Report on Kanlaon (Philippines) — May 1987
Scientific Event Alert Network Bulletin, vol. 12, no. 5 (May 1987)
Managing Editor: Lindsay McClelland.
Kanlaon (Philippines) Sulfate increased in thermal area before ash eruption
Please cite this report as:
Global Volcanism Program, 1987. Report on Kanlaon (Philippines). In: McClelland, L. (ed.), Scientific Event Alert Network Bulletin, 12:5. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198705-272020.
10.412°N, 123.132°E; summit elev. 2435 m
All times are local (unless otherwise noted)
The ash eruption that occurred 23 or 24 April was preceded by a steady increase in sulfate concentration in the Mambucal aquapool, mudpool, and sulfur spring. The increase began on 19 February when the average sulfate concentration rose from 40 ppm to 89-106 ppm in the aquapool, from 200-364 ppm to 490-708 ppm in the mudpool, and from 100-149 to 356-436 ppm in the sulfur spring (figure 1). Chloride concentration in the aquapool had ranged from 1,682-1,826 ppm but values began fluctuating between 1,870-2,130 ppm on 15 March. No corresponding change in chloride concentration was noted in the mudpool or sulfur spring. Thermal measurements in the Mambucal probe hole, aquapool, and sulfur spring yielded anomalous results but increases of 1.0°, 3.0°, and 5.0° C respectively (compared to the readings of the last quarter of 1986) were noted.
|Figure 1. Sulfate concentration at Mambucal Aquapool, Mudpool, and Sulfur Spring, 9.75 km NNW of Canlaon's summit, 1 January-4 April 1987. Courtesy of PHIVOLCS.|
Geodetic measurements on 28-29 April revealed a slight inflation of 2.61 mm along a 400-m levelling line on the SE flank. Seismicity began increasing on 30 March 1987 and reached 74 low-frequency events on 22 April (see figure 2 and 12:4).
|Figure 2. Number of low-frequency volcanic earthquakes at Canlaon, 1 January 1986-29 April 1987. Courtesy of PHIVOLCS.|
Further Reference. Bautista, L.P., 1987, Volcano Update - Canlaon Volcano; Phivolcs Observer, v. 3, no. 2, p. 5.
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.