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, which itself contains a smaller crater. Below the summit, Ubinas has the shape of an upwards-steepening cone with a prominent notch on the southern side. The gently sloping lower part of the volcano is also known as Ubinas I and the steeper upper part as Ubinas II; they represent different stages in the volcano's geological history.
The most active volcano in Peru, Ubinas has a history of small to moderate explosive eruptions as well as a few larger eruptions, such as in 1667, along with persistent degassing and ash emissions. Activity at the volcano began in the Pleistocene epoch, and led to the growth of the current mountain in two phases. Among the recent eruptions was the 2006–2007 event, which produced eruption columns and led to ash fall in the region, resulting in health issues and evacuations. 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. Ubinas is monitored by the Peruvian geological service INGEMMET, which has published a volcano hazard map for Ubinas and regular volcanic activity reports.
Name and mythology
The historian and geographer Mariano Felipe Paz Soldán relates the name Ubinas to two terms in two different languages. In the indigenous language Quechua, means "to stuff" or "to fill", and is translated as "to grow" or "to increase". In Aymara, means "weep" or "murmur"; is the genitive of . Local inhabitants believed that Ubinas was infested by demons and the souls of people who had fallen from God. The volcano is also known as Uvillas or Uvinas.
Geography and structure
Ubinas lies in the Ubinas District of the General Sánchez Cerro Province, Moquegua Region of Peru, east of Arequipa in the Peruvian Western Cordillera.
Like other Peruvian volcanoes, Ubinas belongs to the Central Volcanic Zone of the Andes. The Central Volcanic Zone is one of four volcanic belts in the Andes; the others are the Northern Volcanic Zone, the Southern Volcanic Zone, and the Austral Volcanic Zone. The Central Volcanic Zone is long, and 69 of its volcanoes have been active in the Holocene epoch.
Peruvian volcanoes include stratovolcanoes, which are typically active for less than 500,000 years, long-lived clusters of lava domes, and monogenetic volcanic fields. Historical eruptions have been recorded at seven Peruvian volcanoes: El Misti, Huaynaputina, Sabancaya, Ticsani, Tutupaca, Ubinas, and Yucamane. The volcanoes Ampato, Casiri, Chachani, Coropuna, and Sara Sara are dormant.
Reaching an elevation of , Ubinas is a conical, truncated stratovolcano with upper slopes that reach angles of up to 45 degrees, and more gently sloping lower flanks. The more gently sloping lower part of the volcano is also known as Ubinas I and the steeper upper part as Ubinas II. The southern flank is cut by a noticeable notch, which is probably not an eruption vent and may have been formed by mudflows and rockslides. Due to weathering, the upper sector of the volcano has a worn appearance. Glacial valleys such as the Ubinas and Para valleys, as well as cirques and moraines down to and at the foot of the volcano, indicate that glaciers developed on Ubinas during the last glacial maximum. Other volcanic cones in the region all show heavy erosion by glaciation.
The volcano rises from a circular surface at the margin of a high plateau. Volcanic ash and some lava flows cover the terrain north and east of Ubinas. Four lava domes crop out around the volcano and may be related to it. The Ubinas and Para valleys border the volcano in its southeastern sector; the difference in elevation between the floor of the Ubinas valley and the plateau is about . The total volume of the mountain is estimated to be about .
The summit of the volcano is an elliptical caldera wide and deep, formed by collapses of the summit and explosive eruptions. The caldera walls are made of lava flows bearing traces of hydrothermal alteration; the caldera floor is covered by lava flows and pyroclastic debris from explosive eruptions. It contains one or two ash cones with a triangle-shaped crater wide and deep; its walls are fractured and hydrothermally altered. Geophysical surveys have indicated the presence of an even larger buried caldera in Ubinas.