IGP reported that during 20-26 August blue-colored gas plumes from Ubinas rose above the crater and eight thermal anomalies were recorded by the MIROVA system. The number of seismic events was 1,736 (all under M 2.4), and there was an increase in the magnitude and number of hybrid and long-period events. Around 1030 on 26 August an ash emission rose to heights below 2 km above the crater rim. Continuous ash emissions on 27 August were recorded by satellite and webcam images drifting S and SW. 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.

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.

Source: Instituto Geofísico del Perú (IGP)