The Philippine Institute of Volcanology and Seismology (PHIVOLCS ) raised the status of Bulusan Volcano in Sorsogon to Alert Level 1 on Sunday, citing “low-level unrest” fueled by weeks of persistent seismic activity.
According to an official advisory, the Bulusan Volcano Network has logged a total of 475 volcanic earthquakes since March 15. Experts described the majority of these as weak volcano-tectonic events, which are typically associated with rock fracturing at shallow depths beneath the volcanic edifice.
PHIVOLCS warned that the current seismic patterns mirror the activity observed prior to the volcano’s previous eruptions in June 2022 and April 2025.
Data from continuous Global Positioning System (GPS) and electronic tilt monitoring reveal a noticeable “inflation” or swelling of the volcano’s western and southeastern flanks, a process that began in late January and early March 2026, respectively.
While degassing from active vents remains “weak to moderate,” consistent with low sulfur dioxide emissions—averaging 91 tons per day as of March 17—PHIVOLCS emphasized that internal processes are shifting.
The agency noted that current parameters indicate active “shallow hydrothermal processes” beneath the volcano. This could trigger sudden steam-driven or phreatic eruptions at any of the summit vents.
Under Alert Level 1, the probability of sudden explosions increases. Consequently, PHIVOLCS and local authorities have issued that entry into the four-kilometer radius is strictly prohibited. High vigilance is also required within the two-kilometer zone on the southeast sector due to risks of rockfalls, avalanches, and pyroclastic density currents. Pilots are urged to avoid flying near the summit, as volcanic ash can cause catastrophic engine failure.
Residents west of the volcano are encouraged to prepare for potential ashfall. Authorities specifically reminded families to prioritize vulnerable members, including the elderly, infants, and those with respiratory conditions.
Furthermore, those living near river channels in the southeast, southwest, and northwest sectors must remain alert for lahars and sediment-laden stream flows, especially during heavy rainfall following a phreatic event.| PNA
