Purupuruni lies in the Cordillera Occidental^[2] 48 kilometres (30 mi) north of the border with Chile,^[3] about 85 kilometres (53 mi) away from Tacna^[4] and only about 70 kilometres (43 mi) from the town of Tarata.^[5] The volcano is part of the Monumento Natural de Los Volcanes de Mauri geopark.^[6] The term Phuru means dung in Aymara.^[7]

The Purupuruni volcano, also known as Purupurini,^[4] is a 0.85 kilometres (0.53 mi) wide complex^[8] of four large lava domes at an elevation of 5,117 metres (16,788 ft)^[4] or 5,315 metres (17,438 ft).^[3] The domes cover an area of about 3.5–7 square kilometres (1.4–2.7 sq mi),^[4] are up to 200 metres (660 ft) high^[9] and are isolated and little eroded.^[10] The domes are accompanied by intrusions^[4] and lava and pyroclastic flow deposits.^[8]

The volcanism appears to come from fissure vents^[11] and the volcanoes have been affected by faulting.^[8] These deposits reach thicknesses of 10 metres (33 ft) and also occur on neighbouring volcanic centres.^[9] Purupuruni has formed on the rim of a depression, which is surrounded by eroded Quaternary volcanoes and appears to be a 13 kilometres (8.1 mi) wide caldera^[4] southwest of the domes.^[12] The volcano lies east-southeast from Yucamane volcano and just south of the Mauri River;^[13] the Mauri River is part of the Lake Titicaca watershed.^[8]

The Borateras geothermal field with about 40 separate manifestations is associated with Purupuruni and neighbouring volcanoes such as Coverane and Jaruma^[8] across the Mauri River and west from Purupuruni respectively.^[14] The Borateras field is used as a spa at the Calachaca spa.^[15] The landscape is relatively dry and cold and thus vegetation is scarce.^[2]

The volcanic rocks are mainly andesitic^[8] and dacitic, and contain amphibole, biotite,^[9] olivine, plagioclase and pyroxene^[8] and are among the most differentiated volcanics in the area.^[10] They are part of the wider "Purupurini Volcanics", which are named after Purupuruni and also form other volcanoes in the region.^[16]

Geological context edit

Rock formations in the region include the Mesozoic Yura Group sediments, the Toquepala intrusive rocks, the 30-24 million years old Tacaza volcanic rocks,^[17] 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.^[18] Purupuruni and neighbouring volcanic centres have formed on the Cretaceous sedimentary basement.^[2]

Volcanism in Peru occurs mainly in the southern part of the country, where there are about 300 separate volcanic systems including El Misti, Ubinas, Ticsani, Sabancaya and Huaynaputina.^[19] In the Tacna Region of Peru alone there are over 60 separate volcanoes, two of which, Tutupaca and Yucamane, have been active in historical time. In addition, there are a number of geothermal systems with temperatures of over 200 °C (392 °F) which could be used to produce geothermal energy. Volcanic and geothermal activity in the region is a consequence of the subduction of the Nazca Plate beneath the South America Plate^[20] at a rate of about 7–9 centimetres per year (2.8–3.5 in/year).^[21]

The volcanic centres in the area including Purupuruni are of Miocene to Pliocene age,^[2] and appear to be of Pleistocene age.^[3] Purupuruni formed during the last 100,000 years^[10] and appears to have developed between two interglacials;^[22] fission-track dating on glasses from Purupuruni has yielded ages of 53,000 ± 8,000 years ago^[23] but more recent surface exposure dating has yielded an age of 5,300 ± 1,100 years before present on one of the southern domes.^[24] The volcano is considered to be a low-hazard system^[25][26] and in 2018 the Peruvian Geological Institute announced it would begin monitoring Purupuruni and nine other volcanoes.^[27] Earthquake swarms in 2020 and 2021 do not appear to have been caused by volcanism;^[28] they are instead linked to local fault activity.^[29]

Glacial erosion took place on Purupuruni during the Pleistocene,^[18] leaving moraines on the domes^[8] 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.^[30] Alluvial, glacial and fluvial deposits occur in the region,^[18] with aeolian sediments consisting of volcanic ash mantling the volcanic structures.^[30]

Sources edit