Cerro Guacha
| Cerro Guacha | |
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 Cerro Guacha
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| Highest point | |
| Coordinates | 22°45′S 67°28′W / 22.750°S 67.467°WCoordinates: 22°45′S 67°28′W / 22.750°S 67.467°W |
Cerro Guacha is a Miocene caldera in southwestern Bolivia's Sur Lípez Province. Part of the volcanic system of the Andes, it is considered to be part of the Central Volcanic Zone (CVZ), one of the three volcanic arcs of the Andes, and its associated Altiplano-Puna volcanic complex (APVC). A number of volcanic calderas occur within the latter.
Cerro Guacha and the other volcanoes of that region are formed from the subduction of the Nazca plate beneath the South America plate. Above the subduction zone, the crust is chemically modified and generates large volumes of melts that form the local caldera systems of the APVC. Guacha is constructed over a basement of sediments.
Two major ignimbrites, the 5.6-5.8 mya Guacha ignimbrite with a volume of 1,300 cubic kilometres (310 cu mi) and the 3.5-3.6 mya Tara ignimbrite with a volume of 800 cubic kilometres (190 cu mi) were erupted from Cerro Guacha. More recent activity occurred 1.7 mya and formed a smaller ignimbrite with a volume of 10 cubic kilometres (2.4 cu mi).
The larger caldera has dimensions of 60 by 40 kilometres (37 mi × 25 mi) with a rim altitude of 5,250 metres (17,220 ft). Extended volcanic activity has generated two nested calderas, a number of lava domes and lava flows and a central resurgent dome.
The caldera was discovered in 1978 thanks to Landsat imagery. It lies in Bolivia next to the Chilean frontier. The terrain is difficult to access being located at altitudes between 3,000–4,000 metres (9,800–13,100 ft). The caldera is named after Cerro Guacha, a feature named as such by local topographic maps. Later research by the Geological Service of Bolivia indicated the presence of three welded tuffs.Paleogene red beds and Ordovician sediments form the basement of the caldera.
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