Altiplano-Puna Volcanic Complex

The Altiplano-Puna volcanic complex (APVC) is a major caldera and silicic ignimbrite volcanic field located in the southern portion of the Altiplano-Puna plateau, an elevated dry region in the central Andes that includes parts of Argentina, Bolivia and Chile. This high plateau region features vast plains punctuated by spectacular volcanoes.

The APVC covers an area of approximately 50,000 sq km (19,300 sq mi) between the Atacama basin and the Altiplano. It is bounded by the Bolivian Cordillera Real in the east and by the main chain of the Andes, the Cordillera Occidental, in the west.

In addition to numerous minor warm springs within the area of the APVC, there are two major active geothermal fields: El Tatio in Chile and Sol de Manana in Bolivia.

The APVC, like the Andes system in general, is generated by the subduction of the Nazca Plate beneath the South American Plate at an angle of nearly 30°.

Delamination of the crust has occurred beneath the northern Puna and the southern Altiplano. At approximately 10 - 20 km (6 - 12 mi) depth, seismic data indicate the presence of melts in a layer called the Altiplano-Puna magma body (or Altiplano-Puna low-velocity zone). It is the largest known active magma body on Earth.

Regional activity variations have been attributed to the southwards moving subduction of the Juan Fernández Ridge. This southward migration results in a steepening of the subducting plate behind the ridge, causing decompression melting. Approximately 25 - 33% of the generated melts erupt to the surface as ignimbrites.

The dry climate and high altitude of the Atacama Desert have protected the deposits of APVC volcanism from erosion. Still, limited erosion also reduces the exposure of buried layers and structures.

_{Map showing the location (in red) of the Altiplano-Puna plateau in South America}

El Tatio

El Tatio is a geothermal field located in the Andes Mountains of northern Chile at 4,320 m (14,170 ft) above sea level. It is the third-largest geyser field in the world and the largest in the Southern Hemisphere. The area is a major tourist attraction in northern Chile.

The geothermal field has many geysers, hot springs and associated sinter deposits. These hot springs eventually form the Rio Salado, a major tributary of the Rio Loa, and are a significant source of arsenic pollution in the river. In addition, the vents are sites of populations of extremophile microorganisms such as hyperthermophiles.

El Tatio lies at the western foot of a series of stratovolcanoes, which runs along the border between Chile and Bolivia. This series of volcanoes are part of the Central Volcanic Zone, one of several volcanic belts in the Andes, and the Altiplano-Puna volcanic complex (APVC). This system of large calderas may be the source of heat for the El Tatio geothermal system.

Sol de Mañana

Sol de Mañana is a geothermal field in the Potosi Department of southwestern Bolivia. It extends over 10 sq km (3.8 sq mi), 4,800 - 5,000 m (15,750 - 16,400 ft) in altitude. Together with El Tatio, it is among the geothermal fields located at high altitudes associated with the Altiplano-Puna volcanic complex's volcanic system and a fault system that connects the two.

This area is characterized by intense volcanic activity, and the sulfur springs field is full of mud lakes and steam pools with boiling mud. Moraines also occur in the area.

Sol de Mañana is part of the geothermal system of the Laguna Colorada caldera. Cerro Guacha and Pastos Grandes have also been proposed as heat sources.

Cerro Guacha

Cerro Guacha is a caldera in southwestern Bolivia. Part of the volcanic system of the Andes, it is considered part of the Central Volcanic Zone and is associated with the Altiplano-Puna volcanic complex (APVC).

Cerro Guacha and the other volcanoes of the region are formed from the subduction of the Nazca Plate beneath the South American Plate. Above the subduction zone, the crust is chemically modified and generates large volumes of melts that form the local caldera systems of the APVC. Cerro Guacha is constructed over a basement of sediments.

Two major ignimbrites, the Guacha ignimbrite and the Tara ignimbrite erupted from Cerro Guacha. More recent activity formed a third, smaller ignimbrite.

The larger caldera has dimensions of 60 by 40 km (37 by 25 mi) with a rim altitude of 5,250 m (17,220 ft). Extended volcanic activity has generated two nested calderas, several lava domes and flows, and a resurgent central dome.

Pastos Grandes

Pastos Grandes is a caldera and crater lake in the Sud Lipez region of Bolivia, geographically a part of the Altiplano. The caldera is part of the Altiplano-Puna volcanic complex within the Central Volcanic Zone of the Andes.

The area of Pastos Grandes is remote and poorly accessible. The existence of the caldera was first established by satellite imagery.

Pastos Grandes has erupted a number of ignimbrites throughout its history. After the ignimbrite phase, the lava domes of the Cerro Chascon-Runtu Jarita complex erupted close to the caldera and along faults.

The caldera is the site of a few lakes, some of which are fed by hot springs. Some minerals, including lithium, are dissolved in the lakes.

Cerro Chao

Cerro Chao is a lava flow complex associated with the Cerro del León volcano in the Andes. It is the largest known Quaternary silicic volcano body and part of the most recent phase of activity in the Altiplano-Puna volcanic complex.

Cerro Chao formed throughout three eruptions preceded by a pyroclastic stage. First, three large lobate lava flows erupted in the col between two volcanoes and advanced a length of 14 km (8.7 mi). The eruption that originated the lava flows probably lasted more than 100 years and occurred before the Holocene.

La Pacana

La Pacana is a Miocene-age caldera in northern Chile's Antofagasta Region. It is also part of the Altiplano-Puna volcanic complex in the Central Volcanic Zone of the Andes.

Along with other regional volcanoes, it was formed by the subduction of the Nazca Plate beneath the South American Plate in the Peru-Chile Trench. The caldera is situated in a basement formed by various Paleozoic formations, Tertiary ignimbrites, and volcanoes. Several major faults cross the region and have influenced its volcanic activity.

La Pacana is a supervolcano and is responsible for the eruption of the giant Atana ignimbrite approximately 3 - 4 million years ago, which constitutes the fifth-largest explosive eruption known.

Cerro Chascon-Runtu Jarita

Cerro Chascon-Runtu Jarita is a complex of lava domes located inside, but probably unrelated to, the Pastos Grandes caldera. It is part of the more recent phase of activity of the Altiplano-Puna volcanic complex.

Accompanied by little explosive activity on the main dome Cerro Chascon, the complex contains ten lava domes arranged in a chain. Located on the Pastos Grandes caldera floor, these domes erupted after the injection of mafic magmas less than 100,000 years ago.