Report on Mayon (Philippines) — 15 February-21 February 2006
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 15 February-21 February 2006
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2006. Report on Mayon (Philippines). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 15 February-21 February 2006. Smithsonian Institution and US Geological Survey.
13.257°N, 123.685°E; summit elev. 2462 m
All times are local (unless otherwise noted)
A minor explosion at Mayon on 21 February at 0941 produced an ash plume that rose to ~500 m above the volcano's crater (or 9,700 ft a.s.l.) and drifted SW. Ash was deposited on the upper slopes of the volcano. The ash emission was accompanied by a small explosion-type earthquake, recorded only by seismographs around the volcano.
Prior to the explosion, an increase in seismicity was recorded at the volcano. Between 1545 on 20 February and 0520 on 21 February, there were 147 low-frequency volcanic earthquakes recorded, considerably above the five or fewer events per day that are normally recorded. Some minor rockfalls were indicated and probably resulted from detachment of lava blocks from the summit. Steaming was observed. No incandescence was visible at the crater due to clouds obscuring the volcano. Mayon remained at Alert Level 2, with a 6-km-radius Permanent Danger Zone in effect. PHIVOLCS expects similar ash explosions in the coming days as magma intrudes the summit area and releases volcanic gases.
Geologic Background. Beautifully symmetrical Mayon, which rises above the Albay Gulf NW of Legazpi City, is the Philippines' most active volcano. The structurally simple edifice has steep upper slopes averaging 35-40 degrees that are capped by a small summit crater. Historical eruptions date back to 1616 and 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 devastated populated lowland areas. A violent eruption in 1814 killed more than 1,200 people and devastated several towns.