Northern Central Andes, Peru
Structure and Evolution
A broad, quasi-symmetrical cone, Ubinas has a truncated appearance from the ground due to a large summit crater. The cone steepens towards the summit with slopes of almost 45° near the summit.
The summit complex consists of a large (1.2 km diameter), steep walled (100 -150 m high) outer caldera whose floor is ash covered. An ash cone occupies the central portion of the caldera and is itself truncated to the south by the most recent vent (SC); a triangular funnel shaped depression 500 m in diameter and ~200 m deep. According to Hantke & Parodi (1966) the floor of the vent is flat and is about 100 m in diameter. It may be a frozen lava lake.
Several young lava flows (L) are present on the western flanks overlying terminal moraines (M) related to the 10,000 yr BP glacial regression. Bright material on the NE slopes is probably an airfall ash from a recent eruption; possibly the 1600 A.D. eruption of Huaynaputina (q.v.) 15 km to the south.
Ubinas has been intermittently active throughout historic time. Eruptions have been reported from 1677, 1784, and there were several in the 1800s. Before the current eruption, the last reported activity was in 1956, which consisted of vulcanian ash eruptions during which crops and livestock in Ubinas village (6 km to SE; U) were damaged (Hantke & Parodi, 1966). Weak fumarolic activity from the crater was also reported during a visit to the summit in 1985 (McLelland et al., 1989).
In 2005, increased fumarolic activity was followed by increased seismic activity at Ubinas. Steam and ash eruptions then began on March 25, 2006, and have continued to occur every 6-8 days as of July 2008.
The main pathways for any pyroclastic flows or mudflows are on the southeastern side of the volcano. Many small settlements (including Ubinas; U) have developed along the deep quebrada which starts on the southeast of the volcano. This quebrada joins the Rio de la Para and then the larger Rio Tambo which continues some 80 -100 km westwards to the Pacific coast. In the event of a pyroclastic eruption, such as occurred at the nearby Huaynaputina, in 1600 A.D., mud flow, or avalanche from Ubinas there would be considerable hazard to the many communities along these quebradas. Recently, an evacuation of the closest town to the volcano, Querapi, was ordered on April 23, 2008 and as of June 30, people and livestock continue to be affected by the continually erupting ash and gas.
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de Silva S.L., & Francis, P.W., 1990. Active and potentially active volcanoes of southern Peru - observations using Landsat Thematic Mapper and Space Shuttle imagery. Bull. Volcanol. 52, 286-301.
Hantke, G., & Parodi, A., 1966. Catalogue of the active volcanoes of the world; Part XIX, Colombia, Ecuador & Peru, I.A.V.C.E.I. Naples, Italy, 73pp.
McLelland, L., Simkin, T., Summers, M., Nielsen, E., and Stein, T.C., (eds.) 1989. Global Volcanism 1975-1985. National Museum of Natural History. Prentice-Hall Inc., New Jersey, pp655.
Smithsonian Institution-GVN, 2000-. [Weekly Smithsonian/USGS event reports]. http://www.volcano.si.edu/reports/.