Evolution of the Coastline
The Ice Age
Scotland’s coastline has not always appeared as it does today. If it were possible to travel back in time 20,000 years, you would see a very different landscape. Back then, the planet was still in the grips of the last Ice Age and sea levels were around 140m lower than they are today. As a result, the English Channel and most of what is now the North Sea was dry land, making it possible for animals to travel between Britain and continental Europe. The edge of the Atlantic Ocean lay many kilometres west of the Hebrides.
In addition, a vast ice sheet up to 1.5km thick – around the same height as Ben Nevis – blanketed Scotland. The coast resembled that of the Arctic today, with pack-ice in winter and icebergs breaking off from the glaciers into the ocean waters.
Rising seas
Scotland’s coastline only began to take on its present appearance following the melting of the last ice sheet between 15,000 and 10,000 years ago. As the glaciers retreated they left behind a barren landscape, carved out by the scouring actions of the massive ice sheets and glacial meltwater. The melting ice resulted in sea levels rising dramatically, by up to 15mm per year. The Atlantic engulfed the low-lying continental shelf around Britain, finally separating England from France about 8,000 years ago. In Scotland the seas flooded the ice-scoured landscape. Groups of islands, such as Orkney and Shetland, were created and the lower lying river channels and glacial valleys were submerged to form many of the firths evident today, such as those of the Clyde and Tay.
The land bounces back
Even today, sea levels around the world continue to rise, though at only around 2mm per year. In spite of this, much of the Scottish coastline has actually been rising slowly back out of the sea again for the last 6,000 years. This is due to the Scottish landmass bouncing back upwards following its release from the crushing weight of ice which formerly lay upon it. Uplift has been greatest where the ice was thickest, around the Western Highlands, and least in areas closer to the margins of the ancient ice sheet, such as the Western Isles, Orkney and Shetland.
The lifting of the land in Scotland, together with rising sea levels worldwide, has produced a range of distinctive coastal features. In areas where land uplift has been more rapid than sea-level rise, ancient cliffs and beaches have gradually been lifted beyond the reach of the waves and are today stranded up to 40m above high-water mark. Striking examples of these raised beaches and sea cliffs occur around Arran, Jura, Islay and the Inner Hebrides.
In contrast, where sea-level rise has outpaced uplift of the land, as in Orkney, Shetland and the Western Isles, drowning of the landscape still continues. This is clearly shown by the presence of peat beds, complete with tree roots, once formed on land but now covered by the sea.
Beach formation
During and immediately after the Ice Age, the glaciers and rivers carried millions of tonnes of sand and gravel towards the sea. Many of these deposits still remain submerged but others have been re-worked by the power of the waves, mixed with shell debris and driven onto the land to make the sand and shingle beaches we see today.