Nevado Sajama ([neˈβaðo saˈxama]; Aymara: Chak Xaña) is an extinct volcano and the highest peak in Bolivia. The mountain is located in Sajama Province, in Oruro Department. It is situated in Sajama National Park and is a composite volcano consisting of a stratovolcano on top of several lava domes. It is not clear when it erupted last but it may have been during the Pleistocene or Holocene. The mountain is covered by an ice cap, and Polylepis tarapacana trees occur up to 5,000 metres (16,000 ft) elevation.
Toponymy The name Sajama comes from the Aymara words chak-jjaña and means "to the west."
Geography and geomorphology Nevado Sajama is located in the Sajama Province of the Oruro Department in Bolivia, about 18.6 kilometres (11.6 mi) from the border with Chile. Cholcani volcano lies southeast of Sajama, and another neighbouring volcano, Pomerape, resembles Sajama in its appearance. A road runs along the southeastern flank of the volcano, with additional roads completing a circle around Sajama. The village of Sajama lies on its western foot, with the village of Caripe to the northeast of the mountain and Lagunas to the southwest, and there are a number of farms. In Bolivia, the Andes mountain chain splits into two branches separated by a 3,500–4,000 metres (11,500–13,100 ft) high plateau, the Altiplano. Nevado Sajama lies in the Western Andes of Bolivia and in the western side of the Altiplano; more specifically the mountain is located before the Western Cordillera. Nevado Sajama rises about 2.2 kilometres (1.4 mi) from the surrounding terrain to a height of 6,542 metres (21,463 ft) (earlier estimates of its height are 6,572 metres (21,562 ft)), making it the highest mountain of Bolivia. Below 4,200 metres (13,800 ft) the mountain is characterized by parasitic vents and a cover of lava fragments and volcanic ash. Two secondary summits 5,031 metres (16,506 ft) and 5,161 metres (16,932 ft) occur west and east-northeast from Sajama respectively; the former is named Cerro Huisalla and the second is Huayna Potosi. The mountain has a conical shape and is capped by a summit crater that, owing to its ice fill, appears to be linked to the flat summit plateau of Sajama but other records do not indicate the presence of a crater. The Patokho, Huaqui Jihuata and Phajokhoni valleys are located on the eastern flank; at lower elevations the whole volcano features glacially deepened valleys. The terrain is characterized by a continuous ice cover in the central sector of the mountain, exposures of bedrock, deposits and rock glaciers in some sites, alluvial fans and scree in the periphery of Sajama and moraines forming a girdle around the upper sector of Sajama. The ground moraines are the most prominent moraines on Sajama, and have varying colours depending on the source of their component rocks. Vegetation and small lakes occur in their proximity, while other parts are unvegetated. They mostly occur within glacial valleys, but some appear to have formed underneath small plateau ice caps on flatter terrain. At lower elevations the glaciers lead to lava flows and matorral and tolar vegetation, and finally to grassland at lower altitudes. A number of wetlands called bofedales occur on the mountain. Starting in the lake Waña Quta on the northwestern foot of Sajama, the Tomarapi River flows first northeastward, then east, south and southeast around the northern and eastern flanks of the volcano; the Sicuyani River, which originates on Sajama, joins it there. The southern flanks give rise to the Huaythana River, which flows directly south and then makes a sharp turn to the east. The Sajama River originates on the western side of the volcano, flowing due south and increasingly turning southeast before joining the Lauca River. The other rivers draining Sajama and its ice cap also eventually join the Lauca River and end in the Salar de Coipasa.
Geology
Nevado Sajama is part of the Central Volcanic Zone of the Andes, where volcanism is triggered by the subduction of the Nazca Plate beneath the South America Plate. Changes in the subduction regime took place during the Oligocene and directed an increase of volcanic activity in the region. Volcanoes in the region have ages ranging from Pleistocene to Miocene and grew on top of earlier ignimbrites; the whole volcanic activity was controlled by faults. The mountain is a stratovolcano located atop several lava domes. The stratovolcano consists of lava flows and pyroclastic material that radiate away from the centre of the volcano. Some parasitic vents occur southeast of Sajama and have produced lava domes and lava flows. The parasitic vents away from the volcano are older and their location appears to be controlled by radial dikes; the whole complex is a compound volcano. Two later volcanic units are known as the Colquen Wilqui lavas and the Jacha Khala tuff. The Sajama volcano rises within a caldera that has been buried by later volcanic activity so that it is only recognizable on its eastern-northeastern side. A circular structure around Sajama may be the origin of the 2.7 million years old Lauca-Perez Ignimbrite. Argon-argon dating has yielded ages of 679,000 years ago from Sajama and of 80,900 to 25,000 years ago for the Kkota Kkotani lavas, which are unrelated to the main Sajama volcano. The date of the last eruption is not known, it may have occurred in the Pleistocene or Holocene. Hot springs occur on the Junthuma River and reflect the presence of geothermal heat with temperatures of about 250–230 °C (482–446 °F) on the western foot of Sajama, and volcanic rocks of Sajama bear traces of fumarolic activity. Three major geologic lineaments occur in the region, the north-northwesterly trending Sajama lineament, a west-southwesterly one aligned with high topographical features and a west-northwesterly one. The west-southwesterly one played an important role in the development of Sajama volcano.
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