High Force Waterfall on the River Tees
High Force is a spectacular waterfall on the River Tees in the County on Durham. High Force was formed where the River Tees crosses the Whin Sill – a hard layer of rock. The waterfall itself consists of two different types of rock. The upper band is made up of whinstone, a hard rock which the waterfall takes a lot of time to erode. Underlying the whin sill is a layer of of Carboniferous Limestone, a softer rock which is easily worn away by the waterfall. This creates a plunge pool beneath the waterfall. As the limestone is eroded the whin sill is left over hanging the waterfall. Eventually the overhang collapses.
If you are in the area it is also worth visiting Low Force.
You can find out more about High Force on Internet Geography.