High Force is a waterfall on the River Tees, near Middleton-in-Teesdale, County Durham, England. The waterfall is within the North Pennines Area of Outstanding Natural Beauty (AONB) and European Geopark.
Despite popular belief that it is the highest waterfall in England, at 71 feet (22 m), others have a longer fall: Cautley Spout, in Cumbria's Howgill Fells, is almost 590 feet (180 m) high, and Hardraw Force, in North Yorkshire, has an unbroken drop of 98 feet (30 m); whilst underground, on the flanks of Ingleborough, Fell Beck falls an unbroken 315 feet (96 m) down the Jib Tunnel of Gaping Gill Hole. However, High Force does have the largest volume of water falling over an unbroken drop when in full spate, thereby earning its Nordic name 'High Fosse'.
The whole of the River Tees plunges over a precipice (cliff edge which is almost vertical) in two stages. In former times flooding created two separate falls, but after the completion of Cow Green Reservoir in the upper Teesdale this seldom happens now except after a very heavy, continuous rainfall. In harsh winters the falls would freeze, creating cathedral-like ice formations.
Access to the northern bank is via a private footpath for which a fee is charged. The southern bank can be reached free-of-charge via a public footpath.
High Force was formed where the River Tees crosses the Whin Sill – a hard layer of igneous rock (also seen at Hadrian's Wall and other locations). The waterfall itself consists of three different types of rock. The upper band is made up of whinstone, or dolerite, a hard igneous rock which the waterfall takes a lot of time to erode. The lower section is made up of Carboniferous Limestone, a softer rock which is more easily worn away by the waterfall. Between these two layers is a thinner layer of Carboniferous sandstone, which was baked hard when the Whin Sill was molten 295 million years ago. The wearing away of rock means that the waterfall is slowly moving upstream, leaving a narrow, deep gorge in front of it. The length of the gorge is currently about 700 metres. The bedload (rocks that the river is carrying) is mainly composed of large boulders, which are rolled along the river bed. Upstream of the waterfall, the river is narrow; downstream, it widens and meanders.
Stock footage of the waterfalls was featured in the movie Mackenna's Gold. Although the story of the film is supposed to occur in the American Southwest, the scene depicting the Apaches chasing the gold hunters through the forest and the river was filmed in Oregon, USA. The subsequent scene of the waterfalls was a stock footage of High Force.