1. Using the Working Classification of Landslides to Assess the Danger from a Natural Slope

A pre-requisite for any calculation of the stability of a natural slope is a hypothesis about how the slope may move. No formal method for estimating likely kinematic modes of slopes exists. We have suggested a working hypothesis that similar landslides in similar materials are caused by similar processes under similar conditions. During the IDNDR (1990–2000), the IAEG Commission on Landslides contributed to the Working Classification of Landslides which now records an international consensus . A landslide can be typed by a term describing the natural materials before they were displaced and a second term describing the movement. Materials are rock, debris or earth; earth may be sand, silt or clay. Movements may be falls, flows, slides, spreads or topples. Water conditions in the displaced material may range from dry thru’ moist and wet to very wet. In permafrost terrain, frozen and thawed displaced material may occur. Water conditions, material and mode of movement may govern the rate of movement of the displacing mass. It can range from extremely slow to the extremely rapid movements, which may have catastrophic impacts. Activity, its distribution and style may affect anticipated modes of movement in preparatory or marginal slopes. Styles of movement may be complex, composite, successive and multiple. Compilations of historic activity as landslide inventories suggest hazard scenarios which can form plausible initial hypotheses for risk assessments.