Kolumbo is an active submarine volcano in the Aegean Sea , about 8 km northeast of Cape Kolumbo , Santorini island . The largest of a line of about twenty submarine volcanic cones extending to the northeast from Santorini , it is about 3 km in diameter with a crater 1.5 km across . It was " discovered " when it breached the sea surface in 1649-50 , but its explosion was not to be compared to the well-known Thera explosion and caldera collapse , currently dated ca. 1630 BCE , with its devastating consequences for Minoan civilization . The Smithsonian Institution 's Global Volcanism Program treats it as part of the Santorini volcano . The 1650 explosion , which occurred when the accumulating cone reached the surface , sent pyroclastic flows across the sea surface to the shores and slopes of Santorini , where about seventy people and many animals died . A small ring of white pumice that formed was rapidly eroded away by wave action . The volcano collapsed into its caldera , triggering a tsunami that caused damage on nearby islands up to 150 km distant . The highest parts of the crater rim are now about 10 m below sea level
Thera explosion
Minoan eruption
Kolumbo