Ubinas is an active stratovolcano in the Moquegua Region of southern Peru, approximately 60 kilometres (37 mi) east of the city of Arequipa.

During the most recent activity, from 2013 to 2017, a lava flow formed inside the crater, and further ash falls led to renewed evacuations of surrounding towns.

[13] Peruvian volcanoes include stratovolcanoes, which are typically active for less than 500,000 years, long-lived clusters of lava domes,[2] and monogenetic volcanic fields.

[11] Historical eruptions have been recorded at seven Peruvian volcanoes: El Misti, Huaynaputina, Sabancaya, Ticsani, Tutupaca, Ubinas, and Yucamane.

[27] A debris avalanche on the southeastern flank reached a distance of 10 kilometres (6.2 mi) from the volcano,[1] and left a collapse scar that is drained by the Volcanmayo River.

[18] This collapse took place early in the history of the volcano and removed a volume of about 2.8 cubic kilometres (0.67 cu mi) of rock from the mountain[28] and underlying basement.

[31] The sloping terrain that Ubinas is built upon predisposes the mountain to south-directed landslides; future collapses in that direction are possible,[32] with the heavily fractured southern flank of the caldera particularly at risk.

[48] This subduction process is responsible for the formation of the Andes and the Altiplano-Puna plateau within the last 25 million years, as well as for volcanism and earthquakes.

[56] Aside from this deep reservoir, Ubinas also has a shallower magma chamber at 4–7 kilometres (2.5–4.3 mi) depth[57] which appears to have a small size.

[9] Even older basement rocks include Paleoproterozoic plutons and the sedimentary Yura Group of Jurassic to Cretaceous age.

[9] Faults cut across the volcano and create unstable areas, especially in its southern sector,[63] and NNW-SSE trending geological lineaments have influenced the stability and the hydrothermal system of Ubinas.

[64] Phenocryst minerals vary between volcanic rocks of different composition and include amphibole, apatite, biotite, clinopyroxene, iron-titanium oxides, olivine, orthopyroxene, plagioclase and zircon.

[29] The last activity of Ubinas I generated more than four units of pyroclastic flows, with a total volume of about 1.8 cubic kilometres (0.43 cu mi),[73] and possibly an old caldera 269,000 ± 16,000 years ago.

A lack of more recent volcanic outcrops suggests a period of dormancy lasting until 25,000–14,700 years ago during which glaciation took place on the volcano.

These eruptions have expelled less than 0.1 cubic kilometres (0.024 cu mi) of material each time and left widespread deposits of ash, volcanic blocks and lapilli.

[82] Most of these eruptions consisted of emissions of ash and gas, sometimes accompanied by explosions, while more intense events such as in 1667 also produced scoria falls and pyroclastic flows.

[83] The 1667 eruption was the largest in historical time, producing about 0.1 cubic kilometres (0.024 cu mi) of scoria[41] and reaching a volcanic explosivity index of 3.

[83] These eruptions have damaged communities around the volcano, and occasionally caused epidemics[78] and human and cattle fatalities resulting from the ingestion of ash.

[41] Aside from regular eruptions, there are fumarolic-seismic events such as in 1995–1996 when sulfur dioxide and water vapour, emitted at temperatures of up to 440 °C (824 °F), formed clouds[78] that rose over 1 kilometre (0.62 mi) above the crater.

[87] The first episode of the 2006–2007 eruption sequence involved the ejection of large volcanic bombs at high speed and the emission of small quantities of ash.

[93] Despite its record of activity, Ubinas was essentially unmonitored before the 2006 event: the inhabitants of the area were largely unaware of volcanic hazards, and there were no emergency plans for future eruptions available.

[25] The ash fall from the eruption caused health problems and disrupted pastures and agriculture in the region around the volcano, resulting in about US$1,000,000 of damage[95] and the flight of local residents to Arequipa and Moquegua.

Strong but variable seismic activity, the observation of thermal anomalies in satellite images and the exhalation of gases characterized this eruption period.

[102] After these events, in 2015–2017 the volcano often persistently released ash and gas, accompanied by earthquakes[1] as well as occasional explosions and eruption columns.

[106] The explosions and ash emissions triggered evacuations[107] and impacted 29,703 people[108] in various districts of the Puno and Tacna Regions,[109] as well as Bolivia and Argentina.

[9] The Volcano Observatory of INGEMMET monitors the seismic activity, any deformation and emissions of the mountain, and hot spring and gas composition at Ubinas.

[112] Hazard maps were created during the 2006 eruptive event to show the relative risk in various locations around the volcano,[116] which is graded in a three-zone scheme with one high-risk, one intermediate-risk and one low-risk zone.

[120] The fumaroles along with the spontaneous potential of Ubinas indicate that the volcano hosts an active hydrothermal system[35] 1–3 kilometres (0.62–1.86 mi) below the caldera.

The region is arid overall, but during the summer wet-season rainfall can cause landslides at lower elevation, and the upper parts of the volcano including the caldera can receive a snow cover.

[38] Animal species have been described mainly in the context of the National Reserve; they include various birds and camelids such as alpacas, guanacos, llamas and vicuñas.