The remains of a long extinct volcano, described as ‘the best section through the flank of a volcano in the UK’
On a typical day at Eshaness it’s hard to imagine that the landscape formed in a tropical environment! 420 million years ago three continents collided to create a huge landmass known as ‘Laurasia’. ‘Shetland’ was landlocked within the continent and situated close to the Equator, with a climate varying from dry and arid to wet and humid.
The continental collision threw up Himalayan-sized mountains that eroded quickly into the valleys below them. 395 million years ago in one of these valleys, a powerful volcano spewed out lava, ash and rocky debris. It was a strato-volcano, with multiple eruptions creating a steep and unstable cone around a central vent. Most of the cone eroded away long ago but a section of the flank remains, and as you walk north from the Eshaness lighthouse you can explore the evidence of volcanic activity exposed along the way.
Directly below the lighthouse, you’ll find agglomerate – rock formed from fragments of other rock, some the size of breezeblocks, that were ripped out of a vent during huge explosive eruptions before cascading back down to earth. This area, known as Kirn o Slettans, is likely only a side vent of the main volcano; the remains of the main vent survive as the small island of Muckle Ossa, visible to the north.
At Calders Geo, a huge sea-cut inlet, the cliff face shows layers of lava, volcanic ash (tuff) and agglomerate, while further along the coast at Drid Geo you can find striking black and red layers – a build-up of countless lava flows, each surface weathering before the next layer was deposited. The domed surface of one such flow is clearly visible at Breigeo, exposed as a weak layer of rock weathers away to undercut the cliff above, resulting in periodic collapse.
At the Grind o da Navir, you can find ignimbrite – further evidence of the violent nature of the Eshaness Volcano. The ignimbrite formed from a pyroclastic flow – ash, dust and lava droplets that cascaded at high speed down the side of the volcano, obliterating everything in its path. Squashed lava droplets can still be seen as orange streaks within the rock.
Today, Eshaness is one of the highest energy coastlines in the world, battered by the North Atlantic. The power of the sea is most dramatically illustrated at the Grind o da Navir, where huge blocks of ignimbrite have been ripped from the bedrock and deposited 50m inland during extreme storms by the water funnelling between the cliffs 15 metres above sea level.
On calmer days this area is one of the most popular and beautiful walks in Shetland. The sea continues to exploit cracks and joints that formed when the lava cooled and shrank, carving out dramatic geos (rocky inlets), stacks and blowholes, along a flat grassy route that is carpeted with sea pinks from May to July. Beneath the coastal route, and accessible only from the sea, is the largest cave in the UK. The Eshaness lighthouse, built by the Stephenson family in 1929, houses self-catering accommodation and provides a great base to explore the area.
Text contributed by Robina Barton
Find out more:
Shetland’s Volcano self guide trail – Shetland Heritage Trails
Geopark Shetland app for iPhone/Android – iTunes / Google Play
A photographic guide to Shetland’s Geology – David Malcolm & Robina R. Barton, Shetland Times Ltd 2015
This web page is published by the Scottish Geodiversity Forum under a Creative Commons ‘Attribution Non-commercial’ (CC BY-NC) licence, which permits non-commercial reuse provided the original work is properly cited.