Misti
Misti is a 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 with active vents that emit volcanic gases. The summit of the volcano lies on the margin of the outer crater at above sea level. Snow covers the summit but does not persist; there are no glaciers. The upper reaches of the slopes are barren but the lower slopes are covered with bush vegetation.
The volcano developed in four 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. The last two significant eruptions were 2,000 years ago and in 1440–1470AD; since then, phases of increased fumarolic activity have sometimes been mistaken for eruptions.
Misti is one of the most dangerous volcanoes in the world, as it lies less than from Arequipa. The city's population exceeds onemillion 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 has set up a volcano observatory in Arequipa, and runs 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 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 Putina, which means 'mountain that growls' in the Puquina language, while the Aymara language terms for Misti are Anukara or Anuqara. All three terms refer to the dog-like appearance of the volcano when viewed from the Andean Plateau, known as the Altiplano. The volcano was originally known as Putina and only became known as Misti beginning in the 1780s. Other names for the volcano are Guagua-Putina, El Volcán, San Francisco and Volcán de Arequipa. Some Spanish chroniclers have confused it with other volcanoes like Ubinas and Huaynaputina.Settlement of the region began more than 1,500 years ago. It is unclear whether the Inca were the first Altiplano political entities to influence the region or whether previous cultures played a role. By the arrival of the Spanish, the area was densely populated, and there were canals, roads and buildings where Arequipa is today. The city was founded on 15 August 1540, and Misti is featured on its seal. The volcano is the hausberg of Arequipa, whose residents view themselves as the offspring of the mountain.
Human geography
Misti lies north of Arequipa, the second-largest city in Peru, and is the best-known volcano of the country. The Inca Empire's Condesuyos province included the volcano; presently Misti is in the Arequipa Department. The mountain is visible from the Pacific Ocean.The volcano rises about above Arequipa. Dirt roads heading from Arequipa to Chivay run along the northern and western foot of Misti, and those to Juliaca along the southern and eastern foot. Inca roads from the Arequipa area passed by the volcano. There are numerous dams on the Rio Chili, including the Aguada Blanca Dam and reservoir north of the volcano, El Frayle and Hidroeléctrica Charcani I, II, III, IV, V and VI along the northwestern foot of Misti; their hydroelectric power plants provide electricity to Arequipa.
Italian geographer in 1925 stated that three small man-made structures in the crater had been known since 1677, but noted that their origin was unknown. Inca ceremonial platforms on the summit associated with human sacrifices were probably destroyed by human activity around 1900.
In 1893, professor Solon Irving Bailey from the Harvard College Observatory installed what was then the world's highest weather station on Misti. The Misti site was, in its time, the highest continuously inhabited location on Earth. The selection of the volcano was motivated by the clear, calm atmosphere at Misti. The station was one of several stations built at the time to investigate the atmosphere at such high altitudes; it was also used for research on the response of the human body to high altitudes. Another weather station, named "Mt. Blanc Station", was installed at the base of the volcano after 1888. Both were shut down in 1901 when Harvard College Observatory decided to only maintain a station in Arequipa; storms have since erased any trace of the summit observatory. Observation of physics phenomena, such as cosmic ray measurements, were sporadically carried out on Misti during the 20th century.
Geography and geomorphology
Regional
The volcanoes of Peru are part of the Andean Central Volcanic Zone, 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. The CVZ extends for - from southern Peru through Bolivia to northern Argentina and Chile. Volcanoes are numerous in the CVZ, but most are poorly known due to the low population density of much of the Central Andes.Several Peruvian volcanoes have been active since the Spanish conquest: the Andagua volcanic field, Huaynaputina, Sabancaya and Ubinas, and possibly Ticsani, Tutupaca and Yucamane. Other Peruvian volcanoes in the CVZ are Ampato, Casiri, Chachani, Coropuna, Hualca Hualca, Huambo volcanic field, Purupuruni and Sara Sara; in total, there are more than 400 volcanoes in Peru, but most are eroded to the point of being hard to recognise. Ubinas is the most active volcano in Peru, having erupted more than 23 times since 1550. 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.
Local
General outline
The volcano is a young, symmetric cone with 30-degree steep slopes. The summit features nested summit craters: the outer crater is wide and deep. There is a gap in the southwestern rim, almost to the bottom of the crater; otherwise the inner crater walls are nearly vertical and consist of small sphere-shaped pieces of volcanic debris called lapilli, lava and volcanic ash. The western rim of the outer crater is about higher than the southern. The and inner crater is in the southeastern part of the outer crater. The inner crater cuts through metre-thick ash, scoria deposits and historical lava domes; it is rimmed by scoria. In the crater is a and volcanic plug or lava dome. It is covered with cracks, boulders and fumarolic sulfur deposits and features active fumaroles. The highest point of the volcano is at on the northwestern outer crater rim; an iron cross marks the highest point. Other mountains of the Western Cordillera, including Ubinas and Pichu Pichu, can be seen from the summit.The volcano is about wide and rises abruptly from the surrounding terrain. Estimates of the mountain's volume range from to more likely values of or. The stratovolcano is made up of pyroclastic rocks and stubby lava flows, which form a pile. On the northwestern foot, there is an outcrop of rhyolite named "Hijo de Misti", while an older, eroded stratovolcano, lies underneath the Misti cone. Misti is surrounded by a fan of volcanic debris, which covers an area of on Misti and extends from the volcano. On the southern side, the volcano is cut by ravines, while the northern side is flatter. Dune fields and volcanic ash deposits extend for northeast of Misti; they are formed by wind-blown ash. The terrain between Arequipa and Misti is initially gently sloping, before reaching the steep flanks of the cone.
Volcanoes often experience the collapse of part of the cone, a so-called sector collapse, which form a landslide. The only obvious trace of collapse is a narrow chute on the northwestern flank of Misti that reaches its summit. Debris avalanche deposits lie on the southeastern and southwestern-southern side of Misti, extending and from the volcano, respectively. The first is made up of hummock-shaped hills of mixed debris and covers an area of ; the second forms a flat-topped terrain with an area of about on both sides of the Rio Chili.
Hydrology and glaciology
The Rio Chili rounds the northern and western sides of Misti, where it has cut the, and in some places only wide Charcani Gorge. 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 join the Rio Chili to the west of Misti and Rio Andamayo to the volcano's south, the latter forming the Rio Tingo Grande which joins the Chili south of Arequipa. Quebrada San Lazaro and Quebrada Huarangual have formed fan-like deposits of material carried by the streams at the foot of the volcano. The quebradas carry water during the wet season in November–December and March–April.The snowline lies above the summit. During December–August, snow can cover an area of on the upper cone and be mistaken for glaciers, but does not persist over time. Unlike neighbouring Chachani, Misti lacks any evidence of glacial or periglacial processes, probably due to its inner heat. Whether there was past glaciation is unclear; a thin ice cover may not have left traces on the volcano. Traces of glacial erosion like cirques, 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.