Harrow and Hillingdon Geological Society

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Santorini June 2006

Jean Sippy and Joan Waters skipped the AGM this year and went to Santorini with a Bristol University field trip, led by Prof Donny Huttton and Dr Peter Hardy.

Santorini is made up of five islands in and around the rim of a volcanic crater. It is most famous for the event in about 1500BC when the island’s central volcano erupted. When the crater collapsed sea water entered causing a tsunami which was thought to have contributed to the collapse of the Minoan civilisation on Crete.

The event is referred to as the Minoan eruption and the four stages of the eruption produced four cream coloured layers of pumice (with various degrees of mafic inclusions) called Minoan 1, 2, 3 and 4, which we soon learnt to recognise.

What is not generally known is that there were at least four other volcanic centres on the island erupting before the Minoan eruption. These rocks are mainly coloured so in most cases easy to distinguish from the Minoan deposits, but are of a very complex nature consisting of lavas, pyroclastic flows, cinder cones and more. Several of these centres were effectively sectioned by the Minoan eruption so the current crater gives a view of their internal dykes.

There is a core of upper Triassic crystalline limestones, which forms Mt Profitis Ilias, the highest point of the island. This was uplifted by the collision of the African tectonic plate with the Eurasian plate. This collision is the cause of the volcanism.

In the centre of the caldera is the growing new volcano of Nea Kameni. The Santorini volcano has had twelve major eruptions in the last 600,000 years and this new volcano is expected to grow and have another major eruption in the next 20.000 years. The last small eruption was in 1951 and the last significant earthquake was in 1956 which badly damaged the northern village of Oia.

For the archaeology, on the Megalo Vuono promontory next to Mt Profitis Ilias is the Ptolomeic old capital, Old Thera. In the south of the island is Old Akrotiri the pre-Minoan settlement overwhelmed by the Minoan eruption.

The other significant aspect of Santorini is its beauty. The blue of the sky, the blue of the sea, the white and blue of the houses and churches, one can understand why the Greek flag is blue and white.

	Mt Profotis Ilias on the left and Megalo Vuono on the right. This is the highest point of the island and is composed of limestone.
	These are the Minoan deposits showing the four stages of erruption. Note the bombs embedded in the layers.
	Red Beach near Akrotiri. The fissure that these pre-Minoan erruptions extruded from can be seen on the right. The paler Minoan deposits form the new land on the left.
	Nea Karmeni, the new volcano forming in the centre of the caldera.
	Approaching Skaros in the boat. This was the site of the Island's capital in the 15th Century. Prints exist showing many houses clinging to the side of this promontary.
	This shows a dyke where the lava forced its way through a pre-existing fault. The downthrow on the right is clearly visible.
	It is a matter of conjecture what caused this massive distortion in otherwise level deposits.
	This shows the idyllic village of Oia. Closer inspection shows the unrepaired damage from the earthquake in 1956.

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