Lahars, muddy volcanic flows composed of ash, debris, and water, were reported on the southern and southwestern slopes of Kanlaon Volcano late Friday, June 6, after intense rains drenched parts of Negros Island, the Philippine Institute of Volcanology and Seismology (Phivolcs) reported.
According to the agency, the sediment-laden flows were observed along Buhangin River and Ibid Creek in La Castellana, Negros Occidental, after 45.5 millimeters of rain fell over a 3.5-hour period.
“Lahars have been reported by netizens in social media and by local officials. Cohesive and cement-like lahars occurred along the Buhangin River and beneath Hacienda 92 Bridge in Brgy. Sag-ang and Ibid Creek in Brgy. Biak-na-bato, La Castellana, Negros Occidental,” Phivolcs said in a lahar advisory issued at 8:30 p.m.
The agency said the low pressure area (LPA) and the southwest monsoon have been dumping moderate to heavy rains across the region, including the upper slopes of the volcano.
“Based on the Philippine Atmospheric Geophysical and Astronomical Services Administration (PAGASA) Regional Weather Advisory No. 2, the Negros Island Region has been under the effect of a Low Pressure Area (LPA) and the Southwest Monsoon,” it stated.
“Furthermore, based on PAGASA’s Heavy Rainfall Warning No. 2 #VISPRSD, moderate to heavy rainfall in the late afternoon to early evening affected portions of Kanlaon Volcano, generating channel-confined volcanic sediment flows or lahars on the southern and southwestern slopes.”
While 45.5 mm of rain was recorded at the Kanlaon Volcano Observatory in La Carlota City, Phivolcs said rainfall volumes near the summit may have been higher.
The agency warned that additional lahars or muddy streamflows could occur in the coming months, especially during periods of intense monsoon rain.
“The Southwest Monsoon season can bring occasionally heavy rains over Negros Island for a few months. These rains could generate lahars, muddy streamflows or muddy run-off in the rivers draining the southern Kanlaon edifice particularly those that have been already affected by lahars. Lahars can threaten communities along the middle and lower slopes with inundation, burial and wash out,” the agency stated.
Phivolcs advised local officials and residents in vulnerable communities to stay alert and respond quickly when rains begin, as precipitation is the only real early-warning signal for these flows.