Kanlaon Volcano experienced another “volcano-tectonic (VT) earthquakes swarm” from Sunday to Monday, Sept. 14 to 15, on its northwestern flank.
This activity could lead to a moderate-sized eruption, Ma. Antonia V. Bornas, chief of the Philippine Institute of Volcanology and Seismology (Phivolcs) Volcano Monitoring and Eruption Prediction Division, said on Monday.
“But while there is always a chance of a moderate eruption, it doesn’t mean it will follow immediately after the VT swarms,” Bornas said.
The Kanlaon Volcano Network recorded 72 VT earthquakes between 12 a.m. Sunday and 8 a.m. Monday, up by 31 from 41 previously reported.
Bornas noted that these earthquakes were relatively strong, with magnitudes ranging from 0.8 to 3.6. The strongest VT earthquake was felt at Intensity I in La Carlota City, Negros Occidental, and Canlaon City, Negros Oriental.
Bornas said that VTs are generated by a rock fracturing processes.
The increase in this activity at Kanlaon strongly indicates progressive rock fracturing beneath the volcano as rising magma or magmatic gas drives a path toward the surface, she said.
On Sunday, volcanic sulfur dioxide (SO2) gas emissions from the summit crater of Kanlaon averaged 2,338 tons, Phivolcs reported.
“These parameters indicate that the blockage of volcanic gas emission (or closed-system degassing) may result in pressurization and swelling of the edifice potentially leading to a moderately explosive eruption,” Bornas said.
Bornas also said that while they expect a major eruption at Kanlaon, it could take years to happen after a long period of unrest.
Alert Level 2 remains in effect for Kanlaon, which means the volcano is in a state of increased unrest. No one should be permitted within the 4-kilometer Permanent Danger Zone (PDZ) around the volcano, she reiterated.
Negros Occidental Governor Eugenio Jose Lacson said the provincial government will be guided by the alert level set by PHIVOLCS.
“Right now, it’s Alert Level 2, nobody should be in the 4-kilometer permanent danger zone and nobody is — those who lived there before are still in evacuation centers,” he said.
Lacson added that the provincial government is hoping the alert level stays at two so they don’t need to evacuate more people.
While the provincial government can help with food needs, the funds of local governments near the volcano, particularly La Castellana, have been depleted, he said.
La Castellana will need help if another evacuation takes place.
In an advisory on Monday, PHIVOLCS said that the increase in VT events could lead to higher chances of steam-driven or phreatic eruptions or short-lived, weak to moderately explosive eruptions.
These could generate life-threatening hazards such as pyroclastic density currents (PDCs), ballistic projectiles, ashfall, and rockfall, it reiterated.
PHIVOLCS again strongly recommended that communities within the 4-km PDZ strictly remain evacuated and that those within a 6-km radius from the summit crater stay vigilant.
It also stressed the need for increased vigilance against potential syn-eruption lahars and sediment-laden streamflows if intense rains occur during eruptive unrest.
Civil aviation authorities are also advised to tell pilots to avoid flying close to the volcano’s summit, as ash from a sudden eruption can be hazardous to aircraft.
Bornas clarified that the recent tectonic earthquakes recorded in some parts of Negros Occidental are not related to the unrest at Kanlaon.
She explained that they are triggered by larger geologic structures, such as the Negros trench and other active faults.
Tectonic earthquakes are different from volcano-tectonic earthquakes, Bornas said.*
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