Taal Volcano alert down to level 3
Credit to Author: Tempo Desk| Date: Sun, 26 Jan 2020 03:08:42 +0000
TAAL Volcano. (Jansen Romero)
Two weeks after its eruption, Taal Volcano has exhibited a decreasing tendency of eruption, prompting authorities to lower its alert status from level 4 to 3 on Sunday.
According to the Philippine Institute of Volcanology and Seismology (Phivolcs), Taal Volcano’s condition in the two weeks following the phreatomagmatic eruption last January 12 and 13 has generally declined into less frequent volcanic earthquake activity, decelerated ground deformation of the caldera and volcano island edifices, and weak steam or gas emissions at the main crater.
Several specific parameters have been considered in the lowering of Taal Volcano’s alert status which include a decline from 959 to 27 significant earthquake events per day in the past two weeks.
The Taal Volcano network likewise recorded a downtrend in volcanic earthquakes from 944 to 420 events daily between January 17 and 24 with a corresponding decline in the daily total seismic energy released.
In particular, hybrid earthquakes that tracked post-eruptive recharge from Taal’s deep magma reservoir to a shallow magma region beneath the Taal Volcano network ceased on January 21, while the number and energy of low frequency events associated with activity in the shallow magma region diminished.
Based on the global positioning system or GPS data, Phivolcs recorded ground deformation after the main eruptive phase that included sudden widening of Taal caldera by about 1 meter, uplift of its northwestern sector by about 20 centimeters, and subsidence of the southwestern part of volcano island by about 1 meter.
“These patterns were followed at much smaller rates between January 15 and 22 and were generally supported by field observations of lake water recession by about 30 centimeters around Taal Lake as of Saturday,” Phivolcs reported.
Field observations also measured around 2.5 m lake water recession along the southwestern lakeshore denoting uplift of portions of the Pansipit River Valley where fissuring has been reported.
The overall pattern of ground deformation is for most part supported by satellite data and yields a net inflation of western Taal Volcano as a consequence of magma intrusion to the shallow magma region until January 21.
After the main eruptive phase, activity in the Taal main crater diminished to infrequent weak ash eruptions and longer episodes of degassing or steaming that generated steam-laden plumes less than 1,000 meters high.
This marked decline coupled with volcanic earthquake activity suggests stalling, degassing and reduction in gas pressures of eruptible magma in the shallow magmatic region that feeds surface eruptive activity, Phivolcs explained.
Likewise, sulfur dioxide (SO2) flux fluctuated between a high of about 5,300 tonnes/day on January 13 to a low of ~140 tonnes/day on January 22 but has steadied at an average of 250 tonnes/day in the last five days.
This low concentration average is consistent with a progressively degassed shallow magma source and diminished plume activity, Phivolcs said.
In lowering Taal Volcano’s alert status, Phivolcs said there is a decreased tendency towards hazardous explosive eruption “but should not be interpreted that unrest has ceased or that the threat of a hazardous eruption has disappeared.”
Should an uptrend or pronounced change in monitored parameters forewarn a potential hazardous explosive eruption, the alert status may be raised back to alert level 4.
People residing within areas at high risk to base surges who have returned were advised to be prepared for a quick and organized evacuation should another eruption occurs.
However, should there be a persistent downtrend in monitored parameters after a sufficient observation period, the alert level will be further lowered to alert level 2.
Phivolcs reminded the public, especially those within the volcano island and nearby lake shores, to be alert against sudden steam-driven and even weak phreatomagmatic explosions, volcanic earthquakes, ash fall and lethal volcanic gas expulsions.
7-KILOMETER DANGER ZONE
It also recommended that entry into the Taal Volcano island, permanent danger zone, as well as into areas over Taal Lake and communities west of the volcano island within a 7 kilometer-radius from the main crater must be strictly prohibited.
Local government units were advised to assess areas outside the seven-kilometer radius for damages and road accessibilities and to strengthen preparedness, contingency and communication measures in case of renewed un
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