The Alport Castles are a

landslip Landslides, also known as landslips, are several forms of mass wasting that may include a wide range of ground movements, such as rockfalls, deep-seated slope failures, mudflows, and debris flows. Landslides occur in a variety of environments, ...

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)-di ...

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 A motte-and-bailey castle is a European fortification with a wooden or stone keep situated on a raised area of ground called a motte, accompanied by a walled courtyard, or Bailey (castle), bailey, surrounded by a protective Rampart (fortification ...

castle A castle is a type of fortified structure built during the Middle Ages predominantly by the nobility or royalty and by military orders. Scholars debate the scope of the word ''castle'', but usually consider it to be the private fortified r ...

. The Alport Castles are on the eastern side of the

River Alport The River Alport flows for in the Dark Peak of the Peak District in Derbyshire, England. Its source is on Bleaklow, east of Glossop, from which it flows south through the Grains in the Water bog, then over gritstone below the Alport Castles la ...

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 ...

High Peak Estate The High Peak Estate is an area of Pennine moorland in the ownership of the National Trust in the Dark Peak area of Derbyshire, England. The National Trust High Peak Estate is to be known as the 'Dark Peak Area' from summer 2010 which is now p ...

; 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 roa ...

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 Ho ...

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 Derbyshire ( ) is a ceremonial county in the East Midlands, England. It includes much of the Peak District National Park, the southe ...

was part of a

river delta A river delta is a landform shaped like a triangle, created by deposition (geology), 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, res ...

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 were ...

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 Gritstone or grit is a hard, coarse-grained, siliceous sandstone. This term is especially applied to such sandstones that are quarried for building material. British gritstone was used for millstones to mill flour, to grind wood into pulp for pa ...

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#Glaciology, ablation over many years, often Century, centuries. It acquires dis ...

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 Right of way is the legal right, established by grant from a landowner or long usage (i.e. by prescription), to pass along a specific route through property belonging to another. A similar ''right of access'' also exists on land held by a gov ...

, and is a popular site for walkers. The site is also of interest for birdwatchers, as both

raven A raven is any of several larger-bodied bird species of the genus ''Corvus''. These species do not form a single taxonomic group within the genus. There is no consistent distinction between "crows" and "ravens", common names which are assigned t ...

s and

peregrine falcons The peregrine falcon (''Falco peregrinus''), also known as the peregrine, and historically as the duck hawk in North America, is a cosmopolitan bird of prey (raptor) in the family Falconidae. A large, crow-sized falcon, it has a blue-grey back, ...

have been known to nest on the crags. The remote Alport Castles Farm lies on the

below the site. This is the farm where the suffragette

Hannah Mitchell Hannah Mitchell (11 February 1872 – 22 October 1956) was an English suffragette and socialist.Routledge, p. 317 Born into a poor farming family in Derbyshire, Mitchell left home at a young age to work as a seamstress in Bolton, where she ...

was born in 1871 and brought up.

References

External links

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