Fewer Taal volcanic earthquakes seen, but 11 harmonic tremors among them

MANILA, Philippines – There were fewer volcanic earthquakes recorded from Taal Volcano in the past 24 hours, but several of these were harmonic tremors or quakes that involved prolonged shaking.

The Philippine Institute of Volcanology and Seismology (Phivolcs) said on Monday, February 10, that the Taal Volcano Network recorded 77 volcanic earthquakes, down from 115 in the previous 24-hour period.

Of the 77, there were 11 harmonic tremors lasting 1 to 4 minutes each.

On its website, the United States Geological Survey states that harmonic tremors "often precede or accompany volcanic eruptions."

Since January 30, Phivolcs has recorded 49 harmonic tremors at Taal, tallied by Rappler based on the agency's daily bulletins.

Phivolcs stressed on Monday that the volcanic earthquakes indicate magma continues to move beneath Taal.

At the volcano's main crater, there was "weak emission of steam-laden plumes rising 20 to 50 meters high." This is weaker compared to "moderate emission of white to dirty white steam-laden plumes rising 200 to 300 meters high" in the previous 3 days.

Phivolcs did not give a new figure for the emission of sulfur dioxide (SO2), a major gas component of magma. It only reiterated that SO2 emission was measured at an average of 116 tons per day last Saturday, February 8.

So far, Taal has been under Alert Level 3 for over two weeks, since January 26, meaning a "decreased tendency towards hazardous eruption." Phivolcs earlier said it could further downgrade the volcano to Alert Level 2, as long as all parameters being monitored continuously go down for a two-week period.

Before being placed under Alert Level 3, Taal was on Alert Level 4 for two weeks, starting January 12. Alert Level 4 had meant that a hazardous eruption could happen within hours to days.

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

Phivolcs again reminded the public that these might happen any moment:

Areas in Batangas within a 7-kilometer radius from Taal's main crater are still on lockdown. These are:

The affected population rose to 134,520 families or 504,709 persons as of Monday, according to the National Disaster Risk Reduction and Management Council. They are in Batangas, Quezon, Laguna, and Cavite.

Of those affected, 6,857 families or 24,153 persons remain in evacuation centers.

When a 14-kilometer-radius danger zone was enforced during Alert Level 4, there were as many as over 38,000 families in evacuation centers. – Rappler.com