Landslides occur ultimately due to the effect of gravity, although other factors such as geology, topography, weathering, drainage and man-made construction can all contribute to the overall stability of a slope.
Landslides are commonly divided into four categories: falls, topples, slides or flows.
Landslides rarely comprise a single type of movement but are often the result of a combination of several types.
Whilst the BGS currently has over 16 500 landslides in its National landslide Database many of these are ancient and occurred under different climatic conditions to those of the present day (e.g. Pleistocene). If left undisturbed these ancient mass movement deposits may remain stable for many years, however poorly planned development can sometimes reactivate these ancient slides.
Downslope movement of materials through landsliding may damage buildings or infrastructure through loss of support or due to direct impact.
Common causes of damage due to landslide relate to:
The potential for landsliding (slope instability) to be a hazard has been assessed using 1:50 000 scale digital maps of superficial and bedrock deposits. These have been combined with information from the BGS National Landslide Database and scientific and engineering reports.
The detailed digital data illustrated in the map are available as attributed vector polygons, as raster grids and in spreadsheet format.
The BGS currently has three datasets providing information on landslides in Great Britain. These products differ in both their collection method and also their intended use.
The BGS National Landslide Database currently documents over 16 500 landslides across Great Britain. The database was an inherited dataset, based on a search of secondary sources conducted for the Department of the Environment (DoE) in the 1980s and 1990s.
Since the foundation of the DoE data set BGS has continued to populate this database using the National Digital Geological Map (DiGMap). Other data has also been collected through media reports, site investigations reports, journal articles and by new mapping.
Data is stored within a fully relational Oracle database, which can be accessed through Microsoft Access ™ or an ESRI ® ArcGIS interface. The purpose of this database is to provide a detailed record of landslide events across Great Britain. The database contains over 35 fields which can be attributed with information on the type of landslide, age and causes.
The DiGMap mass movement layer displays mapped landslides that have been recorded by field geologists. The mass movement layer does not distinguish between different types of failures; it is purely an outline of the landslide deposit.
BGS GeoSure is a national dataset that assesses the potential for ground movement and subsidence across Great Britain. It contains six layers, one of which is for slope instability (landslides).
The slope instability layer defines the susceptibility of an area to undergo landsliding. Unlike DiGMap it does not show where a landslide has already occurred, but where it may occur in the future, due to favourable conditions.
BGS GeoSure takes into account the local geology and slope of an area along with the geotechnical and structural characteristics of a geological formation. These conditioning factors are combined within a GIS and result is a susceptibility map of the UK. The BGS GeoSure assessment does not show risk or seek to determine the temporal distribution of landsliding.