Introduction
The landscape and scenery around the village of Malham in the Yorkshire Dales is one of the most interesting in the UK. The limestone geology of the area and millions of years of earth movements and erosion have been responsible for producing towering cliffs, deep gorges, impressive valleys, beautiful waterfalls and unusual limestone pavement. This spectacular scenery attracts over a million visitors a year.
The geology of the Malham area
The limestone bedrock of the Malham area is responsible for the unique landforms. The geology of any area is a very important factor determining what the landscape looks like.
The limestone of the Malham area is Carboniferous limestone formed during the Carboniferous Period approximately 350-250 million years ago. Limestone is a sedimentary rock formed the shells and skeletons of sea creatures deposited on the bed of a warm tropical sea. Over millions of years layers of these CaCO3 rich shells form sediments that build up, become compressed under the weight and fossilised to form hard, grey limestone rock. The limestone now found around Malham was actually formed under tropical seas near the Equator. Following its formation the drift of the continents and oceans around the globe transported the limestone to its current position.
The CaCO3 that limestone is composed of and the way that it has formed controls the way that it erodes and the landforms that are created. The layers in limestone are separated by horizontal weaknesses called bedding planes and these are split by vertical cracks called joints that formed when the limestone dried. Water can flow down and along these weaknesses and this results in erosion along them. Limestone is a very hard rock but it is readily dissolved by weak acids in water by a process called carbonation or solution.
CaCO3 + H2O + CO2 = Ca(HCO3)2
Calcium carbonate + Water + Carbon dioxide = Calcium bicarbonate
Rainwater combines with carbon dioxide in the atmosphere to form the weak acid, carbonic acid, and this converts the calcium carbonate in the limestone to calcium bicarbonate which is washed away down faults and bedding planes.
Malham Cove
Malham Cove is a huge 80 metre high amphitheatre shaped limestone cliff to the North of Malham village. It towers over the surrounding landscape above a wide flat valley. The Cove as we see it today is the product of a great number of natural processes that have acted over many thousands of years.
Photograph - Malham Cove
Earth movements millions of years ago caused the land below Malham Cove to drop down by around 100 metres along a vertical crack in the rock called the Mid Craven Fault. This produced a massive vertical cliff about 600 m down the valley from The Cove’s current position. Since this time The Cove has been shaped by natural processes into the characteristic semi-circular shape and eroded backward to it’s current position.
During the melting of the many ice ages in the last 2 million years Malham Cove would have been a huge and impressive waterfall. Vast quantities of melt water from the melting ice sheets and glaciers would have poured over the cliff. This water eroded the cliff backwards until today it lies 600m from it’s original position. The rounded face of The Cove is due to the centre of the cliff being eroded most as the water flowed over and down it.
At the base of Malham Cove a stream, Malham Beck, emerges from underground to flow down the valley toward Malham village. This stream disappeared underground several miles behind and above The Cove to flow through a system of caves and passages along bedding planes and faults in the limestone. The point where the stream flows out from under the ground is called the resurgence.
Photograph - The resurgence at the base of Malham Cove
The Limestone Pavement
Limestone pavement is the name given to a large flat area of bare limestone. The surface of the pavement is divided into blocks, called clints, separated by vertical cracks, called grikes. The best example of limestone pavement is up on top of Malham Cove.
Limestone pavement forms because limestone is dissolved down the vertical joints by the process of carbonation. The widened joints become grikes and the blocks in between the clints. The process of carbonation is much more effective when the limestone is covered by soil because the soil keeps the water in contact with the limestone for longer and so more erosion occurs. The limestone pavement on the top of Malham Cove used to be covered by soil and vegetation but this was stripped away by ice flowing over the area during the last ice age.
The surface of limestone pavement has some very interesting features. Many clints, blocks of rock, have round holes on their surface formed by little puddles of water dissolving little depressions, these are called rund karren. Other clints have shallow channels eroded on their surfaces by running water flowing over them, these are called rillen karren. In the grikes, some of which can be several metres deep, rare plants that like shady, damp conditions such as ferns grow.
The surface of the limestone pavement will continue to be weathered by carbonation in future but this process is very slow indeed. The actions of humans are perhaps a greater threat to these interesting landforms. The surface of the limestone pavement at Malham is already shiny and polished by the feet of millions of visitors and large areas of some limestone pavements have been destroyed by people to use the stone for garden rockeries or for buildings.
Watlowes Dry Valley
Watlowes dry valley is an impressive u-shaped valley that runs north-south from the top of Malham Cove. Dry valleys, valleys without rivers in them, are common in limestone areas as rivers disappear below ground to flow through underground caves and passages eroded along faults and bedding planes.
Gordale Scar
Gordale Scar is a very impressive 1 kilometre long, vertical sided gorge with 70-80 metre high cliffs. A very small stream Gordale Beck flows through the gorge but it is obvious that a stream of this size could not possibly be responsible eroding this massive gorge. A stream did erode the limestone to form the gorge but it must have been a much larger and vastly more powerful one than the one flowing today.
Photograph - Gordale Scar
The second and favoured theory is that at the end of the last Ice Age, which was at it’s maximum around 25,000 years ago, a huge melt water river flowed along the route of the present gorge. As the limestone was frozen the river flowed over the surface and eroded out the gorge that we see today. The tiny river flowing through the gorge today is called a misfit stream because it obviously could not have formed the valley that it flows through.
Photograph - The small waterfall and stream now found in Gordale Scar.
