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

In Santorini, the caldera was not open to the sea during the main phase of the eruption, but was flooded once the eruption had finished. Inflow of water and associated landsliding cut a deep, 2.0–2.5 km³, submarine channel, thus filling the caldera in less than a couple of days. If, as at most such volcanoes, caldera collapse occurred syn-eruptively, then it cannot have generated tsunamis.

http://www.nature.com/articles/ncomms13332