The Philippine Institute of Volcanology and Seismology (Phivolcs) has recorded a series of relatively weak tremors at Taal Volcano from 5 a.m. to 3 p.m. on Monday, Feb. 15.

Fifty tremor episodes ranged in duration from two to five minutes and occurred at shallow depths of less than 1 kilometer, signaling increased hydrothermal activity beneath the Taal Volcano Island (TVI), Phivolcs said.

Since Feb. 13, a total of 68 shallow tremor episodes have occurred in TVI, it added.

Moreover, Phivolcs noted that geochemical data on the main crater lake "indicate a continuous acidification of lakewater from a pH 2.79 to pH 1.59 between January 2020 and February 2021, an unseasonal temperature high of 77 degrees Celsius (ºC), and carbon dioxide/hydrogen sulfide gas flux ratios consistent with shallow magma degassing."

It further noted that ground deformation data from continuous electronic tilt on the volcano island recorded a slight deflation localized around the main crater, "although very slight inflation from GPS (global positioning system) data and InSAR (Interferometric Synthetic Aperture Radar) analysis and positive microgravity changes have been steadily recorded across the Taal region consistent with continuous magmatic degassing and hydrothermal unrest."

Phivolcs reminded the public that Taal Volcano is still under Alert Level 1 as there remains an increased possibility of sudden steam-driven or phreatic explosions, lethal accumulations or expulsions of volcanic gas and minor ashfall from the main crater that can occur and threaten areas within the volcano island.

Entry into the TVI, Taal’s permanent danger zone, especially the vicinities of the main crater and Daang Kastila fissure, should be strictly prohibited.

Local government units were advised to continuously assess previously evacuated barangays around Taal Lake for damages and road accessibilities and to strengthen preparedness, contingency, and communication measures in case of renewed unrest.

People were also asked to observe precautions due to possible ashfall, ground displacement across fissures and minor earthquakes in the event of a phreatic eruption.

Civil aviation authorities should advise pilots to avoid flying close to the volcano as airborne ash and ballistic fragments from sudden explosions and wind-remobilized ash may pose hazards to aircraft, Phivolcs said.