Volcanologists say lull in Mayon rumbling could be deceptive

A WOMAN cooks her family’s meal at a shelter for residents of areas within a six-kilometer radius danger zone around Mayon Volcano. MARC ALVIC ESPLANA/INQUIRER SOUTHERN LUZON

LEGAZPI CITY—The Philippine Institute of Volcanology and Seismology (Phivolcs) said Mayon Volcano is now exhibiting a behavior similar to what it displayed in 1984 when there was a lull before the volcano erupted.

Eduardo Laguerta, Phivolcs resident volcanologist at the Ligñon Hill Observatory here, said the volcano showed a lull in activity for two weeks before the 1984 eruption, which did not bring any casualty but led to the evacuation of at least 73,000 people.

“What Mayon is telling us is to look back at the 1984 eruption wherein there was a lull of two weeks, then early morning of Sept. 23 it exploded, resulting in a scar, or destruction of, (on) the crater wall sliding to southeast of Mayon,” he said.

Phivolcs referred to the 1984 eruption as “vulcanian type,” in which there were explosions similar to those produced by cannons being fired.

Boulders, lava

These explosions, said the volcanologist, had short intervals. During this episode, the Phivolcs said, the volcano spewed boulders the size of houses and discharged glowing lava.

Laguerta said the volcano has been on a lull for five days now as indicated by fewer quakes. It means the volcano is simmering down but volcanologists said the possibility of eruption is still there.

In its Sept. 24 bulletin, Phivolcs recorded no volcanic quake, four rock fall events while the amount of sulfur dioxide that the volcano emits has fallen to 569 tons per day compared to 1,048 tons per day recorded on Sept. 22.

Laguerta said the decrease in volcanic quakes and rock fall events are effects of the slow movement of magma to the crater but this does not mean that the volcano has calmed down as signs of eruption are still there, like reduced sulfur dioxide emission.

“The sulfur dioxide emission has lessened but this means that the volcano is building up more strength or pressure for a big eruption,” Laguerta said.

Lava dome

He said Mayon’s alert level could not be lowered because the accumulation of lava is still highly visible. Phivolcs raised Mayon’s alert level to 3 on Sept. 15, which means the volcano would erupt in weeks.

According to the Phivolcs, the lava dome is now nearly 46 meters high with an estimated volume of 563,604 cubic meters, which is equivalent to more than 141,000 truckloads of rocks that would explode should there be an eruption.

Laguerta said recent aerial survey showed the lava dome is tilted to the southeastern side of the volcano so areas on this side would be exposed to pyroclastic flow and even lava flow.

These areas, which are within the six-to eight-kilometer

extended danger zone, include 32 villages in Legazpi City and the municipalities of Camalig, Daraga and Sto. Domingo.

Albay’s Disaster Risk Reduction and Management Council said at least 86,961 people need to be evacuated in these areas should eruption be imminent and the alert level is raised to 4.