PHIVOLCS reported that at 1509 on 13 July a minor rockfall descended the Mi-isi drainage on Mayon’s S flank, generating a brownish ash cloud. The event was preceded by heavy rainfall on the upper flanks. Sulfur dioxide emissions were 2,398 tonnes/day. Precise leveling data obtained during 2-14 April indicated inflation relative to data collected in late March; electronic tilt data showed pronounced inflation on the mid-flank beginning on 25 June possibly due to a deep aseismic magma intrusion. The Alert Level remained at 2 (on a 0-5 scale) and PHIVOLCS reminded residents to stay away from the 6-km-radius Permanent Danger Zone and the 7-km Extended Danger Zone on the SSW and ENE flanks.

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 periods of andesitic lava flows. Eruptions occur predominately from the central conduit and have also produced lava flows that travel far down the flanks. Pyroclastic density currents 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)