Crater glow, or ‘banaag,’ was observed at the summit of Kanlaon Volcano on Sunday evening, the Philippine Institute of Volcanology and Seismology (Phivolcs) reported Monday.
In a Facebook post, Phivolcs said the Kanlaon Volcano Observatory reported seeing ‘with the naked eye for the first time incandescence at the Kanlaon Volcano summit caused by superheated volcanic gas’ at around 7 p.m.
Mari Andylene Quintia, Phivolcs resident volcanologist, explained that the superheated plume consists of magmatic gas being emitted by the volcano.
Such a phenomenon, when it becomes visible to the naked eye, is called ‘crater glow’ or ‘banaag,’ a common precursor of a magmatic eruption at Mayon Volcano, the agency explained.
‘While this is a new development, monitoring parameters have persisted at approximately the same level after Kanlaon’s last moderately explosive eruption on March 15, 2026,’ it added.
The agency said that if Kanlaon’s crater glow becomes sustained and intensifies, it could indicate that magma is close to or already at the crater, warning of increased chances of magmatic unrest within days.
Phivolcs also reported that since Kanlaon’s moderate explosive eruption on March 15, seismic activity has remained steady at an average of six volcano-tectonic earthquakes per day.
Meanwhile, sulfur dioxide emissions averaged 1,646 tons per day and slightly increased to 2,382 tons per day in the past week.
‘Ground deformation parameters have been non-steady but still indicate sustained and slow-rate inflation of the volcano edifice since 2022,’ Phivolcs noted.
Kanlaon remains under Alert Level 2, although Phivolcs said it may be raised to Alert Level 3 should sustained and intensifying crater glow signal a possible magmatic eruption.
Residents within the four-kilometer Permanent Danger Zone were encouraged to evacuate, while those within Pyroclastic Density Current Hazard Zones were advised to remain vigilant and prepare for possible evacuation should volcanic unrest intensify.
Phivolcs also urged local government units and disaster risk reduction officials to prepare response measures and stay alert for ‘potential syn-eruption lahars and sediment-laden streamflow in channels’ during heavy rains.
The agency added that civil aviation authorities should also advise pilots to avoid flying close to Kanlaon’s summit, since ash from any sudden eruption can be hazardous to aircraft.