Patterns in Pebbles


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One of the more mundane jobs of a Ranger is taking water meter readings every so often for some of our troughs.  I had to go to Lee yesterday to do this and decided to take a short detour to Sandy Cove to check the long flight of wooden steps which lead down to the beach.  Sandy Coves is a lovely isolated little beach to the west of Lee.  Steps were all fine but I had a little explore and came across some strange patterns in the flat pebbles.  Amongst the flat ones where masses which had been up ended I guess as the tide surges in and out though the rock gullies leaving amazing patterns.

 

2 responses to “Patterns in Pebbles

  1. Paul Madgett

    Hi Jonathan – it’s the pebbles made of slate (rather than of sandstone or vein quartz) which have this slim shape, and slate is abundant in the “solid” rocks of this part of the coast, so when the waves erode the cliffs copious amounts of thin slatey fragments fall on the beach and their sharp edges are fairly rapidly worn away by the constant movement of the waves and tides. When water currents, caused by waves washing in and out with the tide, move the pebbles along the numerous essentially linear gullies present at Lee Bay and other points along this stretch of coast, these slim pebbles are re-oriented so that they have minimal resistance to the water. Thus they line up more or less paralell to one another along the gullies, and become tighly packed down into the bases of the gullies. Once tightly packed like this they are then difficult to move, so these fascinating patterns remain for a long time. We’ve had Christmas cards sent us with the Lee Bay pebble patterns, and have used our own photos in the same way.

    Check out our local fast-moving inland streams (e.g. the Lyn around Watersmeet) and you find an analogous pattern, though much less pronounced – the flattish pebbles and boulders tend to be orientated on the bed of the stream so that they slope upstream, and stack up on one another – technically an “imbricate structure”. Any finding themselves in the opposite orientation tend to get flipped over the next time there is a substantial flow of water in the stream.

    Paul.

    • Hi Paul

      Thanks for the explanation. I’ve been here almost ten years now and first time I have noticed them. There’s always something new to see and discover. Jonathan

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