Abstract
Deep-seated landslides pose a dilemma for land managers who must utilize certain natural resources while protecting others from adverse environmental impacts. The physical factors controlling deep-seated mass movement are often poorly constrained, and the consequences of a particular land use may therefore be unknown. Empirical techniques work well for mapping areas affected by deep-seated landsliding, but may be incapable of predicting the impacts of land use on specific landslides. Numerical models of the physical processes of mass movement offer an alternative method for determining landslide potential and provide additional information for evaluating hazards where empirical evidence is insufficient or ambiguous. Modeling efforts can utilize topographic and geotechnical data mapped at regional scales (typically 1:24,000) if the physical controls on landsliding are resolved. A strategy for coupling the data processing capabilities of geographic information systems (GIS) software with the predictive power of a physical model is demonstrated with a small basin in northwestern Washington state, managed for timber production, where deep-seated landsliding has degraded an important fisheries resource. Historic data were insufficient to clearly identify the primary factors controlling landslide activity. Modelling results, however, indicate that certain deep-seated landslides react primarily to increases in pore-water pressure, while others react primarily to stream-channel incision. These results guide further field efforts and provide a rational basis for land-use decisions.
