IGP reported that during 17-19 July gas-and-ash emissions occasionally rose from Ubinas’s summit crater and drifted N, E, and SE. Beginning at 0227 on 19 July as many as three explosions (two were recorded at 0227 and 0235) generated ash plumes that rose to 5.8 km above the crater rim. The Buenos Aires VAAC reported that ash plumes rose as high as 6.5 km above the crater rim (or to 40,000 ft. a.s.l.) based on satellite images. The Alert Level was raised to Orange (on a 4-level scale). Ash plumes drifted as far as 250 km E and SE, reaching Bolivia. Ashfall was reported in areas downwind including the towns of Ubinas (6.5 km SSE), Escacha, Anascapa (11 km SE), Tonohaya (7 km SSE), Sacohaya, San Miguel (10 km SE), Huarina, and Matalaque, causing some families to evacuate. The VAAC reported that during 20-23 July ash plumes rose to 7.3-9.5 km (24,000-31,000 ft) a.s.l. and drifted E, ESE, and SE.

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), Gobierno Regional de Moquegua, Buenos Aires Volcanic Ash Advisory Center (VAAC), Instituto Nacional de Defensa Civil Perú (INDECI)