Cerro Galán is a caldera in the Catamarca Province of Argentina. It is one of the largest exposed calderas in the world and forms part of the Central Volcanic Zone of the Andes, one of the three volcanic belts found in South America. One of several major caldera systems in the Central Volcanic Zone, the mountain is grouped into the Altiplano–Puna volcanic complex. Volcanic activity at Galán is the indirect consequence of the subduction of the Nazca Plate beneath the South America Plate, and involves the infiltration of melts into the crust and the formation of secondary magmas which after storage in the crust give rise to the dacitic to rhyodacitic rocks erupted by the volcano. Galán was active between 5.6 and 4.51 million years ago, when it generated a number of ignimbrites known as the Toconquis group which crop out mainly west of the caldera. The largest eruption of Galán was 2.08 ± 0.02 million years ago and was the source of the Galán ignimbrite, which covered the surroundings of the caldera with volcanic material. The volume of this ignimbrite has been estimated to be about 650 cubic kilometres (160 cu mi); after this eruption much smaller ignimbrite eruptions took place and presently two hot springs are active in the caldera.
Geography and geomorphology The Galán caldera lies in the northwestern Catamarca Province of Argentina and was discovered in 1975 in a remote region of the Andes, using satellite images. The town of Antofagasta de la Sierra lies west-southwest of the Galán caldera, Tacuil is almost due northeast from the caldera and El Penon southwest of the volcano. The caldera is difficult to access. An Inka tambo was situated at Laguna Diamante, and an important prehistoric travel route passed through the caldera. Sacrificial offers were given on the summit of Galán. Galán is part of the Central Volcanic Zone of the Andes, which lies on the western margin of South America, where the Nazca Plate subducts beneath the South America Plate. There are about 50 volcanoes with recent activity in the Central Volcanic Zone, and additional volcanoes exist in the Northern Volcanic Zone and the Southern Volcanic Zone, two other volcanic belts north and south. The volcanic arc runs along the borders between Bolivia and Argentina with Chile, and behind the volcanic arc lies a chain of silicic volcanoes, of which Galán is a southern member. The whole region has been subject to substantial ignimbrite-forming volcanism with many eruptions producing volumes of rock larger than 100 cubic kilometres (24 cu mi), although the actual vents often are only visible from space imagery. Many vents cluster in an area known as the Altiplano-Puna volcanic complex which occupies a surface of about 70,000 square kilometres (27,000 sq mi) approximately 200 kilometres (120 mi) north of Galán, and which includes the large calderas of La Pacana, Cerro Guacha, Pastos Grandes and Cerro Panizos as well as more recent geothermal systems. This volcanism appears to be a surface expression of a pluton, and at depths of 17–19 kilometres (11–12 mi) beneath the Altiplano-Puna volcanic complex electrical, gravity and seismic tomography data have localized a structure of partially molten rock called the "Altiplano Puna Magma Body". Volcanism in this "back" region may not be directly related to subduction processes despite the region itself being close to a subducting margin. The Galán caldera lies on the eastern margin of the Andes, where the Sierras Pampeanas begin. The region is characterized by the Puna, a high plateau similar to Tibet in Asia. A magmatic body has been found under Galán, inside the crust.
Local
Galán is a caldera with topographic dimensions of 38 by 26 kilometres (24 mi × 16 mi), of which about 26 by 18 kilometres (16 mi × 11 mi) are part of the caldera proper. Such dimensions make Galán one of the biggest calderas on Earth; it has been described as a supervolcano. The floor of the caldera reaches an elevation of 4,500 metres (14,800 ft) or about 4,600 metres (15,100 ft), and the whole caldera has an elliptical shape extending in the north–south direction. Only the western margin of the caldera structure appears to be a true caldera margin, however, with different landforms forming the rest of the caldera walls and the actual collapse caldera covering only a portion of the topographic caldera expression; the latter has been defined to be a volcano-tectonic depression. The caldera contains a resurgent dome, whose highest point in the frost-shattered Galán massif reaches an elevation of about 5,912 metres (19,396 ft)-6,100 metres (20,000 ft). Seismic tomography has identified a slow-speed anomaly beneath Galán, which has a volume of about 22,000 cubic kilometres (5,300 cu mi) and is considered to be a magma reservoir of the volcano. Summits along the caldera margin include Cerro Aguas Calientes (a lava dome) to the north, Cerro Leon Muerto to the southeast, Cerro Pabellon to the southwest and Cerro Toconquis to the northwest. On the western rim, elevations of 5,200 metres (17,100 ft) are reached. Younger volcanoes have developed on the western and northern rim of the Galán caldera.
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