Phivolcs warns public vs lahar flows in Albay, Sorsogon

LEGAZPI CITY -- The Philippine Institute of Volcanology and Seismology (Phivolcs) has warned disaster officials and responders to be on guard as re-mobilization of volcanic debris from the slopes of Mounts Mayon in Albay and Bulusan in Sorsogon threatens the communities around them once Typhoon Ruby (Hagupit) makes landfall on Saturday.

Ed Laguerta, Phivolcs chief resident volcanologist in Bicol, said during the Provincial Disaster Risk Reduction and Management Council (PDRRMC) emergency briefing on Thursday afternoon that lahar flows will hit low-lying areas due to typhoon with heavy-to-intense rainfall.

“Most probably the remnants of the 2006 eruption and in quarrying sites of volcanic debris will cause the re-mobilization of lahar in low lying-areas near Mayon volcano," Laguerta said.

"Based on Phivolcs study, a 6-mm-per-hour precipitation could initiate re-mobilization of volcanic materials," he added.

Based on Phivolcs advisory issued at 3:00 p.m. Thursday, lahar flows from the slopes of two most active volcanoes in Bicol is expected to cascade down to low-lying areas once Ruby makes landfall on Saturday.

The agency said Ruby is estimated to bring heavy-to-intense amount of rainfall within its 700-kilometer-diameter coverage area, thus, posing grave threat of extreme rainfall-induced landslides and lahar in volcanic edifices, particularly in Albay and Sorsogon Provinces.

In Albay province, extreme rainfall may trigger landslides and excessive erosion of old pyroclastic deposits in the upper-to-middle slopes of Mayon Volcano, generating lahar in all river drainage.

Potentially, large-magnitude lahar can threaten downstream communities along river channels with inundation, burial and washout.

The greatest lahar hazard can consequently be faced by communities along the Masarawag (Guinobatan), Maninila (Guinobatan), Buyuan-Padang (Legazpi City), Lidong (Sto. Domingo), Mabinit (Legazpi City), Basud (Sto. Domingo), Miisi (Daraga), Anoling (Daraga) and Nabonton (Ligao City) channels.

Lahar-related flooding, washout and siltation can subsequently occur along the Yawa River, threatening adjacent and low-lying areas of Legazpi City.

In Sorsogon province, extreme rainfall may cause excessive erosion of existing pyroclastic deposits in the upper slopes of Bulusan Volcano, triggering lahar in rivers draining the southeastern, southwestern and northwestern flanks.

Potential moderate-volume lahar can threaten downstream communities along the Malunoy (Patag), Mapaso, Cadac-an, Tinampo and Cogon Rivers in Irosin and the Añog-Rangas River in Juban.

The Phivolcs strongly recommended vigilance and readiness of communities in pre-determined zones of lahar hazards in the above volcanoes.

Preparedness on clearing and rehabilitation operations is also recommended in the event of debris deposition on roads and bridges that traverse lahar channels.

The Phivolcs has reiterated the strict implementation of no entry on the declared permanent danger zones in both Mayon and Bulusan volcanoes due to the potentially amplified dangers of rockfalls, avalanches, landslides and steam-driven explosions at the summit area.

The Philippine Atmospheric, Geophysical and Astronomical Services Administration (Pagasa) in Bicol has warned disaster officials and responders that with 700 diameter associated with heavy-to-intense precipitation, Ruby will be causing massive landslides across the region, storm surges, and flashfloods, thus, re-mobilizing lahar flows from the restive Mayon volcano. (PNA)


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