Misti

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Template:Short description {{#invoke:other uses|otheruses}} Template:Good article Template:Use dmy dates Template:Use British English Template:Infobox mountain

Misti is a dormant volcano located in the Andes mountains of southern Peru, rising above Peru's second-largest city, Arequipa. It is a conical volcano with two summit craters, one nested within the other. The inner crater contains a lava structure (either a volcanic plug or a lava dome) with active vents that emit volcanic gases. The summit of the volcano lies on the margin of the outer crater at Template:Convert above sea level. Snow covers the summit but does not persist; there are no glaciers. The upper slopes of the volcano are barren, while the lower slopes are covered by bush vegetation.

The volcano developed over four different stages. During each stage, lava flows and lava domes built up a mountain, whose summit then collapsed to form a bowl-shaped depression. The volcano is part of a volcano group with Chachani to the northwest and Pichu Pichu to the southeast, which developed on top of the debris of other volcanoes. Numerous intense explosive eruptions took place during the last 50,000 years and covered the surrounding terrain with tephra (rocks fragmented by volcanic eruptions). The last two significant eruptions were 2,000 years ago and in 1440–1470Template:NbspAD; since then, phases of increased fumarolicTemplate:Efn activity have sometimes been mistaken for eruptions.

Misti is one of the most dangerous volcanoes in the world, as it lies less than Template:Convert from Arequipa. The city's population exceeds oneTemplate:Nbspmillion people and its northeastern suburbs have expanded onto the slopes of the volcano. The narrow valleys on western and southern flanks are particularly threatening, as mudflows and flows consisting of hot volcanic debris could be channelled into the urban area and into important infrastructure, like hydropower plants. Even moderate eruptions can deposit volcanic ash and tephra over most of the city. Until 2005, there was little awareness or monitoring of the volcano. Since then, the Peruvian Geological, Mining and Metallurgical Institute (INGEMMET) has set up a volcano observatory in Arequipa, and run public awareness campaigns on the dangers of renewed eruptions and published a hazard map. The Inca viewed the volcano as a threat and during the 1440–1470 eruption offered human sacrifices (Template:Lang) on the summit of Misti and neighbouring mountains to placate the volcano; the mummies on Misti are the largest Inca human sacrifice known.

Name and settlement history

The name "Misti" originates from either the Quechuan language or Spanish. It means 'mixed', 'mestizo' or 'white' and may refer to the volcano's snow cover. The indigenous names are Template:Lang,Template:SfnTemplate:Sfn which means 'mountain that growls'Template:Sfn in the Puquina language, while the Aymara language terms for Misti are AnukaraTemplate:Sfn or Template:LangTemplate:Sfn ('dog'). All three terms refer to the dog-like appearance of the volcano when viewed from the Andean Plateau, known as the Altiplano.Template:Sfn The volcano was originally known as Putina and only became known as Misti beginning in the 1780s.Template:Sfn Other names for the volcano are Guagua-Putina, El Volcán ('the volcano'), San Francisco and Volcán de Arequipa ('Arequipa volcano').Template:SfnTemplate:Sfn Some Spanish chroniclers have confused it with other volcanoes like Ubinas and Huaynaputina.Template:Sfn

Settlement of the region began more than 1,500 years ago.Template:Efn It is unclear whether the Inca were the first Altiplano political entities to influence the region or whether previous cultures played a role,Template:Sfn but by the arrival of the Spanish, the area was densely populated,Template:Sfn and there were canals, roads and buildings where Arequipa is today.Template:Sfn The city itself was founded on 15 August 1540,Template:Sfn and Misti is featured on its seal.Template:Sfn The volcano is the house mountain of Arequipa,Template:Sfn whose residents view themselves as the offspring of the mountain.Template:Sfn

Human geography

Misti lies north of Arequipa,Template:Sfn the second-largest city in Peru,Template:Sfn and is the best known volcano of Peru.Template:Sfn The Inca empire's Condesuyos province included the volcano;Template:Sfn presently Misti is in the Arequipa Department.Template:Sfn The mountain is visible from the Pacific Ocean.Template:Sfn

The volcano rises about Template:Convert above Arequipa.Template:Sfn Dirt roads heading from Arequipa to Chivay run along the northern/western foot of Misti, and those to Juliaca along the southern/eastern foot.Template:Sfn Inca roads from the Arequipa area passed by the volcano.Template:Sfn There are numerous dams on the Rio Chili, including the Aguada Blanca Dam and reservoir north of the volcano, El Frayle (both north of the volcano)Template:SfnTemplate:Sfn and Hidroeléctrica Charcani I, II, III, IV, V and VITemplate:Sfn along the northwestern foot of Misti;Template:Sfn their hydroelectric power plants provide electricity to Arequipa.Template:Sfn

Italian geographer Template:Interlanguage link in 1925 stated that three small man-made structures in the crater had been known since 1677, but noted that their origin was unknown.Template:Sfn Inca ceremonial platforms on the summit associated with human sacrifices were probably destroyed by human activity around 1900.Template:Sfn

In 1893Template:Efn,Template:Sfn professor Solon Irving Bailey from the Harvard College Observatory installed what was then the world's highest weather station on Misti.Template:SfnTemplate:Sfn The Misti observatory was in its time the highest permanently inhabited location on Earth.Template:Sfn The selection of the volcano was motivated by the clear, calm atmosphere at Misti.Template:Sfn The station was one of several stations built at the time to investigate the atmosphere at such high altitudes;Template:Sfn it was also used for research on the response of the human body to high altitudesTemplate:Sfn and on the solar eclipse of 16 April 1893.Template:Sfn Another weather station, named "Mt. Blanc Station",Template:Sfn was installed at the base of the volcanoTemplate:SfnTemplate:Sfn after 1888.Template:Sfn Both were shut down in 1901 when Harvard College Observatory decided to only maintain a station in Arequipa;Template:SfnTemplate:Sfn storms have since erased any trace of the summit observatory.Template:Sfn Observation of physics phenomena, such as cosmic ray measurements,Template:Sfn were sporadically carried out on Misti during the 20th century.Template:Sfn

Geography and geomorphology

Regional

The volcanoes of Peru are part of the Andean Central Volcanic Zone (CVZ),Template:Sfn one of the four volcanic belts of the Andes; the others are the Northern Volcanic Zone, the Southern Volcanic Zone and the Austral Volcanic Zone.Template:Sfn The CVZ extends for Template:ConvertTemplate:Sfn from southern Peru through Bolivia to northern Argentina and Chile.Template:Sfn Volcanoes are numerous in the CVZ, but most are poorly known due to the low population density of much of the Central Andes.Template:Sfn Several Peruvian volcanoes have been active since the Spanish conquest: the Andagua volcanic field, Huaynaputina, Sabancaya and Ubinas, and possibly Ticsani, Tutupaca and Yucamane.Template:Sfn Other Peruvian volcanoes in the CVZ are Ampato, Casiri, Coropuna, Huambo volcanic field, Purupuruni and Sara Sara;Template:Sfn in total, there are more than 400 volcanoes in Peru but most are eroded to the point of being hard to recognize.Template:Sfn Ubinas is the most active volcano in Peru, having erupted more than 23 times since 1550.Template:Sfn The 1600 eruption of Huaynaputina claimed more than 1,000 casualties; recent eruptions of Sabancaya 1987–1998 and Ubinas 2006–2007 had severe economic and social impacts on the local populations.Template:Sfn

Local

General outline

The volcano is a young, symmetricTemplate:Efn cone with 30° degree steep slopes.Template:Sfn The summit features nested summit craters: The outer crater is Template:ConvertTemplate:SfnTemplate:Sfn wide and Template:Convert deep.Template:Sfn There is a gap in the southwestern rim, almost to the bottom of the crater;Template:Sfn otherwise the inner crater walls are nearly verticalTemplate:Sfn and consist of small sphere-shaped pieces of volcanic debris called lapilli,Template:Sfn lava and volcanic ash.Template:Sfn The western rim of the outer crater is about Template:Convert higher than the southern.Template:Sfn The Template:Convert and Template:Convert inner craterTemplate:Sfn is in the southeastern part of the outer crater.Template:Sfn The inner crater cuts through metre-thick ash, scoriaTemplate:Efn depositsTemplate:Sfn and historical lava domes; it is rimmed by scoria.Template:Sfn In the crater is a Template:Convert and Template:Convert volcanic plugTemplate:EfnTemplate:Sfn or lava domeTemplate:Efn.Template:Sfn It is covered with cracks,Template:Sfn boulders and fumarolic sulfur depositsTemplate:Sfn and features active fumarolesTemplate:Efn.Template:Sfn The highest point of the volcano is at Template:ConvertTemplate:EfnTemplate:Sfn on the northwestern outer crater rim; an iron cross marks the highest point.Template:Sfn Other mountains of the Western Cordillera, including Ubinas and Pichu Pichu, can be seen from the summit.Template:Sfn

A crater-like depression with grey and white rocks
The inner crater of Misti (2005)

The volcano is about Template:Convert wideTemplate:Sfn and rises abruptly from the surrounding terrain.Template:Sfn Estimates of the mountain's volume range from Template:Convert to more likely values of Template:ConvertTemplate:Sfn or Template:Convert.Template:Sfn The stratovolcanoTemplate:Efn is made up of pyroclastic rocks and stubby lava flows, which form a Template:Convert pile.Template:Sfn On the northwestern foot, there is an outcrop of rhyolite named "Hijo de Misti" ("son of Misti"),Template:Sfn while an older, eroded stratovolcano ("Misti 1"), lies underneath the Misti cone.Template:Sfn Misti is surrounded by a fan of volcanic debris,Template:Efn which covers an area of Template:Convert on Misti and extends Template:Convert from the volcano.Template:Sfn On the southern side, the volcano is cut by Template:Convert ravines,Template:Sfn while the northern side is flatter.Template:Sfn Dune fields and volcanic ash deposits extend for Template:Convert northeast of Misti; they are formed by wind-blown ash.Template:SfnTemplate:SfnTemplate:Sfn The terrain between Arequipa and Misti is initially gently sloping, before reaching the steep flanks of the cone.Template:Sfn

Volcanoes often experience the collapse of part of the cone, a so-called sector collapse, which form a landslide ("debris avalanche").Template:Sfn There are no obvious traces of such on Misti,Template:Sfn except on its western footTemplate:Sfn and a narrow chute on the northwestern flank of Misti that reaches its summit.Template:Sfn Two debris avalanche deposits lie on the southeastern and southwestern-southern side of Misti, extending Template:Convert and Template:Convert from the volcano respectively. The first is made up by hummock-shaped hills of mixed debris and covers an area of Template:Convert; the second forms a flat-topped terrain with an area of about Template:Convert on both sides of the Rio Chili.Template:Sfn

Hydrology and glaciology

The Rio ChiliTemplate:Efn rounds the northern and western sides of Misti,Template:Sfn where it has cut the Template:Convert and Template:ConvertTemplate:Sfn Charcani Gorge.Template:Sfn From southeast to southwest the Quebrada Carabaya, Quebrada Honda, Quebrada Grande, Quebrada Agua Salada, Quebrada Huarangual, Quebrada Chilca, Quebrada San Lazaro and Quebrada Pastores drain the mountain. They eventually join to the Rio Chili west and Rio Andamayo south of Misti;Template:Sfn the Andamayo joins the Chili south of Arequipa.Template:Sfn Quebrada San Lazaro and Quebrada Huarangual have formed fan-like deposits of material carried by the streams at the foot of the volcano.Template:SfnTemplate:Sfn The quebradas (dry valleys) carry water during the wet season in November–December and March–April.Template:Sfn

The snowline lies aboveTemplate:Efn the summit.Template:Sfn During December–August,Template:Sfn snow can cover an area of Template:Convert on the upper coneTemplate:Sfn and be mistaken for glaciers,Template:Sfn but does not persist over time.Template:Sfn Unlike neighbouring Chachani, Misti lacks any evidence of glacial or periglacialTemplate:Efn processes, probably due to its inner heat.Template:Sfn Whether there was past glaciation is unclear;Template:SfnTemplate:Sfn a thin ice cover may not have left traces on the volcano.Template:Sfn Traces of glacial erosionTemplate:Sfn like cirques,Template:Sfn evidence of volcanic activity involving magma-water interaction and mudflows imply that Misti was glaciated during the first phase of the last glacial maximum of the Central Andes 43,000 years ago.Template:SfnTemplate:Sfn

Geology

Regional setting

Off the western coast of Peru, the Nazca Plate subducts (descends) under South AmericaTemplate:Sfn at a rate of Template:Convert.Template:Sfn The subduction is responsible for the volcanism of the CVZ,Template:Sfn as the downgoing slab releases fluids that chemically modify the mantle situated above the slab, causing it to produce melts.Template:Sfn Most Peruvian volcanoes have produced potassium-rich andesitic magmas, derived from the mantle and further modified by fractional crystallizationTemplate:Efn and the entry of material from the often thick crust into the magma.Template:Sfn

Volcanic activity in southern Peru goes back to the Jurassic,Template:EfnTemplate:Sfn but the currently recognizable volcanic arcs in Peru are more recent: the Tacaza Arc formed 30–15 million years ago, the Lower Barroso 9–4 million, the Upper Barroso 3–1 million and the Pleistocene-Holocene Frontal Arc during the past one million years. Two distinct episodes of uplift took place 24–13 and 9–4 million years ago, and were accompanied by the emplacement of numerous large ignimbritesTemplate:Efn.Template:Sfn

During the Cretaceous–Paleogene, the Toquepala Group of volcanics was emplaced. The Tacaza Arc is the source of the Huaylillas Formation and the Barroso arc of the Sencca Formation.Template:Sfn The Nazca fracture zone on the Nazca Plate projects under Misti.Template:Sfn

Local setting

A landscape with mountains and a lonely cloud, seen from space
Aerial picture of Ubinas with Misti in the back (2015)

Misti is part of the Andean Western Cordillera.Template:Sfn It is the youngest of a group of three Plio-Pleistocene volcanoes;Template:Sfn the others are the dormant Chachani Template:Convert northwest and extinct Pichu Pichu Template:Convert southeast.Template:Sfn This group lies at the margin of the Altiplano,Template:Sfn next to the Template:ConvertTemplate:Sfn tectonic depression of Arequipa where the city lies.Template:Sfn The depression has dimensions of Template:Convert and appears to be formed by fault activity.Template:Sfn The terrain under Misti slopes south and this might make the mountain slip southward over time.Template:Sfn Another group of volcanoes lies south of Chachani: The Yura volcanic group with Cerro Nicholson.Template:Sfn

A northwest-southeast trending fault system includes the Huanca fault at Chachani and the Chili fault on Misti.Template:Sfn The faults were active during the Holocene, offsetting tephra deposits,Template:Sfn and may have provided a pathway for magma to ascend and form the volcanoes of Arequipa.Template:SfnTemplate:Sfn One of these faults, the Incapuquio fault, produced two earthquakes that coincide with Misti's last eruptions.Template:Sfn Other faults include north- and northeast-trending faults, which are inactive but could have influenced the formation of the Rio Chili canyon.Template:Sfn The crust under the volcano is Template:Convert thick.Template:Sfn

Basement

The basement under Misti is exposed in the Rio Chili gorge. It consists of Proterozoic rocks of the Arequipa Terrane, which are more than a billion years old, Triassic-Jurassic sediments of the Chocolate Formation, Socosani FormationTemplate:SfnTemplate:Sfn and Yura Group, and the Cretaceous–Paleogene La Caldera batholith.Template:Sfn The batholith forms the hills south of Arequipa.Template:Sfn These formations are covered by rhyodacitic ignimbritesTemplate:Sfn known as "sillars".Template:Sfn They are between 13.8 and 2.4 million years old;Template:Sfn the older ignimbrites are part of the Huaylillas Formation and the younger of the Barroso Arc.Template:Sfn Individual ignimbrites are exposed in the Rio Chili gorgeTemplate:Sfn and include the Template:Convert thick Rio Chili ignimbrite from 13.19 ± 0.09 million years ago, the 4.89 ± 0.02 million-year-old La Joya ignimbrite or "sillar", the 1.65 ± 0.04 million-year-old Aeropuerto or Sencca ignimbrite,Template:Sfn and the 1.02 million-year-old Yura Tuff and Capillune Formation.Template:Sfn These ignimbrites were erupted from multiple calderasTemplate:Efn, one of which is now buried under Chachani.Template:SfnTemplate:Sfn The ignimbrites are covered by volcanic sedimentary rocksTemplate:Sfn and debris from the sector collapse of Pichu Pichu.Template:Sfn

Composition

Misti has erupted rocks mainly of andesitic composition, while daciticTemplate:Sfn and rhyolitic compositions are less common.Template:Sfn Rhyolites and dacites are associated with explosive eruptions.Template:Sfn The volcanic rocks are subdivided into several classes: Pyroxene-amphibole andesites, amphibole andesites, amphibole dacites and amphibole rhyolites.Template:Sfn There are reports of trachyandesite erupted during the Holocene eruptions.Template:Sfn Mica has also been reported.Template:Sfn The rocks define a potassium-rich calc-alkaline suiteTemplate:Sfn typical for Peruvian volcanoes.Template:Sfn PhenocrystsTemplate:Efn include amphibole, augite, biotite, enstatite, plagioclase and titanomagnetite.Template:Sfn Magma composition has varied over time and the most recent volcanic stage has produced slightly different magmas, but overall the composition of Misti magmas is highly homogeneous.Template:Sfn The composition of Misti magmas and those of its neighbours Pichu Pichu and Chachani resemble adakite, an unusual kind of volcanic rock formed by the direct melting of a subducting plate.Template:Sfn Some rocks erupted by the volcano show evidence of hydrothermal alteration, colouring them yellow.Template:Sfn

Magma genesis and storage

The formation of the Misti magmas involves the arrival of new magma, assimilation of crustal material and fractional crystallization.Template:Sfn Initially mantle-derived melts pool in a reservoir at the base of the crust, where they assimilate crustal material and undergo fractional crystallization. Afterwards they ascend to a shallower reservoir,Template:Sfn where they interact with Proterozoic gneisses.Template:Sfn Assimilation of basement rocks gave rise to the rhyolitic magmas erupted 34,000–31,000 years ago.Template:Sfn Crystal-poor magma can form in the magma plumbing system through numerous processes and gives rise to the rhyolites and the volcanic plug.Template:Sfn The existence of a third magma storage zone hosting mafic magmas at the base of the crust has been proposed.Template:Sfn

It is not clear whether Misti has a single magma chamber or multiple magma reservoirs at depth, although the rock composition implies that only one large magma system is present.Template:Sfn The reservoir appears to be Template:Convert undergroundTemplate:Sfn and has a volume of several cubic kilometres.Template:Sfn Every few millennia, a secondary rhyolitic reservoir forms at about Template:Convert depth;Template:Sfn it was last reactivated during the eruption 2,000 years ago.Template:Sfn The magma system is periodically recharged, but such an influx of new magma does not trigger eruptions;Template:Sfn instead multiple recharges are necessary to cause activity.Template:SfnTemplate:Sfn Numerous mixing and decompression events can happen to each magma batch before it is erupted,Template:Sfn with mixing particularly important during the last 21,000 years.Template:Sfn A recharge of the magma chamber may have occurred at some point before 2000 AD.Template:Sfn The overall rate of magma supply is Template:Convert, comparable to other stratovolcanoes in volcanic arcs, but with brief surges reaching about Template:ConvertTemplate:Sfn and an increased rate during the last 21,000 years.Template:Sfn

Eruption history

Misti is a young volcano.Template:Sfn It developed in four stages, numbered 1 through 4; a pre-Misti volcano may have formed the southwestern debris avalancheTemplate:Sfn and the older volcanic structures lie mainly in the western sector of Misti.Template:Sfn On average, sub-Plinian eruptions take place every 2,000–4,000 years, while ash fallout occurs every 500–1,500 yearsTemplate:Sfn and large ignimbrite-producing eruptions every 20,000–10,000 years.Template:Sfn Rock formations showing the stratigraphy of Misti are found mainly in the ravines on the southern sideTemplate:Sfn and the Rio Chili gorge;Template:Sfn only a few eruptions have been thoroughly investigated.Template:Sfn Seismic tomography has identified solidified buried magma bodies from the early stages of volcanism.Template:Sfn

Long andesitic lava flows and ignimbrites, which reach a thickness of more than Template:Convert, form the oldest part of the volcano.Template:Sfn They have an age of 833,000 years, but it is not clear if the ignimbrites and lava flows should be considered part of "Misti 1" or of a pre-Misti volcano.Template:Sfn Sometimes, they are considered the first stage of Misti activity, with all the subsequent activity making up the second stage.Template:Sfn After the south-southwestern collapse, the present stratovolcano began to grow 112,000 years ago. During the following 42,000 years lava flows and lava domes built a mountain with an elevation of Template:Convert, in the southern and eastern sectors of present-day Misti.Template:Sfn During the subsequent 20,000 years, repeated collapses of lava domes deposited blocks, fallout deposits and scoria on the southern side of Misti and on Chachani to the northwest.Template:Sfn

Between 50,000 and 40,000 years ago, the summit of Misti collapsed one or more times above Template:Convert elevation,Template:Sfn forming a Template:Convert caldera.Template:Sfn Intense pyroclastic eruptions yielded ignimbrites with volumes of Template:Convert, which cover an area of Template:Convert on the southern side of Misti.Template:Sfn This activity brought "Misti 2" to an end;Template:Sfn subsequently lava domes built "Misti 3" to an elevation of Template:Convert, almost entirely erasing the caldera.Template:Sfn Between 36,000 and 20,000 years ago, collapses of lava domes produced numerous block-and-ash flows of dacitic to andesitic composition, which reach thicknesses of several tens of metres on the southern side of Misti.Template:Sfn The activity between 50,000 and 20,000 years ago has been christened "Cayma stage",Template:Sfn and several eruption deposits from this time have been named:Template:Sfn

Eruptions 43,000 and 14,000 years ago dammed the Rio Socabaya and Rio Chili, forming temporary lakes south and north of the volcano that were later affected by earthquakes.Template:Sfn Between 24,000 and 12,000 years ago, ice fields formed on Chachani and Misti during the last glacial maximum; tephra fell on ice and was reworked by meltwater.Template:Sfn Two eruptions 13,700 and 11,300 years ago produced pyroclastic surges that extended Template:Convert away from the volcano; a Template:Convert wide caldera formed at an elevation of Template:Convert.Template:Sfn

Holocene

More than 10 eruptions took place during the last 11,000 years,Template:Sfn with only brief pauses in activity.Template:Sfn The activity between 21,000 and 2,000 years ago is known as the "Pacheco" stage.Template:Sfn Holocene activity filled the younger caldera with scoria and lava flows, forming the "Misti 4" volcanic structure with the nested summit craters. Tephra forms Template:Convert thick deposits around the volcano, and pyroclastic surges reached distances of many kilometres more than 6,400 and 5,200 years ago.Template:Sfn The 9,000 and 8,500 years old eruptions produced the "Sándwich" deposits.Template:Sfn They extend for more than Template:Convert on the southwestern flank of MistiTemplate:Sfn produced ash fall over the Pacific Ocean and Lake Titicaca.Template:Sfn Radiocarbon dating has identified eruptions 8,140, 6,390, 5,200, 4,750, 3,800 and 2,050 years ago;Template:Sfn the 3,800 eruption deposited fallout on Nevado MismiTemplate:Sfn more than Template:Convert northwest of Misti.Template:Sfn The Global Volcanism Program lists eruptions in 310 BCE ± 100 years, 2230 BCE ± 200 years, 3510 BCE ± 150 years, 4020 BCE ± 200 years, 5390 BCE ± 75 years and 7190 BCE ± 150 years.Template:Sfn

Eruption 2,000 years ago and later activity

The last major explosive eruption took place about 2,000 years ago in one or multiple events.Template:Sfn The date is constrained to 2,060–1,920 years before present; ages of 2,300 BP are probably too old.Template:Sfn It produced about Template:Convert dense rock equivalents of rockTemplate:Sfn and probably lasted a few hours.Template:Sfn The event had a volcanic explosivity index of 4 or 5.Template:Sfn

The eruption was probably triggered when fresh andesitic magma entered a pre-existent rhyolitic body.Template:Sfn Magma rose through the volcano and expelled part of the hydrothermal system,Template:Sfn causing initial phreatic eruptionsTemplate:Efn.Template:Sfn Tephra rained down around the mountain,Template:Sfn with pumice falling Template:Convert from the volcano.Template:Sfn Owing to magma mixing, the pumice deposits have an appearance resembling chocolate and vanilla swirls.Template:Sfn Eventually, the conduit fully cleared and a Template:Convert high eruption column rose above the volcano.Template:Sfn Pyroclastic flowsTemplate:Efn emanated from the column and descended the southern flanks of the volcano, possibly through the gap in the crater rim.Template:Sfn During the course of the eruption, collapses of the crater and conduit walls caused a temporary decline in the intensity of the column.Template:Sfn The eruption column periodically collapsed and reformed, until the eruption ended with phreatomagmaticTemplate:Efn explosions.Template:Sfn

Mudflows descended the mountain,Template:Sfn although their importance relative to the pyroclastic flows is contentious.Template:Sfn The water source for the mudflows is unclear, but the eruption took place during the neoglacial between 2,500 and 1,000 years ago. Thus Misti may have featured a snow or ice cap at the time of the eruption; its melting would have given rise to mudflows.Template:Sfn Rainfall generated further mudflows after the eruption.Template:Sfn The outer summit crater probably formed during this eruption.Template:Sfn Tephra layers in the Sallalli and (in this case with less certainty) Mucurca peat bogs close to Sabancaya,Template:Sfn and (tentatively) in an ice core in the Antarctic Plateau in Antarctica, are attributed to this eruption.Template:Sfn The 2,000 years eruption is the only Plinian eruption during the Holocene at Misti.Template:Sfn

After the eruption 2,000 years ago, activity was limited to small Vulcanian eruptions, mudflows and tephra fallout, including scoria and volcanic ash. Dating has yielded ages of 330, 340, 520, 620, 1035 and 1,300 years before present for several such events.Template:SfnTemplate:Sfn Pyroclastic flows and ash falls were emplaced 1,290 ± 100 and 620 ± 50 years ago.Template:Sfn MudflowsTemplate:Endashnot all associated with eruptionsTemplate:SfnTemplate:SfnTemplate:Endashtook place 1,035 ± 45, 520 ± 25, 340 ± 40 and 330 ± 60 years agoTemplate:Sfn and left Template:Convert thick deposits.Template:Sfn Template:Sfn

Historical activity and seismicity

The last eruption took place in AD 1440–1470Template:EfnTemplate:Sfn and produced about Template:Convert of ash.Template:Sfn It was probably a prolonged eruption that lasted for months or years,Template:Sfn depositing ash in the Peruvian Laguna SalinasTemplate:Sfn and possibly as far as Siple DomeTemplate:Sfn and Law Dome in Antarctica.Template:Sfn It is the oldest eruption of a South American volcano for which historical records exist.Template:Sfn The eruption was severe enough that Mama Ana Huarque Coya,Template:Sfn the wife of the Inca emperor Pachacutec,Template:Efn came to ChiguataTemplate:Sfn to provide assistance.Template:Sfn There is no evidence that a supposed Inca settlement was destroyed by this eruption,Template:Sfn but the local population fled and the Inca had to resettle the area.Template:Sfn Along with other volcanic eruptions around that time and the beginning Spörer solar minimum, the AD 1440–1470 eruption of Misti may have affected global climate conditions.Template:Sfn In 1600, the volcano was covered by ash from Huaynaputina.Template:Sfn

Most sources state that there is no clear evidence of eruptions after the arrival of the Spaniards,Template:SfnTemplate:Sfn while the Global Volcanism Program reports a last eruption in 1985.Template:Sfn Mudflows descended the southern valleys until the 17th century.Template:Sfn The mountain is sometimes reported to be "smoking" at its summit,Template:Sfn including water vapour clouds.Template:Sfn Phreatic eruptions may have taken place in 1577,Template:Sfn 2 May 1677, 9 July 1784, 28 July 1787 and 10 October 1787. Questionable eruptions are recorded in 1542, 1599, 1826, 1830, 1831, 1869, 1870. They probably constitute fumarolic activityTemplate:Sfn and often took place after heavy precipitation; the water would have infiltrated the mountain and evaporated from the volcanic heat.Template:Sfn There is no record of the structure of the summit craters changing in historical records, implying that the craters and volcanic plug were emplaced in prehistoric times.Template:Sfn Comparisons between 1967 photos of the volcanic plug and more recent images show no changes.Template:Sfn

The volcano is seismically active, with long-period earthquakes, tremors, "tornillos"Template:Efn and volcano tectonic earthquakes recorded.Template:Sfn The hypocentres, the actual sites of the earthquakes, are found within the volcanic structure of MistiTemplate:Sfn and cluster on the northwest flank of the volcano. The seismic activity appears to be linked to Misti's hydrothemal system.Template:Sfn Seismic swarms were recorded in August 2012, May 2014 and June 2014.Template:Sfn No deformation of the volcano is evident in satellite images.Template:SfnTemplate:Sfn Clouds rising from the mountain are sometimes mistaken for renewed activity.Template:Sfn

Hazards

A mountain seen from above, next to green parks and cities
This mosaic of two astronaut photographs illustrates the proximity of Arequipa to Misti, just 17 km away (2009)

Misti is Peru's most dangerous volcano and one of the most dangerous in the world,Template:SfnTemplate:Sfn owing to its location just Template:Convert from Arequipa,Template:Sfn a city of over one million residents.Template:Sfn Over time the city has expanded and newTemplate:Sfn and neighbouring towns such as Chiguata get within Template:Convert of Misti.Template:Sfn About 8.6% of Peru's GDP depends on Arequipa and would be impacted by a future eruption of Misti.Template:Sfn The city is constructed on mudflow and pyroclastic flow deposits of the volcanoTemplate:Sfn and all the valleys that drain Misti pass directly or indirectly through Arequipa.Template:Sfn At least 220,000 people south of Misti are threatened by floods, mudflows and pyroclastic flowsTemplate:Sfn channelled through the ravines.Template:Sfn

Individual threats from Misti include:

  • The eruptions 2,000 years ago and 1440–1470 AD eruptions deposited tephra over what today is Arequipa.Template:Sfn Tephra falloutTemplate:Efn can cause health problems, pollute water resources, cause roofs to collapse, bury fields,Template:Sfn and cause road accidents and accidents during cleanup.Template:Sfn Much closer to the volcano, large rocks can fall.Template:Sfn
  • Mudflows are mixtures of rocks and water. They are caused by rainfall or the melting of snow and ice and can happen without volcanic activity.Template:SfnTemplate:Sfn At Misti, they occur on average every century or two.Template:Sfn Small mudflows can reach the cityTemplate:Sfn and bury and destroy everything in their path.Template:Sfn Eruptions of Misti could generate mudflows on Chachani, thus threatening settlements that are on the other side of the Rio Chili.Template:Sfn
  • Pyroclastic flows are hot Template:Convert masses of gas and rocks that can descend the slopes at speeds of Template:Convert; they can flow over topographic obstacles and reach large distances from the volcanic vent.Template:Sfn Pyroclastic flows and surges can extend Template:Convert from the volcano,Template:Sfn although denser flows are likely to stop before reaching the city.Template:Sfn
  • The steep slopes put Misti at risk of sector collapses. Debris avalanches from the collapse of volcanoes can reach large distances, larger than that between Arequipa and Misti.Template:SfnTemplate:Sfn Debris flows, like mudflows, can destroy everything in their path.Template:Sfn Such collapses could also dam the Rio Chili, producing mudflowsTemplate:Sfn and threatening neighbourhoods like Vallecito, Av. La Marina and Club Internacional.Template:Sfn Small landslides on the western side of the volcano could threaten the water supply of Arequipa.Template:Sfn
  • Toxic gases can accumulate in closed spaces to dangerous concentrations, or interact with precipitation to form acid rain. Lava flows are highly destructive, but their slow speed does not constitute a major threat to life.Template:Sfn

Hazards at Misti not related to volcanic activity include flooding during the wet season in Arequipa.Template:Sfn Heavy metals, presumably from Misti and Chachani, have been found in river water.Template:Sfn

Monitoring and hazard management

In 2001, there was neither emergency planning nor land-use planning around Misti;Template:Sfn the 2002–2015 development plan mentioned volcanic hazards but did not envisage specific measures.Template:Sfn The last eruption of Misti had taken place shortly before the foundation of Arequipa, and thusTemplate:Emdashunlike for earthquakesTemplate:Emdashthere is no memory of the hazards of volcanic activity.Template:Sfn Before the eruption of Ubinas in 2006–2007, volcanic hazards drew little attention from the Peruvian state and there was little awareness in Arequipa.Template:Sfn The volcano is frequently considered a protective figure and not as a threat.Template:Sfn A number of people associate volcanoes with lava flows and neglect other volcanic hazards.Template:Sfn

Beginning in 2005, INGEMMET began monitoring volcanoes in Peru;Template:Sfn the first monitoring equipment was at the Charcani V hot spring. Later the monitoring was extended to other hot springs, and the crater fumaroles were surveilled both from Arequipa and from the crater.Template:Sfn Monitoring of seismic activity commenced in 2005.Template:Sfn Beginning in 2008, geodesic measurement stations were installed on the northeastern and southern slopes of the volcano,Template:Sfn and a new monitoring station for the volcano was inaugurated in 2012.Template:Sfn In May 2009 and April 2010, two exercise evacuations of several suburbs of Arequipa were carried out.Template:Sfn The Peruvian Volcano Observatory (OVI) was inaugurated in Arequipa in 2013; it monitors Misti, Ubinas, Ticsani and other Peruvian volcanoes.Template:Sfn Template:As of, the monitoring network on Misti includes seismometers, equipment that measures the composition and temperature of hot springs and fumaroles, and sensors for movements or deformations of the mountain.Template:Sfn These efforts have yielded an increased awareness of the dangers posed by Misti, which is now being increasingly perceived as an active volcano.Template:Sfn Efforts have been made to slow the growth of the northern suburbs of Arequipa, which are closest to Misti.Template:Sfn

A volcano hazard map was developed in 2005 by numerous local and international organizations,Template:Sfn and officially presented in early 2008.Template:Sfn It defines three hazard categories: a red "high risk" zone, an orange "intermediate risk" zone and a yellow "low risk" zone.Template:Sfn These are defined by the risk of debris flows, lava flows, mudflows, pyroclastic flows and tephra fallout.Template:Sfn The "high risk" zone encompasses the entire volcanic cone, its immediate surroundings and the valleys that emanate from it. Parts of Arequipa lie in the "high risk" zone. The "intermediate risk" zone surrounds the "high risk" zone, including the lower slopes of neighbouring mountains and most of the northeastern parts of Arequipa. The "low risk" zone in turn surrounds the "intermediate risk" zone and includes the rest of the city.Template:SfnTemplate:Sfn Additional maps show areas at risk of tephra falloutTemplate:Sfn and of being flooded by mudflows.Template:Sfn The hazard map of Misti is the first hazard map of a Peruvian volcano.Template:Sfn These maps serve to mitigate volcano hazards and to inform local development.Template:Sfn A 3D map was published in 2018.Template:Sfn In 2010, the municipality of Arequipa decreed that the hazard map would have to be considered in future city zoning decisions.Template:Sfn

Scenarios

Three different scenarios of future eruptions have been evaluated.Template:Sfn The first envisages a small eruption, similar to recent activity at Sabancaya,Template:Sfn or the 1440–1470 AD eruption of Misti.Template:Sfn Ash fall would occur around the volcano, reaching Template:Convert in the urban area and shutting down the Arequipa Airport, landslides could damage the dams on the Rio Chili, and mudflows would descend the southern slopes. The second scenario involves an eruption like the eruption 2,000 years ago. Thicker ash falls (exceeding Template:Convert) could cause building collapse and pyroclastic flows down the steep slopes south of Misti, reaching the suburbs of Arequipa and Chiguata.Template:SfnTemplate:Sfn Most risk assessments are based on these two scenarios.Template:Sfn

The third scenario is a Plinian eruption like the "Fibroso" and "Sacaroso" events or the 1600 Huaynaputina eruption;Template:Sfn pyroclastic flows would sweep all the flanks of Misti and past Arequipa, blocking the Rio Chili. Thick ash fall would occur over the entire region,Template:Sfn including over the cities of El Alto, La Joya and agricultural areas.Template:Sfn A Plinian eruption would require the evacuation of Arequipa.Template:Sfn Other hazard scenarios are the emissions of short lava flows, the formation and collapse of lava domes and the collapse of part of the mountain.Template:Sfn

Fumarolic and geothermal system

Fumaroles exist in several places: the volcanic plug; the northern and northeastern walls of the volcano's inner crater; and the volc southeastern flank of the volcano.Template:Sfn They make noises,Template:Sfn produce visible clouds of water vapour and the smell of hydrogen sulfide. The smell reaches the crater rim,Template:Sfn and, at times, the gas becomes so concentrated that it causes irritations to the eyes, nose and throat.Template:Sfn Fumarolic activity has been reported since the 1440–1470 eruption.Template:Sfn In 1948–1949 and 1984–1985, it was intense enough that it could be seen from Arequipa.Template:Sfn The fumarolic activity is visible in satellite images as a temperature anomaly of about Template:Convert.Template:Sfn

Water is the most important component of the fumarole gases, followed by carbon dioxide, sulfur dioxide, hydrogen sulfide and hydrogen.Template:Sfn The hydrogen chloride and hydrogen sulfide content makes them highly acidic.Template:Sfn Fumarole temperatures have varied through the years, generally they are between Template:ConvertTemplate:Sfn with peaks of Template:Convert.Template:Sfn The present-day (21st century) fumarole gases appear to derive directly from magma, with no interaction with a hydrothermal system.Template:Sfn The fumaroles outside of the summit crater are colder, with temperatures of Template:Convert,Template:Sfn and do not smell of sulfur.Template:Sfn

Fumarolic vents are surrounded by concentric deposits of anhydrite close to the vent, gypsum at some distance and sulfur in the colder vents. Other minerals are ammonium sulfate, hematite, ralstonite, soda alum and sodium chloride.Template:Sfn Elemental compositions and isotope ratios indicate that the fumarole deposits are derived from the leaching of volcanic rocks and the water from precipitation.Template:Sfn The chemistry of the deposits changed between 1967 and 2018, with decreasing zinc and increasing lead concentrations, alongside with a warming of the fumarolic systemTemplate:Sfn that may have been due to the arrival of new magma in the volcano during the 20th century.Template:Sfn Sometimes the temperature of the fumaroles is high enough to melt the sulfurTemplate:Sfn and the fumarolic gases can ignite.Template:Sfn

Hot springs occur at the foot of the volcano. To the north is the Humaluso (Umaluso) spring, while to the south and southwest lie Agua Salada, Bedoya (La Bedoya), Calle Cuzco, Charcani V, Chilina Norte, Chilina Sur, Jésus, Ojo de Milagro, Puente de Fierro, Sabandia, Tingo, Yumina, and ZemanatTemplate:SfnTemplate:Sfn south and southwest of Misti.Template:Sfn The hottest of these is the Charcani V springTemplate:Sfn in the Rio Chili gorge;Template:Sfn it is also the closest to the volcano, being only Template:Convert from the crater.Template:Sfn The Jésus and Umaluso springs produce gas bubbles. The springs are fed by a low-temperature geothermal system that mostly produces alkaline waters containing bicarbonate, chloride and sulfate.Template:Sfn Their waters appear to originate through the mixing of freshwater, magmatic water and chloride-rich deep water.Template:Sfn Many of these springs form artificial pools or have water intakes,Template:Sfn and several are monitored by INGEMMET for changes in activity.Template:Sfn

High soil temperatures on the cone,Template:Sfn hot springs and fumaroles indicate that Misti contains a hydrothermal system.Template:Sfn Electric potential measurements indicate that the system appears to be confined between faultsTemplate:Sfn or to the older caldera.Template:Sfn The activity has not been stable over time; after the 2001 southern Peru earthquake, flow at the Charcani V spring and the temperature of the crater emissions increased noticeably.Template:Sfn Water temperatures decreased after the 2007 Peru earthquake.Template:Sfn Over time old fumarolic vents shut down and new vents develop,Template:Sfn but the configuration of the dome vents is stable over time.Template:Sfn The fumarolic activity is correlated to earth tides,Template:Sfn the deformation of the Earth caused by the Moon's and Sun's gravity.Template:Sfn

Climate and vegetation

The region has a semi-arid climate with mild temperatures.Template:Sfn In Arequipa, temperatures are stable throughout the year, with minima of Template:Convert and maxima of Template:Convert.Template:Sfn Temperatures decrease with elevation:Template:Sfn In 1910, monthly mean temperatures at the summit ranged from Template:Convert in January to Template:Convert in May, June and August.Template:Sfn In 1968 temperatures at the summit rose above freezing for a few days per year.Template:Sfn

The summit is often covered in clouds.Template:Sfn For most of the year, dry westerly winds blow over the Western Cordillera; during summer convection over the Amazon forces easterly flow that draws moisture to the Cordillera.Template:Sfn Wind speeds at the summit can reach Template:Convert, with gusts to Template:Convert.Template:Sfn Most precipitation falls during the austral summer (December to March); according to a 1974 publication, it reached Template:ConvertTemplate:Sfn and a 1910 study found most precipitation to be in the form of snow or hail.Template:Sfn During the wet season, rainstorms and flash floods erode the volcanic debris deposits.Template:Sfn The snow cover rapidly melts away during the dry season.Template:Sfn The El Niño–Southern Oscillation and sea surface temperatures in the Atlantic and Pacific Oceans govern annual rainfall.Template:Sfn After a wet and cold start to the Holocene, the climate in the Western Cordillera may have been moist until 5,200–5,000 years ago. A subsequent dry period lasted until the 16th century AD, when the Little Ice Age began.Template:Sfn

The region west of the Andes, including the terrain at the foot of Misti,Template:Sfn is mostly desert with cacti and dwarf shrubs as the principal vegetation forms.Template:Sfn The vegetation belt is known as the "Misti zone". There is an altitudinal gradation: vegetation is dominated by Franseria bushes between Template:ConvertTemplate:Sfn and by the bushTemplate:Sfn Diplostephium tacorense above Template:Convert.Template:Sfn Other bushes occur mainly in creeks and valleys.Template:Sfn At higher elevations, other genera such as Adesmia and Senecio idiopappus become more frequent, and at an elevation of about Template:Convert Lepidophyllum quadrangulare becomes the dominant plant.Template:Sfn Cacti, herbs, yareta cushion plants, ichu (Jarava ichu), as well as pioneer species like lichens and mosses, are important above Template:Convert.Template:SfnTemplate:Sfn Polylepis species form woodlands.Template:Sfn Vegetation cover decreases above Template:Convert elevation.Template:Sfn

Insects are the most important animals in the Peruvian mountains, and include beetles and hymenopterans (ants, bees, sawflies and wasps). Birds include the Andean condor.Template:Sfn 358 plant, 37 mammal and 158 bird species have been recordedTemplate:Efn in the region, including alpacas, guanacos, llamas and vicuñas.Template:Sfn Most of the volcano is within the Salinas y Aguada Blanca National Reserve, which extends northwest of MistiTemplate:Sfn and includes the volcano among its main attractions.Template:Sfn

Religious importance

A conical mountain rises above a brown slope
Misti, as seen from Arequipa (2015)

The mountain was considered the apuTemplate:EfnTemplate:Sfn and "volcano of the city".Template:Sfn It was venerated by the inhabitants of Arequipa, a common practice for inhabitants of the Andes.Template:Sfn The Aymara people viewed it as an abode of deceased souls,Template:Sfn with different regions regarding it as either a friendly or hellish final destination.Template:Sfn According to the late 16th-century chronicler Cristóbal de Albornoz,Template:SfnTemplate:Sfn Misti was one of the important mountains (Template:Lang, a kind of deity or idolTemplate:Sfn) of the Arequipa area of the Inca Empire, along with Ampato, Coropuna, Sara Sara and Solimana.Template:Sfn This tradition probably originated with the previous inhabitants of the area and was taken over by the Inca when they conquered the region.Template:Sfn The Middle HorizonTemplate:Sfn Millo archeological site in the Rio Vitor valley was constructed in a manner that allowed a good view of Misti, which was probably the apu of this place.Template:Sfn Petroglyphs at Toro Muerto may represent astronomical alignments of Misti and Chachani.Template:Sfn

The Inca gave the apus cups of gold and silverTemplate:Sfn and settled people around Misti that would continue the mountain veneration.Template:Sfn People used to alter the shape of the skulls of their infant children so that they resembled the volcano.Template:Sfn Misti was considered to be an aggressive mountain that was always demanding sacrifices,Template:Sfn and the mountain had to be exorcised in colonial times.Template:Sfn After the Spanish conquest, the mountain was consecrated to St. Francis.Template:Sfn According to the Jesuit College of Arequipa, "Indian sorcerers" thought that Huaynaputina volcano had asked Misti for assistance in expelling the Spaniards; Misti however had turned down, saying it was already Christianised, so Huaynaputina had proceeded alone.Template:Sfn During episodes of increased activity, the inhabitants of Arequipa carried out religious ceremonies, including public penance and flagellations, to discourage the volcano.Template:Sfn A group of converts and Franciscans in 1600 climbed on Misti and threw saints' relics and a cross into its crater to discourage the volcano.Template:Sfn Another expedition was launched in 1784, after an earthquake had destroyed Arequipa, and planted a cross on the summit. This cross was replaced twice: first a decade later and then in 1900Template:Sfn as a celebration of the new century.Template:Sfn The cross on the summit of Misti supposedly protects the city.Template:Sfn To this day, religious ceremonies are carried out on the volcano.Template:Sfn Peasants believe that after offering gifts to Misti will bear boys, while the same offers to Chachani will make them bear girls.Template:Sfn Geologists are known to offer objects to the volcano before carrying out investigations.Template:Sfn

Mummies

Eight or nine mummies were found on Misti by the North American anthropologist Johan ReinhardTemplate:SfnTemplate:Sfn and the Arequipan archaeologist José Antonio ChávezTemplate:Sfn in 1998, inside the crater and below the summit.Template:Sfn The mummies were of children, mostly boys around six years oldTemplate:Sfn and some infants, which were sometimes buried one on top of the other.Template:Sfn Unusually, the mummies were buried in shared tombs.Template:Sfn Along with the mummies were figurines, ceramics and other objects;Template:Sfn the high number of figurines found on Misti (47) indicates that the site was important to the Incas.Template:SfnTemplate:Sfn These mummies were Inca human sacrifices, called capacochas,Template:Sfn and the Misti capacocha is the largest known.Template:SfnTemplate:Sfn However, the hostile conditions within the crater had seriously damaged the mummies.Template:Sfn

The sacrifices on Misti, and others on Chachani and Pichu Pichu, were probably motivated by the 1440–1470 eruption of Misti,Template:SfnTemplate:SfnTemplate:Sfn which may explain the unusual location within the crater rather than on a summit.Template:Sfn According to the 16th-century chronicler Martín de Murúa,Template:Sfn the Inca emperor Thupa Yapanki sacrificed llamas to calm a volcano Putina close to Arequipa (probably Misti),Template:Sfn going as closely as possible to the summit.Template:Sfn According to stories, previous ceremonies had failed to calm the volcano and only the emperor's direct intervention quelled its anger.Template:Sfn This description most likely refers to the 1600 eruption of Huaynaputina, rather than of eruptions at Misti.Template:Sfn

Climbing and recreation

Misti was first ascended by pre-Columbian people, who left archaeological evidence around the summit.Template:Sfn The first documented ascent was by Álvaro Meléndez, a priest from Chiguata, on 1 May 1667.Template:Sfn Numerous ascents of the volcano were made already during the 18th and 19th centuries.Template:Sfn On 9 July 1988, U.S. cyclist Terry Powers went to the summit of Misti with a mountain bike from the southern slopes and rode down the northern slopes.Template:SfnTemplate:Sfn The main ascent route according to mountaineer John Biggar is from the Aguada Blanca dam; a permit is needed to cross the dam. There are campsites at around Template:Convert elevation, accessible from the Aguada Blanca dam and the town of Chihuata south of Misti. The ascent to the summit takes about one long day. A less common route starts at Apurimac San Luis on the southern flank, through Tres Cruces and Los Pastores.Template:Sfn Ascent from Chiguata takes a few days.Template:Sfn Climbers report difficulties due to the loose ground, noxious gasesTemplate:Sfn and altitude sickness.Template:Sfn John Biggar cautioned that there is no source of potable water on the mountain.Template:Sfn

The volcano is frequently visited by tourists,Template:Sfn who come for the sight of the landscape surrounding Misti.Template:Sfn Tourist activities at Misti include mountaineering,Template:Sfn trekkingTemplate:Sfn and running down scree slopes.Template:Sfn Ascents take place almost year-round.Template:Sfn Misti and its neighbouring volcanoes have been investigated as potential geosites.Template:Sfn

See also

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Notes

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References

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Sources

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Further reading

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