The ash drifted southeast of the volcano, blanketing barangays in Irosin, Bulusan and Casiguran towns.
Volcanologist Alex Baloloy said the Cabid-An monitoring station of the Philippine Institute of Volcanology and Seismology (Phivolcs) in Sorsogon City also detected six volcanic earthquakes in the past 24-hour observation period.
Baloloy said the explosion brought ashfalls in Barangays San Roque, Monbon and Mapaso in Irosin town, and Patag in Bulusan town, all located on the volcano’s southeast side.
Casiguran Mayor Edwin Hamor said Barangay Gulang-Gulang in his town also experienced heavy ashfall.
Despite this latest ash explosion, the third this month, Baloloy said Bulusan would remain at alert level 1, explaining that its present abnormal signs were not yet enough to raise the five-step alert level.
"We still have to observe Bulusan’s abnormal activities further to determine whether to raise its alert status or not," Baloloy told The STAR.
He, however, warned residents at the foot of the 1,559-meter high volcano not to venture within the four-kilometer permanent danger zone.
Arnel Capili, Bicol director of the Office of Civil Defense, said his office will send surgical masks to ashfall-affected areas, depending on the requests of the municipal governments concerned.
After its alert level was lowered to 1 last July, Bulusan again spewed ash some three kilometers above its crater last Oct. 10, sending panic among villagers who fled their homes last April following a series of ash explosions. — With Celso Amo and Helen Flores