The terrible wet weather of last weekend provided an opportunity to witness close up the process which so significantly contributes to the wonderful coloured patterns in the sand at Rhossili, Gower. These patterns have been illustrated in earlier postings, and were very much in evidence following the recent stormy conditions.
Basically, the flat platform that runs along the foot of Rhossili Down contains red soil derived from Old Red Devonian Sandstone in the hill. The red soil and lumps of stone result from the shattering of this rock in icy conditions associated with glacial and periglacial events – eventually being washed downhill and seawards.
At first it would have formed a massive tongue of sediments reaching out into the bay. With time, the outward edge of this material has been eroded back by the sea. Today, it remains as a long narrow terrace with a soft, crumbling cliff edge.
In the top photograph you can see this cliff face with a face of eroding red soil sandwiched between the green turf above and the wind-blown sand below. The pebbles and cobbles below the sand would also have fallen from the cliff. During and after heavy rainfall, water seeps down through the sediments and carries some of these red pigments with it as it spills out onto the beach. The pigments are also washed down in streams. Here, the red slurry is forming dendritic patterns as the seepage runs over the dry beach sand.
The red particles normally mix evenly with the yellow sand grains and the black-stained sediments from below the surface. However, during the weather and wave-driven processes that stir up and redistribute the beach sands, the different grain sizes and colours can separate out again. Then they form an endless-seeming variety of designs in two or three dimensions.
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