This month I escaped the August Festival chaos of Edinburgh to visit the quiet island of Orkney. The island boasts fantastic geology which outcrops along its impressive high sea cliffs. The rich archaeological heritage was largely built upon the available good quality and varied rocks that could be used as building stones, tools and navigation aids. The early settlers were also sustained by the right waters surrounding the island. Now, the water ways are famous for their innovative in wave and tidal power uses.
Geology
The Devonian Old Red Sandstone Group (ORS) form the majority of the outcrop. These were deposited over 360 million years ago, when the Orkney was in the centre of a large continent of Baltic close to the Equator. The Caledonian Mountains were being eroded, and provided huge volumes of sediment to be deposited in lakes and river valleys across the UK. In Orkney, three main Devonian lithologies are common:
1. Lower ORS Sands. The earliest Devonian rocks found on Orkney demonstrate the continental nature of the island at the time of deposition. Alluvial fan deposits are seen in the Hara Ebb formation – depositing sediment directly eroded from the Caledonian Mountain range. Elsewhere, sand dunes were formed, and their remnants can be seen at Yesnaby (Locality 1). The Yesnaby Sea Stack is an impressive 35 m tall and show beautiful large-scale Aeolian cross bedding.
2. Mid ORS Flagstones. The flagstones comprise of sediments deposited in a huge lake named Lake Orcadie that buried valleys and hills of the Orkney. The lake level fluctuated over time, leading to high lake level times depositing dark muds (in which fish remains have been found) and lower levels where coarser sediment reached the lake centres and were reworked by waves. These grey, thin bedded silts and sands break to form sheets of rock that have become valuable paving stones. They are characteristic of the Orkney landscape, with the many old ruined cottages and dry stone walls across the island being made from them. Orkney’s many famous archaeological sites show that the earliest settlers used these stones to build sophisticated settlements even as far back as Neolithic times. One significant modern building that shows these rock off well is the Highland Park Distillery in Kirkwall which is well worth a visit (and a dram!) (see locality 1).
3. Upper ORS Sandstones. Lake Orcadie filled, and was covered by the Upper Devonian red and yellow sands. These sands of the Hoy and Eday Formations were deposited by large rivers with periodic lake formation. The sands show small-scale cross bedding laminations, and rare fish remain have been found. Muddier layers represent flood plain deposits, and sands can show some reworking by the wind in places. The most famous outcrop to see these rocks is the Old Man of Hoy Sea Stack and the surrounding cliffs. The sea stack (Figure 1) is number 54 on the Top 100 Great Geosites is one of the highest in Britain and well worth a visit (Locality 3) For those unable to make the trip to Hoy, the St Magnus Cathedral in Kirwall is a great place to see them. The soft nature of these sands has allowed stone masons to carve them into intricate shapes. Unfortunately, the relentless wind and salty sea air has caused a great deal of weathering, and mush of the original decoration of the Cathedral has been destroyed. This does however allow for the cross lamination of the sands to be clearly seen!. Now, restoration works is ongoing with replacement carving being placed where requires. This makes for a very beautiful and interesting restored building!
Resources
The availability of soft, carvable rocks on Orkney has no doubt shaped it history in allowing multiple groups to settle on the island over the last 5000 years. Stones were used to build shelter (e.g. Neolithic broghs), tools (axe heads, knifes etc.) and ceremonial sites (standing stone circles such as the Ring of Brodgar).
The accessibility to ocean resources no doubt also played a vital role in sustaining the Neolithic, Iron Age, and Viking communities. Today, the ocean remains an important part of Orkney Life. On my trip I was lucky enough to join the staff of the European Marine Energy Centre for a tour of their Tidal Energy Test Site. The company provides for and supports companies working on wave and tidal energy generation with two test sites for the technology off Orkney. The energy generated is received at the EMEC substation on Eday (locality 4) and is used for household power on Orkney. The test site is so successful, the company is now looking for ways to store the energy that cannot be used immediately on the Island and were in the process of developing a mechanism to convert the excess electricity into Hydrogen. The Hydrogen can then be stored and converted back into electricity when required and will soon begin servicing the ferries overnight energy needs. The site really did give a great glimpse into the future of our energy infrastructure in the UK, with tidal, wave and wind energy supplying much of Orkney’s energy needs today.
Après Geology
There is so much to do in Orkney! Below are some recommendations to enjoy after those long walks round sea cliffs looking at Geology.
The Orkney Museum: If the weather is bad, The Orkney Museum (opposite the Cathedral in Kirkwall) gives a great overview to the human history of the Islands. It is free and located close to the Main street which is full of shops selling local products (I bought so much cheese and gin!)
Orkney Fossil and Heritage Centre: Again a good wet weather activity. The centre is not large, but gives a good overview to the geology of the island. There is a café, but I recommend resisting the cake and heading South to the Skerries Bistro. From there you can look out over the Pentland Firth towards the Scottish Mainland while enjoying their fabulous local seafood.
The Gloup: If, after those museums, you are need of some fresh air again, the Gloup (located east of Kirkwall) is an interesting collapsed sea cave. If you are brave enough I hear that it makes for a brilliant snorkel route on a calm day (look out for the seal though!)
Finally, a work of warning when looking at the rocks in Orkney. Not all of them are what they seem! At the Brough of Birsay (Locality 5), some impressive renovation work has created a new rock type on the island. Although the outcrop is made from concrete, the builders have spent some time making the rock look natural with beds and laminations! Can you spot the real vs. fake?
--- Happy Exploring ---
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