Report on Mayon (Philippines) — 25 July-31 July 2001
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 25 July-31 July 2001
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2001. Report on Mayon (Philippines). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 25 July-31 July 2001. Smithsonian Institution and US Geological Survey.
13.257°N, 123.685°E; summit elev. 2462 m
All times are local (unless otherwise noted)
After the pyroclastic-flow producing eruptions on 26 July Mayon entered an effusive eruptive phase. During 27-31 July lava flowed up to 3.75 km toward the SE in the Bonga Gully, accompanied by numerous high-frequency short-duration tremor events caused by rock fragments detaching from the newly deposited lava flow. Incandescence was visible at the crater, and thick steam plumes and occasional short-lived ash emissions were seen. SO2 emission rates were high, with a maximum of 9,900 metric tons measured on 31 July, which was well above the baseline value of 500 metric tons/day. Due to the possibility of further explosions, Alert Level 5 (the highest level) remained in effect. According to news reports, on 31 July officials allowed residents who live outside of the 7-km danger zone to return to their homes.
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.