Extent of permafrost in southern Britain in relation to geothermal flux

Abstract

Introduction The scarcity of relic permafrost features in southwest England, except on the high ground of Dartmoor, was noted by Williams (1965, 1969). Following Manley (1951, 1953) he concluded that this was due primarily to a moderation of the Pleistocene climate by invasions of milder Atlantic air. Subsequent work through the CLIMAP project ( McIntyre et al 1976 ), however, suggests that at 18000 years BP, the North Atlantic polar front was at about the latitude of Portugal. Comparison of Williams' map of the areal extent of permafrost in southern Britain with the detailed heat flow map of the UK ( Wheildon & Rollin 1986 ) indicates that regions where evidence of former permafrost is largely absent tend to coincide with areas of high heat flow. The technical note discusses possible relationships between heat flow and permafrost phenomena in southern England as it is clearly important that engineers making site assessments are aware of the likely causes and extent of the disturbance associated with former frozen ground. Extent and depth of former permafrost in southern Britain Figure la is a reproduction of Williams' (1969) map which was based on the deeper periglacial features, particularly ice-wedge casts. It shows that there are far fewer permafrost features in the southwest than in most of Britain. Since then more ice-wedge casts have been found in southwest England, but it is nevertheless generally accepted that in this area the frequency and depth of these is significantly less than