A “weak explosion” detected at Mount Pinatubo in Central Luzon on Tuesday, November 30, turned out to be a phreatic or steam-driven eruption.

The Philippine Institute of Volcanology and Seismology (Phivolcs) confirmed the phreatic eruption in an update on Tuesday evening.

The eruption took place between 12:09 pm and 12:13 pm.

Phivolcs had said on Tuesday afternoon that the source of the “weak explosion” was still being determined.

The eruption had “produced a plume that was detected by the Himawari-8 satellite” and reported to Phivolcs by Japan’s Tokyo Volcanic Ash Advisory Center.

“So far, there has been no reports of ashfall from communities of Zambales over which the eruption plume dispersed,” Phivolcs said on Tuesday evening.

The agency added that the phreatic eruption “was likely driven by shallow hydrothermal processes beneath the edifice.”

Phivolcs reiterated that there has been “very low seismic activity” or few volcanic earthquakes at Mount Pinatubo in the past days.

The level of diffuse volcanic carbon dioxide emission measured at the Pinatubo Crater Lake in November has been low as well.

Phivolcs earlier said it was looking at other potential sources of the explosion, including aircraft activity or ordnance disposal.

It confirmed on Tuesday evening that the phreatic eruption occurred after the Armed Forces of the Philippines conducted ordnance disposal activities on the northern flanks of Mount Pinatubo in the morning, but this “has no relation to the condition of the volcano.”

Phivolcs reiterated that the public must stay away from the vicinity of Mount Pinatubo.

“Shallow phreatic or hydrothermal explosions such as the event of today can occur without warning,” the agency said.

Phivolcs also reminded local government units and residents of areas surrounding the volcano to always be “prepared for both earthquake and volcanic hazards.”

Mount Pinatubo has been under Alert Level 0, the lowest alert level, since August 12.

Phivolcs said this alert level is “currently under consideration pending the results of ongoing GPS and InSAR data processing.” – Rappler.com