Pebbles, spits & banks at Whiteford (2)

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At the remotest end of the Whiteford National Nature Reserve is a tranquil place where wild ponies and sheep graze. Here, you can find clues to the geological past of the area and observe evidence of current geological processes that will change and shape its future appearance.

Beneath the 3 Km length of the dune-covered Whiteford Burrows, lies a spit of  glacial till deposited by the ice sheet that once occupied the Loughor valley in the late Devensian period of 17000 years ago. These boulders, cobbles, and gravels were scooped up by the scouring action of the thick and heavy layer of ice as it extended downwards and outwards towards the sea. They can be seen outcropping between Whiteford Point and the old derelict Whiteford Lighthouse.

Despite subsequent sea level rises and falls, the deposit remains more or less intact. In some rocks there is evidence of ancient frost damage * from the ice sheet. Such damage facilitates the eventual break up of the rock into smaller, often flat, pieces. Once loosened, these smaller pieces are rolled around by the tides – thus acquiring rounded edges.

These pebbles have washed out from the original galacial deposit to form the base of a further spit that extends eastwards from the Point. Most of the time the pebbles here are covered by sand but they are sometimes visible as a band of stones at the top of the tidal reach especially when stormy waves have licked the sand away.

The pebbles within these exposures (of  the spit’s foundation) frequently appear to be layered or orientated in curving lines – reflecting the direction of the currents that carried them into position. In one particular place there is an additional recurved spit of pebbles, never covered by sand, pointing inland rather than offshore.  This is near to a branch of the Burry Pill stream that drains Landimore saltmarsh.

I am not certain what accounts for this structure because it looks as if  some sustained power would have been needed to create it. The sea does regularly cover the marshes but mostly creeps slowly up as the incoming tide combines with the outgoing estuary waters to raise the water level. I wonder whether the recurved pebble spit forms in extreme storm conditions when the sea takes a short cut across the main sand-covered spit. There is certainly a lower area of damper ground that could provide such a route.

* See the following post for more about frost-damaged rocks at Whiteford.

If you would like to read in some more detail about the geology of  this area, I would recommend two publications:

Classic Land Forms of the Gower Coast by E. M. Bridges (1997) published by the British Geomorphological Research Group and The Geographical Association. ISBN 1 899085 50 5

Carmarthen Bay by V. J. May (2007) Vol. 28: Coastal Geomorphology of Great Britain. Chapter 11: Coastal assemblage GCR sites. Site: CARMARTHEN BAY (GCR ID: 2102). Extracted from the Geological Conservation Review. 

 

COPYRIGHT JESSICA WINDER 2012

All Rights Reserved

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