Rolly can be expected to trigger lahar, mud flows - PHIVOLCS

The Philippine Institute of Volcanology and Seismology (PHIVOLCS) has issued a warning, considering potentially high-volume rainfall, that lahar and muddy streamflows from three active volcanoes may be expected in several areas along the path of Typhoon Rolly.

Rolly, based on the forecast made by PAGASA, will make landfall over the provinces of Aurora and Quezon and move through central Luzon as the effects would be felt in the entire island of Luzon.

"Due to its (Rolly) 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," according to the Lahar Advisory issued by PHIVOLCS late Friday evening.

"DOST-PHIVOLCS thus strongly recommends increased vigilance and readiness of communities in pre-determined zones of lahar and related hazards on these volcanoes," the agency stated.

The agency added that prolonged and heavy rainfall may generate post eruption lahars on major channels draining Mayon Volcano by incorporating loose materials from remnant pyroclastic density current (PDC) deposits from the January to March 2018 eruption.

The bulk of the PDC deposits is expected in watershed areas, namely: Miisi, Mabinit, Buyuan, and Basud channels.

Potential lahars and sediment streamflows may occur along the following channels:

• Miisi
• Binaan
• Anoling
• Quirangay
• Maninila
• Masarawag
• Muladbucad
• Nasisi
• Mabinit
• Matan-ag
• Basud

Pinatubo lahars, meanwhile, area likely to be channel confined and occur on the upper to middle reaches of Sto. Tomas-Marella and Bucao River systems but may transition to muddy streamflows and floods that may affect the following areas:

• San Marcelino
• San Narciso
• San Felipe
• Botolan, Zambales province

Muddy streamflows may be expected along O'Donnell ad Pasig-Potrero River systems draining the Pinatubo edifice to the north and southeast affecting downstream communities in:

• Tarlac
• Pampanga

Muddy streamflow and run-off from Taal Volcano may affect the following areas in Batangas:

• Agoncillo
• Laurel

The DOST-PHIVOLCS is advising the local government units in the affected areas to continue to monitor weather conditions and to conduct pre-emptive response measures.  -- BAP, GMA News