PHIVOLCS reported that the rate of lava-dome extrusion at Mayon’s summit crater increased, leading to an Alert Level increase and evacuations. Sulfur dioxide emissions were at or near baseline levels of 500 tonnes per day, averaging 574 and 332 tonnes per day on 6 and 7 June, respectively. The total number of rockfalls increased from 54 during 1-4 June to 267 during 5-8 June. Additionally, the volumes of the individual rockfall events became larger on 3 June. The rockfalls were generated by partial collapses of the growing lava dome and indicated an increasing extrusion rate. Three pyroclastic density currents (PDCs, or pyroclastic flows) were recorded at 0618, 0953, and 1100 on 8 June, each lasting 4-5 minutes based on the seismic signals. The PDCs traveled as far as 2 km down the Mi-Isi (S), Bonga (SE), and Basud (E) drainages and indicated that new, less degassed lava was collapsing from the summit dome. The Alert Level was raised to 3 (on a 0-5 scale) at 1200 on 8 June and recommended the evacuation of the 6-km radius Permanent Danger Zone.

Six PDCs generated by collapses at the lava dome and 199 rockfall events were recorded during 8-9 June, based on seismic data and visual observations. Material from the rockfalls and PDCs descended the S flank within 2 km. Steam-and-gas plumes from the dome rose 800 m and drifted S, and light-brown ash plumes from the rockfalls drifted S. Minor crater incandescence from newly extruded lava and incandescent rockfalls were observed through the night. Rockfall events continued during 9-10 June with total of 59. A new dome, contacting a part of the remnant dome on the SE part of the crater floor, was visible during the morning of 10 June. Sulfur dioxide emissions increased to moderate levels, averaging 1,205 tonnes per day that same day. The DROMIC report stated that 9,314 people from 21 neighborhoods (barangays) spanning six municipalities were in evacuation centers by 10 June.

A total of 177 rockfalls traveled as far as 700 m down the S and SE flanks during 10-11 June. Plumes of steam and gas from the dome and minor ash plumes from the rockfalls descended the flanks and then drifted E and SE. Incandescence from the dome and rockfalls was visible at night. Sulfur dioxide emissions averaged 642 tonnes per day on 11 June. Lava flows emerged at about 1947 on 11 June and produced two 500-m-long lobes; lava avalanches from the ends of the flows descended the Mi-Isi, Bonga, and Basud drainages within 2 km of the summit. Effusion of the lava flows was preceded by slight inflation at the upper flanks based on tiltmeter data and accompanied by minor seismicity. During 11-12 June the monitoring network recorded 260 rockfall events, and three collapses at the dome that produced PDCs (each lasting 2-4 minutes). The lava flows continued to be active. There were 14,360 people that had evacuated by 12 June; of those, 584 people were staying in places other than evacuation centers.

During 12-13 June the monitoring network recorded 221 rockfall events and collapses at the dome that produced PDCs (each lasting 2-4 minutes). Lava continued to slowly effuse at the summit crater and collapsed material traveled 1 km down the Mi-isi and Bonga drainages. One PDC lasting two minutes was observed and detected by the seismic network. Diffuse ash from the rockfalls and steam-and-gas emissions from the dome drifted downslope and then NE. Rockfalls exposed incandescent material at the summit. By 13 June a total of 16,152 people had evacuated; of those, 15,493 people were in evacuation shelters and 659 people were staying with friends and family.

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 term andesitic lava flows. Eruptions occur predominately from the central conduit and have also produced lava flows that travel far down the flanks. Pyroclastic flows 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)