Report on Kanlaon (Philippines) — December 2004
Bulletin of the Global Volcanism Network, vol. 29, no. 12 (December 2004)
Managing Editor: Richard Wunderman.
Kanlaon (Philippines) Alert level lowered after seismic decrease; January 2005 phreatic ash emission
Please cite this report as:
Global Volcanism Program, 2004. Report on Kanlaon (Philippines) (Wunderman, R., ed.). Bulletin of the Global Volcanism Network, 29:12. Smithsonian Institution.
10.412°N, 123.132°E; summit elev. 2435 m
All times are local (unless otherwise noted)
The Philippine Institute of Volcanology and Seismology (PHIVOLCS) noted in a March 2004 report that the most recent eruptive episode of Canlaon had begun on 7 March 2003. Their 2003 Annual Report described a mild ash-and-steam emission on 7 March that rose 1 km above the summit and resulted in traces of ash deposited at Cabagnaan, 5.5 km S. On 17 March 2003 the hazard status had been raised to Alert Level 1 (BGVN 28:03, 28:06, 28:07, and 28:08). A total of 46 minor ash ejections were documented or observed, most from June to July 2003, characterized by steam clouds with minor ash that rose as high as 1,500 m. Prevailing winds dispersed the ash over the mid-upper slopes in the SW and SE sectors of the volcano.
Sporadic recordings of high-frequency volcanic earthquakes (HFVQ) and low-frequency volcanic earthquake swarms (LFVQ) starting in January 2003 prompted PHIVOLCS to issue a warning on the possibility of sudden phreatic explosions. In June 2003 daily occurrences of LFVQs increased dramatically and these heightened levels were sustained until July 2003. Low-frequency short-duration harmonic tremors (SDHLF) also appeared in June 2003 and increased like the LFVQs, indicating a continuous supply and transport of volcanic fluids towards the shallow levels of the crater area.
A general trend towards volcanic quiet was recognized during August 2003, but the status was maintained at Alert Level 1 because HFVQs, LFVQs, and SDHLFs persisted, though in diminishing numbers, until September 2003. After that time, steam emissions from the summit crater were only weak or absent, with normal levels of seismic activity. On 1 March 2004 PHIVOLCS lowered the hazard status to Alert Level 0, meaning the volcano has returned to a quiet state. The public was strongly advised, however, to consider the risk when entering the 4-km Permanent Danger Zone because sudden phreatic explosions may occur without warning. People planning to climb the volcano are advised to check with an observatory first.
Phreatic emission, January 2005. The value of continued warnings was shown on 21 January 2005, when Canlaon generated a sudden brief ash emission. The PHIVOLCS observatory at La Carlota City College reported moderate emission of a grayish volcanic plume at about 0930 that rose to ~ 500 m above the active crater and drifted WNW and SW, depositing light ash on the upper SW slopes. Traces of ash deposits were also observed at Cabagnaan, 5.5 km SW of the active crater. No coincident volcanic earthquakes were recorded, and Canlaon continued to be seismically quiet. These observations suggest the activity is hydrothermal in nature and occurring at very shallow levels near the crater floor.
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 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 SW from Kanlaon. The summit contains a 2-km-wide, elongated northern caldera with a crater lake and a smaller, but higher, historically active vent, Lugud crater, to the south. Historical eruptions, recorded since 1866, have typically consisted of phreatic explosions of small-to-moderate size that produce minor ashfalls near the volcano.
Information Contacts: Philippine Institute of Volcanology and Seismology (PHIVOLCS), Department of Science and Technology, PHIVOLCS Building, C.P. Garcia Avenue, Univ. of the Philippines Campus, Diliman, Quezon City, Philippines (URL: http://www.phivolcs.dost.gov.ph/).