Valley bulge folding at Rowlee Bridge, Ashop Valley, Derbyshire

The folds are superficial valley-bulge structures in the weak Namurian shales and do not extend more than a few metres into the subsurface. They have formed as a result of the differential loading of the valley sides and valley bottom - the weak valley floor sort of squidges up. This originates mainly from melting of permafrost conditions at the end of the last glacial period around 11,500 years ago.

Continuing movement of the valley sides causes the landslides which periodically disrupt the A57 Snake Pass road nearby on the north flank of the valley.