The Philippine Institute of Volcanology and Seismology (Phivolcs) on Friday evening, Nov. 15 issued a lahar advisory for three active volcanoes—Mayon, Pinatubo, and Taal—due to the anticipated heavy rainfall from Typhoon “Pepito” (international name: Man-yi), which is expected to make landfall over the eastern coast of Southern Luzon between Nov. 16 and 17.

Phivolcs urged heightened vigilance and readiness of communities near these volcanoes as Pepito’s rainfall could trigger volcanic sediment flows or lahars and muddy streamflows or muddy run-off in rivers, which pose significant risks to lives and properties.

Mayon

Mayon Volcano in Albay remains at heightened risk, particularly along the major river channels draining the volcano’s slopes.

Phivolcs said prolonged intense to torrential rainfall associated with the typhoon could lead to post-eruption lahars, which are loose material from remnant pyroclastic density current (PDC) deposits from the January-March 2018 eruption.

Mayon lahars pose a threat to communities downstream of the Miisi, Mabinit, Buyuan, and Basud channels, with risks of inundation, burial, and washouts.

Potential lahars and sediment-laden streamflows could also affect areas along the Miisi, Binaan, Anoling, Quirangay, Maninila, Masarawag, Muladbucad, Nasisi, Mabinit, Matanag, Basud, and Bulawan channels in Albay.

Pinatubo

Phivolcs also cautioned that prolonged and heavy rainfall could trigger non-eruption lahars along major rivers draining the western slopes of Mt. Pinatubo, where significant deposits of PDCs from the 1991 eruption remain in the watershed.

These lahars are expected to be confined to river channels, particularly in the upper to middle reaches of the Sto. Tomas-Marella and Bucao River systems.

However, they could transition into muddy streamflows and flooding in the lower reaches, potentially affecting nearby communities in San Marcelino, San Narciso, San Felipe, and Botolan in Zambales.

In addition, muddy streamflows may develop along the O'Donnell and Pasig-Potrero River systems, which drain the northern and southeastern flanks of Pinatubo. These flows could impact downstream communities in Tarlac and Pampanga.

Taal 

Phivolcs also warned that prolonged and heavy rainfall could trigger muddy streamflows, runoff, and even volcanic debris flows around Taal Volcano, particularly on the slopes to the west and north of Taal Lake.

It added that saturated volcanic deposits from previous rains are highly susceptible to being remobilized by the storm, flowing down streams, roads, and across the lakeward slopes.

In particular, communities in Agoncillo, Laurel, and Talisay in Batangas, which have been previously affected by similar hazards, are at risk of renewed muddy and debris flows.

Phivolcs advised local government units and residents in the identified high-risk areas to closely monitor weather updates and take preemptive safety measures to protect themselves from the impacts of Pepito.