Friday, January 21, 2011
Chile - Villarrica Volcano
Villarrica volcano, view from Calafquén Lake.
Sent by Daniela from Santiago, Chile.
This is from Wikipedia : Snow-covered Villarrica, one of Chile's most active volcanoes, rises above the lake and town of the same name. The volcano is also known as Rucapillán, a Mapuche word meaning "House of the Pillán". It is the westernmost of three large stratovolcanoes that trend perpendicular to the Andean chain along the Gastre Fault. Villarrica, along with Quetrupillán and the Chilean portion of Lanín, are protected within Villarrica National Park. Ascents of the volcano are popular with several guided ascents reaching the top during summer.
Villarrica, with its lava of basaltic-andesitic composition, is one of only five volcanoes worldwide known to have an active lava lake within its crater. The volcano usually generates strombolian eruptions, with ejection of incandescent pyroclasts and lava flows. Melting of snow and glacier ice as well as rainfalls often cause massive lahars (mud and debris flows), such as during the eruptions of 1964 and 1971.
Villarica's symmetrical edifice stands in the Chilean Central Valley as the westernmost of an alignment of three large stratovolcanoes. The alignment is attributed to the existence of an old fracture in the crust, the North West-West trending sinistral Gastre Fault Zone, the other volcanoes in the chain Quetrupillán and Lanín are far less active. This alignment is unusual as it crosses the N-S running Liquiñe-Ofqui Fault, around which most currently active volcanoes are aligned. Currently the volcano covers up an area of 400 km2 and has a volume 250 km3 according to estimates.
About 25 scoria cones dot Villarica's flanks. It also has volcanic caves. The constant degassing at the lava lake turns Villarrica's otherwise quite effusive lava more viscous, heightening its explosive potential. Two large ignimbrite layers are visible around the volcano; the Licán Ignimbrite and later the Pucón Ignimbrite.
Villarrica emerged as a volcano during the Middle Pleistocene and grew forming a large stratocone of similar dimensions to the current edifice. 100 thousand years ago during the Valdivia Interglacial the ancestral Villarrica collapsed following an eruption and formed a large elliptical caldera of 6.5 and 4.2 km in diameter. During the Llanquihue Glaciation (Last Glaciation) Villarrica produced pyroclastic flow deposits, subglacial andesite lavas and dacite dykes. The volcano collapsed once again 13,700 years ago forming a new smaller caldera, among other pyroclastic flows the Licán Ignimbrite has been related to this event. Beginning with the Licán Ignimbrite, generated just after the last deglaciation, activity continued in similar fashion. The Pucón Ignimbrite was ejected during a minor collapse the uppermost stratocone 3,700 years ago.