Report on Kanlaon (Philippines) — April 1987
Scientific Event Alert Network Bulletin, vol. 12, no. 4 (April 1987)
Managing Editor: Lindsay McClelland.
Kanlaon (Philippines) Ash eruption follows increased seismicity
Please cite this report as:
Global Volcanism Program, 1987. Report on Kanlaon (Philippines). In: McClelland, L (ed.), Scientific Event Alert Network Bulletin, 12:4. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198704-272020.
10.412°N, 123.132°E; summit elev. 2435 m
All times are local (unless otherwise noted)
Increased seismicity and thermal activity were followed by a small ash eruption.
On 30 March the number of volcanic earthquakes reached 9/day, an increase from the previous level of 1-3/day. Seismicity continued at moderate to low levels until 22 April when 74 low-frequency volcanic events were recorded and steam emission increased. Steam plume height increased to 150-200 m from a normal of 50-100 m, and 40-50% of the vent opening was filled with steam. PHIVOLCS officially informed the Secretary of Science, Department of Science and Technology that the condition of the volcano was unstable but since no harmonic tremor was being recorded, only a mild ash ejection was expected if activity increased.
On the morning of 24 April a fresh ash deposit ~1-2 km wide and 6.5 km long extended down the SW flank. No eruption signals were recorded by seismometers and no sounds were heard by nearby residents. A sulfur smell was reported from the Cabagnaan Observatory (approximately 6 km SW of the crater) on the same day.
Geochemical studies of the Mambucal aquapool, mudpool, and sulfur spring (9.5 km NNW of the summit) showed increasing sulfate and chloride concentrations starting 19 February.
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: PHIVOLCS.