PHIVOLCS reported that during 16-17 September the seismic network at Mayon recorded 38 volcanic earthquakes and 277 rockfall events. Bright incandescence from the crater was visible at night, and rolling incandescent rocks in the uppermost part of Bonga Gully indicated that the lava dome was breaching the SE part of the crater. The Alert Level was raised to 3 (on a 0-5 scale). PHIVOLCS recommended enforcement of the 6-km radius Permanent Danger Zone (PDZ) around the volcano and the 7-km Extended Danger Zone (EDZ) on the SE flank. On 17 September a news article indicated that almost 24,000 people from villages within an 8-km radius from the crater had been evacuated.

During 17-18 September the network recorded 142 volcanic earthquakes and 251 rockfall events. Although rain clouds prevented visual observations of the crater, white steam plumes drifting SSW were noted. The network recorded 38 volcanic earthquakes and 277 rockfall events during 18-19 September; cloud cover prevented visual observations. During 19-21 September four volcanic earthquakes along with 8-22 rockfall events per day were recorded. White steam plumes drifted ENE and NNE during 20-21 September. During 21-23 September three volcanic earthquakes per day and 13-18 rockfall events per day were recorded; white steam plumes drifted NNE, NE, ENE, and SW.

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), Associated Press