Kolumbo submarine volcano is located about 8 km northeast of Thera volcano (fig. 1). It is elliptical in shape, rises about 300 m from the surrounding seafloor, and extends for 8 km along its long axis. Initial construction of the volcano involved the eruption of 2 km3 of dacitic to andesitic magma. An explosive eruption from 1649-1650 AD produced a submarine caldera 3 km in diameter and 500 m deep.
The 1649-1650 AD eruption involved the discharge of about 1 km3 of gas-rich rhyodacite to andesite magma. This magma erupted explosively due to the release of dissolved gases in the magma and interaction of the magma with seawater. An eruption column was formed over the vent and broke through the surface of the sea. It would probably have looked like the explosive eruption of Kavachi submarine volcano in the SW Pacific that took place in 2000 (fig.2). At Kolumbo, the volcano emerged briefly above the sea surface as erupted material accumulated around the vent, but subsequently collapsed during the formation of the caldera (fig. 3). The collapse triggered a tsunami that caused damage on nearby islands up to 150 km away. In addition, the release of gas during the eruption caused the deaths of more than 70 people and more than 1000 animals on the island of Thera.