Calabozos is a Holocenecaldera in central Chile's Maule Region (7th Region). Part of the Chilean Andes' volcanic segment, it is considered a member of the Southern Volcanic Zone (SVZ), one of the three distinct volcanic belts of South America. This most active section of the Andes runs along central Chile's western edge, and includes more than 70 of Chile's stratovolcanoes and volcanic fields. Calabozos lies in an extremely remote area of poorly glaciated mountains.
Calabozos is responsible for the huge Loma Seca Tuff, a body of material 200 cubic kilometres (48cumi) to 500 cubic kilometres (120cumi) in volume. It accumulated over at least three eruptive periods, beginning 800,000 years ago (0.8 mya) and lasting until 150,000 years ago (0.15 mya).
The caldera's dimensions are 26 kilometres (16mi) by 14 kilometres (8.7mi), and it has an elevation of 3,508 metres (11,509ft).[2] Activity from the caldera has produced many other stratovolcanoes to form a complex volcano.[2]
Geography and structure
Calabozos lies in central Chile's Maule Region, near Curicó and Talca, on the western Andes.[3] This is an area of poorly glaciated mountains that is not permanently populated. There are no roads, and it is only accessible via horse or on foot.[4]
Calabozos is part of the South Volcanic Zone, which runs along the western edge of central Chile and extends south, jumping the border to continue its course in Argentina. This range includes at least nine caldera complexes, more than 70of Chile's stratovolcanoes and volcanic fields that have been active in the Quaternary, and hundreds of minor eruptive centers. The South Volcanic Zone is the most volcanically active region in Chile, and produces around one eruption per year. Its largest historical eruption was at Quizapu Crater, located 15 kilometres (9mi) to 20 kilometres (12mi) from the north side of Cerro Azul's summit,[5] and its most active volcanoes are Llaima and Villarrica.[6]
Calabozos is a ring-shaped caldera26 kilometres (16mi) by 14 kilometres (9mi) wide,[3] with an elevation of 3,508 metres (11,509ft).[2] Volcanoes have been formed by eruptions in the crater. The largest, which is on the southern rim of the caldera, is the Holocene Cerro del Medio complex with an elevation of 3,508 metres (11,509ft).[1] It is made mainly of andesite and dacite, and has a volume of 20 cubic kilometres (5cumi) to 25 cubic kilometres (6cumi). On the southwestern edge several eruptions have created the Descabezado Chico volcano (elevation: 3,250 metres (10,663ft))[1] which consists of four overlapping volcanic craters.[2] The last eruption occurred during Holocene time, and produced a dacitic lava flow (2.5 cubic kilometres (1cumi) in volume) that extends for 30 kilometres (19mi).[2] Cerro Colorado, with an elevation of 2,928 metres (9,606ft), forms another cone in the complex.[1]
Towards the center of the caldera, hot springs including Cajon Los Calabozos and Baños de Llolli[1] are present.[2] The springs are as old as 0.3 mya, and may have formed directly after Calabozos's second eruption as a result of uplift caused by re-occurring activity in the caldera.[7][2] The vents occur in two clusters, Colorado and Puesto Calabozos, and are located along the margin of a fault at the southwestern edge of the caldera.[7] Hildreth et al. (1983) evaluated that Calabozos could potentially be useful for the harvesting of geothermal energy,[8] and exploratory holes have been drilled.[9]
Geology
The subduction of the Nazca Plate resulted in the formation of the Andean Volcanic Belt and the Peru–Chile Trench.
Calabozos is one of 45 Holocene epoch volcanoes located in central Chile and Argentina.[11] It is included within the Southern Volcanic Zone, the most active section of the Chilean Andes.[6] The date of its last known eruption is not known with precision, though it took place during the Holocene.[2]
Through K-Ar dating, geologist Robert Edward Drake established the age of 66 events in central Chile, and divided them into groups based on the time of their origin. In a paper published in 1976, he described the location of each group and the west–east-trending movement of volcanism in the range.
To the west of the Chilean Andes are an early group of eruptions, dated from the Oligocene and the Early Miocene (33.3–20.2mya). The scale of the eruptive events that produced these features remains unclear. Further east, in the actual range, are huge numbers of eruptions. Between 15.3 and 6.4mya, widespread volcanism took place, followed by extensive folding; this process then repeated itself from 18.4 to 13.7 mya during the Miocene. Beginning 6.4 mya the Chilean Andes were quiet, though whether or not this quiet period took place throughout all of the Andes remains unknown. Central Chilean volcanoes became active once again around 2.5mya, and have erupted almost continuously since.[12]
Local
Calabozos lies in an area between thick and thin continental crust, and its eruptions are probably fed from a pool of andesitic and rhyolitic magma that sits just under its caldera.[13] The caldera is underlain by a layer of volcaniclasticsedimentary rock from the Mesozoic era coalesced with intrusive and volcanic rocks of Tertiary age, over a layer of Precambrian-Triassic sedimentary and metamorphic rock formed from later plutons (magma intrusions).[14] Under its northeast edge, Calabozos is cut by a north–south trending segment of sedimentary rock that includes gypsiferous and carbonates.[4]
Calabozos is similar in age to Cerro Azul and Descabezado Grande, and its eruptions may correspond to past activity at both volcanoes. Eruption products of very similar composition (including mafic andesite, agglutinates, and dacite) make up the volcanoes. There is also a similarity in size (all are between 40 and 70 cubic kilometers in volume).[5]
The volcano appears to be part of a north–south trending group of rhyolitic, silicic Quaternary volcanoes (including Puelche Volcanic Field, Laguna del Maule, and Volcán Domuyo) that veers off the north-northeast direction of the rest of the Andes. The directional formation of this belt corresponds to the fold-and-thrust movement of the nearby Malargüe fault, which formed in the Tertiary and remained active until the early Pliocene or late Miocene. This may suggest that Calabozos' activity is more dependent on local processes than subduction of the Nazca Plate.[15]
Geologic record
In comparison to the well-preserved rocks of the dry, central part of the Andes, the record that defines the southern sector is poorly preserved. Remnants of Miocene and Quaternary eruptions within the central part are clearly preserved in the rock record. Ash flow sheets constitute as much as 40percent of the area's total erupted material, suggesting that pyroclastic eruptions were rather important during this time. By examining the eruption rate of individual volcanoes, Hildreth et al. concluded that similar amounts of ash-flow volcanism took place in the southern sector as well. Their study established that in particular silicic ash was missing from the record, and concluded that erosion had probably disrupted deposition of volcaniclastic rock.[3]
While the volcanic history of the area extends back far further, the earliest fully recognizable events in the region are recorded in the pyroclastic Campanario Formation. This sequence appears to begin at Laguna de la Invernada and ranges from 15 to 6mya. Remnants of magma intrusions as young as 7mya can be found at the lake (Laguna de la Invernada).[16]
The most recent volcanic phase began about 4mya, producing largely andesitic eruptions. A series of eruptions built up a broad plateau of lava, and extended over the area where Calabozos now lies. Locally, this plateau was composed of mafic andesite with olivine, which over time gathered to form 300-metre (1,000ft) to 500-metre (1,600ft) thick layers. Nearby volcanoes sit on top of two mya lavas that formed during this period, while the Loma Seca Tuff lies atop andesitic deposits from Descabezado Grande.[16]
The area's rainfall averages 134 centimetres (53in) annually, varying from 50 centimetres (20in) at its lowest to 225 centimetres (89in) at its highest. Precipitation between May and August (primarily snow) is normally 20 to 35 centimetres, dropping to below one centimetre during summer. Temperature is also variable, typically registering 25 degrees Celsius during the summer, but dropping below freezing at high elevations (above 2,500 metres (8,200ft)).[4]
Vegetation is rare in the area. The 1932 eruption of Cerro Azul's Quizapu Crater reduced much of the land to a pumice desert. Above 1,200 metres (3,900ft), vegetation becomes even more sparse.[4]
Eruptive history
Calabozos' tuff eruptions were mostly rhyodacitic and dacitic in origin.
During the late Pleistocene, Calabozos erupted tuff composed primarily of rhyodacite and dacite. Three distinct eruptions have taken place within the last million years. The sheets of remaining ash left over from all of the eruptions together range from 200 cubic kilometres (48cumi) to 500 cubic kilometres (120cumi) in volume and are known as the Loma Seca Tuff.[2]
The first eruption, which took place 0.8mya, was distinct from later eruptions in that its product lacks flattened lenticles (lens-shaped layers of mineral or rock embedded in rock). The tuff is dotted with predominantly plagioclase phenocrysts, which make up between less than 5 to approximately 15percent of each particle's mass. After being erupted, the material settled in canyons, where it underwent glaciation. This carved cliffs which drop as much as 100 metres (328ft). The tuff is limited to just a few kilometers around the complex.[18]
Taking place 0.3mya, the second eruption was the most extensive. It was probably between 250 cubic kilometres (60cumi) and 300 cubic kilometres (72cumi) in volume and extended past the reaches of the caldera, down the adjacent foothills. Beyond the caldera, the eruptive products are poor in phenocrysts (unlike those of the first eruption). They are instead rich in lithic material, which makes up as much as 10percent of the rock in parts (50percent at the base of the caldera). As the first of the ash was deposited, it accumulated in layers that formed quickly and resisted erosion, but only partially melded together. However, except for these basal layers and thin zones where the ash was devitrified (loses the properties of a glass and becomes brittle), the entire sheet is melded together. Inside Calabozos, the ash resisted welding and contains more phenocrysts. Instead, erosion ate away at it, in the form of acid leaching, and broke down much of its pumice content. Still, the rock layer here contains five to 30percent phenocrysts, and has high levels of devitrification and lithic content.[18]
The differences between these two deposits can be accounted for by a few factors, including time of eruption and placement. The material inside the caldera must be younger and erupted from a pool of magma that had larger crystals. Its extensive erosion can be explained by the presence of hydrothermal vents, and its high levels of lithics probably originate from either being exposed to the rocks after they were erupted, lying adjacent to them while they underwent subsidence, or is a result of long, slow formation. Any of these reasons would also effectively account for the poor mixing of the lavas.[18]
The third eruption was high in fiamme (on the right), and erupted material with large phenocrysts.
Activity continued for approximately 150,000 years in the form of quiet andesitic eruptions, as glaciation took place. About 0.15mya (150,000 years ago), a third and final ash flow was erupted. With a volume of 175 cubic kilometers (42cumi) to 250 cubic kilometres (60cumi), it was smaller than the second eruption, but acted similarly, and had much more densely welded tuff. The ash was thickest at 300 metres (984ft), at Loma Seca, and the top of the deposit has undergone erosion. It is densely welded in crevasses, but not at thin 50 metres (164ft) layers, where much of the material is barely welded or not welded at all.[18]
The first layers of the last deposit were alternating belts of light and dark-colored material, and were densely welded. They appear to have been erupted in pulses, and continue for hundreds of meters. Deposition was continuous except for one interruption, which can be seen at proximity to the caldera, where the layers are replaced by thin, nonwelded sheets of lava. Another zone of nonwelded material, about 20 metres (66ft) and near Cajon Los Calabozos, underwent no erosion, suggesting that activity stopped, then began again.[18]
High in fiamme, the third tuff layer differs from the second in that it has even higher phenocryst content, but poor lithics. In the fiamme, phenocrysts constitute between 5 and 15 percent of the rock, increasing to 25 to 30percent near the caldera. In the younger emplacements, clinopyroxene is evident along with an increase in mafic content.[19]
Threats and preparedness
Calabozos is in the South Volcanic Zone, which contains potentially deadly and active volcanoes such as Mount Hudson, Llaima, and Villarrica.[20] Villarrica and Llaima together have more than 80reported episodes of volcanism since 1558, and at least 40South Volcanic Zone volcanoes have had Holocene-age eruptions.[6] After the 2010 Maule earthquake, vertical movement took place along the caldera margins.[21]
Its remoteness means that Calabozos poses little threat to humans, but if necessary relief efforts could be orchestrated. The Volcanic Disaster Assistance Program (VDAP) formed in response to the famous eruption of Nevado del Ruiz in Colombia and saved lives following the 1991 eruption of Mount Hudson in Chile by organizing evacuations. The team's stated aim is to "reduce eruption-caused fatalities and economic losses in developing countries". Made up of various USGS offices such as the Cascades Volcano Observatory (CVO), responsible for monitoring Mount St. Helens, the team has equipment to monitor any volcano, allowing the timely prediction of volcanic eruptions and the evacuation of nearby homes.[22]
Novarupta is a volcano that was formed in 1912, located on the Alaska Peninsula on a slope of Trident Volcano in Katmai National Park and Preserve, about 290 miles (470 km) southwest of Anchorage. Formed during the largest volcanic eruption of the 20th century, Novarupta released 30 times the volume of magma of the 1980 eruption of Mount St. Helens.
Aracar is a large conical stratovolcano in northwestern Argentina, just east of the Chilean border. It has a main summit crater about 1–1.5 kilometres (0.6–0.9 mi) in diameter which sometimes contains crater lakes, and a secondary crater. The volcano has formed, starting during the Pliocene, on top of a lava platform and an older basement. Constructed on a base with an altitude of 4,100 metres (13,500 ft), it covers a surface area of 192.4 square kilometres (74.3 sq mi) and has a volume of 148 cubic kilometres (36 cu mi). The only observed volcanic activity was a possible steam or ash plume on March 28, 1993, seen from the village of Tolar Grande about 50 km (31 mi) southeast of the volcano, but with no evidence of deformation of the volcano from satellite observations. Inca archeological sites are found on the volcano.
Cerro Azul, sometimes referred to as Quizapu, is an active stratovolcano in the Maule Region of central Chile, immediately south of Descabezado Grande. Part of the South Volcanic Zone of the Andes, its summit is 3,788 meters (12,428 ft) above sea level, and is capped by a summit crater that is 500 meters (1,600 ft) wide and opens to the north. Beneath the summit, the volcano features numerous scoria cones and flank vents.
Lascar is a stratovolcano in Chile within the Central Volcanic Zone of the Andes, a volcanic arc that spans Peru, Bolivia, Argentina and Chile. It is the most active volcano in the region, with records of eruptions going back to 1848. It is composed of two separate cones with several summit craters. The westernmost crater of the eastern cone is presently active. Volcanic activity is characterized by constant release of volcanic gas and occasional vulcanian eruptions.
Nevado de Longaví is a volcano in the Andes of central Chile. The 3,242 m (10,636 ft) high volcano lies in the Linares Province, which is part of the Maule Region. It features a summit crater and several parasitic vents. The volcano is constructed principally from lava flows. Two collapses of the edifice have carved collapse scars into the volcano, one on the eastern slope known as Lomas Limpias and another on the southwestern slope known as Los Bueye. The volcano features a glacier and the Achibueno and Blanco rivers originate on the mountain.
Aucanquilcha is a massive stratovolcano located in the Antofagasta Region of northern Chile, just west of the border with Bolivia and within the Alto Loa National Reserve. Part of the Central Volcanic Zone of the Andes, the stratovolcano has the form of a ridge with a maximum height of 6,176 metres (20,262 ft). The volcano is embedded in a larger cluster of volcanoes known as the Aucanquilcha cluster. This cluster of volcanoes was formed in stages over eleven million years of activity with varying magma output, including lava domes and lava flows. Aucanquilcha volcano proper is formed from four units that erupted between 1.04–0.23 million years ago. During the ice ages, both the principal Aucanquilcha complex and the other volcanoes of the cluster were subject to glaciation, resulting in the formation of moraines and cirques.
Volcán Tupungatito is the northernmost historically active stratovolcano of the southern Andes. Part of the Chilean Andes' volcanic segment, it is the northernmost member of the Southern Volcanic Zone (SVZ), which is one of several distinct volcanic belts in the Andes. Over 70 Pleistocene or Holocene age volcanoes make up this volcanic belt, which on average has one eruption per year.
Mentolat is an ice-filled, 6 km (4 mi) wide caldera in the central portion of Magdalena Island, Aisén Province, Chilean Patagonia. This caldera sits on top of a stratovolcano which has generated lava flows and pyroclastic flows. The caldera is filled with a glacier.
San Pedro is a Holocene composite volcano in northern Chile and at 6,155 metres (20,194 ft) in elevation one of the highest active volcanoes in the world. Part of the Chilean Andes' volcanic segment, it is part of the Central Volcanic Zone of the Andes, one of the four tracts of the Andean Volcanic Belt. This region of volcanism includes the world's two highest volcanoes Ojos del Salado and Llullaillaco. San Pedro, like other Andean volcanoes, was formed by the subduction of the Nazca Plate beneath the South America Plate. It has a neighbouring volcano, San Pablo, and is itself formed by two separate edifices usually known as the Old Cone and the Young Cone. These edifices are formed by rocks ranging from basaltic andesite over andesite to dacite and are emplaced on a basement formed by Miocene volcanic rocks.
This timeline of volcanism on Earth includes a list of major volcanic eruptions of approximately at least magnitude 6 on the Volcanic explosivity index (VEI) or equivalent sulfur dioxide emission during the Quaternary period. Other volcanic eruptions are also listed.
La Pacana is a Miocene age caldera in northern Chile's Antofagasta Region. Part of the Central Volcanic Zone of the Andes, it is part of the Altiplano-Puna volcanic complex, a major caldera and silicic ignimbrite volcanic field. This volcanic field is located in remote regions at the Zapaleri tripoint between Chile, Bolivia and Argentina.
The Altiplano–Puna volcanic complex, also known as APVC, is a complex of volcanic systems in the Puna of the Andes. It is located in the Altiplano area, a highland bounded by the Bolivian Cordillera Real in the east and by the main chain of the Andes, the Western Cordillera, in the west. It results from the subduction of the Nazca Plate beneath the South American Plate. Melts caused by subduction have generated the volcanoes of the Andean Volcanic Belt including the APVC. The volcanic province is located between 21° S–24° S latitude. The APVC spans the countries of Argentina, Bolivia and Chile.
Cerro Chao is a lava flow complex associated with the Cerro del León volcano in the Andes. It is the largest known Quaternary silicic volcano body and part of the most recent phase of activity in the Altiplano–Puna volcanic complex.
Cerro Guacha is a Miocene caldera in southwestern Bolivia's Sur Lípez Province. Part of the volcanic system of the Andes, it is considered to be part of the Central Volcanic Zone (CVZ), one of the three volcanic arcs of the Andes, and its associated Altiplano-Puna volcanic complex (APVC). A number of volcanic calderas occur within the latter.
Cerro Chascon-Runtu Jarita is a complex of lava domes located inside, but probably unrelated to, the Pastos Grandes caldera. It is part of the more recent phase of activity of the Altiplano-Puna volcanic complex.
Corral de Coquena is a volcanic spatter rampart in the Andes, over the Tropic of Capricorn. The rampart at its highest point is 4,572 metres (15,000 ft) high.
Incapillo is a Pleistocene-age caldera in the La Rioja Province of Argentina. It is the southernmost volcanic centre in the Andean Central Volcanic Zone (CVZ) that erupted during the Pleistocene. Incapillo is one of several ignimbrite or caldera systems that, along with 44 active stratovolcanoes, comprise the CVZ.
Laguna del Maule is a volcanic field in the Andes mountain range of Chile, close to, and partly overlapping, the Argentina–Chile border. The bulk of the volcanic field is in the Talca Province of Chile's Maule Region. It is a segment of the Southern Volcanic Zone, part of the Andean Volcanic Belt. The volcanic field covers an area of 500 km2 (190 sq mi) and features at least 130 volcanic vents. Volcanic activity has generated cones, lava domes, lava coulees and lava flows, which surround the Laguna del Maule lake. The field gets its name from the lake, which is also the source of the Maule River.
Ubinas is an active stratovolcano in the Moquegua Region of southern Peru, approximately 60 kilometres (37 mi) east of the city of Arequipa. Part of the Central Volcanic Zone of the Andes, it rises 5,672 metres (18,609 ft) above sea level. The volcano's summit is cut by a 1.4-kilometre-wide (0.87 mi) and 150-metre-deep (490 ft) caldera, which itself contains a smaller crater. Below the summit, Ubinas has the shape of an upwards-steepening cone with a prominent notch on the southern side. The gently sloping lower part of the volcano is also known as Ubinas I and the steeper upper part as Ubinas II; they represent different stages in the volcano's geological history.
Cerro Overo is a volcanic crater in Chile. It lies at the foot of Chiliques volcano and close to Laguna Lejía, over ignimbrites of Pliocene age erupted by the La Pacana volcano. It is 480 by 580 metres wide and 72 metres (236 ft) deep and formed through combined explosive-effusive eruptions. The lavas are of lower crustal provenience and are among the least silicic in the region.
Stern, Charles R.; Moreno, Hugo; López-Escobar, Leopoldo; etal. (2007). "Chilean Volcanoes". In Moreno, Teresa; Gibbons, Wes (eds.). The Geology of Chile. Naranjo, Jose A., Parada, Miguel A., and Skewes, M. Alexandra. London: Geological Society of London. ISBN978-1-86239-220-5.
Further reading
Simkin, Tom; Siebert, Lee (1994). Volcanoes of the World (2nded.). Smithsonian Institution. ISBN0-945005-12-1.
González-Ferrán, Oscar (1995). Volcanes de Chile (in Spanish). Santiago, Chile: Instituto Geográfico Militar. ISBN956-202-054-1.
Note: volcanoes are ordered by latitude from north to south
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