Global Volcanic Activity – New Activity for the week of 25 September – 1 October 2019

Copahue | Central Chile-Argentina border : On 30 September OVDAS-SERNAGEOMIN, ONEMI, and SEGEMAR reported that three long-period (LP) earthquakes with notable magnitudes were located about 5.8 km NE of Copahue’s El Agrio Crater. In addition, abundant LP and volcano-tectonic (VT) signals with relatively lower magnitudes were also located in the same area. Some of the events were felt by residents of Caviahue (10 km E) and Copahue 7 km NE) in Argentina. SERNAGEOMIN raised the Alert Level to Orange (second highest level on a four-colour scale) and ONEMI updated the Yellow Alert (the middle level on a three-colour scale) for residents, noting a restriction for entering a 5-km radius from El Agrio Crater. The seismic network recorded a local M 3.1 VT earthquake at 2340 on 30 September, and a local M 3.7 VT event at 0628 on 1 October. The report also noted that 14 lower-energy events (largest was M 2.4) were recorded.

Poas | Costa Rica : OVSICORI-UNA reported that during 16-26 September sulfur dioxide emissions from Poás drifted W and NE, causing a sulfur odor in Alajuela, Heredia, San José, and Cartago. Acidic rain was recorded at the official’s house in the Poás Volcano National Park (PNVP) on 23 September and at Universidad Nacional Costa Rica (UNA) in Heredia on 26 September. At 0540 on 30 September a five-minute-long phreatic eruption ejected sediment, and produced a plume that rose 2 km above the crater rim and drifted SW. Ashfall and a sulfur odor was reported in Trojas de Sarchi and Grecia. Officials closed the PNVP because of the eruption and ongoing elevated seismicity; the park remained closed the next day.

Ulawun | New Britain (Papua New Guinea) : RVO reported that small, discrete, volcano-tectonic earthquakes at Ulawun began occurring more regularly around 1000 on 30 September; by 1130 they were frequent and by 1220 they were characterized as a swarm. The magnitude of the events overall increased with time and some were felt by residents and accompanied by booming sounds. Events were less frequent and intense during 1730-1930. Sometime afterwards RSAM values erratically increased, reaching a high of 10,000 units between 0130 and 0200 on 1 October. The Alert Level was raised to Stage 2 (the second lowest level on a four-stage scale). Periods of volcano-tectonic earthquakes slowly transformed into continuous tremor with distinct bursts of high-frequency signals marking discrete volcano-tectonic events during 0430-0500 on 1 October. During this time a new vent opened in a deep valley on the SSW flank at 700 m elevation. The eruption was described as a distinct incandescent glow formed from ejecting material rising less than 100 m above the vent. By dawn light-gray ash plumes were visible rising several hundred meters and drifting NW. Lava fountaining continued throughout the day, and gray ash plumes rose several kilometers above the vent and drifted W. RVO recommended that the Alert Level be raised to Stage 3. On 2 October lava fountains rose several hundred meters and ash-and-steam plumes rose to variable heights between 2 and 5 km, causing ashfall in Navo (W). A lava flow which emerged during the night traveled 1-2 km NW, though visibility was hindered due to weather conditions. Loud rumbling and roaring was noted. Seismicity remained high with RSAM values passing 12,000 units.

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