Assessment of landslide risks requires an understanding of how future landslide behaviour (the hazard) could have an adverse impact on people, property and the environment (the consequences). However, what will happen in the future cannot be known precisely and often cannot be predicted with confidence. This ‘radical uncertainty’ results from incomplete knowledge about slope systems and their response to energy inputs (e.g. waves, rainfall, earthquakes). Probability is a measure of uncertainty. However, estimating landslide probability should not rely on ‘geology-free’ statistical models. The geology does matter. It will be necessary to make judgements based on an understanding of slope conditions and behaviour as well as historical data. This paper examines the way in which geomorphology and an understanding of slope behaviour are critical to landslide risk assessment in the presence of radical uncertainty. The focus is on predictions of landslide probability made for economic risk assessments on the UK's Yorkshire coast. This coast is associated with rapid cliff recession rates (e.g. the Holderness coast) and major landslide events (e.g. the Holbeck Hall landslide, Scarborough). However, the central messages of this paper can apply to landslide risk studies everywhere, both at the coast and inland.

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