has erupted andesite and dacite, with dacite dominating. Phenocrysts found in the rocks of the avalanche include the minerals augite, hornblende, hypersthene, magnetite and plagioclase; dacites also contain biotite while andesites also contain olivine. In the summit area, hydrothermal alteration took place and clay, silt and sulfur bearing rocks are also found. Climate and ecology There are few data on climate at Socompa. The area is windy and dry given that the volcano lies in the Desert Puna, with frequent snow cover and penitentes but no glaciers. The relatively low cloud cover means that insolation is high. Weather data collected in 1991 found an average temperature of , a large diurnal air temperature cycle (and a larger soil temperature cycle of ) and low evaporation. The present-day precipitation has been estimated to be , with other estimates assuming less than . Periglacial landforms indicate that in the past the area was wetter, possibly thanks to the Little Ice Age. There is, however, no evidence for Pleistocene glaciation including no cirques, which may be due to the volcano's young age. Socompa features autotrophic communities associated with fumaroles and thermal anomalies at high altitude, between of elevation. The autotrophic communities on Socompa are the highest known in the world, and they occur both on the actual fumaroles and on "cold fumaroles". The various species are often extremophiles since the environment on Socompa is harsh, and the communities also include heterotrophic species. Such heterotrophs include ascomycota and basidiomycota, the latter of which have noticeable similarity to Antarctic basidiomycota. The fumaroles on Socompa also feature stands of bryophytes such as liverworts and mosses as well as lichens and algae, and animals have been found in the stands. These stands are among the highest in the world and cover noticeably large surface areas despite their elevation, and are fairly remote from other plant life in the region. There is a noticeable diversity between separate stands, and the vegetation is quite dissimilar to the vegetation in the surroundings but resembles that found in the paramo and cloud forests in South America and the subantarctic islands. A sparse vegetation cover is also found on the lower slopes of Socompa. The black-headed lizard and its relative Liolaemus porosus live on its slopes, and mice have been observed in the summit area. Eruptive history Activity at Socompa commenced with the extrusion of andesites, which were followed later by dacites.