Cave Walls at Mewslade 1

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Naturally sculpted walls in a cave passage at Mewslade Bay

There are lots of small caves on the beach at Mewslade Bay in Gower, eroded into the High Tor Limestone rock face. The rock walls at the entrances to these caves are naturally ornamented with fairly regular patterns of shallow ‘scoop’ marks that look as if they might have resulted from the percussive action of stones washing in and out with the tides – rather like the marks made by knapping on a flint axe head. The size of these depressions varies widely – but with a tendency to gradate to greater size towards the deeper recesses of the caves.

The inner passages of the cave illustrated in this post, additionally displayed series of approximately horizontally, almost parallel, shallow linear grooves with more or less sharp edges. This kind of surface pattern and texture occurred in discrete patches, most noticeably in areas of slight overhang. These features remind me of the rillenkarren that I photographed in rocks near Chillagoe in Queensland – a well known erosional characteristic in limestone karst landscapes – although in Chillagoe all the grooves were aligned vertically with a down hill orientation.

I am inclined to think that the groove patterns on the cave walls at Mewslade could be the result of a similar process of solution by slightly acid water – from the evaporation and dissolving action of drips and surface water films originating from slowly percolating ground water and the surface residual sea water after high tides.

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7 Replies to “Cave Walls at Mewslade 1”

  3. I was walking across Mewslade Bay towards Tears Point yesterday when I came across what seemed unusual rock formations. I posted a photograph on Instagram and on Geograph (https://www.geograph.org.uk/photo/6411860) and thanks to a reply from the Gower Society I came across your blog.
    The thought occurred to me that whereas controlled directional chipping would create a flint axe, the rough and tumble of pebbles would have rounded the rocks and eroded the jagged edges.
    I’m not a geologist and would welcome your thoughts.
    Thanks. Alan.

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  5. Hello, Alan. The natural sculpturings in the limestone rocks at Mewslade are spectacular, aren’t they? I have visited Mewslade quite a few times at different times of the year, taking many photographs of the rock formations and patterns in the rocks. I think that these are what are called Karst formations. Karst scenery is the result of carbonic acid from rainfall dissolving the limestone. Karst hydrogeology is also responsible for the formation of the caves on Gower. I guess one of the best known examples of this kind of rock erosion is The Burren in Ireland. I have also seen it myself in the Queensland outback; and some of the most outstanding mountain scenery in China is also a result of this geological process. Each kind of shape and formation is named scientifically. The forms can be on a large scale down to microscopic. At Mewslade you can see that the erosion occurs both above high tide level and below. Much of it may not be recent in its formation. I think it could be palaeokarst. There is a platform of palaeokarst high up the shore in Caswell Bay where it has been exposed to view after previously being covered by other strata, now worn away.
    It is intriguing that so much of the formation at Mewslade remains sharp and well defined, as if someone has just taken a giant spoon and scooped out great chunks from the rock. Looking back over my photographs I can say that some outcrops have been indeed been smoothed out lower down the shore. I can also say that, as far as I can tell, there are not many pebbles or beach rocks at Mewslade (at least at the times my visits). They seem to be mostly confined to the narrow fault gully by which you access the beach from a walk down the valley from Middleton. Some of these pebbles originate from the fault breccia at that entrance point, while others are derived from the limestone quarrying and scree in the valley above. Even when the sand was temporarily washed away by storms some years back, it was mostly plain bedrock that was exposed without noticeable quantities of pebbles. So it looks like wearing down of the sharp edges of the formations is limited by the relatively few pebbles moving up and down with the tides, and tends to be restricted to a few minor areas which may also be covered by the waves. Sharp edges of rocks above the high tide and splash zone continue to be eroded by acid rain even if their original formation was many thousands of years ago as part of a palaeokarst surface.
    I hope this helps answer your questions. I am not a geologist either, but I am curious about the natural world and have a wish to understand.

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  6. Thank you, Jessica, for such a clear, detailed reply. I am sure you are right. I had wondered whether the shortage of pebbles at Mewslade might have been an explanation. I live in Newton, Porthcawl, and so my experience is of the constant pounding of pebbles on Newton Bay. There’s not a sharp edge to be seen!

    My visit to Mewslade on Wednesday was timed to coincide with the lowest spring tide and I was amazed at the rich variety of rock pool vegetation in the extensive pools off Tears Point – pools which are not often exposed. An example: https://www.geograph.org.uk/photo/6411856

    Thank you again for your help and expertise.

    Alan

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  7. You were lucky to explore the beach at that very low tide. Always a special event. There is indeed a wonderful array of seashore creatures and seaweeds at Mewslade, as at many other locations around the Gower peninsula. The Wormshead Causeway is full of life. I wish I could have been there for that low tide.

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