PHIVOLCS reported that eruptive activity continued at Mayon during 5-11 July. Daily steam-and-gas emissions rose as high as 1 km above the crater and drifted in multiple directions. Average daily measurements of sulfur dioxide emissions fluctuated between 721 and 1,621 tonnes per day. Slow lava effusion from the summit crater continued to feed lava flows on the flanks. The length of the lava flow in the Mi-Isi (S) drainage remained at 2.8 km. The flow in the Bonga (SE) drainage advanced 100 m during 10-11 July, with a total length of 1.4 km. The growing lava dome remained unstable and produced incandescent rockfalls and pyroclastic density currents (PDCs, or pyroclastic flows) that descended the Basud (E) drainage as far as 4 km. Seismic stations recorded 216-511 daily rockfall events, 5-39 daily PDC events (from dome and lava front collapse) lasting 1-3 minutes, and 1-109 volcanic earthquakes. Ashfall was reported during 10-11 July in Legazpi City (13 km SSE), and Budiao (8.1 km S), Salvacion (8.6 km S), Daraga (12 km S), and Camalig (11 km SSW), in Albay. The Disaster Response Operations Monitoring and Information Center (DROMIC) reported that as of 1800 on 10 July, the number of displaced persons and total number of overall affected persons from 26 barangays in the province of Albay increased to 20,141 and 38,376, respectively. 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)