By CESAR JOLITO III
State volcanologists have recorded a significant increase in seismic activity at Kanlaon Volcano, which could potentially lead to a moderately explosive eruption, after a total of 45 volcano-tectonic earthquakes were monitored yesterday.
In an advisory, the Philippine Institute of Volcanology and Seismology (Phivolcs) said volcano-tectonic earthquakes, detected by the Kanlaon Volcano Network since 12:00 midnight yesterday, ranged in magnitude from 0.6 to 3.9 and originated at depths of zero to 13 kilometers beneath the northwestern flanks of the volcano.
The strongest earthquake recorded, with a magnitude of 3.9, struck at 4:06 a.m. at a depth of 10 kilometers.
Its epicenter was located about nine kilometers north-northeast of Negros Occidental’s La Carlota City.
Instrumental intensity reached Intensity 5 in La Carlota City, while Intensity 2 was recorded in Bacolod City.
Residents in the cities of La Carlota, Bago and Bacolod, as well as Negros Oriental’s Canlaon City reported felt intensities ranging from Intensity 1 to 4.
According to Phivolcs, volcano-tectonic earthquakes are caused by rock fracturing beneath Kanlaon, a process commonly associated with rising magma or magmatic gases forcing their way toward the surface.
“These volcanic earthquakes indicate magma intrusion or the ascent of magma beneath the volcano, which could eventually lead to an eruption, although we cannot determine exactly when,” Phivolcs resident volcanologist Mari-Andylene Quintia said.
The recent increase in these events “strongly indicates progressive rock-fracturing beneath the volcano,” the agency said.
Quintia said the current seismic pattern is similar to past episodes of magma intrusion observed before previous eruptions.
“Overall parameters indicate that renewed magma intrusion is taking place beneath the edifice, which could potentially lead to a moderately explosive eruption,” she warned.
Phivolcs cautioned that the heightened seismic activity raises the possibility of steam-driven or phreatic eruptions, as well as short-lived weak to moderately explosive eruptions at the summit.
These could generate hazardous phenomena such as pyroclastic density currents, ballistic projectiles, ashfall, and rockfall.
Quintia noted that in some cases, such as in 2020, a long interval separated the initial increase in earthquakes and the eventual eruption, while in other instances, eruptions followed shortly after heightened seismicity.
“At this time, there is no basis yet to raise the alert level to Alert Level 3,” she added, emphasizing the importance of preparedness for communities living near the volcano.
Alert Level 2, which signifies increased volcanic unrest, remains in effect over Kanlaon.
Emissions
Volcanic gas measurements also point to ongoing unrest.
Sulfur dioxide emissions from Kanlaon’s summit crater averaged 1,248 tons per day, based on campaign measurements conducted on January 13.
While this figure is close to the medium-term average of 1,767 tons per day since the start of the year, emissions earlier peaked at 4,126 tons per day on January 9.
Communities within the four-kilometer permanent danger zone were reminded to strictly remain evacuated, while those within a six-kilometer radius from the summit were urged to stay vigilant and ready for possible escalation of unrest.
Authorities also advised increased alertness against potential lahar flows and sediment-laden streamflows, especially during periods of heavy rainfall.
Civil aviation authorities were likewise advised to keep aircraft away from the volcano’s summit area, as ash from sudden eruptions could pose serious risks to flights./CJ, WDJ