Photo courtesy of Philippine News Agency (PNA).
The Philippine Institute of Volcanology and Seismology (Phivolcs) lowered Mayon Volcano’s status from Alert Level 3 to Alert Level 2 on Wednesday after monitoring data showed a sustained decline in unrest since July 23.
Phivolcs said eruptive activity at the summit crater had weakened, with fewer Strombolian events, lava-collapse rockfalls and pyroclastic density currents.
Lava flows along the Mi-isi, Bonga and Basud gullies stopped advancing on July 22, indicating that fresh magma was no longer reaching the crater during the period.
Rockfall activity also dropped sharply, from an average of 278 events per day since the eruption began on Jan. 6 to 12 per day from July 23.
The agency said Strombolian activity and pyroclastic density currents had ceased after the last recorded events on July 26 and 28. The total volume of erupted lava and related deposits was estimated at 89 million cubic meters.
Volcanic earthquakes fell from an average of 57 events per day to 13, while seismic energy returned to pre-eruption levels.
Sulfur dioxide emissions also declined from a June peak of 13,128 tonnes per day, although Phivolcs said gas output remained above baseline levels.
Ground deformation data showed that Mayon remained generally pressurized, suggesting that magma was still being stored beneath the volcano despite the slowdown in surface activity.
Phivolcs warned that Alert Level 2 did not mean the unrest had ended. The public was advised to stay out of the six-kilometer Permanent Danger Zone because of the risk of sudden explosions, rockfalls, ashfall and pyroclastic density currents.
Communities near channels draining the Mi-isi, Bonga and Basud gullies were also urged to prepare for possible lahars and sediment-laden flows during heavy rain. Aviation authorities were advised to keep aircraft away from the summit.
