Misti | Read 10 Min

Misti
Misti as viewed from Arequipa
Highest point
Elevation	5,822 m (19,101 ft)
Coordinates	16°17′47″S 71°24′38″W / 16.29639°S 71.41056°W / -16.29639; -71.41056
Geography
Misti Location within Peru
Country	Peru
Region	Arequipa

Misti is a volcano in the southern Peruvian Andes, rising above Arequipa, Peru's second-largest city. It has a steep conical profile and two nested summit craters. The inner crater contains an active lava plug or dome, pierced by vents that emit volcanic gases. The summit reaches 5,822 metres (19,101 ft) above sea level, on the rim of the outer crater. Snow covers the summit but does not persist, and there are no glaciers. The upper slopes are largely barren, while lower elevations support scrub and other bushy vegetation.

The volcano grew in four stages. Each stage built the mountain with lava flows and domes, then ended with a summit collapse that formed a bowl-shaped depression. Misti forms a local volcanic group with Chachani to the northwest and Pichu Pichu to the southeast, built on debris from older volcanoes. Over the past 50,000 years, numerous intense explosive eruptions have covered the surrounding terrain with tephra (rocks fragmented by volcanic eruptions). The last two significant eruptions were 2,000 years ago and in 1440–1470 AD; since then, periods of increased gas release have sometimes been mistaken for eruptions.

Misti is considered one of the most dangerous volcanoes in the world, as it lies only 12 kilometres (7.5 mi) from Arequipa. The city's population exceeds one million people and its northeastern suburbs have expanded onto the slopes of the volcano. Narrow valleys on its western and southern flanks pose particular threats, as mudflows and fast-moving flows 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 established a volcano observatory in Arequipa, runs public-awareness campaigns, and has published hazard maps. The Inca viewed the volcano as a threat and during the 1440–1470 eruption offered human sacrifices (capacocha) on Misti and neighbouring mountains to placate the volcano; the mummies on Misti form the largest known Inca human sacrifice.

Name and settlement history

The name "Misti" may derive from either Quechuan or Spanish. It means 'mixed', 'mestizo' or 'white' and may refer to the volcano's snow cover. In Spanish the name is arthrous (written with the definite article el, as el Misti) and some English sources call it "El Misti". Indigenous names include Putina, meaning 'mountain that growls' in the Puquina language, while the Aymara language terms for Misti are Anukara or Anuqara ('dog'). All three names refer to the dog-like appearance of the volcano when viewed from the Andean Plateau, known as the Altiplano. Earlier sources referred to the volcano as Putina; the name "Misti" appears from the 1780s onward. Other names for the volcano are Guagua-Putina, El Volcán ('the volcano'), San Francisco, and Volcán de Arequipa ('Arequipa volcano'). Some Spanish chroniclers have confused it with other volcanoes like Ubinas and Huaynaputina.

Settlement in the region began over 1,500 years ago, most likely during the time period named "Middle Horizon". It is unclear whether the Inca were the first Altiplano civilizations 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 the city of Arequipa is today. The city was founded on 15 August 1540. Misti is the hausberg (lit. 'house mountain') of Arequipa and features on its seal; the residents view themselves as the offspring of the mountain.

Human geography

Misti is often described as Peru's best-known volcano and rises just north of Arequipa, being visible from the Pacific Ocean. Historically the area formed part of the Inca Empire's Condesuyos province; today it lies in the Arequipa Department.

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: North of the volcano are Aguada Blanca and El Frayle, while Hidroeléctrica Charcani I, II, III, IV, V and VI are along the northwestern foot of Misti; their hydroelectric power plants provide electricity to Arequipa.

In 1925, the Italian geographer Gustavo Cumin reported that three small man‑made structures in the crater had been known since 1677, although their origin was unclear. 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 site was chosen for its clear, calm atmosphere and became the highest continuously inhabited location on Earth for a time. 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. A second station ("Mt. Blanc Station") was built after 1888, at the volcano's base; both closed in 1901 when Harvard consolidated operations in Arequipa. Storms have since erased any trace of the summit observatory. Observations of physical phenomena, such as cosmic‑ray measurements, were carried out sporadically on Misti during the 20th century.

Geography and geomorphology

Regional

The volcanoes of Peru are part of the Andean Central Volcanic Zone (CVZ), 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 roughly 1000–1500 km from southern Peru through Bolivia to northern Argentina and Chile. Although volcanoes are numerous in the CVZ, most are poorly studied because the Central Andes are sparsely populated.

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, symmetrical cone with slopes of about 30 degrees. The summit features nested summit craters: the outer crater is 835 to 950 m wide and 120 m deep. There is a gap in the southwestern rim, almost to the bottom of the crater; elsewhere, 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 150 m higher than the southern. The 550 m-wide and 200 m-deep 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. The inner crater contains a 120 m-wide and 15 m-high plug or dome. Its surface is cracked and boulder‑strewn, and it hosts sulfur deposits and active fumaroles. The highest point of the volcano is at 5822 m 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 20 km wide and rises abruptly from the surrounding terrain, towering about 3.5 km above Arequipa. Published estimates of Misti's volume vary widely, from about 40 km³ to 150 km³. The stratovolcano is made up of pyroclastic rocks and stubby lava flows, which form a 2.2 km-thick pile. On the northwestern foot, there is an outcrop of rhyolite named "Hijo de Misti" ('son of Misti'), while an older, eroded stratovolcano ("Misti 1"), lies underneath the Misti cone. Misti is surrounded by a fan of volcanic debris, which covers an area of 200 km² on Misti and extends 25 km from the volcano. On the southern side, the volcano is cut by 20 m to 80 m-deep ravines, while the northern side is flatter. Dune fields and volcanic ash deposits extend for 20 km 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 can undergo sector collapse, when part of the cone fails and forms a debris avalanche. The only obvious trace of such a collapse at Misti is a narrow chute on the northwestern flank that reaches its summit. Debris avalanche deposits lie on the southeastern and southwestern-southern side of Misti, extending 25 km and 12 km from the volcano, respectively. The first is made up of hummock-shaped hills of mixed debris and covers an area of 100 km²; the second forms a flat-topped terrain with an area of about 40 km² on both sides of the Rio Chili.

Rivers and glaciers

The Rio Chili rounds the northern and western sides of Misti, where it has cut the 20 km-long, 150–2600 m-deep and in some places only 30 m 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 (dry valleys) carry water during the wet season in November–December and March–April.

The permanent snowline lies above the summit. During December–August, snow can cover an area of 1–7 km² 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. 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. Ice cover might have been thin, however, and some sources question whether Misti was ever glaciated.

Geology

Regional setting

Off Peru's west coast, the Nazca Plate subducts beneath South America at about 5–6 centimetres per year (2.0–2.4 in/year). The subduction is responsible for the volcanism of the CVZ. As the slab descends, it releases fluids that chemically modify the mantle above it, generating melt. Most Peruvian volcanoes have produced potassium-rich andesitic magmas, derived from the mantle and further modified by fractional crystallization and the absorption of crustal rocks into the magma.

Volcanism in southern Peru dates back to the Jurassic, but the modern volcanic arc system is much younger. The older arcs are 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. The Frontal Arc, which is the youngest, includes Misti and similarly aged volcanoes. The Tacaza Arc is the source of the Huaylillas Formation and the Barroso arc of the Sencca Formation. An older (Cretaceous–Paleogene) volcanic formation is the Toquepala Group. Two distinct episodes of uplift took place 24–13 and 9–4 million years ago, accompanied by the emplacement of large ignimbrites.

Local setting

Misti is part of the Andean Western Cordillera. It is the youngest of a group of three Plio-Pleistocene volcanoes; the others are the dormant Chachani 15 km northwest and extinct Pichu Pichu 20 km southeast. The Yura volcanic group with Cerro Nicholson lies south of Chachani. The Chachani-Misti-Pichu Pichu group lies at the margin of the Altiplano, next to the 600 km² tectonic depression of Arequipa where the city lies. The depression has dimensions of 30 km × 15 km and appears to be formed by fault activity. The terrain under Misti slopes south and this might make the mountain slip southward over time.