A sapping erosion susceptibility model for the southern Cantabrian Range, North Spain S. Fernández ⁎ , J. Marquínez, R. Menéndez-Duarte Institute of Natural Resources (INDUROT), University of Oviedo, Mieres Campus, 33006 Mieres, Spain Received 12 September 2006; received in revised form 17 May 2007; accepted 22 May 2007 Available online 8 June 2007 Abstract 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 km 2 . 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. © 2007 Elsevier B.V. All rights reserved. Keywords: Sapping erosion; Gully processes; Land use changes; Multivariate susceptibility models; Mahalanobis distances 1. Introduction A vast part of the northern boundary of the Duero Tertiary Basin, located in the northwest of the Iberian Peninsula, has been undergoing soil erosion processes under semi-arid climatic conditions. These processes are caused mainly by overland flow on hillslopes without dense and continuous vegetation cover (Poesen and Hooke, 1997; Oostwoud Wijdenes et al., 2000; Vande- kerckhove et al., 2000; Kirkby and Bull, 2000). In many cases the lack of continuous vegetation cover is related to the historical management of the territory. The use of fire to remove the forest cover or the transformation of large forested areas into farm land in marginal territories with a self-supplying economy, were common practices until recent years. Most of these farm lands have rapidly been abandoned in recent times. This phenomenon of land abandonment and its relationship to the development of gully erosion has been widely documented in other parts of the Iberian Peninsula with similar environmental conditions (Ruiz-Flaño et al., 1991; García Ruiz et al., 1997; Casalí et al., 1999). The development of gullies in the Duero Basin could result from laminar and concentrated overland flow. At Available online at www.sciencedirect.com Geomorphology 95 (2008) 145 – 157 www.elsevier.com/locate/geomorph ⁎ Corresponding author. Fax: +34 9854458110. E-mail address: smdez@indurot.uniovi.es (S. Fernández). 0169-555X/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.geomorph.2007.05.013