According to Observatorio Volcanológico del Sur (OVS) and Observatorio Vulcanológico del INGEMMET (OVI), six explosions from Ubinas were recorded during 15-17 April, producing ash plumes that drifted 15 km SW, S, and SE. The largest ash plume, generated from an explosion detected at 0759 on 15 April, rose 3.5 km. The other explosions (at 1408 on 15 April, at 0600 on 16 April, and at 0743, 0936, and 1518 on 17 April) generated ash plumes that rose 1.5-1.8 km. Seismicity consisting of tornillos, hybrid events, and long-period events decreased from the previous week; the dominant signal was tremor characteristic of emissions and hydrothermal activity.

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)