QUAKES ON PINATUBO, MAYON NOT SIGNS OF IMMINENT ERUPTION—PHIVOLCS

An increasing number of volcanic earthquakes have been recorded by government volcanologists on Mt. Pinatubo in Central Luzon region and on Mt. Mayon in Bicol region recently, but the Philippine Institute of Volcanology and Seismology (Phivolcs) said these should not cause alarm.

The Pinatubo Volcano Network and Philippine Seismic Network have recorded 826 quakes around Pinatubo since Jan. 20, which they said were “imperceptible,” or not easily noticed, in the vicinity of Mabalacat City in Pampanga province.

Quiescent condition

In its advisory on Wednesday, Phivolcs said these were not signs that the volcano, which erupted almost 30 years ago, was restive again. It gave assurance that Pinatubo remained at Alert Level 0 and in “quiescent condition” (inactive).

Under the volcano’s alert signals, Level 0 means no eruption in the foreseeable future.

The temblors happened along a segment of the Sacobia Lineament, which the agency said was a fault that was last active during the posteruption period of 1991.

Preparation

It said there was no threat from the quakes, but communities and local governments surrounding the volcano must always be prepared for both earthquake and volcanic hazards.

The most recent strongest temblor in the area was of 6.1-magnitude and occurring on the southern foot slopes of Pinatubo on April 22, 2019.

Pinatubo’s eruption on June 15, 1991, sent 2 million residents in Pampanga, Tarlac and Zambales to hundreds of evacuation centers, killed more than 1,000 people and altered the landscape of Central Luzon.

In its Wednesday bulletin, Phivolcs said 36 quakes were recorded on Mayon Volcano within a 24-hour period. From Jan. 16 to Jan. 27, 88 volcanic quakes and several rockfall events in the area were listed.

Normal occurrences

Paul Alanis, Phivolcs resident volcanologist in Legazpi City, dismissed speculations of Mayon’s increasing level of unrest.

The increasing number of quakes are normal occurrences exhibited by the volcano when it is under abnormal condition, or Alert Level 1, he said.

Alanis, in a phone interview on Wednesday, said the quakes were not related to magma buildup but only surface volcanic movements caused by hydrothermal activity inside the vent, when water interacts with rocks to cause ground movements.

A total of 106 volcanic quakes have been recorded on Mayon since Jan. 1.

Faint crater glow at the summit was also noted by Phivolcs on Jan. 6, Jan. 18 and Jan. 20. “So far, the faint crater glow could not be seen by a naked eye without the help of a special camera or telescope,” Alanis said.

Mayon last erupted in January 2018. S.