MANILA — Government is reminding people to still avoid nearing Bulusan volcano in Sorsogon despite the lull in steam-driven explosions there, warning this mountain continues being in a state of unrest.
“People must refrain from entering Bulusan’s permanent danger zone (PDZ) and going near that volcano as we can still expect sudden ash and steam explosions there anytime,” said volcanologist Winchelle Sevilla from State-run Philippine Institute of Volcanology andSeismology (Phivolcs).
He warned such explosions can even be more intense than what Phivolcs monitored in Bulusan earlier this May.
According to Phivolcs, hydrothermal processes may be already underway beneath Bulusan.
Such processes may lead to more steam-driven explosions there, noted Phivolcs.
Steam-driven or phreatic explosions are eruptions that occur when water beneath the ground or on the surface is heated by magma, lava, hot rocks or new volcanic deposits.
Bulusan’s volcanic hazards are pyroclastic flows, lava flows, lahar and ashfall, Phivolcs said.
Government set for Bulusan a PDZ covering a radius of four kilometers from that volcano’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.
Sevilla noted that volcanic earthquakes Phivolcs monitored in Bulusan this week indicate hydrothermal disturbance in that volcano.
“It’s possible those earthquakes are related to movement of small faults in Bulusan’s upper part as the edifice of this volcano adjusts to explosions there,” he also said.
In its 8 a.m. bulletin released Thursday (May 14), Phivolcs reported recording six volcanic earthquakes in Bulusan volcano during the agency’s 24-hour observation period.
Phivolcs also reported on May 13 and 12 this year occurrence of four and five volcanic earthquakes in Bulusan, respectively.
Sevilla said the number of volcanic earthquakes in Bulusan this week represents a “significant rise” from the one to two tremors Phivolcs usually monitors there during the volcano’s normal times.
“The number of volcanic earthquakes there is above normal already” he noted.
He clarified such rise in volcanic earthquakes doesn’t indicate a major eruption is already forthcoming in Bulusan, however.
On May 7, Phivolcs raised Bulusan’s alert level status from zero to one after monitoring there “abnormal” conditions marked by steam-driven explosions on May 1 and 6.
The May 6 explosion even propelled an ash plume about 250 meters high, noted Phivolcs.
In contrast, Phivolcs’ May 12 bulletin cited observations of “weak to moderate” white steam emissions in Bulusan.
“Steaming activity was not observed due to thick clouds covering the summit area,” Phivolcs also reported in its May 13 and 14 bulletins for Bulusan.
Despite the lull in explosions, Phivolcs said Bulusan Volcano continues to be on alert level one status.
Such status remains in effect as steam-driven or phreatic eruptions in Bulusan can’t be discounted yet, Phivolcs said.
Data show Bulusan had phreatic eruptions between 1918 and 1922 as well as in 1980.
Since Bulusan is on alert level one status, Phivolcs reiterated people must avoid entering this volcano’s PDZ.
Pilots must avoid flying their planes close to Bulusan’s summit as phreatic eruptions can be hazardous, Phivolcs added.
“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 also said.
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.
The agency added Bulusan had 16 to 17 historical eruptions already with the last one occurring from Nov. 6, 2010 to May 13, 2011.