Post-eruptive flooding of Santorini caldera and implications for tsunami generation

The explosive eruption of Santorini volcano in Greece in the Late Bronze Age, 3600 years ago, was one of the largest eruptions known from the past 10,000 years. It was at least 3 times larger than the eruption of Krakatoa, Indonesia in 1883, and evacuated large volumes of magma causing collapse of the caldera, which is now flooded with seawater. Tsunamis from this eruption are thought to have swept across the southern Aegean Sea, causing damage to coastal towns, harbours, shipping and maritime trade, while ash was deposited as far away as the eastern Mediterranean and the Black Sea. For some time, this eruption was thought to have precipitated the collapse of the Bronze Age ‘Minoan’ civilization on Crete, although this is now thought to have happened a couple of centuries after the Santorini eruption.

New work, involving Tony Watts, Tamsin Mather and David Pyle from Oxford, sheds light on when and how these tsunamis formed; and on what the island of Santorini looked like before the Bronze Age eruption. A detailed survey of the present day sea floor shows that the caldera was not open to the sea during the main phase of the eruption, and only flooded after the main phases of the eruption had finished. Before the eruption, there would have been an older crater in the northern part of Santorini, partly filled with a shallow lagoon – but not open to sea. During eruption, this surface would have collapsed dramatically, leaving a narrow barrier of rock between the new caldera and the sea. Rapid inflow of seawater then cut a deep channel, that can still be seen in north of the island today; and the present-day caldera would have filled up in just a couple of days.

It was previously thought that collapse of the caldera led to the formation of a major tsunami; but this is ruled out by our new evidence. Instead, any tsunamis would have been generated during the eruption, as pyroclastic currents entered the sea around the edges of the volcano.

Paper

Nomikou, P, T.H. Druitt, C. Hübscher, T.A. Mather, M. Paulatto, L.M. Kalnins, K. Kelfoun, D. Papanikolaou, K. Bejelou, D. Lampridou, D.M. Pyle, S. Carey, A.B. Watts, M.M. Parks,2016,  Post-eruptive flooding of Santorini caldera and implications for tsunami generation, Nature Communications, http://dx.doi.org/10.1038/NCOMMS13332

Image

Photo of the northern entrance to the Santorini caldera, Greece. New work suggests that this formed shortly after an eruption 3,600 years ago, allowing the sea to rush in.