Date and Time
Bath Royal Literary and Scientific Institution, 16-18 Queen Square, Bath BA1 2HN
Gypsum (hydrated Calcium Sulphate CaSO4.2H2O, the raw material for plaster) is widespread throughout the world, but it dissolves so rapidly that it poses a threat to any development that encounters it. More than one metre of gypsum per annum can be easily dissolved by moderate river action on natural exposures. Where this dissolution occurs underground at similar rates, caves can develop, expand rapidly and suddenly collapse. Such caves occur in the Permian rocks of the Vale of Eden, Cumbria and beneath Ripon, North Yorkshire.
Under suitable groundwater flow conditions caves in gypsum can enlarge at a rapid rate resulting in large chambers. Collapse of these chambers produces breccia pipes which propagate through the overlying strata to break through at the surface and form subsidence hollows. Subsidence problems at Ripon (UK) are due to this phenomenon and periodically affect local properties. By this mechanism holes, commonly up to 20m deep and 40m or more across, continue to appear suddenly in gypsiferous terranes throughout the world.
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