INGEMMET's Observatorio Vulcanológico (OVI) reported that after a decline in activity at Ubinas during the previous five months two phreatic explosions were detected on 8 April. The explosions occurred at 0424 and 0550, generated ash-and-gas plumes that rose 2-2.5 km above the crater and drifted SE. According to Observatorio Volcanológico del Sur (OVS) snowmelt during 12-13 April led to large lahars that descended the S flank. A report on 13 April noted that large volumes of ash continued to be emitted during the previous 48 hours.

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

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.