Recent growth and decay of the hydration (swelling) caves in the former gypsum quarry of Dingwall in Cape Breton, Nova Scotia, Canada

The article deals with the very special phenomenon of formation of the hydration or swelling caves (Quellungshöhlen in German), known also as the bubble or dwarf caves (Zwergenhöhlen in German), observed today in the weathering zone of the Lower Carboniferous anhydrites of the Windsor Group in the Canadian Maritimes. The caves form due to volume increase during transition of anhydrite into secondary gypsum, i.e. hydration of anhydrite. Hundreds of such hydration caves have developed – and collapsed – in the abandoned gypsum quarry of Dingwall, a fishing village at the north eastern tip of the Cape Breton Island, Nova Scotia. The largest one is ca. 10.7 × 6.6 ×1.1 m in size (as documented in 2008). The speed of lateral growth of the hydrating anhydrite layers, which are now the floors of the quarry abandoned in 1956, has been systematically measured and estimated at ca. 2 cm/year, similar to the values recorded in Europe, in the similar caves from the Harz Mts. region in Germany. It seems that the salty sea spray of the nearby Atlantic Ocean accelerates the hydration of anhydrite.