Geologist on Pinatubo blast: No cause for alarm

The serenity offered by the crater lake formed after Mt. Pinatubo’s eruption in 1991 calms weary visitors.  (File photo by TONETTE OREJAS / Inquirer Central Luzon)

MABALACAT CITY, Pampanga, Philippines — At least 15 villages in the province of Pampanga are being closely monitored by disaster response authorities following the “weak explosion” on Mt. Pinatubo on Tuesday, an official of the Provincial Disaster Risk Reduction and Management Office (PDRRMO) said.

According to geologist Zacarias Daniel Baricuatro, chief of the climate change division of the PDRRMO, these villages in the towns of Porac and Floridablanca and Mabalacat City are within the 20-kilometer radius from the volcano’s crater lake and will be under tight watch for possible similar volcanic activities.

“But there’s nothing to be afraid of. The public should know that there’s still no cause for alarm,” Baricuatro said in a local television interview on Wednesday.

He said Mt. Pinatubo remained under alert level zero (normal) since Aug. 12 or four months after it was placed under alert level 1 (low-level unrest) due to the series of volcanic earthquakes that began in January.

“We’re always advising the public to be prepared knowing that Mt. Pinatubo is an active volcano and that the [warning status] could change anytime,” Baricuatro said.

He said local officials were also asked to stop all tourism-related activities near the volcano, especially within the 10-km radius from the crater lake, which is also a permanent danger zone.

Hydrothermal processes

The weak explosion on Mt. Pinatubo was likely caused by hydrothermal processes, the Philippine Institute of Volcanology and Seismology (Phivolcs) said in an advisory on Tuesday. Hydrothermal processes involve contact between water and the magma underneath a volcano.

The blast on the northern flanks of the volcano before noon on Tuesday produced an eruption plume that rose above the clouds.

Phivolcs said an ordnance disposal activity was conducted in the area before the weak explosion on Mt. Pinatubo but this “has no relation to the condition of the volcano.”

In another advisory, Phivolcs confirmed that the explosion that occurred between 12:09 p.m. and 12:13 p.m. was a phreatic eruption, also known as steam-blast eruption, which occurs when the extremely hot magma heats groundwater or surface water.

Although the eruption plume rose above the clouds, Phivolcs said there were no reports of ashfall in Zambales where it dispersed.

The agency has advised the public to refrain from going near Mt. Pinatubo as it also asked local governments around the volcano to prohibit people from entering the crater lake.