PHIVOLCS reported that geochemical data collected from Taal’s Main Crater lake indicated a continuous acidification of the water from pH 2.79 to 1.59 between January 2020 and February 2021. A maximum temperature of 77.1 degrees Celsius was unseasonably high, and carbon dioxide/hydrogen sulfide gas flux ratios were consistent with shallow magma degassing. Tilt data indicated minor deflation around Main Crater, though minor inflation was consistently recorded across the Taal region as indicated by analysis of GPS data, InSAR, and microgravity changes.

A total of 68 relatively weak tremor signals were detected during 13-15 February; 50 of those were recorded during 0500-1500 on 15 February. The events on 15 February ranged in duration from two to five minutes and occurred at depths less than 1 km. The depth and location of the earthquakes suggested increased hydrothermal activity beneath Taal Volcano Island. Increased seismic activity continued through 16 February; from 0800 on 15 February to 0800 on 16 February there were a total of 98 earthquakes. The Alert Level remained at 1 (on a scale of 0-5) and PHIVOLCS strongly recommended no entry onto the island, and the Main Crater and the Daang Kastila fissure (along the walking trail) was strictly prohibited.

Geological Summary. Taal is one of the most active volcanoes in the Philippines and has produced some powerful eruptions. The 15 x 20 km Talisay (Taal) caldera is largely filled by Lake Taal, whose 267 km2 surface lies only 3 m above sea level. The maximum depth of the lake is 160 m, with several submerged eruptive centers. The 5-km-wide Volcano Island in north-central Lake Taal is the location of all observed eruptions. The island is composed of coalescing small stratovolcanoes, tuff rings, and scoria cones. Powerful pyroclastic flows and surges have caused many fatalities.

Source: Philippine Institute of Volcanology and Seismology (PHIVOLCS)