BGS Geohazard 5km Hex Grids (GeoSure)

These datasets provide a generalised overview of the susceptibility to six naturally occurring geohazards in Great Britain. The hexagon grid provides a national-scale summary of the GeoSure data product. The detailed dataset (see https://www.bgs.ac.uk/products/geosure/home.html) is also available to licence and provides further detail (see examples below) at a scale of 1:50 000. The data has been generalised into a vector map of interlocking hexagon cells (a side length of 5km), with an area approximately 65km2. There are 3 classes included within the data, as described in the tables below. The six layers of data provided are as follows: Landslides (slope stability) Slope instability occurs when particular slope characteristics (such as geology, gradient, sources of water, drainage, or the actions of people) combine to make the slope unstable. Downslope movement of materials, such as a landslide or rockfall may cause damage, such as a loss of support to foundations or services or, in rare cases, impact damage to buildings. Shrink Swell potential Swelling clays can change volume due to variation in moisture, this can cause ground movement, particularly in the upper two metres of the ground that may affect many foundations. Ground moisture variations may be related to a number of factors, including weather variations, vegetation effects (particularly growth or removal of trees) and the activities of people. Such changes can affect building foundations, pipes or services. Soluble rocks (dissolution) Ground dissolution occurs when certain types of rocks, containing layers of soluble material, get wet and the soluble material dissolves. This can cause underground cavities to develop. These cavities reduce support to the ground above and can lead to a collapse of overlying rocks. Compressible ground Some types of ground, may contain layers of very soft materials like peat or some clays. These may compress if loaded by overlying structures, or if the groundwater level changes. This compression may result in depression of the ground surface, potentially disturbing foundations and services. Collapsible deposits Some kinds of rocks and soils may collapse when a load (such as a building or road traffic) is placed on them, especially when they become saturated. Such collapse may cause damage to overlying property or services. Running sand Some rocks can contain loosely packed sandy layers that can become fluidised by water flowing through them. Such sands can ‘run’, potentially removing support from overlying buildings and causing damage. Limitations * Data has been generalised to 5km2 hexagon grid, it must not therefore be used at larger scales (i.e. not to be used with higher resolution maps, or data). * Summarising via spatial statistics may lead to under or over estimation of the extent of a hazard. For example the highlighted cell in the Ripon area (shown below) has a narrow but continuous area of soluble rocks which are classed as a high hazard susceptibility, however because of generalisation, this detail is not evident. In these cases we have included a field ‘Advisory’ which indicates where areas of significant rating occur, but are not large enough to code the hex grid at this scale. *  Conversion to a hexagon grid generalises the data altering perception of the spatial distribution. Results of any analysis and subsequent interpretation should be viewed with care. * Comparison with the underlying source data will reveal variations due to the generalisation process applied. * GeoSure is concerned with potential ground stability relating to NATURAL geological conditions only. GeoSure does not include man made hazards such as contaminated land or mining. The only exception is the compressible ground layer which does consider man-made ground e.g. landfill. * GeoSure is based on, and limited to an interpretation of the records in the possession of British Geological Survey at the time the dataset was created. * An indication of natural ground instability does not necessarily mean that a location will be affected by ground movement or subsidence. Such an assessment can only be made by inspection of the area by a qualified professional.