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Caldera:
the Spanish word for cauldron, a basin-shaped volcanic depression;
by definition, at least a mile in diameter.
Up
to about two million years ago, Santorini was a small non-volcanic
island. Remains of this can still be seen at Mount Profitis
Ilias in the southeast of the present island, which is made
from non-volcanic limestone. |
About two million years ago, volcanoes
under the sea to the west of the island started producing
magma, resulting in a number of small islands. Eventually
(around 500,000 years ago) there were two giant 'shield
volcanoes'. These are mountains in the shape of flat cones.
These mountains united with the non-volcanic island to make
one big island. Although neither of these mountains exist
any longer, geologists have given them names. The northern
mountain is called Mount Peristeria while the southern one
is called Mount Thera.
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About
200,000 years ago, things started hotting up. Mount Thera
started to produce vast amounts of magma and ash, eventually
completely emptying the magma chamber under the mountain.
The structure of the mountain was not able to support itself
and it went crashing downwards into the empty magma chamber,
leaving a caldera - a wide, deep hole in the ground. |
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This process was repeated in a whole series of eruptions over
the next 200,000 years, with both mountains producing magma,
collapsing, regrowing and collapsing again, each time deepening
the caldera and eventually leaving the island in the shape
it is today.
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Caldera
is nowadys covering approximately 32 square miles and the
water's depth varies from 300 to 600 meters. At the western
end of the caldera, we find the island of Therasia and an
inhabitant island, Aspronissi. By taking a good look at those
three islands we can easily distinguish a virtual borderline
of what used to be there before the caldera was formed. |
The
height of the Santorini caldera is 150 to 350 meters. The
length of the island from cape Exomitis to cape Mavropetra
is 18 kilometres. Her width varies from 2 to 6 kilometres.
The
shape of the present-day caldera has been changed many times
during the centuries, because of the uninterrupted volcanic
activity. |
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