PHIVOLCS reported that the eruption at Mayon continued during 9-15 August, with slow lava effusion from the summit crater feeding flows on the S, SE, and E flanks. The length of the lava flow in the Mi-Isi (S) drainage remained at 2.8 km and the flow in the Bonga (SE) drainage was 3.4 km long. The advancing flow in the Basud (E) drainage reached 1 km long by 9 August and was 1.1 km by 13 August. Collapses at the lava dome and from the lava flows produced incandescent rockfalls and pyroclastic density currents (PDCs, or pyroclastic flows) that descended the Mi-Isi, Bonga, and Basud drainages as far as 4 km. Each day seismic stations recorded 45-201 rockfall events and 1-4 PDC events. There 42-259 volcanic earthquakes, including 42-91 low-frequency volcanic earthquakes and 56-167 tremor events, each with durations of 1-45 minutes. Sulfur dioxide emissions were reported on most days, averaging between 799 and 2,689 tonnes per day, with the highest value recorded on 10 August. There was a total of five emissions of short, dark ash plumes (called “ashing” by PHIVOLCS) during 10-12 August. The Alert Level remained at 3 (on a 0-5 scale) and residents were reminded to stay away from the 6-km-radius Permanent Danger Zone (PDZ). PHIVOLCS recommended that civil aviation authorities advise pilots to avoid flying close to the summit.

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)