page_title: Ubinas
section_title: Geology
hierarchical_section_title: Ubinas / Geology
caption_attribution_description: English: A map of the Nazca Plate
context_page_description: Ubinas is an active stratovolcano in the Moquegua Region of southern Peru, approximately 60 kilometres east of the city of Arequipa. Part of the Central Volcanic Zone of the Andes, it rises 5,672 metres above sea level. The volcano's summit is cut by a 1.4-kilometre-wide and 150-metre-deep 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.
context_section_description: Off the western coast of South America, the Nazca Plate subducts beneath the South American Plate at a rate of 7–9 centimetres per year (2.8–3.5 in/year) in the Peru-Chile Trench. 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. The magma erupted by the volcanoes is formed by the partial melting of the mantle after fluids originating in the downgoing slab have altered the mantle; the magmas often undergo fractional crystallization and absorb crustal material.
  Southern Peru has been affected by volcanic activity since the Ordovician and the Permian-Jurassic period, subduction-related volcanism becoming important from the Cretaceous onwards. Beginning 91 million years ago, several volcanic arcs have been active in southern Peru: from the Toquepala arc 91 – c. 45 million years ago over the Andahuaylas-Anta c. 45–30 million years ago, the Huaylillas 24–10 million years ago, the two Barroso arcs 10–1 million years ago, to the recent arc in the last million years. The switching between the volcanic arcs was accompanied by northeastward or southwestward shifts of the zone of main volcanic activity. Furthermore, there was little relief in the region before about 45 million years ago when major uplift commenced.
caption: Map of the Nazca Plate and adjacent regional blocks of South America
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