Janet's Foss. The name "Foss" has its origins in Scandinavia where it is comparable with "Force". A cave behind the waterfall exists because considerable tufa deposits have been built over the rock face by a process similar to the one that builds stalactites and stalgmites. Gordale Beck contains a great deal of dissolved carbonate - the source material for tufa formation.
On the east side of the beck is a small cave which was once thought to have been inhabited by miners from Pikedaw.
Limestone is made of almost soluble calcium carbonate. It’s solubility is greatly increased by the presence of carbon dioxide (as found in rain water). The interaction of rain water and limestone leads to the formation of soluble calcium bicarbonate. When the carbon dioxide is later released from solution, (typically in flowing water and spray over a waterfall) the carbonate is reformed and deposited as tufa. Below is the chemical reaction that takes place during tufa formation.