With Typhoon "Rolly," which is now nearing super-typhoon category, expected to dump torrential heavy rains in Luzon, communities around Mayon Volcano, Mount Pinatubo, and Taal Volcano are now facing the threat of lahar.
This prompted the Philippine Institute of Volcanology and Seismology (Phivolcs) to warn these residents, especially those in pre-determined zones of lahar and related hazards, to increase their vigilance and take precautionary actions against the possible phenomenon.
“Due to its trajectory, current severe intensity and potentially high-volume rainfall, Rolly can be expected to generate volcanic sediment flows or lahar, muddy streamflows, or muddy runoff in rivers and drainage areas on the monitored active volcanoes of Mayon, Pinatubo, and Taal,” Phivolcs said in an advisory.
State volcanologists said prolonged and heavy rainfall could generate post-eruption lahar from Mayon Volcano in Albay to flow to the watershed areas of the Miisi, Mabinit, Buyuan, and Basud Channels.
Mayon lahar may threaten communities downstream of the said channels, including the Miisi, Binaan, Anoling, Quirangay, Maninila, Masarawag, Muladbucad, Nasisi, Mabinit, Matan-ag, and Basud Channels in Albay.
For Pinatubo, which is in the boundary of Zambales, Tarlac, and Pampanga, Phivolcs said non-eruption lahar are likely to be “channel-confined” and could occur in the upper to middle reaches of the Sto. Tomas-Marella and Bucao River systems.
Phivolcs said this could transition to muddy streamflows and floods on the lower reaches and affect nearby communities of San Marcelino, San Narciso, San Felipe, and Botolan in the Zambales Province.
Muddy streamflows could also 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 the provinces of Tarlac and Pampanga.
As Rolly moves near Luzon landmass, it could also trigger lahar around Taal Volcano in Batangas, 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.
With this development, Phivolcs said muddy streamflow and runoff may recur on previously affected communities of Agoncillo and Laurel in Batangas.
Rolly, which continues to gather more strength while moving toward the country, is expected to cross Central Luzon and will affect the whole Luzon mainland, the Philippine Atmospheric, Geophysical, and Astronomical Services Administration (PAGASA) said in its latest forecast.
Due to “very favorable conditions,” PAGASA said Rolly is more likely to be near super typhoon category by the time it grazes Bicol Region.
As of Saturday morning, the state weather bureau raised a tropical cyclone wind signal over areas where the three volcanoes are located – storm warning signal No. 2 in Albay, while signal No. 1 is up over Zambales, Tarlac, Pampanga, and Batangas.
While the typhoon continues to intensify ahead of its landfall in Polillo Islands and mainland Quezon on Sunday, PAGASA said parts of Bicol Region could be placed under storm warning signal No. 3, which could bring “destructive typhoon-force winds.”
Phivolcs strongly advised local governments involved to continue to monitor the typhoon conditions and take pre-emptive response measures to ensure the safety of the public.