Hazardous phreatic eruptions increasingly possible in Mt. Bulusan


MANILA: There is an increased possibility for sudden and potentially deadly phreatic eruptions in Sorsogon province’s Bulusan Volcano.

Changes in Bulusan’s sulfur dioxide (SO2) emission level and in the inflation of its edifice are among the developments that raise such a possibility, noted volcanologist Paul Alanis of the state-run Philippine Institute of Volcanology and Seismology (Phivolcs).

“At times, we even monitor increases in the number of Bulusan’s volcanic earthquakes,” he also said.

Alanis again cautioned about entering Bulusan’s 4-km. radius permanent danger zone (PDZ) and 2-km. extended danger zone (EDZ), noting phreatic eruptions can occur anytime without warning.

“Phreatic eruptions can also occur anywhere in that volcano,” he said.

According to experts, phreatic eruptions are steam-driven blasts that occur when water beneath the ground or on the surface transform into steam after coming into contact with hot volcanic materials.

Phivolcs volcanologist, Winchelle Sevilla, earlier said there is still no means of giving advanced warnings about looming phreatic eruptions.

Research into the matter is still in progress, he noted.

A sudden phreatic eruption in Mayon Volcano on May 7, 2013 killed five people who were within the PDZ at the time.

In its bulletin released Friday, Phivolcs saidhydrothermal processes in progress beneath Bulusan Volcano may lead to steam-driven or phreatic eruptions.

Phivolcs reminded the public to refrain from entering Bulusan’s PDZ due to the high possibility of “sudden and hazardous” phreatic eruptions in this volcano.

Such danger also raised the need for vigilance in Bulusan’s EDZ, noted Phivolcs.

On Oct. 18 this year, Phivolcs declared on Bulusan’s southern slope an EDZ stretching 2 km. downslope of the PDZ as an extra precaution against possible phreatic eruptions when alert levels 1 and 2 are prevailing in the volcano.

Alert level 1 is prevailing in Bulusan at present as it is manifesting low-level volcanic unrest, noted Phivolcs.

Alanis said such alert level indicates that magmatic eruption is not yet imminent there.

“Phreatic eruptions are still possible even if alert level 1 or even zero is prevailing, however,” he said.

The deadly May 2013 phreatic eruption in Mayon Volcano occurred while alert level zero was prevailing.

Citing latest available data, Phivolcs reported in its bulletin Bulusan Volcano’s SO2 emissions averaged some 232 tons/day last Monday.

That’s higher than the 43 tons/day SO2 emission average Phivolcs reported for Bulusan last November 7.

“Precise leveling data obtained on Oct. 17 to 23, 2016 indicated inflationary changes of the edifice relative to August 2016,” PAGASA said in its bulletin. PNA



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