Report on Mayon (Philippines) — 27 June-3 July 2001
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 27 June-3 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, 27 June-3 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 large eruption on 24 June volcanic activity returned to relatively low levels for several days. During this period, rockfalls dominated the seismic records as lava slowly flowed to the SE down the Bonga Gully. PHIVOLCS reported that due to diminished lava extrusion lava was not expected to reach populated areas. Volcanic activity increased on 29 June when explosions occurred at 1605 and 1702. These explosions generated pyroclastic flows that traveled down the Bonga Gully and generated billowing ash clouds that ascended to ~4 km above the volcano. The pyroclastic flows reached ~3 km to the SE of the summit towards the general direction of Matanag Gully. During the eruption a portion of the Upper Basud Gully in the volcano's eastern sector collapsed. On 1 July, SO2 emission rates were as high as 8,700 metric tons per day, a value about 5-fold higher than on 29 June. By 2 June the rate of SO2 emission greatly decreased to 840 tons per day. PHIVOLCS stated that due to the ongoing significant inflation of the volcanic cone and anomalous rapid decline of SO2 emission rates a high likelihood of continued explosive eruptions in the coming days remains. Accordingly, the hazard status remained in the top category, Alert Level 5 (hazardous eruption in progress).
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.