Thursday, 27 June 2013

Orkney, June 2013, Part 5

I mentioned in Part 2 that I would return to the subject of the cliffs on the north and west coast of the Aikerness peninsula, so I had better be true to my word and make good my promise.

Whilst I know little about the geology of Orkney and understand even less, the Westray Heritage Trust came to my rescue with their excellent publication 'Westray Flagstone, Guide to the Geology of an Island' by David Leather. This was published in 2006, but I don't think the intervening 7 years are going to make my comments too inaccurate, as the bedrock is actually 380 million years old! The facts in the following account rely heavily upon this solid tome.

The Orkney Flagstone Group of rocks has a total thickness of 750m. Towards the top of this, the Westray rocks are from the Middle Devonian period and are around 190m thick. Within this formation are 18 cycles of deposition made up from consecutive layers that were laid down in flood plains, salt flats, shallow lake shores and a deep lake. Within the individual layers can be seen many fossilised features, including wave ripple marks, river ripple marks, mud cracks, stromatolites and rain drops, as well as actual fossil remains of fish and plants.

Westerly gales blowing in from the Atlantic bring violent storms that have formed a boulder beach on the cliff tops of the Aikerness peninsula. Here, 14m above sea level, the storm beach is up to 30m back from the cliff edge and stretches for 400m in length. At its highest, the boulder pile is 4m high, with some individual blocks measuring 3m long and 30cm thick. This isn't a place where you would want to be during a storm!

Fortunately, on the day that we walked along the west coast, the weather was relatively benign.

Standing on the storm surge beach, looking towards the cliff edge. For scale, Our Lass is left of centre.
Standing on the cliff top (14m above the sea, remember) looking at the boulder pile at the back of the beach. The power of the waves has left the clifftop completely clean of debris.
Some ominous holes in the otherwise smooth surface hint at the destructive forces at work here.
We reasoned that these were probably impact craters from huge blocks of stone hurled from the cliff face.
You could wear a hard hat in this natural quarry, but I don't think it would help!
Our Lass standing on the edge of a rocky outcrop, The Nev.
Sea cave
Coastal scenery looking north from Vaval's Geo
The Three-cornered Kirn, a blowhole in the cliff, with the churning sea below.
During the walk, we rested in a small depression a little way back from the cliff edge. It was sufficiently far from the effects of the sea to be grass-lined, but with a small pile of stones at the bottom. It is only this evening, whilst researching this blogpost, that I've realised that this was another blowhole. Apparently, at high tide, it roars like a dragon and sends plumes of vapour from its nostrils. Y'know, a Winter visit does sound rather tempting!


Martin said...

The only downside with a winter visit I can see, is timing your arrival and departure from the island, you might miss the storm stuck in Kirkwall waiting for the first ferry in 3 weeks, or be marooned... I recommend taking plenty of beer to tide you over :)

Imperfect and Tense said...

Try as I might, I cannot find the flaw in your plan. It is a good plan. And will require much preparation and practice?