IGP's Observatorio Volcanologico de Arequipa (IGP-OVA) and Observatorio Vulcanológico del INGEMMET (OVI) reported that 21 moderate explosions at Ubinas were detected during 11-16 April along with a sharp increase in seismicity; the magnitude and frequency of explosions increased during 14-16 April. Multiple explosions during 16-22 April ejected incandescent tephra, and generated plumes of gas, water vapor, and ash that rose at most 5 km above the crater. Ash fell in multiple areas in almost all directions, but was most concentrated to the S, SW, and W; towns affected included Querapi (4 km S), Ubinas (6.5 km SSE), Sacuaya, Huatagua (14 km SE), Escacha, Quinistaquillas, San Miguel (10 km SE), Tonohaya, and Matalaque. On 18 April at 1836 a significant gas-and-ash emission was accompanied by the ejection of incandescent blocks that landed up to 2 km from the crater. Explosions on 19 and 22 April ejected incandescent tephra, 20-30 cm in diameter, up to 2.5 km away from the crater. Fine ash fell in Omate, 37 km SSW. According to a news article, an evacuation of 4,000 residents was underway, along with nearly 30,000 livestock.

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), Disaster News Network