Volcanologist Alex Baloloy said the explosions occurred at 8:22 a.m., 11:19 a.m., 11:37 a.m. and 6:13 p.m., with the ash rising 100 to 150 meters high.
Baloloy attributed the ash explosions to small pockets of pressure inside the vent, causing "systematic clogging" as evidenced by the drop in sulfur dioxide emissions from 1,066 tons to 349 tons a day.
Baloloy noted that magma is ascending at a very slow rate.
Based on Mayon’s previous eruptions, he said ash puffs are critical indicators that the volcano is going to erupt soon.
"When it will erupt is what we cannot exactly predict," he said, adding that there are other parameters to consider.
Last Sunday, the volcano puffed out ash at 7:45 a.m., 12:45 p.m. and 4:09 p.m.  Celso Amo