The Alport Castles are a landslip feature in the

Peak District National Park Peak or The Peak may refer to: Basic meanings Geology * Mountain peak ** Pyramidal peak, a mountaintop that has been sculpted by erosion to form a point Mathematics * Peak hour or rush hour, in traffic congestion * Peak (geometry), an (''n''-3)-d ...

Derbyshire Derbyshire ( ) is a ceremonial county in the East Midlands, England. It includes much of the Peak District National Park, the southern end of the Pennine range of hills and part of the National Forest. It borders Greater Manchester to the nor ...

. 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. The Alport Castles are on the eastern side of the River Alport valley, part of the

National Trust The National Trust, formally the National Trust for Places of Historic Interest or Natural Beauty, is a charity and membership organisation for heritage conservation in England, Wales and Northern Ireland. In Scotland, there is a separate and ...

's High Peak Estate; they lie north of the

Snake Pass Snake Pass is a hill pass in the Derbyshire section of the Peak District, crossing the Pennines between Glossop and the Ladybower Reservoir at Ashopton. The road was engineered by Thomas Telford and opened in 1821. The pass carries the A57 ...

and north-west of

Ladybower Reservoir Ladybower Reservoir is a large Y-shaped, artificial reservoir, the lowest of three in the Upper Derwent Valley in Derbyshire, England. The River Ashop flows into the reservoir from the west; the River Derwent flows south, initially through How ...

Formation

300 million years ago, the area now known as the

Peak District The Peak District is an upland area in England at the southern end of the Pennines. Mostly in Derbyshire, it extends into Cheshire, Greater Manchester, Staffordshire, West Yorkshire and South Yorkshire. It includes the Dark Peak, where moorla ...

was part of a

river delta A river delta is a landform shaped like a triangle, created by deposition of sediment that is carried by a river and enters slower-moving or stagnant water. This occurs where a river enters an ocean, sea, estuary, lake, reservoir, or (more ra ...

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 A turbidite is the geologic deposit of a turbidity current, which is a type of amalgamation of fluidal and sediment gravity flow responsible for distributing vast amounts of clastic sediment into the deep ocean. Sequencing Turbidites wer ...

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 still debated. One theory is 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" the rock to the point where one layer slid over another, causing the landslide. A further possibility is that a valley

glacier A glacier (; ) is a persistent body of dense ice that is constantly moving under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires distinguishing features, such as ...

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.

Today

The rock faces and cliffs are unstable and unsuitable for climbing and scrambling; however, the site is accessible along some well-trodden public rights of way, and is a popular site for walkers. The site is also of interest for birdwatchers, as both ravens and peregrine falcons have been known to nest on the crags. The remote Alport Castles Farm lies on the River Alport below the site. This is the farm where the suffragette Hannah Mitchell was born in 1871 and brought up.

References

External links

* {{Authority control Landslides in the United Kingdom Peak District