Purupuruni

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]

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]