Prior to the volcanic eruption, the island of Thera had a circular shape and was known as Stroggyli, meaning ‘round’. In the eruption, large quantities of molten materials were forced out of the earth’s core, forming an underground magma chamber. When the roof of the chamber collapsed, a large portion of the island became submerged, leaving in its place the caldera, extending over a surface of 85 square kilometres.

The sea flowed into the caldera, creating large tidal waves, which overwhelmed the surrounding islands within a 50-60 kilometre radius.