PHIVOLCS issued a special notice for Kanlaon at 1000 on 21 July, noting increased seismicity. The seismic network detected 35 volcano-tectonic earthquakes between 2200 on 20 July and 0906 on 21 July at depths of 12-15 km beneath the summit crater. The earthquakes had local magnitudes of 0.9-2.3. Ground deformation data from continuous GPS and electronic tilt data had been recording inflation at the mid-flanks of the volcano since March. Sulfur dioxide emissions at the summit crater averaged 786 tonnes per day (t/d) on 18 July and 230 t/d on 21 July, slightly higher than the average of 566 t/d measured in March. The number of volcano-tectonic earthquakes decreased during the rest of the week; there were 16 recorded during 21-22 July and 1-2 daily earthquakes during 23-25 July. The Alert Level remained at 1 (on a scale of 0-5) and PHIVOLCS reminded the public to remain outside of the 4-km-radius Permanent Danger Zone.

Geological Summary. Kanlaon volcano (also spelled Canlaon) forms the highest point on the Philippine island of Negros. 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.

Source: Philippine Institute of Volcanology and Seismology (PHIVOLCS)