of which is the Andes Mountains. If ocean crust is driven
beneath ocean crust, an island arc is formed. An example
of this is the Aleutian Islands. The final type of convergent
boundary is a continent-continent collision. Because conti-
nental crust is so light, it cannot be driven into the asthe-
nosphere as can oceanic crust. It is too buoyant. Instead,
the crust is greatly thickened and pushed back onto itself in
huge thrust faults. It winds up looking like shingles on a
roof. The best example of a continent-continent convergent
boundary is the Himalaya Mountains.
converted wave When seismic waves hit a boundary
between two rock types of strongly varying seismic charac-
ter, a whole new set of waves is generated. These waves are
far weaker than the original wave and do not cause damage.
However, they are recorded by local seismographs at much
lower amplitude.
Copahué caldera, Chile Copahué is located on the border
between Argentina and Chile. The caldera includes a cen-
tral cone with more than one crater. The level of the lake in
Los Copahués crater reportedly fell more than 100 feet (30
m) between 1940 and 1945, and temperature and acidity
increased.
Corbetti See Asawa.
Cordillera Nevada caldera, Chile The Cordillera Nevada
caldera has experienced eruptions in 1921–22, 1929, 1934,
and 1960. The caldera is similar in some ways to the Long
Valley caldera in California.
core See Earth, internal structure of.
Corinth earthquakes, Greece The ancient city of Corinth,
Greece, and its modern successor have experienced contin-
ued seismic activity. The intensity of the early earthquakes
is debatable, but the city has an interesting earthquake history
nonetheless. The earliest record of an earthquake in Corinth
is from the summer of 420 b.c. The earthquake had an esti-
mated Richter magnitude of less than 6.0, but there are no
other details available. The next major earthquake, in 373
b.c., devastated the whole Gulf of Corinth. The earthquake
had an estimated magnitude of 6.8 on the Richter scale and
an X on the modified Mercalli scale at the city of Helike.
It generated a huge tsunami that engulfed the city of Helike
so that only the treetops were visible above the sea. Helike
was later discovered by archaeologists, completely submerged
in mud. Corinth was damaged by both the earthquake and
tsunami, but there are no details available. The next major
earthquake occurred during the night of June 20, a.d. 74.
It had an estimated magnitude of 6.3; three temples were
destroyed, but there are no other accounts.
There are reports of earthquakes from Corinth in a.d.
521, a.d. 543, and a.d. 580, with estimated Richter magni-
tudes of 6.3, 6.2, and 6.3, respectively. The real dilemma is
with a.d. 856. Some sources claim that a huge earthquake
destroyed Corinth that year, killing an estimated 45,000 peo-
ple. This would be one of the greatest disasters in the area.
Other reliable sources do not even mention an earthquake in
the region for that year. It remains unresolved.
The next important earthquake in Corinth occurred at
9 a.m. on February 21, 1858. Its estimated Richter magni-
tude was 6.5, and it caused destruction described as X on
the modified Mercalli scale. The shock lasted more than 10
seconds, and the maximum damage area was about 21 miles
(35 km) across. fissures opened in the ground, but the main
damage came from a rockfall into the city. It was reported
that only 21 people died and 65 were injured, but the damage
was so great and the aftershocks so persistent (they lasted
through May) that the city of Corinth, which was established
by Sisyfos in 1438 b.c., was abandoned. The survivors of
the earthquake established the city of New Corinth approxi-
mately eight miles (13 km) away. Unfortunately, that location
was no safer. On April 22, 1928, at 8:13 p.m., an earthquake
of Richter magnitude 6.3 caused damage of IX on the modi-
fied Mercalli scale. It destroyed 3,000 houses and made
15,000 homeless. It is considered to be the 33rd destruction
of Corinth since it was established.
Cos earthquake, Greece After nearly two years of fore-
shocks, a very destructive earthquake struck the small Greek
island of Cos, off the Turkish coast, on October 3, 1493. The
quake had an estimated Richter magnitude of 6.8 and an
intensity of X on the modified Mercalli scale in the town
of Kephalos. Many houses were destroyed in Antimacheia,
Kardamaena, as well as Kephalos and two historic towers.
The shock was felt in Egypt and Israel and was damaging in
Turkey. The death toll for this event was approximately
5,000 people.
Cosigüina volcano, Nicaragua Located on the Gulf of
Fonseca, Cosigüina has a history of violent eruptions, notably
that of 1835, which reportedly was heard from Colombia to
British Honduras, a distance greater than 1,000 miles (1,600
km). This eruption lasted more than four days. The caldera
rim of Cosigüina rises to an altitude of more than 2,800 feet
(853 m), and the inner walls of the caldera extend almost
3,000 feet (914 m) in places above a crater lake.
The 1835 eruption of Cosigüina occurred after a long
period of apparent quiescence, and it was widely believed
before this eruption that the volcano was extinct. Much of
the information on this eruption comes from the account of
the commandant of the port of La Union in El Salvador,
approximately 30 miles (48 km) from the volcano. A large
white cloud emerged from the summit of Cosigüina on the
morning of January 20, 1835. The cloud then changed color,
becoming first gray, then yellow, and then red. Evidently, no
seismic activity preceded the eruption. Shortly before noon,
the volcano’s emissions had produced such darkness over the
area that lamps had to be lighted in La Union. Fine pumice
began to fall in great quantities that afternoon, and darkness
in some places became virtually total. Several inches of ash
accumulated by late afternoon at one community in Hon-
duras, some 40 miles (64 km) north of Cosigüina. Ash fell
in El Salvador, more than 100 miles (161 km) northeast of
the volcano, by nightfall. Darkness continued the following
day, and residents of the area around the volcano felt strong
Cosigüina 57