Licancabur

Licancabur is a stratovolcano on the border between Bolivia and Chile, south of the Sairecabur volcano and west of Juriques. Part of the Andean Central Volcanic Zone, it has a prominent, 5916 m-high cone. A 400 - 500 m summit crater containing Licancabur Lake, a crater lake which is among the highest lakes in the world, caps the volcano. There are no glaciers owing to the arid climate. Numerous animal species and plants live on the mountain.

Licancabur formed atop of Pleistocene ignimbrites and has been active during the Holocene, after the ice ages. Three stages of lava flows emanate from the edifice and have a young appearance. Although no historic eruptions of the volcano are known, lava flows extending into Laguna Verde have been dated to 13,240 ± 100 BP and there may be residual heat in the mountain. The volcano has primarily erupted andesite, with small amounts of dacite and basaltic andesite.

Several archaeological sites occur on the mountain, both on its summit and at its northeastern foot. They were built presumably by the Inca or Atacama people for religious and cultural ceremonies, and are among the most important in the region. The mountain is the subject of a number of myths, which view it as the husband of another mountain, the hiding place of Inca or the burial of an Inca king.

Name and importance
The name Licancabur comes from the Kunza language, where lican means "people" or "town" and cábur/ caur, caure or cauri "mountain"; it may refer to the archaeological sites at the mountain. The name of the volcano has also been translated as "upper village". Other names are Licancáguar, Licancaur (which is another orthography), Tata Likanku and Volcán de Atacama.

It is one of the best known volcanoes of Bolivia and Chile and can be seen from San Pedro de Atacama. The Inca conquered the region in the 14th century, with the Spaniards following in the 16th; today mountaineering and tourism are increasingly important. Research on animal health, remote sensing, telecommunication and Mars-like environments has been conducted at Licancabur.

Geography and geomorphology
The volcano is in the Puna de Atacama/Cordillera Occidental of the Andes. Politically, it is located in the Antofagasta Region of Chile and the Potosí Department of Bolivia; the border goes over Licancabur. Less than 20 km south is the Llano del Chajnantor Observatory. San Pedro de Atacama is 20 mi west of Licancabur while the adjacent region in Bolivia is largely uninhabited. The border crossing Paso de Jama and the Chile Route 27 between Argentina and Chile pass along the southern foot of Licancabur. In 1953, a road led to 14000 ft elevation.

Licancabur is a 1.5 km high and 9 km wide uneroded symmetrical cone with steep slopes. The mountain dominates its surroundings. The summit at 5916 m elevation is capped by a 500 m-400 m wide summit crater. The 70 x freshwater Licancabur Lake in the crater is one of the highest lakes in the world. The western slopes are better developed than the eastern. The total volume of the volcano is about 35 km3 or 44 km3, formed by layers of lava and pyroclastics. There are traces of lahars.

Young-looking black-grey lava flows emanate from the summit crater and surround the cone, reaching distances of 15 km from the summit west of Licancabur. The flows are 10 - 50 m thick block lavas, and feature structures like ridges, levees and blocks several metres thick. A debris avalanche deposit is found on the western side of Licancabur. The slopes of the mountain are notably unstable. The landscape around the volcano consists of basins separated by mountain chains. At the northeastern foot of Licancabur is Laguna Verde. The mountain is part of the drainage divide between the Altiplano and the Salar de Atacama. Southwest of Licancabur are the Vilama and San Pedro rivers, which flow to San Pedro de Atacama.

Geology
Starting in the Jurassic, the Farallon Plate and later the Nazca Plate have been subducting under the South American Plate in the Peru-Chile Trench. The subduction is still ongoing at a rate of 6.6 cm/year and is responsible for the volcanism in the Andes, as fluids emanating from the downgoing plate trigger melting within the overlying asthenosphere. The Andean Central Volcanic Zone (CVZ) extends from southern Peru over Bolivia to Chile and Argentina, it features the highest volcanoes in the world (Ojos del Salado) and the Altiplano-Puna volcanic complex, one of the largest ignimbrite provinces on Earth. Licancabur is part of the southern CVZ, where there are over a thousand volcanoes. Older (Miocene) volcanoes are widespread, while Pleistocene-Holocene systems are concentrated in the main volcanic chain. Lascar erupts every few years.

The volcanic chain continues north across Portezuelo Chaxas mountain pass, beginning with Sairecabur. To the southeast is 5704 m high Juriques, which formed during the Pleistocene and has a 1.5 km wide summit crater; the two volcanoes form an offset in the volcanic chain. Farther south next to Portezuelo del Cajon is Cerro Toco of the Purico complex. The Chaxas lava dome was active during the Pliocene, forming ignimbrites that are now buried under Licancabur.

The volcano is on the edge between the Altiplano and the Salar de Atacama basin. The basement contains intrusions of Paleozoic and sedimentary rocks of Mesozoic age, forming the "Antofalla domain" of the Arequipa-Antofalla tectonic block that originated separately from South America. Between 4 km and 30 km depth is the Altiplano-Puna Magma Body, a giant magma chamber that extends under the southern Altiplano and to Licancabur. At the volcano, the basement is covered by ignimbrites from the Chaxas, La Pacana and Purico volcanoes, and lava domes of dacitic-rhyodacitic composition. Ignimbrites crop out in gorges south of Licancabur. Faults associated with the Calama-Olacapato-El Toro lineament cut through the basement in southeast direction and probably influenced the growth of Licancabur and Juriques. Some faults were active during the Holocene.

Composition
Andesites are the main rocks at Licancabur, with some basaltic andesite and dacite. They define an adakite-like suite, and are less crystalline than rocks of other CVZ volcanoes. The lavas were highly viscous, explaining why the Licancabur cone is so steep. The main phenocryst phase is plagioclase, while amphibole, clinopyroxene, iron-titanium oxides, olivine and orthopyroxene are subordinate. Crystals often form aggregates. Xenoliths of gabbro are found within the rocks. Unlike many neighbouring volcanoes, Licancabur lacks sulfur deposits.

The magmas that built Licancabur formed through melting of altered oceanic crust in the slab at 50 - 100 km depth, which in turn leads to melting in the mantle wedge that gives rise to the Licancabur magmas. Assimilation of continental crustal rocks and fractional crystallization of amphibole and garnet would explain trace element patterns. The magmas were stored in a magma chamber, where crystals formed.

Climate and vegetation
The climate is cold, dry, windy with low atmospheric pressure and large day-night temperature differences. On the summit, daytime temperatures range between 5 - -25 C and nighttime temperatures between -25 - -40 C. Annual mean precipitation at Licancabur is estimated to reach 360 mm, decreasing to 200 m at its base, but is highly variable in space and time. The Atacama Desert is one of the driest on Earth. The arid climate is due to subsidence of air within the South Pacific Anticyclone, which extends to the Andes. Owing to the dry climate, snow cover on Licancabur is ephemeral and there are no glaciers. During the local Last Glacial Maximum the snowline may have decreased to 4000 - 4800 m elevation but there is no evidence of glacial activity on Licancabur. Periglacial phenomena occur on Licancabur. The region likely has Earth's highest insolation rate.

Plants growing on Licancabur include grasses, tola and yareta at high and cacti at low elevations. There is a vertical structure, with cushion plants and tussocks dominating between 3850 - 4200 m elevation, widely spaced shrubs between 2700 - 3100 m, and the highest plant density found between these belts. Some areas are used as pastures. Isolated wetlands occur at the foot of the volcano.

The fauna includes birds (black-hooded sierra finch, black-winged ground dove and Puna tinamou), frogs (Rhinella spinulosa), insects (butterflies, cuckoo bees and flies), lizards (Liolaemus audituvelatus, Liolaemus barbarae, Liolaemus constanzae, Liolaemus fabiani and Liolaemus puritamensis), mammals (Andean hairy armadillo, chinchilla, culpeo, guanaco, southern vizcacha and vicuña) and toads (Telmatobius vilamensis). The Bolivian sector is part of the Eduardo Avaroa Andean Fauna National Reserve. In Chile, there were plans to create a protected area including Licancabur and El Tatio, but no progress had been made.

Eruption history
The volcano formed mostly during the Late Pleistocene-Holocene, and bears no traces of glacial erosion. There are three generations of lava flows distinguishable through their appearance and chemistry: The basal unit, which crops out at the western and northeastern foot of the volcano and are the most primitive magmas; the intermediate unit, which forms most of its western and southern sectors; and the upper unit, which forms the central cone and represents the most differentiated magmas. The older flows are found north and west of Licancabur, overlap with flows from Sairecabur and are partly buried by debris avalanche deposits and moraines. Activity at Licancabur impacted the environment at Laguna Verde, causing changes in water chemistry.

An explosive eruption took place at some point, producing pyroclastic flows. The flank lava flows are the most recent activity. There are no known historical or Holocene eruptions, and the preservation of Inca ruins in the summit crater implies that it has been inactive for 600–1000 years. However, the elevated temperatures of the summit crater lake imply there is still heat in the volcano, and lava flows overran 13,240 ± 100 years old shorelines at Laguna Verde.

Licancabur is considered to be potentially active owing to its good preservation. SERNAGEOMIN deems it a low-hazard volcano, Chile's 68th most dangerous volcano out of 87. Future eruptive processes will probably involve the emission of lava or pyroclastic flows from the summit and the flanks of Licancabur, especially the western one. The volcano is remote from inhabited areas and pyroclastic fallout would be of limited extent. Impacts may extend to Argentina.

Archaeology and religious importance
Prehistoric manmade constructions are widespread on the mountains of the region, including Licancabur and Juriques. The complex on Licancabur includes multiple structures with mostly semicircular or rectangular shapes and a ceremonial platform, all in the eastern part of the crater. The structures may have had had roofs and are built like pircas (no mortar). Reports in 1887 and 1955 mention piles of wood. A semicircle of stones surrounding an upright stone has been compared to an altar, ushnu. The summit sites were presumably used for equinox and solstice feasts. Notably, no human sacrifices (capacocha) are associated with Licancabur.

Another site, Tambo de Licancabur or Tambo Licancabur, lies at 4600 m elevation on the northeastern foot of Licancabur. It consists of over a hundred man-made structures and a 70 m long public square. More than a hundred people could stay at Tambo de Licancabur, which was not permanently inhabited. Both Inca and local pottery styles have been found there. From Tambo de Licancabur, a zig-zag path led up to the mountain, along which there are further Inca structures from which Tambo de Licancabur was visible; today the path is largely destroyed or blocked by landslides. Tambo de Licancabur has been interpreted either as a site where, during festivities, people who could not ascent the mountain congregated – a base camp, corpahuasi – or as a tambo, an Inca waystation, on the road between San Pedro de Atacama and Inca territories in present-day Bolivia. This interpretation is not mutually exclusive with the former. The whole Licancabur complex was one of the most important in the region, and may have been part of a wider regional religious centre. The archaeological sites on Licancabur are sometimes interpreted to be part of a lookout system for the region, or as a symbol of Inca dominance in the San Pedro de Atacama area. The Inca road passed at the foot of the volcano, making the site easily accessible.

The mountain was worshipped by the Atacameno and Inca until the 20th century. Licancabur was important in local cultural rituals, and is to this day used in culturally important events. At least one burial in a local cemetery was oriented to Licancabur.

There are several legends tied to the mountain: The male Licancabur was married to female Quimal in the Cordillera Domeyko, and the two are considered paramount mountains which protect the local communities and fertilize the ground during their copulation. In the local Atacameno mythology the mountain controls fire (and San Pedro water), while in Socaire's mythology it is a source of water. In another myth Licancabur is the tomb of a legless Inca king that was carried around the region in a litter. A final tale says that once, the crater lake had fresh water. When Inca fled from white people to Licancabur, they hid their treasures. The waters of the lake turned bitter and its colour green. Ascending the mountain was considered taboo, and the mountain vigorously defends against violations of its summit; allegedly the 1953 Calama earthquake was in retaliation for the ascent of the mountain in that year. Whether there are legends of Inca treasury associated with Licancabur is unclear.

Ascent
The mountain was first ascended by the Inca or the Atacameno people. The first documented ascent was by Severo Titichoca in November 1884, and the first by Westerners in 22 November 1953 by a group of engineers in Chuquicamata, which reached the summit from the northwest.

Licancabur is frequently climbed from the Bolivian side. It can be ascended year round, although more caution is needed during winter. Ascents take six hours, descents about half that. There is a wide panorama from the summit. Bad weather can develop quickly, and ascending Licancabur is difficult owing to the unstable slopes of the upper cone.