The history of the Santorin caldera is much the same. Before the caldera was formed, between 1800 and 1500 B.C., the island of Santorin was a complex of overlapping cones, like Mount Mazama. A long period of quiet preceded the climax. Here again, the first eruptions were mild. The inhabitants of the island had time to escape and their buildings remained intact. As the eruptions continued, they became more violent. Of all the material erupted, only 1 per cent consisted of old rock fragments; the rest came from the magma chambers. Obviously, therefore, the formation of the caldera was not caused by explosive shattering of the old cones, but by collapse. Engulfment was controlled partly by the positions of the original cones, for the scalloped margin of the caldera is determined by concentric fractures about separate vents. Just as Cleetwood Cove and perhaps Grotto Cove, on the edge of Crater Lake, lie on the sites of former vents, so do the semicircular coves along the edge of the Santorin caldera. Collapse was also controlled, as at Krakatau, by radial zones of weakness, and by regional, tectonic lines which determined the roughly rectilinear outline of the caldera. Fifteen hundred years elapsed before renewed activity began on the caldera floor. In 197 B.C., a dome of dacite rose from the sea. Since then, several other domes have risen at long intervals, the last during the years 1925 to 1928.
The great calderas of Japan, particularly those of Kyushu, also owe their origin to engulfment following copious eruptions of pumice and tuff. Lake Taupo and other lakes on the North Island of New Zealand are clearly related to crustal foundering along tectonic lines following immense outpourings of rhyolite tuff from swarms of fissures. So are the great lakes along the Barisan rift zone in Sumatra. It is the absence, near all these calderas and volcano-tectonic depressions, of an adequate volume of old, lithic detritus that explodes the explosion hypothesis.
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