Geography and Geology
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.
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