According to IGP's Observatorio Vulcanológico del Sur (OVS) seismicity at Ubinas increased during 9-14 September, characterized by an increased number of volcano-tectonic and hybrid events. Volcano-tectonic vents also became more intense. A small thermal anomaly was detected on 20 September. According to a news article, an "exhalation" occurred at 1921 on 2 October, and was followed by explosions detected at 2250 that same day, and 0424 and 0552 on 3 October. The largest explosion, at 2250 on 2 October, emitted a dense ash plume that rose 1.7 km and drifted 10 km NE and NW, causing ashfall in Santa Rosa de Phara and Yanapuqui.

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), Peru 21, Correo