With Typhoon Uwan unleashing intense to torrential rainfall across Bicol, the Philippine Institute of Volcanology and Seismology (Phivolcs) on Saturday, Nov. 8, cautioned residents in Albay against possible life-threatening lahar flows from Mayon Volcano.

Citing state weather bureau PAGASA’s Weather Advisory No. 6, Phivolcs said up to 400 millimeters of rain may fall over Bicol until Sunday, Nov. 9, possibly triggering volcanic sediment flows or lahars around Mayon Volcano.

“DOST-PHIVOLCS thus strongly recommends increased vigilance, readiness and if necessary, pre-emptive evacuation of communities in pre-determined zones of lahar and related hazards in the Province of Albay,” the agency said in an advisory.

Phivolcs warned that intense rainfall could remobilize loose volcanic materials from the 2018 and 2023 eruptions, generating post-eruption lahars on major channels draining Mayon Volcano.

“The bulk of erodible deposits occupy the watershed areas of the Miisi, Binaan, Mabinit, Buyuan, Anoling, Matanag, Bonga, and Basud Channels, such that communities along and downstream of these channels could be severely threatened by post-eruption lahars,” it said.

Per the agency, older pyroclastic materials on the southwestern slopes—continuously eroded during heavy rains through the Masarawag and Maninila Channels—could again trigger non-eruption lahars that threaten Guinobatan and nearby communities.

Likewise, it noted that older volcanic deposits in other sectors of Mayon could be eroded by heavy rains and carried down through the Quirangay, Tumpa, Sua, Muladbucad, Nasisi, Nabonton, Buang, San Vicente, Bulawan, and Lidong Channels, posing risks to riverside and downstream communities.

“Mayon lahars, which are characteristically strong enough to transport enormous volumes of gravel and boulders, have historically and continue to threaten communities by their force of impact, inundation, burial and wash out to sea,” Phivolcs said.

As Typhoon Uwan continues to threaten the region with heavy rains, the agency urged local governments and residents to stay vigilant and closely monitor rainfall levels.