THE Philippine Institute of Volcanology and Seismology (Phivolcs) yesterday said it recorded 309 volcanic quakes from Bulusan Volcano since Friday last week.
In an advisory, Phivolcs said 287 of the volcanic quakes were volcano-tectonic earthquakes that are “associated with rock fracturing occurring at shallow depth less than 4 kilometers beneath the southeastern edifice of Bulusan Volcano.”
The 22 others, Phivolcs said, were “low frequency volcanic earthquake associated with movement of fluid.”
It said the volcano’s degassing activity has been “weak to moderate” in the past days.
Phivolcs said there was an “increase of seismic activity at Bulusan Volcano” but did not elaborate.
“These changes in parameters may indicate shallow hydrothermal activity of Bulusan Volcano,” said Phivolcs.
Bulusan had two phreatic eruptions last month, the last on April 29. The first, which occurred last April 28, prompted Phivolcs to raise the volcano’s alert status to Alert Level 1 (low level unrest), from Alert Level O (quiet or no alert).
In its advisory yesterday, Phivolcs said: “Alert Level 1 is maintained over Bulusan Volcano, which means that there are increased chances of phreatic eruptions.”
It reminded local government units and the public that entry to the four-kilometer permanent danger zone is “strictly prohibited” and vigilance should be observed in the two-kilometer extended danger zone on the southeast sector “due to the possible impacts of volcanic hazards.”
It said people who experience ashfall “must take all necessary precautions and use protective masks or wet cloth to prevent ash inhalation.”
Phivolcs said people living within valleys and along river/stream channels “should be vigilant against sediment-laden stream flows and lahars in the event of heavy and prolonged rainfall should phreatic eruption occur.”
It urged civil aviation authorities to advise pilots to avoid flying close to the volcano’s summit “as ash from any sudden phreatic eruption can be hazardous to aircraft.”
