PHIVOLCS reported that slow lava effusion at Mayon’s summit crater continued during 11-17 October. The lengths of the lava flow in the Mi-Isi (S), Bonga (SE), and Basud (E) drainages remained at 2.8 km, 3.4 km, and 1.1 km, respectively. Collapses at the lava dome and from the margins of the lava flows produced incandescent rockfalls and occasional pyroclastic density currents (PDCs, or pyroclastic flows) that descended the flanks as far as 4 km. Each day, seismic stations recorded 43-175 rockfall events and 9-70 daily volcanic earthquakes including 2-67 tremor events that lasted as short as one minute to as long as about four and a half hours. Sulfur dioxide emissions measured near-daily averages between 727 and 1,521 tonnes per day, with the highest value recorded on 17 October. Short-lived bursts of gas were recorded in seismic and infrasound data at 1836 on 20 October and 0006 on 21 October. A period of increased lava effusion that started at 2210 on 21 October was characterized by more intense incandescence at the summit crater, followed by rockfalls and lava flows in the Mi-Isi and Bonga drainages. One PDC per day was recorded on 19, 21, and 22 October and two were recorded during 23-24 October; 53 were recorded during 24-25 October, accompanying a second period of increased effusion on 24 October. 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 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)