 

indicated that part of Lö‘ihi’s summit had collapsed to 

form a new pit crater (called Pele’s Pit), about 1,800 feet 

across and 900 feet deep.

Lō‘ihi: Hawai‘i’s Newest Volcano

Above: The manned 

research submarine 

Pisces V of the Hawai‘i 

Undersea Research 

Lab (HURL) of the 

University of Hawai‘i, 

Mänoa, being launched 

by its mother ship R/V 

Ka‘imikai-o-Kanaloa. 

(HURL photograph by 

Alexander Malahoff, 

University of Hawaii.) 

Below: A closeup view 

of the Pisces V on shore. 

(HURL photograph by 

Brian P. Midson, University of Hawai‘i.)
49

30’ 20’ 10’ 155 ̊

19°

10’

50’

Kïlaue a

Volcano

Summit Crater

of

Lö‘ihi Volcano

Earthquake swarms

during 1970s

Earthquake swarm

July-August 1996 

0

0 10 km

5 miles

PACIFIC

OCEAN

Within this new crater, several new 

hydrothermal vents were observed, issuing 

the hottest waters ever measured at Lö‘ihi 

(about 390°F). Also, the observations showed 

the deposition of large quantities of glassy 

sand and gravel. While not conclusive, dating 

of two samples of young lava flows by an 

experimental isotopic technique has been 

interpreted by some scientists to suggest at 

least one, possibly two eruptions slightly 

preceded the 1996 earthquake swarm. Thus, 

from the periodic earthquake swarms and 

associated changes in structure, Lö‘ihi 

appears to be a dynamic, actively growing, 

but still submarine, volcano.

Seismic data also indicate that the deepest earthquakes beneath Lö‘ihi merge with 

the deep earthquakes beneath neighboring 

Kïlauea. This downward convergence implies 

that Lö‘ihi, Kïlauea, and Mauna Loa all tap 

the same deep magma supply. The triangular 

zone defined by the summits of these three 

active volcanoes perhaps can be taken to lie 

over the postulated Hawaiian hot spot.

Studies of Lö‘ihi provide a unique 

opportunity to decipher the youthful submarine stage in the formation and evolution of 

Hawaiian volcanoes. Scientists wonder when 

the still-growing Lö‘ihi will emerge above 

the surface of the Pacific to become Hawai‘i's 

newest volcano island. It will almost certainly take several tens of thousands of years, 

if the growth rate for Lö‘ihi is comparable to 

that of other Hawaiian volcanoes (about 0.1 

foot per year averaged over geologic time). It 

is also possible that Lö‘ihi will never emerge 

above sea level and that the next link in the 

island chain has not yet begun to form.

Map showing the locations of earthquakes that occurred 

during the 1970s and in the July–August 1996 period 

in the vicinity of Lö‘ihi. These earthquake swarms, plus 

similar occurrences in 1984–85 and the early 1990s, 

provide seismic evidence that Lö‘ihi is an active submarine volcano.

The flank of Lö‘ihi, showing broken pillow 

lava of a fresh flow, as seen from about 7 feet 

above the volcano's surface at a water depth 

of about 4,200 feet. (Photograph by Alexander 

Malahoff, University of Hawai‘i.)

The Shinkai 6500 of the Japan Agency for 

Marine Science and Technology (JAMSTEC) 

is the world’s deepest manned research 

submersible, capable of operating at ocean 

depths down to 4 miles. It was used in 1999 

by Japanese and U.S. scientists to study Lö‘ihi 

Volcano. (Photograph courtesy of JAMSTEC.)
50

In the short term—on a human time scale—some Hawaiian eruptions can be extremely destructive, causing major disruptions in the daily lives of the people affected by them. On 

a geologic time scale (hundreds to millions of years), however, the eruptions have been beneficial. The benefits directly 

or indirectly derive from the volcanic formation of the island 

chain itself and include: scenic beauty, fertile soils, comfortable climate, and exploitable volcanic (geothermal) energy.

Volcanic Hazards

About 300,000 people have been killed directly or 

indirectly by volcanic activity worldwide during the past 500 

years. Nearly all of those deaths have been caused by explosive eruptions of composite volcanoes along the convergent 

boundaries of the Earth's tectonic plates. The worst recent 

volcanic disaster was in November 1985, when mudflows 

triggered by a relatively small explosive eruption of glaciercapped Nevado del Ruiz Volcano, Colombia, buried the town 

of Armero and killed about 25,000 people. In contrast, fewer 

than about 5,000 people have been killed directly by eruptions in the recorded history of Hawai‘i and only 5 of them 

since the beginning of the 20th century.

Left: A house is consumed by advancing lava 

during Kïlauea’s 1960 Kapoho eruption. (Photographer unknown.) Below: View of Kapoho 

village during the 1960 eruption before it was 

entirely destroyed (Photograph by Gordon 

Morse) Bottom: A posteruption scene showing 

the remnants of corrugated iron roofs to mark 

the site of the lava-buried village. (USGS photograph by Robert I. Tilling).

Volcanic Hazards 

and Benefits
51

Although the usually gentle Hawaiian eruptions generally 

pose little danger to people, their lava flows and the building of 

ejecta cones can be highly destructive to populated and cultivated areas. For example, the villages of Kapoho in 1960 and 

Kalapana in 1990 were destroyed by eruptions on the east rift 

zone of Kïlauea. Flows from the ongoing Pu‘u ‘Ö‘ö-Kupaianaha eruption have buried a total of 211 buildings, including 

several residential areas in addition to Kalapana village and the 

Waha‘ula Visitor Center in Hawai‘i Volcanoes National Park.

Above right: Lava flows from the Kupaianaha vent on Kïlauea’s 

east rift zone cross the highway to enter Kalapana in December 

1989. By late 1990, the community lay buried beneath 50–80 feet 

of lava. (USGS photograph by J.D. Griggs.) Below right: Lava 

flows from Pu‘u ‘Ö‘ö ignite the Waha‘ula Visitor Center, Hawai‘i 

Volcanoes National Park, in June 1989. (USGS photograph by J.D. 

Griggs.)
52

Parts of Hilo, the largest city on the Island of 

Hawai‘i, with a population of about 40,000, are 

built on the pähoehoe lava flows of the 1881 Mauna 

Loa eruption. During the March–April 1984 eruption of Mauna Loa, Hilo was again threatened. Lava 

flows advanced nearly 16 miles in about 5 days, and 

a bright red glow in the sky above the incandescent 

flows could be seen on clear nights. The citizens and 

officials of Hilo became increasingly concerned as 

the eruption continued. Fortunately, the flows stopped 

about 4 miles short of the city's outskirts.

Because of the frequent Kïlauea and Mauna Loa 

eruptions, the Hawaiian Volcano Observatory conducts 

round-the-clock monitoring to detect early signs of 

impending activity and to advise local officials on a 

timely basis. A key component in reducing volcanic 

hazards is the preparation of volcanic-hazards zonation maps. These maps, which delineate the zones of 

relative severity of volcanic hazards, are based on an 

assessment of eruption frequency, nature of expected 

activity, and likely vent areas and lava-flow paths.

The infrequent explosive eruptions can pose a 

potential hazard to people in the area of ash fallout. 

Nearly all of the volcanic-caused fatalities in Hawai‘i 

in the past 220 years were caused by explosive activity. In 2008, small explosions in Halema‘uma‘u hurled 

blocks weighing more than 200 pounds onto a visitor 

overlook, fortunately closed by Hawai‘i Volcanoes 

National Park officials several weeks earlier. An 

explosive eruption is an example of a low-frequency 

but highly hazardous volcanic event.

It is useful to distinguish between the terms 

hazard and risk. Evaluation of hazards is based on 

geologic information only and considers the likelihood 

of destructive volcanic phenomena and products in a 

given area. Assessment of risks evaluates the likelihood of loss of life and property in the area being considered. Thus, volcanic "risk" increases as the zones 

defined as hazardous become cultivated, populated, 

or otherwise developed. Even areas with a very low 

severity of volcanic hazards may be classified as high 

risk if they are densely populated. Hazard-zonation 

maps provide government officials and the public with 

critical information that allows them to assess the risks 

of volcanic hazards and apply the results in long-term 

land-use planning, estimates of the socioeconomic 

and political impact of eruptions, and preparation of 

contingency plans in case of volcanic emergencies.

Night view of the lava flows of the 1984 

Mauna Loa eruption, with the lights of 

downtown Hilo in foreground. (USGS 

photograph by David Little.)
53

MAUNA KEA

KOHALA

9

8

7

4

6

6

5

3

3

3

2

2 1

Lava flows since 1800

HUALÄLAI

KÏLAUEA

MAUNA LOA

3

2 2

1

1

1

1

1

0 20 miles

0 30 kmIncreasing severity

of hazard

1

2

3

4

5

6

7

8

9

Map of Island of Hawai‘i showing the volcanic hazards from lava flows. Severity 

of the hazard increases from zone 9 to zone 1. Shaded areas show land covered 

by flows erupted in the past two centuries from three of Hawai‘i’s five volcanoes 

(Hualälai, Mauna Loa, and Kïlauea).

A volcanic-hazards map has been prepared for the Island of 

Hawai‘i, in which the areas of increasing relative severity of lava-flow 

hazards are designated "9" through "1." Related maps have been prepared for hazards from ash fall, ground failures, and subsidence. Similar 

volcanic hazards-assessment studies have been made for the islands 

of Maui and O‘ahu, although the expected frequency of future eruptions on those islands is much lower. Boundaries drawn between the 

hazard zones are necessarily gradational and reflect the judgment of 

experienced volcanologists. Hazards-assessment studies assume that 

probable future eruptive behavior is most likely to be similar to a given 

volcano's past behavior. As a volcano's eruptive history becomes better 

documented by additional studies, the hazards-zonation maps for it need 

to be revised and updated to reflect the incorporation of new and better 

information.

Mention should be made of another type of volcanic hazard—

highly destructive but very, very infrequent—that has affected the 

Hawaiian Islands in the geologic past. Since the mid-1960s, mapping 

studies of the sea floor around the islands have recognized deposits of 

debris from more than fifteen gigantic landslides, covering many hundreds of square miles. Such underwater landslides, which have also been 

identified at other volcanic islands in the world [for example, Canary 

Islands (Atlantic Ocean), Cape Verde Islands (Atlantic Ocean), and La 

Réunion Island (Indian Ocean)], are among the largest known on Earth. 

They result from catastrophic collapses of the unstable flanks of active 

volcanoes, which can suddenly remove huge chunks of land and trigger 

towering waves (“mega-tsunamis”) that have carried rocks and sediments as high as 1,000 ft above sea level. The youngest giant Hawaiian submarine landslide, produced by a widespread collapse of Mauna 

Loa’s west flank, occurred about 120,000 years ago. Subsequent smaller 

landslides from both Mauna Loa and Kïlauea have been recognized, but 

their precise geologic ages are not well known. It is important to study 

Hawai‘i’s giant submarine landslides, despite their infrequency, because 

the devastating potential hazards they pose can cause enormous loss of 

life, property, and resources. However, the close monitoring of the measurable flank movement of Hawaiian volcanoes by the Hawaiian Volcano Observatory should detect any sudden acceleration in movement 

that may provide earning warning for any possible flank collapse.
54

Volcanic Air Pollution

Since mid-1986, in addition to the lava 

erupted and associated lava-flow hazards, the continuous activity at Pu‘u ‘Ö‘ö-Kupaianaha has also 

emitted on average about 2,000 tons of polluting 

sulfur dioxide gas (SO2) per day. This emission 

rate is not trivial—considerably higher than that 

of the single dirtiest coal-fired power plant in 

the mainland U.S. Keep in mind, however, that 

most volcanic gases, including those from active 

Hawaiian volcanoes, are composed primarily of 

water vapor (H2O, 70–90 percent), with decreasing abundances of carbon dioxide (CO2), sulfur 

dioxide (SO2), and trace amounts of other gases. 

Also, it be must emphasized that SO2 and other 

gases generated by all the world’s volcanoes pale 

by comparison with the total output of gases produced by human activity (mostly the combustion 

of fossil fuels). For example, the world’s volcanoes spew about 200 million tons of CO2 annually, while human activities worldwide produce 

some 24 billion tons of CO2 each year—about 120 

times more!

Nevertheless, Kïlauea’s high and steady 

output of SO2 poses a persistent natural hazard for 

Hawai‘i residents and visitors: volcanic air pollution, commonly called “volcanic smog,” or vog. 

Vog is a visible haze comprising gas and an aerosol of tiny particles and acidic droplets, created 

when SO2 and other gases emitted from Kïlauea 

interact chemically with sunlight and atmospheric 

oxygen, moisture, and dust. Depending on wind 

patterns (primarily) and other atmospheric conditions, vog can drift 100 miles or more from the 

eruption site. Near Kïlauea's active vents, vog consists mostly of SO2 gas, but, by the time it reaches 

the Kona coast on the west side of the island, vog 

is mostly an aerosol of sulfuric acid and other sulfate compounds. When the prevailing northeasterly trade winds are disrupted, vog is dispersed 

more widely, affecting the entire Island of Hawai‘i 

and, sometimes, other Hawaiian islands.

In mid-2008, because of the new vent in 

Halema‘uma‘u Crater, SO2 emissions from 

Kïlauea’s summit increased from about 150 tons 

per day to as much as 2,000 tons per day. During 

late 2009, summit emissions were fluctuating 

between about 400 and 1,500 tons per day. High 

vog levels result in regionally hazy sky conditions 

that degrade air clarity and reduce visibility for 

motorists and air traffic. Exposure to vog is known 

to exacerbate existing respiratory problems and 

can produce symptoms such as headaches and 

eye irritation in some otherwise healthy individuals. Several studies to determine the effects of 

vog on human health have been conducted on the 

island and others are underway (see the Hawaiian 

Volcano Observatory’s website for links to vog 

studies: http://hvo.wr.usgs.gov/hazards/). Hawai‘i 

Volcanoes National Park maintains an up-to-date 

website on current SO2 conditions inside the 

park: http://www.nature.nps.gov/air/webcams/

parks/havoso2alert/havoalert.cfm. In addition, the 

Department of Health of the State of Hawaii maintains another useful website about SO2 levels for 

the southern half of the Island of Hawai‘i: http://

www.hiso2index.info/.

The droplets of sulfuric acid suspended in vog 

combine with atmospheric moisture to form acid 

rain, which damages agricultural crops and accelerates rusting and corrosion of metal. Acid rain 

can also contaminate household drinking water 

by leaching lead from the roofing and plumbing 

materials of rooftop water-catchment systems 

used in many homes on the Island of Hawai‘i.

Volcanic air pollution is also caused when 

molten lava spills into the ocean and reacts with the 

chlorides in seawater, creating large steam plumes 

laden with hydrochloric acid (HCl). The impacts 

of these highly acidic coastal plumes—sometimes 

called laze (abbreviated from “lava haze”)—are 

limited to within a few miles downwind of their 

source; thus, laze mainly poses a hazard to people 

who visit sites of lava entry into ocean. Although 

Above: View on a day free of vog (see text) looking northwest from the Island of Hawai‘i toward the 

island of Maui; flank of Kohala Volcano is seen upper 

right. Haleakalä Volcano (east Maui), about 80 miles 

away, is clearly visible on the horizon, attesting to 

exceptional atmospheric clarity. (USGS photograph 

by Christina Heliker). Below: View from same spot 

on a day with heavy vog. Haleakalä cannot be seen, 

and even Kohala is barely visible. (USGS photograph 

by Tamar Elias).

No Vog

Heavy Vog

Haleakalä
55

Left: Pressure testing in 1976 of a geothermal well drilled into Kïlauea’s lower 

east rift zone. A power plant later constructed in this area produces about 30 

megawatts of electricity, about 30 percent of the island’s needs. (Photograph 

courtesy of the Hawai‘i Geothermal Project.) Right: Some of the power-generating equipment at this plant, the only commercial producer of geothermal energy 

in the State of Hawai‘i. (Photograph courtesy of Puna Geothermal Venture.)

Above: A luxuriant crop of burdock—a root vegetable widely used in 

Japanese cuisine—growing in the fertile volcanic soils derived from 

products of past Hawaiian eruptions. Mauna Kea Volcano is visible in 

the distance. (USGS photograph by Taeko Jane Takahashi.)

awareness of the environmental hazards of volcanic 

air pollution has increased greatly since the mid1980s, more studies are needed to better understand 

how vog and laze affect human health.

Volcanic Benefits

First of all, the Hawaiian Islands would not 

exist were it not for volcanic activity. Equally 

important, many factors that combine to make the 

islands an attractive place to live or visit depend 

directly or indirectly on the results of past and 

present eruptions.

Hawai‘i's majestic volcanic mountains, 

beautiful beaches, and pleasant climate combine 

to make the islands a popular tourist destination, 

which includes two heavily visited national parks. 

Haleakalä National Park on Maui, founded in 

1961, features the spectacularly eroded summit 

crater of 10,023-foot-high Haleakalä Volcano, last 

active in the 15th or 16th century. Hawai‘i Volcanoes National Park, created by Congress in 1916, 

contains the two historically active Hawaiian volcanoes, Mauna Loa and Kïlauea. This park is one 

of the few places in the world where the processes 

and products of active volcanism can be viewed in 

relative safety by both scientists (volcanologists) 

and nonscientists (general public). Indeed, millions of park visitors have personally experienced 

the sights, sounds, and smells of volcanic eruptions and gained a firsthand appreciation of the 

phenomena that created and shaped these beautiful Hawaiian Islands.

Given enough rainfall, areas buried by new 

lava recover quickly; revegetation can begin less 

than one year after the eruption. Erosion and 

breakdown of the volcanic material can form 

fertile soils over periods of tens to thousands of 

years. These rich soils fostered the agricultural 

development of the Hawaiian Islands, as represented principally by the sugar, pineapple, coffee, 

and macadamia nut industries. Some volcanic 

products provide an abundant local source of raw 

materials for landscaping, housing and construction, and road building. 

In recent decades, volcanic energy has 

been harnessed by a geothermal power plant on 

Kïlauea’s east rift zone. As of 2009, 30 megawatts 

of electricity were being produced and fed into 

the grid of the local utility company. However, 

it should be mentioned that the exploitation of 

Kïlauea’s geothermal potential also has generated 

controversy among Hawai‘i’s residents, particularly those living near the geothermal plant. Thus, 

the increased production envisaged in this century 

will need to be balanced by fuller consideration of 

environmental and cultural concerns.
56

Benefits of Research at the

Hawaiian Volcano Observatory

Hawai‘i is both a natural laboratory for the study 

of eruptive processes and a volcanic wonderland for 

visitors. The huge challenge facing scientists and government officials is clear: Work to reduce the adverse 

impact of eruptions in the short term, so that residents 

and visitors can continue to enjoy the long-term benefits 

of volcanism. Toward this end, the Hawaiian Volcano 

Observatory (HVO) will continue to give timely warnings of anticipated volcanic activity, reliable and current 

progress reports once an eruption starts, and the best 

possible technical information on volcanic hazards posed 

by any eruption, present or future.

In addition, the high eruption frequency of its volcanoes and the availability of state-of-the-art research 

facilities at HVO combine to make Hawai‘i an excellent training ground for volcanologists from around the 

world. HVO and other scientists are striving to improve 

volcano-monitoring and eruption-forecasting techniques, 

in order to reduce the risks associated with eruptions 

of active volcanoes in Hawai‘i and elsewhere. Along 

with HVO, the U. S. Geological Survey operates four 

other volcano observatories: Alaska Volcano Observatory (in Anchorage, in cooperation with the Geophysical 

Institute of the University of Alaska-Fairbanks and the 

State of Alaska Division of Geological and Geophysical 

Surveys); Cascades Volcano Observatory (in Vancouver, 

Washington, in cooperation with the Geophysics Program of the University of Washington-Seattle); Long 

Valley Observatory (monitoring Long Valley Caldera, 

east-central California); and Yellowstone Volcano Observatory (monitoring Yellowstone Caldera, Wyoming, in 

cooperation with University of Utah-Salt Lake City and 

the National Park Service).

Below left: Park visitors safely 

watch spectacular lava cascades and fountains during the 

August 1971 eruption at Kïlauea’s 

summit. (Photograph courtesy 

of the National Park Service.) 

Below right: Some of many thousands of visitors who in recent 

years have safely observed the 

slow advance of pähoehoe lava 

erupted from Kïlauea’s east-rift 

zone. (USGS photograph by 

Steven R. Brantley.)
57

Selected Readings

The publications listed below furnish additional information on topics not covered, or only 

briefly discussed, in this booklet. Some of the 

listed publications are accessible on the Internet.

Decker, Robert, and Decker, Barbara, 2005, 

Volcanoes (4th ed.): San Francisco, W.H. 

Freeman and Company, 320 p. [An information-packed introduction to the study of 

volcanoes written in an easy-to-read style.]

Decker, R.W., Wright, T.L., and Stauffer, P.H., 

editors, 1987, Volcanism in Hawai‘i: U.S. 

Geological Survey Professional Paper 1350, 

1,667 p. Online version: http://pubs.usgs.

gov/pp/1987/1350/.

Dzurisin, Daniel, 2007, editor, Volcano deformation; geodetic monitoring techniques: 

Chichester, U.K.,Springer-Praxis Publishing, 441 p. [An authoritative treatment of 

the geodetic techniques used to monitor 

active and potentially active volcanoes.]

Heliker, Christina, 1997 (revised), Volcanic and 

seismic hazards on the island of Hawaii: 

U.S. Geological Survey general-interest 

publication, 48 p. [A nontechnical, wellillustrated summary of the natural hazards 

affecting the Island of Hawai‘i.] Online version: http://pubs.usgs.gov/gip/hazards/.

Heliker, Christina, and Brantley, S.R., 2004, The 

ongoing Pu‘u ‘Ö‘ö-Kupaianaha eruption of 

Kïlauea Volcano, Hawai‘i: U.S. Geological Survey Fact Sheet 2004–3085, 2 p. [A 

single-sheet, nontechnical summary of the 

first 20 years of this prolonged and continuing eruption.] Online version: http://pubs.

usgs.gov/fs/2004/3085/.

Heliker, Christina, Stauffer, P.H., and Hendley, 

J.W., II, 2000 (revised), Living on active 

volcanoes—the Island of Hawai‘i: U.S. 

Geological Survey Fact Sheet 074–97, 2 

p. [A single-sheet, nontechnical summary 

of Hawaiian volcanoes and their associated hazards.] Online version: http://wrgis.

wr.usgs.gov/fact-sheet/fs074-97.

Heliker, Christina, Swanson, D.A., and Takahashi, T.J., 2003, editors, The Pu‘u ‘Ö‘öKupaianaha eruption of Kïlauea Volcano, 

Hawai‘i; the first 20 years: U.S. Geological 

Survey Professional Paper 1676, 206 p. [A 

collection of 12 scientific papers—richly 

illustrated by many maps, diagrams, and 

photographs—that summarizes all aspects 

of the first two decades of this ongoing 

eruption, the longest and largest rift-zone 

activity at Kïlauea in more than 600 years.] 

Online version: http://pubs.usgs.gov/pp/

pp1676/.

Helz, R.L., 2005, Monitoring ground deformation from space: U.S. Geological Survey 

Fact Sheet 2005–3025, 4 p. [A well-illustrated, simple-to-read summary of a satellite-based technique increasingly being used 

to monitor the active volcanoes of Hawai‘i 

and elsewhere: Interferometric Synthetic 

Aperture Radar (InSAR).] Online version: 

http://pubs.usgs.gov/fs/2005/3025/.

Johnson, Jenda, Brantley, S.R., Swanson, D.A., 

Stauffer, P.H., and Hendley, J.W., II, 2004, 

Viewing lava safely—common sense is not 

enough: U.S. Geological Survey Fact Sheet 

152–00, 4 p. [A nontechnical summary of 

potential hazards associated with closeup 

viewing of Kïlauea eruptive activity, with 

emphasis on safety measures observers 

should take.] Online version: http://geopubs.

wr.usgs.gov/fact-sheet/fs152-00.

Juvik, S.P., and Juvik, J.O., 1998, editors, Atlas 

of Hawai‘i (3d ed.): Honolulu, University of 

Hawai‘i Press, 333 p. [A very handy reference volume compiled by the Department of 

Geography, University of Hawai‘i, describing the natural, cultural, and social environment of Hawai‘i, the 50th State.]

Kious, W.J., and Tilling, R.I., 1996, This 

dynamic Earth—the story of plate tectonics: U.S. Geological Survey generalinterest publication, 77 p. [A beautifully 

illustrated, jargon-free introduction to 

explain the theory of plate tectonics for 

nonscientists. This booklet nicely complements the world map “This dynamic 

planet” (Simkin and others, 2006).] Online 

version: http://pubs.usgs.gov/publications/

text/dynamic.html.

Klein, F., and Wright, T.L., 2000, Catalog of 

Hawaiian earthquakes, 1823–1959: U.S. 

Geological Survey Professional Paper 1623, 

97 p. [A comprehensive compilation of 

Hawaiian earthquakes through 1959, including events that occurred before availability 

of modern seismic data.] Online version: 

http://pubs.usgs.gov/pp/pp1623.

Lipman, P.W., and Mullineaux, D.R., editors, 1981, The 1980 eruptions of Mount 

St. Helens, Washington: U.S. Geological 

Survey Professional Paper 1250, 844 p. 

[The most comprehensive collection of 

scientific articles on Mount St. Helens' spec-
58

tacular 1980 eruption; it contains 62 reports 

on many aspects of this best-known U.S. 

explosive volcano. This volume provides an 

instructive comparison with U.S. Geological Survey Professional Paper 1350, edited 

by Decker and others, which summarizes 

present knowledge on Hawaiian volcanoes, 

the best-known U.S. (usually) nonexplosive 

volcanoes.]

Macdonald, G.A., Abbott, A.T., and Peterson, 

F.L., 1983, Volcanoes in the sea; the geology of Hawai‘i (2d ed.): Honolulu, University of Hawai‘i Press, 517 p. [A handsome 

book that provides an excellent overview of 

the eruptive and other geologic processes 

that have shaped the Hawaiian Islands.]

Mastin, L.G., Christiansen, R.L., Swanson, D.A., 

Stauffer, P.H., and Hendley, J.W., II, 1998, 

Explosive eruptions at Kïlauea Volcano, 

Hawai‘i: U.S. Geological Survey Fact Sheet 

132–98, 2 p. [A single-sheet nontechnical summary of the occasional explosive 

eruptions of Kïlauea Volcano, which usually erupts nonexplosively.] Online version: 

http://geopubs.wr.usgs.gov/fact-sheet/fs132-

98.

Sherrod, D.R., Sinton, J.M., Watkins, S.E., and 

Brunt, K.M., 2007, Geologic Map of the 

State of Hawai‘i: U.S. Geological Survey 

Open-File Report 2007–1089. [Contains 

a series of geologic maps of the Hawaiian 

Islands (scale of 1:250,000 for the Island of 

Hawai‘i and scale of 1:100,000 for the other 

islands) and an 85-page explanatory pamphlet. The geologic maps and pamphlet can 

be downloaded as pdf files.] Online version: 

http://pubs.usgs.gov/of/2007/1089/.

Sherrod, D.R., Scott, W.E., and Stauffer, P.H., 

editors, 2008, A volcano rekindled; the 

renewed eruption of Mount St. Helens, 

2004–2006: U.S. Geological Survey Professional Paper 1750, 856 p. [After being dormant during 1986–2003, Mount St. Helens 

came back to life in 2004. This collection of 

37 papers, which provides a comprehensive 

summary of the renewed 2004–2006 eruptive activity, complements USGS Professional Paper 1250 (1981).] Online version: 

http://pubs.usgs.gov/pp/1750/.

Sigurdsson, Haraldur, Houghton, B.F., McNutt, 

S.R., Rymer, Hazel, and Stix, John, editors, 2000, Encyclopedia of volcanoes: San 

Diego, Academic Press, 1,417 p. [Perhaps 

the most comprehensive review of the 

state-of-the-art knowledge about volcanoes, 

volcano hazards, and volcano monitoring, as 

the relatively young science of volcanology 

entered the 21st century.]

Simkin, Tom, Tilling, R.I., Vogt, P. R., Kirby, S., 

Kimberly, Paul, and Stewart, D.B., compilers, 2006, This dynamic planet; world map 

of volcanoes, earthquakes, impact craters, 

and plate tectonics (3d ed.): U.S. Geological Survey Geologic Investigations Map 

I–2800, Mercator projection with scale 

1:30,000,000 at equator. Online version: 

http://mineralsciences.si.edu/tdpmap/.

Sutton, Jeff, Elias, Tamar, Hendley, J.W., II, and 

Stauffer, P.H., 1997, Volcanic air pollution—a hazard in Hawai‘i: U. S. Geological 

Survey Fact Sheet 169–97, 2 p. [A singlesheet, nontechnical summary of the hazards 

posed by volcanic air pollution created by 

the recent prolonged eruptions of Kïlauea 

Volcano.] Online version: http://wrgis.

wr.usgs.gov/fact-sheet/fs169-97.

Tilling, R.I., 1993 (reprinted), Volcanoes: U.S. 

Geological Survey general-interest publication, 45 p. [A general introduction to the 

study of volcanoes for the nonspecialist, 

with focus on the nature, types, workings, 

products, and hazards of volcanoes.] Online 

version: http://pubs.usgs.gov/gip/volc/.

Tilling, R.I., Topinka, Lyn, and Swanson, D.A., 

1990 (revised), Eruptions of Mount St. 

Helens— past, present, and future: U.S. 

Geological Survey general-interest publication, 46 p. [A nontechnical summary, 

illustrated by many color photographs and 

diagrams, of the abundant scientific data 

available for the volcano, with emphasis on 

the catastrophic eruption of May 18, 1980, 

which caused the worst volcanic disaster in 

U.S. history.] Online version: http://pubs.

usgs.gov/publications/msh/.

Trusdell, F.A., Wolfe, E.W., and Morris, Jean, 

2005, Digital database of the geologic map 

of the Island of Hawai‘i: U.S. Geological 

Survey Data Series 144, version 1.0. Online 

at: http://pubs.usgs.gov/ds/2005/144/.

Westervelt, W.D., 1963, Hawaiian legends of 

volcanoes: Rutland, Vermont, Charles E. 

Tuttle Company, 205 p. [An interesting 

collection of legends and stories about Pele, 

Hawaiian goddess of volcanoes, and her 

volcanic exploits and deeds.]

Wolfe, E.W., and Morris, Jean, 1996 (reprinted 

2009), Geologic map of the island of 

Hawai‘i: U.S. Geological Survey Miscellaneous Investigations Series Map I–2524–A 

and I–2524–B (three map sheets, scale 
59

1:100,000). [These maps summarize a 

half-century of new geological knowledge 

gained since the classic geologic map of the 

island published by Harold T. Stearns and 

Gordon A. Macdonald in 1946. This monumental work is the first to show in detail the 

age and distribution of both prehistoric lavas 

and those erupted during written history 

(that is, the past two centuries), including 

a compilation of the sample locations and 

chemical analyses of hundreds of Hawaiian lavas.] Digital version: see Trusdell and 

others (2005).

Wright, T.L., Takahashi, T.J., and Griggs, J.D., 

1992, Hawai‘i volcano watch; a pictorial 

history, 1779–1991: University of Hawai‘i 

Press and Hawai‘i Natural History Association, 162 p. [A highly readable, richly 

illustrated account of “volcano monitoring” 

in Hawai‘i, from the earliest observations to 

modern scientific studies.]

Selected Viewings

The best way to see Hawaiian eruptive 

activity is to visit Hawai‘i Volcanoes National 

Park—at the right time and place. The next best 

thing is to view videos or DVDs of Hawaiian 

eruptions, some of which are listed here. Some 

school and public libraries might have them in 

their collections.

Videos and (or) DVDs

Eruption of Kïlauea, 1959–60: U.S. Geological Survey, 345 Middlefield Road, Menlo 

Park, California 94025. [Originally an 

award-winning movie jointly produced (in 

1961) by the USGS and the National Park 

Service that contains spectacular footage 

of the highest lava fountains ever recorded 

in Hawai‘i and of the formation of Kïlauea 

Iki lava lake. This classic film has been 

beautifully restored and is now available as 

a 28-minute DVD created by Michael M. 

Moore (USGS Library, Menlo Park). The 

DVD can be accessed online at: http://education.usgs.gov/common/video_animation.

htm]

Fire Under the Sea—The Origin of Pillow Lava: 

Moonlight Productions, 73-1132 Ahikawa 

Street Kailua-Kona, Hawaii 96740. [Originally a 20-minute movie that first captured 

the actual sights and sounds of underwater 

movement of red-hot lava and formation 

of pillow lava, as filmed by scuba-diving 

scientists during the 1969–1974 Mauna Ulu 

eruptions of Kïlauea. A 10-minute excerpt 

from this classic original film can be seen 

on YouTube at: http://www.youtube.com/

watch?v=H7DPL0YYGL4.

Inside Hawaiian Volcanoes: Department of 

Mineral Sciences, Smithsonian Institution, NHB-119, Washington, DC 20560. 

[A 25-minute video jointly produced by 

the USGS and the Smithsonian Institution 

showing the geologic settings and structures 

of Hawaiian volcanoes and the methods 

used to monitor volcanic behavior.]

Rivers of Fire: Hawai‘i Natural History Association, Ltd., P.O. Box 74, Hawai‘i Volcanoes 

National Park, HI 96718. [A 25-minute 

videotape of the March–April 1984 eruption 

of Mauna Loa Volcano that contains some 

of the best footage of Hawaiian lava flows 

ever filmed.]

The Hawaiian Volcanoes: a Force for Creation: 

Harada Productions, 22 Malanai Street, 

Hilo, HI 96720. [A 30-minute videotape 

containing dramatic scenes of the Pu‘u 

‘Ö‘ö-Kupaianaha activity of Kïlauea 

through 1989 and of the 1984 eruption of 

Mauna Loa Volcano.]

Volcanoscapes V: Hawai‘i Volcanoes National 

Park: Tropical Visions, Inc., 62 Halaulani 

Place, Hilo, HI 96720. [A 70-minute video, 

the latest in a series featuring not only 

Kïlauea’s current eruption at Pu‘u ‘Ö‘öKupaianaha, but also other major Hawaiian 

eruptions. It also covers flora and fauna of 

the National Park and historical information and images about the Big Island of 

Hawai‘i.]

A Firsthand Account of the Current Eruption 

of Kïlauea Volcano: Winter 2010 Eruption 

Update: Volcano Video Productions, P.O. 

Box 909, Volcano, HI 96785. [A 60-minute 

videotape summarizing the course of the 

1983–present Pu‘u ‘Ö‘ö-Kupaianaha eruption of Kïlauea Volcano through 2009, 

including the perspective of, and narration 

by, a former staff member of the USGS 

Hawaiian Volcano Observatory.]

Lava Flows and Lava Tubes: What they are, 

how they form: Volcano Video Productions, 

P.O. Box 909, Volcano, HI 96785. [Awardwinning 42-minute video.]

Kïlauea: Mountain of Fire: Public Broadcast 

System. [This 50-minute video, produced 

in March 2009, contains excellent footage 
60

of the current activity at Kïlauea along with 

informative commentary. It also shows scientists of the Hawaiian Volcano Observatory 

making studies of the eruption. This video 

can be seen in its entirety at: http://video.

pbs.org/video/1133372360/.]

Selected Websites

The following websites provide national and 

worldwide information on volcanoes, eruptions, 

and volcano hazards.

http://hvo.wr.usgs.gov

[Maintained by the USGS Hawaiian Volcano 

Observatory (HVO), this site provides the most 

comprehensive and authoritative online information about the volcanoes and associated hazards 

in Hawai‘i and how HVO scientists monitor 

them.]

http://volcanoes.usgs.gov

[The official site of the USGS Volcano Hazards 

Program, this site contains much useful information about the volcanoes of the United States and 

the hazards they pose; it also provides links to 

the websites of the other volcano observatories 

operated by the USGS in Alaska, the Cascades 

(California, Oregon, Washington), Long Valley 

(California), and Yellowstone (Wyoming-Montana).]

http://www.nmnh.si.edu/gvp

[Maintained by Global Volcanism Program of 

the Smithsonian Institution, Washington, D.C., 

this site is the best source for information about 

volcanoes of the world and their eruptive activity; it is the “telephone book” of the world’s 

volcanoes.]

http://www.geology.sdsu.edu/how_volcanoes_

work

[Supported NASA as part of Project ALERT

(Augmented Learning Environment and Renewable Teaching), this site has a wealth of educational materials about volcanoes and their 

eruptive processes and products. It is intended 

for use by college-level students of geology and 

volcanology and by teachers of earth science.]

http://www.swisseduc.ch/stromboli/index-en.

html

[Developed and maintained by Italian and Swiss 

volcanologists, this site provides abundant materials and use links to volcanoes and eruptions. 

Although it emphasizes Etna and Stromboli volcanoes, the site also contains great photographs 

and video clips of many other volcanoes in the 

world, including those of Hawai‘i.]

http://www.photovolcanica.com/index.html

[This commercial website, which is maintain by 

Dr. Richard Roscoe (Munich, Germany), contains many excellent photo galleries of volcanoes 

and eruption scenes (mostly non-Hawaiian), in 

addition to a diverse collection of nonvolcanic 

photographs.]
61

Conversion of Units

Metric units of measurement are the standard in virtually every country in the world. However, 

the United States still adheres to English units, as used in this booklet. For readers in countries that use 

Metric units and for U.S. students learning the Metric system, a conversion table is given below.

 To convert To

 English units Metric units Calculation

 Multiply by:

Length inch centimeter 2.5

 foot centimeter 30.5

 yard meter 0.91

 miles (statute) kilometer 1.61

 Multiply by:

Area square inch square centimeter 6.4

 square foot square meter 0.09

 square yard square meter 0.84

 square mile square kilometer 2.6

 Multiply by:

Volume gallon (U.S.) liter 3.8

 cubic foot cubic meter 0.03

 cubic yard cubic meter 0.76

 cubic mile cubic kilometer 4.0

Temperature degree degree Subtract 32, then

 Fahrenheit (°F) Centigrade (°C) multiply by 0.56
62

Glossary

Terms shown in bold type within definitions are separately defined in this listing. Some 

terms (for example, ash and dome) have other 

meanings, but only their use in volcanology is 

covered in these definitions. For more information, the interested reader should consult the 

website “USGS Photo Glossary of volcanic 

terms”: http://volcanoes.usgs.gov/images/pglossary/index.php

Agglutinate. A welded pyroclastic deposit; 

term is commonly used for deposits of volcanic 

ejecta fused while hot and viscous. Agglutinate 

typically occurs in spatter cones.

Andesite. Volcanic rock, typically dark gray to 

black, with about 57–63 percent silica.

Ash. Fine fragments, less than 2 millimeters 

(about 0.1 inch) across, of volcanic rock erupted 

during an explosive eruption.

Basalt. Volcanic rock with about 47–53 percent 

silica, typically gray to black. Basaltic lavas

are more fluid than andesites or dacites, which 

contain more silica.

Caldera. A large, basin-shaped volcanic depression, more or less circular in form; typically 

more than 1 to 2 miles (several kilometers) 

across. Commonly formed by collapse during 

withdrawal or ejection of a large volume of 

magma that leaves the roof of the magma reservoir unsupported.

Dacite. Volcanic rock, commonly light colored, 

with about 64–69 percent silica. Dacite lavas are 

viscous and tend to form thick blocky lava flows 

or steep-sided piles of lava called lava domes. 

Dacitic magmas tend to erupt explosively, thus 

also ejecting abundant ash and pumice.

Dome. A steep-sided mass of viscous and often 

blocky lava extruded from a vent; typically has 

a rounded top and covers a roughly circular area. 

Typically silicic (rhyolite or dacite) in composition.

Ejecta. Material explosively ejected from a 

volcano.

Lava. Molten rock (magma) that reaches the 

earth’s surface by explosive or effusive volcanic 

activity.

Magma. Molten rock beneath the Earth’s surface. All magmas and lavas consist mainly of a 

liquid, along with smaller and variable amounts 

of solid and gaseous matter.

Pumice. Highly vesicular volcanic ejecta, 

typically silicic in composition. It is essentially 

magma that has been frothed up by escaping 

gases and then cooled and solidified during eruption.

Pyroclastic. General term applied to volcanic 

products or processes that involve explosive 

ejection and fragmentation of lava. Literally 

means “fire-broken” (from the Greek pyro=fire, 

klastos=broken).

Pyroclastic flow. A hot (typically >1,450°F or 

800°C), turbulent, ground-hugging mixture of 

rock fragments, gas, and ash that travels very 

rapidly (hundreds of miles per hour) away from 

a volcanic vent or collapsing lava dome. Commonly associated with an overriding less dense 

flow component called pyroclastic surge.

Pyroclastic surge. The less dense component of 

a pyroclastic flow, with a low concentration of 

solids and a density much less than that of the 

resulting deposit. Pyroclastic surges flow mostly 

above rather than hugging the ground.

Rhyolite. Volcanic rock, typically light colored, 

with 70–77 percent silica. Rhyolite lavas are 

viscous and tend to form thick blocky lava flows 

or steep-sided piles of lava called lava domes. 

Rhyolite magmas tend to erupt explosively, 

commonly also producing abundant ash and 

pumice.

Scoria. Vesicular volcanic ejecta, essentially 

magma that has been frothed up by escaping 

gases. It is a textural variant of pumice, with 

scoria typically being less vesicular, denser, and 

usually andesitic or basaltic in composition.

Silica. Silica is silicon dioxide (SiO2) the 

predominant molecular constituent of volcanic 

rocks and magmas. It tends to polymerize into 

molecular chains, increasing the viscosity of the 

magma. Basalt magma, having relatively low 

content of SiO2, is fairly fluid, but with increasing SiO2, andesite, dacite, and rhyolite magmas 

are progressively more viscous. Because it is 

more difficult for dissolved gas to escape from 

more viscous magma, higher silica magmas 

generally erupt more explosively.

Silicic. Describes magma that contains more 

than ~63 percent silica and is generally viscous, 

gas-rich, and tends to erupt explosively. Includes 

rhyolite and dacite.
63

Spatter cone. A steep-sided cone constructed 

of agglutinate at a vent. Most spatter cones 

are small, typically 30 feet (10 meters) or less 

in height, and commonly form in linear groups 

along a fissure.

Tephra. A general term for any airborne pyro-

clastic material, regardless of the shape or size 

of the fragments. Most commonly applied to 

smaller size volcanic ejecta (such as ash and 

scoria).

Vent. Any opening at the Earth’s surface through 

which magma erupts or volcanic gases are emit-

ted.

Vesicular. Describes lava whose texture is 

marked by conspicuous cavities, which represent 

volcanic-gas bubbles trapped in magma.

Volcanic glass. A natural glass formed by the 

rapid cooling (quenching) of the liquid compo-

nent of magma.
Produced in the Menlo Park Publishing Service Center

Manuscript approved for publication, November 23, 2010

Revision edited by Peter H. Stauffer

Layout and design by Darlene A. Ryan

Modified from original graphics and design by Bobbie Myers and Martha Kiger
Sunrise view in August 2002 of lava from the Pu‘u ‘Ö‘ö-Kupaianaha eruption cascading into the ocean on the south coast of the Island of Hawai‘i. (USGS 

photograph by Donald A. Swanson.)
As the Nation's principal conservation agency, the Department of the 

Interior has responsibility for most of our nationally owned public lands 

and natural and cultural resources. This includes fostering sound use of 

our land and water resources; protecting our fish, wildlife, and biologi-

cal diversity; preserving the environmental and cultural values of our 

national parks and historical places; and providing for the enjoyment of 

life through outdoor recreation. The Department assesses our energy and 

mineral resources and works to ensure that their development is in the 

best interests of all our people by encouraging stewardship and citizen 

participation in their care. The Department also has a major responsibility 

for American Indian reservation communities and for people who live in 

island territories under U.S. administration. 

Mosaic of the Island of Hawai‘i by Pamela Owensby (Hawai‘i Insti-

tute of Geophysics, Honolulu) from 20 NASA Landsat images taken 

between July 1999 and June 2000. Note the fume cloud at the Pu‘u 

‘Ö‘ö vent and the trail of volcanic smog (vog) drifting along the south-

eastern coast of the island. (Image courtesy of Peter Mouginis-Mark, 

Hawai‘i Institute of Geophysics.)

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