By CESAR JOLITO III
Kanlaon Volcano remains under Alert Level 2 after the Philippine Institute of Volcanology and Seismology (Phivolcs) reported heightened unrest, marked by a surge in seismic activity and a series of earthquakes that rattled Negros Island over the weekend.
A total of 41 volcano-tectonic (VT) earthquakes ranging from magnitude 0.8 to 4.6 at depths of up to seven kilometers beneath Kanlaon’s northwestern flanks were recorded from 11:00 p.m. on Saturday, September 13 to 10:00 a.m. yesterday, the Kanlaon Volcano Network said.
The strongest of these tremors was widely felt across Negros Occidental and Negros Oriental.
Phivolcs said the increase in VT activity indicates progressive rock fracturing beneath the volcano, a sign that magma or magmatic gas is driving its way toward the surface.
“As the magma or magmatic gas rises, it forces rocks to crack in order to find a pathway toward the surface,” Pearly Sianson, science research specialist at the Phivolcs-Kanlaon Volcano Observatory in La Carlota City said in a radio interview yesterday.
The strongest quake struck northeast of La Castellana town with a magnitude of 4.7 at 5:30 a.m. yesterday, Phivolcs said in an advisory.
It was felt at Intensity 4 in La Carlota City; Intensity 3 in Canlaon City, Bacolod City and Bago City, and Intensity 1 in Iloilo City.
A separate magnitude 4.6 earthquake was recorded in Canlaon City, where reported intensities reached Intensity 3 in Canlaon and Bacolod.
Instrumental readings registered Intensity 4 in La Carlota, Intensity 3 in Bago, and Intensity 1 in Iloilo.
The sequence of tremors continued with a magnitude 1.3 earthquake in Don Salvador Benedicto town at 5:48 a.m. yesterday, a magnitude 1.7 quake in Canlaon City at 6:04 a.m., and a magnitude 1.4 tremor in Murcia town at 6:06 a.m.
Phivolcs warned that aftershocks remain possible following the sequence.
Meanwhile, a 600-meter steam plume drifting southwest, and continuous ground swelling were also observed at Kanlaon.
Volcanic gas monitoring showed sulfur dioxide emissions averaged 1,122 tons per day on Saturday.
This was below the medium-term average of 2,594 tons per day since January 2025, data revealed.
Phivolcs explained that reduced emissions may suggest blocked gas pathways, causing pressure build-up beneath the surface.
With these parameters, Phivolcs cautioned that steam-driven explosions or weak to moderately explosive eruptions could occur, producing hazards such as pyroclastic density currents, ashfall, ballistic projectiles, and rockfall.
On September 8, Kanlaon produced a weak ash emission activity that lasted for about 55 minutes after nearly four months of no ash emission since its last eruptive activity in May 2025.
The Office of Civil Defense said that while no communities were reported to have been hit by ashfall, the public must always be on alert and prepared for any development at the volcano.
Authorities reiterated that communities within Kanlaon’s four-kilometer permanent danger zone should remain evacuated.
Residents living within the six-kilometer expanded danger zone are urged to stay vigilant.
Civil aviation authorities were also reminded to advise pilots against flying close to Kanlaon’s summit due to the risk of ash emissions.
Phivolcs assured that it continues to closely monitor the volcano and will immediately release updates on any significant developments./CJ, WDJ