INGEMMET reported intermittent explosions from Ubinas along with continuing daily tremor and long-period earthquales during 18-23 June. Two explosions were noted on 18 June, as were six gas-and-ash emissions that generated diffuse plumes 400-700 m above the summit. Ashfall was reported in Querapi (located 4 km S). On 19 June the seismic network detected two explosions, and gas-and-ash emissions were observed nine times, reaching 300-1,200 m above the crater. Ashfall was reported in the areas of Querapi, Ubinas (6.5 km SSE), Escacha, Tonohaya (7 km SSE), and San Miguel (10 km SE).

No explosions were recorded on 20 June, but seven gas-and-ash emissions were observed (200-500 m above the crater) with the webcamera. On 21 June, six explosions were recorded, with gas-and-ash plumes seen nine times to heights of 500-1,200 m above the crater. Light ashfall was reported in the towns of Ubinas, Lloque, and Yunga. Seismicity on 22 June included one explosion signature. The webcamera captured views of eight gas-and-ash plumes that reached 300-1,000 m above the crater. No explosions were registered on 23 June, although six gas-and-ash plumes were observed with plume heights as high as 1,300 m above the crater.

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)