IGP and INGEMMET reported that the eruption at Ubinas continued during 26 June-4 July. A thermal anomaly in the crater was detected for the first time on 26 June and continued to be periodically detected through 4 July. According to IGP there were 98 Volcano-tectonic (VT) earthquakes indicating rock fracturing and 52 long-period (LP) earthquakes signifying the movement of gas and magma recorded during 26-28 June. Earthquakes indicting emissions decreased. Ash-and-gas emissions were visible in webcam images rising as high as 1 km above the crater rim and drifting NW, W, and SW. Seismic activity significantly increased during 29-30 June with 173 VT earthquakes, 351 LP events, and harmonic tremor, which signified rising magma. Ash-and-gas plumes rose 800 m and drifted SW, NW, NE, and E. Sulfur dioxide emissions were 600-1,150 tons per day (t/d). The Gobierno Regional de Moquegua raised the Alert Level to Orange (the third level on a four-color scale) on 30 June based on the recommendation from IGP and INGEMMET.

IGP noted that ash emissions were continuously observed in satellite and webcam images during 30 June-1 July and drifted more than 10 km S and SE. During 1-2 July there were 72 VT events and 114 LP events; seismic signals indicating emissions decreased on 2 July. Ash-and-gas plumes rose as high as 1.7 km above the crater rim and drifted SE, S, SW, and NW. Ashfall was reported in Ubinas (6.5 km SSE) and Ouerapi (4.5 km SE). During 2-3 July INGEMMET noted that ash-and-gas plumes rose 400 m and drifted SW, causing ashfall in areas within 5 km downwind. Sulfur dioxide emissions were 700 t/d.

Activity significantly increased on 4 July. IGP counted 16 seismic signals associated with explosive activity. According to INGEMMET an explosion ejected ballistics and produced an ash-and-steam plume that rose 5.5 km and drifted SW and S. Ashfall was recorded in Querapi, Ubinas, Sacohaya (7 km SSE), Anascapa (11 km SE), San Miguel (10 km SE), Tonohaya (7 km SSE), Huatahua, Huarina, Escacha (9 km SE), and Matalaque (17 km SSE), and was most significant within 5 km of the volcano. IGP noted that ash fell within a radius of 20 km and deposits were 1 mm thick in towns in the district of Ubinas.

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 Geológico Minero y Metalúrgico (INGEMMET), Instituto Geofísico del Perú (IGP), Gobierno Regional de Moquegua