In its bulletin yesterday, the Philippine Institute of Volcanology and Seismology (Phivolcs) said 21 high frequency volcanic earthquakes and at least seven low frequency or magma-related tremors were recorded in the past day.
Phivolcs director Renato Solidum said Bulusan’s activities were the same as in the previous months, but stressed they were not discounting the possibility of a major explosion.
"We continue to monitor its activities," Solidum assured in a phone interview.
The sustained high level of Bulusan’s unrest started with an ash-explosion at 1:09 a.m. on Wednesday, accompanied by rumblings and tremors that lasted for 20 minutes.
Orlando Guardacasa, Phivolcs resident volcanologist at the Inlagadian monitoring station in Sorsogon City, said there might be more ash explosions due to the continuing deep and shallow originating tremors within the volcano.
"We are on close watch after that early Wednesday morning ash ejection. We are not yet discounting that more explosions might take place over Bulusan volcano," Guardacasa told The STAR.
He said they have already officially informed the Provincial Disaster Coordinating Council (PDCC) of Sorsogon about the renewed abnormality of Mt. Bulusan.
Aside from ash fall, Guardacasa said they have also alerted PDCC officials for possible lahar flow should heavy rains continue over Bulusan.
"We told them that they should also include in their disaster mitigation plan the possibility of lahar flow due to the continuing heavy downpour over Bulusan. We already gave them the hazard map against lahar," he added.
Phivolcs also observed moderate to voluminous steam emission reaching up to 100 meters above the summit crater.
Guardacasa admitted that they were having a hard time measuring the sulfur dioxide (SO2) emissions of the Sorsogon volcano as thick clouds have been covering it in the past days.
Mt. Bulusan last exploded ash last Oct. 30 after its third level alert from April to May was lowered back to 1, which remained as its alert status until yesterday.
The volcano, which lies in Sorsogon province, emitted four-millimeter ashes before dawn Wednesday, blanketing the towns of Irosin and Bulan.
The ash explosion lasted for about 20 minutes and has reached more than 15 kilometers from the volcano.
Solidum said Phivolcs has recorded 16 explosions of Bulusan since March, when it first displayed unrest.
He warned the public not to venture inside the four-kilometer radius permanent danger zone (PDZ) as this area is at risk to sudden steam and ash explosions, adding that ash ejected from the volcano is detrimental to one’s health.
With Alert Level 1 in place, residents near river and stream channels around the volcano are advised to keep alert against life-threatening volcanic flows because ash and other loose volcanic deposits from the upper slopes may be remobilized and impact areas near the PDZ during heavy rainfall.
Some 10,000 families in 62 villages in Sorsogon were forced to evacuate in April when Bulusan expelled ash in a series of explosions.
Solidum meanwhile said that the stolen equipment at the foot of Mt. Bulusan might hamper the agency’s monitoring of volcanic earthquakes and other seismic activities.
Reports said that Phivolcs officials learned that the equipment was missing last Sunday, or three days before the new ash explosion.
— With Helen Flores