Instituto Geofísico del Perú (IGP) reported that the eruption at Ubinas continued during 23-29 October at low-to-moderate levels. There were daily averages of 175 volcano-tectonic earthquakes indicating rock fracturing and 17 long-period earthquakes signifying the movement of gas and magma. Daily gas-and-steam plumes rose as high as 500 m above the crater rim and drifted in multiple directions. At 0043 on 27 October an ash, gas, and steam emission rose 500 m above the crater rim and drifted SE and E. A minor thermal anomaly on the crater floor was visible. 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.

Source: Instituto Geofísico del Perú (IGP)