Abstract
Abstract. Sea cliff evolution is dominated by the occurrence of slope mass movements of different types and sizes, which are a considerable source of natural hazard, making their assessment a relevant issue in terms of human loss prevention and land use regulations. To address the assessment of the spatial component of sea cliff hazards, i.e. the susceptibility, a statistically based study was made to assess the capacity of a set of conditioning factors to express the occurrence of sea cliff failures affecting areas located along their top. The study was based on the application of the bivariate information value and multivariate logistic regression statistical methods, using a set of predisposing factors for cliff failures, mainly related to geology (lithology, bedding dip, faults) and geomorphology (maximum and mean slope, height, aspect, plan curvature, toe protection), which were correlated with a photogrammetry-based inventory of cliff failures that occurred in a 60 yr period (1947–2007). The susceptibility models were validated against the inventory data using standard success rate and ROC curves, and provided encouraging results, indicating that the proposed approaches are effective for susceptibility assessment. The results obtained also stress the need for improvement of the predisposing factors to be used in this type of study and the need for detailed and systematic cliff failure inventories.
Highlights
Slope mass movements, which include rockfalls, toppling and different types of landslides, are the dominant and more visible process of sea cliff retreat (Trenhaile, 1987; Sunamura, 1992), a significant source of natural hazard, and a constraint for human activities and safe land use in cliffed coastal areas (e.g. Moore and Griggs, 2002)
The statistical methods used in this study include the bivariate information value method (Yin and Yan, 1988) and the multivariate logistic regression method (Cox, 1958, Hosmer and Lemeshow, 2000), applied to a set of predisposing factors mainly related to geology and geomorphology, which were correlated with an inventory of past cliff failures
We only considered 119 cliff failures or groups of failures which occurred in the same place and could not be separated due to the wide time gap between aerial photograph surveys, which causes an inevitable degree of data amalgamation (Dong and Guzzetti, 2005)
Summary
Slope mass movements, which include rockfalls, toppling and different types of landslides, are the dominant and more visible process of sea cliff retreat (Trenhaile, 1987; Sunamura, 1992), a significant source of natural hazard, and a constraint for human activities and safe land use in cliffed coastal areas (e.g. Moore and Griggs, 2002). For landslides in non-coastal areas, a complete hazard assessment includes the space, time (Varnes, 1984) and magnitude components (Guzzetti et al, 2005), with the first, designated as susceptibility, being usually the less difficult to deal with and the one which is more frequently assessed Transposing this concept to sea cliffs results that, the susceptibility of the occurrence of cliff failures corresponds to the propensity of a given area for being affected by these phenomena, based solely on terrain conditions (Soeters and Van Westen, 1996), without any implication of the time component, i.e. time frequency or recurrence periods. The results obtained are compared with the inventory data using standard success rate curves and receiver operating characteristic curves (ROC), which enable an objective assessment of the adequacy of the susceptibility models computed
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