The Taal unrest began last January 12, triggered by a phreatic or steam-driven eruption, which later progressed into a phreatomagmatic eruption, or an eruption that results from the interaction of magma and water. Alert Levels 2, 3, and 4 were raised in a matter of hours that day.
The volcano was eventually downgraded from Alert Level 4 to Alert Level 3 on January 26. To date, the chances of a hazardous eruption remain lower, but the threat has not disappeared.
The Philippine Institute of Volcanology and Seismology (Phivolcs) stressed on Sunday that volcanic earthquakes indicate the continuing movement of magma beneath Taal's crater.
In the past 24 hours, the Taal Volcano Network recorded 115 volcanic earthquakes, including 2 low-frequency events and 5 harmonic tremors lasting 1 to 4 minutes each.
The total number of volcanic earthquakes is exactly the same as the figure recorded in the previous 24-hour period.
As for low-frequency events, these are "caused by cracks resonating as magma and gases move toward the surface," according to the United States Geological Survey (USGS).
A harmonic tremor, meanwhile, is a type of volcanic earthquake where the shaking is prolonged. The USGS said harmonic tremors "often precede or accompany volcanic eruptions."
For the 3rd straight day, Phivolcs also observed "moderate emission of white to dirty white steam-laden plumes rising 200 to 300 meters high" from Taal's main crater.
Steam also continues to emerge from fissure vents along the Daang Kastila Trail, a trail once used by tourists trekking to view the volcano's main crater. This is the 3rd straight day as well that Phivolcs noted this observation, but added this time that the steam is 10 to 20 meters high.
Taal is still emitting sulfur dioxide (SO2) as well – another indicator of rising magma. Phivolcs said SO2 emission was measured at an average of 116 tons per day on Saturday, February 8, higher than the average of 54 tons per day on Friday, February 7, but still a relatively low figure.
Phivolcs warned that these could still occur given the current situation:
If the situation eases, Taal could be downgraded further to Alert Level 2. But if the unrest escalates again, the volcano may be back to Alert Level 4.
The highest category is Alert Level 5, which would be raised if a hazardous eruption occurs.
Areas in Batangas within a 7-kilometer radius from Taal's main crater remain off-limits. These include:
The affected population stayed at 133,696 families or 501,908 persons as of Sunday, according to the National Disaster Risk Reduction and Management Council. They are in Batangas, Quezon, Laguna, and Cavite.
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. (READ: With Taal Lake off-limits, Batangas highlights other tourist spots to lift economy) – Rappler.com