The Philippine Institute of Volcanology and Seismology (Phivolcs) lowered the status of Taal Volcano from Alert Level 3 to Alert Level 2 on Saturday morning, April 9, two weeks after the occurrence of a phreatomagmatic eruption in the main crater.
“Following the phreatomagmatic eruption of the main crater on 26 March 2022 and six weak phreatomagmatic bursts until 31 March 2022, unrest at Taal Volcano has markedly declined. Activity in the past two weeks has been characterized by a significant drop in volcanic degassing from the Main Crater and in the incidence of volcanic earthquakes,” Phivolcs said in an advisory.
Phivolcs explained that since the March 26 eruption, only 86 small-magnitude and imperceptible volcanic earthquakes have been recorded by the Taal Volcano Network, comprising 26 volcanic tremors, 59 low-frequency volcanic earthquakes, and one volcano-tectonic event, most of which occurred seven kilometers beneath the main crater and the eastern sector of the volcano island.
Most earthquakes were generated by volcanic degassing from the shallow magma and hydrothermal region beneath the TVI edifice.
In addition, background tremor associated with shallow hydrothermal activity ceased on March 31.
“There has been no recorded seismic activity related to new magmatic intrusions from Taal’s deeper magma source since unrest began last year,” Phivolcs pointed out.
Moreover, after sulfur dioxide or SO2 gas flux elevated in the first three weeks of March and peaked at 21,211 tons per day on March 16, emissions suddenly dropped on April 3.
“SO2 flux since then has averaged 240 tons per day, decreasing to 103 tons per day yesterday, 8 April, the lowest flux recorded since unrest began in 2021,” Phivolcs said.
It noted that the recent volcanic gas emissions suggest that the potential for eruptive activity at present is low.
Phivolcs also pointed out that the activity in the main crater in the past week has been characterized by occasional weak plumes and longer periods of absence thereof, consistent with the significant decrease in magmatic degassing.
Placing Taal Volcano under 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.”
“Should an uptrend or pronounced change in monitored parameters occur, 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,” Phivolcs said.
“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,” it added.
Phivolcs reminded the public that at Alert Level 2, sudden steam-driven or phreatic explosions, volcanic earthquakes, ashfall and lethal accumulations or bursts of volcanic gas can occur and threaten areas within the volcano island and along its coast.
“Entry into TVI (Taal Volcano Island), Taal’s permanent danger zone, must therefore be strictly prohibited,” it said.
Local government units are advised to continually strengthen preparedness, contingency and communication measures, especially for previously evacuated high-risk barangays in case of renewed unrest.