LEGAZPI CITY, Philippines– Mt. Bulusan in Sorsogon province spewed a 500-meter high grayish ash column around 5 p.m. Monday, drifting toward villages in the towns of Juban and Irosin, the Philippine Institute of Volcanology and Seismology (Phivolcs) said.
Ed Laguerta, Phivolcs’ resident volcanologist, said the volcano exhibited two successive minor explosions that produced a grayish ash plume followed by a steam and ash plume 500 meters high that drifted to the western side of the volcano.
Laguerta said the eruption was “phreatic” as indicated by the two steam-driven explosions that occurred.
The eruption was accompanied by a series of earthquakes that lasted at least four minutes.
Prior to the low energy ash and steam ejection on Monday afternoon, Phivolcs’ seismic instruments detected no volcanic earthquake, although increased seismicity was recorded on February 20 and 21.
Laguerta, in a telephone interview, said the easterly wind has triggered the ash fall to drift to the villages of Cogon and Bulos in Irosin town and Puting Sapa and Sangkayon in Juban town. These communities are in the western flank of the volcano.
He said Phivolcs would examine Tuesday the extent of ashfall that drifted toward Juban and Irosin.
Laguerta, when asked about what might have generated the phreatic explosion, said it could be produced by hydro-thermal fluid or steam.
He said the steam pressurization underneath the volcano might have triggered the movements in local faults. He, however, said this needs to be evaluated further.
He said that it needs close monitoring because the volcano, although still on a restive state, did not show signs of magma movement signified by volcanic tremors or ground deformation.
Laguerta said Mt. Bulusan remained restive following a series of eruptions starting June last year.
Alert Level 1 remains in effect in areas surrounding the volcano. Phivolcs warns residents not to venture in the 4-km Permanent Danger Zone due to sudden phreatic explosions.
Civil aviation authorities were also notified to advise pilots to avoid flying close to the volcano’s summit as ash from any sudden phreatic eruption can be hazardous to aircraft.
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