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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 - current distribution of Skaros lavas and Therasia dome complex - Doc. Druitt & al. 1999

Santorini - current distribution of Skaros lavas and Therasia dome complex - Doc. Druitt & al. 1999

A little jumpto north of Santorini, towards the Skaros Shield and the Therasia Dome Complex.
 

The Skaros Shield was built inside the Caldeira generated by Middle tuff eruptions (70,000 - 54,000 years ago) and covered it. The remains of the shield can be seen in Cape Tourlos (on Thêra) and on the island of Therasia.

The remains at Cap Tourlos consist of a basal complex of domes and dacitic flows, surmounted by a sequence 300 meters thick of basalts and andesites, and capped by a welded spatter agglomerate of Upper Scoriae 2, resulting from the of the development of the Skaros Shield and an explosive andesitic eruption.

Cape Tourlos, seen from the caldera - we can distinguish the succession of dacitic flows, the thickness of basalts and andesites, capped by a welded spatter agglomerate of Upper Scoriae 2 - photo © Bernard Duyck 09.2019

Cape Tourlos, seen from the caldera - we can distinguish the succession of dacitic flows, the thickness of basalts and andesites, capped by a welded spatter agglomerate of Upper Scoriae 2 - photo © Bernard Duyck 09.2019

Cap Tourlos, formed from the remains of the Skaros Shield, seen from the village of Imerovigli on Thêra - The upper part consists of a welded spatter agglomerate of the Upper Scoriae 2 - photo © Bernard Duyck 09.2019
Cap Tourlos, formed from the remains of the Skaros Shield, seen from the village of Imerovigli on Thêra - The upper part consists of a welded spatter agglomerate of the Upper Scoriae 2 - photo © Bernard Duyck 09.2019

Cap Tourlos, formed from the remains of the Skaros Shield, seen from the village of Imerovigli on Thêra - The upper part consists of a welded spatter agglomerate of the Upper Scoriae 2 - photo © Bernard Duyck 09.2019

Following the Upper Scoriae 2 episode, the extrusion of rhyodacites from many vents constructed the lava domes complex on the western flank of Skaros. The remains dominate the walls of the current caldera in Therasia, in a succession of more than 200 meters thick.

Thin flows of weakly phyric andesite to Oia (Oia andesites, etc.) occupy the same stratigraphic level and were probably erupted by mouths on the flank of the Skaros Shield.

Santorini - Therasia, view from Nea Kameini in the center of the caldera - - photo © Bernard Duyck 09.2019

Santorini - Therasia, view from Nea Kameini in the center of the caldera - - photo © Bernard Duyck 09.2019

Santorini - Therasia - rhyodacites surmounting the ancient western flank of the Skaros Shield - photo © Bernard Duyck 09.2019

Santorini - Therasia - rhyodacites surmounting the ancient western flank of the Skaros Shield - photo © Bernard Duyck 09.2019

Santorini - Therasia, the lavas of the northern tip - photo © Bernard Duyck 09.2019

Santorini - Therasia, the lavas of the northern tip - photo © Bernard Duyck 09.2019

The so called Cape Riva eruption occurred 21,000 - 18,000 years ago; Its products are largely dacitic or rhyodacitic, and chemically resemble to the lavas of the Therasia dome complex.

The initial phase was Pliny, with falls and deposits of pumice preserving much of the walls of the northern caldera.

The collapse of the Plinian column occurred at the end of eruption, and produced a distinctive red-brown weld ingnimbrite. The eruption then became more violent with discharge of pyroclastic flows and unfused ignimbrite. It ended with the installation of a second welded ignimbrite on the north of Thêra.

A distal distribution of tephra on the eastern Mediterranean, towards Lesbos and the Sea of ​​Marmara, is recognized as a y-2 bed of marine ash.

Morphological evolution of Santorini between 70 and 21 ka - according to Druitt & al. 1999 / via Evi Nomikou

Morphological evolution of Santorini between 70 and 21 ka - according to Druitt & al. 1999 / via Evi Nomikou

Santorini - the walls of the caldera under Oia - photo © Bernard Duyck 09.2019

Santorini - the walls of the caldera under Oia - photo © Bernard Duyck 09.2019

Santorini - the red ignimbrites of the Cape Riva eruption - photo © Bernard Duyck 09.2019

Santorini - the red ignimbrites of the Cape Riva eruption - photo © Bernard Duyck 09.2019

Let's go back to Cap Tourlos, which has been inhabited since 1207, after the integration of the island into the Venetian Duchy of the Aegean Sea. The natural rock fortress was chosen as the seat of the capital, and numerous seigniorial and religious buildings were built there. In 1480, the island gave to Pizanias Domenico, son of the Duke of Crete as dowry for his marriage to Princess Fiorentza, daughter of the Duke of Naxos. One hundred years later, the Duchy of the Aegean Sea passed into the hands of the Ottoman Empire.

Thomas Hope describes the colony, in his book "Images of the 18th Century", as a fortress to defend itself from pirate raids; A continuous facade of houses with a few small openings protected the village from the only possible access to the east, and doors accessed by a movable wooden bridge, could close in the event of a hostile invasion.

An earthquake in 1650 caused terrible damage, after which the inhabitants abandoned this narrow and difficult environment for Fira. The move was not final until the last decades of the 18th century, due to the continuing pirate raids.

Santorini - Cap Tourlos - drawing from the Thomas Hope Collection (Benaki Museum) and its interpretation - the current photo of the site is located higher in the article - Doc. Santorini.net - one click to enlarge

Santorini - Cap Tourlos - drawing from the Thomas Hope Collection (Benaki Museum) and its interpretation - the current photo of the site is located higher in the article - Doc. Santorini.net - one click to enlarge

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

- Santorini.net - Skaros, the capital of Thêra under the Venetian occupation - by Clairy Palyvou, architect, professor emeritus of the Aristotle University of Thessaloniki

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