MANILA – The head of the Philippine Institute of Volcanology and Seismology (Phivolcs) has clarified that there is always a possibility of a phreatic eruption even when a volcano is at Alert Level 0 or normal.

Phivolcs reported a "phreatic eruption from the Mayon Volcano summit" at 4:37 p.m. Sunday, which lasted 4 minutes and 9 seconds, and generated a booming sound, rockfall, pyroclastic density currents and a 1,200 meter-tall plume that drifted to the southwest.

Phreatic or steam-driven eruptions are sudden-onset and short-lived events and happen without warning or any precursors, according to Phivolcs. It happens when hot material comes into contact with water.

"There are still hot materials from last years eruption at the crater of Mayon Volcano and when this comes into contact with water, it may release steam, ash and gases," Phivolcs Director Teresito Bacolcol told the Philippine News Agency on Sunday.

Bacolcol added that Phivolcs recorded an effusive eruption of Mayon from June 11 to Dec. 8, 2023.

"Since we do not know when phreatic eruptions will happen, it is best not to venture inside the 6-km. permanent danger zone (PDZ)," he said.

Mayon Volcano has been under Alert Level 2 (decreased unrest) since Dec. 8, 2023.

Entry into the 6-kilometer PDZ should be prohibited to minimize risks from explosions, rockfalls and landslides.

Phivolcs is urging aviation authorities to advise pilots to avoid flying close to the volcanos summit, as ash from any sudden eruption can be hazardous to aircraft.

The Civil Aviation Authority of the Philippines on Sunday said no ashfall was detected at the Bicol International Airports runway.