Phivolcs warns of lahar flow due to Dante

MANILA, Philippines — Rains spawned by Tropical Storm Dante can trigger lahar flow around Taal Volcano in Batangas, Mt. Pinatubo in Zambales and Mayon Volcano in Albay.

“Due to its trajectory and potentially high-volume rainfall, Dante can be expected to generate volcanic sediment flows or lahar and muddy streamflows in rivers and drainage areas on... Taal and Pinatubo,” the Philippine Institute of Volcanology and Seismology (Phivolcs) said in an advisory.

Citing the latest forecast of the state weather bureau, Phivolcs said Dante was expected to make landfall over Batangas yesterday and then traverse western and Central Luzon in the next two days.

“Phivolcs strongly recommends increased vigilance and readiness of communities in pre-determined zones of lahar and related hazards on these volcanoes,” the agency said.

It said prolonged and intense rainfall could generate non-eruption lahar in major rivers draining western Pinatubo Volcano, where significant pyroclastic flow deposits of the 1991 eruption remain in the watershed.

Phivolcs said Pinatubo lahar would likely be channel-confined and occur in the upper to middle reaches of the Sto. Tomas- Marella and Bucao River systems, but could transition to muddy streamflows and floods and affect San Marcelino, San Narciso, San Felipe and Botolan towns in Zambales.

Muddy streamflows may be generated along the O’Donnell and Pasig-Potrero River systems draining the Pinatubo edifice to the north and southeast, respectively, and affect downstream communities in Tarlac and Pampanga, according to the agency.

Phivolcs said prolonged and heavy rainfall could also generate muddy streamflows around Taal Volcano, particularly on the slopes west of Taal Lake, where thin remnant ash can be remobilized in streams, roads and overland of the lakeward slopes.

Muddy streamflows can recur in previously affected communities of Agoncillo and Laurel, Batangas, it said.

On Tuesday night, Phivolcs issued an advisory, warning the public of possible lahar and muddy streamflows in rivers around Mayon Volcano.

Phivolcs said prolonged and heavy rainfall could generate post-eruption lahar in major channels draining Mayon by incorporating loose material from remnant pyroclastic density current deposits from the 2018 eruption.

The bulk of the erodible deposits occupy the watershed in Miisi, Mabinit, Buyuan and Basud channels.

Phivolcs said older and erodible deposits on the eastern and western slopes of the edifice could be remobilized as non-eruption lahar.

“Potential lahar and sediment-laden streamflows may occur along the Miisi, Binaan, Anoling, Quirangay, Maninila, Masarawag, Muladbucad, Nasisi, Mabinit, Matan-ag and Basud, Bantayan channels in Albay,” it said.

Phivolcs said Mayon lahar could threaten communities along the middle and lower slopes as well as downstream of these channels.