PHIVOLCS noted in a 21 March report that since January 2001 earthquake clusters or occurrences have been recorded by the seismic monitoring network around the volcano. These earthquakes may signify a reactivation of the volcanic system at depth and could be a precursor to more vigorous activity, such as ash explosions. This interpretation is based on similar earthquake clusters manifested prior to the 10 August 1996 phreatic explosion from the active summit crater of the volcano. In view of the possibility of a sudden ash ejection, PHIVOLCS recommends the immediate suspension of all treks to the summit crater until further notice. As an additional precaution, the pre-defined 4-km-radius Permanent Danger Zone (PDZ) should be avoided at all times.

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.

Source: Philippine Institute of Volcanology and Seismology (PHIVOLCS)