IGP's Observatorio Volcanologico de Arequipa (IGP-OVA) reported that during 29 March-2 April seismicity at Ubinas increased significantly. The increase began at 1000 on 29 March with energetic tremor (indicating magma ascent and degassing) and small explosions. On 2 April harmonic tremor was detected. Gas-and-ash plumes rose 0.9-2.2 km above the crater and drifted SE and E. Minor ashfall was reported in Tonohaya (7 km SSE), San Miguel, and Ubinas (6.5 km SSE). Based on webcam views, the Buenos Aires VAAC reported that on 3 April gas-and-steam plumes possibly containing ash rose 6.1-7.3 km (20,000-24,000 ft) a.s.l. and dissipated around the crater. IGP-OVA noted that on 4 April there were 23 explosions detected; ash plumes drifted S and SE. During 5-7 April explosions generated ash plumes that rose as high as 2 km and drifted S and SW. During 7-8 April explosions also ejected incandescent fragments, up to 20 cm in diameter, no more than 1 km away. Ash plumes rose as high as 3 km.

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), Buenos Aires Volcanic Ash Advisory Center (VAAC)