PHIVOLCS reported that eruptive activity continued at Mayon during 20-27 June. Slow aseismic lava effusion few a growing lava dome in the summit crater and fed lava flows that advanced down the Mi-isi (S) and Bonga (SE) drainages. Previously reported maximum lava flow lengths of 2.5 km along the Mi-isi and 1.8 km along the Bonga drainages were revised on 24 June to 1.3 km and 1.2 km, respectively; by 27 June the Mi-isi flow was 1.6 km long. The dome remained unstable and produced incandescent rockfalls and pyroclastic density currents (PDCs, or pyroclastic flows). The collapse material traveled as far as 3.3 km away from the crater. Daily steam-and-gas emissions rose as high as 800 m above the crater and drifted SW, WSW, and W. Average daily measurements of sulfur dioxide emissions fluctuated between 507 and 925 tonnes per day. Each day, seismic stations recorded 241-339 rockfall events and 1-17 PDC events, each lasting up to five minutes. On 26 June PHIVOLCS released an advisory due to increased seismic activity and ground deformation, noting that the number of volcano-tectonic earthquakes increased during the week; there were two during 20-21 June, two during 23-24 June, and 107 during 26-27 June. The increased seismicity was accompanied by a sharp increase in ground tilt on the SW part of the volcano. The Disaster Response Operations Monitoring and Information Center (DROMIC) reported that as of 1600 on 27 June, the increased unrest had affected a total of 41,488 people and displaced a total of 20,138 people from 26 barangays within the province of Albay. The Alert Level remained at 3 (on a 0-5 scale). Residents were reminded to stay away from the 6-km-radius Permanent Danger Zone (PDZ), and 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.

Sources: Philippine Institute of Volcanology and Seismology (PHIVOLCS), Disaster Response Operations Monitoring and Information Center (DROMIC)