Purupuruni is a group of

lava dome 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 eruptions ...

s in southern

Peru Peru, officially the Republic of Peru, is a country in western South America. It is bordered in the north by Ecuador and Colombia, in the east by Brazil, in the southeast by Bolivia, in the south by Chile, and in the south and west by the Pac ...

and a correlative geological formation. They are among the many volcanoes that exist in Peru and whose activity has been associated with the

subduction Subduction is a geological process in which the oceanic lithosphere and some continental lithosphere is recycled into the Earth's mantle at the convergent boundaries between tectonic plates. Where one tectonic plate converges with a second p ...

of the

Nazca Plate The Nazca plate or Nasca plate, named after the Nazca region of southern Peru, is an oceanic list of tectonic plates, tectonic plate in the eastern Pacific Ocean basin off the west coast of South America. The ongoing subduction, along the Peru– ...

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- ...

. Purupuruni is associated with a geothermal field and a

caldera A caldera ( ) is a large cauldron-like hollow that forms shortly after the emptying of a magma chamber in a volcanic eruption. An eruption that ejects large volumes of magma over a short period of time can cause significant detriment to the str ...

. Volcanic activity occurred during the

Pleistocene The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...

53,000 ± 8,000 years ago but also during the

Holocene The Holocene () is the current geologic time scale, geological epoch, beginning approximately 11,700 years ago. It follows the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene to ...

about 5,300 ± 1,100 years ago; today the volcano is considered to be a low hazard volcano but is being monitored nevertheless.

Geography and geomorphology

Purupuruni lies in the Cordillera Occidental north of the border with

Chile Chile, officially the Republic of Chile, is a country in western South America. It is the southernmost country in the world and the closest to Antarctica, stretching along a narrow strip of land between the Andes, Andes Mountains and the Paci ...

, about away from

Tacna Tacna, officially known as San Pedro de Tacna, is a city in southern Peru and the regional capital of the Tacna Region. A very commercially active city, it is located only north of the border with Arica y Parinacota Region from Chile, inland f ...

and only about from the town of Tarata. The volcano is part of the

geopark A geopark is a protected area with internationally significant geology within which Sustainability, sustainable development is sought and which includes tourism, conservation, education and research concerning not just geology but other relevant s ...

. The term means dung in

Aymara Aymara may refer to: Languages and people * Aymaran languages, the second most widespread Andean language ** Aymara language, the main language within that family ** Central Aymara, the other surviving branch of the Aymara(n) family, which today ...

. The Purupuruni volcano, also known as Purupurini, is a wide complex of four large

s at an elevation of or . The domes cover an area of about , are up to - high and are isolated and little eroded. The domes are accompanied by

intrusions In geology, an igneous intrusion (or intrusive body or simply intrusion) is a body of Intrusive rock, intrusive igneous rock that forms by crystallization of magma slowly cooling below the surface of the Earth. Intrusions have a wide variety o ...

and

lava Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a Natural satellite, moon onto its surface. Lava may be erupted at a volcano or through a Fissure vent, fractu ...

and

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 ...

deposits. The volcanism appears to come from

fissure vent A fissure vent, also known as a volcanic fissure, eruption fissure or simply a fissure, is a linear volcanic vent through which lava erupts, usually without any explosive activity. The vent is often a few metres wide and may be many kilo ...

s and the volcanoes have been affected by faulting, such as the Pacollo fault. These deposits reach thicknesses of and also occur on neighbouring volcanic centres. Purupuruni has formed on the rim of a depression, which is surrounded by eroded

Quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS), as well as the current and most recent of the twelve periods of the ...

volcanoes and appears to be a wide

southwest of the domes. The volcano lies east-southeast from

Yucamane Yucamane, Yucamani or Yucumane is an andesitic stratovolcano in the Tacna Region of southern Peru. It is part of the Peruvian segment of the Central Volcanic Zone, one of the three volcanic belts of the Andes generated by the subduction of the N ...

volcano and just south of the

Mauri River The Mauri River is a river of Bolivia and Peru. It rises on the frontier between Chile and Bolivia near Charaña and flows east-northeast for about 100 km where it joins the Desaguadero. In fact the Mauri is much larger than the Desaguadero ...

; the Mauri River is part of the

Lake Titicaca Lake Titicaca (; ; ) is a large freshwater lake in the Andes mountains on the border of Bolivia and Peru. It is often called the highest navigable lake in the world. Titicaca is the largest lake in South America, both in terms of the volume of ...

watershed. The Borateras

geothermal Geothermal is related to energy and may refer to: * Geothermal energy, useful energy generated and stored in the Earth * Geothermal activity, the range of natural phenomena at or near the surface, associated with release of the Earth's internal he ...

field with about 40 separate manifestations is associated with Purupuruni and neighbouring volcanoes such as Coverane and Jaruma across the Mauri River and west from Purupuruni respectively. The Borateras field is used as a

spa A spa is a location where mineral-rich spring water (sometimes seawater) is used to give medicinal baths. Spa health treatments are known as balneotherapy. The belief in the curative powers of mineral waters and hot springs goes back to pre ...

at the Calachaca spa. The landscape is relatively dry and cold and thus vegetation is scarce.

Geology

The volcanic rocks are mainly

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 predomina ...

and

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 rhyolite. ...

, and contain

amphibole Amphibole ( ) is a group of inosilicate minerals, forming prism or needlelike crystals, composed of double chain tetrahedra, linked at the vertices and generally containing ions of iron and/or magnesium in their structures. Its IMA symbol is ...

biotite Biotite is a common group of phyllosilicate minerals within the mica group, with the approximate chemical formula . It is primarily a solid-solution series between the iron- endmember annite, and the magnesium-endmember phlogopite; more al ...

olivine The mineral olivine () is a magnesium iron Silicate minerals, silicate with the chemical formula . It is a type of Nesosilicates, nesosilicate or orthosilicate. The primary component of the Earth's upper mantle (Earth), upper mantle, it is a com ...

plagioclase Plagioclase ( ) is a series of Silicate minerals#Tectosilicates, tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continu ...

and

pyroxene The pyroxenes (commonly abbreviated 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 ions of calcium (Ca), sodium (Na), iron ( ...

and are among the most differentiated volcanics in the area. They are part of the wider "Purupurini Volcanics", which are named after Purupuruni and also form other volcanoes in the region.

Geological context

Rock formations in the region include the

Mesozoic The Mesozoic Era is the Era (geology), era of Earth's Geologic time scale, geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceous Period (geology), Periods. It is characterized by the dominance of archosaurian r ...

Yura Group sediments, the Toquepala

intrusive rock Intrusive rock is formed when magma penetrates existing rock, crystallizes, and solidifies underground to form ''Igneous intrusion, intrusions'', such as batholiths, dike (geology), dikes, Sill (geology), sills, laccoliths, and volcanic necks.I ...

s, the 30-24 million years old Tacaza volcanic rocks, the 24-10 million years old Huaylillas volcanic rocks and the 10-3 million years old Barroso volcanic rocks; Purupuruni is considered to be part of this Barroso formation. Purupuruni and neighbouring volcanic centres have formed on the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

sedimentary basement. Volcanism in Peru occurs mainly in the southern part of the country, where there are about 300 separate volcanic systems including

El Misti Misti is a dormant volcano located in the Andes mountains in southern Peru, rising above Peru's second-largest city, Arequipa. It is a conical volcano with two nested summit craters, the inner one of which contains a volcanic plug or lava dome ...

Ubinas Ubinas is an active stratovolcano in the Moquegua Region of southern Peru, approximately east of the city of Arequipa. Part of the Central Volcanic Zone of the Andes, it rises above sea level. The volcano's summit is cut by a and caldera, w ...

Ticsani Ticsani is a volcano in Peru northwest of Moquegua and consists of two volcanoes ("Old Ticsani" and "Modern Ticsani") that form a complex. "Old Ticsani" is a compound volcano that underwent a large collapse in the past and shed of mass down the ...

Sabancaya Sabancaya is an active stratovolcano in the Andes of southern Peru, about northwest of Arequipa. It is considered part of the Central Volcanic Zone of the Andes, one of the three distinct volcanic belts of the Andes. The Central Volcanic Zone i ...

and

Huaynaputina Huaynaputina ( ; ) is a volcano in a volcanic high plateau in southern Peru. Lying in the Central Volcanic Zone of the Andes, it was formed by the subduction of the oceanic Nazca Plate under the continental South American Plate. Huaynaputina ...

. In the

Tacna Region Tacna (; Aymara language, Aymara and Quechuan languages, Quechua: ''Taqna'') is the southernmost Regions of Peru, department and Regional Government of Tacna, region in Peru. The Chilean Army occupied the present-day Tacna Department during the W ...

of Peru alone there are over 60 separate volcanoes, two of which,

Tutupaca Tutupaca is a volcano in the region of Tacna in Peru. It is part of the Peruvian segment of the Central Volcanic Zone, one of several volcanic belts in the Andes. Tutupaca consists of three overlapping volcanoes formed by lava flows and lava do ...

and Yucamane, have been active in historical time. In addition, there are a number of geothermal systems with temperatures of over which could be used to produce

geothermal energy Geothermal energy is thermal energy extracted from the crust (geology), crust. It combines energy from the formation of the planet and from radioactive decay. Geothermal energy has been exploited as a source of heat and/or electric power for m ...

. Volcanic and geothermal activity in the region is a consequence of the

of the

beneath the

at a rate of about .

Geologic history

The volcanic centres in the area including Purupuruni are of

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 ...

Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58Pleistocene The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...

age. Purupuruni formed during the last 100,000 years and appears to have developed between two

interglacial An interglacial period (or alternatively interglacial, interglaciation) is a geological interval of warmer global average temperature lasting thousands of years that separates consecutive glacial periods within an ice age. The current Holocene i ...

s; fission-track dating on glasses from Purupuruni has yielded ages of 53,000 ± 8,000 years ago but more recent

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 hist ...

has yielded an age of 5,300 ± 1,100 years before present on one of the southern domes. The volcano is considered to be a low-hazard system and in 2018 the Peruvian Geological Institute announced it would begin monitoring Purupuruni and nine other volcanoes. Earthquake swarms in 2020 and 2021 do not appear to have been caused by volcanism; they are instead linked to local fault activity. Purupuruni appears to be the heat source for the Kovire geothermal field.

Glacial A glacier (; or ) is a persistent body of dense ice, a form of rock, that is constantly moving downhill under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires ...

erosion took place on Purupuruni during the Pleistocene, leaving

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 on the domes although research published in 2019 has found that the domes have not been eroded by glaciers even though evidence of glaciation occurs in the wider area.

Alluvial Alluvium (, ) is loose clay, silt, sand, or gravel that has been deposited by running water in a stream bed, on a floodplain, in an alluvial fan or beach, or in similar settings. Alluvium is also sometimes called alluvial deposit. Alluvium is ...

, glacial and

fluvial A river is a natural stream of fresh water that flows on land or inside caves towards another body of water at a lower elevation, such as an ocean, lake, or another river. A river may run dry before reaching the end of its course if it ru ...

deposits occur in the region, with aeolian sediments consisting of

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

mantling the volcanic structures.

References

Sources

* * * * * * * * * {{Andean volcanoes Five-thousanders of the Andes Mountains of the Department of Tacna Holocene volcanoes