Tocorpuri is a volcano in Chile, close to the border with Bolivia. Its peak height is most recently given as and it features a wide summit crater. The volcano consists mainly of

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 pyroclastic deposits and is subdivided into two separate edifices. Just west of Tocorpuri, the La Torta lava dome is a high flat-topped structure. The volcanoes are formed by

andesitic 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 predomin ...

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 ...

and

rhyolitic Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained groundmass. The mineral ...

rocks. The Tocorpuri volcanoes developed in the late

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 ...

in three separate stages and were subject to

glaciation 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 be ...

and tectonic

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 ...

. The most recent eruption generated the La Torta lava dome 34,000 ± 7,000 years ago; presently there is geothermal activity which may be connected to that of the neighbouring El Tatio geothermal field.

Geomorphology

Tocorpuri lies in northern Chile, about east of Calama. The border with Bolivia runs around the eastern side of Tocorpuri's summit crater. The area lies in Chile's Antofagasta Department and on Bolivia's Sur Lipez Department and a

pre-Hispanic In the history of the Americas, the pre-Columbian era spans from the original settlement of North and South America in the Upper Paleolithic period through European colonization, which began with Christopher Columbus's voyage of 1492. Usually, th ...

road connecting the Bolivian

Altiplano The Altiplano (Spanish for "high plain"), Collao (Quechua and Aymara: Qullaw, meaning "place of the Qulla") or Andean Plateau, in west-central South America, is the most extensive high plateau on Earth outside Tibet. The plateau is located at the ...

with the

San Pedro de Atacama San Pedro de Atacama is a Chilean town and commune in El Loa Province, Antofagasta Region. It is located east of Antofagasta, some 106 km (60 mi) southeast of Calama and the Chuquicamata copper mine, overlooking the Licancabur volcano. ...

region passes south of the volcano. This road system is considered to be the oldest in Chile, was in use since the

Formative Period Several chronologies in the archaeology of the Americas include a Formative Period or Formative stage etc. It is often sub-divided, for example into "Early", "Middle" and "Late" stages. The Formative is the third of five stages defined by Gord ...

. The name comes from the

Kunza language Kunza is an extinct language isolate once spoken in the Atacama Desert of northern Chile and southern Peru by the Atacama people, who have since shifted to Spanish. The last speaker was documented in 1949. Other names and spellings include C ...

, is also known as Michina, Cerro de Tocorpuri Cerros de Tocorpuri or Volcán Tocorpuri. Tocorpuri volcano is a complex of three different edifices. East Tocorpuri is high and rises around the surrounding terrain. A large, slightly elongated wide summit crater caps the summit. From Tocorpuri's summit, the

Salar de Atacama Salar de Atacama is the largest salt flat in Chile. It is located south of San Pedro de Atacama, is surrounded by mountains, and has no drainage outlets. In the east it is enclosed by the main chain of the Andes, while to the west lies a secondar ...

salt flat and the

Chuquicamata mine Chuquicamata ( ; referred to as Chuqui for short) is the largest open pit copper mine in terms of excavated volume in the world. It is located in the north of Chile, just outside Calama, at above sea level. It is northeast of Antofagasta and ...

, the largest

copper mine Copper extraction refers to the methods used to obtain copper from its ores. The conversion of copper consists of a series of physical and electrochemical processes. Methods have evolved and vary with country depending on the ore source, loca ...

in the world, are visible. Sulfur deposits can be found in the summit region and were mined in the past. Other craters are heavily eroded and old, eroded lava flows occur on the southern flank, with younger, smaller flows present in the summit region. West Tocorpuri consists mainly of blocky lava flows which are particularly noticeable on the western side while East Tocorpuri consists of lava flows, pyroclastic deposits and

tuff Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock ...

-like

breccia Breccia () is a rock composed of large angular broken fragments of minerals or rocks cemented together by a fine-grained matrix. The word has its origins in the Italian language, in which it means "rubble". A breccia may have a variety of ...

. There is evidence of a southeastward

sector collapse A sector collapse is the collapse of a portion of a volcano due to a phreatic eruption, an earthquake, or the intervention of new magma. Occurring on many volcanoes, sector collapses are generally one of the most hazardous volcanic events, and will ...

of Tocorpuri, which crops out on an area of on the southeastern flank within a horseshoe-shaped scar. Tocorpuri is part of the main volcanic chain of the border region between Chile and Bolivia. The La Torta ("cake" in

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 ...

) lava dome is located between the Tocorpuri volcano to the east and Tatio volcano to the west. It is a flat-topped, about high body with steep flanks that covers a surface of about in a flat area. Its flanks are covered with

scree Scree is a collection of broken rock fragments at the base of a cliff or other steep rocky mass that has accumulated through periodic rockfall. Landforms associated with these materials are often called talus deposits. Talus deposits typically ...

, while its top features flow folds and wrinkles. The dome reaches an elevation of . Two separate vents and two different geologic units are discernible. It and Tocorpuri, which are distant from each other, have been described as a volcano pair, whose existence may be a consequence of tectonics.

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 ...

erosion has cut into the flanks of the volcanoes, with moraines and

mudflow A mudflow or mud flow is a form of mass wasting involving fast-moving flow of debris that has become liquified by the addition of water. Such flows can move at speeds ranging from 3 meters/minute to 5 meters/second. Mudflows contain a significa ...

deposits covering the foot of La Torta and cirques and

glacial striation Glacial striations or striae are scratches or gouges cut into bedrock by glacial abrasion. These scratches and gouges were first recognized as the result of a moving glacier in the late 18th century when Swiss alpinists first associated them w ...

s occurring on the Tocorpuri volcanoes. In the past, a

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 ...

filled the crater of Tocorpuri. South of La Torta, moraines extending from East Tocorpuri extend south-southwestward. Between Tatio and La Torta, there are two tongues of moraines side-by-side. The moraines from the western valley have overrun the eastern valley moraines and are accompanied by thin

drift Drift or Drifts may refer to: Geography * Drift or ford (crossing) of a river * Drift, Kentucky, unincorporated community in the United States * In Cornwall, England: ** Drift, Cornwall, village ** Drift Reservoir, associated with the village ...

deposits. These moraines have been dated by

surface exposure dating Surface exposure dating is a collection of geochronological techniques for estimating the length of time that a rock has been exposed at or near Earth's surface. Surface exposure dating is used to date glacial advances and retreats, erosion histo ...

: They formed during the regional last glacial maximum and by about 30,700 years ago the western glaciers were gone. Erosional debris covers the flanks of Tocorpuri.

Climate and hydrology

The region has a high-altitude steppe climate with a low mean temperature of and a diurnal temperature range of . Annual precipitation on the summit has been estimated to exceed , while about fall every year south of Tocorpuri. Most of it occurs during summer as

convective precipitation In meteorology, the different types of precipitation often include the character, formation, or phase of the precipitation which is falling to ground level. There are three distinct ways that precipitation can occur. Convective precipitation is g ...

. Snow has been observed on the summit, and a 1985 map displays a persistent ice/snow cover there. The Putana River south of Tocorpuri flows towards the Salar de Atacama and receives important tributaries from the Tocorpuri area, such as Quebrada La Torta, Rio Blanco o Tocorpuri and Quebrada Agua Brava.

Geology

Off the western coast of South America, the Nazca Plate

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. This subduction process is responsible for volcanism in most of the

Andean Volcanic Belt The Andean Volcanic Belt is a major volcanic belt along the Andean cordillera in Argentina, Bolivia, Chile, Colombia, Ecuador, and Peru. It is formed as a result of subduction of the Nazca Plate and Antarctic Plate underneath the South American ...

, which consists of the Northern Volcanic Zone (NVZ), the Central Volcanic Zone (CVZ), the

South Volcanic Zone The Andean Volcanic Belt is a major volcanic belt along the Andean cordillera in Argentina, Bolivia, Chile, Colombia, Ecuador, and Peru. It is formed as a result of subduction of the Nazca Plate and Antarctic Plate underneath the South American ...

(SVZ) and the Austral Volcanic Zone (AVZ). Tocorpuri is part of the CVZ. The Altiplano-Puna volcanic complex (APVC) has been episodically active between 10 and 1 million years ago. Surges in activity took place 8, 6 and 4 million years ago; since 2.6 million years ago activity has declined. In the late

, the lava domes Cerro Chanka,

Cerro Chao Cerro Chao is a lava flow complex associated with the Cerro del León volcano in the Andes. It is the largest known Quaternary silicic volcano body and part of the most recent phase of activity in the Altiplano–Puna volcanic complex. Cerro Chao ...

, Cerro Chascon-Runtu Jarita complex,

Chillahuita Chillahuita is a dacitic lava dome in northern Chile. It may have formed after the Pleistocene, although argon-argon dating on amphibole has indicated an age of 370,000 ±40,000 years. It has an altitude of about . It formed in a single non- exp ...

and Tocorpuri were emplaced around 100,000–90,000 years ago. The total volume of these domes exceeds , of which Cerro Chao is by far the largest. These domes are part of a northwest–southeast alignment that is associated with the margin of the Pastos Grandes caldera. Volcanism today is focused on the arc and is mainly

, having built numerous volcanic cones. The formation of a batholith under the APVC may be ongoing. Most of the region is covered by

Tertiary Tertiary ( ) is a widely used but obsolete term for the geologic period from 66 million to 2.6 million years ago. The period began with the demise of the non-avian dinosaurs in the Cretaceous–Paleogene extinction event, at the start ...

ignimbrite Ignimbrite is a type of volcanic rock, consisting of hardened tuff. Ignimbrites form from the deposits of pyroclastic flows, which are a hot suspension of particles and gases flowing rapidly from a volcano, driven by being denser than the surro ...

s, except for the area at the frontier between Bolivia and Chile which features Quaternary volcanics; the pre-ignimbrite basement crops out only farther west. These ignimbrites were produced by eruptions in the APVC. Geologic

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 ...

s have influenced the development of the volcanoes, including that of Tocorpuri, and La Torta formed at the end of a

thrust fault A thrust fault is a break in the Earth's crust, across which older rocks are pushed above younger rocks. Thrust geometry and nomenclature Reverse faults A thrust fault is a type of reverse fault that has a dip of 45 degrees or less. If ...

that may have served as the path of ascent of magma.

Composition

The volcanic rocks of Tocorpuri consist of

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 ...

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 ...

and rhyolite and define a

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

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 ...

suite.

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 include biotite,

clinopyroxene The pyroxenes (commonly abbreviated to ''Px'') are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. Pyroxenes have the general formula , where X represents calcium (Ca), sodium (Na), iron (Fe I ...

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 ...

, orthopyroxene and

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 ...

and differ between the various rocks. An origin through fractional crystallization has been proposed. The volcanic rocks in the summit region are

hydrothermal Hydrothermal circulation in its most general sense is the circulation of hot water (Ancient Greek ὕδωρ, ''water'',Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon. revised and augmented throughout by Sir Henry Stuart Jones. with th ...

ly altered. The crystal-rich

composition of La Torta resembles that of the other APVC lava domes.

Hydrothermal system

Tocorpuri is reported to be

solfataric 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 ...

ally active, and 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, gas seeps and bubbling pools at elevation north of La Torta. The El Tatio and Sol de Manana geothermal fields lie north and east of Tocorpuri, respectively, and Trujillo-Ramírez 1974 reported additional manifestations south of Tocorpuri. El Tatio may receive its heat flux from a heat reservoir under La Torta. Geotérmica del Norte, a consortium between the companies

ENEL Enel S.p.A. is an Italian multinational manufacturer and distributor of electricity and gas. Enel, which originally stood for Ente nazionale per l'energia elettrica (National Electricity Board), was first established as a public body at the ...

and the

Empresa Nacional del Petróleo Empresa Nacional del Petróleo, or ENAP (English: ''National Petroleum Company'') is a state-owned company in Chile, based in Las Condes. The company is engaged in the exploration, production, refining, and marketing of hydrocarbons and their deri ...

, holds concessions for geothermal power prospecting in the El Tatio-La Torta area.

Geologic history

Volcanism in the area commenced 800,000 years ago. Tocorpuri formed in four stages, the first two built the two Tocorpuri volcanoes, the third produced lava flows emanating from fissure vents on Tocorpuri's southern and northwestern flank and the fourth the La Torta dome. Déruelle 1979 inferred that East Tocorpuri was more recent than La Torta or West Tocorpuri. Between the two stages of volcanic activity, the edifices were tectonically deformed.

Thrust Thrust is a reaction force described quantitatively by Newton's third law. When a system expels or accelerates mass in one direction, the accelerated mass will cause a force of equal magnitude but opposite direction to be applied to that sys ...

s and

normal fault 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 tecton ...

s have offset Pliocene to Quaternary deposits around and on Tocorpuri, including in the summit region and the summit crater.

La Torta

Ages of less than one million years ago and of 101,000 years ago have been reported. A

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 ...

age was inferred from the fact that on its southeastern flank, La Torta overlies late Pleistocene moraines. Argon-argon dating eventually yielded an age of 34,000 ± 7,000 years ago. The La Torta lava dome was emplaced through an effusive eruption that commenced with weak explosive activity; it appears to have formed through a single event. It is not clear whether volcanism at La Torta and the other lava domes is a relic of the previous activity of the APVC or the beginning of a new magmatic cycle. La Torta has been mentioned as a possible vent of the 700,000 years old Tatio ignimbrite, whose actual vent is probably buried under the Tatio volcanoes.

Notes

References

Sources

* * * * * * *

External links

* * {{Andean volcanoes Volcanoes of Antofagasta Region Volcanoes of Potosí Department Stratovolcanoes of Chile Complex volcanoes Pleistocene stratovolcanoes