THE Philippine Institute of Volcanology and Seismology (Phivolcs) on Thursday said 11 harmonic tremors, or prolonged shaking, were recorded over the past 24 hours.
Phivolcs said in its 8 a.m. bulletin that the Taal Volcano Network registered 132 volcanic earthquakes, including 3 low-frequency events and 11 harmonic tremors that lasted 2 to 3 minutes.
A harmonic tremor is a “continuous rhythmic earthquake that often accompanies volcanic eruptions.” It is a long-duration release of seismic energy that indicates underground movement of magma, according to United States Geological Survey (USGS).
“These earthquakes signify magmatic activity beneath the Taal edifice that could lead to eruptive activity at the main crater,” the seismology agency said.
Alert Level 3 status remains over Taal Volcano, which means “sudden steam-driven and even weak phreatomagmatic explosions, volcanic earthquakes, ashfall, and lethal volcanic gas expulsions” could still happen.
Phivolcs characterized the activity of Taal Volcano by “weak emission of steam-laden plumes 50 to 100 meters high before drifting southwest” in the past 24 hours.
There was no sulfur dioxide emission activity in the past 24 hours, the seismology agency noted.
Phivolcs recommended that entry into the Taal Volcano island, as well as into areas over Taal Lake and communities west of the island within a 7-kilometer radius from the main crater, was prohibited.
It advised local government units to assess areas outside the 7-km radius for damage and road accessibilities and to strengthen preparedness, contingency and communication measures in case of renewed unrest.
Phivolcs urged the public to observe precautions due to ground displacement across fissures, frequent ashfall and minor earthquakes.