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Earth of fire

Actualité volcanique, Articles de fond sur étude de volcan, tectonique, récits et photos de voyage

Publié le par Bernard Duyck
Publié dans : #Excursions and trips, #Historical eruptions
Santorini - pumice deposits above the port of Athinios - photo © Bernard Duyck 09.2019

Santorini - pumice deposits above the port of Athinios - photo © Bernard Duyck 09.2019

The eruption of Santorini at the end of the Bronze Age, also called the Minoan eruption because it may have influenced the decline of the Minoan Civilization, is both an event marking volcanology and archeology.

 

The last Plinian eruption of Santorini emitted between 30 and 80 km³ (equivalent in dense rocks) of rhyodactic magma, largely in the form of pyroclastic flows, deposits preserved as ignimbrites in the different surrounding submarine basins.

The eruption impacted the Mediterranean world from the end of the Bronze Age through a combination of ashfall, climate change and tsunamis.

 

Its dating : the last dating was done by the method 14C on a piece of olive wood buried in the deposits of the eruption (Friedrich & al., 2006 - reliability 95%).

The dead insects found refine the month of eruption in June - early July (Panagiotakopulu & al 2013)

Santorini - Friedrich showing the place of discovery of the olive wood in the pumice wall phase P1 of the Minoan eruption - Doc. Science AAAS

Santorini - Friedrich showing the place of discovery of the olive wood in the pumice wall phase P1 of the Minoan eruption - Doc. Science AAAS

Santorini - pumice deposits above the cliffs of the caldera, internal side - photo © Bernard Duyck 09.2019

Santorini - pumice deposits above the cliffs of the caldera, internal side - photo © Bernard Duyck 09.2019

Its course :

According to many volcanological studies, there is a consensus that it has taken place in four major phases (P1 to P4), and a precursory initial phase (P0).

 

- Phase 0, based on a layer of 10 cm. between the pre-Minoan deposits and those of phase 1, consisting of two layers of lapilli and ash, corresponds to explosions and a subplinian plume 7-10 km in height.

- Phase 1, the first phase of the Plinian eruption, generated a plume of height estimated at 36 +/- 5 km.and produces deposits of pumice between 10 cm. and 6 meters thick on Thêra, Therasia and Apronisi.

- Phase 2 is marked by violent phreatomagmatic explosions, caused by contact between marine waters and magma; base surges were generated, which produced startified deposits of more than 12 cm. Thick. (analysis of P2 and P3 deposits in the Mavromatis quarry)

- During phase 3, the increase in the water-magma ratio produced dense, moist, low temperature pyroclastic flows with a transition to muddy flows.

Collapses of the eruptive column produced the largest unit, in the form of massive ignimbrite, thick up to 55 meters in the field, and composed of multiple units and created a cone of tuff, which filled the existing caldera.

- Phase 4 saw the production of high-temperature pyroclastic flows (300-500 ° C), which formed fine-grained, non-welded ignimbrites around the caldera and on the costal plains.

The dominant facies is brownish to pink ignimbrite, called "tan-ignimbrite", which may be contemporaneous with the major collapse of the caldera. A cliff of this ignimbrite "tan" of 40 meters high borders the beach of Vlychada south of Akrotiri.

 

- At the end of the eruption, the caldera was dry and isolated from the sea, probably due to eruptive tufa accumulation. The multi-day flooding of the caldera began on the northwestern side following sea erosion associated with landslides.

Regional tsunamis have been generated by the flooding of P3 and P4 pyroclastic flows, possibly augmented by the mass collapse of pyroclastic deposits rapidly deposited on the slopes of the island's volcano, facing the sea. (Nomikou & al.2016)

Summary of the development of the Santorini caldera before, during and after the eruption of the LBA. (Late Bronze age) - Doc. E.Nomikou & al 2016

Summary of the development of the Santorini caldera before, during and after the eruption of the LBA. (Late Bronze age) - Doc. E.Nomikou & al 2016

Santorini - "Tan ignimbrite" of the southern area of ​​Akrotir, Vlychada beach - photo © Bernard Duyck 09.2019

Santorini - "Tan ignimbrite" of the southern area of ​​Akrotir, Vlychada beach - photo © Bernard Duyck 09.2019

Santotin - detail on the ignimbrites of Vlychada - photo © Bernard Duyck 09.2019

Santotin - detail on the ignimbrites of Vlychada - photo © Bernard Duyck 09.2019

Discovery of prehistoric structures :

The construction of the Suez Canal in 1856, linking the Mediterranean Sea and the Red Sea, required materials such as pumice, which was used in the composition of concrete.

Quarries opened on Santorini, and allowed to discover prehistoric structures, first on Therasia, analyzed by F.Lenormant in 1865, then on Thêra, where the French geologist Ferdinand Fouqué made a major discovery near Akrotiri in 1867.

The excavations, interrupted by the Franco-Prussian War of 1870, really resumed in 1967, under the direction of the Greek archaeologist Spyridon Marinatos, who attributed the decline of the Minoan civilization to the eruption of Santorini.

The site of Akrotiri has been inhabited since the middle of the 5th millennium BC; at the end of the third millennium and the beginning of the second millennium BC, Akrotiri was an important commercial and urban center of cosmopolitan character, with sophisticated culture.

Akrotiri - model of the excavation site - photo © Bernard Duyck 09.2019

Akrotiri - model of the excavation site - photo © Bernard Duyck 09.2019

To follow: the discovery of the excavation site of Akrotiri

 

Sources:

- The morphodynamic evolution of Santorini volcanic complex - 09,2019 - Paraskevi Nomikou, Konstantinos Vouvalidis and Spyros Pavlides

- Geological Society memoir n ° 19 Santorini volcano - T.H.Druitt & al.1999

- Akrotiri - Thera and the Mediterranean - by Nanno Marinatos / Edit. Militos

- Santorini Eruption Radiocarbon Dated at 1627-1600 B.C. by Walter L. Friedrich, Bernd Kromer, Michael Friedrich, Jan Heinemeier, Tom Pfeiffer, and Sahra Talamo - Science, 28 April 2006


- Santorini Eruption Radiocarbon Dated at 1627-1600 B.C.
https://science.sciencemag.org/content/sci/suppl/2006/04/25/312.5773.548.DC1/Friedrich.SOM.pdf

note in Volcanodiscovery by Tom Pfeiffer https://www.volcanodiscovery.com/en/santorini/minoan_eruption/1613bc_olive-tree-date.html

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