A further decline in Mayon's activity is apparent since yesterday afternoon. Sulfur dioxide (SO2) emission rate decreased from the previous measurement of 8,740 tonnes per day (t/d) to yesterday's reading of 4,640 t/d. PHIVOLCS also noted the absence of ash from overhead steam clouds that emanated from the crater. Ground deformation measurements from tiltmeters and the Electronic Distance Meter also showed a decrease in the inflated state of the edifice.
Integrating observations over the past few days, a trend of decreasing unrest has become evident and a corresponding reduction in eruption-related hazard is recognized. In view of these developments, PHIVOLCS is lowering the alert condition from Alert Level 5 to Alert Level 4, which means that hazardous eruptions have ceased. For this Alert Level 4, PHIVOLCS recommends decreasing the eight (8) kilometer-radius Extended Danger Zone (EDZ) in the Southeast to seven (7) kilometers radius so that the residents temporarily displaced beyond seven (7) kilometers in this part of the volcano may now return to their homes. PHIVOLCS reminds the public that the six (6) kilometer-radius PDZ and seven (7) kilometer-radius EDZ should remain off limits because sporadic explosions may still occur and produce dangerous conditions within these zones.
With the ongoing strong rains over the volcano, PHIVOLCS emphasizes that lahars or mudflows may occur independent of eruption-related Alert Levels. Prolonged and intense rainfall may remobilize loose deposits, whether new or previously deposited, so that hazardous volcanic flows may impact river channels and their immediate vicinities. The Mabinit and Buyuan river channels are the main passageways where significant flows may pass but other gullies around Mayon may also channel life-threatening lahars. Thus, the public is strongly advised to be alert and to be prepared to move to higher grounds whenever river waters become noticeably swift and muddy.