Geoscience Reference
In-Depth Information
6
Krakatoa Shakes the World
On 27 August 1883, the island of Krakatoa (Krakatau) in the
Sunda Strait, midway between Java and Sumatra, exploded with
a noise that woke the planet.ยน
The Krakatoa 'event', as volcanologists disarmingly put it,
profoundly disrupting and disturbing though it was for the im-
mediate area, was just one of many cataclysmic eruptions within
historic memory that were of the scale Volcanic Explosivity Index
(vei) of 6.5. This was larger than Vesuvius in ad 79 (vei 5.8), but
smaller than Tambora in 1815 (vei 7.3). It was still smaller than
some prehistoric eruptions, and yet larger ones had taken place in
the millions of years when the earth was still forming, but after
animal life began. This is a well-shaken planet.
The volcanic Krakatoa island, which before 1883 had been
known as the 'island with a pointed mountain', straddled the
area of sea where the Indo-Australian tectonic plate, colliding
into the Eurasian plate, is diverted downwards towards the
earth's core. As a consequence, there is a line of active volcanoes
along its leading edge. To say that the island was destroyed by
the volcano would be misleading, as it and the sea basin around
it had also been formed as a result of eruptions, and this was just
one step in a continuous process. Volcanoes explode at points
where pressure from simple mechanical shifts beneath the earth's
crust is too strong for the crust to hold in place.
Until mid-summer 1883, the Sunda Strait was the highway
for vessels trading east and west from Sumatra and Java. There
had been preliminary events beginning around 10 May, when
