LEGAZPI CITY – The Philippine Institute of Volcanology and Seismology (Phivolcs) would be sending this weekend teams to assess the present position and volume of lahar materials swept from the slopes of Mayon Volcano by rampaging floodwaters spawned by Super Typhoon Rolly.
Paul Alanis, Phivolcs resident volcanologist at Lignon Hill Observatory here, said they want to determine the volume of the volcanic debris that cascaded and the potential danger this could bring should another rampaging flood occurs.
“First the teams will determine the volume of the lahar flows, then they will assess if these materials will pose a potential danger to the communities at the foot-slopes of Mayon,” Alanis told the Philippine News Agency (PNA).
Alanis refused to estimate the volume of eroded volcanic debris, saying it is no longer accurate to use old figures of the ejecta, or the material that is forced or thrown out as a result of volcanic eruption after Mayon erupted in 2018.
“There are several typhoons already that hit Albay between Mayon’s eruption in 2018 and at the present time. And these typhoons and heavy rains had already washed down the significant volume of volcanic materials into the gullies and river channels at its foot,” Alanis said.
He said a new assessment must be done to come up with a reliable estimate of the lahar now deposited at the upper and middle slopes of Mayon that could be washed down should heavy to torrential rains happen again over the active volcano.
Alanis said the lahar sediments are now observed in Anoling gully in Camalig; Padang-Bonga channel in Legazpi City; Budiao gully in Daraga; and Basud River in Sto. Domingo.
“We had been monitoring lahar movements in these rivers, gullies, and channels until March. But it was stopped when limited movements were imposed by IATF due to the Covid 19 pandemic,” Alanis said.
As “Rolly” brought heavy to torrential rains on Sunday, rampaging floods carried lahar materials to the communities in Barangays San Francisco and Travesia in Guinobatan that killed six people and either buried or half-buried their houses.
Guinobatan Mayor Anne Gemma Ongjoco requested that technical teams from the Department of Environment and Natural Resources should immediately assess the present location of the lahar materials and order the dredging of rivers and channels that are now fully silted.
“Volcanic materials have now silted the rivers and gullies at the foot of Mayon here in Guinobatan. There is an urgent need to take them out of these rivers and gullies,” Ongjoco told PNA.
She said if these rivers and gullies would remain silted, rampaging floods could again potentially wash away downslope communities.
In its daily volcano bulletin, Phivolcs reminded that active stream or river channels and those identified as perennially lahar-prone areas on all sectors of the volcano should also be avoided especially during extreme weather conditions when there is heavy and prolonged rainfall. (PNA)