Ojos del Salado

The name "Ojos del Salado" refers to a river that the 1937 Polish expedition used to reach the mountain,[2] although the river Salado does not originate on Ojos del Salado[3][lower-alpha 1] and the name was already known before.[2] Another theory posits that the volcano was named after mineral deposits on its flanks.[5] There are two summits, known as the eastern or Argentine and western or Chilean summit; both lie along the international boundary and get their names after the country from which they can be more easily reached.[6]

Ojos del Salado is part of the High Andes[7] and rises from the southern end of the Puna de Atacama,[8] a high plateau next to the Atacama Desert with an average elevation of 4,000 metres (13,000 ft) metres.[9] The border between Argentina and Chile runs across the summit of the mountain in east-west direction.[7] The Argentine part is within Catamarca Province[10] and the Chilean in Copiapo Province[11] of the Atacama Region.[12] The highway Chile Route 31 runs between the city of Copiapo west of the volcano and the Paso San Francisco[lower-alpha 2] to Argentina,[7] lying about 20 kilometres (12 mi) north of the volcano, making it more accessible than many other volcanoes there.[15] The region is uninhabited and lacks water resources; many parts are only accessible through dirt roads.[16]

Ojos del Salado is a dormant volcano that rises to 6,893 metres (22,615 ft),[17][8][9] 6,879 metres (22,569 ft)[1] or 6,887 metres (22,595 ft) elevation.[15] It is the world's highest volcano[lower-alpha 3] and the second-highest summit of the Andes,[19] and the highest summit in Chile.[20] Ojos del Salado is not a single conical summit but a massif/complex volcano[15][21] formed by overlapping smaller volcanoes,[22] with over 20 craters.[23] Two edifices, less than 2.5 kilometres (1.6 mi) wide, flank the 1.3 by 0.5 kilometres (0.81 mi × 0.31 mi) wide summit crater on its eastern and western side.[24] Basalt, gravel, pumice and scoria crop out in its rim, which is lower on the northern side.[25] A second 300–400 metres (980–1,310 ft) wide crater lies just west of the summit crater.[23] Reportedly, the summit is separated by a deep gap into two separate peaks.[26] Thick short dacitic lava flows make up the core 13 by 12 kilometres (8.1 mi × 7.5 mi) area of the volcano but pyroclastic fall material covers much of the summit area.[27]

The massif rises about 2 kilometres (1.2 mi) above the surrounding terrain and covers an oval area of about 70 square kilometres (27 sq mi)[15]-160 square kilometres (62 sq mi),[28] consisting of lava domes, lava flows,[29] pyroclastic cones and volcanic craters[1] that rise about 2 kilometres (1.2 mi) above the surrounding terrain.[18] The massif appears to feature a buried caldera,[1] visible through a slope break from the western side,[30] and/or a 2.5 kilometres (1.6 mi) wide depression.[31] The occurrence of a rift-like structure with numerous small craters has also been reported.[32] Volcanic cones form a north-northeast trending alignment on the western flank.[33] Cerro Solo and El Fraile are large lava domes on the flanks of Ojos del Salado,[29] and produced pyroclastic flows.[34]

Wind-driven erosion has produced megaripple sand fields on the northern flank. Above 6,000 metres (20,000 ft) elevation talus-covered slopes and lava flows form the bulk of the surface, while the vast desert plains begin below 5,000 metres (16,000 ft) elevation.[35] The ground above 4,000–5,600 metres (13,100–18,400 ft) elevation is expected to contain permafrost,[36] which is likely continuous at higher elevations[37] and overlaid with a thin active layer.[38] Cryoturbation[lower-alpha 4] landforms were not conspicuous according to Nagy et al. 2019,[39] presumably because wind-driven phenomena overprint the effects of cryoturbation.[40] Mass movements have left traces on the mountain.[41]

Surroundings

The landscape is dominated by volcanoes,[52] many of Pleistocene or Holocene age,[53] and is the highest volcanic region in the world.[54] Young volcanoes have conical shapes and often feature summit craters.[55] Travellers have compared the region to a "moonscape".[56] There are hot springs in the region,[57] such as the Termas Laguna Verde at the shores of Laguna Verde, which are frequented by visitors.[58]

Volcanic Landscapes of the Central Andes. Shown are Nevado Ojos del Salado, Cerro El Cóndor, and Peinado, along the Argentina-Chile border. Astronaut photo from International Space Station, 2010.

The volcano lies in the middle of an over 80 kilometres (50 mi) long east-west trending chain of volcanoes[15] that form a drainage divide and includes the volcanoes Nevado Tres Cruces, Incahuasi[59] and Cerro Blanco. This chain of volcanoes appears to be part of the Ojos del Salado-San Buenaventura tectonic lineament,[60] which corresponds to a geographic (southern boundary of the Puna de Atacama)[60] and tectonic discontinuity in the region.[61] The lineament may be a consequence of the subduction of the Copiapo Ridge at this latitude.[61] An alternative view is that the subducting Copiapo Ridge is actually located north of the lineament; this would be more consistent with the theory that the subduction of such ridges gives rise to gaps in the volcanic chain.[62]

Penitente field at an altitude of approximately 6500 m on northern face of Ojos del Salado in summer of 2020

Except for firn and small glaciers in sheltered parts of the mountain, Ojos del Salado lacks substantial ice cover. This is due to the arid climate of the region, which causes the equilibrium line altitude of ice to rise above the top of the mountain[36] and keeps most peaks in the area ice-free.[8] Glacier areas shown on maps are often actually immobile firn fields.[63] The ice reaches thicknesses of only 10–15 metres (33–49 ft) and areal extents of a few hundred metres. Meltwater feeds streams.[64]

Climbing parties in 1956 reported two glaciers on the northwestern slope,[65] a 1958 report indicated that an ice body at 6,600 metres (21,700 ft) elevation descends into two branches and is followed at lower elevation by another glacier also with two branches—but in neither case with any evidence of movement—[66]and in 2014 there was ice in the summit crater[67] and substantial glaciers on the eastern and southern slopes, which reached elevations below 6,000 metres (20,000 ft).[68] There have been increases in ice area between 1974 and 1983[69] but between 1986 and 2000, ice area decreased by 40%.[70] The melting of the ice is expected to produce an increased discharge at first, but eventually ice diminishes to the point that runoff will decline.[71]

Penitentes have been encountered by climbers as early as 1937,[48] in 1949 there were reportedly 5–8 metres (16–26 ft) high penitentes on Ojos del Salado.[72] Penitentes are high ice spires[73] which form when ice sublimates in the intense insolation.[68]

Subsurface ice

Ice buried beneath sand

Ice buried beneath sand[74] and encased in moraines is more important than surface ice at Ojos del Salado. It is retreating but the insulating effect of the cover slows the retreat.[75] Cryokarst,[76] erosional gullies and so-called "infilled valleys"[lower-alpha 7] have been observed; they most likely form when buried ice and snow melt.[78] The combined effect of erosion by the meltwater and the disappearance of ice volume creates cavities that collapse and form the valleys and pseudokarst landforms.[75] Pseudokarst landforms and dolines are other structures generated by the melting of buried ice.[79]

In South America, there are about 200 volcanoes with evidence of eruptions during the Pleistocene and Holocene[89] along the western coast, where the Nazca Plate and Antarctic Plate subducts beneath the South America Plate in the Peru-Chile Trench. Volcanic activity is localized in four major volcanic belts, the Northern Volcanic Zone, the Central Volcanic Zone (CVZ), Southern Volcanic Zone and the Austral Volcanic Zone; these are separated by belts without volcanic activity.[90] Where volcanic activity occurs, the subduction process releases fluids from the downgoing slab which trigger the formation of melts in the mantle that eventually ascend to the surface and give rise to volcanism.[89][lower-alpha 8] Ojos del Salado is part of the Pacific Ring of Fire.[52]

The CVZ spans Peru, Bolivia, Chile and Argentina and contains about 1,100 recognized volcanoes, many of which are extremely old and are still recognizable owing to the low erosion rates in the region.[89] Apart from stratovolcanoes, the CVZ includes numerous calderas, isolated lava domes and lava flows, maars and pyroclastic cones. Most of the volcanoes are remote and thus constitute a low hazard.[93] Ojos del Salado is part of the CVZ and constitutes its southern boundary.[lower-alpha 9] South of the volcano[90] volcanism ceased during the last six million years[97] and until 32° south, subduction takes place at a shallow angle and volcanism is absent in the "Pampean flat-slab". The shallow angle may be a consequence of the subduction of submarine topography, such as the Copiapo Ridge at the northern and of the Juan Fernández Ridge at the southern margin of the gap.[98][89]

Detailed climate data do not exist for the area.[56] The Puna de Atacama region has an extreme climate with strong wind, high elevation, a dry climate[9] and high insolation;[107] the area is just south of the Arid Diagonal.[52]

Temperatures at lower elevations can exceed 10 °C (50 °F) but mean annual temperatures only reach −10 °C (14 °F).[108] Mean winds at Laguna Verde reach maximum speeds of 8–10 metres (26–33 ft) in winter, on the mountaintops they can exceed 10 metres per second (33 ft/s) and can impede climbing attempts. Winds blow strongest in the afternoon.[107] The winds produce aeolian landforms such as aeolian sediments,[109] dunes, gravel pavements, abraded rocks and megaripples at lower elevations,[110] and redeposit snow.[107]

Annual precipitation consists mostly of hail and snow.[16] It either amounts to less than 150 millimetres (5.9 in) per year[111] or reaches 300–500 millimetres (12–20 in) per year. Compared to sites farther north falls primarily during winter[52] although snowfall is common in summer.[111] Precipitation probably peaks at 5,500 metres (18,000 ft) where the cloud base lies;[107] above that elevation it decreases to about 200 millimetres (7.9 in).[112] Snow cover in the area is sporadic[113] and quickly sublimates,[37] which hinders its measurement;[111] the average snow cover is less than 5 centimetres (2.0 in) thick.[114] The dry climate prevents the development of substantial glaciers in the region; only farther south at Tronquitos does more extensive glaciation begin[52] although temporary ice and snow accumulations can be mistaken for glaciers.[115]

Bouldery landscape of Ojos del Salado

Due to the dry climate, the region is a desert with no vegetation occurring above 4,600 metres (15,100 ft) elevation.[37] However, lichens and mosses have been found at higher elevations[116] and green growths have been reported from the summit region.[117] As of 2007, there were no reports of plants in the waterbodies on Ojos del Salado.[43] Salt, acid and cold-tolerant bacteria have been recovered from sediments in the lakes on Ojos del Salado, consistent with microorganism samples from similar dry volcanic environments.[118]

A diverse flora and fauna has been described in the lower elevation regions south-southeast of Ojos del Salado.[119] Birds such as ducks, flamingos and geese and mammals such as guanacos and vicuñas occur in the Santa Rosa-Maricunga-Negro Francisco region.[11] Chinchillas and vicunas live in the valleys south of Ojos del Salado, and have drawn humans to the region.[120] Earwigs have been observed at 5,960 metres (19,550 ft) elevation.[121]

West of the volcano lies the Nevado Tres Cruces National Park[7] and in 1991/1994 there were plans to make a national park on the Argentine side as well.[122] As of 2020, the establishment of a "zone of touristic interest" encompassing Ojos del Salado was under discussion in Chile.[123]

Volcanic activity probably commenced 26 million,[87] 3.3-1.5 million years ago[29] or during the late Pleistocene.[15] The 3.7±0.2 million years old Las Lozas Andesite may have been a precursor of Ojos del Salado.[29] The oldest rocks of Ojos del Salado are 3.5-3.4 million years old dacites in the lower parts of the volcano.[27] Argentine geological maps define a "Ojos del Salado basal complex", which consists of a number of Miocene volcanoes that have erupted andesite and dacite, partially in glacial environments.[124]

The volcano developed in two stages, with the more recent one grown on top of the older.[23] A somma volcano structure may have formed during an eruption that generated the pumice deposits on the lower slopes of the volcano, and there are potential air fall deposits north of it. Ojos del Salado may[15] or may not have produced pyroclastic flows; the neighbouring Nevado Tres Cruces c. 67,000 years ago produced extensive deposits on, around Ojos del Salado and in the valley between the two volcanoes; these were originally interpreted to have originated at Ojos del Salado.[125][126][28] A pyroclastic flow erupted by Ojos del Salado descended the Cazadero valley and constitutes the "El Quemado Ignimbrite".[127] Cerro Solo, whose emplacement was probably accompanied by intense pyroclastic flow activity,[128] and lava domes in the summit region are of Pleistocene age.[31] The long-term growth rate of Ojos del Salado amounts to 0.03–0.04 cubic kilometres per kiloare (0.0072–0.0096 cu mi/ka).[129]

Radiometric dating has yielded ages of 1.53 ± 0.13,[27] 1.2 ± 0.3 million and less than one million years ago for rocks in the northwestern part of Ojos del Salado,[130] 1.08 ± 0.09 million years for flows underlying the summit,[24] 1.08 ± 0.04 million years for the northern flank of Ojos del Salado, 700,000±50,000 for its western flank, 450,000±60,000 for El Muerto,[106] 340,000 ± 190,000 years for the summit rocks,[24] and 230,000±40,000 years for El Fraile.[106] Lava flows and a lava dome on the northern flank have yielded ages of 100,000 ± 17,000 and 35,000 years, respectively.[28][131] The "El Quemado Ignimbrite" may be either 200,000 or less than 50,000 years old.[109] The youngest dates reported are 30,000 years ago.[87]

As Ojos del Salado is hidden behind[144] and nested among many peaks of similar elevation, for centuries travellers and mountaineers paid little attention to the mountain.[2] Its remoteness meant that for a long time, both its elevation and exact topography were unclear.[56] The positions and names of the mountains were frequently confused.[145][2]

The Inca used the Paso San Francisco as a major crossing of the Andes[146] but there is no evidence of them building any archeological sites on Ojos del Salado[lower-alpha 11][149] even though a number of such sites exist in the surrounding region.[13] The Spanish conquistador Diego de Almagro[150] crossed the Andes at Ojos del Salado but did not mention it.[2][lower-alpha 12] Ojos del Salado is likewise absent from the 1861 plans of William Wheelwright for a railway across Paso San Francisco.[73] The explorer Walter Penck crossed the area in 1912/13 and 1913/14[57] but did not identify the mountain.[151]

Ojos del Salado and the surrounding mountains draw fewer mountaineers than Aconcagua, with only several hundred climbers every year. Since the 1990s commercial tours have become important facilitators for ascents. The mountain can be ascended from both the Argentine and the Chilean side, but owing to the better logistics most ascents occur from the Chilean side.[164] The high elevation, cold and windy weather and impassable terrain are common challenges for would-be climbers.[165] The mountain is also accessible by vehicle, up to 6,650 metres (21,820 ft) elevation.[166]

Ascent from the Chilean side is easier as the first refuge can be reached by car, but the actual climb is easier from the Argentine side.[167] A dirt road departing from the Chile Route 31 highway to Paso San Francisco heads south to Ojos del Salado, past Refugio Murray to the bivouac Refugio Universidad de Atacama/Jorge Rojas at 5,200 metres (17,100 ft) elevation,[8] from there a path goes to Refugio Tejos at 5,825 metres (19,111 ft) elevation and eventually to the summit of Ojos del Salado.[168] From Argentina, the path runs from Cazadero Grande (Quemadito hut) along a large creek to its origin at Aguas Calientes at 4,200 metres (13,800 ft). From there it continues first up dry valleys to Acqua di Vicuna at 4,950 metres (16,240 ft) elevation, to the El Arenal plateau at 5,500 metres (18,000 ft) elevation and eventually along various routes to Ojos del Salado.[169]

Astronomers have reconnoitered the volcano for the possibility of creating an observatory there.[15][lower-alpha 14] The landforms such as the gullies[78] and crater lakes and their conditions,[171] and climatic conditions around Ojos del Salado have also led researchers to investigate it as a potential analogue to environments on Mars.[108]

• Cerro El Muerto
• Cerro Solo
• Incapillo
• Incahuasi
• Laguna Verde
• List of volcanoes in Argentina
• List of volcanoes in Chile
• Lists of volcanoes
• Llullaillaco
• Monte Pissis
• Nevado Tres Cruces
• Tipas
• Volcanic Seven Summits

• Biggar, John (2005). The Andes: A Guide for Climbers. Andes. ISBN 978-0-9536087-2-0.
• Radehose, Eckehard (2002). Traumberge Amerikas: von Alaska bis Feuerland (in German). Bergverlag Rother GmbH. ISBN 978-3-7633-3006-5.

Wikimedia Commons has media related to Ojos del Salado.

• Fleischer, K. (2004). Erstellung der Alpenvereinskarte "Nevado Ojos del Salado" (Thesis) (in German).
• Complete description of Ojos del Salado in Andeshandbook
• December 1, 2006, Star Trails at 19,000 Feet - NASA Astronomy Picture of the Day
• Andes information
• Ojos del Salado Satellite Elevation Data
• Peak bagger
• Summit post
• Peak list
• Virtual Aerial Video