The Puyehue-Cordón Caulle Volcanic Complex is in southern Chile, about 450 miles south of the capital Santiago, and about 20 miles west of the Argentine border. Chile has about 3000 volcanoes running from north to south along the whole length of the country, which about 80 are still periodically active. These occur as the Nazca Plate (part of the Pacific sea floor) is forced below the South American Plate; the South American plate is lifted up, forming the Andes Mountains, as the Pacific Plate is subducted into the Earth's mantle lighter minerals are melted and bubble up to the surface, creating a string of volcanoes throughout the Andes. The Andes are among the fastest growing mountains on Earth, and were where mountain orogeny (the growth of mountains) was first understood.
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The Puyehue-Cordón Caulle Volcanic Complex lies on the Liquiñe-Ofqui Fault, where the Nazca, South American and Antarctic Plates collide, an area of intense volcanic activity. The Puyehue-Cordón Caulle Volcanic Complex itself is between 200 000 and 300 000 when a shift in the fault shifted to the east and narrowed. A series of older volcanoes to the east all ceased activity at this time, and were replaced by younger larger volcanoes such as Puyehue-Cordón.
Technically Puyehue is a stratocone volcano, i.e. a classic cone-shaped volcano, whereas Cordón Cauelle is an adjacent volcanic fissure. The volcanic complex is very active, with a record of observed eruptions going back to 1759 when the first permanent European settlements in the area were established. There were nine eruptions during the twentieth century, including one in 1960 associated with the May 22 Valdivia earthquake, the most powerful earthquake ever recorded.
The complex began to erupt again on the 4th of June this year (2011), an eruption accompanied by a swarm of earthquakes and throwing an ash-cloud high into the air. It is not yet clear if this originates from the Puyehue stratocone or the Cordón Cauelle fissure, due to the remote location of the complex, within the Puyehue National Park and the fact that it is mid-winter in the southern hemisphere in June.
The Chilean government has responded by ordering the evacuation of around 3000 people from the area around the volcano, although it is unclear how many people have actually left; the raising livestock is an important part of the local economy and people are often reluctant to leave their animals.
The ash cloud has blown eastward over Argentina where two small airports servicing ski resorts among the extinct volcanoes of the eastern Liquiñe-Ofqui. Unlike British and Irish airlines, Argentine ones seem happy to accept that volcanic ash-clouds are dangerous to aircraft.
See also The Puyehue Eruption, Chile, 2011.
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