The Philippine Institute of Volcanology and Seismology warned the public that the heavy torrential rains brought by the super typhoon ‘Karding’ over Southern and Central Luzon could generate volcanic sediment flows or lahars in rivers and drainage areas on Pinatubo and Taal volcanoes.
The state seismic bureau disclosed that prolonged and intense rainfall can cause non-eruption lahars on major rivers draining western Pinatubo Volcano where significant deposits of the 1991 PDCs remain on the watershed.
It added that Pinatubo lahars are likely 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 in 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 Province,” Phivolcs said.
Meanwhile, the prolonged and heavy rainfall may result in muddy streamflow and muddy runoff around Taal Volcano, particularly on the slopes of the western Taal Caldera 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 in previously affected communities of Agoncillo and Laurel in Batangas.
Phivolcs added the extensive fissures on the northeast and southwest sectors of Taal Caldera generated by the 2020 eruption may be eroded and enlarged by heavy rains, as was the case in previous typhoons when even previously undetected fissures emerged and caused damages to overlie or adjoining buildings and houses.
The eruption fissures occur in the Municipalities of Agoncillo, San Nicolas, Lemery and Taal on the southwest caldera, and in the Cities of Talisay and Tanauan on the northeastern side.
The potential fissure enlargement with rains brought by ‘Karding’ brought was seen to cause structural damage or even collapse of structures that are situated right on or beside the fissure traces.
Phivolcs recommended extreme vigilance and readiness in the pre-determined zone of lahar and related hazards of Taal and Pinatubo volcanoes.