Encyclopedia of earthquakes and volcanoes 3rd ed a gates (FOF, 2007)

ENCYCLOPEDIA OF
EARTHQUAKES AND VOLCANOES
third EDITION



ENCYCLOPEDIA OF

EARTHQUAKES AND
VOLCANOES
third EDITION

Alexander E. Gates, Ph.D.
AND David Ritchie


Encyclopedia of Earthquakes and Volcanoes, Third Edition
Third edition copyright © 2007, 2001, 1994 by Alexander E. Gates, Ph.D., and David Ritchie
All rights reserved. No part of this book may be reproduced or utilized in any form or by any
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Library of Congress Cataloging-in-Publication Data
Gates, Alexander E., 1957–
Encyclopedia of earthquakes and volcanoes.—3rd ed. / Alexander E. Gates and David Ritchie.
p. cm.

Ritchie’s name appears first on the previous ed.
Includes bibliographical references and index.
ISBN 0-8160-6302-8 (acid-free paper)
1. Earthquakes—Encyclopedias. 2. Volcanoes—Encyclopedias. I. Ritchie, David, 1952 Sept. 18II. Title.
QE521.R58 2007
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This book is dedicated to my father, David L. Gates,
and to my mentor, Dr. Lynn Glover III



CONTENTS
Preface: An Essay on Plate Tectonics
ix
Acknowledgments
xiii
Introduction

xv
Entries A–Z
1
Appendix A. Chronology of Earthquakes and Volcanic Eruptions
291
Appendix B. Eyewitness Accounts of Major Eruptions
and Quakes
299
Appendix C. Further Reading and Web Sites
313
Appendix D. The Deadliest Earthquakes
317
Appendix E. The Deadliest Volcanoes
319


Appendix F. The Highest Magnitude Earthquakes
321
Appendix G. The Frequency of Occurrence of Earthquakes
323
Appendix H. Magnitude v. Ground Motion and Energy
325
Index
327


PREFACE:
An Essay on
Plate Tectonics
Until the 1950s, the various branches of geology, including the study of volcanoes

and earthquakes, appeared to have no real connection, and the progress of the
science was toward continued divergence. What pulled everything back together
was the radical concept of plate tectonics that came into fruition in the 1960s
and 1970s. Plate tectonics is sometimes referred to as “the glue that holds geology together” to reflect this power. It explains virtually all volcanoes and the lion’s
share of earthquakes and even relates them to each other.
The following review of plate tectonics is a good place to start for anyone
needing a refresher.

Earth Architecture
The Earth is a sphere that is flattened at the poles and bulging at the equator.
Internally, it is like a hard-boiled egg. In the center, instead of a yolk, it has a core.
The core is composed of iron-nickel and contains an inner core that is solid and
an outer core that is liquid. The spinning of the Earth causes the two to interact as a self-exciting dynamo that gives Earth its strong magnetic field. The egg
white is equivalent to the Earth’s mantle, which encases the core. The mantle is
composed of dense minerals that are rich in iron and magnesium. It has several layers reflecting different minerals and mechanical properties. The shell of the egg is
equivalent to the Earth’s crust, a thin layer of light rock upon which humans live.
Unlike the shell, which is uniform, there are two types of crust. Thin, dense, young
crust is pulled toward the center of the Earth by gravity and sinks down, whereas thick, light, old crust floats higher. The deeper crust is covered by oceans and
called oceanic crust, whereas the lighter crust forms the continents and is called
continental crust. The concept of isostasy is the balance between them.
If a person dropped the egg and the shell cracked into fragments that remained
stuck to the egg, these would be the plates of the Earth. However, the plates are
not only composed of crust. If the egg was not placed in cold water after it was
boiled, a thin layer of egg white would be stuck to the shell. This sandwich of shell
and white is equivalent to the sandwich of crust and rigid mantle and is called the
lithosphere. Plates are considered lithospheric plates because they are not only
composed of crust. The complication arises below the lithosphere because rather
than the mantle staying rigid throughout, there is a gummy layer of mantle beneath
the lithosphere called the asthenosphere. (Imagine a layer within the egg in which
the egg white remained runny.) It is the floating, moving, and interacting of the

lithospheric plates that defines the science of plate tectonics.
ix


x

Preface: An Essay on Plate Tectonics

Plate Margins
A plate margin, or plate boundary, occurs where lithospheric plates meet. Adjacent
plates interact at plate margins in one of three ways:
1. They move away from each other in a divergent margin;
2. They move toward or into each other in a convergent margin; or
3. They slide past each other in a transform margin.
But why should they move at all? Why don’t they just remain in one spot? The
answer is convection. There are hotter and cooler areas in the mantle. The hotter mantle is less dense and tends to rise, just like hot air or hot water. The cooler
mantle is more dense and tends to sink. When mantle is heated in the hotter areas,
it rises to the upper mantle and spreads out, cooling as it moves away from the
heat source and sinking back to the lower mantle where it can be reheated. In this
way the mantle circulates in a convection cell similar to a boiling pot of soup. The
lithospheric plates float on the flowing, circulating mantle.

Divergent Margins
Divergent margins typically begin on continental crust but quickly wind up on oceanic crust. There are several distinct stages in these margins. The process of pulling
crust apart is called rifting. The initiation of rifting appears to involve the formation of triple junctions. Mantle plumes strike the underside of the plates, leaving
a hole with three cracks emanating from it at 120° angles. Two of the cracks on the
Earth will become active rift zones and mature divergent margins that connect with
other triple junctions, while the third crack will start to rift but eventually fail. The
failed crack is called an aulocogen. The best example of a triple junction is at the
southern tip of the Arabian crustal plate. The Gulf of Aden and Red Sea represent the two active cracks, and the East African rift system is the aulocogen.

The early stage of rifting is short-lived, if present at all, and involves bulging
of the continental crust and uplift. The second stage involves thinning of the continental crust. The lower crust is ductile and stretches thinner, whereas the upper
crust is brittle. Brittle deformation includes the development of active normal
faults and consequently horsts and grabens (similar to the modern Basin and
Range Province of the southwestern United States). Eventually, mafic magma from
the upper mantle reaches the surface in fissure eruptions. flood basalts cover
the landscape with massive flows (such as the Laki eruptions of Iceland or the
Columbia River Plateau of Washington). These lava plateaus are the largest accumulations of lava on the continents. In some cases rhyolite volcanoes may also
be produced by the melting of continental crust from the elevated heat flow from
the basalt. These volcanoes can be violent, producing huge eruptions, such as at
Yellowstone National Park.
The next stage involves the development of a narrow ocean basin such as
the Red Sea. Volcanic activity continues, but it is submarine and purely basalt.
Earthquakes can continue on land, but they are less common and less intense. Most
of the earthquake activity is also submarine. The final stage is the mature ocean
basin such as the Atlantic Ocean. The coasts are passive margins with no volcanic
activity and rare seismic activity. All of the volcanic and seismic action is submarine and occurs at the mid-ocean ridge at the center of the basin. A mid-ocean
ridge is where new ocean crust is continuously being formed. The Mid-Atlantic
Ridge is a huge submarine mountain range that extends almost from pole to pole.
It surfaces at Iceland, which provides a glimpse of the intense volcanic and seismic
activity associated with these margins.

Convergent Margins
There are three types of convergent margins depending upon the type of crust on
the colliding plates:
1. ocean-ocean convergent margins
2. ocean-continent convergent margins
3. continent-continent convergent margins

Preface: An Essay on Plate Tectonics
It is at convergent margins where ocean crust is consumed at the exact rate as it
is being produced in the mid-ocean ridge. This balance is necessary or the Earth
would be constantly changing size.
At an ocean-ocean convergent margin, ocean crust is driven beneath facing
ocean crust in a feature called a subduction zone. On the ocean floor, the top
edge of the subduction zone is marked by a trench that contains the deepest ocean
depths on Earth. The downgoing or subducting plate drives deeper into the asthenosphere, where it first partially melts and then is absorbed. Earthquakes occur
all along the surface of the subducting plate and are thus of progressively deeper
focus away from the trench. The melted ocean crust forms magma of intermediate composition that rises through the overlying crust eventually to form submarine volcanoes. These volcanoes continue to grow until they breach the ocean
surface to become volcanic islands. This chain of islands forms an arcuate map
pattern called an island arc. The Aleutian Islands are a good example of an
island arc. These andesite volcanoes are explosive and among the most dangerous on Earth. They are also very seismically active primarily as the result of movement on reverse and thrust faults. Krakatoa is a subduction zone volcano.
Subduction zones are the source of megathrusts that produce such disasters as
the 2004 Banda Aceh tsunami.
Ocean-continent margins are geometrically similar to ocean-ocean margins.
The difference is that the overriding plate is continental rather than oceanic crust.
Instead of island arcs, there are volcanic mountain ranges called magmatic arcs.
The Andes Mountain range is the best example of a magmatic arc. These margins
also have subduction zones and Benioff zones with both seismic and volcanic
activity. The volcanoes are at higher elevations than those in island arcs, and the
magma chambers are much larger.
Connected to the subducting ocean crust, somewhere far behind, is another
continent. Eventually, the ocean crust is completely consumed in the subduction
zone, and the two continents face each other and collide. The subducting plate
attempts to follow the ocean crust down the subduction zone, but it is too buoyant to enter the asthenosphere. Instead, the two plates collide. The subducting
plate plows beneath the overriding plate and then large thrust faults develop on
the subducting plate, moving large amounts of rock away from the collision zone
accompanied by a series of massive earthquakes. The overriding plate crumples
while building huge mountains that progressively grow away from the collision

zone. This crumpling involves intense seismic activity. The only potential volcanic activity is leftover from the subduction zone activity on the old magmatic
arc.
There is an odd effect that occurs in continent-continent collisions called
extrusion or escape tectonics. If one or both sides of the overriding plate
(at a high angle to the collision zone) faces an open ocean basin, it is said to
have a “free face.” As the continental collision proceeds, chips of the overriding plate are shoved laterally and out of the way of the intense collision zone
along large strike-slip faults. Basically, land is being squirted sideways, away
from the zone of high force. The strike-slip faults accommodate up to 621 miles
(1,000 kilometer) offset and produce regular, intense earthquakes. An example
of extrusion tectonics is Turkey, which is being squirted westward into the
Mediterranean Sea along the strike-slip North Anatolian fault. Some of the more
devastating earthquakes of the 20th century have occurred along this fault as the
result of extrusion tectonics.

Transform Margins
Transform Margins or faults are strike-slip faults that separate two lithospheric plates. Furthermore, they must connect two other types of plate margins.
Therefore, there are three types of transform margins based upon the margins connected. There are:
1. divergent-divergent transform margins;
2. convergent-convergent transform margins; and
3. divergent-convergent transform margins.

xi


xii

Preface: An Essay on Plate Tectonics
Because they are plate tectonic margins, they are constantly active, potentially
for very long periods of time. They are some of the most active faults on Earth.
Luckily, more than 99 percent of transform faults are on the ocean floor. The vast

majority of these are divergent-divergent transform margins that accommodate
bends and offsets on the mid-ocean ridges. These faults are also called geofractures
or fracture zones and can be seen on bathymetric maps of the ocean floor at high
angles to the mid-ocean ridges. The offsets give them a dentate appearance with the
high density of transform faults along the ridge. Convergent-convergent transform
margins accommodate jogs and offsets in island arcs, but they are not common.
Divergent-convergent transform margins are also uncommon and are usually associated with smaller plates such as the Caribbean plate.
Transform faults on continental crust are very dangerous because of their persistent activity. The best example is the San Andreas Fault in California. Every
few years it produces an earthquake with a magnitude of 7.0 or greater, many
of which cause great damage. Another example is the South Alpine Fault in New
Zealand, which also produces numerous strong earthquakes.


ACKNOWLEDGMENTS
My thanks to the Department of Earth and Environmental Sciences at Rutgers
University–Newark for support and resources; to the students in my natural disasters classes for leading me to new resources for earthquakes and volcanoes; and
to reference librarian Veronica Calderhead at Dana Library for efforts above and
beyond the call of duty in finding obscure references for me.
To Dr. Tobi Zausner for her excellent work in scanning slides and improving images, and to Colin Gates for producing several of the tables. To Dr. David
Valentino at SUNY–Oswego for his suggestions to improve this volume; to executive editor Frank K. Darmstadt for his suggestions, encouragement, and patience;
to Alana Braithwaite for her invaluable help in getting the manuscript into shape;
and to literary agent Max Gartenberg for his sage advice.
I would also like to acknowledge the phenomenal resources of the U.S.
Geological Survey and National Oceanographic and Atmospheric Administration,
without which the production of this book would have been impossible.

xiii

INTRODUCTION
The volcano on the island of Thira (now Santorini) in the Aegean Sea exploded
in about 1500 b.c. As a result, it sent a tsunami now estimated at over 200
feet (61 m) high across the eastern Mediterranean Sea that destroyed the dominant Minoan civilization on the island of Crete. The hill people of Greece
thereby formed the dominant culture, eventually heralding the Golden Age of
Greece. The huge tsunami caused an extensive retreat of seawater along the
Mediterranean shoreline for up to 10 minutes before it came crashing back. It is
possible that this opening of the sea allowed Moses and the Israelites to escape
the Egyptians in 1500 b.c., as described in the Bible.
It is to this astounding degree that earthquakes and volcanoes have affected
humans’ history, culture, and civilization. In ancient times, earthquakes sometimes
tipped the scales in power struggles, allowing one kingdom to defeat another. It
is no wonder that earthquakes are sometimes said to be connected to punishment
imposed by a displeased deity in ancient and even modern religions. Volcanoes
have even been credited with altering the Earth’s climate, thereby causing some of
the major famines and even plagues in history. Earthquakes and volcanoes are the
most powerful and destructive natural phenomena on the planet, fascinating people
both young and old.
It was this fascination that inspired David Ritchie to write the first edition
of the Encyclopedia of Earthquakes and Volcanoes. Untrained in science, he concentrated on historical accounts of the disasters. When I revised the first edition,
I added the missing scientific aspect to the encyclopedia. I also expanded the coverage of volcanoes as well as updated information on recent geological phenomena. In addition, new photos and maps were added to show where the events took
place, and diagrams were provided to illustrate the processes.
One would think that with all the human advances in monitoring technology
and earthquake engineering that earthquakes and volcanoes would become less
damaging and thus less important with every year. However, the still young 21st
century is showing humans that this is not the case. The horrifying recent disasters associated with the Banda Aceh, Indonesia, tsunami and the Bam, Iran, and
Muzaffarabad, Pakistan, earthquakes are among the worst in history. The burgeoning world population in geologically hazardous areas is clearly growing faster than
the disaster-reduction technology.
These new events made it clear that the second edition of the encyclopedia
lacked the resources to put these disasters into proper historical context. This third

edition not only includes the new events but also many examples of historical
earthquakes for contrast or comparison. The third edition has earthquake information for Italy, Greece, Egypt, Iran, Pakistan, China, India, and several other areas.
It is especially timely, with greatly expanded coverage in the Middle East, where
the world’s focus has rested in recent years. Because many of these disasters involve
destruction by landslides and avalanches, entries related to such events and processes are significantly expanded. Tsunami research and technology is also updated
in the new edition to answer questions about the Banda Aceh disaster, and many

xv


xvi

Introduction
other tsunamis are described for comparison. Finally, there are many tables to
place the magnitude of these recent disasters into historical context.
The third edition of Encyclopedia of Earthquakes and Volcanoes provides a
unique single source on historical earthquakes and volcanic eruptions for students
or laypeople. Many of the sources included are obscure and difficult to obtain.
With the new “Preface Essay on Plate Tectonics,” this edition may serve as a standalone reference for introductory courses on earthquakes and volcanoes.


ENTRIES A–Z



A
Native American word Mackimoodus, meaning “meetingplace.”
The acoustic effects of volcanic eruptions can be surprising. The noise that accompanied the explosion of the volcano
Krakatoa in 1883, for example, was heard some 3,000 miles
(4,828 km) away on the island of Rodrigues in the Indian

Ocean. This is said to be the greatest distance at which the
noise of a natural event has been heard within historic times
without the aid of electronic communications. In some eruptions, the noise may be audible hundreds of miles away and
yet go unheard in areas much closer to the point of eruption.
When Mount Katmai in Alaska erupted on June 6, 1912,
for example, the sound of the eruption was heard some 800
miles (1,287 km) away but reportedly was not distinct at
Kodiak, only about 100 miles (161 km) from the volcano.

aa A Hawaiian word (pronounced AH-ah), aa is a particular kind of lava flow with an irregular, jagged surface. Aa
is very stiff and blocky because much of its mass is hardened
lava. It flows slowly, with lava rubble tumbling down the
advancing slope. It typically occurs far from the volcanic
vent at the leading edge of the flow.
See also pahoehoe.

acceleration The rate at which velocity of a body or particle is increased as compared with deceleration which is the
rate at which velocity is decreased. When seismic waves pass
through some material (soil, rock, or buildings), the shaking
produces acceleration of the contained particles. The measure
of this acceleration from shaking determines the amount of
potential damage. Shaking is among the most deadly forces
in an earthquake.

active fault A fault that is actively moving. Each increaccelerogram The typically graphic recording of the

ment of movement, each jerk, produces earthquakes.

acceleration of the ground surface as surface waves arrive
at an accelerograph station. The accelerograph produces

the accelerogram.

active volcano An active volcano is considered to be one
that has shown activity within historical times or the past several thousand years. A historically active volcano, however,
may be inactive at present and indeed may have shown no
activity for hundreds of years. Approximately 500 volcanoes
around the globe are thought to be active, but this figure may
be a serious underestimate because of some submarine volcanoes whose activity has not been observed and reported.

accelerograph An instrument that measures the acceleration of the ground surface at a given location. The record
produced by an accelerograph is called an accelerogram.

acidic An old term for felsic.

Adana earthquake, Turkey On May 27, 1998, an earthquake of magnitude 6.2 occurred. It killed 145 people and
injured 1,500. More than 17,000 houses were destroyed. Several major aftershocks also occurred.

acoustics Various noises are associated with earthquakes
and volcanic eruptions. Earthquakes are often accompanied
by a deep, audible, rumbling noise. The noise often is compared to that of thunder or of heavy traffic or trucks passing on the streets. In one instance, noises associated with
an area of occasional earthquake activity have become a
tourist attraction. This case involves the “Moodus noises”
in the state of Connecticut. These are mysterious sounds
similar to gunfire that have been reported in the vicinity
of East Haddam. The name Moodus is derived from the

Adatara volcano, Honshu, Japan It is a stratovolcano
that is located nine miles (15 km) from Fukushima City. It
contains three cones (Adatara, Maegatake, and Osoyozan)
that are andesitic (with minor basalt) in composition. Adatara has experienced two historical eruptions, the last in 1990.

1


2

Advanced National Seismic System

to the severe seismic risk that Americans are exposed to in
many areas of the country, the U.S. government established
the ANSS. This program provides accurate and timely data
as well as information on seismic events, including the effects
on buildings and other structures. The ANSS is a basic function of the National Earthquake Hazard Reduction Program.
When the system is complete, it will have some 7,000 seismic
stations, with dense concentrations at 26 designated high-risk
urban centers. Functions of the ANSS include constant monitoring of seismicity, thorough analysis of seismic events, and
automatic broadcasts of potential seismic hazards, all in real
time.

shocks. For example, if a magnitude 6.4 earthquake occurs
after a series of foreshocks, it could be the main shock; all
succeeding earthquakes would be aftershocks. If a magnitude
7.4 earthquake occurs three earthquakes later, then the 6.4
earthquake was merely a strong foreshock, and aftershocks
only start after the 7.4 earthquake. Aftershocks may continue
for weeks or months after the main shock and be nearly as
powerful. They tend to be quite destructive to property, as
they can topple structures left unstable by the main shock.
In the North Ridge earthquake of 1994, strong aftershocks
continued for a year after the main shock. They had a terrifying psychological effect on the populace of Los Angeles,
California.

Aeolian Islands See Lipari Islands.

Agadir earthquake, Morocco The earthquake of February

Advanced National Seismic System (ANSS) In response

Aeseput (Aeseput-weru) See Tondano.
Afghanistan Although it is one of the more seismically
active countries in the world, the lack of accurate records
makes reporting on Afghanistan’s historical earthquakes difficult. Recent earthquakes have been better reported, such as
the Rostaq and Mazar-e Sharif earthquakes of 1998 and
the series of earthquakes of 2002 during the U.S.–Al Qaeda
conflict. Prior earthquakes are said to have killed as many
as 20,000 people in a single event, but information is largely
conflicting. The seismic activity results from the position
of Afghanistan as a promontory of the Eurasian crustal
plate pushing southward into the Indian and Arabian
crustal plates. The southern boundary of Afghanistan is
marked by deep earthquakes associated with the subduction of the Arabian plate beneath the Makran Coast. Both
the western boundary with Iran and the eastern boundary
with Pakistan have a long history of intense seismic activity.
Fortunately, the central part of the country is less active. The
exception is the active Chaman Fault, which shows a seismic
gap near Kabul. If it produces a major earthquake, it could
be devastating.

Africa The African continent has areas of strong seismic
and volcanic activity. Much volcanism and earthquake activity is concentrated along Africa’s Great Rift Valley, which
extends through the eastern portion of the continent and

contains numerous volcanoes and calderas. The East African Rift is the third arm of a triple junction that includes
active arms of the Red Sea and the Gulf of Aden. Africa is
also moving north relative to Europe. A subduction zone
in the Mediterranean Sea produces earthquakes and volcanoes that cause tsunamis that affect the north coast of
Africa. The Betic Zone largely lies in Spain but also affects
the nearby African coast. Volcanoes and volcanic deposits
of Africa include Asawa, the Barrier, Cameroon, Corbetti,
Deriba, Fantale, Kilimanjaro, K’One, Land of Giant Craters,
Ngorongoro, Nyamulagira, and Nyos.
aftershocks Earthquakes less intense (weaker) than the
main (strongest) earthquake. Aftershocks can be determined
only in retrospect. Typically, seismic events begin with
foreshocks, followed by the main shock and finally after-

29, 1960, struck the community of Agadir with a population of 33,000 at the foot of the Atlas Mountains at 11:45
p.m. It killed some 12,000 people and injured 12,000 others. Destruction of the old part of the city was complete, and
some 70% of the new structures in the city were destroyed.
The earthquake measured 6.25 on the Richter scale of magnitude and was preceded by two milder shocks. The earthquake was also accompanied by a tsunami that reached
almost a hundred yards inland from the sea. Effects of the
earthquake included ruptured sewers, from which large numbers of rats were reportedly released into the city. The earthquake neutralized the city’s fire-fighting capability, with the
result that fires burned unchecked. The dome of a mosque
collapsed on a group of praying Muslims, and the Jewish
community of Agadir was devastated; of some 2,200 Jews in
Agadir, approximately 1,500 were said to have died in the
earthquake. Corpses were so numerous in Agadir after the
earthquake that most of the 12,000 dead were simply buried
in common graves, using a bulldozer.
The reasons that this earthquake was so devastating were
threefold. First, the focus of the earthquake was very shallow (less than two miles [3 km]). Typically, the energy from
a deep earthquake is already spread out and somewhat diffuse by the time the waves reach the surface. In this case, the

energy was still concentrated so it was more destructive than
many earthquakes of higher magnitude. Second, the epicenter was right in the middle of the city. The zone of highest
potential destruction was in the worst possible place. Third,
the city was totally unprepared for the earthquake. There had
been a very destructive earthquake in Agadir in 1751 (more
than 200 years earlier) but only minor seismic events since.

agglomerate A chaotic jumble of mixed sizes and types of
pyroclastic material (ejecta) that is lithified into a rock.
An agglomerate is typically formed close to a volcanic vent
where the power of the eruption can pulverize the existing rock and dump it into a deposit. They indicate very high
energy and must include a large component of bombs and
blocks.

Agnano volcano, Italy The Agnano volcano formed a crater in the Phlegraean Fields near Naples. The crater once
was filled with a lake but later was drained and converted
into a racetrack.


Aira

Agua de Pau caldera, Azores The stratovolcano Agua de
Pau has a record of historical activity extending back to 1563,
when an eruption of pumice reportedly covered the nearby
island of São Miguel. Strong earthquakes preceded and continued during the eruption and destroyed most of the community of Ribeira Grande, several miles north of the Agua de Pau
caldera. basalt lava extruded from the volcano following the
eruption from the main vent. Another, less powerful eruption
took place in the caldera the following year. In October 1952,
destructive earthquakes preceded an eruption in which fissures
opened at the foot of Agua de Pau. This eruption lasted one

week and produced a lava flow and a small cone. Very small
earthquakes occurred at Agua de Pau during the 1980s.

Agung volcano, Bali, Indonesia Agung is regarded as
the “Navel of the Universe” and the home of the Supreme
God by the Balinese. It is best known for its powerful eruption in 1963, which killed between 1,200 and 2,000 people
and sent large amounts of ash into the upper atmosphere.
This airborne material is thought to have caused spectacular atmospheric effects in the following weeks, such as brilliant red sunsets and halos around the Moon and Sun. The
high-altitude cloud from this eruption of Agung was also
implicated in a sharp decrease in starlight as measured at
observatories. Average temperatures at Earth’s surface
dropped measurably for three years after this eruption.
Many of the fatalities occurred at a religious festival that
was in progress near the volcano at the time of the eruption.
Clouds of lethal gas swept down from the volcano and killed
large numbers of participants in the religious rites. Lava overwhelmed the villages of Sebih, Sebudi, and Sorgah. A combination of heat, ash, and poisonous gases is said to have killed
animals for miles around the volcano. Huge boulders cast out
from the volcano during the eruption landed in the village of
Subagan.
See also climate, volcanoes and.

Aira caldera, Japan The Aira lies a few miles north of the
Ata caldera in southern Japan, in the region of Kagoshima
Bay. The bay itself is thought to be a graben, formed by volcanic and tectonic activity. Uplift of the bay floor has also
occurred on occasion, and the Aira caldera has been cited to
show that volcanically related uplift and subsidence can affect
the whole area of a caldera even when an active volcano is
located at the caldera’s edge. The Aira caldera is famous for
the violent eruptions of the Sakurajima volcano (now known
as On-take), although volcanic activity occurs at other points

in the caldera as well.
An eruption from 1779 to 1781 began with a series of
strong earthquakes in early September. Changes in water
level (sometimes involving energetic spouting) were observed
at water wells on Sakurajima on the morning of November
8, 1779, at about the same time clouds of steam started to
rise from the summit of the volcano. On the afternoon of
November 8, a major eruption started. After several days,
small islands began to emerge from the waters near Sakurajima. These islands are thought to have been formed partly
through underwater eruptions but also in part through uplift
of the bay floor.

3

Changes in hot springs in the vicinity also were observed;
two new hot springs emerged, and another stopped flowing. The area around Sakurajima appears to have subsided
in the decades following this eruption because the waters
encroached on low areas along the shore, flooding parts of
the city of Kagoshima. In some areas, floods covered the land
to a depth of perhaps 10 feet (3 m) or more. Local authorities tried building embankments to bar the rising waters but
were unsuccessful. The rising waters wiped out some communities along the shore. Uplift affected other areas around
Sakurajima about this time. A seacoast road on the southern
shore of Sakurajima rose several feet until it lay more than
100 feet (30 m) inland from the waters. Uplift also affected
the northwest shore of Kagoshima Bay so that trade in the
harbor at one community had to be conducted using wagons
rather than boats.
Another major eruption began in 1913, when earthquake activity to the north in May and June signaled the
beginnings of renewed volcanism. The nearby Kirishima volcano erupted in late 1913 and early 1914. Strong earthquakes
occurred near Kagoshima in late June. Dramatic changes also

were observed in the activity of local hot springs. On the
eastern shore of Sakurajima, hot springs stopped flowing in
the spring of 1913, and shortly afterward, other hot springs
on the south side of the volcano became too hot for bathing
when the tide was low. Changes in the water table occurred
early in 1914; a pond on the south side of Sakurajima dried
up, killing the fish in it, while the water table dropped, and
some of the island’s water wells went dry. On the morning
of January 12, 1914, a spring at a beach on the north side of
Sakurajima emitted a gush of cool water while water spouted
to a height of several feet from hot springs on the other
side of the island. In addition, extremely hot water poured
out from the ground at several other locations. On the same
morning, a powerful eruption of Sakurajima began. This
eruption was preceded by strong earthquake activity over
more than 24 hours. Earthquakes were especially frequent on
Sakurajima itself. A particularly strong earthquake occurred
several hours after the eruption began. Since the 1913–15
eruptions, numerous small eruptions have been recorded. In
1935 earthquakes felt on the southern side of Sakurajima
in the middle of the year were followed by eruptions of ash
beginning in September. Occurring only a few years after the
violent events of 1913–15, these eruptions convinced several
hundred residents of the area to evacuate. Ash was deposited
to a depth of several inches on the south and east sides of the
volcano, and some damage to crops occurred. An eruption
may have occurred underwater on March 13, 1938, when
waters about 1,000 feet (304 m) offshore rose abruptly while
a roar was heard. This phenomenon was repeated soon afterward, some distance away. Sakurajima itself started to erupt
again two weeks later. Minor eruptions took place between

1939 and 1942. In 1946, the volcano exhibited explosive
activity and extruded lava. Minor explosions also occurred
during the next eight years. Starting in 1955, explosions concentrated on the summit of the volcano. In the middle to late
1980s, explosive activity appeared to become more frequent
after a comparatively quiet period. Earthquake activity at the
Aira caldera has not always been related clearly to eruptions,


4

Akan

although in some cases, eruptions plainly had earthquakes as
precursors. The character of slippage along faults has been
seen to change during periods of eruptive activity. When the
mountain is not erupting, earthquakes are characterized by
strike-slip (or predominantly horizontal) movement, which
changes to oblique-slip normal faulting in the initial stages
of eruptions and then to oblique-slip normal or reverse
faulting when eruptive activity is at its height. As the eruption subsides, movement along faults returns to strike-slip or
reverse.
As noted earlier, the Aira caldera is noted for the dramatic uplift and subsidence it has displayed on occasion.
After the eruption of 1914, the caldera and adjacent areas
displayed dramatic subsidence, almost 20 feet (6 m) in some
locations. A few months later, uplift started again and has
continued through the 1980s. Measurements of uplift at various points on and around Sakurajima indicate that a reservoir
of magma under the caldera has expanded at an average rate
of perhaps 30 million cubic feet (850,000 m3) per year, at an
estimated depth of perhaps four miles (6 km). The caldera
does not appear to show deformation in a uniform pattern; some scientists have suggested that there is more than

one source of uplift within Aira. In addition to deformation
patterns observed in the caldera as a whole, Sakurajima may
exhibit comparatively brief and shallow deformations.
In the 20th century, the Aira caldera has shown some
curious phenomena related to heat flow. After the major
eruption in 1914, the temperature of the soil began to rise
near the northwest shore of Sakurajima. Fruit trees and
other flora died. Eventually, trees were killed within an
area some 500 feet (152 m) wide, and benzene and chlorine fumes were detected there. Some months earlier, similar
emissions of fumes at a spot on the mainland, near a line of
vents passing through the summit of Sakurajima, reportedly
killed an ox and made several humans sick. By the spring of
1915, soil dug up at the heat-affected area was too hot to
hold in one’s hands. After 1915, this unusual concentration
of heat diminished.

Akan caldera, Japan The Akan caldera is located in
northern Japan near the south end of the Kuril Islands. Lake
Akan occupies part of the caldera. Several cones are also
found in the caldera; these include Furebetsu, Fuppushi, 0akan and Me-akan, the last of which has been active within
historical times. Strong earthquakes were felt in the vicinity
of Akan caldera in the late 1920s and early 1930s, and in late
1937, a cloud of vapor was seen rising from the foot of Meakan. Marked seismic activity increased in the early 1950s,
and small quantities of ash may have been released during
this period, although it is not known if there was any direct
relationship between eruptive and seismic activity at that
time. An eruption began in November 1955, and the following year, observations of earthquakes showed a rise in activity
of earthquake swarms several days before an explosion on
June 15. Seismicity increased for approximately three weeks
preceding an explosion in 1959. Earthquakes accompanied

eruptions of ash in 1988. The Akan caldera has been studied
intensively to examine the relationship between earthquakes
and a magmatic system. tectonic (as opposed to volcanic)

earthquakes have also been studied for their relationship to
earthquake swarms at Akan. On one occasion, a major tectonic earthquake followed changes in temperature at hot
springs in Akan.

Akutan volcano, Aleutian Islands, Alaska, United States
There is a stratovolcano on Akutan Island in the eastern
Aleutian Islands. Akutan has a summit crater with a lake
and a cinder cone. It has erupted at least 27 times since its
discovery in 1790. The most recent full eruption was in 1992.
In March 1996, earthquake activity intensified with many
swarms and magnitudes up to 5.1.

Alabama United States The state of Alabama varies geographically in its degree of seismic risk. The southern portion
of the state is characterized by low seismic risk, whereas the
degree of risk generally increases northward toward the Tennessee border. There have been several notable earthquakes
in the history of Alabama, including the earthquakes of February 4 and 13, 1886, in Sumter and Marengo Counties,
where perceptible movement of Earth was reported along the
Tombigbee River. An earthquake on May 5, 1931, in northern Alabama was felt in Birmingham and caused minor damage at Cullman; the Mercalli intensity was V–VI, and the
affected area was about 6,500 square miles (17,000 km2). On
April 23, 1957, an earthquake in the area of Birmingham,
estimated at intensity VI on the Mercalli scale and affecting an area of about 2,800 square miles (7,000 km2), caused
minor damage in Birmingham; loud noises were associated
with this earthquake in some locations. The August 12, 1959,
earthquake along the border of Alabama and Tennessee
caused minor damage and was estimated at intensity V; the
earthquake affected an area of some 2,800 square miles. An

earthquake on February 18, 1964, along the border of Alabama and Georgia measured Mercalli intensity V and Richter magnitude 4.4.

Alaska United States The largest and northernmost state of
the United States, Alaska also is one of the most seismically
and volcanically active parts of the country. Earthquakes in
Alaska are concentrated in two belts, one extending along the
southeast coast and another reaching from the interior near
Fairbanks southwestward along the Aleutian Islands. The
1964 Good Friday earthquake, one of the most powerful and destructive earthquakes of the 20th century, occurred
along the southern coast of Alaska and, along with the tsunami associated with it, caused extensive destruction as far
south as Crescent City, California.
Volcanism in Alaska has been both frequent and destructive throughout history. A familiar case in point is the eruption of Katmai in 1912. This eruption created a caldera
some three miles wide and laid down a plain of fumaroles
later named the Valley of Ten Thousand Smokes. The
volcanic arc in Alaska extends more than 1,000 miles (1,600
km), from Cook Inlet in the east to Buldir Island near the tip
of the Aleutian chain in the west. More than 70 volcanoes
exist in the Aleutian Islands and on the Alaska Peninsula.
The Alaskan volcanoes and earthquakes are an expression
of activity along a subduction zone marked by the Aleu-


Alaska

As a result of the 1964 Good Friday earthquake in Alaska, a rockslidedebris avalanche (dark area) was generated in Shattered Peak and
spilled over Sherman Glacier (white). (Courtesy of the USGS)

Locations of many active volcanoes of the Aleutian arc, Alaska

5

tian Trench south of the Alaska Peninsula and the Aleutian
Islands. The Aleutian Trench reaches depths greater than
20,000 feet (6,000 m). North of the Aleutian Islands, in the
Bering Sea, lie the Pribilof Islands, which were formed by
eruptive activity but do not constitute part of the Aleutians.
A history of earthquakes and volcanism in Alaska would
occupy an entire volume, and all an article of this length can
do is present a few examples.
A very strong earthquake accompanied the eruption of
Pavlof volcano on the Alaska Peninsula in 1786. A tsunami,
or seismic sea wave, reportedly flooded land on Sanak Island,
the Shumagin Islands, and the Alaska Peninsula on July
27, 1788, with considerable loss of human life and of livestock. In May 1796, an earthquake with frightening noises
affected Unalaska Island, and Bogoslof volcano cast out
rocks as far away as Umnak Island. In 1812, powerful earthquakes accompanied an eruption of a Sarycheff volcano on
Atka Island. Umnak Island underwent a strong earthquake
in April 1817, when Yunaska volcano erupted. Sometime in
1818, an earthquake near Makushin volcano and Unalaska
Island is said to have caused great alterations in the landscape. Unalaska Island experienced two earthquakes in June
1826, but details are unavailable. An earthquake described as
“severe” struck the Pribilof Islands on April 14, 1835; and
in April 1836, the Pribilofs were subjected to shocks so powerful that they knocked people off their feet. An earthquake
on September 8, 1857, was very powerful but apparently
caused no damage. A minor earthquake on May 3, 1861,
at St. George Island in the Pribilof Islands was accompanied


6

Alaska

by noise from underground. On August 29, 1878, an entire
town on Unalaska Island appears to have been destroyed by
a tsunami and earthquake.
Augustine volcano erupted on October 6, 1883; a very
powerful earthquake and a tsunami occurred in connection
with this eruption. An earthquake in the area of Prince William Sound in May 1896 was so violent that people who
were standing had trouble remaining on their feet. The Yakutat Bay earthquakes of September 3 and 10, 1899, were estimated at Mercalli intensity XI and at Richter magnitudes
8.3 and 8.6, respectively. The epicenter was located near
Cape Yakataga. The first of these earthquakes was felt with
tremendous violence at Cape Yakataga, but the second earthquake was the one that caused major changes in topography.
A U.S. Geological Survey expedition to the region six years
after the earthquakes found widespread evidence of topographic changes. Beaches had been raised, and barnacles and
other aquatic organisms were lifted out of the water. On the
west shore of Disenchantment Bay, an uplift of more than
47 feet (14 m) was measured—approximately the height of
a five-story building. Over a wide area, uplift of 17 feet (6
m) or more was observed. In some areas, depressions of several feet occurred. A tsunami thought to have been perhaps
35 feet (11 m) high occurred in Yakutat Bay, and tsunamis
were reported at other locations along the coast of Alaska as
well. There were reports of volcanic eruptions associated with
these earthquakes, but the “eruptions” are presumed to have
been merely large clouds of snow released in slides caused
by the earthquakes. Strong aftershocks occurred over several months following these earthquakes. No loss of life was
attributed to the earthquakes because the area was not yet
settled; a small number of Native Americans and prospectors,
however, witnessed the earthquakes firsthand.
On September 21, 1911, an earthquake of Richter magnitude 6.9 on the Kenai Peninsula and Prince William Sound
broke cables, caused great rockslides, and killed large numbers of fish; water at Wells Bay was reportedly disturbed

greatly. Cables broke also in another earthquake on January 31, 1912, in the vicinity of Prince William Sound; this
earthquake, which was measured at Richter magnitude 7.25,
appears to have been centered west of Valdez and was felt
in Fairbanks. Very strong shocks occurred at Kanatak, Nushagak, and Uyak on June 4–5, 1912, and were felt more than
100 miles (161 km) away from Mount Katmai, although the
earthquakes may have been unaffiliated with the June 6 eruption of Mount Katmai. An earthquake of Richter magnitude
6.4 at Cook Inlet on June 6, 1912, coincided with a bright
display of light from Katmai, and the shock was recorded
at many distant locations, including Ottawa, Ontario, and
Irkutsk in Russia. Very strong earthquakes were reported on
the night of June 6 at Kodiak, and on June 7, a strong earthquake struck Kanatak, together with rockslides and a powerful rumbling noise.
An earthquake near Seward on January 3, 1933, measured at Richter magnitude 6.25, was felt very strongly at
Anchorage, and caused alarm at Seward; the ground cracked
in numerous places in the vicinity of Seward, notably for a
distance of 20 miles (33 km) along a road extending north
from the city. On April 26, 1933, an earthquake northwest

of Anchorage severed telegraph lines and broke plate-glass
windows and was felt also in Fairbanks and in the Aleutian
Islands. Houses were displaced from their foundations at
Old Tyonek. The principal shock measured Richter magnitude 7.0. Old Tyonek experienced further damage several
weeks later when an earthquake of magnitude 6.25 occurred
there on June 13, 1933. The May 14, 1934, earthquake on
Kodiak Island measured magnitude 6.5 and was felt strongly
on Whale and Kodiak Islands; plaster was cracked, and roads
were blocked by landslides. An earthquake of magnitude
6.75 in south central Alaska was strong enough to break
plate glass in Anchorage on August 1, 1934.
Tsunami damage was remarkable in the magnitude 7.4
earthquake of April 1, 1946. Centered about 90 miles (145

km) southeast of Scotch Cap Lighthouse, the earthquake produced a tsunami that demolished the lighthouse and caused
damage at widely separated locations in and around the
Pacific Basin, along the Pacific coasts of North and South
America, in the Aleutian Islands, and in the Hawaiian
Islands, where 173 persons drowned and property damage
was estimated at $25 million.
The earthquake of March 9, 1957, measured Richter
magnitude 8.3 and was one of the greatest natural calamities
in Alaskan history. The earthquake, which involved hundreds
of aftershocks and affected an area approximately 700 miles
(1,127 km) in length along the southern border of the Aleutian Islands between Amchitka Pass and Unimak Island, was
accompanied by a tsunami 40 feet (12 m) high that struck
the shore at Scotch Cap, and a 26-foot (8-m)-high tsunami
that caused extensive damage at Sand Bay. On the islands of
Kauai and Oahu in Hawaii, the waves destroyed two villages
and caused several million dollars in damage. The tsunami
was 10 feet (3 m) high along the coast of Japan, and a wave
six feet (2 m) high was reported in Chile.
The earthquake of July 9, 1958, is famous for the dramatic effect it produced at Lituya Bay, on the Gulf of Alaska
in the southeastern part of the state. A tremendous rockslide
at the head of the bay produced a giant wave (seiche)—more
than 1,700 feet (518 m) high—that swept outward through
the mouth of the bay and is thought to have killed two people who were caught in the wave. A fishing boat with two
occupants was carried out of the bay by the wave front and
reportedly cleared the spit at the mouth of the bay by at
least 100 feet (30 m). The wave also wiped the rim of the
bay clean of trees. Otherwise, little damage was reported
from this earthquake, except that underwater communication
cables were broken in the vicinity of Skagway, and Yakutat
experienced damage to bridges, a dock, and oil lines. Great

landslides reportedly occurred in the mountains, and fissures and sand blows were reportedly widespread on the
coastal plain near Yakutat.
The Good Friday earthquake of March 27, 1964, is covered in detail elsewhere in this volume.
Among the volcanoes of Alaska are Katmai, Augustine,
Pavlof, Redoubt, Iliamna, and Shishaldin. Numerous
calderas, indicative of eruptive activity followed by collapse,
are found at locations such as Aniakchak, Emmons Lake,
Fisher, Little Sitkin, Okmok, Semisopochnoi, Veniaminof, and the Wrangell Mountains.