Catastrophic rockslide-debris avalanche at St. Bernard, Southern Leyte, Philippines
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On 17 February 2006, a rockslide-debris avalanche cascaded down the steep slope of Mt. Can-abag, burying the entire village of Guinsaugon in St. Bernard, Southern Leyte, Philippines. Casualties include 139 dead with 980 still missing and presumed dead, making it perhaps the most catastrophic landslide in Philippine history. The landslide started at the ridge top along a fault plane associated with the active Philippine Fault Zone. It started as a block slide that transformed into an avalanche. The entire event lasted for only a few minutes. Estimated maximum landslide velocity is 120–130 m/s. The landslide left behind a deep, wedge-shaped scarp. The central part of the deposit exhibits a hummocky topography typical of avalanches, in contrast to the flatter surface of the debris-flow-type marginal deposit. High amounts of soil in the matrix were derived from the scouring of ancient landslide deposits and rice fields in the valley. The landslide has a total area of 3.2 km2 and a runout distance of 4.1 km. Estimated volume of debris is approximately 20 Mm3. At least four streams were dammed by the landslide debris. Intense precipitation and earthquakes preceding the landslide are the potential triggers. Preliminary back analyses assuming a planar and wedge slip surface yielded very low factors of safety even under dry conditions. A more rigorous analysis of the failure mechanism of the landslide is needed.
KeywordsLandslide Debris avalanche Slope stability Guinsaugon Philippines
We thank UP-NIGS, NIGS’s Commission on Higher Education (CHED) Grant, and PNOC-EDC for supporting this initial study. Technical and logistic support extended by Joseph Foronda, Peter Zamora, Allan Mandanas, Leo Campo, and Ms. Sampaguita Capili is highly appreciated. We also thank Hiroshi Suwa for the critical review and editorial handling.
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