Extreme rainfall-induced lahars and dike breaching, 30 November 2006, Mayon Volcano,Philippines |
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| Authors: | E M R Paguican A M F Lagmay K S Rodolfo R S Rodolfo A M P Tengonciang M R Lapus E G Baliatan Jr" target="_blank">E C ObilleJr |
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| Institution: | (1) National Institute of Geological Sciences, College of Science, University of the Philippines, Diliman, Quezon City, 1101, Philippines;(2) Department of Earth and Environmental Sciences, University of Illinois at Chicago, 845 W. Taylor St., Chicago, IL 60607, USA;(3) Earthprobe Incorporated, P. Guevarra, San Juan, Metro Manila, Philippines;(4) Department of Physical Sciences, College of Science, University of the Philippines, Governor Pack Road, Baguio City, 2600, Philippines;(5) National Institute for Science and Mathematics Education, University of the Philippines, Diliman, Quezon City, 1101, Philippines |
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| Abstract: | On 29–30 November 2006, heavy rains from Supertyphoon Durian remobilized volcanic debris on the southern and eastern slopes
of Mount Mayon, generating major lahars that caused severe loss of life and property in downstream communities. The nearby
Legaspi City weather station recorded 495.8 mm of rainfall over 1.5 days at rates as high as 47.5 mm/h, far exceeding the
initiation threshold for Mayon lahars. For about 18 h, floods and lahars from the intense and prolonged rainfall overtopped
river bends, breaching six dikes through which they created new paths, buried downstream communities in thick, widespread
deposits, and caused most of the 1,266 fatalities. In order to mitigate damage from future lahars, the deposits were described
and analyzed for clues to their generation and impact on structures and people. Post-disaster maps were generated from raw
ASTER and SPOT images, using automated density slicing to characterize lahar deposits, flooded areas, croplands, and urbanized
areas. Fieldwork was undertaken to check the accuracy of the maps, especially at the edges of the lahar deposits, and to measure
the deposit thicknesses. The Durian event was exceptional in terms of rainfall intensity, but the dikes eventually failed
because they were designed and built according to flood specifications, not to withstand major lahars. |
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