MANILA -- State seismologists lowered Friday the alert status of Mayon volcano in Albay province from 3 to 2 due to a decline in its "overall activity."
Alert Status 2 means that the likelihood of hazardous eruption within days to weeks has lessened.
The Philippine Institute of Volcanology and Seismology (Phivolcs) said in its December 19 bulletin that since the last recorded seismic swarm on November 29, the volcano's "seismic activity has declined to an average two to three mostly volcano-tectonic earthquakes daily that are attributed to rock fracturing beneath the northern flank of the edifice."
This decline was observed for nearly the past three weeks, added the Phivolcs.
It also said that there have been even lesser low frequency earthquakes associated with magma or volcanic gas movement, while "few minor rockfall events detected were more likely enhanced by intense rainfall over the volcano summit rather than by lava extrusion at the crater."
"Such overall low-level seismicity indicates that there is currently no active transport of eruptible magma to the shallow levels of the volcano," the agency said.
Phivolcs also observed that since June 2014, "Mayon's edifice has been inflating or swelling due to very slow intrusion of subsurface magma beneath the northern flank of the edifice, based on Precise Leveling (PL) surveys and continuous electronic tilt measurements."
"Distinct short-term increases in edifice inflation in October 2014 notably preceded episodes of short lava flow from the summit crater on October 12 and 19. However, short-term increase in edifice inflation recorded by PL surveys in the last week of November 2014 was not succeeded by lava extrusion," it said.
Intrusion to shallow levels has not occurred in nearly three weeks, while no new lava materials has been observed at Mayon's summit crater since November 28, according to Phivolcs.
The agency warned though that although the alert status has been lowered, it should not be interpreted that the volcano's unrest has ceased, "considering that deeper beneath it, eruptible magma has already accumulated."
"If there is a resurgence of volcanic unrest based on any one or combination of the above monitoring parameters, the alert status may step up to Alert Level 3 again," Phivolcs said.
"On the other hand, if there is a noticeable return to baseline levels of ground deformation and sustained low levels of other parameters, then the Alert Level may further step down," it added.
With this, the public is still reminded to avoid entry into the six-kilometer Permanent Danger Zone "due to perennial hazards of rockfalls, avalanche, ash puffs and sudden steam-driven or phreatic eruptions at the summit area."
People living in valleys and active river channels were advised to remain vigilant against sediment-laden streamflows and lahars in the event of prolonged and heavy rainfall. (LMY/Sunnex)