Socompa

Socompa is a large stratovolcano (composite volcano) on the border of Argentina and Chile. It has an elevation of and is part of the Chilean and Argentine Andean Volcanic Belt (AVB). Socompa is within the Central Volcanic Zone, one of the segments of the AVB, which contains about 44 active volcanoes. It begins in Peru and runs first through Bolivia and Chile, and then Argentina and Chile. Socompa lies close to the pass of the same name where the Salta-Antofagasta railway crosses the Chilean border.

Most of the northwestern slope of Socompa collapsed catastrophically 7,200 years ago to form an extensive debris avalanche deposit. The Socompa collapse is among the largest known on land with a volume of and a surface area of ; its features are well-preserved by the arid climate. The deposit was at first considered to be either a moraine or a pyroclastic flow deposit, until the 1980 eruption of Mount St. Helens prompted awareness of the instability of volcanic edifices and the existence of large-scale collapses. There are large toreva blocks, which were left behind within the collapse crater. After the landslide, the volcano was rebuilt by the effusion of lava flows and much of the scar is now filled in.

Socompa is also noteworthy for the high-altitude biotic communities that are bound to fumaroles on the mountain. They are well above the sparse regular vegetation in the region, which does not extend up the mountains. The climate on the mountain is cold and dry.

Geography and geomorphology

Socompa is on the border between Argentina and Chile,Template:Sfn east-southeast of the Monturaqui railway stationTemplate:Sfn of the Salta–Antofagasta railway.Template:Efn The railway crosses the border between the two countries just below Socompa, making the volcano easily accessible despite its remote location. The same pass was an important route between the two countries and reportedly between 1940 and 1970 the Carabineros de Chile had a post there. Rails and roads at Socompa go up to an elevation of ; from there the volcano can be climbed from its southern, eastern and northern flank.Template:SfnTemplate:Sfn The mountain is considered to be an apu by the local population, and Inca constructionsTemplate:Efn have been reported either from its slopes or from its summit. The name comes from the Kunza language and may be related to and , which mean "spring" or "arm of water". Presently, the volcano is within two protected areas.Template:Sfn

The volcano is part of the Central Volcanic Zone, one of the four volcanic zones of the Andean Volcanic Belt. This volcanic zone spans Peru, Bolivia, Chile and Argentina and contains about 44 active volcanoes and several monogenetic volcanoes and silicic caldera volcanoes. Some older inactive volcanoes are well-preserved owing to the dry climate of the region. Many of these volcanoes are in remote regions and thus are poorly studied, but pose little threat to humans. The largest historical eruption in the Central Volcanic Zone occurred in 1600 at Huaynaputina in Peru, and the recently most active volcano is Lascar in Chile.

Socompa is a Template:EfnTemplate:EfnTemplate:Sfn composite volcanoTemplate:Sfn consisting of a central cone and several lava domes;Template:Sfn it is the most voluminous conical volcano of the Central Volcanic ZoneTemplate:Sfn and one of the highest edifices there, rising more than above the surrounding terrain.Template:Sfn Several dacitic lava flows form the summit area of the volcano, the youngest of which originates from a summit dome. This summit dome is capped off by a summit crater at an altitude of ,Template:Sfn and four other craters occur northeast of the summit at altitudes of .Template:Sfn Northwest of the summit, a dacitic lava dome is the source of a talus slope.Template:Sfn The summit area is surrounded by an inwards-dropping scarp that opens to the northwest and whose southern margin is buried by lava flows. Pyroclastic flows crop out beneath lava flows in the northwestern segment of the volcano, within the scarp. On the southern and eastern side there are long high cliffs;Template:Sfn the southern scarp is about long in total.Template:Sfn A large wedge-shaped scar is recognizable on the northwestern flank,Template:Sfn delimited by prominent scarps running through the western and northern flanks of the edifice.Template:Sfn The existence of a lake in the summit area within the scarps at an elevation of has been reported.Template:Sfn

A pumice deposit is visible on the northeastern flank.Template:Sfn Lava domes of various shapesTemplate:Sfn are recognizable on the southern and western slopes; lava flows appear mainly on the eastern and northern slopes. The whole edifice has a diameter of and, like many Central Andes volcanoes, is probably made up of lava domes, lava flows and pyroclastic formations.Template:Sfn Its volume is about , making Socompa one of the largest stratovolcanoes with Quaternary activity.Template:Sfn The volcano apparently developed within a northwest-striking valley, the southern part of which now contains Laguna Socompa. This lake lies at an elevation of ; to the north the volcano is bordered by the high Monturaqui basin.Template:Sfn The water table is at depths of , but surface runoff is only ephemeral.Template:Sfn Magnetotelluric investigation has identified a structure at depthTemplate:Sfn which may be Socompa's magma chamber.Template:Sfn

Sector collapse

Socompa suffered a major sector collapse during the Holocene,Template:Sfn forming one of its largest terrestrial deposits.Template:Sfn The deposit left by the collapse was first discovered on aerial photography in 1978 but it was correctly identified as a landslide in 1985;Template:Sfn at first, it was interpreted as a form of moraine, then as a large pyroclastic flowTemplate:Sfn and the scar as a caldera.Template:Sfn Traces of such events are widespread on Central Andean volcanoes;Template:Sfn Socompa's is the largest in the regionTemplate:Sfn and one of the better studied.Template:Sfn

The event removed a 70° sector (about of circumference and of radiusTemplate:Sfn) on Socompa's northwestern side. The landslide descended over a vertical distance of about and spread over distances of over ,Template:Sfn at a modelled speed of c. .Template:Sfn As it descended, the landslide had sufficient energy that it was able to override topographic obstacles and climb over an elevation of about ; secondary landslides occurred on the principal depositTemplate:Sfn and there is evidence that the landslide was reflected back from its margins.Template:Sfn The event occurred in several steps, the first parts to fail ending up at the largest distances from the volcano;Template:Sfn it is not established whether the collapse happened in a single event or as several separate failures.Template:Sfn

The total volume of material removed was about , which was dilated as it flowed and eventually ended up as a deposit with a volume of ;Template:Sfn thorough mixing of the avalanche material occurred as the landslide progressed.Template:Sfn The summit of the volcano was cut by the collapse and some lava domes embedded within the volcano were exposed in the rim of the collapse amphitheatre;Template:Sfn before the collapse the volcano was about high.Template:Sfn

The collapse left a triangle-shaped collapse scarTemplate:Sfn partly filled by leftover blocks. The walls of the amphitheatre were about high, so high that secondary landslides occurred. The largest of these detached from a dome northwest of the summit and descended a horizontal distance of , forming a landslide structure notable in its own right and covering about .Template:Sfn The central section of the collapse amphitheatre was not a simple collapse structure, but instead contained a secondary scarp.Template:Sfn At the mouth of the collapse scar, the walls were lower, about .Template:Sfn After the principal collapse, lava flows and pyroclastic flows – some of which emerge from the western rim of the collapse scar – filled up the scar left by the collapse.Template:Sfn A structure in the scar, named Domo del Núcleo, might either be a remnant of the pre-collapse volcano, or collapse debris.Template:Sfn

The collapse happened about years agoTemplate:Sfn and is estimated to have lasted around 12 minutes, based on simulations.Template:Sfn The growth rate of the volcano increased, in the aftermath probably due to the mass removal unloading the magmatic system.Template:Sfn A similar collapse took place in the 1980 eruption of Mount St. Helens.Template:Sfn Identification of the Socompa deposit as a landslide remnant was made after the occurrence of the large landslide at Mount St. Helens drew more attention to such events.Template:Sfn Other volcanoes have suffered from large-scale collapses as well; this includes Aucanquilcha, Lastarria and Llullaillaco.Template:Sfn In the case of Socompa, the occurrence of the collapse was probably influenced by a northwest tilt of the basement the volcano was constructed on; it caused the volcano to slide downward in its northwestern sector and made it prone to a collapse in that direction.

The precise circumstances leading to the collapse are unknown, although there are several hypotheses.Template:Sfn There is evidence in the deposit that a lava flow was being erupted on the volcano when the landslide occurred,Template:Sfn which together with the presence of pyroclastic fallout on the southwestern side of Socompa implies the event may have been started by volcanic activity. The quantity of water in the edifice rocks was probably minor.Template:SfnTemplate:Sfn Another theory assumes that the volcanic edifice was destabilized by ductile and mechanically weak layers beneath Socompa; under the weight of the volcano these layers can deform and "flow" outward from the edifice, causing the formation of thrusts at its foot.Template:Sfn Evidence of such spreading of the basement under Socompa has been found.Template:Sfn Other potential causes are earthquakes and the intrusion of new magma.Template:Sfn Climatic factors for the Socompa collapse, which have been proposed as triggers for other volcanoes,Template:Sfn are speculative.Template:Sfn

The event released a large amount of energy, about .Template:Sfn Some evidence in the form of tephra suggests that the collapse was accompanied by a lateral blast,Template:Sfn but other research found no such evidence.Template:Sfn Such events are classified as catastrophic phenomena, and the debris avalanches associated with them can reach large distances from the original volcano.Template:Sfn The fragmentation of rocks during the landslide and the fine material generated during this process might enhance the fluidity of the avalanche, allowing it to spread far away from the source.Template:Sfn

Landslide deposit

A number of tongue-like protrusions expand radially from a central point

Socompa from space. The sector collapse deposit lies on the upper part of the image.

The collapse deposit covers a surface area of ,Template:Sfn and is thus not as large as the deposit left by the Mount ShastaTemplate:Sfn or Nevado de Colima collapses.Template:Sfn The deposit forms the Negros de Aras (also a name for the depositTemplate:Sfn) surface northwest of the volcano and the El Cenizal surface due north, where it has a hook-like surface distribution.Template:Sfn The thickness of the deposit varies, with thin segments in the extreme southeastern and southwestern parts being less than thick and the central parts reaching .Template:Sfn

The deposit spreads to a maximum width of and is bounded by levees higher than , which are less prominent on the eastern side.Template:Sfn As later parts of the collapse overrode the earlier segments, they formed a northeast-trending scarp in the deposit, across which there is a striking difference in its surface morphology.Template:Sfn The landslide deposit has been stratigraphically subdivided into two units, the Monturaqui unit and the El Cenizal unit. The first unit forms most of the surface and consists of several subunits, one of which includes basement rocks that were integrated as it occurred.Template:Sfn Likewise, the El Cenizal unit entrained basement rocks such as playa deposits.Template:Sfn The amount of basement material is noticeably large and might form as much as 80% of the landslide volume;Template:Sfn the topography of the northwestern side of the volcano may have prevented the mass failure from being localized along the basement-edifice surface area, explaining the large volume of basement involved.Template:Sfn Further, the basement-derived material was probably mechanically weak and thus allowed the landslide to move over shallow slopes.Template:Sfn This basement material forms part of the white surfaces in the landslide deposit; other bright areas are formed by fumarolically altered material.Template:Sfn The basement material was originally considered to be pumice.Template:Sfn

The landslide deposit contains large blocks, so called toreva blocks, which were torn from the mountain and came to a standstill unmodified, forming ridges up to several hundred metres high;Template:Sfn the largest such blocks are long and wide,Template:Sfn and their total volume is about .Template:Sfn These blocks form an almost closed semicircle at the mouth of the collapse amphitheatre and in part retain the previous stratigraphy of the volcano.Template:Sfn Such toreva blocks are far more frequent in submarine landslides than subaerial ones and their occurrence at Socompa may reflect the relatively non-explosive nature of the collapse and material properties of the collapsed mass.Template:Sfn Aside from the toreva blocks, individual blocks with sizes of up to occur in the deposit and form large boulder fields. As well as the blocks, the surface of the landslide deposit contains hummock-like hills and small topographic depressions.Template:Sfn Part of the landslide deposit was later covered by pyroclastic flows, and this covered area is known as the Campo Amarillo. As it descended, the landslide deposit filled a shallow valley that previously existed northwest of the volcano,Template:Sfn as well as a larger northeast-striking depression.Template:Sfn A lava flow was rafted on the avalanche to the El Cenizal area and ended up there almost unmodified.Template:Sfn

The collapse deposit is well-preserved by the arid climate, among the best-preserved such deposits in the world.Template:Sfn Owing to its sheer size,Template:Sfn its structure and stratigraphy were only appreciated with the help of remote sensing.Template:Sfn Pleistocene lava flows and a northwest-striking drainage were buried by the landslide but can still be discerned from aerial imagery; apart from these and some hills most of the area covered by the landslide was relatively flat.Template:Sfn At La Flexura, part of the basement beneath the avalanche crops out from the ground.Template:Sfn

Geology

File:Estación Socompa.jpg

Socompa as seen from the nearby railway station Socompa

Regional

The volcanism in the Central Volcanic Zone of the Andes results from the subduction of the Nazca Plate beneath the South America Plate in the Peru-Chile Trench at a rate of . Volcanism does not occur across the entire length of the trench, where the slab is subducting beneath the South America Plate at a shallow angle there is no recent volcanic activity.

The style of subduction has changed over time. About 27 million years ago, the Farallon Plate had been subducting beneath South America but broke up and the pace of subduction increased, leading to greater levels of volcanism. Around the same epoch, after the Eocene, the subduction angle increased beneath the Altiplano and caused the development of this plateau either from magmatic underplating and/or from crustal shortening; eventually the crust there became much thicker.

Local

A few black tongues in the middle between orange rocks left and white powdery-appearing rocks right

El Negrillar volcano just north of Socompa. The white area to the right is part of the Socompa landslide deposit.

Socompa forms a northeast-trending alignment with neighbouring volcanoes such as Pular and Pajonales, which reach elevations of about ;Template:Sfn Socompa is their youngest member. The presence of two calderas southeast and east of Socompa has been inferred.Template:Sfn Monogenetic volcanoes were active in the area as well during the Pliocene and Quaternary and generated lava flows.Template:Sfn One of these centres is El Negrillar just north of the collapse deposit,Template:Sfn which was active during the Pleistocene and issued andesite-basaltic andesite lavas unlike the eruption products of Socompa itself.Template:Sfn

A elongated geologic structure (a lineament) known as the Socompa Lineament is associated with the volcano. Other volcanoes such as Cordon de Puntas Negras and the rim of the large La Pacana caldera farther north are also influenced by this lineament. A north-south trending lineament called the Llullaillaco Lineament is also linked to Socompa and to the Mellado volcano farther south.Template:Sfn

To the west Socompa is bordered by the Sierra de Alameida (or Almeida), which farther north merges into the Cordon de Lila. To the east the high Salín volcano neighbours Socompa;Template:Sfn other volcanoes in the area are the Cerro Bayo and the Socompa Cairis,Template:Efn all of which show evidence of glacial activity unlike the younger Socompa.Template:Sfn

Basement

A multicoloured landscape of Chile taken from space

A spaceborne image of the region northwest of Socompa, which is recognizable in the lower right corner

The basement at Socompa is formed by Paleozoic and Mesozoic formations and by Quaternary sedimentary and volcanic rocks. The former crop out in the Sierra de Alameida and Alto del Inca west of Socompa and the latter as the Quebrada Salin Beds east of the volcano. Part of these beds were taken up into the avalanche as it collapsed and form the Flexura inliner,Template:Sfn others appear in the Loma del Inca area north and the Monturaqui area due west of Socompa.Template:Sfn The basement rocks are subdivided into three named formations, the Purilactis Formation of Paleozoic–Mesozoic age, the San Pedro and Tambores formations of Oligocene–Miocene age and the Miocene–Pliocene Salin formation;Template:Sfn part of the latter formation may have been erupted by Socompa itself.Template:Sfn The volcano is at the point where the Sierra de Alameida meets the Puna block.Template:Sfn

During the Pliocene this basement was covered by the Arenosa and Tucucaro ignimbrites (2.5 and 3.2 million years ago by potassium–argon dating, respectivelyTemplate:Sfn) which also crop out west of Socompa; Socompa is probably constructed on top of these ignimbrites.Template:Sfn The Arenosa ignimbrite is about thick, and the Tucucaro reaches a thickness of .Template:Sfn

Some normal faults appear in the area north of Socompa and appear to run through the edifice. Although they are not visible in the edifice itself, Socompa was uplifted on its southeastern side by the fault motion.Template:Sfn This might have aided in the onset of edifice instability and the collapse event.Template:Sfn Directly north-northwest of Socompa lie three anticlinesTemplate:Efn probably formed under the influence of the mass of both Socompa and Pajonales: The Loma del Inca, Loma Alta and La Flexura.Template:Sfn

Composition

Socompa has erupted andesite and dacite,Template:Sfn with dacite dominating. Phenocrysts found in the rocks of the avalanche include the minerals augite, hornblende, hypersthene, magnetite and plagioclase;Template:Sfn dacites also contain biotite, and andesites also contain olivine. In the summit area, hydrothermal alteration took place,Template:Sfn and clay, silt and sulphur bearing rocks are also found.Template:Sfn

Climate and ecology

There are few data on climate at Socompa. The area is windy and dry given that the volcano lies in the Desert Puna, with frequent snow cover,Template:Sfn there are penitentes but no glaciers. The low cloud cover means that insolation is high.Template:Sfn Weather data collected in 1991 found an average temperature of , a large diurnal air temperature cycle (and a larger soil temperature cycle of c. Template:Sfn) and low evaporation.Template:Sfn The present-day precipitation has been estimated to be ,Template:Sfn with other estimates assuming less than .Template:Sfn Periglacial landforms indicate that in the past the area was wetter, possibly thanks to the Little Ice Age.Template:Sfn The last ice age in the region ended 12,000-10,000 years ago;Template:Sfn there is no evidence for Pleistocene glaciation on Socompa, including no cirques, which may be due to the volcano's young age.

Socompa features autotrophic communities associated with fumaroles and thermal anomalies at high altitude, between of elevation.Template:Sfn The autotrophic communities on Socompa are the highest known in the world,Template:Sfn and they occur both on the actual fumaroles, on "cold fumaroles"Template:Sfn and at a few metres from the vents. The different species are often extremophiles since the environment on Socompa is harsh,Template:Sfn and the communities also include heterotrophic species.Template:Sfn Such heterotrophs include ascomycota and basidiomycota, the latter of which are similar to Antarctic basidiomycota.Template:Sfn

The fumaroles on Socompa also feature stands of bryophytes such as liverworts and mossesTemplate:Efn as well as lichens and algae, and animals have been found in the stands.Template:SfnTemplate:Sfn These stands are among the highest in the world and cover noticeably large surface areas despite their elevation,Template:Sfn and are fairly remote from other plant life in the region.Template:Sfn There is a noticeable diversity between separate stands, and the vegetation is quite dissimilar to the vegetation in the surroundings but resembles that found in the paramo and cloud forests in South America and the subantarctic islands.Template:Sfn A sparse vegetation cover is also found on the lower slopes of Socompa.Template:Sfn The black-headed lizard and its relative Liolaemus porosus live on its slopes,Template:Sfn and mice have been observed in the summit area.

Eruptive history

Activity at Socompa commenced with the extrusion of andesites, which were followed later by dacites.Template:Sfn Several Plinian eruptions have occurred from Socompa;Template:Sfn one Holocene eruption reached a volcanic explosivity index of 5.Template:Sfn Several dates have been obtained on rocks, including 2,000,000 ± 1,000,000, 1,300,000 ± 500,000, 800,000 ± 300,000, and less than 500,000 years ago. An age of 3,340,000 ± 600,000 years may be of an older volcano, now buried beneath the Socompa edifice.Template:Sfn Lava domes and lava flows on the southern side of the volcano have yielded ages of 69,200 ± 6,000, 31,400 ± 3,200, 29,800 ± 3,300 and 22,100 ± 1,900 years ago.Template:Sfn An eruption 7,220 ± 100 years before present produced the El Túnel pyroclastic deposit on the western side of Socompa.Template:Sfn After the sector collapse 7,200 years ago, activity continued filling the collapse scar. The explosion craters on the summit are the youngest volcanic landforms on Socompa. One dome in the scar has been dated to 5,910 ± 430 years ago;Template:Sfn the Global Volcanism Program gives 5,250 BCE as the date of the last eruption.Template:Efn

The absence of moraines on Socompa suggests that volcanic activity occurred during post-glacial time.Template:Sfn The volcano also has a young appearance, similar to historically active Andean volcanoes such as San Pedro, implying recent volcanic activity.Template:Sfn

There is no evidence for historical activity at SocompaTemplate:Sfn and the volcano is not considered an active volcano,Template:Sfn but both fumarolic activity and the emission of carbon dioxide have been observed.Template:Sfn The fumarolic activity occurs at at least six sites and is relatively weak;Template:Sfn anecdotal reports indicate a smell of sulphur on the summit. Uplift of the edifice began inTemplate:Sfn November 2019 and was ongoing since October 2021Template:Dated maintenance category (articles),Template:Sfn and could be caused by the arrival of new magma.Template:Sfn since 2023Template:Dated maintenance category (articles) there is no ground-based monitoring of the volcano.Template:Sfn

Socompa is considered to be a high-risk volcano;Template:Sfn a 2021 survey labelled it Argentina's 13th most dangerous volcano out of 38. The area is only thinly populated,Template:Sfn and apart from the Socompa railway station and mining camps west of the volcano, there is little infrastructure that could be impacted by future eruptions. Large explosive eruptions during summer may result in pyroclastic fallout west of the volcano; during the other seasons fallout would be concentrated east of it.

Groundwater is warmer and richer in carbon dioxide the closer to Socompa it is pumped, also suggesting that volcanic gas fluxes still occur at the volcanoTemplate:Sfn and that the volcano influences groundwater systems. Hot springs are found at Laguna Socompa as well.Template:Sfn In 2011, the copper mining company Minera Escondida was considering building a geothermal power plant on Socompa to supply energy; the Argentine Servicio Geológico Minero agency started exploration work in January 2018 for geothermal power production.

References

Sources

• Template:Cite report
• Template:Cite report
• Template:Cite report

External links

• "Volcán Socompa, Argentina/Chile" on Peakbagger