Socompa is a large stratovolcano at the border of Argentina and Chile with an elevation of metres. Part of the Chilean and Argentine Andean Volcanic Belt (AVB), it is part of the Central Volcanic Zone, one of the various segments of the AVB. This part of the Andean volcanic arc begins in Peru and runs first through Bolivia and Chile, and then through Argentina and Chile, and contains about 44 active volcanoes. Socompa lies close to the pass of the same name, where the Salta-Antofagasta railway crosses the border. Socompa is known for its large debris avalanche, which was formed 7,200 years ago when most of the northwestern slope collapsed and slid down, forming an extensive deposit. It was at first considered to be either a moraine or a nuee ardende deposit, until the 1980 eruption of Mount St. Helens prompted awareness of the instability of volcanic edifices and the existence of large scale collapses on them. The Socompa collapse is among the largest known with a volume of and covers a surface area of , and its features are well preserved by the arid climate. Notable are the large toreva blocks which were left behind within the collapse crater. After the landslide, the volcano was rebuilt by the effusion of lava flows and much of the scar is now filled in. Socompa is also noteworthy for the high-altitude biotic communities that are bound to fumaroles on the mountain and form well above the regular vegetation in the region. The climate on the mountain is cold and dry. Geography and geomorphology Socompa is situated on the border between Argentina and Chile, due east of Monturaqui. The Salta–Antofagasta railway crosses the border between the two countries just below Socompa, rendering the volcano easily accessible despite its remote location. The same pass was an important route between the two countries and reportedly between 1940 and 1970 the Carabineros de Chile had a post there. Rails and roads at Socompa go up to an elevation of ; from there the volcano can be climbed from its southern, eastern and northern flank. The mountain is considered to be an apu by the local population, and Inca constructions have been reported either from its slopes or from its summit. The name comes from the Kunza language and may be related to and , which mean "spring" or "arm of water". The volcano is part of