New evidence on what caused tsunamis after massive Santorini volcanic eruption in the Bronze Age

Scientists had previously believed that the nine-metre tsunamis that smashed into the shores of Crete, dealing a severe blow to the Minoans that had dominated the region until that time, were caused by the collapse of the island's caldera, or volcanic crater, created during an eruption that blasted 80 cubic kilometres of rock into the ocean. 
Geologist-Oceanographer Dr. Paraskevi Nomikou and her colleagues from Athens University's Geology and Geo-Environment Department have now suggested an entirely different time line for these tsunamis, based on new seismic and ocean floor data, combined with modelling. According to their theory, published in Nature Communications, the tsunamis were the result of 'pyroclastic flow' - the hot ash, rock and lava that was spewed into the ocean before the crater's collapse.
The new data from their study seems to indicate that the caldera was not open to the sea during the main phase of the volcanic eruption but flooded afterwards, when the eruption was over. The Greek scientists have discovered a submarine channel measuring one kilometre across and three kilometres in length that links the caldera with the sea. They said that this was initially blocked by ash and other material from the explosion, acting like a dam. This subsequently gave way and filled the previously dry bed of the caldera with sea water in less than two days, or possibly even hours.
Talking to the Athens-Macedonian News Agency (ANA), Dr. Nomikou said that scientists have been studying the morphology of the Santorini volcano for years to discover which sections sank and which remained on the surface after it erupted.
"The new study shows us that there was a channel between Oia and Thirasia that was filled in by the explosion, so that the main caldera collapsed without causing a tsunami. Afterward, when the dam in the channel between Oia and Thirasia broke, sea water entered the caldera in two days at the most.
"Something like this, however, did not cause a tsunami. This was caused because, during the third and fourth phase of the eruption, huge quantities of volcanic ash were blown up into the air, and pyroclastic flows then entered the sea. These were what caused the tsunami that affected northern Crete and all the eastern Mediterranean," she said.
While the main eruption was in full swing, the Greek scientists suggest, there may have been little of no water inside the crater, which was cut off from the surrounding sea. They believe that a shallow caldera may have already existed in the north section of the island's volcanic field, created by a previous eruption 18,000 years ago. The major volcanic eruption in 1610 B.C. then made this more ancient caldera deeper and wider until it was flooded with water. 
In support of this theory, researchers have found deposits of pyroclastic material up to 60 metres thick on the seabed around the shores of Santorini, in quantities sufficient to cause a tsunami-like wave. This also agrees with later studies on the eruption of Krakatoa in 1883, which identified pyroclastic flows as the culprit for the tsunami generated at that time.
Scientists estimate that the eruption of Santorini took place at around 1610 B.C. - give or take 15 years -and was probably one of the largest the world has seen for the last 10,000 years. According to Nomikou, however, it was not responsible for wiping out Minoan civilisation as popularly supposed. She pointed out that Crete's Minoan civilisation managed to survive for almost two centuries after the tsunami hit - until roughly 1450 B.C. - and finally collapsed due to endogenous causes, though it was made more vulnerable.
Working with Nomikou on the Greek study were Dr. Dimitris Papanikolaou and Danae Lambridou, along with other scientists from France, Britain, Germany, the United States and Iceland.
The original paper is available at the address: nature.com/articles/doi:10.1038/NCOMMS13332.