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Ampato (possibly from Quechua language hamp'atuYachakuqkunapa Simi Qullqa - Qusqu Qullaw. Qhichwa Simipi (monolingual Quechua and bilingual Quechua-Spanish dictionary) or from Aymara language jamp'atu, both meaning "frog") is a dormant stratovolcano in the Andes of southern Peru. It lies about northwest of Arequipa and is part of a north-south chain that includes the volcanoes Hualca Hualca and Sabancaya, the last of which has been historically active.
Ampato consists of three volcanic cones, which lie on top of an older eroded volcanic edifice. They were formed sequentially by extrusion of , but Ampato has also had explosive eruptions which have deposited ash, lapilli and pumice in the surrounding landscape. One young lava flow has been dated to 17,000 ± 6,000 years before present, but a summit lava dome is even younger, and Holocene ash layers in surrounding peat bogs may testify to the occurrence of recent eruptions.
The present-day volcano is covered by an ice cap, and during the last glacial maximum glaciers advanced to low altitudes. In 1995, an Inca mummy known as Mummy Juanita was discovered on Ampato by Johan Reinhard; it had been offered as a human sacrifice more than six hundred years earlier on the mountain.
Ampato is part of the Central Volcanic Zone of the Andes, which in Peru manifests itself as several dozen Pleistocene volcanoes, some of which erupted in historical time including El Misti, Huaynaputina, Sabancaya and Ubinas. The largest historical eruption of the Andes took place at Huaynaputina. Other volcanoes in the Peruvian Central Volcanic Zone are Sara Sara, Solimana, Coropuna, Andagua volcanic field-Huambo volcanic field, Chachani, Ticsani, Tutupaca, Yucamane, Purupuruni and Casiri.
The volcano Ampato consists of three individual steep-sided cones which rise from a gentle glacially eroded foot. These three cones are lined up in southwest-northeast direction and the highest one reaches an elevation of or . Ampato is one of the highest volcanoes in the Central Volcanic Zone and the 35th highest summit in the Andes. The volume of the edifice is about , it covers an area of about .
The summit of the volcano is covered with an ice cap, and the edifice is incised by and glacial valleys. The volcano is surrounded by three sets of , the lowermost one at elevation has been attributed to the last glacial maximum between 25,000-17,000 years ago, the middle one between to a late readvance at the Pleistocene-Holocene epoch boundary and the higher ones above to Holocene advances.
Volcanic arc-associated volcanism originally occurred within the Cordillera de la Costa in the Jurassic, but later it migrated resulting in the emplacement of the Tacaza and Toquepala groups and finally the Neogene Barroso group. The present-day volcanic arc is situated in the area of the Barroso group but has a narrower extent. The pre-volcanic basement consists of 1.9-1.0-billion-year-old rocks of the "Arequipa Massif", which consists of gneiss and granulite. They are covered by the Yura Group of the Mesozoic and the Mesozoic-Paleogene Tiabaya unit; the former consists of marine sediments and the latter of volcanic sediments intruded by . The Tacaza and Barroso groups are emplaced on the sediments.
The basement beneath Ampato is formed by sedimentary and volcanic rocks of the Western Cordillera of Peru, and the rocks are of Mesozoic to Cenozoic age. A high plateau formed by and of Pliocene to Miocene age rises above this basement. The terrain is cut by several different fault systems; one of these, the northeastward striking Sepina fault has been seismically active in the 20th and 21st centuries and seems to have controlled the development of the Ampato and Sabancaya volcanoes.
The magmas derive from mantle melts, but undergo additional differentiation processes before reaching the surface. Processes such as fractional crystallization, magma mixing and the absorption of crustal material by developing magmas have been invoked to explain the formation of the magmas of both Ampato and Sabancaya. Estimating the rate of magma production at Ampato is difficult owing to the uncertainties in determining the volume of the edifice and the duration of repose times between eruptions; on average it appears to be . This rate does not consider "spurt"-like behaviour; volcano growth in fits and spurts has been observed at many other volcanic arc volcanoes. The rate is about one order of magnitude less than at neighbouring Sabancaya volcano.
After a pause in volcanic activity and an intermediary stage ("Yanajaja stage"; one date obtained on this stage is 77,000 ± 4,000 years before present) that produced andesitic-dacitic lava flows which form a thick unit on top of eroded remnants of the older Ampato volcanics, the andesitic northern cone formed as the first of the three present-day cones. The southern cone developed in several different stages; a first stage generated lava flows emanating from the summit; dating of two such flows has produced ages of 34,000 ± 8,000 and 40,000 ± 3,000 years before present. More than of block-and-ash flows was erupted onto the eastern and western flanks of Ampato, and these flows consist of one andesitic and one dacitic formation; both appear to relate to a lava dome forming stage of volcanic activity. These block-and-ash flows are themselves covered on both the eastern and the western flanks by more thick lava flows, which make up a thick unit and again consist of one andesitic and one dacitic unit; both units appear to have been erupted during the last glacial maximum.
Either during or before the last glacial maximum, Ampato erupted tephra during multiple explosive eruptions which today is preserved in two units, the Baylillas and the Corinta deposits. The first consists of lapilli, pumice and scoria and individual layers form thick sequences at large distances from the volcano, but are heavily eroded and thus difficult to measure in extent. Scoria identified on the southwestern-southern flanks of Ampato correspond to this unit. The dacitic Corinta deposits conversely were created during one large eruption which also left a Volcanic crater on Ampato; it generated stratified thick tephra deposits which contain pumice embedded within ash-rich layers, and it is probably also the source of the pumice flow deposits on the south-southwestern flank. These contain dacitic pumice fragments in a matrix rich in ash and have thicknesses of more than in the few outcrops; much of this unit was likely eroded away by glacial activity. The central cone grew in the gap between the northern and southern edifice and consists of lava flows again of andesitic to dacitic composition. These flows are together maximally thick and one flow has been dated to 17,000 ± 6,000 years before present. A dacitic summit lava dome is not affected by glacial erosion and appears to be the youngest eruption product of Ampato.
Early Holocene (11,000 - 8,000 years before present) ash layers in around the volcano may have originated either on Ampato or on Sabancaya. Late Holocene tephra layers dated to 1,790 ± 110, 2,050 ± 70 and 4,500 ± 125 likewise may have been erupted from Ampato, but Sabancaya is a more likely source for these ash layers.
The Peruvian geological service has published a hazard map that describes danger areas of both Ampato and Sabancaya. Hazards mapped include both the fall of ash and the formation of lahars which can advance to distances of in the southerly valleys of Ampato. primarily threatens the vicinity of the volcano but large eruptions can result in fallout over large areas around the volcanic complex.
Such sacrifices with children being the usual subjects are known as capacocha and the discoveries of their mummies on mountains in the Andes has gained them a lot of attention. The process served to tie the Inka empire more closely together, since children to be sacrificed were selected from the entire realm and the children adorned and their names remembered after the sacrifice.
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