Albay execs bracing for collapse of Mayon’s crater

LEGAZPI CITY, Philippines – Disaster management officials here disclosed yesterday that they are bracing for three worst-case scenarios that include a collapse in the upper portion of the crater wall of Mayon Volcano.

Cedric Daep, chief of the Albay Public Safety and Emergency Management Office (Apsemo), said that local officials are anticipating three scenarios, considering the previous and prevailing behavior of Mayon.

Daep said the first scenario would be a Vulcanian eruption that could result in a lateral collapse of the volcano’s upper slope. Second is pyroclastic materials flow on the northern flank down to the San Vicente and Bunga gullies facing the Tabaco City area, and third is if the volcano ejects ash columns with volcanic debris upwards and which could fall anywhere around the volcano.

In case of sectoral collapse, Daep said they would evacuate at least 12,000 more families from Legazpi City’s foothill villages. In the second scenario, residents at the northern portion of Mayon would be moved to safer ground although they did not evacuate in past eruptions, including in 2009. And in the last scenario, all residents surrounding Mayon within the 8-kilometer to 10-kilometer danger zone would be advised to be prepared for evacuation depending on the magnitude of eruption in progress.

“But in all the three scenarios, we will be evacuating more people, particularly those in the extended danger zone facing Legazpi City,” Daep told The STAR.

Ed Laguerta, head volcanologist of the Philippine Institute of Volcanology and Seismology (Phivolcs) in Bicol, said Mayon could still erupt – despite the decline in gas emission following gradual closing of the crater caused by sustained surface inflation – due to either magma intrusion or increasing gas pressurization inside the volcano.

The latest data issued yesterday by Phivolcs said that their instruments did not detect any volcanic earthquake and the sulfur dioxide emission remained low at 148 tons a day and 138 tons the other day.

“These emissions which are even lower than the baseline or normal volume of 500 tons a day could have been very positive development that Mayon is now going back to normal. But this is negated by the continuous increase in the surface inflation,” Laguerta said.

He said the Sunday aerial survey failed to get a clear image, as the crater was hazy at the time. He said they would conduct another aerial inspection once the crater is visible.

But he said that the latest initial ground deformation survey showed that Mayon’s surface inflated further by at least one-half millimeter, adding to the previous 13-millimeter surface inflation.

“With this development, there is no reason really to lower Mayon’s alert level. In fact, we are even more vigilant in observing the possible sudden change in the seismicity of the volcano as the inflation continues,” Laguerta stressed.

Daep requested Laguerta to explain the extent of eruption activities when Mayon exploded violently in 1984, which triggered the collapse of its crater wall facing Legazpi City, now know as the Bunga Gully.

Laguerta said the present behavior of Mayon resembles that of the 1984 pre-eruption episode.

“But in 1984, Mayon first had a series of phreatic or ash explosions before it went on a two-week lull. Then it erupted very violently that the intensity of its volcanic quake was felt all over Albay,” Laguerta recalled. –  With Celso Amo