By Mar S. Arguelles
LEGAZPI CITY ---The Philippine Institute of Volcanogy and Seismology (Phivolcs) yesterday (Wednesday) warned residents in low lying areas surrounding Mount Mayon to be cautious of possible lahar flows in case of heavy rains.
Eduardo Laguerta, resident volcanologist, said ash and pyroclastic flow spewed by the volcano could produce huge volume of lahar that can be mobilized during moderate to heavy rainfall.
Laguerta said “all low lying areas around are potential threats to lahar flows during rainfall.”
Laguerta in an interview said despite the river channels and the dikes around the volcano there is a possibility the lahar generated from ash plume and lava flows could saturate river channels and dikes that could trigger lahar flows posing danger to residents living in low lying areas.
Laguerta said the currently Mayon eruptive event has 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 it 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.
Lahar threatened villages are Miisi and Salvacion in Daraga, Anoling in Camalig, Maninila and Masarawag in Guinobatan, and Buyoan in this city.
Rains spawned by Supertyphoon Reming in 2006 swept millions of cubic meters of lahar deposited at the slopes of the volcano where massive lahar flows and flooding hit Legazpi City and the neighboring town of Daraga.
“Lahat ng lahar deposit na erode ng Reming,” he said.
Laguerta at a PDRRMC news conference said Mayon volcano on Tuesday exhibited five intense but sporadic lava fountaining from the summit crater.
The lava fountains have reached 500 to 600 meters high it also generated ash plumes as high as 5 kilometers from the summit.
The event also fed lava flows on the Miisi and Bonga Gullies, sprayed near-vent lava spatter, and fed incandescent rockfall on the summit area.
Pyroclastic materials cascaded down the gullies heading the Miisi, Lidong/Basud, and Buyuan channels which according to volcanologist pyroclastic flows on the Buyuan channel has exceeded 5 kilometers from the volcano’s summit.
Laguerta clarified that the current eruptive episode of Mayon volcano of 4 to 5 hours interval could signify that the volcano possibly is at the “peak” of the eruption stage or it could mean that the volcano is still gathering strength and continue its eruption activities.
On the issues whether to raise the volcano’s alert status to level 5, Laguerta explains the Alert Level 4 and 5 are all the same (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.
So far volcanologist has raised the volcano’s Alert Level 4 where it recommended that a 8-kilometer extended danger zone be declared.
“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,” he said.