PHIVOLCS reported Mayon’s earthquakes, rockfall events, and an inflationary trend from leveling surveys on 15 September. A noticeable escalation occurred later that day, including 39 rockfall events and 32 low-frequency volcanic earthquakes. Crater glow became visible around 2000 and PHIVOLCS released an informational bulletin at 2200 announcing Alert Level 3. On 16 September incandescent rockfalls spread to the upper reaches of Bonga Gully on the SE flank.

News reports highlighted the evacuation orders announced by the governor of Albay province, which included the 6 km permanent danger zone surrounding the volcano; an assisted evacuation was enforced for the 6-8 km extended danger zone. In an interview with the press, the governor noted that some residents had already fled their homes in Guinobatan (11.8 km SW) on the evening of 15 September.

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.

Sources: Philippine Institute of Volcanology and Seismology (PHIVOLCS), ABS-CBN News