Santorini – The volcanic caldera – The volcanic eruption

The volcanic eruption
The clearly-defined and variedly-coloured strata of the cliff-face as seen from the water are a legible section through the geological history of the island, showing that the island had been volcanically active for centuries before the ‘Great’ eruption. The uppermost layers give vulcanologists a picture of the various stages of that final cataclysm. It appears to have taken place over several months—perhaps even more than a year, beginning with premonitory tremors which gave the prehistoric inhabit ants of the island warning to leave. There appear to have been moments of quiescence, in which the inhabitants re turned to repair damage to their buildings, before being forced to leave once again on a journey which almost certainly culminated later in a gruesome death, even if they had managed to reach dry land on Crete. The final stages were a crescendo of eruptions covering the island with increasingly large volcanic debris settling to ever greater depths on the surface. As the core of the island was destroyed, a column of volcanic ash and steam was ejected into the atmosphere to a height of over thirty kilometres, where the lightest particles were distributed through the stratosphere by currents of air. The heavier tephra, also carried on a prevailing northwest wind, was spread across the southeast Aegean: deposits of up to a metre in depth have been found, for example, on the island of Rhodes .
   The immediate effects of this cataclysm can be under stood by an invaluable point of comparison: the well documented eruption of Krakatoa in Indonesia in 1883. After Krakatoa’s explosion, darkness lasting more than a day covered an area in excess of four hundred kilometres from the eruption: closer to the epicentre, the impenetrable darkness (of a kind described also by Pliny in relation to the comparatively tiny eruption of Vesuvius) lasted for three days. The colour of skies especially at sunset was affected all over the world; the changes were observed in London, and the sky’s unworldly hue is frequently referred to by Theodore Bent in the accounts of his last visits to the Cyclades in the winter of 1884. As a result of the destruction of Krakatoa, over 36,000 people lost their lives and more than three hundred villages were destroyed on neighbouring Java. The most dramatic damage was caused by the tidal surges and tsunami: waves in excess of 30m in height radiated out from the epicentre, carrying, in one case, a gun-boat which was moored in a harbour eighty kilometres north of Krakatoa, a distance of over three kilometres inland. The caldera left by the eruption of Krakatoa is between one quarter and one third of the size of that at Santorini; so the effects reliably recounted of its eruption need considerably magnifying when we are considering the eruption of Santorini. The immediate effect of this on Crete, ninety five kilometres to its south, is not hard to imagine: its coastal villages must have been destroyed along with all its harboured sea-craft; its coast al fields would have been inundated and then rendered impracticable for a long period by the layer of ash, and its buildings shaken down by the alternating tremors and blasts from across the water.