Socompa

Socompa is a large stratovolcano (composite volcano) on the border of Argentina and Chile. It has an elevation of and is part of the Chilean and Argentine Andean Volcanic Belt (AVB). Socompa is within the Central Volcanic Zone, one of the segments of the AVB, which contains about 44 active volcanoes. It begins in Peru and runs first through Bolivia and Chile, and then Argentina and Chile. Socompa lies close to the pass of the same name where the Salta-Antofagasta railway crosses the Chilean border. Most of the northwestern slope of Socompa collapsed catastrophically 7,200 years ago to form an extensive debris avalanche deposit. The Socompa collapse is among the largest known on land with a volume of and a surface area of ; its features are well-preserved by the arid climate. The deposit was at first considered to be either a moraine or a pyroclastic flow deposit, until the 1980 eruption of Mount St. Helens prompted awareness of the instability of volcanic edifices and the existence of large-scale collapses. There are 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.…

Socompa is a large stratovolcano (composite volcano) on the border of Argentina and Chile. It has an elevation of and is part of the Chilean and Argentine Andean Volcanic Belt (AVB). Socompa is within the Central Volcanic Zone, one of the segments of the AVB, which contains about 44 active volcanoes. It begins in Peru and runs first through Bolivia and Chile, and then Argentina and Chile. Socompa lies close to the pass of the same name where the Salta-Antofagasta railway crosses the Chilean border. Most of the northwestern slope of Socompa collapsed catastrophically 7,200 years ago to form an extensive debris avalanche deposit. The Socompa collapse is among the largest known on land with a volume of and a surface area of ; its features are well-preserved by the arid climate. The deposit was at first considered to be either a moraine or a pyroclastic flow deposit, until the 1980 eruption of Mount St. Helens prompted awareness of the instability of volcanic edifices and the existence of large-scale collapses. There are 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. They are well above the sparse regular vegetation in the region, which does not extend up the mountains. The climate on the mountain is cold and dry. ===Sector collapse=== Socompa suffered a major sector collapse during the Holocene, forming one of its largest terrestrial deposits. The deposit left by the collapse was first discovered on aerial photography in 1978 but it was correctly identified as a landslide in 1985; at first, it was interpreted as a form of moraine, then as a large pyroclastic flow and the scar as a caldera. Traces of such events are widespread on Central Andean volcanoes; Socompa's is the largest in the region and one of the better studied. The event removed a 70° sector (about of circumference and of radius ) on Socompa's northwestern side. The landslide descended over a vertical distance of about and spread over distances of over , at a modelled speed of . As it descended, the landslide had sufficient energy that it was able to override topographic obstacles and climb over an elevation of about ; secondary landslides occurred on the principal deposit and there is evidence that the landslide was reflected back from its margins. The event occurred in several steps, the first parts to fail ending up at the largest distances from the volcano; it is not established whether the collapse happened in a single event or as several separate failures. The total volume of material removed was about , which was dilated as it flowed and eventually ended up as a deposit with a volume of ; thorough mixing of the avalanche material occurred as the landslide progressed. The summit of the volcano was cut by the collapse and some lava domes embedded within the volcano were exposed in the rim of the collapse amphitheatre; before the collapse the volcano was about high. The collapse left a triangle-shaped collapse scar partly filled by leftover blocks. The walls of the amphitheatre were about high, so high that secondary landslides occurred. The largest of these detached from a dome northwest of the summit and descended a horizontal distance of , forming a landslide structure notable in its own right and covering about . The central section of the collapse amphitheatre was not a simple collapse structure, but instead contained a secondary scarp. At the mouth of the collapse scar, the walls were lower, about . After the principal collapse, lava flows and pyroclastic flows – some of which emerge from the western rim of the collapse scar – filled up the scar left by the collapse. A structure in the scar, named Domo del Núcleo, might either be a remnant of the pre-collapse volcano, or collapse debris. The collapse happened about years ago and is estimated to have lasted around 12 minutes, based on simulations. The growth rate of the volcano increased, in the aftermath probably due to the mass removal unloading the magmatic system. A similar collapse took place in the 1980 eruption of Mount St. Helens. Identification of the Socompa deposit as a landslide remnant was made after the occurrence of the large landslide at Mount St. Helens drew more attention to such events. Other volcanoes have suffered from large-scale collapses as well; this includes Aucanquilcha, Lastarria and Llullaillaco. In the case of Socompa, the occurrence of the collapse was probably influenced by a northwest tilt of the basement the volcano was constructed on; it caused the volcano to slide downward in its northwestern sector and made it prone to a collapse in that direction. The precise circumstances leading to the collapse are unknown, although there are several hypotheses. There is evidence in the deposit that a lava flow was being erupted on the volcano when the landslide occurred, which together with the presence of pyroclastic fallout on the southwestern side of Socompa implies the event may have been started by volcanic activity. The quantity of water in the edifice rocks was probably minor. Another theory assumes that the volcanic edifice was destabilized by ductile and mechanically weak layers beneath Socompa; under the weight of the volcano these layers can deform and "flow" outward from the edifice, causing the formation of thrusts at its foot. Evidence of such spreading of the basement under Socompa has been found. Other potential causes are earthquakes and the intrusion of new magma. Climatic factors for the Socompa collapse, which have been proposed as triggers for other volcanoes, are speculative. The event released a large amount of energy, about . Some evidence in the form of tephra suggests that the collapse was accompanied by a lateral blast, but other research found no such evidence. Such events are classified as catastrophic phenomena, and the debris avalanches associated with them can reach large distances from the original volcano. The fragmentation of rocks during the landslide and the fine material generated during this process might enhance the fluidity of the avalanche, allowing it to spread far away from the source. ==Notes== ===Sources=== ==External links== "Volcán Socompa, Argentina/Chile" on Peakbagger

Text derived from https://en.wikipedia.org/w/index.php?oldid=1373926232 under CC BY-SA 4.0; modifications have been made.