June 2016 – PHILIPPINES – The Philippine Institute of Volcanology and Seismology yesterday warned residents living near Mount Bulusan in Sorsogon of the possibility of more steam-driven eruptions, following an explosion last Friday. Thin ash caused by the steam-driven eruption in Mount Bulusan last Friday was observed in Casiguran and Juban in Sorsogon. Ash fell over Barangays Añog, Juban, and Mabini in Casiguran. Traces of volcanic ash were observed in Barangays Casay, Casiguran proper, Escuala, Inlagadian, San Antonio, and San Juan in Casiguran, and Barangays Aroroy, Juban proper, Puting Sapa, and Rangas in Juban.
Steam-driven explosion, also called phreatic explosion, happens when groundwater is heated by magma. The eruption that occurred at 11:35 a.m. Friday was observed on the west-northwest vent of the volcano. A two-kilometer-high grayish ash plume, which drifted to the northwest, was visible after the explosion. Phivolcs recorded an explosion-type earthquake that lasted approximately five minutes, which was accompanied by rumbling sound reportedly heard at Barangays Puting Sapa, Ranga, and Añog in Juban, and Barangays Mabini and Inlagadian in Casiguran.
From 8 a.m. Friday to 8 a.m. Saturday, Bulusan’s seismic monitoring network recorded a total of five volcanic earthquakes, including the explosion-type earthquake Friday. Phivolcs said weak to moderate emission of white steam plumes that rose up to 150 meters and drifted towards north-northwest remain visible. Alert Level 1, which is the lowest of five-tier level of volcanic unrest, remains in effect over Mount Bulusan. This indicates that hydrothermal processes are ongoing beneath the volcano that may lead to steam-driven eruptions, Phivolcs said.
It warned local government units and the public from entering four-kilometer permanent danger zone surrounding the volcano due to possible sudden and hazardous steam-driven eruptions. Civil aviation authorities were advised to warn pilots to from flying close to the volcano’s summit as ash from any sudden phreatic eruption can be hazardous to aircraft. People living within valleys and along river or stream channels, especially on the southwest and northwest sector of the edifice, were also advised to be vigilant from sediment-laden stream flows and lahars in the event of heavy and prolonged rainfall. –Tempo