Thera and the Minoans

I first became interested in the Minoans when I read an article in the New Scientist by Stuart Manning (S.Manning 'A new age for Minoan Crete' New Scientist 11. Feb. 1989). The article was on the dating of pottery which was important, but the issue which took my attention was a description of a theory due to Marinatos that the demise of the Minoans was due to the eruption of Thera, a group of volcanic islands in the Aegean about 120 kms north of Crete. The largest island is Thera with two other smaller islands Therasia and Aspronisi. These islands form the rim of the caldera of the volcano. Incidentally Thera is also called Santorini after a chapel to Saint Irene. Dating of tree rings, and indicators from ice cores suggested a date for the Bronze Age eruption as around 1628/7 BC. date. However, the chemical composition from volcanic glass found in the ice cores does not agree with the composition of volcanic glass from Thera (G. A. Zielinksi and M. S. Germani J. Archaeological Sc. 25, page 279, (1998)). The date of the eruption must now be considered very uncertain.

Marinatos was captivated by the idea that the eruption of Thera was similar to the eruption of Krakatoa in 1883. He had begun excavating near the village of Akrotiri and found a Minoan city which had been buried by the bronze age eruption of the island. If you go to Thera you will see two main islands forming the edge of the caldera. Marinatos thought that in the bronze age the island would have appeared like Krakatoa before it erupted: an island with a towering volcanic cone. Since he knew that the eruption of Krakatoa had produced giant waves which killed around 36,000 people in coastal communities, he argued that Thera would have done the same. He therefore suggested that the Minoan coastal communities of northern Crete would have been devastated by the bronze age eruption. In fact, geological work by Tim Druitt and others has shown that before the bronze age eruption there was no towering volcanic cone and the caldera with the surrounding cliffs was similar to its present day caldera. The main difference is that the northern part of the caldera was possibly a shallow lagoon which collapsed after the bronze age eruption to complete the deep caldera you see today. Here are some useful references about the Minoans and Marinatos' theory.

R. Casteldon LIFE IN BRONZE AGE CRETE
1990. Publ. Routledge.

J. Lesley Fitton THE DISCOVERY OF BRONZE AGE CRETE
1995 British Museum Press.

S. Marinatos THE VOLCANIC DESTRUCTION OF MINOAN CRETE
Antiquity vol 13, page 425, (1939).

O. Rackman and J. Moody THE MAKING OF THE CRETAN LANDSCAPE
1996 Manchester Univ. Press.

Volcanic generation of Tsunamis

Tsunamis are giant waves which are produced by a rapid dislocation of huge volumes of water in the ocean. The dislocation can be due to the motion of the sea bed, to underwater landslides, and various disturbances associated with volcanoes. For example the collapse of a volcanic island, as was the case with Krakatoa, or pyroclastic flows bursting from the volcano and driving into the sea. An illustration of the power of the pyroclastic flow was the flow from the eruption of Mount St Helens.

The bronze age eruption of Thera produced massive pyroclastic flows which were able to climb over cliffs up to 300 metres high. The deposits from these flows are now about 60m deep over a large part of the main island.

Our initial research was focussed on the generation of tsunamis by pyroclastic flows and what happens when they run onto a beach.

J.J.Monaghan, R.F. Cas, A. Kos, and M. Hallworth. J. Fluid Mechanics (1999).

J.J.Monaghan, and A. Kos J. Waterways, Ports, Coastal and Ocean Eng. (2000).

Where does the Tsunami go ?

A tsunami generated at Thera travels across the sea in a manner dictated by the bottom topography. It goes faster where the depth is greater. Taking account of the depth we find the wave front varies as shown in the adjacent illustration. The wave is therefore very greatly weakened west of Mirabello bay. If it had been 20m high at Thera it would have been only about 4m high near Iraklion. This is quite large but only comparable to severe winter storm waves. On the other hand East of Mirabello bay the waves are focussed and nearly as large as at Thera. A likely Minoan site is Mochlos where Prof. Geoffrey Soles has led an excavation for a number of years. He finds Theran ash on Mochlos but no indication that the island was devastated by waves.

Coring on Crete

Extensive investigations of the north coast of Crete from Rethymnon to Zakros by a team involving E.Zangger, A.Kos and myself found only one place where sediments could have been retained for the roughly 3500 years since the eruption of Thera. That was the swamp at Malia. We cored this swamp in 1997 in the company of Dr. D. Dominey-Howles whose Ph.D. thesis described his extensive coring along the coast of Crete.

Our coring produced the deepest cores obtained on this coast and indicate at least one singular event where the salt water content of the swamp increased significantly. This work is incomplete and we are planning a more extensive coring of the swamp in 2002.

Projects

We plan to core the swamp at Malia in June 2002. If you are interested in joining us then please let me know.

There are opportunities for people with the appropriate skills to join us in the following project:

1. The construction of a model of Santorini to study waves generated during caldera collapse