Mayon remains under Alert Level 3 Bulusan records sharp quake surge

By JORDAN DOMINGO

LEGAZPI CITY — The Philippine Institute of Volcanology and Seismology (Phivolcs) has maintained Mayon Volcano in Albay under Alert Level 3 despite a noticeable decline in volcanic activity, while Bulusan Volcano in Sorsogon has recorded a sharp surge in seismic activity, prompting authorities to renew calls for heightened public vigilance across the Bicol Region.

Dr. Paul Karson Alanis, senior science research specialist of Phivolcs, said Mayon has shown a downward trend in activity over the past two weeks, but the decrease remains insufficient to warrant a lowering of the alert status.

He explained that as of July 29, the volcano was still effectively at “Day 0” under the agency's protocol, which requires at least two consecutive weeks of sustained decline in key monitoring parameters before an alert level can be downgraded.

Phivolcs said recent unrest at Mayon was marked by increased volcano-tectonic earthquakes in Sto. Domingo and Bacacay, triggering strombolian eruptions, lava fountaining, intensified rockfalls, pyroclastic density currents (PDCs), and sulfur dioxide (SO₂) emissions that peaked at 13,128 tonnes per day—the highest level recorded in the past 26 years.

Although seismic activity has eased and rumbling sounds have ceased in recent days, Alanis stressed that the agency's “stand-down” procedure requires careful evaluation of sulfur dioxide emissions, ground deformation, volcanic earthquakes, rockfalls, plume activity, lava effusion, and other indicators before any downgrade can be considered.

Since the onset of the current eruption, Mayon has produced an estimated 88 million cubic meters of lava, ash, gases, and pyroclastic materials that remain deposited on its upper slopes. Phivolcs warned that these unstable deposits could still generate deadly pyroclastic density currents and ash clouds even without a new eruption, while heavy rains may trigger dangerous lahars along rivers and drainage channels.

As of July 29, the agency recorded four volcanic earthquakes, 10 rock-fall events, two PDCs, and sulfur dioxide emissions of 1,318 tonnes per day. Residents were again reminded to stay out of the six-kilometer Permanent Danger Zone and remain alert against ashfall and lahar hazards.

Meanwhile, Bulusan Volcano exhibited a dramatic increase in activity after Phivolcs recorded 196 volcanic earthquakes within a 24-hour period from July 28 to July 29, with 47 events precisely located. The sudden spike came after several days of relatively quiet conditions, when only 23 earthquakes were recorded the previous day, seven on Monday, five on Sunday, and none on Saturday.

Despite the significant increase in seismicity, Bulusan remains under Alert Level 1, indicating low-level volcanic unrest. However, Phivolcs cautioned that hazardous activity remains possible, including steam-driven or phreatic eruptions capable of producing ash clouds, hot gas, rockfalls, ballistic projectiles, avalanches, and dangerous volcanic gases.

Communities south and downwind of the volcano were advised to prepare for possible ashfall, while residents near rivers and stream channels were urged to watch for lahars during periods of heavy and prolonged rainfall following any eruption.

Phivolcs also called on local government units to ensure the protection of vulnerable sectors, including senior citizens, pregnant women, infants, and individuals with existing medical conditions. Civil aviation authorities were likewise advised to keep aircraft away from Bulusan's summit due to the risk posed by volcanic ash from sudden phreatic eruptions.

With Mayon continuing to exhibit potentially hazardous eruptive activity and Bulusan showing renewed signs of unrest, Phivolcs urged residents throughout Bicol to closely monitor official advisories and strictly comply with safety measures, emphasizing that both volcanoes remain capable of producing dangerous volcanic hazards with little warning.