THE Philippine Institute of Volcanology and Seismology (Phivolcs) decided to lower the alert status of Taal Volcano to level 2 on Saturday after it noticed a stop in the eruptive activity of the volcano, following its July 1 phreatomagmatic (combination of magma and water) eruption.

"There has been a cessation of eruptive activity in the past weeks. So, from alert level 3, which means there is magmatic unrest, Taal Volcano [is now] under alert level 2, which means there is already [decreased] unrest," Renato Solidum Jr., Phivolcs chief, told The Manila Times.

"Unrest since then has been characterized by renewed seismic activity, generally declining volcanic gas emission, very slight ground deformation and positive microgravity anomalies," he added.

These observations, Solidum said, were supported by the following monitoring parameters such as since July 1, 2021, volcanic earthquakes recorded by the Taal Volcano Network (TVN) totaled 1,195 events and ranged in strength from magnitude 1.8 to magnitude 4.6.

Of these 789 volcanic tremors, 365 low-frequency, 26 hybrid and three volcano-tectonic earthquakes were generated by activity in the shallow magma and hydrothermal region beneath the Taal Volcano Island or TVI edifice, he said.

He further explained that most earthquakes occurred beneath its main crater and the north-eastern sector of TVI, indicating migration of shallow degassed magma, volcanic gas and/or hydrothermal fluids beneath these areas.
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Phivolcs said sulfur dioxide or SO2 gas averaged 12,161 tons in the first week of July 2021 with the highest emission of 22,628 tons recorded on July 4, 2021.

"The decrease in degassing activity reflects the diminishing volumes of accumulated volcanic gas beneath TVI as well as the 'scrubbing' effects of rainfall-fed water recharge into Taal's hydrothermal system," Solidum said.

Activity in its main crater has been more often characterized by the generation of moderate steam-laden plumes and periodic but generally less vigorous lake upwelling, consistent with decreased magmatic degassing, he said further.

"In view of these observations, Phivolcs is lowering the alert status of Taal Volcano from alert level 3 to alert level 2 to reflect the overall decreasing trend in the level of monitoring parameters," Solidum said.

"Alert level 2 means that there is decreased unrest but should not be interpreted that unrest has ceased or that the threat of an eruption has disappeared. Should an uptrend or pronounced change in monitored parameters forewarn a potential eruption, the alert level may be raised back to alert level 3," he said.