The Philippine Institute of Volcanology and Seismology (Phivolcs) has detected increased seismic activity at Bulusan Volcano, but it is still under “low-level unrest.”

“A total of 116 volcanic earthquakes have been recorded by Bulusan Volcano Network (BVN) since 9 p.m. of Dec. 29, 2023. Of these, 110 were volcano-tectonic (VT) earthquakes associated with rock fracturing beneath the southern flanks at depths of two to six kilometers and six were low frequency volcanic earthquakes (LFVQ) associated with movement of volcanic fluids,” Phivolcs said in a bulletin issued at 8 p.m. on Tuesday, Jan. 2.

Phivolcs explained that increased seismic activity and pressurization of the volcano edifice may indicate that hydrothermal processes are occurring beneath the volcano, which could lead to steam-driven eruptions at any of the summit vents.

The public is reminded that Bulusan Volcano is currently at Alert Level 1, which means it is experiencing low-level unrest with increased chances of steam-driven or phreatic eruptions.

Local government units and the general public are also reminded that entry into the four-kilometer radius permanent danger zone is prohibited, and that vigilance is required in the two-kilometer extended danger zone on the southeast sector due to the possibility of sudden and hazardous phreatic eruptions.

Civil aviation authorities are also requested to ask pilots to refrain from flying near the summit of the volcano, as any sudden phreatic eruption could pose a risk to aircraft due to the ash cloud.

Likewise, if a phreatic eruption coincides with heavy and prolonged rainfall, residents in valleys and along river or stream channels should exercise caution to avoid lahars and sediment-laden stream flows, Phivolcs said.