A volcanically-induced tsunami
Krakatau was a small volcanic island located in the Sunda Strait
between Java and Sumatra. Its activity has been chronicled by Simpkin and
Fiske (1983). The volcano began erupting in May, 1883, with
small ash clouds and rumblings. Although the modern scientific
approach to the study of volcanoes has exonerated the gods Pluto and
Vulcan from blame, the belief in myths and gods still tends to be
directly proportional to the proximity of the person to the eruption
-- certainly those who were close to Krakatau when it roared into vigorous
action at about 1:00 p.m. on 26 August. This event produced an
eruption column 30 kilometers high, and by 5:00 p.m. the first of
several giant sea waves (tsunamis), hit the coasts of Java and
Sumatra. The noise of explosions was described as deafening 40
kilometers from the volcano, but these explosions were only a prelude
to the main eruptions. The following day, at 10:02 a.m., most of the
island disappeared in a giant cataclysm that produced an ash column
that rose to a height of 80 kilometers. At about the same time that the
island disappeared, gigantic tsunamis rushed toward the Java and
Sumatra coasts. Several coastal villages were completely destroyed as
the giant waves rushed onto land as far up as 240 meters above sea
level. There were nine gigantic waves in all and 36,000 people
perished because of them.
It was originally thought that Krakatau beheaded itself in the
explosion, but pieces of the volcano that should have been abundantly
distributed in the area surrounding the volcano, were absent, leading
to the conclusion that so much pyroclastic material had emptied into
the atmosphere, that it created an empty chamber beneath the volcano.
Removal of support caused the volcano to collapse into the hole.
Recently, evidence has shown that the tsunamis were created by
displacement of sea water from the fall back of pyroclastic material
from the lower part of the towering eruption column (Sigurdsson et al., 1991).
Because Krakatau is an island, the enormous volume of material from the
collapsing eruption column entered the sea and displaced enough water to
generate the killer waves.
Sigurdsson, H., Carey, S. and Mandeville, C., 1991. Krakatau.
National Geographic Research, 7:310-327.
Simkin, T. and Fiske, R.S., 1983. Krakatau 1883: the volcanic
eruption and its effects. Smithsonian Institution, Washington, D.C.,