LEGAZPI CITY: The Philippine Institute of Volcanology and Seismology (Phivolcs) is closely watching Mount Bulusan for possible magma build up that might lead to a dangerous explosion in the coming days.
Phivolcs director Renato Solidum said that yesterday’s phreatic eruption is stronger than the previous four successive steam-driven explosions that occurred last week.
“Yesterday’s explosion is more explosive and the ash plume is quite heavy but the ashfall concentrated mainly within the four kilometre danger zone,” Solidum said.
The Phivolcs chief said a possible bigger explosion might take place if magma builds up after the series of phreatic eruption.
“Mount Bulusan erupted five times this week though all steam-driven but a possible bigger explosion might occur if there will be a magma build that’s why we’re closely looking at volcano’s abnormality,” he said.
Alert level 1 remains in effect but once a magmatic substance beneath the restive volcano will be detected, Solidum said alert level 2 will be raised if this episode will lead to a dangerous eruption.
He said that in 1900, Bulusan volcano erupted with magma and pyroclastic flow.
Unlike Mount Mayon in Albay, Mount Bulusan in Sorsogon has four craters and could eject ash plumes simultaneously depending on the pressure beneath the restive volcano.
For the past 24 hours, Bulusan seismic monitoring network recorded at least one explosion-type and four volcanic earthquakes.
Yesterday’s explosion event occurred at 2:55 PM and lasted for seven-minute based on its seismic record, and produced a 1.5 kilometer-high grayish ash plume above the summit before drifting towards west-southwest.
A low-level ash cloud, possibly from a short pyroclastic current, was also generated over the northwest upper slopes, but cloud cover partially obscured observation.
Rumbling sounds were reportedly heard by residents of Barangays Puting Sapa, Rangas and Mabini in Juban, Sorsogon.
Meanwhile, traces of ash fell on Barangays Bacolod, Buraburan, Mapili and Puting Sapa, also in Juban. The event was followed by continuous emission of a voluminous to moderate-volume dirty white plume, later turning into a white steam plume, that reached 250 m high above the summit before drifting southwest.
Precise leveling surveys on May 5-14, 2015 indicate very slight inflation of the volcano’s edifice relative to March 2015.
Solidum reiterated to local government units and the public that entry to the 4-kilometer radius Permanent Danger Zone (PDZ) is strictly prohibited due to the possibility of sudden and hazardous steam-driven or phreatic eruptions.
Similarly, people living within valleys and along river and stream channels especially on the northwest sector of the edifice (Juban) should be vigilant against sediment-laden stream flows and lahars in the event of heavy and prolonged rainfall.
The civil aviation authorities must also advise pilots to avoid flying close to the volcano’s summit as ash from any sudden phreatic eruption can be hazardous to aircraft.