Craven Fault System

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The Craven Fault System is a group of large cracks in the Earth's crust in the Pennines. They form the southern edge of the Askrigg Block and partly border the Craven Basin. You can see evidence of these faults on the surface as scarps where Carboniferous Limestone meets harder rocks like millstone grit, especially at Malham Cove, Gordale Scar, and Giggleswick Scar.

The fault system runs along the southwestern edge of the Yorkshire Dales National Park and the northeastern edge of the Bowland Fells. It stretches across England from Leck in Lancashire and then branches in three main directions, forming the Craven Gap (also called the Aire Gap). The Aire Fault continues from the south end of the South Craven Fault, from Gargrave toward Leeds, and is more clearly traced by the River Aire. The Aire Gap separates the Yorkshire Dales from the Bowland Fells and the millstone-grit plateaus of the South Pennines.

The Craven Fault System includes the North Craven Fault, Middle Craven Fault, South Craven Fault, and Feizor Fault, along with several unnamed faults. The Middle Craven Fault moved mainly during the Carboniferous period and marks the southern limit of the Askrigg Block. The North and South Craven faults continued to be active into post-Triassic times.

Limestone rocks are exposed near these faults, including the Great Scar Limestone north of the Middle Craven Fault at Malham Cove and Gordale Scar, and along the South Craven Fault at Giggleswick Scar. This limestone layer is more than 200 metres thick, with overlying rocks (the Yoredale Series) originally more than 300 metres thick before weathering.

The vertical movement along this fault zone can be large—up to about 1,800 metres in places. For example, the North Craven Fault near Ingleton has a downthrow of about 200 metres, while the nearby South Craven Fault has a downthrow of about 1,200 metres. The plane of the North Craven Fault is exposed in Swilla Glen.

Charles Darwin used the Craven Fault to illustrate how nature can hide dramatic events: a long fault line can show only small surface features while the true, powerful movements happened deep underground.