Bronze Age tsunamis driven by massive Santorini eruption

The Greek island of Santorini is famous for its picturesque whitewashed houses, clinging to cliffs above a pure azure sea.

But around 3,600 years ago, it was a different story.

The islands, arranged in a half-moon, are what remains after a massive volcanic eruption blasted up to 80 cubic kilometres of rock into the ocean.

At some point, the volcanic crater collapsed – thought to have initiated a tsunami that travelled to the neighbouring island of Crete and leading to the demise of the Minoan civilisation there.

But now, new seismic and ocean floor data – along with modelling – suggests something different: that the flow of hot ash, rock and lava (called pyroclastic flow) that tumbled into the ocean before the crater collapsed was the culprit behind the tsunamis.

Paraskevi Nomikou from the University of Athens and colleagues published their theory in Nature Communications.

The Bronze Age Minoan civilisation had a pretty good run. It arose on Crete and other Aegean islands around 5,800 years ago and flourished for more than 2,000 years.

But all good things must come to an end.

For the Minoans, their demise is thought to have come from the volcanic island of Thera – present-day Santorini – some 100 kilometres from Crete.

Ash and rock layers speak to a spectacular eruption – perhaps one of the largest Earth saw in the past few thousands of years.

Debris layers at the Minoan archaeological site of Paleokastro on Crete show waves of at least nine metres washed along the Thera-facing coast, destroying towns and harbours.

The tsunamis, archaeologists suspected, were created when the Thera volcanic crater collapsed, dropping vast amounts of the island into the sea.

But Nomikou and colleagues think otherwise – they suggest the crater collapsed later in the piece, and that the tsunamis were generated by vast pyroclastic flows from the eruption.

While computer modelling of a crater collapse recreated the nine-metre waves on Crete – as did pyroclastic flows – the researchers analysed the sea floor beneath the crater and its surrounds by measuring shockwaves travelling through the rock to ascertain their composition.

Pyroclastic rock deposits, some 60 metres thick, lay offshore. Deep sea “megaturbidities” – vast sediments deposited by a turbidity current – were found in the Creten basin south of Santorini.

The crater, they state, was not open to the sea while the eruption was in full swing. But once the main eruption passed, the crater walls started falling.

Those landslides let ocean water rush into the crater through a channel to the north-west, and filled the crater in less than a couple of days.

Cosmos Magazine, 8/11/16

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