Phreatic eruption, resumption of degassing at Kanlaon volcano, Philippines

A phreatic (steam-driven) eruption started at Kanlaon volcano in Negros Island, Philippines at 01:47 UTC (09:47 local time) on December 9, 2017. The eruption was preceded by a resumption of degassing at the summit crater at 22:34 UTC, December 8 (06:34 local time, December 9), which was last observed in September 2016.

Based on the seismic record, the eruption lasted approximately 10 minutes, the Philippine Institute of Volcanology and Seismology (PHIVOLCS) reports.  

The event ejected steam and dark ash but was poorly observed due to clouds covering the summit region. Rumbling sound was reportedly heard in Brgy. Manghanoy, La Castellana, and thin ash fell on Sitio Guintubdan, Brgy. Ara-al, La Carlota City.

Today’s eruption was preceded by a resumption of degassing at the summit crater at 22:34 UTC on December 8, which was last observed September 2016.

Seismic unrest under the volcano started on August 18, 2017 and continued increasing, forcing PHIVOLCS to raise the Alert Level from 1 to 2 on Wednesday, November 15, 2017.

Alert Level 2 status remains to date, which means that the volcano is undergoing a moderate level of unrest. There is a probable intrusion of magma at depth which may or may not lead to a magmatic eruption, the agency said.

The local government units and the public are strictly reminded that entry into the 4-kilometer radius (2.5 miles) Permanent Danger Zone (PDZ) is strictly prohibited due to the further possibilities of sudden and hazardous steam-driven or phreatic eruptions.

Civil aviation authorities must also advise pilots to avoid flying close to the volcano’s summit as ejecta from any sudden phreatic eruption can be hazardous to aircraft. DOST-PHIVOLCS is closely monitoring Kanlaon Volcano’s activity and any new development will be relayed to all concerned.

The last eruptive episode of this volcano started on November 24, 2015 and ended on June 18, 2016. It had Volcanic Explosivity Index of 2 (out of 7).

Geological summary

Kanlaon volcano (also spelled Canlaon), the most active of the central Philippines, forms the highest point on the island of Negros. The massive 2435-m-high (7 989 feet) andesitic stratovolcano is dotted with fissure-controlled pyroclastic cones and craters, many of which are filled by lakes.

The largest debris avalanche known in the Philippines traveled 33 km (20.5 miles) to the SW from Kanlaon. The summit of Kanlaon contains a 2-km-wide (1.2 miles), elongated northern caldera with a crater lake and a smaller, but higher, historically active vent, Lugud crater, to the south. 

Historical eruptions from Kanlaon, recorded since 1866, have typically consisted of phreatic explosions of small-to-moderate size that produce minor ashfalls near the volcano. (GVP)

Featured image: Phreatic eruption at Kanlaon volcano on December 9, 2017. Credit: PHIVOLCS