During 20-26 August INGEMMET reported that the eruption of Ubinas was continuing. During 20-25 August water vapor, gas, and minor ash plumes rose 200-1800 m above the crater and drifted E, NE, and S. On 21 August an explosion was followed by an ash plume that rose 4.2 km (13,800 ft) above the summit and drifted S and expelled incandescent blocks up to 2 km from the crater, primarily on the S flank. The explosion was heard up to 10 km from the volcano. On 22 August an ash plume rose to 1.8 km (5,900 ft) and drifted E and NE. On 21-22 August ashfall was reported in the towns of Querapi, Ubinas, Escacha, Tonohaya, and Yalahua.

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), Buenos Aires Volcanic Ash Advisory Center (VAAC)