The mapping of regolith is a very important technique necessary for many soil uses and planning applications. However, the scarcity of outcrops usually hampers the mapping by direct field or photo-interpretation surveys, and the mapping must be supported by topographic and geomorphologic interpretations. In order to quantify the topographic variation and to analyse the statistic relationships between topographic variables and regolith thickness we have develop a technique that uses Digital Terrain Models (DTM). This technique allows the analysis and implementation of a spatial distribution model of regolith thickness, based on construction of automatic maps.

In order to test and validate this methodology we have applied it to a geological and geomorphologic homogeneous area of the N-Iberian coast, near the village of Villaviciosa (Asturias). The lithologies of the substratum are mostly marls and sandstones of Jurassic age and the relief is characterized by gentle slopes modeled on an elevated old submarine erosion surface. In this area, the humid and temperate climatic conditions have produced a dense and continuous vegetation cover. In this conditions, the thickness of the regolith is mostly related to accumulations by soil creep in the zones of gentler dip and in the lower parts of the slopes.

The statistic analysis based on slope values, elevations, sun radiation, cumulative flow and concavity values, using 60 sample points, indicates a probability for the presence of more than 0.25 m thick regolith. The obtained regolith distribution model was validated using 84 new sample points and its accuracy was compared with other regolith thickness map obtained by traditional field survey and photo-interpretation. The methodology developed provides a competitive way to obtain reliable information about regolith thickness and its spatial distribution, that is an important information in geographical data bases for environmental and planning purposes.