In the 17th century B.C., Santorini was a small volcanic island in the Aegean Sea, home to Akrotiri, a Late Bronze Age outpost of Minoan civilization, which preceded ancient Greece. Then the volcano erupted, burying Akrotiri in ash and obliterating much of Santorini, turning it into a few smaller islands.
The eruption was one of the world’s most powerful in the past 10,000 years, spewing some 20 cubic miles of rock into the skies and spawning a tsunami that struck the nearby island of Crete, which was the center of Minoan culture. Many archaeologists believe the tsunami was disruptive enough that the Minoans became easier prey for the outside invaders who conquered them a century and a half later and brought an end to one of the first European civilizations.
But what caused the tsunami? Research published Tuesday, including seafloor surveys, suggests that it was likely caused by huge amounts of hot ash and lava spewing from the volcano — what volcanologists call pyroclastic flows — and pouring down its slopes into the water at high speed.
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The study contradicts earlier explanations that the tsunami must have been the result of a caldera collapse, which occurs when the crust above a volcano’s magma chamber slips swiftly downward as the chamber empties during an eruption. At Santorini, the thinking went, much of the island — the caldera was huge — sank suddenly into the Aegean, triggering the tsunami.
The new data suggests that the caldera was cut off from the sea. “When the caldera collapsed, it was isolated — there was no water inside,” said Paraskevi Nomikou, a geologist at the National and Kapodistrian University of Athens and the lead author of the study in Nature Communications.
Dr. Nomikou said that other surveys show deposits of pyroclastic material up to 200 feet thick just off Santorini. Pyroclastic flows can travel at speeds of several hundred miles an hour down slopes, so there was enough lava and ash, moving quickly enough, to spawn a tsunami.
In this respect, Dr. Nomikou said, the eruption at Santorini is comparable to another eruption, at Krakatoa in the Sunda Strait in Indonesia in 1883. Pyroclastic flows from that eruption caused a tsunami that killed more than 35,000 people.