Volcanic activity timetable until Minoan eruption
1645 BC - The Minoan eruption
It was one of the largest plinian eruptions in younger time. It erupted ca. 30-40 km 3 rhyodacitic magma and is ranked VEI=6 (Volcanic Explosivity Index after Simkin and others, 1981). The eruption was followed by collapse of the magma chamber that enlarged an existing caldera.
The height of the plinian eruption column is estimated 36-39 km (Pyle, 1990). It dispersed tephra throughout the Eastern Mediterranean and might have led to global climatic impacts. Its deposits on Santorini consist of up to 50 m thick layers of white pumice and ash.
[bbc] The Minoan civilisation on Crete came to a sudden end in the middle of the 2nd Millennium BC when all the Minoan palaces were burnt down and never rebuilt. In 1939, Spyridion Marinatos, a Greek archaeologist, came up with the theory that the eruption of Mount Thera brought about the end of the Minoan Civilisation. At the time, the dates of the palace burning and the eruption were not known very accurately. Marinatos's theory was that when the mountain collapsed into the caldera, a giant wave would have been formed which would struck the north coast of Crete, which is only 125km away. Since most of the Cretan civilisation was along the coast, this would have been destroyed. Looters then finished the job by burning what was left.
This theory is very popular and is often quoted in guidebooks about Crete. Unfortunately for the theory, the dates of the two events are now known more accurately. The burning of the Minoan palaces happened around 1450 BC. There are two possible dates for the Minoan eruption, but they are both before 1600 BC. An analysis of tree growth rings sets the eruption at 1628 BC, while counting the seasonal layers in cores of ice from the Greenland ice-cap sets the date at 1645 BC. So the Minoan civilisation didn't fall until nearly 200 years after the eruption.
180 ka - 1600 BC - Second eruptive cycle and the northern lava shields
The second cycle comprises at least 7 bigger eruptions: Cape Thera, Middle Pumice at 60 ka, Vourvoulos, Upper Scoriae 1 and 2 at circa 40 ka, Cape Riva at 21 ka and the Minoan eruption at ca. 1645 BC. Parallel to or preceding these eruptions different lava shields grew in the northern part of the caldera: Simandiri lavas at ca. 170 ka, the Skaros and the Therasia shields probably between 60 and 20 ka.
Caldera collapse happened at least 3 times during that cycle and destroyed the biggest parts of the existing lava shield complex. The first one occurred after the Middle Pumice, Vourvoulos, Upper Scoriae 1 or 2 or incrementally during all of these eruptions. It created the so-called Skaros caldera that successively was filled by the almost horizontal lava flows of a large stratovolcano which are preserved at Cape Skaros. The Skaros caldera walls are visible at the steep contact of the Skaros lavas against the older cliff walls in north Thera.
The Skaros shield was probably destroyed by collapse during the Upper Scoria 2 or Cape Riva eruption. Finally, another collapse after the Minoan eruption (ca. 1645 BC) deepened and created the present-day caldera.
360-180 ka - First eruptive cycle
Druitt and others (1989) recognized two cycles of large explosive eruptions with chemical transition from mafic to silicic lavas. The first one began with the Cape Therma 1 eruption, a thick scoria flow deposit in southern Thera, and includes the deposits of Cape Therma 2, Cape Therma 3. It terminated with the rhyodacitic and very prominent Lower Pumice 1 and 2 (BU 1 and BU 2 ) eruptions at about 200 and 180 ka. All of these were probably erupted from vents of the Thera Volcano. The first cycle concluded with caldera collapse and created the BU-caldera. Rests of this caldera can be seen at the cliffs below Fira where a discontinuity separates the BU 2 deposits from the overlying layers.
530-180 ka - Peristeria and Thera Volcanoes
Between 530 and 430 ka a large stratovolcano called Peristeria volcano formed in the north of the present caldera. The cinder cones on the Akrotiri peninsula are probably later products of these shields, too. Today, the remnants comprise most of Megalo Vouno and Mikro Profitis Ilias. At about 350-250 ka another shield volcano grew within the center of the present-day caldera, called Thera volcano. Some of its lava flows are visible at Cape Alai and Cape Alonaki near Fira. The formation of that shield united the former isolated centers and the limestone massif to a compact island.
2000-500 ka - Akrotiri Volcanoes and cinder cones
The oldest volcanic rocks are found on the Akrotiri peninsula and the Christiania islands. They are composed of dacitic lavas that updomed the sea floor and produced various flows and pyroclastic deposits. They have been strongly altered by hydrothermal activity. The updomed areas still are well visible on the Akrotiri peninsula (Lumaravi and Archangelos hills). From marine fossils embedded in the tuffs, Seidenkrantz and Friedrich (1992) concluded a minimum age for the Akrotiri peninsula of 2 million years.
At the localities of Balos ("Red Beach"), Kokkinopetra, Mavropetra and Mavrocachidi, basaltic to andesitic strombolian scoria cones are exposed that flank the Akrotiri volcanoes. They might be related to the later volcanic centers of northern Thera (Megalo Vouno and Mikro Profitis Ilias). Druitt and Sparks (1996) recently dated them to 344" 25 thousand years.
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