Bulusan’s eruptions can intensify — Phivolcs

Mount Bulusan (Wikipedia photo)

MANILA — A Philippine Institute of Volcanology and Seismology (Phivolcs) expert isn’t discounting the possibility Bulusan Volcano’s on-going eruptions can worsen.

“It’s possible for eruptions there to be more intense,” Phivolcs volcanologist Paul Alanis said, noting communities concerned must be on guard for this scenario.

Citing historical data, he noted eruptions in Bulusan usually start as minor explosions such as what Phivolcs already observed there.

The eruptions can eventually intensify over time, he warned.

Bulusan Volcano lies in Sorsogon province and is about 250 kilometers southeast of Manila.

On Thursday (May 7), Phivolcs raised Bulusan’s alert level status from zero to one as monitoring of this agency showed “abnormal” conditions there.

“This indicates hydrothermal processes may be underway beneath the volcano that may lead to more steam-driven eruptions,” Phivolcs said in its 8 a.m. Bulusan Volcano bulletin released Thursday.

Bulusan’s volcanic hazards are pyroclastic flows, lava flows, lahar and ashfall, noted Phivolcs.

Government already set a permanent danger zone (PDZ) covering a radius of four kilometers from Bulusan’s summit to help protect people from such hazards.

For further protection, government also designated a probable danger zone spanning four kilometers to 10 kilometers from Bulusan’s summit.

Phivolcs reminded the public to avoid entering Bulusan’s PDZ, warning this volcano can manifest “sudden and hazardous steam-driven or phreatic eruptions.”

Phreatic eruptions are steam-driven explosions that occur when water beneath the ground or on the surface is heated by magma, lava, hot rocks or new volcanic deposits.

Data show Bulusan had phreatic eruptions between 1918 and 1922 as well as in 1980.

“People living within valleys and along river/stream channels should be vigilant against sediment-laden stream flows and lahar in the event of heavy and prolonged rainfall,” Phivolcs continued in its bulletin.

Pilots must refrain from flying their planes close to Bulusan’s summit since ash from sudden phreatic eruptions can be hazardous to these aircraft, Phivolcs said further.

According to Phivolcs, steam-driven explosions that occurred in Bulusan on May 1 and 6 are typical to that volcano during its restive period when either the hydrothermal system there is disturbed or steamaccumulates and pressurizes at the mountain’s shallow levels.

“Based on past records, more explosions can be expected to occur with varying intensity, duration and distribution of ash,” said Phivolcs.

The May 6 explosion propelled an ash plume approximately 250 meters high, Phivolcs noted.

“That plume is still low compared to the kilometer-high column of ash Mt. Pinatubo spewed when it erupted in 1992, however,” said Alanis.

Phivolcs lists Bulusan as among the country’s active volcanoes.

Active volcanoes are those that erupted within historical times which cover the last 600 years, noted Phivolcs.

According to Phivolcs, Bulusan had 16 to 17 historical eruptions already with the last one occurring from Nov. 6, 2010 to May 13, 2011.

“That last one was explosive,” said Alanis.

He noted historical data show Bulusan’s eruptions are usually explosive.

Explosive eruptions occur when volatile magma and volcanic gases are discharged from a volcano, said experts.

They noted lava pours from vents onto the ground during effusive eruptions which are gentler than volcanoes’ explosive blasts.

Phivolcs assured continuing to monitor Bulusan so this agency can relay to the public latest information on activities in this volcano.