Geological and Geotechnical Hazards in South East England: Part 2 Solution Features in Chalk
This is the 2nd part of a talk on Geological and Geotechnical Hazards in South East of England to the South East Regional Group of the Geological Society in January by our former director Roger Smith.
Solution features (or dissolution features) occur where surface water runoff, which is slightly acidic, has discharged into and dissolved the underlying chalk (calcium carbonate). Following this the dissolved zone becomes infilled with loose soils which, if inundated, will subside.
Areas of high risk were often near where there is a cover of clay strata such as the Lambeth Group (formerly called Woolwich and Reading Beds), Clay with Flints and Glacial Deposits. A map was shown which indicated the areas where solution feature risks may be anticipated. These included most areas where Chalk outcropped with particularly high risk areas in North Kent, Sussex, Hampshire, Dorset, Buckinghamshire, Hertfordshire and East Anglia. The area of Welwyn Garden City was of particular high risk.
In some areas quite large solution features are shown on the 1:10000 scale geological maps, for example near Chichester in Sussex and in the Cowplain area in Hampshire, north of Portsmouth.