Founded 1906
Archaeology Report Spring 2020
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Selected Article from the BHAS Bi-Annual magazine "Flint" Spring 2020
The Geology of the Mediterranean: BHAS Day School Tony Corrigan made an excellent job of explaining the complex geology of the Mediterranean Basin and the way in which its current configuration came into being. As archaeologists we are used to dealing with events that happened thousands of years ago but the time frame of geological processes extends many millions of years into the past and it can be difficult for the unini-tiated to get their minds around this. Tony began the day with a description of the make-up of Earth, as it is understood now. The outer crust on which we live lies over the mantle, which Is divided into two zones and reaches 2,900 kilometres down to the core. The ocean crust, mainly bas-alt, is about 5 km thick while the continental crust, mainly sili-cates and limestone is mostly 30-40 km thick but can extend to 100km in places. The crust and upper mantle are made up of tectonic plates which move over the mantle and faults in be-tween these plates allow for molten magma from the lower lev-els to erupt into the atmosphere as volcanoes. He then described what is believed to have been the way in which the Earth’s crust has changed over those millions of years: tectonic plates meet and coalesce into one, creating con-tinents and oceans; then break up and create new configura-tions. About 250 million years ago (mya) the giant continent Pangea broke up and formed two land masses separated by the huge Tethys Ocean but they are now moving together again. About 5.96 mya the nascent Mediterranean Sea was closed off from the oceans and dried up in an episode known as the Mes-sinian Salinity Crisis. About 5.33 mya the Gibraltar Straits reo-pened and the Mediterranean Sea filled up. This event, known as the Zanclean Flood, could have taken place over as short a time as one to two years. It is, however, still an area of negative precipitation and needs its link to the Atlantic Ocean to maintain its existence. Meanwhile, the tectonic plates which have been moving to-gether and created the more or less enclosed basin of the Mediterranean continue to push against each other as they have done over the millions of years, causing the formation of the mountain ranges which surround the Mediterranean Sea. Some of these mountain ranges and parts of the sea-bed have become very distorted by these tectonic pressures and the depth of the sea bed varies greatly. A major fault line runs more or less the length of Italy and extends south in to the sea. This has resulted in the many volcanic eruptions and earthquakes which both the mainland and islands experience. So the next time you visit Italy or other Mediterranean lands and islands try to imagine what will happen as the surrounding land masses move ever closer together, eventually strangling the Mediterranean Sea again and creating a new continent!
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