During 10-15 September the number of seismic events at Ubinas totaled 4,093, with volcano-tectonic (VT) signals being the most numerous, averaging 572 events per day, and all having magnitudes under M 2.5. Hybrid events averaged 299 events per day. Continuous emissions of blueish gas and water vapor were recorded by the webcam rising to heights less than 1.5 km above the summit. Two thermal anomalies were recorded by the MIROVA system. An explosion at 0725 on 12 September produced a gas-and-ash plume that rose 1.5 km and affected several districts S and SE in the Moquegua region. The Alert Level remained at Orange (the second highest level on a four-color scale) and the public were warned to stay outside of a 10-km radius.

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)