The Kame on Foula, at 376 m one of the highest sea cliffs in Britain
Try here for a fly-by of Foula's cliffs
Streetmap extract of the west coast of Papa Stour
Geography worksheet on classic landforms of coastal erosion on Shetland
Winter storm waves at Stenness in the 1990s and the scene today. Image courtesy of Tangwick Haa Museum.
"These isles are exposed continually to the uncontrolled violence of the Atlantic, for no land intervenes between their western shores and America. The prevalence, therefore, of strong westerly gales, causes the waves to be sometimes driven with irresistible force upon the coast, while there is also a current setting from the north. The spray of the sea aids the decomposition of the rocks, and prepares them to be breached by the mechanical force of the waves. Steep cliffs are hollowed out into deep caves and lofty arches; and almost every promontory ends in a cluster of rocks, imitating the forms of columns, pinnacles, and obelisks. Modern observations show that the reduction of continuous tracts to such insular masses is a process in which Nature is still actively engaged."
Charles Lyell (1835) Principles of Geology
The outer coast of Shetland is one of the best places in the world to study the erosion of hard rock coasts. Evidence of major erosion is not hard to find. The domes of hills at Fitful and Sumburgh Head are half lost to the sea. Hermaness is being steadily nibbled away. The ridge of Sandness Hill has been similarly foreshortened, together with the spine of Foula. Archaeological sites are threatened, including Sand Wick on Unst. Historical records mention the collapse of cliffs and arches and we have photographic evidence from 1900 onwards of significant changes. The sea caves on Shetland are amongst the longest in the world.
The postglacial submergence of the islands has allowed waves to attack progressively higher parts of the coastline as sea level has risen. The waves themselves have prodigious energy derived from the huge fetch across the Atlantic and the ferocity of North Atlantic storms. The rocks of the Shetland are highly varied, allowing the effects of lithology and structure on cliff form to be identified. The cliff-top storm deposits found at a few localities mark the combination of extreme waves and deep water close offshore that can be matched at only a handful of sites elsewhere around the coasts of western Europe. Rates and styles of marine erosion and cliff retreat can be assessed on Shetland, unlike many other coasts where change is usually regarded as very slow.
Classic models of the erosion of hard rock coasts do not appear to apply to Shetland. Deep water at the base of many cliffs means that abrasion is limited and cliff erosion is very largely a product of various forms of hydraulic action interacting with the rock mechanics of cliffs up to 50 m high. The role of weathering is often muted, as blocks are removed by waves rather than worn away by salt weathering or other forms of subaerial decay.
As elsewhere in Scotland, inherited elements of the coastline can be identified. Flinn describes the inner coast between Sand, Tresta and Bixter where wave action has achieved little more than the partial removal of peat, till, rotten granite and shattered rock. Hansom (2003) notes that on Foula that the geos of the northern and east coasts are often partially plugged by drift, whereas cliffs oriented towards the prevailing winds and waves show only fresh forms.
Willis (2007) reminds us of the crucial role of sea level change in shaping the human landscape of Shetland. He points out that since the arrival of the Neolithic farmers 20% of the total land area of Shetland has been lost to the sea. This includes perhaps >60% of the best low-lying arable land, meaning that the earliest farmers and hunter gatherers lived in an environment of great richness compared to that of today.