pile. Different materials (gravel, clay, boulders, etc.) form dif-
ferent slope angles; typically, the more friction among parti-
cles, the steeper the slope.
The condition of the material may also control the angle
of repose. For example, the angle of repose of damp sand is
very high. The moisture has surface tension that produces
capillary action among the grains and holds them tightly
together. That is why people can make sand castles on the
beach. On the other hand, if a lot of water is added to a mate-
rial, it turns into a slurry and has a very low angle of repose.
Soupy mud lies almost flat when spilled onto the floor. If a
slope is frozen, it can maintain a much higher angle of repose
than one that is simply wet. Temperature may also play a role
in some cases, as can wind, which may blow down slopes in
some cases, or earthquakes and other vibrations, which tend
to shake slopes down.
Vegetation can also enhance the angle of repose for large
slopes outside. Trees have very deep roots and tend to hold
the soil together, thus greatly enhancing the angle of repose.
Grass can also hold the slope together a little but not as
well as trees. People also affect the angle of repose for larger
slopes through a variety of methods, such as cement, retain-
ing walls, gravel or riprap, netting, and drainage ditches and
culverts, among others. Typically, people attempt to increase
the angle of repose with varying degrees of success. The
landslides and mudflows in California that are reported
by the media on occasion are examples of poor results.
Aniakchak caldera, Aleutian Islands, Alaska, United
States The Aniakchak caldera is located in the eastern
Aleutian island arc near Bristol Bay. Surprise Lake occu-
pies part of the crater. Several cones and necks are found
on the floor of the caldera, including Vent Mountain. Aniak-
chak formed about 3,400 years ago and has had about 10
eruptions since. Powerful explosions occurred at Aniakchak
in 1931, possibly from a cinder cone. A dome formed in the
vent late in the eruption.
Ansei Tokai earthquake, Japan A strong earthquake
struck the island of Honshu, Japan, on December 23, 1854,
in the Ansei-Tokai area. The main shock was estimated at
8.4 on the Richter scale, but a strong aftershock with
estimated magnitude of 7–7.5 occurred less than 24 hours
later, at 8 a.m. on December 24, 1854. The focus was on
the Tokai Fault, which extends from the east coast of the Kii
Peninsula to the Suruga Bay. It was generated at a shallow
level in the crust, unlike the typical subduction zone earth-
quakes in Japan.
The thick, soft sediment in this part of Japan enhanced
the surface waves, which led to excessive ground move-
ment. liquefaction produced large water spouts that were
even seen being emitted from Suruga Bay. One of the most
devastating effects of both strong shocks were the tsunamis
they produced. These waves ranged from 6.5 to 23 feet (2 to
7 m) in height and reportedly battered and beached some 200
boats in Osaka Bay alone. The reported death tolls for this
combined event were conflicting. The most reliable figure was
in excess of 5,000 people, but some reports were as high as
31,000 people. One of the most ominous aspects of this event
is the lack of subsequent large earthquakes in the area. With
a recurrence interval of 100–150 years, the Tokai area is
overdue. The predicted casualties in this now highly popu-
lated area from a magnitude 7 earthquake are approximately
6,000 deaths and 19,000 injuries. Another 8.4 earthquake
would be even more disastrous.
Antarctica Although the historical record of seismic and
volcanic activity in Antarctica is not as extensive as the
record for more densely settled portions of the world, much
is known about earthquake and volcanic activity on the Ant-
arctic continent. The volcano Mount Erebus was discovered
by Captain James Clark Ross of Britain on an expedition to
reach the south magnetic pole. Erebus reportedly was erupt-
ing at the time of Ross’s visit. The volcano and a nearby
crater were named Erebus and Terror respectively after the
two ships on Ross’s expedition. A later expedition under the
command of Ernest Shackleton climbed Erebus in the first
ascent of a mountain in Antarctica. However, Antarctica is
considered tectonically quiet, and earthquakes and volcanoes
are few and are mostly located along the edges of the conti-
nent and offshore. Other sites of volcanic activity on or near
Antarctica include Deception Island, Hampton/Whitney,
Takahe, Thule Island, and Waesche.
Antioch earthquake, Syria On the evening of May 29, a.d.
526, one of the world’s great natural disasters struck the city
of Antioch, Syria, which is now Antakya, Turkey. The city of
Antioch was founded about 300 b.c. by Syrian emperor Seleu-
cus I but was captured by Rome in a.d. 25. Saint Paul selected
it as the center of his work in Galatia around a.d. 50. Antioch
thus became a prominent city for both trade and Christian-
ity. During the sixth century a.d., the Feast of the Ascen-
sion, 40 days after Easter, became one of the most prominent
Christian festivals. In a.d. 526, the holiday fell on May 30,
and hordes of people flooded Antioch in the preceding days
in anticipation. When the huge earthquake, estimated at a
9.0 on the Richter scale, struck the city, it was devastating.
It was reported that most buildings simply collapsed, killing
virtually all inside, when the main shock struck. Fire swept
through the remaining buildings, and aftershocks toppled
remaining walls and buildings on escaping survivors. In all, a
shocking 250,000 people were said to have perished. The sur-
vivors fled from the city and were accosted and even killed by
people in the surrounding countryside. Sensing an opportunity
to advance their standing, bands of these country people came
back into Antioch to loot the city. They were reported to have
stripped rotting corpses of jewelry and other valuables. Rescue
and relief efforts appeared to have been slow and only under-
taken by a small group of survivors. Fortunately, Emperor
Justin I (a.d. 518–527) made a strong commitment to rebuild-
ing the city, which was carried on by his successor, Emperor
Justinian I (a.d. 527–565). The city never regained its former
splendor or prominence.
Aoba volcano, Vanuatu A shield volcano, Aoba is
basaltic and is situated along a fissure system that has
given the island an elongated shape. Although the volcano
appears to have grown through outpourings of fluid lava,
12 Aniakchak