Keen of Hamar
Mesozoic West Shetland Platform
Mesozoic Northern North Sea
Tertiary West Shetland Platform
Tertiary Northern North Sea
Quarff wind gap
Geology of Shetland
Shetland has many fascinating geological localities that show most of the pages of Earth History stretching back almost 3 billion years. All across Shetland the rocks and landscapes tell amazing stories of oceans opening and closing, of mountain building and erosion, of ice ages and tropical seas, of volcanoes, deserts and ancient rivers, of land use, climate change and sea level rise, and of minerals and miners.
On Unst you can walk across what was once the Earth’s crust just beneath an ancient sea floor progressing downwards until you reach what was once the Earth’s mantle. Here too you can see how minerals formed in these ancient rocks and where and how some of these were mined and processed. On the Keen of Hamar we see rare plants growing on the serpentine grassland formed on the thin soil cover afforded by these rocks. Although some distance away from Unst, lavas that spewed out on the floor of this ancient sea can be seen at Cunningsburgh. A walk up the quarry track above Cunningsburgh at Catpund shows how these lavas became altered to serpentine then steatite or soapstone (‘clebber’) and talc. In the nearby burn and hillside outcrops of the easily worked steatite were extensively quarried in Viking times to produce various artefacts both for local use and export. Chisel marks and hollows where bowls had been fashioned and extracted can be seen on many outcrops both here and at Cross Geo at Clibberswick on Unst.
At Funzie on Fetlar you can see in three-dimensional detail how boulders on an ancient beach were squashed and stretched by enormous tectonic forces as they pushed the bed of the ancient sea up and over continental rocks. Cross the sound and the “Wilds o’ Yell” tell us of rocks that were once sands and muds on an ancient ocean floor that became contorted and veined as they became the roots of mountains that were once higher than the Himalayas.
A trek across Fethaland shows how great rock slices of vastly different ages and types were torn up and thrust north-westward by tectonic forces to lie next to each other. In Northmaven you can follow and step across an ancient geological fault of a San Andreas type that was active hundreds of millions of years ago as ancient continents collided and slid past each other. Here too you can see how huge masses of magma squeezed, forced and eventually punched their way up through the crust beneath an ancient continent. From North Roe you can walk back across rocks hundreds of millions then billions of years old seeing as you go where Neolithic man made his tools and how ice formed the landscape and then find the remnants of trees that once grew by a lake some 120,000 years ago.
At Melby and Huxter and on Papa Stour you can view lavas spewed out by ancient volcanoes onto the sands and rivers at the margin of the ancient Lake Orcadie, then look out across St. Magnus Bay and speculate if it really started life as a meteorite impact crater. Take a walk around Papa Stour and marvel at its geos, stacks and caves then turn inland and ponder on how the hand of man has changed the landscape.
Near Eshaness lighthouse you can stand in volcanic cone surrounded by rocks that once were blasted high into the air as the cone grew on the side of a massive volcano almost 400 million years ago. Then as you ‘tak your fit in your hand’ along one of the best coastal walks anywhere, you cross progressively older lava flows that reveal in graphic detail the best exposure of the anatomy of a volcano in Britain. This walk will take you to the Grind o da Navir where the rock started life as massive red-hot pyroclastic flows that swept down the volcanic slope. See how the forces of nature still operate here in a big way today where a spectacular amphitheatre is being hewn out of the rock by gigantic storm waves that carry huge blocks of rock far inland to form beach ridges many metres high.
Take a whistle stop tour of geological sites from west to east across central Mainland and visit a quarry in unusual granite type at Bixter. This granite takes different forms as it shows itself further south at Hamnavoe and Spiggie. On Hildasay it was quarried for building stone and may have found its way to Australia as ballast on wool clippers. Heading east you cross a boundary zone between rocks that began life on the floors of two different oceans at different times, now welded together by tectonic forces. Marvel at how these forces have caused fist sized crystals to grow in narrow zone of rock that can be traced over a distance of 80 kilometres. This is one of Shetland’s most spectacular rocks and is exposed to great effect in Grut Wick quarry on Lunnaness. See too how Shetland’s most fertile valleys lie on beds of crystalline limestone that once was carbonate muds on a warm shallow sea and observe how these sequences of rocks have been offset by major geological fault that cuts through Nesting and Scalloway.
Around 370 million years ago a walk through where Lerwick is now would have meant a wade across fast flowing rivers in a climate not unlike the Death Valley of today. These rivers were fed by run off from high mountains to the west and carried sediments east to be deposited in lakes. The cobbles, gravels and sands of these rivers can be best seen at Gulberwick and the massive rounded boulders, rocks and sands swept down mountain gorges to build alluvial fans can be best seen near ‘da North Mooth’. A river such as these may have made the deep valley that cuts across Shetland at Quarff. The scree that once mantled the mountain slopes now form low hills around Brindister while lake sediments are found at various places all the east side from Bressay to Sumburgh. Plant leaves and other debris swept out into the lakes can be found as fossils on Bressay and the fossil remains of fish that swum in the lakes appear among the classic rock formations at Exnaboe. The rivers that fed the lakes in this area were not so fast flowing as those near Lerwick and meandered between sand dune fields that show up in the cliffs north of Exnaboe.
A visit to Garths Ness, beneath the shadow of Fitful Head, will show you where hot springs concentrated minerals on the bed of an ancient ocean and where attempts were made to mine copper ore in the 19th century. The inhabitants of Jarlshof and Scatness may have exploited the minerals of this area in earlier times. Mineral deposits like these eventually became buried deep in the rocks beneath between Bressay and Sandwick only to be dissolved once more and carried upwards to form the veins of copper and iron that were mined at Sand Lodge.