Report on Ubinas (Peru) — 28 March-3 April 2007
Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 28 March-3 April 2007
Managing Editor: Sally Sennert.
Please cite this report as:
Global Volcanism Program, 2007. Report on Ubinas (Peru) (Sennert, S, ed.). Weekly Volcanic Activity Report, 28 March-3 April 2007. Smithsonian Institution and US Geological Survey.
16.355°S, 70.903°W; summit elev. 5672 m
All times are local (unless otherwise noted)
Based on pilot reports, the Buenos Aires VAAC reported that an ash cloud from Ubinas rose to 5.5-6.1 km (18,000-20,000 ft) a.s.l. on 30 March and drifted E. According to a news article, local residents observed rockfalls and reported ashfall. A scientist from the Geological, Mining, and Metallurgic Institute (INGEMMET) reported that the eruption was the largest in a two-week period characterized by an increased rate of explosions. A diffuse ash plume was visible on satellite imagery on 3 April drifting NE.
Geological Summary. A small, 1.4-km-wide caldera cuts the top of Ubinas, Perú's most active volcano, giving it a truncated appearance. It is the northernmost of three young volcanoes located along a regional structural lineament about 50 km behind the main volcanic front. The growth and destruction of Ubinas I was followed by construction of Ubinas II beginning in the mid-Pleistocene. The upper slopes of the andesitic-to-rhyolitic Ubinas II stratovolcano are composed primarily of andesitic and trachyandesitic lava flows and steepen to nearly 45 degrees. The steep-walled, 150-m-deep summit caldera contains an ash cone with a 500-m-wide funnel-shaped vent that is 200 m deep. Debris-avalanche deposits from the collapse of the SE flank about 3,700 years ago extend 10 km from the volcano. Widespread Plinian pumice-fall deposits include one of Holocene age about 1,000 years ago. Holocene lava flows are visible on the flanks, but historical activity, documented since the 16th century, has consisted of intermittent minor-to-moderate explosive eruptions.