A sapping erosion susceptibility model for the southern Cantabrian Range, North Spain

A susceptibility model of sapping-related depressions has been produced by analysing the statistical relationship between the location of depressions and topographical variables. Sapping erosion plays an important role in the growth of gullies developed over poorly-consolidated quartzite conglomerates in the northern sector of the Duero Tertiary Basin (the Cantabrian Mountain Range of Spain). Gullies, topsoil subsidence depressions related to sapping processes, and shallow slides have been identified over sandy soils in an area of 37 km². This area underwent major changes in land use during the 20th century, leading to the expansion of gully erosion processes. On the surface, depressions of several meters in diameter, caused by internal erosion related to sapping processes, can be identified. Using the topographical location of these topsoil depressions and several topographical variables, 14 discriminate functions were derived to provide information about the influence of topography on the development of sapping erosion processes. The functions have accuracy levels varying from 56 to 81%. The most accurate function was regionalized by means of a Geographical Information System and was used to complete a land classification method which is based on the Mahalanobis distance to the multivariate average (centroid) of a sapping erosion form group. The classification of this model allows the identification of areas with different relative probabilities of sapping processes and the resultant growth of gullies.