By Alexandria Dennise San Juan
A slight increase in volcanic quakes has been observed in Taal Volcano, while emission of sulfur dioxide dropped more than a month after its initial eruption, the Philippine Institute of Volcanology and Seismology (Phivolcs) said Wednesday.
The main crater of the Taal Volcano is seen during an aerial survey done by government officials, more than a week after the eruption of Taal Volcano in Batangas. (Mark Balmores / MANILA BULLETIN FILE PHOTO)
State volcanologists advised residents to still be ready on threats posed by the Taal Volcano despite the downgrading of its danger level from Alert Level 4 to 3, meaning there is a "relatively high unrest manifested by seismic swarms including the increasing occurrence of low-frequency earthquakes and/or harmonic tremors where some events are felt."
According to Phivolcs, sudden steam-driven and even weak phreatomagmatic explosions, volcanic earthquakes, ashfall, and lethal volcanic gas expulsions can still occur and threaten areas within Taal Volcano Island and nearby lakeshore communities.
With this, the state volcanology agency maintained its recommendation that entry into the Taal Volcano Island, areas over Taal Lake, and communities west of the island within a seven-kilometer radius from the Main Crater must be "strictly prohibited."
Phivolcs continues to monitor Taal Volcano since its phreatic or steam-driven eruption on January 12 as the parameters being used to assess the volcano's activity continue to rise and fall in previous days.
In the latest bulletin issued by Phivolcs, the Taal Volcano Network plotted a total of 101 volcanic quakes from Tuesday morning to Wednesday morning including four low-frequency events, a slight increase on the 87 tremors recorded the other day.
"These earthquakes signify magmatic activity beneath the Taal edifice that could lead to eruptive activity at the Main Crater," Phivolcs reiterated.
Meanwhile, sulfur dioxide (SO2) emission was measured at an average of 67 tonnes per day on Tuesday, February 11, significantly lower than the 105 tonnes per day recorded on Monday, February 10.
SO2 levels have been rising and falling in the previous days and sometimes very low to be detected. A higher level of SO2, which is a major gas component of magma, is being released when magma or molten rocks are near the surface of a volcano indicating a possible magmatic eruption, Phivolcs said.
Apart from these parameters, Phivolcs also observed weak emission of steam-laden plumes on Taal's Main Crater rising from 50 to 100 meters high before drifting southwest.
While Taal's activity persists, Phivolcs advised local government units to assess areas outside the seven-kilometer radius for damages and road accessibilities and to strengthen preparedness, contingency and communication measures in case of renewed unrest.
Residents are also advised to observe precautions due to ground displacement across fissures, frequent ashfall, and minor earthquakes.
Communities beside active river channels particularly where ash from the main eruption phase has been thickly deposited should increase vigilance when there is heavy and prolonged rainfall since the ash can be washed away and form lahars along the channels.