PHIVOLCS reported that slow lava effusion at Mayon’s summit crater continued during 13-21 November. 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 produced rockfalls and occasional pyroclastic density currents (PDCs, or pyroclastic flows) that descended the flanks as far as 4 km. Seismic stations recorded 37-166 rockfall events each day. During 14-15 and 20-21 November there were 8-9 daily volcanic earthquakes, including 2-5 volcanic tremors, each lasting 1-4 minutes; three volcanic earthquakes were recorded during 17-18 November, and one was recorded during 19-20 November. There were 1-2 daily PDC events detected during 14-15 November and 17-21 November. Sulfur dioxide emissions averaged 1,408 and 1,709 tonnes per day on 14 and 16 November, respectively. One ash emission was recorded during 20-21 November. 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)