Report on Ubinas (Peru) — 27 August-2 September 2008
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 27 August-2 September 2008
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2008. Report on Ubinas (Peru). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 27 August-2 September 2008. 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 SIGMET reports, analysis of satellite imagery, and pilot observations, the Buenos Aires VAAC reported that during 26-27 August and on 2 September continuous ash plumes from Ubinas rose to altitudes of 5.5-6.1 km (18,000-20,000 ft) a.s.l. Plumes drifted N on 27 August and S on 2 September.
Geologic Background. A small, 1.4-km-wide caldera cuts the top of Ubinas, Peru'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 of Perú. 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 3700 years ago extend 10 km from the volcano. Widespread plinian pumice-fall deposits include one of Holocene age about 1000 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.