High Force

The River Tees has been plunging into this gorge for thousands of years. The river drops 21 metres over hard whin sill rock into a plunge pool. The hard rock of the whin sill forms a resistant lip over which the river plunges, where it comes into contact with softer sandstone material at the base of the gorge. Over thousands of years the force of the water erodes away the sandstone, undercutting the hard material at the surface. Overtime, blocks of whin sill rock break off and the process starts again. This continuous process means that the waterfall is gradually retreating upstream.