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Coastal cliffs

The Scottish coast has a complex geology, and the sea has exploited the softer rocks and lines of weakness to produce a spectacularly varied landscape, ranging from the wave-battered cliffs of St Kilda, honeycombed with caves and tunnels, to the more sheltered slopes of the Fife coastline; ironically the latter are more subject to coastal erosion because the rocks are softer. The coast also includes 'fossil' cliffs, where raised beaches now separate old cliffs from the sea, sometimes by considerable distances. Scottish cliffs in clay and other soft deposits usually overlie bedrock, which protects them from much of the rapid erosion seen in true soft cliffs such as those of north Norfolk.

An extreme landscape

Structural features of sea cliffs include not only the expected caves and overhangs, but also spectacular natural arches and bridges, and even flying buttresses. There are several cliff-top blow-holes, the most imposing of which is probably on the island of Stroma in the Pentland Firth. The most important Scottish cliffs are those in the Outer Hebrides, Orkney and Shetland, Grampian, Galloway, and much of the northern mainland from Wester Ross round to the southern side of the Moray Firth. Because cliffs have no agreed definition, estimates of the length of cliff in Scotland vary, from 1778km to 4060km, with the latter representing some 60% of the cliffs of Britain. The highest sea cliffs are those of Conachair on St Kilda, which reach 426m. The highest mainland cliffs are at the Clo Mor, near Cape Wrath. The highest sea stack in the UK is also at St Kilda, where Stac an Armin reaches 196.3m.

Life on the edge

Seabirds can find a nesting ledge on most types of rock, but rocks that are horizontally bedded, such as sandstone, are particularly suitable. Most cliff vegetation can be reached by some grazing animals, but those ledges that are inaccessible to grazers possibly provide the habitat least altered by human influence in the United Kingdom. Where cliffs are on exposed coasts, the salt spray encourages unusual vegetation types such as the maritime heaths and grasslands of northern Scotland, where spring squill and Scots primrose flourish. On parts of Hirta, St Kilda, the extreme sea spray and heavy grazing support vegetation that is dominated by plantains. In parts of northern Scotland, there can be so much sea spray that 'perched' saltmarsh forms high above tidal limits. In contrast, some cliffs in SW Scotland may be so sheltered that they support woodland just above High Water Mark, and south-facing cliffs can have their own warmer 'microclimate' allowing southern species a northern toehold.

Last updated on Wednesday 25th November 2015 at 15:05 PM. Click here to comment on this page