Report on Ubinas (Peru) — 21 October-27 October 2015
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 21 October-27 October 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, 21 October-27 October 2015. Smithsonian Institution and US Geological Survey.
16.355°S, 70.903°W; summit elev. 5672 m
All times are local (unless otherwise noted)
Instituto Geofísico del Perú (IGP) Observatorio Volcanológico del Sur (OVS) reported that during 20-26 October seismicity at Ubinas decreased overall; the level of long-period earthquakes remained high while hybrid and volcano-tectonic signals were at low levels. On 21 October an ash plume rose 1 km and drifted NE and E. Bluish gas-and-steam plumes rose from the crater during the rest of the period.
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.