People living in the vicinity of the volcano were advised to not enter the 4-km-radius permanent danger zone following a mild phreatic explosion at 0519 on 25 August that produced a voluminous gray steam cloud to 800 m height before drifting NNE. Steaming from the summit area increased following the explosion, and later that morning (0600-1045) a dirty white steam plume rose to heights that varied from 200 to 500 m. Moderate steam emission to 100-200 m was observed in the afternoon and evening. Radio reports stated that ash fell as far away as Panay Island, about 65 km W. Harmonic tremor was detected for 20 minutes during the eruption by a seismometer at Cabagnaan Station, 5.5 km SW of the summit, and an earthquake accompanied by rumbling sounds was felt at the station at 0526. The seismometer also recorded 21 low-frequency volcanic earthquakes within 3 hours after the explosion. Seismicity then rapidly declined, with only two high-frequency and three low-frequency events recorded from 1200 on 25 August through 0500 the next day. Seismicity prior to the explosion was at normal background levels of 0-2 events/day.

Canlaon had another mild phreatic explosion at 2329 on 3 September, which lasted for 8 minutes and produced a grayish steam-and-ash column that rose 1,000 m above the summit before drifting SSW and SSE. Traces of ash fell at the Canlaon Volcano Observatory, 8 km SSE of the summit. The phreatic explosion was accompanied by an earthquake felt at the Cabagnaan Station. Moderate-to-strong emission of dirty white steam was observed for 6 hours after the explosion; steaming activity then declined and the steam became white. Increased seismicity was noted during the explosion along with strong steaming, similar to previous phreatic activity at the volcano. Seismicity returned to background levels the next day. EDM surveys conducted after the 3 September event did not indicate significant inflation. Petrographic examination of the ash deposited by the 25 August and 3 September explosions indicated no juvenile component.

Geological Summary. Kanlaon volcano (also spelled Canlaon) forms the highest point on the island of Negros, Philippines. The massive andesitic stratovolcano is covered 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 active vent, Lugud crater, to the south. Eruptions recorded since 1866 have typically consisted of phreatic explosions of small-to-moderate size that produce minor local ashfall.

Information Contacts: R. Solidum, PHIVOLCS; AP.