Instituto Geofísico del Perú (IGP) and Instituto Geológico Minero y Metalúrgico (INGEMMET) reported that the eruption at Ubinas continued during 31 July-7 August. According to IGP a daily average of 115 volcano-tectonic earthquakes indicating rock fracturing and 124 long-period earthquakes signifying the movement of gas and magma 31 July-6 August. In addition, there were four seismic signals associated with explosive events (mainly on 1 and 6 August) and 6-9 daily hours of seismic signals related to ash emissions. At 2110 on 1 August a major explosion produced an ash plume that rose as high as 5.4 km above the crater rim and ejected blocks as far as 3 km from the crater onto the SW, S, and SE flanks. The ash plume drifted 30 km E, SE, S, SW, and W, causing ashfall in the districts of Ubinas (6 km SE) and Chojata (19 km ESE). Ash-and-gas emissions rose as high as 2 km and drifted in multiple directions on the other days of the week. Ashfall was reported within a 15-km radius. An explosion at 0009 on 6 August produced a gas-and-ash plume that rose 1.4 km and drifted SE and E, causing ashfall in Ubinas and Chojata and other areas within a 30-km radius. INGEMMET noted that sulfur dioxide emissions were low on 7 August, averaging 400 tons per day. The Alert Level remained at Orange (the third level on a four-color scale) and the public was warned to stay 4 km away from the crater.

Geological Summary. The truncated appearance of Ubinas, Perú's most active volcano, is a result of a 1.4-km-wide crater at the summit. 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°. The steep-walled, 150-m-deep summit crater 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 from about 1,000 years ago. Holocene lava flows are visible on the flanks, but activity documented since the 16th century has consisted of intermittent minor-to-moderate explosive eruptions.

Sources: Instituto Geofísico del Perú (IGP), Instituto Geológico Minero y Metalúrgico (INGEMMET)