MANILA, Philippines – Another harmonic tremor, or rhythmic shaking associated with magma movement, was recorded from Taal Volcano in Batangas in the past 24 hours, said state volcanologists on Saturday morning, February 1.

The Philippine Institute of Volcanology and Seismology (Phivolcs) said the harmonic tremor lasted 3 minutes.

Phivolcs also recorded a 97-second harmonic tremor last Thursday, January 30. Director Renato Solidum Jr said then that it indicated magma continues to rise toward the surface of the volcano, which remains under Alert Level 3.

In the past 24 hours, the Taal Volcano Network recorded a total of 182 volcanic earthquakes, including the 3-minute harmonic tremor and one low-frequency event.

Low-frequency quakes are “caused by cracks resonating as magma and gases move toward the surface,” according to the United States Geological Survey.

The latest figure of 182 is higher than the 116 recorded in the previous 24-hour period, which was stated in Phivolcs’ bulletin on Friday, January 31.

Phivolcs stressed on Saturday that the volcanic earthquakes show “magmatic activity” persists beneath Taal’s crater.

Sulfur dioxide (SO2) emission, meanwhile, was measured at an average of 65 tons per day, coming from a level that was too low to be detected. SO2 is a major gas component of magma.

At the main crater, there was “wispy to weak emission of white to dirty white steam-laden plumes 50 meters tall” in the past 24 hours. The plumes described in the previous bulletin were higher – 500 to 700 meters tall.

Given the conditions, Phivolcs said it is maintaining Alert Level 3 (magmatic unrest) for Taal.

The volcano has been on Alert Level 3 since the morning of January 26. Before that, it was on Alert Level 4 for two weeks, beginning the evening of January 12. The highest possible status is Alert Level 5, which would be raised when a hazardous eruption is in progress.

For now, these could still happen:

• sudden steam-driven and even weak phreatomagmatic explosions
• volcanic earthquakes
• ashfall
• lethal volcanic gas expulsions

Taal Volcano Island; the barangays of Bilibinwang, Subic Ilaya, and Banyaga in Agoncillo; and the barangays of Gulod, Buso-Buso, and Bugaan East in Laurel remain on lockdown.

These areas are within a 7-kilometer radius from the main crater, which is Phivolcs’ recommended danger zone while Taal is under Alert Level 3.

The ongoing Taal eruption has affected at least 126,952 families or 473,332 persons in Batangas, Quezon, Laguna, and Cavite, said the National Disaster Risk Reduction and Management Council on Saturday.

Of those affected, 10,848 families or 37,163 persons remain in evacuation centers. (READ: In Talisay, desperate residents beg on the street for money, water)

Even Phivolcs’ team at the Taal Volcano Observatory in Talisay had to flee when the eruption began. They continue monitoring the restive volcano round-the-clock from the Phivolcs office in neighboring Tagaytay City. (WATCH: Evacuated Phivolcs scientists continue to keep Filipinos safe) – Rappler.com