Mayon, Pinatubo, Taal mudflow, lahar possible as ‘Rolly’ nears Luzon — Phivolcs 

Mayon Volcano (INQUIRER file photo by Ed Lustan)

MANILA, Philippines — State volcanologists have warned of possible lahar and mudflow from three active volcanoes as Typhoon Rolly threatens Luzon, and is expected to bring its high volume of rainfall.

In a lahar advisory issued Friday, the Philippine Institute of Volcanology and Seismology (Phivolcs) said that the typhoon’s heavy rains may trigger lahar and muddy streamflows in rivers and drainage areas of Mayon, Pinatubo and Taal volcanoes. 

Based on the Philippine Atmospheric, Geophysical and Astronomical Services Administration’s (Pagasa) monitoring, “Rolly” is expected to make landfall over Quezon province, and may even reach super typhoon category.

Currently, Tropical Cyclone Wind Signal No. 2 is hoisted over the eastern portion of Camarines Sur,  Catanduanes, Albay and Sorsogon.  

Mayon status

Phivolcs warned that heavy rainfall may generate lahar on major channels draining Mayon Volcano by incorporating  loose material from remnant pyroclastic density current (PDC) deposits from the volcano’s January to March 2018 eruption. 

“The bulk of erodible PDC deposits occupy the watershed areas of the Miisi, Mabinit, Buyuan and Basud Channels,” Phivolcs said.

”In addition, older and erodible eruption deposits occupy the watershed areas on the eastern and western slopes of the edifice and can be remobilized as non-eruption lahars by erosion of banks and channel beds.”

Hence, lahar and sediment-laden streamflows may occur in the Miisi, Binaan, Anoling, Quirangay, Maninila, Masarawag, Muladbucad, Nasisi, Mabinit, Matan-ag, and Basud Channels. 

Pinatubo situation

“Prolonged and intense rainfall may generate non-eruption lahars on major rivers draining western Pinatubo Volcano where significant deposits of the 1991 PDCs remain on the watershed,” Phivolcs then said of Mount Pinatubo. 

“Pinatubo lahars are 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. 

Taal outlook

Likewise, the typhoon’s heavy rainfall may generate muddy streamflow 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.” 

Taal Volcano (taken October 26, 2020). Photo by Mike Frialde/INQUIRER.net

Muddy streamflow and run-off may recur previously affected communities of Agoncillo and Laurel, Batangas province, Phivolcs said. 

“DOST-Phivolcs strongly advises the communities and local government units of the above-identified areas of risk to continually monitor the typhoon conditions and take pre-emptive response measures for their safety from Rolly,” the agency warned. 

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