These formations are found where rainwater flowing through lime-bearing deposits dissolves calcium carbonate. Carbon dioxide is lost from the water into the air, and calcium carbonate is deposited as tufa near water sources such as springs, or as speleothems in caves. These conditions usually occur in areas underlain by thick limestone, but Cornwall is so poor in lime-rich rocks, that limestone was imported from the 18th century onwards.
Tufa is a white to straw-coloured deposit formed on cliffs open to the atmosphere. While it is forming it is soft, spongy and has been largely ignored as ‘yucky’. As it gets older it hardens and becomes a rock. On cliffs it is commonly associated with green, filamentous algae close to sea-level, but higher up mosses take over. The plant material, as it decays, provides a framework for further carbonate deposition, leading to a naturally porous fabric. There are also higher plants characteristic of tufa deposits: the calcium-loving maidenhair fern for example.
The flowstone, stalactites and stalagmites of speleothems, are far more spectacular. The best example in Cornwall is the often photographed cave at Holywell Bay, but other examples have been coming to light in many places.
Where the calcium carbonate comes from is still a mystery. On the north Cornwall coast the beaches and dunes are known to have an abnormally high calcareous content due to all the shell fragments. However, it is becomingly increasingly clear that there must be other sources and that inland occurrences of tufa and speleothems in stream beds and on quarry faces, railway cuttings and mine shafts and adits need to be mapped to help solve the mystery.
The current map of tufa and speleothems in Cornwall did not exist two years ago and has only been made possible by reports from interested individuals. Members of Cornwall Wildlife Trust are in an ideal position to help with this research and plug the holes in our coverage/knowledge in inland Cornwall and along the coast north of Padstow and east of Fowey. You can tell us about your tufa sightings using our online form. You will need to tell us the name of the place you saw the tufa and a six figure grid reference. A brief description and digital photos would also be useful if you have them.
