Supposing 3600 years ago Santorini went through a 50km3 caldera eruption (as cited in wikipedia), I tried to calculate the resultant Archimede push-up and force in Newtons in order to get an idea of the tsunami that followed. I'm pretty sure I'm wrong but it gave me 50 giganewtons (490.000.000 newtons) which means a force 10 puissance 9 (when Hiroshima was only 10 puissance 5)