The Philippine Institute of Volcanology and Seismology (Phivolcs) on Monday, Dec. 9 warned of an increased risk of lahars following the eruption of Kanlaon Volcano, as heavy rainfall may trigger dangerous mudflows in the surrounding areas.
Phivolcs-Volcano Monitoring and Eruption Prediction Division Chief Maria Antonia Bornas in a press conference warned that the ash and pyroclastic materials ejected by Kanlaon Volcano could be mobilized as lahars during heavy rainfall, similar to what occurred after the June 3 eruption.
“Intense rainfall is not required; even heavy rain can trigger lahars, as the newly deposited ash and broken rocks remain unconsolidated, loose, and easily washed away. These materials can quickly turn into lahars when exposed to rain. Communities that were previously affected by lahars must stay vigilant, as the risk remains in areas that experienced lahars before,” Bornas explained in Filipino.
Based on the Kanlaon Volcano lava flow hazard map, areas at risk of lahars include Canlaon City, La Castellana, La Carlota City, Bago City, Moises Padilla, San Carlos City, and Murcia, all in Negros Occidental.
Kanlaon Volcano had an “explosive eruption” at 3:03 p.m. on Monday. The event produced a voluminous plume that rapidly ascended to 4,000 meters above the summit vent and drifted west-southwest.
Bornas said ashfall was reported in Bago City, as well as in the barangays of Mambukal, Murcia, Guintubdan, and Ara-al in La Carlota City.
A 3.4-kilometer pyroclastic density current (PDC) was also observed on the southeast slope of the volcano, specifically on the side of La Castellana.
Bornas explained that the PDC is regarded as the most dangerous volcanic hazard due to its fast-moving flow of hot gas, ash, and volcanic debris.
The intense heat and suffocating ash can kill instantly, and even survivors of the initial impact may face long-term health risks, such as respiratory issues and ash fallout, she added.
Heightened alert status
Alert Level 3 (magmatic unrest) has been raised due to ongoing volcanic activity, indicating the potential for further eruptions.
Bornas said an explosive eruption may be followed by similar, short-lived explosive events in the near term, which could generate PDCs within a six-kilometer radius from the summit.
“As a precautionary measure, we have escalated the alert level to ensure the safety of residents and to facilitate necessary preparations in the affected areas,” she added.
She said the evacuation of residents within the six-kilometer radius should be mandatory at this time.
Local goverment units, disaster officials, and the general public are urged to prepare for possible escalation to Alert Level 4 should the volcanic activity persist or worsen.
Bornas also advised civil aviation authorities to warn aircraft to avoid flying near the Kanlaon summit.