Resident volcanologist Ed Laguerta said the "phreatic explosion" occurred at 11:20 a.m. and the ash drifted toward the southwest direction.
Another such explosion was observed at 3:09 p.m. Sunday, with the ash column reaching about 150 meters high.
"(Mayon) is not yet silent," he said, adding the volcano remains inflated due to rising magma.
A faint crater glow was also observed Sunday night. Volcanologist Alex Baloloy said Mayon’s continued abnormal behavior will prevent Phivolcs from lowering the present alert level 3. — Celso Amo, Cet Dematera