Report on Ubinas (Peru) — 8 April-14 April 2015
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 8 April-14 April 2015
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2015. Report on Ubinas (Peru). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 8 April-14 April 2015. Smithsonian Institution and US Geological Survey.
16.355°S, 70.903°W; summit elev. 5672 m
All times are local (unless otherwise noted)
INGEMMET's Observatorio Vulcanológico (OVI) reported that after a decline in activity at Ubinas during the previous five months two phreatic explosions were detected on 8 April. The explosions occurred at 0424 and 0550, generated ash-and-gas plumes that rose 2-2.5 km above the crater and drifted SE. According to Observatorio Volcanológico del Sur (OVS) snowmelt during 12-13 April led to large lahars that descended the S flank. A report on 13 April noted that large volumes of ash continued to be emitted during the previous 48 hours.
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.