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Geography

Rural land resources

Limestone pavements and swallow holes

The Pennines is the backbone of Northern England, running from Northumberland in the north to Derbyshire in the south. It's also one of the areas in the United Kingdom where upland limestone scenery is found. In the North Pennines this type of scenery is found in the Yorkshire Dales, and in the South Pennines the Peak District is well known. Both these areas are National Parks because of their beautiful scenery, range of wildlife and local history. The examples we're using in this bite are from the Yorkshire Dales National Park.

If carboniferous limestone is capped by impermeable rock, surface streams can run on to limestone. However, this water disappears from the surface, either by seeping through joints in the limestone or as streams disappearing down through swallow holes. It is the action of water which is responsible for many of the distinctive features of upland limestone scenery.

When you study upland limestone scenery remember you should describe and explain both surface and underground features. Surface features include limestone pavements, dry valleys, gorges and scars. Underground features include caverns, potholes, stalactites and stalagmites.

Limestone pavement

Limestone pavement, near Malham

Carboniferous limestone is made of blocks of rock. The clear horizontal lines are called planes and the vertical cracks are called joints. The rock is permeable which means water can pass through the lines of weakness - the bedding planes and joints.

Rainwater is a weak carbonic acid which reacts with the limestone as it passes through the rock. It dissolves the stone, enlarging joints and bedding planes. On the surface the chemical weathering widens and deepens cracks to form grykes. This leaves exposed blocks of limestone called clints and the resulting pattern of blocky rock is called a limestone pavement.

Clints and grykes

Chemical weathering of limestone pavement

The chemical weathering is shown by the formula:

CaCO3 + H2CO3→Ca(HCO3)2

(limestone + carbonic acid →calcium hydrogen carbonate solution)

Shakeholes and potholes

Occasionally, hollows are created on the surface of limestone. They form where drift material falls into joints which have been enlarged and widened by chemical solution. The hollows are called dolines or shakeholes.

The shakehole is then eroded by streams and a vertical hole known as a pothole or swallow hole is formed. These holes can, in turn, be enlarged by heavy rainfall or glacial meltwater. Gaping Gill, in the Yorkshire Dales, is an example of an enlarged swallow hole.

Watch

Limestone scenery in the Yorkshire Dales.

Class Clips

How the weathering of limestone rock has shaped areas of the Yorkshire Dales

Watch the following clips for more on upland limestone:

Chemical weathering by solution in upland limestone scenery

Upland limestone drainage feature

Audio

Human use of glaciated areas

Try something different - download this Audio Bite (mp3). You can also download the transcript too (pdf, 32.4 kB).

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