MANILA – The Philippine Institute of Volcanology and Seismology (Phivolcs) on Friday lowered Alert Level 3 further down to No. 2 owing to improved conditions monitored by the agency on Taal Volcano.
Philvolcs explained its lowering of alert level has been characterized by less frequent volcanic earthquake activity, stabilizing ground deformation of the Taal Caldera and Taal Volcano Island (TVI) edifices and weak steam/gas emissions at the Main Crater.
These observations are supported by the following monitoring parameters:
1. Since 26 January, volcanic earthquakes recorded by the Taal Volcano Network (TVN) averaged 141 events/day while the number of significant events recorded by the Philippine Seismic Network across the Taal region declined to 127 events of magnitudes M1.4 to M4.3. The number and energy of tremor and low-frequency events associated with activity in the shallow magma and hydrothermal region beneath the TVI edifice have also diminished. These parameters are consistent with degassing ponded magma rather than active magma transport to and from the shallow magma reservoir beneath TVI.
2. Continuous Global Positioning System (GPS) data from 13 January to 11 February recorded a net subsidence of the Taal Caldera and TVI, following uplift on the northwestern caldera and subsidence of TVI on 12-13 January. Subsidence along thePansipit River Valley, where extensive fissuring occurred, was also recorded by campaign GPS monitoring between 24 and 27 January. The overall ground deformation behavior of Taal Volcano for the above periods indicates post-eruptive subsidence and relaxation of the edifice after the cessation of magma transport, signaled by hybrid earthquake activity, on 18 January.
3. Sulfur dioxide or SO2 flux based on campaign Flyspec data averaged 62 tonnes/day since 26 January, consistent with a weakly degassing shallow magma source, diminished plume activity or absorption of volcanic gas by a recovering lake at the Main Crater and by TVI’s recovering hydrothermal system.
4. Activity in the Main Crater has been characterized by the generation of weak steam-laden plumes, consistent with decreased magmatic unrest.
In view of the above observations, DOST-PHIVOLCS is lowering the alert status of TaalVolcano from Alert Level 3 to Alert Level 2 to reflect the overall decreasing trend in the level of monitoring parameters the agency said.
Alert Level 2 means that there is decreased unrest but should not be interpreted that unrest has ceased or that the threat of an eruption has disappeared.
Phivolcs warned that “should an uptrend or pronounced change in monitored parameters forewarn a potential eruption, the Alert Level may be raised back to Alert Level 3.”
At such time, people residing within areas at high risk to base surges who have returned after the step-down to Alert Level 2 must therefore be prepared for a quick and organized evacuation.
Conversely, should there be a persistent downtrend in monitored parameters after a sufficient observation period, the Alert Level will be further lowered to Alert Level 1.
DOST-PHIVOLCS reminds the public that at Alert Level 2, sudden steam-driven or phreatic explosions, volcanic earthquakes, ashfall and lethal accumulations or expulsions of volcanic gas can occur and threaten areas within TVI and along its coast.
DOST-PHIVOLCS recommends that entry into TVI, Taal’s Permanent Danger Zone must be strictly prohibited.
Local government units are advised to additionally assess previously evacuated areas within the seven-kilometer radius for damages and road accessibilities and to strengthen preparedness, contingency and communication measures in case of renewed unrest.
People are also advised to observe precautions due to ground displacement across fissures, frequent ashfall, and minor earthquakes. Communities beside active river channels particularly where ash from the main eruption phase has been thickly deposited should increase vigilance when there is heavy and prolonged rainfall since the ash can be washed away and form lahars along the channels.
Civil aviation authorities must advise pilots to avoid flying close to the volcano as airborne ash and ballistic fragments from sudden explosions and wind-remobilized ash may pose hazards to aircraft.
DOST-PHIVOLCS is still closely monitoring Taal Volcano’s activity and any new significant development will be immediately communicated to all stakeholders. (IAMIGO/sovereignph.com)