The Philippine Institute of Volcanology and Seismology on Thursday reported that from the recorded 140 volcanic earthquakes on Monday, Mount Bulusan showed a decrease in seismic activity, now registering five volcanic earthquakes in the past 24 hours.

Phivolcs said that the volcano in Sorsogon, Bicol, which emitted 202 tons of sulfur dioxide on 18 January, remains under Alert Level 1, an indication that there is a low level of unrest with increased chances of steam-driven or phreatic eruptions.

Furthermore, the volcano’s plume is obscure, and its edifice is inflated.

Entry into the four-kilometer-radius permanent danger zone and entry without vigilance into the Extended Danger Zone are still prohibited, as is the flying of aircraft close to the volcano’s summit, as ash from sudden phreatic eruptions can be hazardous to the plane.

On Wednesday, Phivolcs director Teresito Bacolcol said that at present, the number of volcanic earthquakes recorded in Bulusan is fluctuating, but he assured that the agency is closely monitoring the situation.

“We also look at other parameters such as elevated levels of steam or gas emission; when there is inflammation in the edifice of the volcano; and when your spring water rises. So if there are sustained increases in these parameters, then we have to raise it to Alert Level 2,” Bacolcol said.