Communities near the surrounding slopes of Mayon Volcano in Albay and Bulusan Volcano in Sorsogon were warned of possible lahar flows and landslides due to moderate to heavy rains that may be spawned by typhoon “Tisoy” (international name “Kammuri”) over the Bicol region this week.
The Philippine Institute of Volcanology and Seismology has issued lahar advisories for Mayon Volcano and Bulusan Volcano to warn the public of the impending threat of lahar flows.
It urged residents living in pre-determined zones of lahar hazards in Mayon Volcano to remain vigilant and prepared.
“Prolonged and heavy rainfall may generate post-eruption lahars on major channels draining the Mayon Volcano edifice from thick pyroclastic density current material and ashfall deposited during the January-March 2018 Mayon eruption,” it said.
Phivolcs advised that the bulk of erodible pyroclastic density current deposits occupy the watershed areas of the Miisi, Mabinit, Buyuan, and Basud channels.
These deposits can be remobilized by rainwater and incorporate existing erodible material on channel banks and channel beds to generate boulder-rich or sediment-rich lahars, it explained.
It warned of potential lahars and sediment-laden stream flows on all river channels draining the slopes of Mayon Volcano, particularly the Miisi, Mabinit, Matan-ag, Basud, Masarawag-Maninila, and Quirangay channels, that may be generated by heavy rainfall brought about by Tisoy.
Communities and local government units beside these drainages were advised to be extra vigilant and to move residents to high ground when heavy rains occur.
Phivolcs also noted that prolonged and heavy rainfall may cause excessive erosion of existing pyroclastic deposits in the upper slopes of Bulusan Volcano, which can trigger lahars in rivers draining the southeastern, southwestern, and northwestern flanks.
It said potential lahars can threaten downstream communities along the Malunoy (Patag), Mapaso, Cadac-an, Tinampo, and Cogon Rivers in Irosin, Sorsogon and the Añog-Rangas River in Juban, also in Sorsogon.
Phivolcs recommended vigilance and readiness among communities in Taal Volcano island that may also be affected by Tisoy. (Ellalyn V. Ruiz)