Report on Mayon (Philippines) — 11 July-17 July 2001
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 11 July-17 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, 11 July-17 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)
Volcanic activity continued to decrease at Mayon during 8-16 July, with low seismicity, occasional SE-directed rockfalls, and a general decrease in SO2 emission rates. Although the volcano's edifice remained slightly inflated, a gradual deflationary trend was detected. The activity decrease led PHIVOLCS to reduce the Alert level from 4 (hazardous eruption imminent) to 3 (increased tendency towards eruption). Authorities removed the 7-km-radius Extended Danger Zone in the SE, but left the 6-km-radius Permanent Danger Zone in effect on a long-term basis.
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.