Report on Ubinas (Peru) — 28 August-3 September 2019
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 28 August-3 September 2019
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2019. Report on Ubinas (Peru). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 28 August-3 September 2019. Smithsonian Institution and US Geological Survey.
16.355°S, 70.903°W; summit elev. 5672 m
All times are local (unless otherwise noted)
IGP reported that during 27 August-2 September gas-and-water-vapor plumes from Ubinas rose to heights less than 1 km above the summit, and three thermal anomalies were recorded by the MIROVA system. The number of seismic events was 2,828 (all under M 2.3), with volcano-tectonic (VT) signals being the most numerous. There was a slight increase in the number of long-period, hybrid, and VT events compared to the previous week. Beginning at 2145 on 1 September a period of continuous ash emissions was recorded by the webcam. An explosion at 1358 on 3 September generated an ash plume that rose 1.3 km above the summit and drifted more than 10 km S and SE. Prior to this event, the last explosion as recorded on 22 July. The Alert Level remained at Orange (the second highest level on a four-color scale) and the public were warned to stay outside of a 15-km radius.
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.