Spike in seismic activity raises phreatic eruption risk at Kanlaon volcano, Philippines

The Philippine Institute of Volcanology and Seismology (PHIVOLCS) reported sustained unrest at Kanlaon volcano, Negros Island, following a sharp increase in volcanic earthquakes and signs of pressurization in the edifice.

A total of 176 volcanic earthquakes were recorded during the 24 hours leading up to 00:00 LT on September 16, with 139 events precisely located beneath the volcano. Sulfur dioxide (SO₂) emissions measured on September 15 averaged 1 071 tonnes/day, below the medium-term baseline but still indicating active degassing.

Moderate gas plumes rose up to 600 m (2 000 feet) above the summit and drifted northwest, while ground deformation monitoring showed inflation of the edifice. PHIVOLCS said these parameters confirm continued pressurization beneath the volcano and increase the likelihood of sudden phreatic eruptions.

Phivolcs Director Teresito Bacolcol added in a September 16 briefing that the probability of phreatic activity is now “high compared to previous days,” though no specific probability can be given. He noted that even short-lived weak to moderately explosive eruptions could generate ashfall, ballistic projectiles, rockfall, and pyroclastic density currents.

Alert Level 2 remains in place, meaning the volcano is in a state of increased unrest. Entry into the 4 km (2.4 miles) Permanent Danger Zone (PDZ) is strictly prohibited, and communities within a 6 km (3.7 miles) radius are advised to remain alert.

Authorities also warned that lahars and sediment-laden streamflows are possible if heavy rainfall coincides with eruptive activity.

Kanlaon volcano, also known as Mount Kanlaon, is a large stratovolcano forming the highest point on Negros Island at 2 465 m (8 087 feet) above sea level. It is one of the most active volcanoes in the Philippines and part of the Negros Volcanic Belt.

The volcano is structurally complex. Its summit hosts a 2 km (1.2 miles) wide, elongated northern caldera that contains a crater lake, and a smaller but higher active vent, Lugud crater, to the south. Kanlaon has produced the largest known volcanic debris avalanche in the Philippines, which traveled about 33 km (20 miles) southwest of the edifice.

Historical eruptions, recorded since 1866, have been predominantly phreatic (steam-driven) in nature, generally small to moderate in size, producing localized ashfall. Larger eruptions remain possible due to the volcano’s size and history of edifice collapse.

References:

¹ Kanlaon volcano summary – PHIVOLCS – September 16, 2025

² Kanlaon volcano advisory – PHIVOLCS – September 15, 2025

³ Kanlaon volcano geologic summary – GVP – Accessed September 16, 2025

Teo Blašković

I'm a dedicated researcher, journalist, and editor at The Watchers. With over 20 years of experience in the media industry, I specialize in hard science news, focusing on extreme weather, seismic and volcanic activity, space weather, and astronomy, including near-Earth objects and planetary defense strategies. You can reach me at teo /at/ watchers.news.

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