One of the outcrops known as "The Tower"
Alport Castles shown within Derbyshire
The Alport Castles are a landslip feature in the Peak District National Park in Derbyshire. At over half a mile long, it is thought to be the largest landslide in the United Kingdom. The name "castles" comes from the debris from the landslide, which has produced several gritstone mounds that tower over the valley and appear from the distance to look like castles. Viewed from a distance the largest of these, the "Tower", resembles a full-scale motte and bailey castle.
300 million years ago, the area now known as the Peak District was part of a river delta that flowed into the sea. The deposits were sorted such that the finest material travelled the furthest and was deposited in the deep ocean as black shales. Further deposits accumulated on the slopes of the oceans and collapsed, resulting in turbidite deposits. Further turbidite flows eroded into previous ones, resulting in the type of deposit seen at Alport Castle. As the delta prograded (the mouth of the river moved further out to sea), the deposits become coarser. In the Peak District this coarse material is the gritstone that caps high points, protecting them from erosion.
The exact cause of the landslide is unknown, but similar if less dramatic landslips occur all around the Dark Peak, notably on Mam Tor.
One theory is that the river eroded the softer layers, causing the landslide. Other theories suggest that the soft shales below are too weak to support the weight of the heavy sandstone above and collapse under it, or that, because water can run through gritstone but not shale rock, trapped water may have "lubricated" to the rock to the point where one layer slid over another, causing the landslide. A further possibility is that a valley glacier steepened the sides of the valley, leaving unstable slopes that failed after the glacier melted, causing the landslide. However, immediately upstream is a normal river valley so any glacier would have been small.
Alport Castles has been selected for geological conservation as one of the most significant landslips in Britain.
- "Peak District: Alport Castles". National Trust. Archived from the original on 14 June 2013. Retrieved 3 May 2013.
- "Peakland Heritage: Alport Castles". Retrieved 3 May 2013.
- "Walks: Alport's Castles in the Sky". The AA. Retrieved 3 May 2013.
- Cooper, R.G. (2007). Mass Movements in Great Britain (PDF). Geological Conservation Review Series. Peterborough: JNCC. p. 20. ISBN 978 1 86107 481 2. Retrieved 9 February 2018.
- "Suffragettes". Peakland Heritage. Archived from the original on 25 April 2016. Retrieved 9 February 2018.
Media related to Alport Castles at Wikimedia Commons