LEGAZPI CITY -- The Philippine Institute of Volcanology and Seismology (Phivolcs) said Wednesday Mayon Volcano continued its ash and pyroclastic flows and phreatomagmatic eruption, and advised disaster officials and responders to be on guard for possible lahar flows that may be triggered by intense rains.
Ed Laguerta, Phivolcs chief resident volcanologist in Bicol, said during the Provincial Disaster Risk Reduction and Management Council media briefing here on Wednesday morning that lahar flows would hit low-lying areas if a heavy-to-intense rainfall continued.
Weather advisory from the Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) in Bicol said the northeast monsoon or "amihan" would affect the region today. Partly cloudy to cloudy skies with isolated rain showers would prevail, it added.
Laguerta said, “Because of the series of phreatomagmatic, ash and pyroclastic flow spewed by the continuous Mayon Volcano activity, it may produce huge volume of lahar that can be mobilized by heavy rain".
"Based on Phivolcs study, a 1-mm-per-minute precipitation could initiate re-mobilization of volcanic materials," he added.
Phivolcs advisory issued at 12:30 p.m. Wednesday showed five episodes of intense but sporadic lava fountaining from the summit crater lasting seven minutes to one hour and 24 minutes occurred between 8:54 a.m. Tuesday to 3:57 a.m. Wednesday.
The lava fountains reached 500 meters to 600 meters high and generated ash plumes that reached three kilometers to five kilometers above the crater.
The events fed lava flows on the Mi-isi and Bonga Gullies, sprayed near-vent lava spatter, and fed incandescent rock fall on the summit area.
Pyroclastic density currents or PDCs on gullies heading the Mi-isi, Lidong/Basud, and Buyuan Channels were also observed.
The runout of PDCs on the Buyuan Channel is now exceeding five kilometers from the summit crater.
“Extreme rainfall may trigger landslides and excessive erosion from the pyroclastic and ash flows in the upper-to-middle slopes of Mayon Volcano, generating lahar in all river drainage,” Laguerta said.
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.
Furthermore, lahar-related flooding, washout and siltation can subsequently occur along the Yawa River, threatening adjacent and low-lying areas of Legazpi City.
The Phivolcs strongly recommended vigilance and readiness of communities in pre-determined zones of lahar hazards in the mentioned channels.
Preparedness on clearing and rehabilitation operations is also recommended in the event of debris deposition on roads and bridges that traverse the lahar channels.
Laguerta said currently, Mayon’s eruptive event hasd produced 6.2 million cubic meters of molten rocks or lava. He, however, could not yet figure out the volume of new lahar generated from the ash plume and pyroclastic flows ejected by the volcano.
He said, “What is closely being monitored is lahar deposit at the volcano edifice where its layer is described as ‘sandy’ and can be scoured during rainy days”.
“You can imagine how the speed of lahar in the upper portion of the volcano – the velocity of it when it cascades down to low-lying areas,” Laguerta said.
Similarly, the Phivolcs reiterated the strict implementation of the “no entry” advisory on the declared 6-km permanent danger zone and 2-km buffer danger zone due to the potentially amplified dangers of rockfalls, avalanches, landslides and steam-driven explosions at the summit area.
Laguerta said the current eruptive episodes of Mayon with 4 to 5 hours interval could signify that the volcano is possibly at the “peak” of eruption stage or could mean that it was still gathering strength and would continue its eruption activities.
On the issue whether to raise the volcano’s alert status to level 5, Laguerta explained that Alert Level 4 and 5 are the same in terms of Mayon manifesting hazardous eruption.
He said the raising of Alert Level 5 would depend not only on the given parameters such as the duration and frequency of the eruption but an assessment whether it would warrant recommending the extension of danger zones around the volcano.
Alert Level 4 remains raised over Mayon, and an 8-kilometer extended danger zone is recommended.
“When we decide to raise it to Level 5, we would also recommend another additional extension of the danger zone. What we are looking at here are the risk areas where it would affect inhabitants living around the volcano,” Laguerta said.
Meanwhile, as the Albay Public Safety Emergency Management Office (APSEMO) extended the danger zone to a 9-km. radius, the number of families affected has increased to 15,468 or 60,564 individuals as of Wednesday afternoon.
APSEMO head Cedric Daep confirmed in an interview that the affected families are residents of 46 barangays in the towns of Camalig and Guinobatan, the city of Ligao, Daraga, Tabaco City, Malilipot, Santo Domingo, and Legaspi City, all in Albay province. (PNA)
