The Philippine Institute of Volcanology and Seismology (Phivolcs) on Wednesday, Dec. 18 issued a lahar warning for areas surrounding Kanlaon and Mayon volcanoes as heavy rainfall from Tropical Depression Querubin and the shear line is expected to continue to affect Bicol Region and Negros Island.
Based on the Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) Tropical Cyclone Bulletin No. 3, issued at 5 a.m., heavy to intense rainfall will affect several areas in southeastern Luzon, Visayas, and Mindanao, including those far from the projected path of the tropical depression.
As moderate to heavy rainfall due to the combined effects of Tropical Depression Querubin and the shear line is expected over Bicol Region and Negros Island in the coming days, Phivolcs warned that it could trigger volcanic sediment flows or lahars, muddy streamflows, or runoff in rivers and drainage areas around the monitored active volcanoes.
The agency urged increased vigilance and preparedness in communities located in lahar-prone zones.
In particular, it said prolonged and heavy rainfall could generate post-eruption lahars in major channels draining Kanlaon Volcano, which may incorporate loose materials from the pyroclastic density current (PDC) deposits of the Dec. 9 explosive eruption.
Lahars and sediment-laden streamflows may impact the Tamburong Creek in Biak-na-Bato, Baji-Baji Falls, and Talaptapan Creek in Cabacungan, La Castellana.
Phivolcs said these events may resemble the lahars observed on June 5, which affected communities downstream of these creeks.
Likewise, heavy rainfall could trigger post-eruption lahars on Mayon Volcano’s major channels, incorporating loose materials from the PDC deposits of the January-March 2018 eruption.
Phivolcs said the bulk of erodible PDC deposits are found in the watershed areas of the Miisi, Mabinit, Buyuan, and Basud Channels.
Erosion of banks and channel beds in both older and recent eruption deposits could result in the remobilization of non-eruption lahars, threatening downstream communities with inundation, burial, and destruction, it added.
Potential lahars and sediment-laden streamflows may affect the Miisi, Binaan, Anoling, Quirangay, Maninila, Masarawag, Muladbucad, Nasisi, Mabinit, Matan-ag, Basud, and Bulawan channels in Albay.