Bulusan quakes raise risk of steam-driven eruptions

By Jordan Domingo with the Bicol Mail Reportorial Team

THE Philippine Institute of Volcanology and Seismology (Phivolcs) has warned of a heightened possibility of steam-driven or phreatic eruptions at Bulusan Volcano in Sorsogon following a significant increase in volcanic activity.

In an advisory issued Tuesday, Phivolcs reported that 109 volcanic earthquakes were recorded since midnight, with nearly all classified as volcano-tectonic events caused by the fracturing of rocks beneath the volcano's shallow structure.

The agency also observed weak to moderate degassing, while sulfur dioxide emissions remained low at 50 tonnes per day based on measurements taken on July 21.

According to Phivolcs, the combination of increased seismic activity and gas emission suggests ongoing shallow hydrothermal or tectonic processes beneath the volcano that could trigger sudden steam-driven eruptions from any of Bulusan’s summit vents.

Bulusan remains under Alert Level 1, indicating low-level unrest. However, the agency emphasized that the recent spike in volcanic earthquakes signals an increased likelihood of phreatic eruptions.

As a precaution, Phivolcs reiterated that the four-kilometer Permanent Danger Zone (PDZ) remains off-limits to the public and advised aircraft to avoid flying close to the volcano's summit.

Residents are likewise urged to remain alert within the two-kilometer Extended Danger Zone (EDZ) on the volcano's south-eastern sector, where hazards such as pyroclastic density currents, ballistic fragments, rockfalls, avalanches, and ashfall may occur.

Communities located south of the volcano and those situated downwind are advised to prepare for possible ashfall should a phreatic eruption take place, with particular attention given to vulnerable groups, including senior citizens, pregnant women, infants, and individuals with existing medical conditions.

Phivolcs also cautioned residents living near valleys and river channels to remain vigilant for sediment-laden stream flows and lahars that could develop during heavy rains following an eruption.