At intermediate level you will also be expected to be able to describe and explain, in detail, how the following features of upland limestone landscapes are formed:
You will be expected to include a labelled diagram(s) in your answer.
During periods of glaciation, glacial abrasion has scraped away the topsoil to expose the bare rock underneath. Limestone is a sedimentary rock that is made up of horizontal cracks called bedding planes and vertical cracks called joints. Limestone is made of Calcium Carbonate which is dissolved by rainfall which is a weak acid. This process is called chemical weathering. As a result of these features water is able to seep down through the cracks and into the rock making it seem to disappear. Therefore limestone is said to be a permeable rock.
A limestone pavement is formed when rain water seeps through the joints and dissolves the limestone on each side making the joint wider. This separates the surface into large cracks separated by flat blocks so that it looks much like the keys on a computer keyboard e.g. Malham Moor. The cracks are called grykes and the blocks are called clints.
Top tip: To remember the difference between a clint and a gryke if you fell into a gryke you would say 'Oh Grykie!'
Where there are streams flowing across an area of impermeable rock and eventually flow across an area of limestone they can dissolve a much larger area of limestone due to the volume of water in the stream. Joints can be enlarged so much that a hole develops through which the stream flows underground e.g. Gaping Gill where the stream looks as if it disappears. This is called a swallow hole and the stream is known as a disappearing stream.
Water which flows underground through a swallow hole, continues its journey along bedding planes and down joints until it reaches impermeable rock, usually clay. A cavern forms where there are many joints and bedding planes close together so that large areas of rock in the same space dissolve quickly. This leaves a large space underground which is called a cavern.
As water flows underground it is still dissolving the limestone around it. This dissolved limestone is carried away by the water in solution. Limestone is made of calcium carbonate so this is what is dissolved and carried in the solution.
Water will drip from the roofs of caverns very slowly and will therefore evaporate. As it does so solid calcium carbonate is deposited on the cavern roof. This will build up over time to form long, thin deposits which grow downwards and look like icicles, due to the drip tip. They hang from the cavern ceiling and are called stalactites, this can be remembered as 'hanging tights'.
Some of the drips of water will not evaporate but will instead fall to the floor of the cavern where it splashes and evaporates. This means that there will be a build up of calcium carbonate on the floor of the cavern. As more and more calcium carbonate builds up on the floor, short, wide, dumpy features grow upwards. These are called stalagmites.
Occasionally stalagmites and stalactites grow towards one another and join to form a pillar.
As the processes of dissolving limestone and cavern formation continue over time then caverns get larger and larger. Eventually there will be less rock supporting the roof of the cavern and it will collapse. This forms a very steep-sided valley called a gorge.
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