Instituto Geofísico del Perú (IGP) reported that the eruption at Ubinas continued during 11-17 September at low-to-moderate levels. There were daily averages of 144 volcano-tectonic earthquakes indicating rock fracturing and 86 long-period earthquakes signifying the movement of gas and magma. One explosion was recorded on 14 September. INGEMMET noted that sulfur dioxide emissions were at low levels during 14-15 September, averaging 900 tons per day. Ash-and-steam plumes rose 1.6 km above the crater rim and drifted SE and NE, causing ashfall in areas within 5 km downwind. IGP noted that seismic signals associated with ash emissions were recorded for an average of three hours per day during 14-16 September. Ash, gas, and steam emissions visible in webcam images rose as high as 2.6 km above the crater rim and drifted as far as 15 km NE, E, and SE. Deformation data indicated a slight trend of inflation with variations less than 5 mm. The Alert Level remained at Orange (the third level on a four-color scale) and the public was warned to stay 4 km away from 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)