Based on the Severe Weather Bulletin # 3 issued at 05:00 PM today by the Philippine Atmospheric Geophysical and Astronomical Services Administration (PAGASA), Typhoon “ROLLY” will make landfall over Aurora-Quezon Provinces on Sunday evening or Monday early morning, traverse Central Luzon and affect nearly the entirety of Luzon Island. Due to its trajectory, current severe intensity and potentially high-volume rainfall, “ROLLY” can be expected to generate volcanic sediment flows or lahars, muddy streamflows or muddy run-off in rivers and drainage areas on the monitored active volcanoes of Mayon, Pinatubo and Taal. DOST-PHIVOLCS thus strongly recommends increased vigilance and readiness of communities in pre-determined zones of lahar and related hazards on these volcanoes.
Prolonged and heavy rainfall may generate post-eruption lahars on major channels draining Mayon Volcano by incorporating loose material from remnant pyroclastic density current (PDC) deposits from the January-March 2018 eruption. The bulk of erodible PDC deposits occupy the watershed areas of the Miisi, Mabinit, Buyuan and Basud Channels. In addition, older and erodible eruption deposits occupy the watershed areas on the eastern and western slopes of the edifice and can be remobilized as non-eruption lahars by erosion of banks and channel beds. Mayon lahars can threaten communities downstream of the above channels with inundation, burial and wash away. Potential lahars and sediment-laden streamflows may occur along the Miisi, Binaan, Anoling, Quirangay, Maninila, Masarawag, Muladbucad, Nasisi, Mabinit, Matan-ag, and Basud Channels in Albay Province.
Prolonged and intense rainfall may generate non-eruption lahars on major rivers draining western Pinatubo Volcano where significant deposits of the 1991 PDCs remain on the watershed. Pinatubo lahars are likely be channel-confined and occur on the upper to middle reaches of the Sto. Tomas- Marella and Bucao River systems but may transition to muddy streamflows and floods on the lower reaches and affect adjacent communities of San Marcelino, San Narciso, San Felipe and Botolan, Zambales Province. Muddy streamflows may likewise 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 Provinces.
Prolonged and heavy rainfall may also generate muddy streamflow and muddy runoff around Taal Volcano, particularly on the slopes west of Taal Lake where thin remnant ash can be remobilized in streams and roads and overland of the lakeward slopes. In particular, muddy streamflow and runoff can recur on previously affected communities of Agoncillo and Laurel, Batangas Province.
DOST-PHIVOLCS strongly advises the communities and local government units of the above identified areas of risk to continually monitor the typhoon conditions and take pre-emptive response measures for their safety from “ROLLY.”
DOST-PHIVOLCS
