LAHAR ADVISORY FOR MAYON VOLCANO

21 July 2023

10:00 AM

Based on its Weather Advisory #5 issued at 11:00 AM on 20 July 2023, the Philippine Atmospheric Geophysical and Astronomical Services Administration (PAGASA) has estimated that a Low Pressure Area (LPA) exists approximately 700 km east of Borongan, Eastern Samar which will bring cloudy skies with scattered rainshowers and thunderstorms across the Bicol Region including Albay Province. It is further expected that the LPA will develop into a Tropical Depression (TD) named “EGAY” which can bring moderate to heavy rain between Sunday (23 July 2023) and Monday (24 July 2023).

Due to this development, communities in pre-determined areas with lahar hazards from Mayon Volcano are strongly recommended to be vigilant and ready. The incoming tropical depression is expected to bring about prolonged and heavy rainfall which may generate syn-eruption lahars along major channels draining the Mayon Volcano edifice by incorporating loose material from thick pyroclastic density current (PDC) deposits and ashfall from the ongoing 2023 eruption. The bulk of erodible PDC deposits currently occupy the watershed areas of the Mi-isi, Bonga and Basud Channels. 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. Mayon lahars can threaten communities along the middle and lower slopes and downstream of these channels with inundation, burial, and wash away.

DOST-PHIVOLCS, therefore, warns of potential lahars and sediment-laden streamflows on all river channels draining the slopes of Mayon Volcano, particularly the Mi-isi, Binaan, Anoling, Quirangay, Maninila, Masarawag, Muladbucad, Nasisi, Mabinit, Matan-ag, and Basud Channels, that may be generated by heavy rainfall brought about by TD “EGAY”. Communities and local government units beside these drainages are advised to be additionally vigilant and to move residents to high ground should heavy rains occur.

DOST-PHIVOLCS