Nevado Ojos del Salado () is a dormant complex volcano in the Andes on the Argentina–Chile border. It is the highest volcano on Earth and the highest peak in Chile. The upper reaches of Ojos del Salado consist of several overlapping lava domes, lava flows and volcanic craters, with sparse ice cover. The complex extends over an area of and its highest summit reaches an altitude of above sea level. Numerous other volcanoes rise around Ojos del Salado.
Being close to the Arid Diagonal of South America, the mountain has extremely dry conditions, which prevent the formation of substantial glaciers and a permanent snow cover. Despite the arid climate, there is a permanent crater lake about in diameter at an elevation of within the summit crater and east of the main summit. This is the highest lake of any kind in the world. Owing to its altitude and the desiccated climate, the mountain lacks vegetation.
Ojos del Salado was volcanically active during the Pleistocene and Holocene, during which it mainly produced lava flows. Activity was in two phases and a depression or caldera formed in the course of its growth. The volcano was also affected by eruptions of its neighbour to the west, Nevado Tres Cruces. The last eruption of Ojos del Salado occurred around 750 CE; steam emissions observed in November 1993 may have constituted another eruptive event.
An international highway between Argentina and Chile crosses north of the mountain. Ojos del Salado can be ascended from both countries; the first ascent was made in 1937 by Jan Alfred Szczepański and , members of a Polish expedition in the Andes. During the middle of the 20th century there was a debate on whether Ojos del Salado or Aconcagua was the highest mountain in South America, which was eventually resolved in favour of Aconcagua.
Name The name refers to a river, ("Salty River"), which was used by a 1937 Polish expedition to reach the mountain. It is unclear whether the name was already in use before by a Chile–Argentina boundary commission. In geographical terms, Ojo is commonly used in Chile and Argentina to denote a spring or source of water; e.g. the nearby source of the Las Lozas river "Ojo de las Lozas".
The mountain is often referred to as Ojos del Salado and Ojos del Salado; the former is a common term for "mountain" in Chile and the latter means "snowy", referring to snow-covered mountains. Another theory posits that the name means "salty eyes" or "salty springs", referring to mineral deposits on its flanks. 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.
Geography and geomorphology Ojos del Salado is part of the High Andes and rises from the southern end of the Puna de Atacama, a high plateau next to the Atacama Desert with an average elevation of . The Argentina–Chile border runs across the summit of the mountain in an east-west direction. The Argentine part is within Catamarca Province and the Chilean in Copiapo Province of the Atacama Region. The highway runs between the city of Copiapo west of the volcano and the Paso San Francisco to Argentina, lying about north of the volcano, making it more accessible than many other volcanoes there. The region is uninhabited and lacks water resources; many parts are only accessible through dirt roads.
Ojos del Salado is a dormant volcano that rises to , or elevation. It is the world's highest volcano and the second-highest summit of the Andes, and the highest summit in Chile. Ojos del Salado is not a single conical summit but a massif/complex volcano formed by overlapping smaller volcanoes, with over 20 craters. Two edifices, less than wide, flank the summit crater on its eastern and western side. Basalt, gravel, pumice and scoria crop out in its rim, which is lower on the northern side. A second crater lies just west of the summit crater. Reportedly, the summit is separated by a deep gap into two separate peaks. Thick short dacitic lava flows make up the core area of the volcano but pyroclastic fall material covers much of the summit area.
The massif rises about above the surrounding terrain and covers an oval area of about –, consisting of lava domes, lava flows, pyroclastic cones and volcanic craters that rise about above the surrounding terrain. The massif appears to feature a buried caldera, visible through a slope break from the western side, and/or a depression. The occurrence of a rift-like structure with numerous small craters has also been reported. Volcanic cones form a north-northeast trending alignment on the western flank. Cerro Solo and El Fraile are large lava domes on the flanks of Ojos del Salado, and produced pyroclastic flows.
Wind-driven erosion has produced megaripple sand fields on the northern flank. Above elevation talus-covered slopes and lava flows form the bulk of the surface, while the desert plains begin below elevation. The ground above elevation is expected to contain permafrost, which is likely continuous at higher elevations and overlaid with a thin active layer. Cryoturbation landforms were not conspicuous according to Nagy et al. 2019, presumably because wind-driven phenomena overprint the effects of cryoturbation. Mass movements have left traces on the mountain.
Lakes Ojos del Salado hosts the highest lake in the world in the form of the crater lake in the summit crater. Fed by permafrost and snowfields, it lies at elevation. It is surrounded by fumaroles and covers an area of . Waters in a creek flowing into this lake reach temperatures of .
There are two lakes at elevation on the northeastern slope, away from the higher lake. Each has an area of and an estimated depth of . Ephemeral lakes occur at elevation, when meltwater from underground snow/ice and permafrost accumulates in closed depressions. Such ponds may form in depressions at elevation. Some of the lakes may be permanently frozen. Lakes might disappear with climate change owing to the breakdown of permafrost. There are no permanent waterbodies, whether creeks or lakes, at low altitudes, except for Laguna Verde.
Surroundings The landscape is dominated by volcanoes, many of Pleistocene or Holocene age, and is the highest volcanic region in the world. Young volcanoes have conical shapes and often feature summit craters. Travellers have called the region a "moonscape". There are hot springs in the region, such as the Termas Laguna Verde at the shores of Laguna Verde, which are frequented by visitors.
The volcano lies in the middle of an over long east–west trending chain of volcanoes that form a drainage divide and includes the volcanoes Nevado Tres Cruces, Incahuasi and Cerro Blanco. This chain of volcanoes appears to be part of the Ojos del Salado–San Buenaventura tectonic lineament, which corresponds to a geographic (southern boundary of the Puna de Atacama) and tectonic discontinuity in the region. The lineament may be a consequence of the subduction of the Copiapo Ridge at this latitude. 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.
Ice and glaciers 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 and keeps most peaks in the area ice-free. Only farther south at Tronquitos does more extensive glaciation begin. Temporary ice and snow accumulations can be mistaken for glaciers, and glacier areas shown on maps are often actually immobile firn fields. The ice reaches thicknesses of only and areal extents of a few hundred metres. Meltwater feeds streams.
Climbing parties in 1956 reported two glaciers on the northwestern slope; a 1958 report indicated that an ice body at 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— and in 2014 there was ice in the summit crater and substantial glaciers on the eastern and southern slopes, which reached elevations below . There have been increases in ice area between 1974 and 1983, but between 1986 and 2000, ice area decreased by 40%. 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.
Penitentes have been encountered by climbers as early as 1937; in 1949 there were reportedly high penitentes on Ojos del Salado. Penitentes are high ice spires which form when ice sublimates in the intense insolation.
Subsurface ice
Ice buried beneath sand 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. Cryokarst, erosional gullies and so-called "infilled valleys" have been observed; they most likely form when buried ice and snow melt. There may be rock glaciers as well. The combined effect of erosion by the meltwater and the disappearance of ice volume creates cavities that collapse and form the valleys, pseudokarst landforms and dolines. Underground ice and permafrost vary in their properties depending on the altitude.
Past glaciation Lateral moraines altered by wind erosion occur north of Ojos del Salado, and some lava flows bear traces of glaciation. Research published in 2019 and 2025 found cirques, trim lines and U-shaped valleys on Ojos del Salado. However, there is no evidence of Pleistocene glacier advances in the region nor any indication of a Pleistocene snowline, although cirques have been reported from Nevado Tres Cruces and some sources propose the existence of glaciers 19,000 years ago. The monsoon reached farther south during the Pleistocene but did not reach Ojos del Salado, allowing the development of glaciers only at more northern latitudes. Westerly winds did not regularly influence the climate at the volcano, either.
Geology In South America, there are about 200 volcanoes with evidence of eruptions during the Pleistocene and Holocene along the western coast, where the Nazca Plate and Antarctic Plate subduct beneath the South America Plate in the Peru-Chile Trench. Volcanic activity is localized in four major volcanic belts, the Northern, Central (CVZ), Southern and Austral Volcanic Zones; these are separated by belts without volcanic activity and form part of the Pacific Ring of Fire. 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.
The CVZ spans Peru, Bolivia, Chile and Argentina and contains about 1,100 recognized volcanoes, many of which are extremely old but are still recognizable owing to the low erosion rates in the region. 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. Ojos del Salado is part of the CVZ and constitutes its southern boundary. South of the volcano volcanism ceased during the last six million years, 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 end of the Juan Fernández Ridge at the southern margin of the gap.
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