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Greece Volcanoes and Volcanics

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Major Volcanoes of Greece

The volcanism of this broad region, stretching from Spain to the Caucasus, is largely the result of convergence between the Eurasian Plate and the northward-moving African Plate. The geology is diverse and complex, with microplates defying easy tectonic generalizations. However, subduction under the Greek islands (Hellenic arc) and southern Italy (Calabrian arc) explains the region's principal volcanic centers.

Kos, Fumarole Fields, 430 meters, Pleistocene - Fumarolic
The island of Kos is dominantly non-volcanic but contains Miocene to Pleistocene volcanic centers. The Kamari caldera is of mid-Pleistocene age and contains the 1.0-0.55 million-year-old, post-caldera Zini lava dome. The widespread Kos Plateau Tuff (160,000 years ago), which blankets much of the western half of Kos, originated from a submarine source between Kos and Nisyros islands and resulted in the formation of a large caldera. The caldera dimensions are uncertain, but may extend as much as 20 kilometers from Kefalos Bay in SW Kos Island to Nisyros Island. Several solfatara fields are found on Kos island, including Vromotopos at Kefalos Isthmus on the western side of the island and a group of thermal areas at the eastern side of Kos. Thermal activity consists of weak hydrogen sulfide emission, sulfur deposits, and two hot springs along the southeastern coast.

Methana, Lava Domes, 760 meters, Historical
Methana volcano consists of a basaltic-andesite to rhyodacitic lava dome complex forming the Methana Peninsula in the Sarronian Gulf on the NE side of Peloponnesus. Potassium-Argon ages for the older part of the complex range from 900,000 to 320,000 years. The youngest dome, Kameno Vouno, on the NW side of the peninsula, was formed in the 3rd century BC and produced a lava flow that traveled 500 meters beyond the coastline.

Milos, Stratovolcanoes, 751 meters, Holocene
Mílos and adjacent small islands have grown from submarine and subaerial volcanism that initially was dominantly andesitic and basaltic, but ended with predominately rhyolitic eruptions. The latest activity during the late Pleistocene was concentrated in the eastern half of the low, U-shaped Mílos Island, forming lava domes and phreatic craters, and on Antimílos Island to the NW, where a composite volcano was constructed. The youngest magmatic eruptions took place about 90,000 years ago, but phreatic explosions, commonly producing overlapping craters rarely more than one kilometer in diameter, continued from late-Pleistocene to Recent times.

Nisyros, Stratovolcano, 698 meters, Historical
The easternmost volcano of the Aegean arc forms the 9-kilometer-wide island of Nisyros, containing a 3-4 kilometer-wide caldera. The island was constructed during the past 100,000 years, with three cone-building stages including explosive and effusive andesitic eruptions and effusive and extrusive dacitic and rhyolitic activity. The age of the caldera is variously considered to be <24,000 years before present (BP) (Keller et al. 1990) and >44,000 years BP (Limburg and Varekamp 1991). Five large post-caldera lava domes completely fill the western part of the caldera. The NE-most (Boriatiko) and SW-most (Karaviotis) lava domes and flows are significantly younger than the other domes. A sixth post-caldera dome, outside the SW caldera rim, produced lava flows that reached the coast. Historical phreatic eruptions occurred within the caldera between 1422 and 1888.

Davis (1968) asserts that Nisyros and Yali Island are located near the intersection of two regional fault lines: The first runs from Episcopi to Patmos, and the second through Soussaki, the Gulf of Saronic, Milos, Santorini, and Dodecanese.

Nisyros Caldera lies at the collapsed top of an andesitic stratovolcano. The caldera-forming eruption began with pyroclastic surges of silicic pumice and evolved to pyroclastic flows and tephra fall of mixed mafic and silicic pumice. Large rhyolitic and rhyodacitic postcaldera domes contain mafic inclusions, inferred to have been clots of mafic magma in silicic magma (Limburg and Varekamp, 1984).

Yali Island, 8 kilometers north-northwest of the center of Nisyros Caldera, has undergone 160 meters of uplift within the late Quaternary, possibly within the Holocene. That uplift apparently occurred as an obsidian dome lifted "roof rock" before and during dome extrusion. The uplift is inferred to have been like that which occurred at Santorini in 1707 and at Usu in 1943-44 (Keller, 1971).

Santorini: Shield Volcanoes, 329 meters, 1,079 feet, Historical
Renowned Santorini (Thera), with its steep-walled caldera rim draped by whitewashed villages overlooking an active volcanic island in the center of a caldera bay, is one of the scenic highlights of the Aegean. The circular island group is composed of overlapping shield volcanoes cut by four partially overlapping calderas. The older southern caldera was formed about 100,000 years before present (BP), followed by the Skaros caldera about 54,000 years BP, and then the Cape Riva caldera about 18,500 years BP. The youngest caldera formed about 3,500 years BP during the Late-Bronze-Age Minoan eruption that forced abandonment of the thriving Aegean Sea island. Post-Minoan eruptions have constructed a series of lava domes and flows that form two islands near the center of the caldera. A submarine eruption took place in 1650 outside the caldera NE of Thera. The latest eruption produced a small lava dome and flow in 1950, accompanied by explosive activity.

Santorini is located on the island of Thira in the Aegean Sea, about 110 kilometers north of Crete. Thira is part of the Cyclades volcanic chain that also includes the young volcanoes Milos and Nisyros. Tectonic analyses cited by Heiken and McCoy (1984) indicate NW-SE extension in the area of Thira during Recent and Quaternary time, consistent with northeast-trending normal faults and vents within the volcanic field.

Santorini consists of a 100,000 year B.P. caldera developed on a group of low volcanoes, and an overlapping around 3,380 years B.P. (perhaps B.C. 1390) caldera of roughly the same size offset to the north (Heiken and McCoy, 1984). The younger caldera formed during or shortly after the famous Minoan eruption of 13-19 cubic kilometers (Heiken and McCoy, 1984) or 27 cubic kilometers (Druitt, 1984) of rhyodacite magma. Buildings were apparently destroyed by earthquakes several years or decades before the cataclysmic eruption, and were being rebuilt when they were abandoned (Vitaliano, 1973; Heiken and McCoy, 1984). The islands were abandoned shortly before the cataclysmic eruption, possibly because of small phreatic or phreatomagmatic eruptions that occurred just before the cataclysmic phase of the eruption (Heiken and McCoy, 1984). The Kameni Islands, a postcaldera dome complex in the center of the caldera, were erupted during the last 2,000 years along northeast-trending fissures in the area of overlap between the two calderas.

Yali, Lava Domes, 176 meters, Holocene
Yali, a small island between the northern coast of Nisyros Island and the SW coast of Kos Island, consists of rhyolitic obsidian domes and pumice deposits. Yali is located within the inferred location of the large submarine caldera associated with the eruption of the voluminous Kos Plateau Tuff, dated about 160,000 years before present. This eruption produced extensive ignimbrites that blanket much of the western half of the island of Kos and produced a caldera whose dimensions are uncertain, but which may extend from Kefalos Bay on the SW side of Kos Island to Nisyros Island, south of Yali. The crescent-shaped island of Yali is oriented NNE-SSW and contains two distinct segments connected by a narrow isthmus formed of modern reef sediments. The SW part of the island consists primarily of a layered pumice-fall unit about 200 m thick, and the NE part contains rhyolitic obsidian lava flows of similar thickness. No historical eruptions are known from Yali, but the most recent pumice eruptions of Yali overlie soils containing pottery and Neolithic obsidian artifacts (Keller 1982).

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