Oxwich Landslides EarthCache
Hidden : 4/30/2013
Difficulty:
1.5 out of 5
Terrain:
2.5 out of 5

Size: Size: other (other)

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Geocache Description:

This earthcache will bring you to Oxwich Bay where there were cliff collapses in December 2009, January 2019 and July 2020.
Please take care in this area. Landslips continue to occur.

EDIT 1: Please note that there was a second fall (actually two within a couple of weeks of each other) of rock in early Jan 2019. These questions refer to the older fall from 2009. The difference between the two is quite obvious by the colour of the rocks.

EDIT 2: Early July 2020 saw another fall. Whilst the questions refer to the oldest of the three falls (which can be determined by colour and weathering), even if you get the succession muddled the answers will likely come out correct. Interesting that this site is so active, plenty of earth science in action here.

To visit the site of this earthcache please park at the beach car park (see waypoints: £4 per day in high season) and walk less than a quarter of a mile across the sand and stones (excellent rock pools here) on the western side of the bay. This must be done in the lower half of the tidal cycle. Please check the tide times before setting out.

Your short walk to the co-ordinates will bring you to large boulders (some the size of houses); the results of cliff collapses, most recently in December 2009. These boulders are known as The Dice. You can easily see from where they have fallen, some distance above the beach. There is a new sixty metre stretch of predominantly red cliff face. Until the end of the nineteenth century, this was a limestone quarry from which stone was shipped to Devon to be burned and turned into agricultural lime. More recently this area has been used for recreational rock climbing, the fall affecting many of the established routes.

This sort of cliff collapse can be triggered by wave action under cutting the cliff base. Each wave erodes a small amount of material until a notch under the base of the cliff is formed. It can also be triggered by freeze-thaw. Water percolates down into small cracks in the cliff and, given sufficiently low temperatures, freezes. As it freezes it expands by about 10% putting pressure on the rock. After repeated cycles of freeze thaw material is loosened and falls away, often in angular lumps.

To claim this earthcache, view the rocks from a safe distance of 25m or more from the fallen rocks and email me through my profile (click on my username at the top of the listing and remember to release your email address so I can reply) with the answers to the following questions:
1. Which method of cliff erosion do you think is most likely to be responsible for the recent collapse; wave action or freeze-thaw? Why?
2. Estimate the mass of the largest boulder in metric tonnes. Use the approximation that one cubic metre of rock is about two and a half metric tonnes.
3. What can you see at the top of the new cliff face that proves this collapse is a relatively recent event?
Finally, you are invited (but not required) to upload a photo of yourself or GPS with the Dice.

Please do not post your answers in your log (email them to me) and try not to give away too much when uploading photos (in particular please avoid the answer to question 4). Any log giving answers to questions will be deleted.

Please go ahead and log your find AFTER you email me your answers. Logs submitted before sending answers may be deleted. Once you've answered, feel free to log. I will email you if there is a problem with your answers.

This cache is placed with the kind permission of The Countryside Council for Wales and the Penrice Estate.

Additional Hints (Decrypt)

Cyrnfr qba'g trg pybfre guna 25z. Nyy dhrfgvbaf pna or nafjrerq sebz guvf qvfgnapr.

Decryption Key

A|B|C|D|E|F|G|H|I|J|K|L|M
-------------------------
N|O|P|Q|R|S|T|U|V|W|X|Y|Z

(letter above equals below, and vice versa)

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