PHIVOLCS reported that 0-3 daily rockfalls and volcanic earthquakes at Mayon were detected by the seismic network during 16-22 July. Moderate levels of emissions drifted mainly NW, W, and SW and occasionally ENE. Faint crater incandescence was only visible using a telescope. A phreatic explosion occurred at 1816 on 18 July and lasted for 45 seconds based on seismic data. According to the Tokyo VAAC the plume rose 2.7 km (9,000 ft) a.s.l., or about 280 m above the summit, and drifted WNW. There were 11 rockfalls recorded during 18-19 July. The Alert Level remained at 1 (on a 0-5 scale); the public was reminded to stay out of the 6-km-radius Permanent Danger Zone (PDZ) and pilots were advised 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)