Report on Mayon (Philippines) — 4 July-10 July 2001
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 4 July-10 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, 4 July-10 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)
A decrease in volcanic activity began on 3 July that led PHIVOLCS to reduce the Alert Level on 4 July from 5 (hazardous eruption in progress) to 4 (hazardous eruption imminent). In comparison to the previous week SO2 emissions decreased, seismic activity was lower, the rate of inflation of the volcano's edifice decreased, and there was no ash in the steam clouds that emanated from the crater. Alert Level 4 was maintained due to the possibility of minor ash puffs and secondary explosions caused by the contact of water with the voluminous hot lava. The extended danger zone was reduced from 8 km to 7 km in radius. On 4 July ~20,000 people who were evacuated from the most distal parts of the evacuation zone were permitted 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.