The first phase of the eruption was Plinian in style, ejecting pumice
and ash from a vent probably located in the center of a volcanic
island within the Thera caldera. During this phase, magma was discharged
at a rate of 2.5x108 kg/s and a 36 km-high eruption column
was produced, reaching well into the Earth’s stratosphere.
Pumice and ash fell all over the island, reaching thickness up to
6 m, with a volume of about 2 km3 of magma.
During the second phase, the volcanic island in the center of the
submerged caldera was disrupted and seawater flooded into the crater.
This caused violent steam explosions as water encountered hot magma,
and formation of dense steam-and-ash-rich clouds that spread over
the island and adjacent ocean. They deposited base-surge deposits
up to 12 m thick, laid down at temperatures of 150 to 250o
The third major phase of the explosive eruption created hot mixtures
of volcanic ash, pumice and gas, called pyroclastic flows, that
moved down the slopes of the volcano at hurricane speeds. These
flows were at a temperature of < 300oC and spread
over the entire island, continuing over the ocean surface. This
pumice and ash layers from this phase are 55 m thick at the caldera
rim, and contain blocks from the volcanic island up to 10 m in diameter.
During the fourth,
final, and most violent phase of the eruption, pyroclastic flows
at 300 to 350oC flowed over the islands and into the
sea. The gas-rich magma was erupting with an increasing flow rate
out of the crater(s) during this phase, resulting in a total erupted
mass equivalent to 40 km3 of magma. At the coast of Thera,
where the flows entered the sea, the deposits are up to 40 m thick,
indicating the great thickness of volcanic material that is likely
to lie on the sea floor from this eruption.