Socompa is a large
complexA complex volcano, also called a compound volcano, is a volcano with more than one feature. They form because changes of their eruptive characteristics or the location of multiple vents in an area...
stratovolcanoA stratovolcano, also known as a composite volcano, is a tall, conical volcano built up by many layers of hardened lava, tephra, pumice, and volcanic ash. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile and periodic, explosive eruptions...
at the border of
ArgentinaArgentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...
and
ChileChile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...
. It is best known for its large debris avalanche deposit, which is widely accepted as the best-preserved example of this type of deposit in the world, and also notable as the home of the world's most elevated known microbial ecosystems.
The western rim of the volcano borders the Monturaqui Basin, which is draped with the aforementioned deposit.
Escondida MiningMinera Escondida, which means 'hidden' in Spanish, is a mining company that operates two open pit copper mines in the Atacama Desert, 170 km southeast of Antofagasta in northern Chile. It is currently the highest producing copper mine in the world...
currently has a network of roads throughout this area, from beneath which they pump ground water for use at the nearby copper mine. The southern margin of the deposit is bordered by the
AntofagastaAntofagasta is a port city in northern Chile, about north of Santiago. It is the capital of Antofagasta Province and Antofagasta Region. According to the 2002 census, the city has a population of 296,905...
to
SaltaSalta is a city in northwestern Argentina and the capital city of the Salta Province. Along with its metropolitan area, it has a population of 464,678 inhabitants as of the , making it Argentina's eighth largest city.-Overview:...
trans-Andean railway, although this is rarely used.
The volcano is difficult to reach - either from the north along dirt tracks south of the Miscanti Pass, or from the west via the Escondida copper mine. Both routes require a full-day's driving and for any reasonable amount of time to be spent at Socompa would need significant planning.
Socompa debris avalanche deposit
The Socompa deposit contains many features that are expected from a debris avalanche, including large-volume, rotated and slumped
toreva blockA Toreva block landslide is a distinctive landslide type which may occur when a stronger material such as sandstone or limestone overlies a weaker material such as shale and an eroding agent undercuts the weaker lower layer. The type was first recognized by Parry Reiche in 1937, and takes its name...
s and hummocky topography. There is also evidence for a
magmaMagma is a mixture of molten rock, volatiles and solids that is found beneath the surface of the Earth, and is expected to exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and dissolved gas and sometimes also gas bubbles. Magma often collects in...
tic component (
BezymiannyBezymianny is an active stratovolcano in Kamchatka, Russia. Prior to its noted 1955-56 eruption, Bezymianny volcano had been considered extinct...
-type collapse) from the breadcrust texture of large dacitic blocks and a thin pyroclastic flow deposit. A large amphitheatre, open at 70° and 10 km wide at its mouth, marks the site of collapse on the remaining edifice. Since the failure, which occurred some 7000 years ago, this has been partially filled by subsequent lavas and pyroclastics.
The deposit's most striking aspects are its volume, deposition and composition. It has a volume of 25 km² (10 sq mi)—around an order of magnitude greater than the Mount St. Helens collapse—
in addition to 11 km² (4 sq mi) of toreva blocks at the mouth of the amphitheatre. These dimensions set it apart from most other known terrestrial debris avalanches.
While a significant component of the deposit clearly originates from the ancestral Socompa edifice, there are also large amounts of
ignimbriteAn ignimbrite is the deposit of a pyroclastic density current, or pyroclastic flow, a hot suspension of particles and gases that flows rapidly from a volcano, driven by a greater density than the surrounding atmosphere....
and
gravelGravel is composed of unconsolidated rock fragments that have a general particle size range and include size classes from granule- to boulder-sized fragments. Gravel can be sub-categorized into granule and cobble...
s which have been shown to have come from the
substrataSubstrata may refer to:*Substrata , plural of substratum, a language influenced by another*Substrata , another term for subsoil*Substrata , an ambient music album by Biosphere-See also:*Substratum...
immediately below Socompa, and which make up the bulk (80%) of the deposit by volume. Despite originating at the lowest part of the failure zone, these units travelled the furthest distance and are found at the base of the deposit. The avalanche travelled down the regional slope for part of its course before mounting at least 250 m (820 ft) of topography near to its distal end, suggesting a high speed of emplacement, low
frictionFriction is the force resisting the relative motion of solid surfaces, fluid layers, and/or material elements sliding against each other. There are several types of friction:...
and great mobility. There was also considerable remobilisation of the deposits and secondary flowage after the initial deposition, creating the lobe which was channeled northwards under gravity towards the Monturaqui Basin.
The large volume and stratification of the deposit suggests that the failure was not merely the result of slope failure of the volcanic cone. Structural evidence has been interpreted by van Wyk de Vries et al (2001) to suggest that prior to the failure, the weak underlying substrata had been spreading under the load of the volcano. The remnants of
thrustThrust is a reaction force described quantitatively by Newton's second and third laws. When a system expels or accelerates mass in one direction the accelerated mass will cause a force of equal magnitude but opposite direction on that system....
anticlineIn structural geology, an anticline is a fold that is convex up and has its oldest beds at its core. The term is not to be confused with antiform, which is a purely descriptive term for any fold that is convex up. Therefore if age relationships In structural geology, an anticline is a fold that is...
s at
La Flexura, west of the collapse amphitheatre, delineate the western edge of this spreading zone. The suggestion is that the deforming substrata suffered catastrophic failure as a result of gravitational spreading and was ejected to the northwest on the collapse of the basal anticlines. The substrata then formed the lower horizon of the debris avalanche, upon which the remainder of the edifice was carried and deposited. As a consequence, the large volume, high fluidity and stratification of the deposit can be explained.
Prior to the
1980 eruption of Mount St. HelensThe 1980 eruption of Mount St. Helens, a stratovolcano located in Washington state, in the United States, was a major volcanic eruption. The eruption was the only significant one to occur in the contiguous 48 U.S. states since the 1915 eruption of Lassen Peak in California...
, many debris avalanches were misinterpreted, and the Socompa deposit was initially linked to
pyroclastic flowA pyroclastic flow is a fast-moving current of superheated gas and rock , which reaches speeds moving away from a volcano of up to 700 km/h . The flows normally hug the ground and travel downhill, or spread laterally under gravity...
products of a cataclysmic eruption. It was first recognised as resulting from volcano collapse by Peter Francis and others in 1985, when they described the major features and reclassified it as a debris avalanche deposit. Subsequent works studied the deposit itself in more detail.
Ecology of Socompa
In the 1980s, Stephan Halloy discovered patches of plant communities (primarily mosses and liverworts) near Socompa's rim. In 2009 a research team from the University of Colorado at Boulder showed that Socompa is also home to bacterial ecosystems that are sustained by gasses from volcanic vents. With respect to elevation, these are the highest known microbial ecosystems in the world.