By Alexandria Dennise San Juan
Despite the lower alert level of Taal Volcano, state volcanologists advised local officials that entry into the seven-kilometer zone around the volcano island and lakeshore communities should remain strictly prohibited as hazards can still occur.
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)
In its latest advisory on Monday, the Philippine Institute of Volcanology and Seismology (Phivolcs) reminded the public that sudden steam-driven and even weak phreatomagmatic explosions, volcanic quakes, ashfall, and lethal volcanic gas expulsions can still occur and threaten areas within and near Taal Volcano Island.
Phivolcs lowered the danger level of Taal Volcano from alert level 4 to 3 on Sunday, two weeks after its eruption, which forced thousands of families in the surrounding areas to evacuate due to thick ashfall that blanketed nearby towns.
Authorities earlier said the tendency towards a hazardous eruption has decreased, noting that Taal's condition in the past two weeks generally declined into "less frequent volcanic activity, decelerated ground deformation of the Taal Volcano caldera and Taal Volcano Island, edifice, and weak steam gas emissions from the Main Crater."
On Monday, Phivolcs observed weak to moderate emission of white steam-laden plumes reaching up to 50 to 800 meters high that drifted northeast.
Lower sulfur dioxide level was measured at 87 tonnes per day, while volcanic quakes recorded by the Taal Volcano Network also decreased with 170 tremors plotted including four low-frequency earthquakes.
However, the state volcanology agency 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."
Nearby residents are also advised to observe precautions due to ground displacement across fissures, frequent ashfall, and minor earthquakes.
Meanwhile, 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 as ash can be washed away and form lahars along the channels, Phivolcs added.
Taal Volcano's phreatic or steam-driven eruption on January 12 surprised unaware residents and tourists visiting the picturesque lake after it spewed 50,000-feet-tall ash plume sent ashes raining to nearby towns including parts of Metro Manila, Calabarzon, and reaching as far as Central Luzon.
Days after its eruption, fissures or cracks on the ground were found in several barangays in Batangas particularly in Sambal Ibaba, Sinisian, Mahabang Dahilig, Dayapan, Palanas, Sangalang, Poblacion, and Mataas na Bayan in Lemery; Pansipit and Bilibinwang in Agoncillo; Poblacion 1, Poblacion 2, Poblacion 3, and Poblacion 5 in Talisay; and Poblacion in San Nicolas.
A fissure was also spotted across the road connecting the municipalities of Agoncillo and Laurel in Batangas.
The cracks documented in these areas have been observed to widen by a few centimeters on Sunday.
According to Phivolcs, fissures were produced through the intrusion of magma into the Taal edifice.
The Taal Volcano's Main Crater Lake also vaporized, while portions of the Pansipit River, which is the sole drainage outlet of Taal Lake, are drying up.
Phivolcs officials cited several explanations but the most evident, it said, is due to the series of volcanic quakes that caused the water in the lake to drain.