A phreatic explosion occurred over Mount Bulusan in Sorsogon on Monday.
The Philippine Institute of Volcanology and Seismology (PHIVOLCS) says, the volcano spewed ash about 1 kilometer high at 7:36 am.
Phreatic explosion is steam-driven and it happens when water beneath the ground or on the surface is heated by magma, lava, hot rocks or new volcanic deposits.
The last time Mt. Bulusan spewed ash was on October 4, 2016.
The volcano remains on Alert Level 1.
PHIVOLCS sees no need to enforce a preventive evacuation of residents following the explosion.