MANILA, Philippines – It’s been more than a month since the Taal Volcano unrest began, and while the situation may have eased somewhat, now is not the time to be complacent.

The Philippine Institute of Volcanology and Seismology (Phivolcs) continues to release daily bulletins on Taal, which remains at Alert Level 3 as of Tuesday, February 11.

“Ang pinakamahalaga, ‘wag magpakampante (The most important thing is not to be complacent),” Phivolcs Supervising Science Research Specialist Winchell Sevilla told Rappler in a phone interview on Tuesday.

Sevilla explained that while the number of volcanic earthquakes and the steaming activity have eased compared to levels seen at the beginning of the unrest – January 12 – these are not enough, so far, to warrant a downgrade to Alert Level 2.

“For now, Alert Level 3 muna. Nasa observation period tayo. Kung in the next few days, biglang mag-escalate, puwede i-maintain (if still within Alert Level 3), or itaas,” he said.

(For now, we’re maintaining Alert Level 3. We’re still in the observation period. If in the next few days, the activity escalates, we could either maintain the alert level, or raise it again.)

It really depends on how the volcanic activity will progress.

When Phivolcs had downgraded Taal from Alert Level 4 to Alert Level 3 last January 26, it explained that there was only a “decreased tendency” towards a hazardous eruption, but the threat of such an eruption remains.

Volcanic earthquakes

In its Tuesday bulletin, Phivolcs said the Taal Volcano Network recorded 87 volcanic earthquakes in the past 24 hours, including 1 low-frequency event and 2 harmonic tremors lasting 1 to 3 minutes each.

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

Harmonic tremors, meanwhile, involve prolonged shaking. These “often precede or accompany volcanic eruptions,” said USGS.

Since January 30, Phivolcs has recorded 51 harmonic tremors at Taal, tallied by Rappler based on the agency’s daily bulletins.

The total number of volcanic earthquakes in the past 24 hours is slightly higher than the 77 recorded in the previous 24-hour period.

Phivolcs reiterated that the volcanic earthquakes show magma is still moving beneath the surface of Taal.

The big question has been whether the magma would rise to the surface and lead to a hazardous eruption, or just remain underneath. This cannot be predicted with certainty.

Possible phreatic eruption ‘anytime’

At the volcano’s main crater in the past 24 hours, there was again “weak emission of steam-laden plumes.” The plumes were 50 to 100 meters high, just slightly taller than the plumes 20 to 50 meters high described in the previous bulletin.

Meanwhile, the level of sulfur dioxide (SO2) emitted was measured at an average of 105 tons per day on Monday, February 10, close to the average of 116 tons per day last Saturday, February 8.

SO2 is a major gas component of magma and its emission is one of the parameters that volcanologists use to assess volcanic activity. When Taal was at Alert Level 4, the measurement had spiked to a high of 5,300 tons per day.

The highest category is Alert Level 5, which would be raised if a hazardous eruption is already in progress.

“Ang pinakamahalaga dito sa kasalukuyang alert level ng Taal (Alert Level 3), ‘wag pupunta sa main island kasi anytime puwede mangyari ang steam-driven explosion,” Sevilla said.

(What’s most important now under the current alert level of Taal is not to go to the main island because a steam-driven explosion can occur anytime.)

Sevilla is referring to Taal Volcano Island, which is classified as a Permanent Danger Zone. The island is within the 7-kilometer-radius area still on lockdown, which also includes these barangays:

• Bilibinwang, Subic Ilaya, and Banyaga in Agoncillo
• Gulod, Buso-Buso, and Bugaan East in Laurel

There are still 4,778 families or 17,088 persons staying in evacuation centers as of Tuesday, from a high of over 38,000 families.

The Taal unrest has affected over half a million people in Batangas, Quezon, Laguna, and Cavite. – Rappler.com