Clett Rock EarthCache
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As coastal headlands erode at different rates, this leads to some very unusual and striking rock formations. A sea stack is an isolated pinnacle of rock entirely surrounded by the sea at high tide. The beauty of sea stacks makes them popular subjects for photographers and painters, as well as providing nesting locations for seabirds, and many are popular for rock climbing. A flat-topped stack is usually called a clett, as here at Holborn Head but if its summit has a larger diameter than its height, then it is an island.
Made of Caithness old red sandstone and separated from the mainland by a channel, Clett Rock is a solitary sea stack off Holborn Head on the Pentland Firth near Scrabster. Its top is covered with grass and the ledges down the sides are home to a great number of sea birds.
There is parking at Scrabster harbour, N58 36.705 W3 32.988, follow small road leading north towards the lighthouse, and just before the lighthouse turn left through a gate marked for Holborn Head and follow the path uphill. There are stiles and bridges, which allow access to the unfenced off promontory of Holborn Head itself. There are clear views over to Dunnet Head and to the Orkney Islands. The spectacular coastal cliff scenery includes sea stacks, blowholes, geos and frequently boiling seas is gorgeous but dangerous. The path goes past a natural arch which also acts as a blow hole (known locally as a gloup) in rough seas. The path passes Robertson's Point and the impressive sea stack of Clett Rock comes into view.
/!\ CAUTION /!\ /!\ CAUTION /!\ /!\ CAUTION /!\ /!\ CAUTION /!\ /!\ CAUTION /!\
Please be aware of the dangers associated with the cliffs, the area is unfenced and terrain is quite rough and can be slippery, you will need at least good walking shoes.
Sea stacks are formed by erosion, the ceaseless pounding of the waves, on the headland. There are different types of wave erosion, the main ones are:
Hydraulic action: which occurs when waves striking a cliff face compress air in cracks on the cliff face. This exerts pressure on the surrounding rock, and can progressively splinter and remove pieces. Over time, the cracks can grow, sometimes forming a cave.
Attrition: which occurs when waves cause loose pieces of rock debris (scree) to collide with each other, grinding and chipping each other, progressively becoming smaller, smoother and rounder. Scree also collides with the base of the cliff face, chipping small pieces of rock from the cliff or have a corrasion (abrasion) effect, similar to sandpapering.
Solution: occurs when acids contained in sea water will dissolve some types of rock such as chalk or limestone
Corrasion: otherwise known as abrasion occurs when waves break on cliff faces and slowly erode it. As the sea pounds cliff faces it also uses the scree from other wave actions to batter and break off pieces of rock from higher up the cliff face which can be used for this same wave action via attrition.
Corrosion: chemical weathering occurs when the sea's pH (anything below pH 7.0) corrodes rocks on a cliff face. Limestone cliff faces are particularly affected in this way. Wave action also increases the rate of reaction by removing the reacted material.
The continuous pounding of the waves on a headland wears away weaknesses in joints, crevasses and softer rock faster then the harder and more solid rock. Enlarging any gaps already there and eventually forming a cave. Sometimes a cave also forms on the other side of the headland and the two eventually meet in the middle forming an arch, or one cave over time erodes all the way through. We now have an arch. Even with the formation of the arch the erosional processes do not stop. The waves continue to widen the gap until the rock above can no longer be supported. At this point, part of the top portion gives way forming a blow hole, and then as the entire top portion falls away into the sea below leaving the furthest away arch support standing alone in the sea as a sea stack. But it doesn’t end there as the relentless seas continue pounding away and the stack is worn down to a stump.
To claim this earthcache, please send the answers to the questions below to us by email /messenger - do not post in your online log. Your log may be deleted if these criteria are not met. Educational guidelines for Earthcaches are set by Geocaching.com and GeoSociety.org (Earthcache) and have to be adhered to.
1. Estimate the height of Clett Rock.
2. How many layers can you see and describe them ( shape colour etc)
3. Estimate the width of the channel between Clett Rock and the main cliff edge at its narrowest part. Please do not get too close to the edge when doing this!
4. What feature can you see to the west of Clett Rock on the mainland ?
5. What wave action process, listed above, do you think occurs along this coastline, specifically?
6. While not compulsory, it is always good to see photos from this stunning location, but be careful where you tread/stand
Enjoy your visit, stay safe on the paths.
Thanks to SNH for their help with this earthcache
Additional Hints
(Decrypt)
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