By ELLALYN DE VERA-RUIZ
The Philippine Institute of Volcanology and Seismology (Phivolcs) on Tuesday lowered the alert status over Mayon Volcano from 4 to 3, having observed “decreased tendency towards hazardous eruption.”
Phivolcs said Mayon Volcano’s condition last week has been characterized by a general decline in unrest reflected by moderate seismicity and degassing, deflation of the edifice and a decrease in eruptive activity.
Specifically, the volcano’s activity has diminished to sporadic degassing with associated ash plumes, weak lava fountaining, quiet lava flow and lava collapse, interspersed with two to four days of relative quiescence.
“The decline in the intensity and frequency of events suggests a gradual depletion of eruptible magma at the shallow levels of the edifice,” Phivolcs pointed out.
Likewise, its seismic activity has been dominated by low frequency events associated with degassing at the summit and signals of rockfall and small-volume pyroclastic density currents (PDCs) or pyroclastic flow generated by the collapsing front and margins of lava flows on the Miisi, Bonga and Basud gullies and intermediary channels.
Phivolcs noted that this is reflected in the diminishing overall seismic energy release from the volcano despite the infrequent occurrence of effusive activity at the summit crater.
From Monday to Tuesday, only four volcanic earthquakes and 44 rockfall events were recorded by the Mayon Volcano’s seismic monitoring network.
In addition, there is a downtrend in ground deformation following a period of continuous inflation that began in October-November 2017 and indicates a decrease in magma recharge from deep to shallow levels of the edifice.
However, Phivolcs clarified that Mayon Volcano is still inflated relative to January 2010 baselines.
Mayon Volcano’s sulfur dioxide flux throughout the eruption has varied from a maximum of 4,270 tons/day on Feb. 21 to 1,400 tons/day on March 3.
