Manila: The Philippine Institute of Volcanology and Seismology (Phivolcs) on Saturday issued a warning about potential lahar flows from the Pinatubo and Taal volcanoes due to the heavy rains brought by the southwest monsoon.

According to Philippines News Agency, Phivolcs highlighted that the intense rainfall could lead to volcanic sediment flows or lahars, as well as muddy streamflows or runoff in the rivers and drainage areas surrounding these volcanoes. The advisory emphasized that prolonged and intense rainfall might trigger non-eruption lahars in the major rivers draining the western side of Pinatubo Volcano, where significant deposits from the 1991 pyroclastic density currents remain.

Phivolcs indicated that the lahar flows from Pinatubo are expected to be confined within channels and occur primarily on the upper to middle reaches of the Sto. Tomas-Marella and Bucao River systems. However, these may transition to muddy streamflows and floods in the lower reaches, impacting nearby communities such as San Marcelino, San Narciso, San Felipe, and Botolan in Zambales province. Additionally, muddy streamflows might also develop along the O'Donnell and Pasig-Potrero River systems, affecting downstream areas in the Tarlac and Pampanga provinces.

The advisory also noted the risk of prolonged and heavy rainfall generating muddy streamflows, runoff, and even volcanic debris flows around Taal Volcano, particularly on the slopes west and north of Taal Lake. The potential for remobilization of old, loose volcanic deposits, which are already saturated from previous rains, could pose a hazard to streams, roads, and lakeward slopes.

Communities previously affected, such as Agoncillo, Laurel, and Talisay in Batangas province, are at risk of experiencing recurrent muddy and debris flows. Phivolcs urged local communities and government units in the identified areas to keep monitoring storm conditions and to implement preemptive response measures to ensure safety.