IGP's Observatorio Volcanologico de Arequipa (IGP-OVA) and Observatorio Vulcanológico del INGEMMET (OVI) reported that during 30 April-1 May seismic activity at Ubinas increased significantly, and then declined through 6 May. Explosions generated ash plumes that rose 0.2-3 km above the crater and drifted in multiple directions, especially to the S, SE, E, and NE. Ash fell in various towns downwind of the plumes including Querapi (4 km S), Ubinas (6.5 km SSE), Escacha, Anascapa, San Miguel, and Lloque. On 4 May minor amounts of ash fell throughout the Ubinas valley, more than 15 km away. Although sulfur dioxide emissions had been declining since the peak on 15 April (4,873 tons per day) they continued to be high at more than 1,000 tons per day; villages downwind reported strong sulfur odors.

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)