On August 13th, 2016 I visited the “High Force” Waterfall, in England.

     “High Force” is a waterfall on the River Tees, near Middleton-in-Teesdale, Teesdale, County Durham, England. The waterfall is within the North Pennines Area of Outstanding Natural Beauty and European Geopark. The whole of the River Tees plunges 21 m over a precipice.

     “High Force” was formed where the River Tees crosses the Whin Sill – a hard layer of igneous rock. It cascades over a fault in the basalt intrusion and thunders down a 21 m drop to the pool below.  The waterfall itself consists of three different types of rock. The upper band is made up of whinstone, 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 meters. The bed-load is mainly composed of large boulders, which are rolled along the river bed.

     “High Force” is a great place to see the famous Whin Sill. This is a layer of a hard, dark rock called dolerite, known locally as ‘whinstone’. The Whin Sill formed about 295 million years ago, when molten rock at over 1000°C rose up from within the Earth and spread out between layers of limestone, sandstone and shale. The molten rock cooled and solidified underground to form a flat sheet of rock, known as a ‘sill’. After million of years of erosion the Whin Sill is now exposed at the Earth’s surface, forming dramatic landscape features such as “High Force”.  “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’.