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20.02.18
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History of the Volcano


Geology

Geological studies have revealed that the first volcanic activity in the broader area of Santorini can be dated to 2.5 million years ago and that it gave rise to the Christiana complex. In the area closely bordering the island of Santorini, the volcano became active about 1 million years ago while, within the last 400 thousand years, it has seen at least 12 violent eruptions. They take place at 20 thousand year intervals, as a rough estimate, and cause giant collapse craters (calderas). In between these violent eruptions that decimate the island, there are intervals characterized by milder outbursts, which vary in duration.
These calm interludes are marked by an array of eruptions of lower intensity, which slowly build up the island's land mass anew. Santorini's volcanic activity is modulated by a tectonic rift, which begins at Christiana, traverses Santorini and culminates in the island of Amorgos. This rift remains active to this day and was responsible for the deadly earthquake of 1956.
It thus follows that Santorini's course of volcanic activity follows a pattern of a cyclical series of eruptions. Over the span of many millennia, the volcano is intermittently activated without exhibiting violent eruptions. Nevertheless, the lava which accumulates in the meantime gradually expands and elevates the volcanic cones. However, the higher the cones rise, the longer the course that needs to be covered by the magma before reaching the surface, thus making it all the harder for it to escape and giving rise to the phenomenon of its more generalized premature freezing within the cones. This way, the Theran magma gradually freezes and solidifies within the cones before reaching the earth's crust, thus blocking the craters.
Following the congestion of the craters, there follows a long period of relative calm, during which large quantities of magma are trapped underground, causing the increasing pressure being exerted on the surface to steadily mount. It periodically finds an outlet for its release by furrowing small explosion vents which, however, do not suffice in order to fully release the pent up energy.
However, as soon as the intensity of the pressure exercised on the subterranean cones exceeds the force binding the overlying cones to one another, which have mounted rows upon rows of lava layers, then the magma finds an outlet for its release through the surface, escaping with ferocious intensity, in an explosive outburst that utterly razes and explodes everything in its path.
The cones are crushed and destroyed and immense quantities of volcanic material are thrust at immense force to great heights and over extensive distances. The remnants of the volcano collapse into the subterranean chambers which, now emptied of magma, can no longer support the weight of the overlying layers. In the place of the cones which have been razed, exploded and collapsed there remains a giant circular collapse crater (Caldera), which is surrounded by tall and steep cliffs and is swiftly infiltrated by the advancing sea, by means of the creation of a vast tidal wave (tsunami).
Steam at an extremely high temperature also escapes together with the magma. It bursts forth through the surface and is instantaneously converted to aqueous vapor.
The two latest violent eruptions on Santorini occurred roughly 21 and 3.6 thousand years ago, respectively. Indeed, the latest one took place during the Minoan Period and has been dated specifically to the second half of the 17th century B.C., based on various methodologies (such as the carbon dating method, as well as by analysis of tree barks and volcanic ash on fossils found in ice). Moreover, this eruption led to the disappearance of a great civilization that had flourished on the island and whose origins dated all the way back to the beginning of recorded history, to the prehistoric era.
However, the Caldera found on Santorini today was not formed during the latest violent eruption, which took place in the Minoan era. It was formed gradually, as the result of a series of collapses spanning a succession of historical periods marked by volcanic activity, which cumulatively led to the geomorphology of the island as we see it today.


INFO

The volcano of Culumbos. Apart from Palia and Nea Kameni, there is the underwater volcano of Culumbos, located 6.5 km southeast of Santorini, near Oia. It was discovered in 1650, during a surge in volcanic activity that lasted two to three months. At the site of the underwater eruption, a small island sprung up, to disappear a while later. The Culumbos, which has also formed its own collapse crater (caldera), measuring roughly 2 km in diameter and of a maximum depth of 500 m from its peak, was caused by the collapse of land following the volcanic eruption. It is home to a unique, fascinating ecosystem consisting of primitive microorganisms capable of metabolizing inorganic nutrients. There are active hydrothermal vents situated concentrically around the volcano, out of which bursts forth boiling hot water containing metallic trace elements. Culumbos erupted in 1650 (see also Culumbos beach).

Source: "Thera, a march through time", by Antonis K. Kontaratos/Heliotopos Publications.

Ηφαίστειο - Ιστορία - Γεωλογία
Ηφαίστειο - Ιστορία - Γεωλογία

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