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Sabancaya is an active stratovolcano in the Andes of southern Peru, about northwest of Arequipa. It is considered part of the Central Volcanic Zone of the Andes, one of the three distinct volcanic belts of the Andes. The Central Volcanic Zone includes a number of volcanoes, some of which like Huaynaputina have had large eruptions and others such as Sabancaya and Ubinas have been active in historical time. Sabancaya forms a volcanic complex together with Hualca Hualca to the north and Ampato to the south and has erupted andesite and dacite. It is covered by a small ice cap which leads to a risk of during eruptions.
Sabancaya has generated numerous long lava flows especially during the early Holocene, while activity in the later Holocene has been more explosive. Historical reports indicate eruptions during the 18th century. The volcano returned to activity in 1986, culminating in a large eruption in 1990. Since then, it has been continuously active with the emission of ash and gas.
Sabancaya is part of a series of volcanoes that line the southwestern coast of Peru at a distance of roughly from the shore. Of these volcanoes, Andagua volcanic field, Sabancaya, El Misti, Ubinas, Huaynaputina, Ticsani, Tutupaca and Yucamane have been active during historical time, erupting forty-five times during the past six centuries. Further volcanoes in the area with Pliocene-Quaternary activity are Sara Sara, Auquihuato, Solimana, Coropuna, Huambo volcanic field, Quimsachata, Chachani, Purupuruni, Casiri and Tacora. All these volcanoes are considered part of the Central Volcanic Zone of the Andes, and lie east of the Peru-Chile Trench. Notable among them are Ampato and Coropuna for exceeding a height of , Huaynaputina and El Misti for their large eruptions and Ubinas and Sabancaya for their recent activity.
These volcanoes are found in places where strike-slip faults which delimit the volcanic arc and strike along its length intersect additional faults formed by extensional tectonics. Such faults, mainly , occur around Sabancaya as well and include the Huambo-Cabanaconde, the Huanca, the Ichupampa, the Pampa Sepina, Sepina, Solarpampa and Trigal faults; the volcanoes Ampato and Sabancaya are aligned on the Sepina fault, which may thus be responsible for their existence. These fault systems are still active and experience occasional earthquakes and deformation, and their activity appears to be in part triggered by underground magma movements at Sabancaya. Large fractures opened up in the ground during the 1990s eruptions. Geological scale fractures in the crust formed by pulling-apart motion may be the ultimate source of volcanism at Sabancaya.
A set of over 42 Holocene emanate from the volcano, and cover a surface area of about , with individual lava flows extending up to east and west from between its two neighbours. The lava flows at larger distances are older than the ones close to the vent. These flows are blocky, have lobe structures and reach thicknesses of ; the total thickness of this pile of lava flows is about . Their diverse structures have been studied. Mudflow deposits have been found around Ampato and Sabancaya. Pyroclastic flow deposits are also found, but they might originate from Ampato rather than Sabancaya.
Sabancaya, like its two neighbours, is covered by an ice cap which in 1988 extended to distances of from the summit. In 1997, a surface area of was reported. The maximum thickness was in the summit area, decreasing to on steeper slopes. Penitents rise from the ice in some places. In 1998, the snowline was at altitude, varying from to the northwest to to the northeast. It lies above the freezing level height, as the climate is dry and impedes glacier development. Between 1986 and 2016 the mountain lost over three quarters of its ice cap, and the remaining ice field broke up into several ice bodies. at elevations of above sea level testify to the occurrence of more extensive glaciation during the last ice age between 25,000 and 17,000 years before present, when ice covered an area of on the three volcanoes; these moraines have diverted some lava flows. In turn, younger lava flows were emplaced on . Younger moraines are found at higher altitudes, above sea level, and may have formed between 13,000 and 10,000 years ago, shortly after the beginning of the Holocene. Most of Sabancaya post-dates the last ice age and is thus relatively unaffected by glaciation.
The magma chamber of Sabancaya is located beneath Hualca Hualca and Pampa Sepina northeast of Sabancaya about away from the summit. Between 1992 and 1996 this area inflated at a depth of below sea level, indicating that the magma supply system of Sabancaya may not be centered directly below the volcano. A phase of ground uplift at Hualca Hualca volcano and earthquake swarms in 1990 and later seismic activity under Hualca Hualca indicate that the magma chamber of Sabancaya is actually under the neighbouring volcano, a not uncommon phenomenon at volcanoes. Uplift was also observed between 2013 and 2019. Electrical techniques like magnetotelluric analysis and spontaneous potential analysis have found a potential hydrothermal system under Sabancaya and traces of an old caldera. Deeper below the volcano, low seismic velocity anomalies in the crust may be associated with volcanism at Sabancaya.
The basement of the volcano is formed by Precambrian rocks of the "Arequipa Massif", which are up to 1.9 billion years old. They are overlaid by various sediments and volcanic formations (Yura Group and Tiabaya unit) of Mesozoic and Cenozoic age. Especially during the Neogene, the supply of volcanic material was high and dominated the region, forming a volcanic "foot"; the present volcanoes are constructed on this volcanic "foot" formed by the Tacaza and Barroso sequences. This "foot" is made out of an ignimbrite plateau that drops down south. The "foot" beneath Ampato, Hualca Hualca and Sabancaya has been dated 2.2 ±0.15 million years ago, while a lava flow beneath the first and the last of these is about 0.8 ±0.04 million years old. Sometimes the volcanoes are classified within the Barroso sequence.
The formed at temperatures of with uncertainties of ; the highest temperatures are associated with the 1992 eruption products. Fluids from the downgoing slab chemically alter (metasomatism) the overlying mantle, which eventually melts to produce a primitive magma. In various magma chambers, magma genesis involved processes of magma mixing which formed at least part of the andesites and fractional crystallization which gave rise to the dacites. Partial crystallization and flow events within the magma chamber caused the formation of the andesite enclaves. The total magma production rate of Sabancaya without accounting for repose periods is about and is stored in a magma chamber under Hualca Hualca, horizontal distance from Sabancaya, at depth.
Sabancaya is a source of such as and . The amount of water emitted by Sabancaya is noticeably large for a volcano (about ); the source of this water might be an evaporating hydrothermal system in the volcano. Together with Ubinas Sabancaya is among the main emitters of , and in the Central Volcanic Zone of the Andes and among the top fifteen volcanic emitters on Earth. Sulfur dioxide is transported by winds on to the Pacific Ocean, where it affects the low stratocumulus clouds, but also to Arequipa where it contributes to air pollution. Much of the gas is derived from magma that does not ascend to the surface. The volcano also produces . The various emissions of Sabancaya have been recorded at research stations (Chacaltaya research station in Bolivia) and (Coropuna and possibly Quelccaya in Peru).
Sabancaya is the youngest volcano of Peru. Dating efforts have yielded ages of 12,340 ±550, 6,650 ±320, 6,300 ±310, 5,440 ±40, 5,200 ±100 and 4,100 ±100 years before present on various lava flows of the basal lava flow field stage, indicating that effusive activity started shortly after the beginning of the Holocene and built the basal edifice. Pyroclastic rock eruptions are less common and have a low volume. Layers dated 8,500 years before present, 2500-2100Anno Domini, 420–150 BC, 100 BC – 150 AD and between 1200 and 1400 AD, could have originated either on Sabancaya or Ampato. There is evidence that early and middle-Holocene Sabancaya mostly erupted lava, while the late-Holocene volcano was more explosive in its activity. Some lava flows might have remained hot for millennia after emplacement. Thirteen tephra-producing eruptions took place between 4,150 ±40 and 730 ±35 years ago. It is possible that the Inca Empire performed in response to eruptions of Sabancaya to calm down the mountain spirits; the Mummy Juanita on Ampato may have been such a sacrifice, or one against a drought.
Ash fell on towns around the volcano, causing irritations at the eyes, throats and intestines, and buried pastures. This eruption displaced between 4,000 and 1,500 people in the region, and there was widespread concern about the volcano, livestock losses, and complaints about government inaction. The US Volcano Disaster Assistance Program provided assistance. Ash fall from the eruption melted ice on the neighbouring Hualca Hualca, producing , and may have caused unusual rainfall during the dry season.
After the large 1990 eruption, the style of activity at Sabancaya changed towards a frequent occurrence of explosive eruptions with however low output, which threw ballistic blocks to distances of about from the summit crater and frequently produce Eruption plume; this pattern of activity is referred to as "Vulcanian eruptions" and was accompanied by a decrease of the magma supply. Ash fall from these eruptions induced melting of the glaciers on Ampato volcano, exposing Inca artefacts including the Mummy Juanita. These explosive eruptions became less common over time (from paroxysms every 20–30 minutes to only 5–6 eruptions per day) and the proportional amount of fresh volcanic material increased at first; since 1997 discontinuous eruptions generate steam columns no higher than and ejected material is almost entirely lithic. Satellite imagery has evidenced the occurrence of temperature anomalies on Sabancaya on the scale of , probably owing to fumarolic activity.
In March and April 2013, fumarolic activity and the occurrence of increased after fifteen years of rest, leading to local infrastructure being damaged; an eruption occurred in August 2014 and blue and yellow gases were emitted between 2013 and 2015. This pulse of activity was accompanied by an increased release of , which was being emitted at a rate of in 2014. Ash was emitted by the volcano multiple times through 2014 and 2015, and there has been steady shallow seismic activity since 2013. The remote location of the volcano means that direct impacts on towns is rare, and no human casualties are known.
A further increase of fumarolic activity was observed in 2016, when new fumaroles appeared and sulfur flux increased to sulfur dioxide. Ash eruptions have occurred since 6 November 2016, with an eruption column high five days later. Since then, the volcano has been continuously active with numerous explosions every day, which produce volcanic ash clouds that can rise to elevations of . A persistent gas plume lies above the volcano and repeated emissions of ash have happened, resulting in several alerts for the local population. have been produced in some occasions, without reports of damage. A lava dome began to grow in 2017 within the crater, with unsteady explosive activity and occasional seismic swarms, and was progressively destroyed in 2020. In 2020, a second lava dome formed in November but it was destroyed between December and February of that year. These lava domes were named after numbers in Quechua: Huk for the first and Iskay for the second. The domes Kimsa formed in 2021 and was destroyed in the same year, while Tawa existed during the winter of 2021-2022. In March and May 2023, Pichqa formed and was destroyed during the later course of the year. Ash emissions and seismic activity associated with the eruption begun in 2016 is ongoing .
Several types of seismic activity occur at volcanoes, and examples of the various types have been found at Sabancaya:
Seismic activity during the 2020s, 2010s and 1990s eruption period concentrated not under the volcano, but under Hualca Hualca north and Pampa Sepina northeast of the volcano. A strong earthquake in 1991, which caused a landslide that destroyed the village of Maca, might be linked to Sabancaya.
The presence of an ice cap is an additional source of danger, as its melting during a volcanic eruption could form hazardous lahars, although the small volume of the ice cap limits their damage potential. The Majes River and Rio Sihuasi drainages would be threatened by such mudflows in case of an eruption; the former is the site of the Majes-Siguas irrigation project, the most important in southern Peru. Other dangers from eruptions at Sabancaya are tephra fallout, which can impact the health of people, animals and plants more than away; and lava flows, which however are not much of a threat to humans owing to their slow speed. Aside from the direct threat of eruptions, Sabancaya also contributes to air pollution in the Colca valley, which can damage plants and cause respiratory distress in animals and humans. Ash clouds from Sabancaya frequently impede air travel over the region; the volcano is one of the most frequent causes of volcanic ash-related air traffic advisories in the world. Wind can blow ash back in the air, thus producing ash falls even when the volcano is not erupting.
Together with Ubinas, Coropuna and Misti, Sabancaya is classified by as a "very high risk" volcano; in the case of Sabancaya because of its threat to the Majes-Siguas irrigation project. Scenarios of future eruptions range from vulcanian eruptions over effusive eruptions (no evidence of effusive eruptions during the past few centuries) and vulcanian-subplinian eruptions to the low-probability scenario of . Scenarios of mudflow emission range from mudflows in the valleys draining Ampato and Sabancaya over to flows that extend from the volcano into surrounding towns.
The landscape around Sabancaya, Ampato and Hualca Hualca is largely unvegetated and resembles a desert. The vegetation forms distinct belts at different altitudes and includes bushes, cacti, Festuca and Stipa (ichu) genera, tolar and yareta. Wetlands called developed in river valleys around Sabancaya. The volcano has covered its immediate surroundings with volcanic ash. Animal life includes , cattle and sheep.
The valley is one of the principal tourism destinations of Peru, with about 190,000 visitors per year. It and Sabancaya have been evaluated for their potential as geotourism targets, the UNESCO Colca y Volcanes de Andagua geopark includes Sabancaya. In 1995, the potential of geothermal power generation and volcano tourism at an active volcano was noted. Volcanic activity is visible from the Chivay-Arequipa road at Patapampa, other Scenic viewpoint are at Mucurca northwest and Coporaque northeast of the volcano.
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