But Phivolcs said the sulfur dioxide level — one of the gauges which volcanologists use to predict an impending eruption — was still "comparatively low." Emission should reach thousands of tons before the volcano erupts.
During the past 24-hour observation period, Phivolcs said Bulusan’s unrest was "unremarkable" with no volcanic earthquakes detected.
It said "wispy to weak" steam emission was observed from the volcano’s "active summit vent and upper tissue."
"There is still a likelihood of more explosions considering (Bulusan’s) historical eruption patterns. The activity in the past week reflects an elevated degree of unrest that could result in hazardous eruption," it added.
Bulusan has been spewing ash since March, more so in the past week, prompting Phivolcs to raise the alert level around the volcano from one to two.
Ashfalls have covered a number of villages, particularly in Irosin and Casiguran towns, where residents are forced to wear surgical masks to prevent contracting respiratory ailments.
Villagers have been warned not to venture into the four-kilometer radius permanent danger zone due to sudden explosions or lahar flows.