The Philippine Institute of Volcanology and Seismology (Phivolcs) on Tuesday, March 9 raised the alert status of Taal Volcano from Level 1 to 2 as the active volcano has been exhibiting increased unrest since Feb. 13, 2021.
"This means that there is probable magmatic activity that may or may not lead to an eruption," Phivolcs said.
The agency's monitoring network recorded a total of 28 volcanic tremor episodes, four low frequency volcanic earthquakes, and one hybrid earthquake at shallow depths of less than 1.5 kilometers beneath the Taal Volcano Island (TVI) in the past 24 hours--from 8 a.m., March 8 to 8 a.m., March 9.
Phivolcs observed that volcanic tremors have increased seismic energy compared to previously recorded episodes and ranged between three to 17 minutes in duration.
It said the total number of volcanic tremor events has risen to 866 since the onset of increased activity on Feb. 13.
Moreover, a total of 141 low-frequency volcanic earthquakes have occurred within one kilometer depths beneath TVI and immediate vicinities.
"Overall, seismic activity in the past month indicates increased magmatic and hydrothermal activity at shallow depths beneath TVI," Phivolcs said.
It also observed changes in the main crater lake having recorded a temperature high of 74.6 degrees Celsius and in mid-February 2021, and continuing increase in acidity to pH 1.59 from a pH of 2.79 in January 2020.
"Increasing acidity is caused by sustained volcanic gas input into the shallow hydrothermal system that feeds into the lake, signifying degassing of magma intruded at depth during the January 2020 eruption," Phivolcs explained.
Likewise, continuous analysis indicate that Taal Volcano is "ongoing slight deformation" centered on a pressure source on its southeast sector.
"A very slow but steady inflation and/or expansion of the Taal region since the end of the 2020 eruption, at very much slower and stabilized rates compared to deformation before and right after the eruption" have also been observed.
Phivolcs said there have been changes across the Taal Caldera after the 2020 eruption consistent with density changes caused by magma migration, magma degassing and hydrothermal activity.
Citing these observations, Taal Volcano is now placed under Alert Level 2 but "evacuation is not yet recommended."
However, Phivolcs reminded the public not to enter the Taal Volcano Island, especially the vicinities of the main crater and Daang Kastila fissure, which are permanent danger zones.
"Local government units are advised to continuously assess and strengthen the preparedness of previously evacuated barangays around Taal Lake in case of renewed unrest," it said.
"Civil aviation authorities must 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," it added.