• GILBERT P. BAYORAN
The Philippine Institute of Volcanology and Seismology has reported increased seismic activity at Kanlaon Volcano, after it recorded 41 volcano-tectonic (VT) earthquakes, as several local government units in central Negros were also rocked by earthquakes on Sunday.
In an advisory, PHIVOLCS said it recorded the VT earthquakes between 11 p.m. of September 13 and 10 a.m. of the 14th.
The events ranged in strength between 0.8 to 4.6 magnitude, and were generated at a depth of zero to seven kilometers beneath the northwestern flanks of the volcanic edifice, it added
The Provincial Disaster Risk Reduction Management Office (PDRRMO) of Negros Occidental reported that Intensity 4 VT earthquake was felt in La Carlota City, and Intensity 3 in Bago City, Negros Occidental, Canlaon City in Negros Oriental, and Don Salvador Benedicto.
However, no damage was reported in those affected LGUs, the PDRRMO said.
VT earthquakes was also reported by PHIVOLCS to have been felt in Bacolod City, Murcia, and La Castellana in Negros Occidental.
Kanlaon Volcano is surrounded by La Castellana, Murcia, and the cities of Bago, La Carlota, and San Carlos in Negros Occidental, and Canlaon City in Negros Oriental.
VTs are generated by rock fracturing processes, and increased activity strongly indicates progressive rock fracturing beneath the volcano, as rising magma, or magmatic gas, drives a path towards the surface, according to PHIVOLCS.
Volcanic sulfur dioxide (SO2) gas emissions from the Kanlaon Volcano summit crater on September 13 was measured at 1,122 tons, lower than the medium term average of 2,594 tons since Jan.1, 2025.
PHIVOLCS said these parameters indicate the blockade of volcanic gas emission, which may result in the pressurization and swelling of the edifice, potentially leading to a moderately explosive eruption.
Alert Level 2 still prevails over Kanlaon, which means that the volcano is in a state of increased unrest.
PHIVOLCS warns that the hike in VT events could lead to increased chances of steam-driven or phreatic eruptions, or short-lived moderately explosive eruptions.
Following the downgrade of the Kanlaon alert level from 3 to 2 last month, residents within the 6-kilometer extended danger zone were allowed by the respective local government units to return to their homes, while those residing within the 4-kilometer danger zone are still occupying evacuation centers in La Castellana, Negros Occidental, and Canlaon City, Negros Oriental.
With this development, PHIVOLCS warned those within the 6-km radius from the summit crater to be ready for evacuation, in case unrest worsens.
Should intense rains occur, PHIVOLCS called for increased vigilance against potential sync-eruption lahars and sediment-laden streamflows in channels draining the edifice.*
