Bulusan Volcano in Sorsogon Shows Signs of Increased Seismic Activity
The Bulusan Volcano in Sorsogon has entered a phase of heightened seismic activity, according to the Philippine Institute of Volcanology and Seismology (PHIVOLCS). In its latest advisory, PHIVOLCS noted a notable uptick in volcanic earthquakes recorded by the Bulusan Volcano Network, signaling ongoing adjustments beneath the volcano’s northern flank.
From midnight Saturday, October 11, PHIVOLCS documented 72 volcanic earthquakes, described as volcano-tectonic (VT) quakes. VT earthquakes are typically linked to fracturing of rocks within the volcano, and in Bulusan’s case, these events are occurring at depths of less than 10 kilometers. The concentration of shallow quakes is a key indicator that the magmatic and hydrothermal system beneath Bulusan remains active, even as surface manifestations vary.
Alongside the quakes, PHIVOLCS observed persistent degassing from Bulusan’s active vents. The degassing intensity ranged from very weak to weak in recent visual observations, a sign that gases are still escaping from the shallow system as magma interacts with groundwater. In a separate metric, the volcano emitted an average of about 31 tonnes of sulfur dioxide (SO2) on Thursday, October 9. While this rate is below the 200 tonnes/day baseline, it reinforces the interpretation of ongoing shallow hydrothermal activity rather than sustained deep magma intrusion.
PHIVOLCS stressed that Bulusan Volcano remains at Alert Level 1 (low-level unrest). This status indicates that while there is no confirmed eruption imminent, there are increased chances of steam-driven or phreatic eruptions from the crater or its summit vents. Such eruptions can occur suddenly and without warning, underscoring the need for vigilance among nearby residents and visitors.
The agency issued practical guidance for local governments and the public, emphasizing the four-kilometer Permanent Danger Zone (PDZ) and the 2-kilometer Extended Danger Zone (EDZ) on the southeast side. Entry into the PDZ must be strictly prohibited due to the potential hazards of pyroclastic density currents, ballistic projectiles, rockfalls, ashfall, and related volcanic phenomena. In the EDZ, residents should remain especially cautious and prepared for possible escalations in activity.
PHIVOLCS also highlighted protective measures for communities experiencing ashfall. People should use protective masks or damp cloths to minimize inhalation, with special attention to vulnerable groups such as the elderly, individuals with respiratory or cardiovascular conditions, pregnant women, and infants. The advisory cautions against flying too close to the summit, as ash clouds from sudden phreatic episodes can pose serious hazards to aircraft and people on the ground alike.
Though the current conditions point to shallow hydrothermal processes rather than a major eruptive event, the situation at Bulusan remains dynamic. Residents and travelers planning to visit the volcano or surrounding areas should monitor PHIVOLCS updates, heed local government advisories, and maintain readiness for possible changes in alert levels or safety protocols.
What to Watch For
- Sudden changes in steam plume intensity or new ground deformation (if measured by monitoring networks)
- Increased ash emission or noises from the crater
- Expansion of the EDZ or PDZ boundaries due to evolving conditions
PHIVOLCS will continue to track seismicity, gas emissions, and other indicators, providing timely advisories as Bulusan’s activity evolves. Community preparedness—such as having masks, emergency kits, and a plan for quick evacuation within the PDZ—remains essential in reducing risk during this phase of unrest.
