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94-754: 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

188-710: A peneplain in the eastern Sierras Pampeanas. Later tectonic movements split this surface into various levels with the highest level being Pampa de Achala . As the South Atlantic opened following the Paraná-Etendeka flood basalts , the Andean orogeny began the formation of the Andes, the product of volcanism and compressional forces along the Pacific margin, but also resulted in the development of extensional basins in South America and

282-426: 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

376-538: A "valley"); these are called "barreales" (mud-flats) or "pampas" (grassy plains). The Sierras Pampeanas are composed of several sub-ranges: The name "Pampean Ranges" can be misleading, since the Argentine Pampas cover most of the country's northern and eastern portion. However, other mountains which rise from these expanses are considered distinct geologic formations, not part of the Sierras Pampeanas. Before

470-420: A 7 by 3 kilometres (4.3 mi × 1.9 mi) lake in its southwestern corner, which is known as Laguna Diamante and may formerly have occupied much of the caldera. Laguna Diamante has gained attention among scientists for the extreme environmental conditions that life within the lake has to withstand, including high arsenic contents of the waters and high insolation with ultraviolet radiation . The water

564-409: A caldera, possibly an ash-flow caldera. The volcanic activity of Mars is concentrated in two major provinces: Tharsis and Elysium . Each province contains a series of giant shield volcanoes that are similar to what we see on Earth and likely are the result of mantle hot spots . The surfaces are dominated by lava flows, and all have one or more collapse calderas. Mars has the tallest volcano in

658-510: A chain of mountains that rise sharply from the surrounding pampa region of Northwest Argentina. They run parallel to the Andes Mountains and their crest line is some 540 km (340 mi) east of the Andes crest line (running from 29° to 35° S latitude at about 65° W longitude). They cross into seven Argentina provinces: San Luis , San Juan , Córdoba , La Rioja , Catamarca , Santiago del Estero and Tucumán . The highest point of

752-476: A consequence of progressive changes in the crust. Such giant eruptions have not been observed during historical time and are considered to be among the most dangerous volcanic phenomena known. Kay et al. proposed that the Galán ignimbrite consisted of three separate units, an intracaldera one emplaced 2.13 million years ago and two extracaldera ones 2.09 and 2.06 million years ago. The main Galán caldera formed during

846-400: A diameter of 290 km (180 mi). The average caldera diameter on Mars is 48 km (30 mi), smaller than Venus. Calderas on Earth are the smallest of all planetary bodies and vary from 1.6–80 km (1–50 mi) as a maximum. The Moon has an outer shell of low-density crystalline rock that is a few hundred kilometers thick, which formed due to a rapid creation. The craters of

940-467: A magma chamber whose magma is rich in silica . Silica-rich magma has a high viscosity , and therefore does not flow easily like basalt . The magma typically also contains a large amount of dissolved gases, up to 7 wt% for the most silica-rich magmas. When the magma approaches the surface of the Earth, the drop in confining pressure causes the trapped gases to rapidly bubble out of the magma, fragmenting

1034-583: A noticeable drop in temperature around the world. Large calderas may have even greater effects. The ecological effects of the eruption of a large caldera can be seen in the record of the Lake Toba eruption in Indonesia . At some points in geological time , rhyolitic calderas have appeared in distinct clusters. The remnants of such clusters may be found in places such as the Eocene Rum Complex of Scotland,

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1128-624: A passive margin along the Atlantic coast, processes still going on today. The basement of the Sierras Pampeanas was uplifted during the Andean orogeny over a near-horizontal segment of the subducting Nazca Plate . Sierras Pampeanas was also affected by Miocene arc magmatism 700 km (430 mi) east of the Chile Trench during this period. This region has a temperate and semi-arid climate, with warm summers and cool winters. The northern east slope

1222-457: 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

1316-478: A separate formation from the other Toconquis group ignimbrites. The later classifications established a 6.5 – 5.5 million-year-old Blanco/Merihuaca ignimbrites, 4.8 million-year-old Pitas, 4.7 million-year-old Real Grande, 4.5 million-year-old Vega and 3.8 million-year-old Cueva Negra ignimbrite. The formation is fairly heterogeneous, with some ignimbrites separated by sharp contacts and the degree of welding and crystal content of pumices varies from one ignimbrite to

1410-502: 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

1504-560: A volume of about 70 cubic kilometres (17 cu mi). The last eruption may have generated a caldera that was later obliterated. Emission of lava flows occurred during the Toconquis phase as well, in general there was vigorous volcanic activity between the eruptions that formed the main ignimbrites. The Cueva Negra ignimbrite was emplaced after the Toconquis Group, and small lava domes and pyroclastic flows continued to be erupted until

1598-410: Is a large cauldron -like hollow that forms shortly after the emptying of a magma chamber in a volcanic eruption . An eruption that ejects large volumes of magma over a short period of time can cause significant detriment to the structural integrity of such a chamber, greatly diminishing its capacity to support its own roof, and any substrate or rock resting above. The ground surface then collapses into

1692-439: 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. The caldera contains

1786-552: Is covered by rainforest, due to high humidity in this subtropical zone. The portions within Córdoba and San Luis enjoy Mediterranean-type climate, with intense summer rainstorms and snowy winters; the vegetation here includes conifer trees. More precipitation falls on the eastern slopes, which meet the moist winds from the Atlantic Ocean . Groundwater is not abundant in most of this area; the eastern slopes show greater population due to

1880-405: Is ejected, the emptied chamber is unable to support the weight of the volcanic edifice above it. A roughly circular fracture , the "ring fault", develops around the edge of the chamber. Ring fractures serve as feeders for fault intrusions which are also known as ring dikes . Secondary volcanic vents may form above the ring fracture. As the magma chamber empties, the center of the volcano within

1974-569: Is heated by solid flexing due to the tidal influence of Jupiter and Io's orbital resonance with neighboring large moons Europa and Ganymede , which keep its orbit slightly eccentric . Unlike any of the planets mentioned, Io is continuously volcanically active. For example, the NASA Voyager 1 and Voyager 2 spacecraft detected nine erupting volcanoes while passing Io in 1979. Io has many calderas with diameters tens of kilometers across. Sierras Pampeanas The Sierras Pampeanas are

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2068-544: Is hyper-alkaline and five times as salty as the sea but supports microorganisms which form microbial mats and provide food for a colony of flamingos . Tube-shaped microbialites have also been reported. A smaller lake known as Laguna Pabellon lies just south of Laguna Diamante. North of the resurgent dome, the Rio Aguas Calientes drains the caldera northward, while east of it the Rio Leon Muerto runs eastward out of

2162-459: Is more abundant is agricultural output destined for outside sale. Tree crops are grown in the foothills of the Sierras de Córdoba, including olives , peach , pear , apricot , fig trees , quince , lemon trees , and plantations of cypress , cedar , ponderosa pine , eucalyptus , poplar , oak , and willow which are grown for timber and forest products. Shrubs and medicinal herbs grown in

2256-555: Is noticeable on satellite images. It covers a surface area of about 3,500 square kilometres (1,400 sq mi) and is the largest ignimbrite system in the Puna plateau. The first stage occurred between 5.60 and 4.51 million years ago and consisted of the eruption of large ignimbrites such as the Blanco, Cueva Negra, several Merihuaca ignimbrites and Real Grande ignimbrite as well as lava domes , all from north–south trending fractures, forming

2350-529: Is relatively young (1.25 million years old) and unusually well preserved, and it remains one of the best studied examples of a resurgent caldera. The ash flow tuffs of the Valles caldera, such as the Bandelier Tuff , were among the first to be thoroughly characterized. About 74,000 years ago, this Indonesian volcano released about 2,800 cubic kilometres (670 cu mi) dense-rock equivalent of ejecta. This

2444-450: Is supplied both by the mantle and by precipitation. A phreatic explosion took place at La Colcha at some point in the past, and stronger hydrothermal activity was necessary to emplace the travertines. An earthquake swarm was recorded on the 25 January 2009 mainly under the resurgent dome, and may reflect hydrothermal or magmatic activity. Caldera A caldera ( / k ɔː l ˈ d ɛr ə , k æ l -/ kawl- DERR -ə, kal- )

2538-532: 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

2632-799: The Famatinian orogeny which accreted the Precordillera Terrane to Gondwana. In the Gondwanide orogeny , Gondwana reached its maximum extent in the Early Carboniferous and began to break-up in the Early Cretaceous. Along the Pacific margin the convergence of tectonic plates lead to renewed subduction which produced the large rhyolitic provinces and plutonic belts of the Permian–Jurassic. Between 530 and 440 million years ago, during

2726-610: 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

2820-581: The Pampean and Famatinian orogenies the area of the Sierras Pampeanas was intruded by a series of pegmatite dykes. Later, around 370 million years ago a smaller event of pegmatite intrusion took place. Today these dykes are collectively known as the Pampean Pegmatite Province . These pegmatites host valuable lithium reserves. By the end of the Paleozoic erosion had led to the formation of

2914-500: The San Juan Mountains of Colorado , where the 5,000 cubic kilometres (1,200 cu mi) Fish Canyon Tuff was blasted out in eruptions about 27.8 million years ago. The caldera produced by such eruptions is typically filled in with tuff, rhyolite , and other igneous rocks . The caldera is surrounded by an outflow sheet of ash flow tuff (also called an ash flow sheet ). If magma continues to be injected into

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3008-647: The Toconquis Group (formerly called the Toconquis Formation ). The Real Grande and Cueva Negra ignimbrites were considered to be homologous, as are the easterly Leon Muerto and several Merihuaca ignimbrites, but it was later found that the Leon Muerto and Merihuaca ignimbrites probably were erupted from distinct vent systems and have distinct compositions, and the Cueva Negra ignimbrite was later considered to be

3102-525: The viscacha and guinea pig . The observed fauna varies according to the combination of three basic natural factors: the arrangement of mountain ranges, altitude and climate. There are important variances of biome in the Pampas Sierras: semi-arid areas, rain-forest areas, and moderately fertile areas covered with natural forests (especially in Córdoba and San Luis). In the arid zone of La Rioja and Catamarca are found vicuña and some alpaca . Earlier in

3196-417: The Earth's volcanic activity (the other 40% is attributed to hotspot volcanism). Caldera structure is similar on all of these planetary bodies, though the size varies considerably. The average caldera diameter on Venus is 68 km (42 mi). The average caldera diameter on Io is close to 40 km (25 mi), and the mode is 6 km (3.7 mi); Tvashtar Paterae is likely the largest caldera with

3290-661: The English term cauldron is also used, though in more recent work the term cauldron refers to a caldera that has been deeply eroded to expose the beds under the caldera floor. The term caldera was introduced into the geological vocabulary by the German geologist Leopold von Buch when he published his memoirs of his 1815 visit to the Canary Islands , where he first saw the Las Cañadas caldera on Tenerife , with Mount Teide dominating

3384-414: The Galán eruption is still one of the biggest known volcanic eruptions and the volcano has produced almost half of the volume of ignimbrites in the southern Puna. The Galán ignimbrite is the largest ignimbrite erupted by this centre; there is a tendency of the volume of individual ignimbrites to increase as the volcanoes grow younger, not only at Galán but also at other Puna ignimbrite centres, and this may be

3478-480: The Galán ignimbrite eruption, and it is possible that the collapse of the magma chamber roof actually started the eruption. Later it was found that a trapdoor collapse is a more plausible interpretation of the caldera structure and that the caldera appears to be much smaller than its present-day topographic expression. Most likely a lake formed within the caldera after its eruption. Later volcanic activity resulted in lava flows of dacitic composition being erupted along

3572-428: The Galán ignimbrite in comparison to the Toconquis Group rocks. The formation of the Galán magma has been explained with melting of lower crustal rocks under the influence of rising basaltic magmas that supplied the heat needed for the melting processes, and which also directly contributed to magma formation through mixing events. Further metasomatism in the crust and fractional crystallization processes completed

3666-413: The Galán ignimbrite proper. The magmatic system shallowed during this time, resulting in composition changes of the erupted ignimbrites and a general increase of elevations in the region. 2.08 ± 0.02 million years ago the rhyodacitic Galán ignimbrite proper was emplaced. Aside from a facies that remained inside the caldera and is minimally 1.4 kilometres (0.87 mi) thick, ignimbrites extend outside of

3760-539: The Galán system was likewise channelled along such fault systems, and neighbouring volcanoes were similarly influenced by them; the fault systems at Galán proper are known as the Diablillos-Galán faults. Another major lineament in the area is the Archibarca lineament, which is formed by a strike-slip fault that extends from the northwest to the southeast in the region and which intersects the Diablillos-Galán faults at

3854-619: The Mesozoic the Sierras Pampeanas was affected by cycles of orogenic events produced by a series continent-continent collisions along the Proto-Pacific margin of Gondwana . The Neoproterozoic–Cambrian Pampean orogeny was a major event along south-western Gondwana that coincided with the end of the Brasiliano – Pan-African orogenies. In the Cambrian, subduction along the Proto-Pacific margin lead to

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3948-510: The Moon have been well preserved through time and were once thought to have been the result of extreme volcanic activity, but are currently believed to have been formed by meteorites, nearly all of which took place in the first few hundred million years after the Moon formed. Around 500 million years afterward, the Moon's mantle was able to be extensively melted due to the decay of radioactive elements. Massive basaltic eruptions took place generally at

4042-597: The Rio de Los Patos in a region where long permanent watercourses are unusual. The western flanks of the caldera drain into the Antofagasta de la Sierra valley through a number of drainages such as Rio Punilla, Rio Toconquis, Rio Miriguaca, Rio Las Pitas; the waters eventually end into the Laguna Antofagasta south of Antofagasta de la Sierra. Two hot springs are found within the caldera, the first close to its northern end and

4136-647: The San Juan Mountains of Colorado (formed during the Oligocene , Miocene , and Pliocene epochs) or the Saint Francois Mountain Range of Missouri (erupted during the Proterozoic eon). For their 1968 paper that first introduced the concept of a resurgent caldera to geology, R.L. Smith and R.A. Bailey chose the Valles caldera as their model. Although the Valles caldera is not unusually large, it

4230-559: The Sierras Pampeanas is Cerro General Belgrano (6250 m above sea level) in La Rioja, in the Sierra de Famatina . Between the mountain ranges are several salt-filled depressions. The Salinas Grandes depression is located in Cordoba, La Rioja, Catamarca and Santiago del Estero. A characteristic of many of these mountain ranges is their morphological asymmetry: the western slopes are usually steeper than

4324-452: The Sierras de Córdoba include peperina , pennyroyal , dandelion , plantain , canchalagua , wild grapes , chamomile , malva , lime and passion fruit . In arid areas such as the center and west of La Rioja and Catamarca, irrigated vines thrive, and large plantations of olive trees, ( jujube was brought by Lebanese immigrants and Syrians in early twentieth century), grains , aloe and jojoba . Most of these products are sold within

4418-564: The Sierras. High-elevation Central Andean Puna grasslands occur along the ridgeline of the Sierra de Aconquija. Extant species include algarrobo blanco (white carob) , algarrobo negro , chañar , jarilla , mistol , piquillin , tala , alpataco , tabaquillo and espinillo . In the more arid regions (the west faces) grow giant or medium cactus and various shrubs ( chilca , tola , etc.) The Southern Andean Yungas are humid forests found on east-facing slopes with higher rainfall. Trees of

4512-720: The Solar System, Olympus Mons , which is more than three times the height of Mount Everest, with a diameter of 520 km (323 miles). The summit of the mountain has six nested calderas. Because there is no plate tectonics on Venus , heat is mainly lost by conduction through the lithosphere . This causes enormous lava flows, accounting for 80% of Venus' surface area. Many of the mountains are large shield volcanoes that range in size from 150–400 km (95–250 mi) in diameter and 2–4 km (1.2–2.5 mi) high. More than 80 of these large shield volcanoes have summit calderas averaging 60 km (37 mi) across. Io, unusually,

4606-456: 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

4700-557: The Yungas include Andean alder ( Alnus acuminata ), the conifer Podocarpus parlatorei , and deciduous trees including walnut ( Juglans australis ), jacaranda , Pisonia , Schinus molle , quebracho , acacia , and flowering plants such as orchids , jasmine and bromeliads . The Sierras de Córdoba in Córdoba and San Luis provinces have abundant vegetation on the eastern slopes, including carob, "coconuts" (local name of palm trees), garabato blanco ( acacia ) and willow . Much of

4794-516: 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

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4888-423: The area is deforested due to desertification , logging ( "clearing"), strip-mining (without resurfacing or replanting), animal overgrazing , and burning to open up areas for grazing. The area boasts a diverse fauna, although several species are moving toward extinction (such as the boa ). Among the native animals: puma , brocket deer (in the north), wildcat , fox , armadillo and mule deer ; rodents such as

4982-411: The base of large impact craters. Also, eruptions may have taken place due to a magma reservoir at the base of the crust. This forms a dome, possibly the same morphology of a shield volcano where calderas universally are known to form. Although caldera-like structures are rare on the Moon, they are not completely absent. The Compton-Belkovich Volcanic Complex on the far side of the Moon is thought to be

5076-467: The caldera and may have reached even larger distances prior to erosion, and they have thicknesses of 300 metres (980 ft). The ignimbrites have a total volume of about 650 cubic kilometres (160 cu mi), with the Real Grande ignimbrite comprising over half of its volume. The volume of the individual ignimbrites increases the younger they are with the initial Blanco and Merihuaca ignimbrites having

5170-577: The caldera atop Fernandina Island collapsed in 1968 when parts of the caldera floor dropped 350 metres (1,150 ft). Since the early 1960s, it has been known that volcanism has occurred on other planets and moons in the Solar System . Through the use of crewed and uncrewed spacecraft, volcanism has been discovered on Venus , Mars , the Moon , and Io , a satellite of Jupiter . None of these worlds have plate tectonics , which contributes approximately 60% of

5264-586: The caldera to distances of 80 kilometres (50 mi) but with an average runout distance of 40 square kilometres (15 sq mi) and have thicknesses of 200–10 metres (656–33 ft); closer to the caldera it has been largely eroded away and there are more complete exposures farther away from Galán. A contrary view is that the Galán ignimbrite was largely eroded only on its northern side by wind action, forming yardangs . The resurgent dome consists of Galán ignimbrite material, along with basement rocks. The "Toba Dacitica" 270 kilometres (170 mi) outcrop away from

5358-403: The caldera. 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

5452-522: The caldera. Another Leon Muerto river drains the southern side of the caldera into Laguna Pabellon. Rivers in the caldera and neighbourhood display river terraces which may reflect pre-caldera formation uplift of the terrain and uplift associated with the resurgent dome. These drainages eventually converge in the Rio de Los Patos and end into the Salar del Hombre Muerto north of Galán. The high Cerro Galán intercepts moisture transported from east, thus nourishing

5546-664: The collapsed magma chamber, the center of the caldera may be uplifted in the form of a resurgent dome such as is seen at the Valles Caldera , Lake Toba , the San Juan volcanic field, Cerro Galán , Yellowstone , and many other calderas. Because a silicic caldera may erupt hundreds or even thousands of cubic kilometers of material in a single event, it can cause catastrophic environmental effects. Even small caldera-forming eruptions, such as Krakatoa in 1883 or Mount Pinatubo in 1991, may result in significant local destruction and

5640-452: The crust. Based on the presence of two separate populations of pumice in the Galán ignimbrite it has been inferred that there were two types of magma in the magmatic system during the Galán eruption, a larger volume of so-called "white" magma and a "grey" magma which was injected into the "white" magma pool and eventually rose above the latter. More generally, it appears that before each eruption there were two batches of magma present beneath

5734-555: 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. 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

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5828-616: The eastern slopes, thus the former are sometimes called coasts and the latter are called skirts . The narrow valleys are called "broken" or "open"; the narrow openings between valleys are called "doors". Due to erosion and other geologic forces (volcanoes, glaciers, rivers, tectonic etc.), the surface of this area varies widely. It includes cliffs and narrow channels of some rivers which are named "drawers" (if they are of moderate size) or "guns "(if they are older); there are abundant caves , grottos and overhangs. Some mountains are separated by significant open areas (too large to be considered

5922-403: The emptied or partially emptied magma chamber, leaving a large depression at the surface (from one to dozens of kilometers in diameter). Although sometimes described as a crater , the feature is actually a type of sinkhole , as it is formed through subsidence and collapse rather than an explosion or impact. Compared to the thousands of volcanic eruptions that occur over the course of a century,

6016-464: The formation of a caldera is a rare event, occurring only a few times within a given window of 100 years. Only eight caldera-forming collapses are known to have occurred between 1911 and 2018, with a caldera collapse at Kīlauea , Hawaii in 2018. Volcanoes that have formed a caldera are sometimes described as "caldera volcanoes". The term caldera comes from Spanish caldera , and Latin caldaria , meaning "cooking pot". In some texts

6110-399: The greater runoff water available there. There are short, torrential rivers and many streams and rivulets that carry low flows, with brief and violent floods caused by summer rains. These rivers are used for the production of hydropower . The flora and fauna of the Sierras Pampeanas varies with elevation and exposure. The Dry Chaco , a region of dry forests, shrublands, and savannas, lies in

6204-463: The human species was reduced to approximately 5,000–10,000 people. There is no direct evidence, however, that either theory is correct, and there is no evidence for any other animal decline or extinction, even in environmentally sensitive species. There is evidence that human habitation continued in India after the eruption. Some volcanoes, such as the large shield volcanoes Kīlauea and Mauna Loa on

6298-442: The ignimbrite apron of the Toconquis group was incised by deep valleys. Mechanistically, the onset of the eruptions has been explained with delamination events during which parts of the lower crust broke off, asthenospheric material replaced the crust lost by delamination and basaltic magmas penetrated the remaining crust. These stages have left an ignimbrite plateau that surrounds the caldera except on its southern side, and which

6392-429: The island of Hawaii , form calderas in a different fashion. The magma feeding these volcanoes is basalt , which is silica poor. As a result, the magma is much less viscous than the magma of a rhyolitic volcano, and the magma chamber is drained by large lava flows rather than by explosive events. The resulting calderas are also known as subsidence calderas and can form more gradually than explosive calderas. For instance,

6486-479: The landscape, and then the Caldera de Taburiente on La Palma . A collapse is triggered by the emptying of the magma chamber beneath the volcano, sometimes as the result of a large explosive volcanic eruption (see Tambora in 1815), but also during effusive eruptions on the flanks of a volcano (see Piton de la Fournaise in 2007) or in a connected fissure system (see Bárðarbunga in 2014–2015). If enough magma

6580-666: The location of the caldera. Galán has erupted mainly potassium -rich dacitic to rhyolitic rocks that are often called rhyodacitic , and which reflect a calc-alkaline suite. Each ignimbrite has usually a uniform composition but there is some variation between individual ignimbrites; for example older rocks contain amphibole and younger rocks instead sanidine . Minerals contained in the eruption products include allanite , apatite , biotite , hornblende , ilmenite , magnetite , orthopyroxene , plagioclase , quartz , sanidine and zircon . Hydrothermal alteration has left calcite in some rocks. Trace element patterns are distinct in

6674-481: The lowlands and foothills to the east. The east-facing slopes of the sierras intercept moisture-bearing winds, and are more humid than the adjacent lowlands. These higher-rainfall slopes are home to the Southern Andean Yungas humid forests. The western slopes are in the more arid rain shadow of the ranges. The High Monte shrublands are found in the western slopes and intermountain valleys and basins west of

6768-411: The magma genesis process. Probably under the influence of larger scale tectonics, magma that accumulated into a mid-crustal mush zone is eventually transferred into shallow magma chambers at depths of 8–4 kilometres (5.0–2.5 mi); recharge events where deep magma entered the shallow magma bodies may have triggered eruptions at Galán. After eruption, a leftover pluton would have been generated inside

6862-561: The magma to produce a mixture of volcanic ash and other tephra with the very hot gases. The mixture of ash and volcanic gases initially rises into the atmosphere as an eruption column . However, as the volume of erupted material increases, the eruption column is unable to entrain enough air to remain buoyant, and the eruption column collapses into a tephra fountain that falls back to the surface to form pyroclastic flows . Eruptions of this type can spread ash over vast areas, so that ash flow tuffs emplaced by silicic caldera eruptions are

6956-462: The main Galán eruption until less than 2 million years ago. These ignimbrites have similar compositions to the Galán ignimbrite and were formed from magma left over by the main Galán eruption. The onset of resurgence within the caldera may have been triggered by the same magma that is responsible for the post-caldera volcanism along the eastern caldera rims. The post-caldera volcanic systems appear to be rather ill-defined, however. The most recent activity

7050-458: The northeastern margin of the caldera. About 14.5 million years ago volcanic activity started in the region, first west of Galán but by 7 million years ago it shifted to the future caldera, forming the Cerro Colorado, Pabellon and Cerro Toconquis composite volcanoes on its future western rim. The more westerly centres are today represented by eroded volcanoes. Since about 6.6 million years ago

7144-625: The northeastern side of the caldera is Piscinas Burbujeantes, with mud volcanoes and small fumaroles. These springs have emplaced clay , salt , sinter and travertine deposits and have been prospected for geothermal power development. The basement beneath the caldera consists of 600–365 million years old metamorphic and sedimentary rocks of Precambrian to Paleozoic age. These include intrusions of granitoid character and are overlain with Paleozoic marine sediments. Ordovician units are also present and form sediment layers up to 7 kilometres (4.3 mi) thick. Basements outcrops occur in

7238-468: The only volcanic product with volumes rivaling those of flood basalts . For example, when Yellowstone Caldera last erupted some 650,000 years ago, it released about 1,000 km of material (as measured in dense rock equivalent (DRE)), covering a substantial part of North America in up to two metres of debris. Eruptions forming even larger calderas are known, such as the La Garita Caldera in

7332-455: The other. Generally the ignimbrites are rich in crystals and pumice, are unwelded and contain few flow structures, with the exception of the welded Cueva Negra ignimbrite. Some ignimbrite eruptions were preceded by the formation of Plinian eruption columns that generated ash fallout, and there is evidence for pulsating flow in the ignimbrites. On the northern side of the Galán complex, ignimbrites extend up to 80 kilometres (50 mi) away from

7426-424: The region have introduced domestic animals such as horses, donkeys, goats, pigs, cattle and sheep. Agriculture is the predominant economic activity in the area. Certain areas are noted for wine and olive oil production, as well as cheeses , homemade breads , pies , sweets (the best known nationally are the sweet potato and quince ) and alcohol . Most products are for local consumption. Only where rainfall

7520-451: The ring fault of the caldera, as well as the formation of the resurgent dome by about 2 kilometres (1.2 mi) uplift along the eastern caldera margin fault. This uplift encompasses both Galán ignimbrite rocks but also parts of the basement, the latter especially in the southern part of the dome. Post-caldera volcanism occurred on the northern margin of the caldera 2.01 ± 0.28 million years ago, and several small ignimbrites were emplaced after

7614-462: The ring fracture begins to collapse. The collapse may occur as the result of a single cataclysmic eruption, or it may occur in stages as the result of a series of eruptions. The total area that collapses may be hundreds of square kilometers. Some calderas are known to host rich ore deposits . Metal-rich fluids can circulate through the caldera, forming hydrothermal ore deposits of metals such as lead, silver, gold, mercury, lithium, and uranium. One of

7708-458: The second on the southwestern foot of the resurgent dome, both emitting water with temperatures of about 56–85 °C (133–185 °F). The first one is known as the Aguas Calientes hydrothermal spring and features deposits of tufa and boiling water. Another geothermal system is known as La Colcha and includes fumaroles as well as boiling water; it drains into Laguna Diamante. Finally, on

7802-513: The summer months. At high elevations there is no vegetation. Between 3,900–5,000 metres (12,800–16,400 ft) elevation, vegetation consists of high altitude steppe dominated by Poaceae (grasses) such as Festuca (fescue) and Stipa (feather grass). At lower altitudes, wetlands have their own vegetation. In sheltered areas birds like ducks and flamingos can be observed. Volcanic activity at Galán occurred in two separate stages, which are separated by an erosional unconformity during which

7896-501: The topography of the region had been flattened by the previous Toconquis ignimbrites, and was still hot by the time it came to a standstill. Pumice is scarce and usually present in only small fragments, and lithic fragments are also uncommon except at the bases of the deposit. Fiamme structures on the other hand are fairly common especially where the ignimbrite crossed river valleys. The ignimbrite displays varying degrees of welding but has often spectacular columnar joints. At first it

7990-413: The twentieth century jaguar were found in the rainforests. In the eighteenth century there were sightings of spectacled bears . The avifauna is diverse and relatively abundant in the higher, mostly arid areas. It includes Andean condors and vultures . In the fertile plains of Tucumán Province previously were found rhea , turkey , parrot , hummingbird , woodpecker and pigeons . Settlers to

8084-419: The valley of Antofagasta de la Sierra and may have continued to less than ten thousand years ago. The positions of the exact vents are controlled by recent fault systems in the region. Since about 10 million years ago, the area has been subject to reverse faulting which has disrupted the basement along north–south lines, forming a rift valley that also stretches from north to south. The magma erupted by

8178-558: The volcanic activity produced rocks of both mafic and silicic compositions. The increase of volcanic activity has been attributed to the steepening of the Nazca Plate slab which allowed mantle material to penetrate into the space between the lower crust and the slab. North of 21° degrees southern latitude ignimbritic volcanism started earlier, generating the Altos de Pica and Oxaya formations . Mafic volcanism occurred south and west of Galán both before its large eruption and afterwards, in

8272-570: The volcano was once considered part of the Galán eruption but later compositional differences were found. The Galán ignimbrite is fairly homogeneous and has a high crystal content; overall it appears that the eruption commenced and reached large dimensions fairly quickly without leaving time for an eruption column or distinct flow units to form, except in some places. Conversely, the produced flows were relatively slow flows that had little capacity to pass above topographic obstacles or to move rocks around. It nevertheless spread over large distances, since

8366-575: The volcano which however were very similar owing perhaps to a homogenization process that took place deep in the crust. Before the eruption, the magma is estimated to have been 790–820 °C (1,450–1,510 °F) hot. Galán lies in a region of arid climate, with annual precipitation amounting to about 65 millimetres per year (2.6 in/year). Frosts occur year-round. Climate data are known for Salar de Hombre Muerto north of Galán; average temperatures there are 8–23 °C (46–73 °F) in summer and winter, respectively. Precipitation occurs mostly during

8460-633: The world's best-preserved mineralized calderas is the Sturgeon Lake Caldera in northwestern Ontario , Canada, which formed during the Neoarchean era about 2.7 billion years ago. In the San Juan volcanic field , ore veins were emplaced in fractures associated with several calderas, with the greatest mineralization taking place near the youngest and most silicic intrusions associated with each caldera. Explosive caldera eruptions are produced by

8554-506: Was assumed that this ignimbrite crops out over a surface of 7,500 square kilometres (2,900 sq mi) but later it was found that it covers a surface closer to 2,400 square kilometres (930 sq mi). Between the intracaldera ignimbrite, the parts of the ignimbrite that extend away from the caldera and outcrops at large distance, the volume is about 650 cubic kilometres (160 cu mi), down from earlier estimated of volumes exceeding 1,000 cubic kilometres (240 cu mi) but

8648-406: Was of tectonic nature and consists of movements along the faults and mafic volcanism ("Incahuasi Formation ") farther west. Seismic tomography indicates that there is still a melt zone under Galán, the "Cerro Galán Mush Body". The volcano produces about 200 kilograms (440 lb) carbon dioxide per day, often within the hot springs. The pre-caldera rocks contain the hydrothermal system, which

8742-452: 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

8836-464: Was the largest known eruption during the ongoing Quaternary period (the last 2.6 million years) and the largest known explosive eruption during the last 25 million years. In the late 1990s, anthropologist Stanley Ambrose proposed that a volcanic winter induced by this eruption reduced the human population to about 2,000–20,000 individuals, resulting in a population bottleneck . More recently, Lynn Jorde and Henry Harpending proposed that

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