Nevado Ojos del Salado is a dormant

complex volcano A complex volcano, also called a compound volcano or a volcanic complex, is a mixed landform consisting of related volcanic centers and their associated lava flows and pyroclastic rock. They may form due to changes in eruptive habit or in t ...

in the

Andes The Andes, Andes Mountains or Andean Mountains (; ) are the longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range is long, wide (widest between 18°S – 20°S ...

on the

Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...

–

Chile Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the east a ...

border. It is the highest

volcano A volcano is a rupture in the Crust (geology), crust of a Planet#Planetary-mass objects, planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and volcanic gas, gases to escape from a magma chamber below the surface. On Ear ...

on Earth and the highest peak in Chile. The upper reaches of Ojos del Salado consist of several overlapping

lava domes In volcanology, a lava dome is a circular mound-shaped protrusion resulting from the slow extrusion of viscous lava from a volcano. Dome-building eruptions are common, particularly in convergent plate boundary settings. Around 6% of erupti ...

lava flows Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or un ...

and

volcanic craters A volcanic crater is an approximately circular depression in the ground caused by volcanic activity. It is typically a bowl-shaped feature containing one or more vents. During volcanic eruptions, molten magma and volcanic gases rise from an unde ...

, with an only 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. Due to its location near the

Arid Diagonal upright=2.5, Map showing Köppens climate classification for South America. The arid diagonal can be seen in the form of the almost contiguous zone of BWh and BWk climate running from Ecuador to Southern Patagonia. The Arid Diagonal ( es, link=n ...

of South America, the mountain has extremely dry conditions, which prevent the formation of

glacier A glacier (; ) is a persistent body of dense ice that is constantly moving under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires distinguishing features, such as ...

s and a permanent

snow cover Snow comprises individual ice crystals that grow while suspended in the atmosphere—usually within clouds—and then fall, accumulating on the ground where they undergo further changes. It consists of frozen crystalline water throughout ...

. Despite the arid climate, there is a permanent

crater lake Crater Lake ( Klamath: ''Giiwas'') is a volcanic crater lake in south-central Oregon in the western United States. It is the main feature of Crater Lake National Park and is famous for its deep blue color and water clarity. The lake partly fill ...

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 The Pleistocene ( , often referred to as the ''Ice age'') is the geological epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was finally confirmed in ...

and

Holocene The Holocene ( ) is the current geological epoch. It began approximately 11,650 cal years Before Present (), after the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene togeth ...

, during which it mainly produced lava flows. Activity was in two phases and a depression or

caldera A caldera ( ) is a large cauldron-like hollow that forms shortly after the emptying of a magma chamber in a volcano eruption. When large volumes of magma are erupted over a short time, structural support for the rock above the magma chamber is ...

formed in the course of its growth. The volcano was also impacted by eruptions of its neighbour to the west,

Nevado Tres Cruces Nevado Tres Cruces is a massif of volcanic origin in the Andes Mountains on the border of Argentina and Chile. It has two main summits, Tres Cruces Sur at and Tres Cruces Centro at and a third minor summit, Tres Cruces Norte . Tres Cruces Sur ...

. The last eruption 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, but the first ascent was made in 1937 by

Jan Alfred Szczepański Jan Alfred Szczepański (9 November 1902 in Kraków – 20 March 1991 in Warsaw Warsaw ( pl, Warszawa, ), officially the Capital City of Warsaw,, abbreviation: ''m.st. Warszawa'' is the capital and largest city of Poland. The metropolis ...

and Justyn Wojsznis, members of a

Polish Polish may refer to: * Anything from or related to Poland, a country in Europe * Polish language * Poles Poles,, ; singular masculine: ''Polak'', singular feminine: ''Polka'' or Polish people, are a West Slavic nation and ethnic group, w ...

expedition in the Andes. During the middle of the 20th century there was a debate on whether Ojos del Salado or

Aconcagua Aconcagua () is a mountain in the Principal Cordillera of the Andes mountain range, in Mendoza Province, Argentina. It is the highest mountain in the Americas, the highest outside Asia, and the highest in the Southern Hemisphere with a summi ...

was the highest mountain in South America which was eventually resolved in favour of Aconcagua.

Name

The name "" refers to a river that the 1937 Polish expedition used to reach the mountain, although the river Salado does not originate on Ojos del Salado and the name was already known before. Another theory posits that the volcano was named after 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 The Puna de Atacama or Atacama Plateau''Atacama Plateau''
article at the ''

high plateau In geology and physical geography, a plateau (; ; ), also called a high plain or a tableland, is an area of a highland consisting of flat terrain that is raised sharply above the surrounding area on at least one side. Often one or more sides ha ...

next to the

Atacama Desert The Atacama Desert ( es, Desierto de Atacama) is a desert plateau in South America covering a 1,600 km (990 mi) strip of land on the Pacific coast, west of the Andes Mountains. The Atacama Desert is the driest nonpolar desert in th ...

with an average elevation of metres. The border between

and

runs across the summit of the mountain in east-west direction. The Argentine part is within Catamarca Province and the Chilean in Copiapo Province of the Atacama Region. The

highway A highway is any public or private road or other public way on land. It is used for major roads, but also includes other public roads and public tracks. In some areas of the United States, it is used as an equivalent term to controlled-acces ...

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 road A dirt road or track is a type of unpaved road not paved with asphalt, concrete, brick, or stone; made from the native material of the land surface through which it passes, known to highway engineers as subgrade material. Dirt roads are suitable ...

s. Ojos del Salado is a

dormant volcano A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plates a ...

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/

formed by overlapping smaller volcanoes, with over 20 craters. Two edifices, less than wide, flank the wide summit crater on its eastern and western side.

Basalt Basalt (; ) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90 ...

, gravel,

pumice Pumice (), called pumicite in its powdered or dust form, is a volcanic rock that consists of highly vesicular rough-textured volcanic glass, which may or may not contain crystals. It is typically light-colored. Scoria is another vesicular v ...

and

scoria Scoria is a pyroclastic, highly vesicular, dark-colored volcanic rock that was ejected from a volcano as a molten blob and cooled in the air to form discrete grains or clasts.Neuendorf, K.K.E., J.P. Mehl, Jr., and J.A. Jackson, eds. (2005) '' ...

crop out in its rim, which is lower on the northern side. A second wide crater lies just west of the summit crater. Reportedly, the summit is separated by a deep gap into two separate peaks. Thick short

dacitic Dacite () is a volcanic rock formed by rapid solidification of lava that is high in silica and low in alkali metal oxides. It has a fine-grained (aphanitic) to porphyritic texture and is intermediate in composition between andesite and rhyol ...

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 cone Volcanic cones are among the simplest volcanic landforms. They are built by ejecta from a volcanic vent, piling up around the vent in the shape of a cone with a central crater. Volcanic cones are of different types, depending upon the nature and s ...

s and

volcanic crater A volcanic crater is an approximately circular depression in the ground caused by volcanic activity. It is typically a bowl-shaped feature containing one or more vents. During volcanic eruptions, molten magma and volcanic gases rise from an und ...

s that rise about above the surrounding terrain. The massif appears to feature a buried

, visible through a slope break from the western side, and/or a wide 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 Cerro Solo is a large stratovolcano on the border between Argentina and Chile, west of Ojos del Salado with an elevation of metres. It consists of nine eruptive centers and is covered in light-colored rhyodacite pyroclastic flow deposits. Its ...

and El Fraile are large lava domes on the flanks of Ojos del Salado, and produced

pyroclastic flow A pyroclastic flow (also known as a pyroclastic density current or a pyroclastic cloud) is a fast-moving current of hot gas and volcanic matter (collectively known as tephra) that flows along the ground away from a volcano at average speeds of b ...

s. Wind-driven erosion has produced

megaripple In geology, ripple marks are sedimentary structures (i.e., bedforms of the lower flow regime) and indicate agitation by water (current or waves) or wind. Defining ripple cross-laminae and asymmetric ripples * ''Current ripple marks'', ''unid ...

sand fields on the northern flank. Above elevation talus-covered slopes and lava flows form the bulk of the surface, while the vast 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 In environments containing permafrost, the active layer is the top layer of soil that thaws during the summer and freezes again during the autumn. In all climates, whether they contain permafrost or not, the temperature in the lower levels of the ...

Cryoturbation In gelisols ( permafrost soils), cryoturbation (frost churning) refers to the mixing of materials from various horizons of the soil down to the bedrock due to freezing and thawing. Cryoturbation occurs to varying degrees in most gelisols. The c ...

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

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 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 In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to ...

owing to the breakdown of permafrost.

Surroundings

The landscape is dominated by volcanoes, many of

age, and is the highest volcanic region in the world. Young volcanoes have conical shapes and often feature summit craters. Travellers have compared the region to a "moonscape". There are

hot spring A hot spring, hydrothermal spring, or geothermal spring is a spring produced by the emergence of geothermally heated groundwater onto the surface of the Earth. The groundwater is heated either by shallow bodies of magma (molten rock) or by c ...

s in the region, such as the Termas Laguna Verde at the shores of Laguna Verde, which are frequented by visitors. Volcanic Landscapes, Central Andes labelled

Volcanic Landscapes, Central Andes labelled

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

Incahuasi Incahuasi (; possibly from Quechua: ''inka'' Inca, ''wasi'' house) is a volcanic mountain in the Andes of South America. It lies on the border of the Catamarca Province of Argentina and the Atacama Region of Chile. Incahuasi has a summit elevat ...

and

Cerro Blanco Cerro Blanco is a hill and historical landmark in the city of Santiago, Chile. This geographic feature rises above the surrounding terrain and covers a surface area of . It is bordered by Recoleta Avenue on the east, Santos Dumont Avenue on ...

. This chain of volcanoes appears to be part of the Ojos del Salado-San Buenaventura tectonic

lineament ''See also Line (geometry)'' A lineament is a linear feature in a landscape which is an expression of an underlying geological structure such as a fault. Typically a lineament will appear as a fault-aligned valley, a series of fault or fold-ali ...

, which corresponds to a geographic (southern boundary of the

Puna de Atacama The Puna de Atacama or Atacama Plateau''Atacama Plateau''
article at 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 __NOTOC__ Firn (; from Swiss German "last year's", cognate with ''before'') is partially compacted névé, a type of snow that has been left over from past seasons and has been recrystallized into a substance denser than névé. It is ice that ...

and small

s in sheltered parts of the mountain, Ojos del Salado lacks substantial ice cover. This is due to the

arid climate The desert climate or arid climate (in the Köppen climate classification ''BWh'' and ''BWk''), is a dry climate sub-type in which there is a severe excess of evaporation over precipitation. The typically bald, rocky, or sandy surfaces in deser ...

of the region, which causes the

equilibrium line altitude Glaciology (; ) is the scientific study of glaciers, or more generally ice and natural phenomena that involve ice. Glaciology is an interdisciplinary Earth science that integrates geophysics, geology, physical geography, geomorphology, clima ...

of ice to rise above the top of the mountain and keeps most peaks in the area ice-free. Glacier areas shown on maps are often actually immobile

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

Sand-covered snow field on Ojos del Salado (4320990586)

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 A gully is a landform created by running water, mass movement, or commonly a combination of both eroding sharply into soil or other relatively erodible material, typically on a hillside or in river floodplains or terraces. Gullies resemble lar ...

and so-called "infilled valleys" have been observed; they most likely form when buried ice and snow melt. 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.

Pseudokarst Karst is a topography formed from the dissolution of soluble rocks such as limestone, dolomite, and gypsum. It is characterized by underground drainage systems with sinkholes and caves. It has also been documented for more weathering-resistant ro ...

landforms and dolines are other structures generated by the melting of buried ice.

Past glaciation

Lateral moraine A moraine is any accumulation of unconsolidated debris (regolith and Rock (geology), rock), sometimes referred to as glacial till, that occurs in both currently and formerly glaciated regions, and that has been previously carried along by a gla ...

s altered by wind erosion occur north of Ojos del Salado and some lava flows bear traces of glaciation. Research published in 2019 found cirques and

U-shaped valley U-shaped valleys, also called trough valleys or glacial troughs, are formed by the process of glaciation. They are characteristic of mountain glaciation in particular. They have a characteristic U shape in cross-section, with steep, straight s ...

s on Ojos del Salado. However, there is no evidence of

glacier advances in the region nor any indication of a Pleistocene

snowline The climatic snow line is the boundary between a snow-covered and snow-free surface. The actual snow line may adjust seasonally, and be either significantly higher in elevation, or lower. The permanent snow line is the level above which snow wil ...

, although cirques have been reported from Nevado Tres Cruces and some sources propose the existence of glaciers 19,000 years ago. The

monsoon A monsoon () is traditionally a seasonal reversing wind accompanied by corresponding changes in precipitation but is now used to describe seasonal changes in atmospheric circulation and precipitation associated with annual latitudinal osci ...

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

and

along the western coast, where the Nazca Plate and

Antarctic Plate The Antarctic Plate is a tectonic plate containing the continent of Antarctica, the Kerguelen Plateau, and some remote islands in the Southern Ocean and other surrounding oceans. After breakup from Gondwana (the southern part of the superconti ...

subduct Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the ...

s beneath the

South America Plate The South American Plate is a major tectonic plate which includes the continent of South America as well as a sizable region of the Atlantic Ocean seabed extending eastward to the African Plate, with which it forms the southern part of the Mid-A ...

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. Where volcanic activity occurs, the subduction process releases fluids from the downgoing

slab Slab or SLAB may refer to: Physical materials * Concrete slab, a flat concrete plate used in construction * Stone slab, a flat stone used in construction * Slab (casting), a length of metal * Slab (geology), that portion of a tectonic plate tha ...

which trigger the formation of melts in the mantle that eventually ascend to the surface and give rise to volcanism. Ojos del Salado is part of the

Pacific Ring of Fire The Ring of Fire (also known as the Pacific Ring of Fire, the Rim of Fire, the Girdle of Fire or the Circum-Pacific belt) is a region around much of the rim of the Pacific Ocean where many volcanic eruptions and earthquakes occur. The Ring o ...

. 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. Apart from stratovolcanoes, the CVZ includes numerous

s, isolated lava domes and lava flows, maars and

s. 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 and of the Juan Fernández Ridge at the southern margin of the gap.

Local

The basement in the region crops out in the Cordillera Claudio Gay area, and consists of

sedimentary rock Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...

s of Devonian- Carboniferous age. The rocks are intruded by and covered by

granite Granite () is a coarse-grained ( phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies under ...

s and rhyolites associated with

Permian The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last ...

volcanic rocks and the Choiyoi Group. Oligocene to recent volcanic rocks and volcano-sedimentary formations cover this basement. The topography at Ojos del Salado bears evidence of what may have been past magmatic uplift. Seismic tomography has yielded evidence of a low

seismic velocity A seismic wave is a wave of acoustic energy that travels through the Earth. It can result from an earthquake, volcanic eruption, magma movement, a large landslide, and a large man-made explosion that produces low-frequency acoustic energy. ...

anomaly underneath the volcano that may constitute the pathway through which water emanating from the downgoing slab rises through the mantle and gives rise to melting. Volcanism in the region commenced 26 million years ago, when the

Farallon Plate The Farallon Plate was an ancient oceanic plate. It formed one of the three main plates of Panthalassa, alongside the Phoenix Plate and Izanagi Plate, which were connected by a triple junction. The Farallon Plate began subducting under the west ...

broke up and subduction speed increased. Initially between 26 and 11 million years ago activity was concentrated in the Maricunga region west of the Ojos del Salado region, where only small-volume volcanism took place and which constituted the

back-arc A back-arc basin is a type of geologic basin, found at some convergent plate boundaries. Presently all back-arc basins are submarine features associated with island arcs and subduction zones, with many found in the western Pacific Ocean. Most o ...

to the Maricunga arc. Between 8-5 million years ago activity declined in the Maricunga region and increased in the Ojos del Salado region, until Maricunga volcanism ceased 4 million years ago. This shift coincided with a gradual flattening of the subduction process since the

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

and was accompanied by change in crustal and mantle properties that are reflected in the

isotope ratio The term stable isotope has a meaning similar to stable nuclide, but is preferably used when speaking of nuclides of a specific element. Hence, the plural form stable isotopes usually refers to isotopes of the same element. The relative abundanc ...

s of erupted volcanic rocks. During the Quaternary, volcanism formed the edifices of

, El Fraile,

, El Muerto, El Muertito,

Falso Azufre Falso Azufre is a complex volcano at the border of Argentina and Chile. Falso Azufre is elongated in east–west direction and contains craters and lava domes; most craters have diameters of with the exception of the main crater, which is wi ...

Nevado San Francisco Nevado San Francisco, or Cerro San Francisco (), is a stratovolcano on the border between Argentina and Chile, located just southeast of San Francisco Pass. It is considered extinct and is one of the several peaks in the area, of which the ch ...

and Ojos del Salado, which together cover over half of the area. Apart from the large volcanoes, many smaller

mafic A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks incl ...

monogenetic volcano A monogenetic volcanic field is a type of volcanic field consisting of a group of small monogenetic volcanoes, each of which erupts only once, as opposed to polygenetic volcanoes, which erupt repeatedly over a period of time. The small monogeneti ...

es developed in the area, especially east of Ojos del Salado.

volcanism was limited to the Ojos del Salado area, where recent

faulting In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...

offset volcanic rocks. The large dimensions of Ojos del Salado indicate that magmatism was focused here.

Composition

Volcanic rocks erupted by Ojos del Salado form a

calc-alkaline The calc-alkaline magma series is one of two main subdivisions of the subalkaline magma series, the other subalkaline magma series being the tholeiitic series. A magma series is a series of compositions that describes the evolution of a mafic m ...

potassium Potassium is the chemical element with the symbol K (from Neo-Latin ''kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmosph ...

-rich suite of

rocks, with occasional

andesite Andesite () is a volcanic rock of intermediate composition. In a general sense, it is the intermediate type between silica-poor basalt and silica-rich rhyolite. It is fine-grained (aphanitic) to porphyritic in texture, and is composed predo ...

and

rhyodacite Rhyodacite is a volcanic rock intermediate in composition between dacite and rhyolite. It is the extrusive equivalent of those plutonic rocks that are intermediate in composition between monzogranite and granodiorite. Rhyodacites form from rap ...

. Earlier in the geological history of the region more

magmas also erupted. The rocks contain

phenocryst 300px, feldspathic phenocrysts. This granite, from the Switzerland">Swiss side of the Mont Blanc massif, has large white plagioclase phenocrysts, triclinic minerals that give trapezoid shapes when cut through). 1 euro coins, 1 euro coin (diameter ...

s like augite, biotite,

hornblende Hornblende is a complex inosilicate series of minerals. It is not a recognized mineral in its own right, but the name is used as a general or field term, to refer to a dark amphibole. Hornblende minerals are common in igneous and metamorphic rock ...

hypersthene Hypersthene is a common rock-forming inosilicate mineral belonging to the group of orthorhombic pyroxenes. Its chemical formula is . It is found in igneous and some metamorphic rocks as well as in stony and iron meteorites. Many references have f ...

, opaque minerals,

plagioclase Plagioclase is a series of tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continuous solid solution series, more pro ...

, pyroxene and

quartz Quartz is a hard, crystalline mineral composed of silica ( silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical ...

. Magma mixing phenomena produced

olivine The mineral olivine () is a magnesium iron silicate with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers quickl ...

and pyroxene

xenocryst A xenolith ("foreign rock") is a rock fragment ( country rock) that becomes enveloped in a larger rock during the latter's development and solidification. In geology, the term ''xenolith'' is almost exclusively used to describe inclusions in ign ...

s and amphibole reaction rims.

Climate

Detailed climate data do not exist for the area. The

Puna de Atacama The Puna de Atacama or Atacama Plateau''Atacama Plateau''
article at the ''

insolation; the area is just south of the

. Temperatures at lower elevations can exceed but mean annual temperatures only reach . Mean winds at Laguna Verde reach maximum speeds of in winter, on the mountaintops they can exceed and can impede climbing attempts. Winds blow strongest in the afternoon. The winds produce aeolian landforms such as aeolian

sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sa ...

s, dunes, gravel pavements, abraded rocks and

s at lower elevations, and redeposit snow. Annual precipitation consists mostly of hail and snow. It either amounts to less than per year or reaches per year. Compared to sites farther north falls primarily during winter although snowfall is common in summer. Precipitation probably peaks at where the

cloud base A cloud base (or the base of the cloud) is the lowest altitude of the visible portion of a cloud. It is traditionally expressed either in metres or feet above mean sea level or above a planetary surface, or as the pressure level corresponding to ...

lies; above that elevation it decreases to about . Snow cover in the area is sporadic and quickly sublimates, which hinders its measurement; the average snow cover is less than thick. The dry climate prevents the development of substantial

s in the region; only farther south at Tronquitos does more extensive glaciation begin although temporary ice and snow accumulations can be mistaken for glaciers.

Vegetation and fauna

Boulders on Ojos del Salado (4320255611)

Due to the dry climate, the region is a desert with no vegetation occurring above elevation. However, lichens and mosses have been found at higher elevations and green growths have been reported from the summit region. , there were no reports of plants in the waterbodies on Ojos del Salado. Salt, acid and cold-tolerant

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...

have been recovered from sediments in the lakes on Ojos del Salado, consistent with microorganism samples from similar dry volcanic environments. A diverse flora and fauna has been described in the lower elevation regions south-southeast of Ojos del Salado. Birds such as

duck Duck is the common name for numerous species of waterfowl in the family Anatidae. Ducks are generally smaller and shorter-necked than swans and geese, which are members of the same family. Divided among several subfamilies, they are a form ...

flamingo Flamingos or flamingoes are a type of wading bird in the family Phoenicopteridae, which is the only extant family in the order Phoenicopteriformes. There are four flamingo species distributed throughout the Americas (including the Caribbea ...

s and

geese A goose ( : geese) is a bird of any of several waterfowl species in the family Anatidae. This group comprises the genera '' Anser'' (the grey geese and white geese) and ''Branta'' (the black geese). Some other birds, mostly related to the she ...

and mammals such as

guanaco The guanaco (; ''Lama guanicoe'') is a camelid native to South America, closely related to the llama. Guanacos are one of two wild South American camelids, the other being the vicuña, which lives at higher elevations. Etymology The guanaco ...

s and

vicuña The vicuña (''Lama vicugna'') or vicuna (both , very rarely spelled ''vicugna'', its former genus name) is one of the two wild South American camelids, which live in the high alpine areas of the Andes, the other being the guanaco, which live ...

s occur in the Santa Rosa-Maricunga-Negro Francisco region. Chinchillas and vicunas live in the valleys south of Ojos del Salado, and have drawn humans to the region.

Earwig Earwigs make up the insect order Dermaptera. With about 2,000 species in 12 families, they are one of the smaller insect orders. Earwigs have characteristic cerci, a pair of forcep-like pincers on their abdomen, and membranous wings folde ...

s have been observed at elevation. West of the volcano lies the Nevado Tres Cruces National Park and in 1991/1994 there were plans to make a national park on the Argentine side as well. , the establishment of a "zone of touristic interest" encompassing Ojos del Salado was under discussion in Chile.

Eruption history

Volcanic activity probably commenced 26 million, 3.3-1.5 million years ago or during the late

. The 3.7±0.2 million years old Las Lozas

Andesite Andesite () is a volcanic rock of intermediate composition. In a general sense, it is the intermediate type between silica-poor basalt and silica-rich rhyolite. It is fine-grained (aphanitic) to porphyritic in texture, and is composed predo ...

may have been a precursor of Ojos del Salado. The oldest rocks of Ojos del Salado are 3.5-3.4 million years old dacites in the lower parts of the volcano. Argentine geological maps define a "Ojos del Salado basal complex", which consists of a number of

volcanoes that have erupted

and

dacite Dacite () is a volcanic rock formed by rapid solidification of lava that is high in silica and low in alkali metal oxides. It has a fine-grained (aphanitic) to porphyritic texture and is intermediate in composition between andesite and rhyolite ...

, partially in

glacial A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate betwe ...

environments. The volcano developed in two stages, with the more recent one grown on top of the older. A

somma volcano A somma volcano (also known as a sommian) is a volcanic caldera that has been partially filled by a new central cone. The name comes from Mount Somma, a stratovolcano in southern Italy with a summit caldera in which the upper cone of Mount Ves ...

structure may have formed during an eruption that generated the

deposits on the lower slopes of the volcano, and there are potential air fall deposits north of it. Ojos del Salado may or may not have produced

s; the neighbouring

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. A

erupted by Ojos del Salado descended the Cazadero valley and constitutes the "El Quemado Ignimbrite". Cerro Solo, whose emplacement was probably accompanied by intense

activity, and lava domes in the summit region are of

age. The long-term growth rate of Ojos del Salado amounts to .

Radiometric dating Radiometric dating, radioactive dating or radioisotope dating is a technique which is used to date materials such as rocks or carbon, in which trace radioactive impurities were selectively incorporated when they were formed. The method compares ...

has yielded ages of 1.53 ± 0.13, 1.2 ± 0.3 million and less than one million years ago for rocks in the northwestern part of Ojos del Salado, 1.08 ± 0.09 million years for flows underlying the summit, 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, 340,000 ± 190,000 years for the summit rocks, and 230,000±40,000 years for El Fraile. Lava flows and a lava dome on the northern flank have yielded ages of 100,000 ± 17,000 and 35,000 years, respectively. The "El Quemado Ignimbrite" may be either 200,000 or less than 50,000 years old. The youngest dates reported are 30,000 years ago.

Holocene and historical activity

The volcano produced lava flows during the

, which cover an area of , as well as pumice deposits at Laguna Verde and elongated fractures in the summit region. A

rhyodacitic Rhyodacite is a volcanic rock intermediate in composition between dacite and rhyolite. It is the extrusive equivalent of those plutonic rocks that are intermediate in composition between monzogranite and granodiorite. Rhyodacites form from rapid ...

eruption was dated with

tephrochronology 250px, Tephra horizons in south-central Iceland. The thick and light coloured layer at the height of the volcanologist's hands is rhyolitic tephra from Hekla. Tephrochronology is a Geochronology, geochronological technique that uses discrete l ...

to have occurred 750 ± 250 CE. Many volcanic rocks have a fresh appearance but there is no clear evidence of recent activity. There are no confirmed historical eruptions and the volcano is presently inactive. In November 1993, observers witnessed ash and steam columns on two separate days but no deformation of the volcano was observed by satellites during this occasion. An ash cloud observed on the June 13, 2015, and which led to a warnings about volcanic ash to aircraft turned out to be wind-blown

volcanic ash Volcanic ash consists of fragments of rock, mineral crystals, and volcanic glass, created during volcanic eruptions and measuring less than 2 mm (0.079 inches) in diameter. The term volcanic ash is also often loosely used to refer ...

in the Fiambala valley.

Hazards

There is no information on volcanic hazards at Ojos del Salado and volcanic hazards in the Central Volcanic Zone are poorly reconnoitered, but a 2018 presentation at the

University of Auckland , mottoeng = By natural ability and hard work , established = 1883; years ago , endowment = NZD $293 million (31 December 2021) , budget = NZD $1.281 billion (31 December 2021) , chancellor = Cecilia Tarrant , vice_chancellor = Dawn F ...

ranked it 14th of 38 Argentine volcanoes and the Chilean geological agency

SERNAGEOMIN 250px, Sernageomin building in Providencia, Santiago. The National Geology and Mining Service ( es, Servicio Nacional de Geología y Minería; SERNAGEOMIN) is a Chilean government agency. Its function is to provide geological information and adv ...

75th out of 92, thus as a very low risk volcano. The latter has published hazard maps for the Chilean part of the volcano. Future eruptions would most likely produce lava domes, lava flows and minor explosive activity, and the presence of ice on the mountain makes it a potential source for lahars. Effects would most likely be limited to the direct surroundings of the volcano, such as

Fumarolic activity

There are

fumarole A fumarole (or fumerole) is a vent in the surface of the Earth or other rocky planet from which hot volcanic gases and vapors are emitted, without any accompanying liquids or solids. Fumaroles are characteristic of the late stages of volcani ...

s that emit sulfurous smokes. Polish climbers in 1937 first observed this activity, below the summit and in the summit crater. Fumarolic activity appears to be linked to a

rift In geology, a rift is a linear zone where the lithosphere is being pulled apart and is an example of extensional tectonics. Typical rift features are a central linear downfaulted depression, called a graben, or more commonly a half-grabe ...

structure on the volcano. Climbers in 1957 reported that the fumaroles were noisy and the emissions intense enough that with unfavourable winds they could suffocate people. The fumaroles can be observed from

satellite A satellite or artificial satellite is an object intentionally placed into orbit in outer space. Except for passive satellites, most satellites have an electricity generation system for equipment on board, such as solar panels or radioi ...

s in the form of temperature anomalies which reach , but the steam plumes are poorly visible from the ground except from close distance. The occurrence of geysers in the summit region has been reported.

Human history

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

Inca The Inca Empire (also known as the Incan Empire and the Inka Empire), called ''Tawantinsuyu'' by its subjects, (Quechua for the "Realm of the Four Parts", "four parts together" ) was the largest empire in pre-Columbian America. The admin ...

used the Paso San Francisco as a major crossing of the Andes but there is no evidence of them building any

archeological site An archaeological site is a place (or group of physical sites) in which evidence of past activity is preserved (either prehistoric or historic or contemporary), and which has been, or may be, investigated using the discipline of archaeology an ...

s on Ojos del Salado even though a number of such sites exist in the surrounding region. The

Spanish Spanish might refer to: * Items from or related to Spain: **Spaniards are a nation and ethnic group indigenous to Spain **Spanish language, spoken in Spain and many Latin American countries **Spanish cuisine Other places * Spanish, Ontario, Can ...

conquistador

Diego de Almagro Diego de Almagro (; – July 8, 1538), also known as El Adelantado and El Viejo, was a Spanish conquistador known for his exploits in western South America. He participated with Francisco Pizarro in the Spanish conquest of Peru. While subd ...

crossed the Andes at Ojos del Salado but did not mention it. Ojos del Salado is likewise absent from the 1861 plans of William Wheelwright for a railway across Paso San Francisco. The explorer Walter Penck crossed the area in 1912/13 and 1913/14 but did not identify the mountain.

Ascents and debate on elevation

In 1896, 1897 and 1903 the Chile-Argentina boundary commission identified a peak in the area and named it "Ojos del Salado"; according to a myth their "Ojos del Salado" was a much smaller mountain and the actual Ojos del Salado was their "Peak 'e'". The

climbers Justin Wojsznis, Stefan Osiecki, Witold Paryski, Jan Szczepański reached the summit on February 26, 1937 and left a cairn but most of the maps and report they drafted were lost during

World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposing ...

. After the Polish expedition, the mountain remained unclimbed, although expeditions went to its lower slopes and sometimes confused other peaks for Ojos del Salado until 1955. In that year an expedition from Tucumán ascended a mountain south of Ojos del Salado, which they mistook for the volcano. They stated that the peak may be higher than Aconcagua, which media reported as if it were proven fact. These measurements set off a debate whether Ojos del Salado was higher than

and thus the highest summit of the

Western Hemisphere The Western Hemisphere is the half of the planet Earth that lies west of the prime meridian (which crosses Greenwich, London, United Kingdom) and east of the antimeridian. The other half is called the Eastern Hemisphere. Politically, the te ...

, and drew attention to the mountain. Three separate Chilean, Argentine and Austrian parties went to Ojos del Salado in 1956; the Chilean party measured an elevation of with a

barometer A barometer is a scientific instrument that is used to measure air pressure in a certain environment. Pressure tendency can forecast short term changes in the weather. Many measurements of air pressure are used within surface weather analysis ...

, a value that was once again presented as proven by the press despite the unreliability of this technique. The Chilean party also claimed seeing the Argentine pampa and the

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the contin ...

from the summit. In 1957, the official elevation of Ojos del Salado was according to Argentina and according to Chile. The debate on the elevation and confusion about which mountain was Ojos del Salado and who climbed which peak prompted an expedition by the

American Alpine Club The American Alpine Club (AAC) is a non-profit member organization with more than 24,000 members. Its vision is to create "a united community of competent climbers and healthy climbing landscapes." The Club is housed in the American Mountaineerin ...

in 1956. The expedition was hindered by bad weather conditions and a gust of wind stretching a measurement line may have almost frustrated the goal to determine the summit elevation of Ojos del Salado. The same party later used

geodetic Geodesy ( ) is the Earth science of accurately measuring and understanding Earth's figure (geometric shape and size), orientation in space, and gravity. The field also incorporates studies of how these properties change over time and equivale ...

methods to establish the elevation of Ojos del Salado as and lower than

. In 1989, Francesco Santon of the

University of Padua The University of Padua ( it, Università degli Studi di Padova, UNIPD) is an Italian university located in the city of Padua, region of Veneto, northern Italy. The University of Padua was founded in 1222 by a group of students and teachers from ...

in Italy and with Argentine assistance, used

GPS The Global Positioning System (GPS), originally Navstar GPS, is a satellite-based radionavigation system owned by the United States government and operated by the United States Space Force. It is one of the global navigation satellite sy ...

-based positioning to determine an elevation of .

Mountaineering and tourism

Ojos del Salado and the surrounding mountains draw fewer mountaineers than

, 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. The high elevation, cold and windy weather and impassable terrain are common challenges for would-be climbers. The mountain is also accessible by vehicle, up to elevation. 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. A dirt road departing from the highway to Paso San Francisco heads south to Ojos del Salado, past Refugio Murray to the bivouac Refugio Universidad de Atacama/Jorge Rojas at elevation, from there a path goes to Refugio Tejos at elevation and eventually to the summit of Ojos del Salado. From Argentina, the path runs from Cazadero Grande (Quemadito hut) along a large creek to its origin at Aguas Calientes at . From there it continues first up dry valleys to Acqua di Vicuna at elevation, to the El Arenal plateau at elevation and eventually along various routes to Ojos del Salado.

Astronomy

Astronomers An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astronomical objects such as stars, planets, moons, comets and galaxies – in either obse ...

have reconnoitered the volcano for the possibility of creating an observatory there. The landforms such as the gullies and crater lakes and their conditions, and climatic conditions around Ojos del Salado have also led researchers to investigate it as a potential analogue to environments on

Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin at ...

Notes

References

Sources

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Bibliography

* *

External links

*
Complete description of Ojos del Salado in Andeshandbook

- NASA Astronomy Picture of the Day
Andes informationOjos del Salado Satellite Elevation Data

Peak bagger

Summit post

{{Authority control Stratovolcanoes of Chile Stratovolcanoes of Argentina Seven Second Summits Volcanic Seven Summits Active volcanoes Andean Volcanic Belt Volcanic crater lakes Volcanoes of Atacama Region Mountains of Atacama Region Volcanoes of Catamarca Province Mountains of Catamarca Province Atacama Desert Argentina–Chile border International mountains of South America Highest points of countries Six-thousanders of the Andes Pleistocene stratovolcanoes Holocene stratovolcanoes