The Philippine Institute of Volcanology and Seismology (Phivolcs) detected 110 volcanic earthquakes in Taal Volcano in Batangas, from 8 a.m., March 18 to 8 a.m., March 19.
Based on Phivolcs' bulletin, of the recorded volcanic earthquakes, 63 were volcanic tremors that lasted one to 15 minutes, and three were hybrid events.
It also observed "weak" emission of steam-laden plumes that rose five meters from the main crater.
Moreover, Phivolcs measured a significant sulfur dioxide emission that averaged 754 tonnes/day last March 18, while temperature highs of 71.8 degrees Celsius and pH of 1.59 were measured from the main crater last March 4 and Feb. 11, respectively.
Ground deformation parameters also indicated a "very slow and steady inflation and expansion of the Taal region since after the January 2020 eruption," it said.
"These parameters may indicate increased magmatic activity at shallow depths beneath the edifice," it pointed out.
Considering these observations, Phivolcs said Taal Volcano remains under alert level 2 due to "increased unrest." Its alert level was raised from 1 to 2 on March 9, 2021.
The possibility of sudden steam-driven or phreatic explosions, volcanic earthquakes, minor ashfall, and lethal accumulations or expulsions of volcanic gas can occur and threaten areas within the Taal Volcano island, it warned.
Phivolcs asked to public to prevent from entering the volcano island, which is a permanent danger zone, especially the vicinities of the main crater and Daang Kastila fissure.
Local government units were advised to continuously assess and strengthen the preparedness of previously evacuated barangays around Taal Lake in case of renewed unrest.
Civil aviation authorities were also asked to 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.