Ed Laguerta, resident volcanologist of the Philippine Institute of Volcanology and Seismology (Phivolcs), said the drop in the volcano’s sulfur dioxide emission — from a high of 12,548 tons per day last July 31 to 7,418 tons on Aug. 1, 7,050 tons on Aug. 2 and 4,760 tons yesterday — could be due to the ascent of new viscous magma.
Laguerta said the ascent of viscous magma could have plugged the exits of sulfur dioxide, causing its emission to drop, but could also increase the build-up of pressure inside the vent.
"This magma build-up may proceed first to fountaining and then to an explosion," he said.
Seismic sensors recorded the ongoing magma ascent through 51 low-frequency volcanic quakes during the past 24-hour observation period, compared to 16 the previous day.
Moderate to voluminous dirty white steam, accompanied by bluish fumes, was observed on Mayon’s crater.
In a bulletin, Phivolcs said large lava blocks flowing down Mayon’s slopes produce fine ash and gases when they break upon impact.
As a result, 343 tremor episodes were recorded as due lava blocks tumbled down Mayon’s slopes.
Cedric Daep, head of the provincial disaster management office, said policemen and Army soldiers have set up a checkpoint in Barangay Mabinit to ensure that nobody enters the six-kilometer radius permanent danger zone. Lava flows have breached the boundary of the danger zone.
Reports said local and foreign tourists have come to see the advancing lava flows, with some even taking samples.
"This is the reason why we have to cordon off the area because we will be the ones blamed if there are casualties," Daep said.
Laguerta said they are optimistic that the lava flows would not affect populated areas since they were heading toward gullies and other channels at the foot of Mayon. — With Cet Dematera