Allen Fraser (UK)
Shetland is a spectacular group of islands with a diverse geology, a beautiful panorama and a particular wildlife, peopled by a tradition distinct throughout the British Isles. Shetland stays certainly one of Britain’s pure treasures.”
(J. Laughton Johnston)
The islands
Shetland sits on the sting of the European continental shelf and is sinking. Because the finish of the final glaciation about 10,000 years in the past, relative sea degree has risen by about 120m and has normal an archipelago of over 100 islands. The island group extends over a distance of 110km from Muckle Flugga (Fig. 2) within the north to Honest Isle within the south, and a convoluted shoreline, over 2,700km in size, signifies that no level on land right here is greater than 5km from the ocean.
The landmasses of the bigger islands are usually within the type of roughly north-south ridges of hills forming the ‘backbone’ of Shetland. The hills, primarily composed of acidic granite, schists and gneisses, are treeless and are usually lined by peat or blanket bathroom. The valley flooring between the hills of the central Mainland (the most important island) are composed of crystalline limestone and are generally more fertile. Together with sandy coastal areas, they form the best agricultural land.
The landscapes
Shetland’s unique landscapes have been sculpted from a diverse geology by rivers, glaciers and the sea over the last few million years. The coastline is stunning in its variety and grandeur. The Atlantic Ocean on the west and the North Sea on the east pound an ‘outer’ coast that has some of the most spectacular cliff scenery in the world. These cliffs stand guard over the tranquil ‘inner’ coast of long voes (sea lochs) adorned by sand and shingle ayres (beaches and sandbars).
Hundreds of lochans and the firths that separate and penetrate the islands attest to glacial erosion. Yet, in a few places, peat deposits still survive from the last interglacial warm period. In fact, many of the major landforms of Shetland date from a prolonged period of sub-aerial weathering and erosion long before the ice age and were merely modified by the ice. Good examples of this are the great granite whaleback of Ronas Hill (450m) and the remarkable parallel valleys that run north-south through the Mainland.
Glaciation
During the last glaciation, the thick ice sheets that covered Scandinavia and Scotland did not reach Shetland. The weight of these depressed the underlying landmasses down into the Earth’s mantle and, at the same time, uplifted the platform of crust supporting Shetland. During this period, Shetland developed an independent ice cap, one of only a small number in the British Isles. This was much thinner than the massively thick ice sheets that covered mainland Britain and Norway, so the impact of glaciation on Shetland was less severe.
Shetland displays many classic glacial landforms including roche moutonnées and over-deepened valleys, now drowned by the sea (Figs. 9 and 10). Glacial moraines occur on a number of valley floors and meltwater has been a significant agent in the shaping the finer detail of the landscape.
Erratic clasts ranging from pebble to boulder size occur at the surface, beneath peat and in glacial tills (Fig. 11). On lower ground, large blocks have been removed from fields to improve land for agriculture and the walls of the field boundaries give a good indication of the large erratic content of local tills.
The diverse geology of Shetland presents many possibilities for the study of directions of erratic carry by glacier ice. Perhaps the largest erratics on Shetland are the ‘Steens of Stofast’ on Lunna Ness (Fig. 13). Here the ‘Steens’ are composed of the remarkably distinctive Valayre Gneiss and lie on bedrock of the same composition. The Valayre Gneiss outcrops across no more than about 300m on this part of Lunna Ness and, therefore, the ‘Steens’ cannot have been moved further than a few tens of meters.
The inner coast
The immediate consequence of the melting of the ice sheets at the end of the last glaciation was a rapid rise in sea level. This was followed by a slower isostatic readjustment of landmasses that had been pushed down into the Earth’s mantle by the weight of ice. Scotland and Scandinavia have risen many metres as a result of this readjustment, as can be seen from their many raised beaches.
Shetland, on the other hand, having been much less heavily loaded by ice, has been sinking. The present day coastline of Shetland is the result of rapid inundation by the sea followed by slower subsidence, creating a classic example of a recently drowned coastline. Shetland’s voes and firths, the ‘Inner Coast’, are valleys that have been drowned by the sea. Some, such as Ronas Voe, are fjords deepened by ice and displaying evidence of glacial erosion with ice-moulded bedrock on steep sides.
Classic examples such as St Ninian’s Ayre show us that progressive flooding since the end of the last glaciation has provided material for the outstanding diversity of sand and shingle bars, spits and tombolos (Fig. 15). Peat formerly developed on boggy surfaces above sea level is now often found at or below sea level and sometimes buried beneath boulder and gravel beaches. In fact, many archaeological sites in bay heads have been exposed by or partly destroyed by coastal erosion.
The outer coast
Shetland’s special qualities have been recognised since the early nineteenth century when Charles Lyell’s classic Principles of Geology mentioned the sea stacks of the Drongs (Fig. 16) and the cliffs at the Grind o’ the Navir (Figs. 17 and 18), as examples of coastal landforms.
Shetland experiences one of the highest wave energy environments in the world. The west coast is exposed to the full force of the Atlantic waves that grow along hundreds of kilometres of ‘fetch’ often driven by hurricane-force wind speeds (Fig. 20). Deep water, close inshore, allows huge waves to arrive at the cliff faces unbroken.
Sea level rise has allowed these waves to attack progressively higher parts of the coastline, so today we see Shetland’s ‘Outer Coast’ as long stretches of sheer cliffs that plunge into deep water. The Kame on Foula, at 376m, is one of the highest sea cliffs in Britain. Cliff-top storm deposits, such as at the Grind of the Navir, demonstrate how the combination of extreme waves and deep water close inshore can strip rocks from the cliffs to produce boulder accumulations up to 50m above the high water mark.
Tsunami
The steady pace of change has been interrupted by a sequence of catastrophic occurrences, including at least three tsunami events that are recorded in coastal fen and lake deposits on Shetland (Figs. 21 and 22).
One of the largest Holocene underwater landslides mapped on Earth is the Storegga area on the Norwegian continental shelf to the north of Shetland. Here, approximately 3,500km3 of material slid out and generated a huge tsunami dated to about 8,000 years BP. On Shetland, a 70m high wave invaded coastal lakes and ran up peaty hillsides, where it deposited sand layers up to 9.2m above the present high tide level. Sea level at around 8,000BP was at least 10 to 15m below that of the present day and, therefore, the run-up exceeded 20m.
Deposits from a second, younger tsunami dated to about 5,500BP have also been found. The sediment facies are similar to those of the Storegga tsunami, consisting of rip-up clasts, sand layers, re-deposited material and marine diatoms. Run-up from this event was probably more than 10m. Yet another sand layer in peat outcrops dates to about 1,500BP. This layer thins and fines inland and was found at two sites 40km apart and traced to about 5 to 6m above present high tide. This youngest event falls within the late Pictish period in Shetland and may be of significance to archaeologists.
Ecology
The establishment of the North Atlantic Current (an extension of the Gulf Stream), which probably occurred soon after the last glaciation, would have been critical in allowing many plants and animals to colonise Shetland. This current brings warmer water into the North Atlantic, which warms the overlying atmosphere. Prevailing winds then carry this heat towards Europe and Shetland. As a result, annual mean air temperatures over the northern North Atlantic and Western Europe are 5 to 10oC warmer than elsewhere at the same latitude. Shetland in winter is somewhat different to St Petersburg in Russia, Cape Farewell in Greenland or Anchorage in Alaska, all of which lie at the same latitude. The relatively warm seas around the islands also result in a high humidity so that, although rainfall in Shetland is not high (1,200mm annually), the climate is damp.
As the most northerly stretch of coast in Britain, Shetland is literally a place on the edge. The shoreline lies in the frontier zone between temperate and sub-arctic marine ecosystems. For some northern species, it is the southern limit of their range and vice versa. The submarine topography is extraordinarily varied over short distances, creating rich habitats for inshore sea life, particularly in the kelp forests that may have an area of over 250 square miles.
The Islands’ populations of grey and common seals (Figs. 22 and 23) and otters are nationally important – Shetland is one of the best places in Britain to watch otters in the wild.
The coastline is also of special botanical interest with rarities such as the oyster plant and lush cliff meadows and plant communities developing on the many small islands where sheep are no longer grazed.
Isolation also prevented colonisation by land mammals. Man has introduced, accidentally or deliberately, all the few species that now occur here, probably even including the otter. By contrast, a combination of productive seas, excellent cliff-nesting sites and an absence of native mammalian predators provide a haven for seabirds whose numbers and diversity are equalled in few other parts of the world.
The seabird colonies are recognised as of international significance and are among the largest in the North Atlantic (Figs. 29 and 30). Shetland is also a vital staging post for migrating birds and has a world famous ornithological observatory on Fair Isle.
Much of the present land surface of Shetland is covered with blanket peat and plant communities dominated by heather, grasses and sedges. The flora is restricted, with only some 400 native vascular plant species. This is due partly to constraints on colonisation of the land at the end of the last glaciation and partly to the limited range of environmental niches available on the islands. However, more recently, impoverishment by man’s activities, especially grazing by sheep, has also played a part.
An unusual feature of Shetland’s flora and fauna is the occurrence of sub-arctic species alongside those from temperate zones, a consequence of Shetland’s northern location and the ameliorating effects of the Gulf Stream. As well as limiting the colonisation of the islands, Shetland’s isolation has contributed to its biodiversity by allowing the evolution of distinct island races and forms of some species. These include several moths, birds such as the starling and wren and a remarkable group of 24 micro-species of hawkweeds (Hieracia) endemic to Shetland.
Life on the edge
Man has been the main agent of landscape change on the islands in the last 6,000 years, initially causing the loss of trees through felling and grazing by domestic animals, but later affecting the entire landscape mosaic of soils, vegetation and peat development. In modern history, we have begun to physically reshape the land, opening quarries, reclaiming land, opening cuttings and creating building sites.
Today, people inhabit only 15 of the islands. Land suitable for agriculture is restricted to small areas of fertile soil derived from limestone or blown sand and to sheltered coastal areas where soil can be augmented by the addition of shell-sand and seaweed as fertiliser. With land so scarce and crops limited by the climate, Shetlanders have always looked to the sea as much as the land for food, so a safe beach or inlet for landing boats was vitally important to the crofter. These two factors have combined to produce the characteristic Shetland landscape of small, coastal crofting settlements set against the backdrop of the islands’ moorland interior. Therefore, the 22,000 population of Shetland is unevenly distributed across the islands with the majority living in and around the capital, Lerwick.
Traditional crofting was never more than a subsistence economy and had to be combined with other activities such as the production of the distinctive Shetland knitwear (with its Fair Isle pattern), fishing and whaling. Today, sheep and wool production, fishing and knitwear are the mainstays of the Shetland economy. However, each has seen periods of boom and bust leading to emigration of Shetlanders to many parts of the world and New Zealand in particular.
Economic circumstances changed with the discovery of North Sea oil in the early 1970s. Europe’s largest oil terminal was built in the islands at Sullom Voe, bringing previously undreamed of prosperity. Oil production is now in decline, but aquaculture has joined fishing as a major industry and Shetland is looking to cash in on its vast resources of wind and waves for renewable power generation.
References
Shetland Landscapes at: www.fettes.com/shetland.
A Naturalist’s Shetland, J. Laughton Johnston. Poyser, 1999
Trending Products
