Report on Kanlaon (Philippines) — June 1986
Scientific Event Alert Network Bulletin, vol. 11, no. 6 (June 1986)
Managing Editor: Lindsay McClelland.
Kanlaon (Philippines) Renewed explosions and seismicity
Please cite this report as:
Global Volcanism Program, 1986. Report on Kanlaon (Philippines) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 11:6. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198606-272020.
10.412°N, 123.132°E; summit elev. 2435 m
All times are local (unless otherwise noted)
Canlaon again erupted on 21 June, almost 19 days after the previous ash ejection. The event started at 1907 and was characterized by a cauliflower-shaped ash-steam cloud that rose to 4,000 m above the volcano's 2,465-m summit. The event was initiated by an explosion-type earthquake felt with intensities III and II at seismic stations 6 and 8.7 km from the summit respectively (Cabagnaan and Canlaon). Booming and hissing sounds accompanied the ash ejection. A strong sulfurous odor was detected at Canlaon station a few minutes after the event. Field investigation the next morning showed that light ashfall had occurred on several villages SE of the summit. The maximum thickness of the wet, rainsoaked ash deposit 4.5 km from the summit was 2 mm. The maximum volume of ejected material was 136,600 m3.
The eruption was anticipated because of the marked increase in steam volume 10 days prior to the eruption. The number of low-frequency volcanic earthquakes had remained at a high level after the ash ejection of 3 June and decreased slightly 9-13 June. Seismicity increased again on 14 June, 8 days earlier.
As of 1 July, seismicity and steaming had decreased slightly. PHIVOLCS noted that other ash ejections are still to be expected based on the eruptive patterns of 1969, 1978, and 1985. Furthermore, PHIVOLCS noted that the continued presence of low-frequency harmonic tremor, not recorded in the past at this volcano, heightens the possibility of magmatic eruption.
Geologic Background. 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: R.S. Punongbayan, PHIVOLCS.