Pagina's

Kos: Part of a Stratovolcano

Nowadays, the island of Kos is dominantly tranquil non-volcanic (and a popular tourist destination). However, around 66,000 years ago a large caldera was formed which deposited the widespread Kos Plateau Tuff, which blankets much of the western half of Kos and originated from a stratovolcano between Kos and Nisyros islands. The exact dimensions of the caldera are still uncertain, but may extend as much as 35 km from the southern coast of the island of Kos to the nearby Nisyros (therefore, largely submerged). Remnants of the pre-eruption stratovolcano are preserved on the islets of Pachia and Pyrgousa and as submarine volcanic rocks on Nisyros.
Kos was constructed with three cone-building stages. The whole scenery was related to the mythical Polybotes, a giant who fought Poseidon in their war against the gods. He was pursued by the god across the sea and crushed beneath the rock of Nisyros which formed the tip of the island of Kos. The numerous earthquakes which shake the island are ascribed to his writhing and his moaning. His name is derived from the Greek noun polyb├┤tos, meaning 'fertile', or more literally 'feeding-many'.

Dating of four volcanic samples (material of eruption ejecta), from the island of Yiali near the Nisyros volcano has revealed, according to the scientists who conducted the measurements, a volcanic eruption which occurred during the second millennium BC (circa 1460 BC)[1]. This eruption could be a ‘rival’ for the environmental disasters correlated to this period. Usually these disasters are blamed on the eruption of Santonini/Thera that resulted in the demise of the Minoan civilization of ancient Greece.
But the volcano has displayed renewed activity. The present geodynamic activity encompasses high seismic unrest, widespread fumarolic activity, and numerous hot springs close to the sea level all around the island. Violent earthquakes and steam blasts accompanied the most recent hydrothermal eruptions in 1871-1873 and 1887.
These seismic events may be generated by magma ascent through the crust opening fissures and plains through magma injection, volume changes of the magma during emplacement and cooling, as well as magma degassing accompanied by immediate volume expansion of the gas[2].

After some intense seismic activity in 1996, a GPS network was installed in June 1997 and re-occupied annually up to 2002. Uplift between 14 to 140 mm was measured at all GPS stations[3].

Which might mean that a large eruption is in the making.

[1] Liritzis et al: A significant Aegean volcanic eruption during the second millennium B.C. revealed by thermoluminescence dating in Geoarchaeology - 1996 
[2] Sakkas et al: Surface Displacement Model of Nisyros Volcanic Field deduced from DlnSAR Analysis & DGPS Measurements in Bulletin of the Geological Society of Greece – 2003
[3] Lagios et al: Ground deformation of Nisyros Volcano (Greece) for the period 1995–2002 in Bulletin of Volcanology – 2005

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