On 8 September PHIVOLCS noted that recent changes at Mayon prompted a change in the Alert level from 0 to 1 (on a 0-5 scale). Continuous gas measurements consistently showed increased sulfur dioxide emissions above the baseline level of 500 tonnes/day, sometimes as high as 1,000 tonnes/day, since July. Global Positioning System data and tilt measurements showed a consistent inflationary trend since July, and precise leveling and electronic distance surveys the last week of August also indicated edifice inflation, possibly due to magma movement at depth. An earthquake swarm (146 events) located 10 km SE during 3-6 August likely indicated rock fracturing processes but may or may not be associated with magmatic activity. Steam emissions from the crater ranged from weak to moderate. PHIVOLCS reminded residents of the 6-km-radius Permanent Danger Zone (PDZ) around the volcano.

Geological Summary. Symmetrical Mayon, which rises above the Albay Gulf NW of Legazpi City, is the most active volcano of the Philippines. The steep upper slopes are capped by a small summit crater. Recorded eruptions since 1616 CE range from Strombolian to basaltic Plinian, with cyclical activity beginning with basaltic eruptions, followed by longer term andesitic lava flows. Eruptions occur predominately from the central conduit and have also produced lava flows that travel far down the flanks. Pyroclastic flows and mudflows have commonly swept down many of the approximately 40 ravines that radiate from the summit and have often damaged populated lowland areas. A violent eruption in 1814 killed more than 1,200 people and devastated several towns.

Source: Philippine Institute of Volcanology and Seismology (PHIVOLCS)