Travel Reference
In-Depth Information
ocean fl oor. On Boxing Day 2004, the tension between the two plates was
suddenly released. A 1600-kilometer stretch of the Indo-Australian plate
slipped to the north, resulting in a powerful 9.2 earthquake that released half
a million times as much energy as the little earthquake I encountered on Yap.
As a result of the earthquake the Indo-Australian plate moved about twelve
meters to the northeast. Dif erent parts of the island of Sumatra rose and
fell by two meters or more, shifts comparable in magnitude to the rise of the
Chilean coast that the crew of the
Beagle
observed.
Another result of the released tension was that a region of seafl oor along
the slip zone suddenly rose several meters, pushing 30 cubic kilometers of
ocean water upwards. It was this displacement that sent a tidal wave across
the entire Indian Ocean basin, killing almost a quarter of a million people.
Indonesia is a region of island arcs, volcanoes, and deep-sea trenches that
spans an area the size of the continental United States. It is daunting to think
about how many such earthquake-triggered tectonic shifts, including many
much larger ones that must have taken place before historical records began,
have played a role in the formation of Indonesia's more than 17,000 islands.
The events that would lead to Indonesia's formation began 250 million
years ago, at a time when the age of dinosaurs still lay 45 million years in
the future. At that time the world's landmasses were concentrated into two
great supercontinents. These in turn were the descendents of an even vaster
supercontinent called Pangaea.
The northern continent of Laurasia would give rise to North America
and Eurasia. The southern continent of Gondwana, which included land that
would contribute to Africa, South America, Antarctica, and Australia, lay far
to the west of Indonesia's present position.
It was at this time, a quarter of a billion years ago, that a severe mass
extinction, the Permo-Triassic event, devastated both supercontinents.
Ninety-fi ve percent of the world's species were wiped out, apparently by vast
volcanic eruptions. Among the many species lost was the little early seed
plant
Glossopteris
that had thrived all over Gondwana.
Soon after the extinction event Gondwana began to break up. Its descen-
dant fragments would eventually give rise to what are now Africa, India,
South America, Antarctica, Australia, and New Zealand.
