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Phivolcs: Steam-driven explosion observed at Bulusan

May 13, 2011 8:01am

Tags: Phivolcs
(Updated 9 a.m.) A steam-driven explosion – accompanied by a rumbling sound heard several kilometers away and 10 volcanic quakes – was observed at Bulusan Volcano in Sorsogon before dawn Friday, but this was not enough basis for state volcanologists to raise the alert level there.

Philippine Institute of Volcanology and Seismology (Phivolcs) director Renato Solidum Jr. said the explosion was more due to rainwater from tropical storm “Bebeng" (Aere).

“Ito ay steam-driven explosion, ground water na tubig galing sa ulan na napapakulo. Yan ang nagiging sanhi ng pressure at nagdulot ng pagsabog. Hindi ito dulot ng pagakyat ng magma," Solidum said in an interview on dzBB radio.

But he stressed the explosion at about 12:25 a.m. was relatively weak.


Solidum also said the alert status at Bulusan remains at “1," where entry to the 4-km radius Permanent Danger Zone (PDZ) is strictly prohibited, since the area is at risk to sudden steam and ash explosions.

Solidum noted the last explosion from Bulusan was last Feb. 21.

Asked if there was a need to raise the alert level, he said, “wala (none)."

A later update from Phivolcs indicated the explosion was not observed due to cloud cover, but was accompanied by a rumbling sound "heard up to five km away from the volcano."

"This event was recorded as an explosion-type earthquake lasting for about 10 minutes," it added.

Meanwhile, Phivolcs said at least 10 volcanic earthquakes were observed at Bulusan in the last 24 hours.

Ash deposits

Phivolcs said field investigation conducted immediately after the explosion confirmed the presence of thin (0.5- 2.5mm) ash deposits in the northwest and southwest sectors reaching approximately 9 km away from the crater.

Affected by light ashfalls were Caladgaw, Rangas, Puting Sapa, Sangkayon, Bacolod, Buraburan, Gurayan, and Aniog villages in Juban town; and Cogon, Bolos, Umagom, and Gulang-gulang villages in Irosin town.

Bulusan Volcano’s status remains at Alert Level 1, meaning the source of activity is hydrothermal and shallow.

Entry to the 4-km radius PDZ is strictly prohibited, since the area is at risk to sudden steam and ash explosions.

"Due to the prevailing wind direction, residents in the northwest and southwest sectors of the volcano are reminded to take precautions against ashfalls," Phivolcs said.

It said civil aviation authorities must also warn pilots to avoid flying close to the volcano’s summit as ejected ash and volcanic fragments from sudden explosions may be hazardous to aircraft.

Aircraft should avoid flying on the western side of the volcano as volcanic debris are likely to be carried in this direction by the prevailing winds, it said.

"Furthermore, people living near valleys and river/stream channels should be vigilant against sediment-laden stream flows and lahars in the event of heavy and prolonged rainfall," it said. — LBG, GMA News

Tags: Phivolcs



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