Alert level 1 remains at Bulusan Volcano in Sorsogon after state volcanologists noted a significant rise in seismic activity in the area, recording 144 volcanic quakes there in the last 24 hours.

The Philippine Institute of Volcanology and Seismology (Phivolcs) said 80 of these quakes were recorded in a seven-hour period on Monday, from 5:00 a.m. to noon.

"The seismic network at Bulusan Volcano detected a total of 144 volcanic earthquakes for the past 24 hours. Steaming activity at the active vents was weak to moderate throughout the observation period," Phivolcs said in its Tuesday update.

Phivolcs warned of possible sudden steam-driven or "phreatic" explosions.

"Similar events are most likely to occur in view of the volcano's reactivation last 13 May 2011 especially with the current increase in the volcano's seismicity," it said.

However, it said Bulusan Volcano's status remains at Alert Level 1, meaning sudden steam and ash explosions can occur.

Entry to the 4-kilometer radius Permanent Danger Zone (PDZ) is strictly prohibited, since the area is at risk to sudden steam and ash explosions, it added.

"Due to the prevailing wind direction, residents in the northwest and southwest sectors of the volcano are reminded to take precautions against ashfalls. Civil aviation authorities must also warn pilots to avoid flying close to the volcano's summit as ejected ash and volcanic fragments from sudden explosions may be hazardous to aircraft," it said.

Phivolcs said aircraft should avoid flying on the western side of the volcano as volcanic debris are likely to be carried in this direction by the prevailing winds.

Also, it said people living near valleys and river/stream channels should be vigilant against sediment-laden stream flows and lahars in the event of heavy and prolonged rainfall.

Six quakes at Mayon

In Albay, Phivolcs said six volcanic earthquakes at Mayon Volcano during the past 24 hours.

Steaming activity was weak to moderate throughout the observation period, while crater glow was observed at Intensity II (can be seen by the naked eye) Monday night.

Alert Level 1 is also still in effect over Mayon Volcano, Phivolcs said.

"Although this means that no eruption is imminent, it is recommended that the public should not enter the 6-kilometer radius Permanent Danger Zone (PDZ) due to the continuing threat from sudden small explosions and rockfalls from the upper and middle slopes of the volcano," it said.

It added active stream/river channels and those perennially identified as lahar prone areas in the southern sector should also be avoided especially during bad weather conditions or when there is heavy and prolonged rainfall.

Six quakes at Taal

At Taal Volcano in Batangas, six volcanic quakes were also observed in the last 24 hours.

One of these quakes at 1:16 p.m. Monday was felt at Barangay Calauit on the southeastern part of the volcano island at Intensity II, accompanied by rumbling sound and two with rumbling sound that occurred at 1:32 and 1:40 p.m. but not felt, Phivolcs said.

Phivolcs said Alert Level 2 is still in effect over Taal Volcano, with the interpretation that magma has been intruding towards the surface.

It advised the public that the Main Crater, Daang Kastila Trail and Mt. Tabaro are strictly off-limits because sudden hazardous steam-driven explosions may occur and high concentrations of toxic gases may accumulate.

"Breathing air with high concentration of toxic gases can be lethal to human, animals and even cause damage to vegetation. In addition, it is reminded that the entire Volcano Island is a Permanent Danger Zone (PDZ), and permanent settlement in the island is strictly not recommended," it said. - VVP, GMA News