Posted by: Rose | November 19, 2009

South West is Best

Way, way back in June I attended Mark’s South West Sea Kayak Meet. It was one of the few occasions this year when I actually got out in a sea kayak (I’ve been locked in battle with DIY, amongst other things). I had a fantastic weekend – lovely paddling, meeting old friends, making new friends, great talks and the Pig’s Nose Inn was its usual bizarre self (the staff thoroughly embarrassed me in exchange for Birthday cake). I don’t think I’ve ever seen so many paddlers on the sea at one time. Great! P&H were also in attendance, so I got a demo boat fix too.

Spot the kayaker, Hallsands. Photo by Anne Hanson.

Saturday brought with it a foggy paddle south of Hallsands, the highlight being seal TV (they sprawled on the rocks, we watched transfixed). I got to paddle a glittery turquoise Quest LV, which I loved. However, I don’t recommend using a VHF tag containing the word ‘glitter’; it upsets the Coastguard!

Atlantic swell, scattered with sunshine, made Sunday’s paddle from Thurlestone Sands a perfect rockhopping opportunity for those who dared. I braved the swell through Thurlestone arch, or maybe it was just a case of demo boat courage?

Thurlestone arch is composed of Permian breccio-conglomerate*. Although the swell didn’t allow for close inspection, it is composed of pebbles (and even boulders) of local Devonian and Carboniferous rocks that were transported by water. This sedimentary rock was created by flash floods in a desert environment, deposited by a wadi.  The very mixed grain size is the result of the sudden cessation of water velocity and the rapid deposition of sediment.

Comparatively, in environments where water velocity decreases slowly, the deposited sediment will gradually decrease in size with smaller and smaller particles being deposited over time (the opposite is never true as increasing water velocity causes erosion and transportation). This sorting of sediment size can be clearly observed in the geological record and is known as a ‘fining upwards sequence’.

A fining upwards sequence can be used as an important tool known as ‘way-up indicator’. It is entirely possible to view rocks that have been completely overturned by folding; they are simply upside down. When it is present, inverted fining upwards can be used as evidence to prove that this is the case.

Here’s to SWSKM 2010…

* A breccia has angular clasts that have been deposited close to source and a conglomerate has rounded clasts that have been smoothed by transportation. A breccio-conglomerate contains a mixture of angular and rounded clasts.

Demo boat courage, Thurlestone arch. Photo by Anne Hanson.

Breccio-conglomerate, Thurlestone arch (you try taking photos of rocks in swell!)

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Responses

  1. Thanks for coming, Liz – I do hope that you’ll come to next years’ event – let’s try and hold it on your birthday again!

    Mark

  2. Ahh, reminded me what a cracking weekend it was. Please may I come too Mark?


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