Distribution, causes and nature of natural landslides in Devon and Cornwall

Abstract

Between 1985 and 1990 a computerised database was assembled that contains information concerning the distribution and nature of 9000 landslides in Great Britain. The South West accounts for 1,700 of the listed slope failures. Problems have arisen because in many areas the database merely serves as an archive of previous studies and is not a true representation of landsliding in an area. The aim of this research was to identify landslide environments correlated with landslide frequency and character and through this develop a landslide susceptibility map. Analyses were undertaken so that distinct inland and coastal landslide environments could be defined. These landslide environments characterised the likely extent and type of landslides that would occur in each land system. In order to compile data over such a large region a land systems approach was taken to characterise areas where the geological and geomorphological conditions were similar. The methods used for primary data collection were aerial photograph interpretation, airborne thematic mapper data, terrain evaluation and limited field mapping for ground truthing purposes. This landslide susceptibility map used probability to assess the relative importance of parameters important to slope stability. The landslide susceptibility map, along with the landslide environments, highlighted areas were landsliding was more prevalent as well as identifying areas where landsliding is less likely to occur. Two landslide environments were identified as being particularly susceptible to landsliding, and this was primarily related to geological conditions. It was found that within environments changes in topography also acted as a strong control on the nature and extent of landsliding. It is anticipated that the method used for assessing landslide susceptibility could have widespread application in all GIS based landslide studies and can be used to develop the potential of the complete UK landslide database, once the rest of the original data have been updated.