The Philippine Institute of Volcanology and Seismology (Phivolcs) on Wednesday urged the public to take precautionary measures due to lahar and muddy streamflows from Taal and Pinatubo volcanoes.

At 10:30 a.m., Phivolcs issued an advisory citing the weather bureau’s forecast that Tropical Storm Dante is expected to make landfall over Batangas at 5 p.m. Wednesday. The heavy rainfall may trigger volcanic sediment flows or lahar, and muddy run-off in rivers and drainage areas in Taal and Pinatubo.

However, during a noontime press conference, the Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) reported that “Dante” has changed its track. The TS is now moving northwestward at 25 kph, and may make landfall over Bataan at night.

“Earlier we issued an advisory. Even if ‘Dante’ slightly changed its track, it may still have an effect, especially on the western side of Taal Lake,” Phivolcs Director Renato Solidum, Jr. said in the press conference.

According to Phivolcs, prolonged and intense rainfall may generate lahars on major rivers draining western Pinatubo Volcano where significant erodible pyroclastic flow deposits of the 1991 eruption remain on the watershed.

Further, Pinatubo lahar will 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, it added.

“Pyroclastic flow deposits are those that were deposited by the flows of ashes during an eruption,” Solidum said.

Phivolcs also mentioned in its advisory that 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.

“(Phivolcs recommends) increased vigilance and to take preemptive actions if necessary,” Solidum told the Philippine News Agency.

He added that people in areas close to the rivers and slopes mentioned in Pinatubo and Taal must monitor the typhoon condition and take precautions as necessary.