Hill End to Spaniard Rocks & Back: Step-by-Step Part 7

Walking back from Spaniard Rocks now, I took a route closer to the dunes where the character of the shore is quite different from the wet sand and strandlines between high and low tide levels. Here there are pebbles. Rhossili’s pebbles intrigue me. I love scrambling over the banks of stones at the very top of the beach. The colours are lovely pastel shades with pinks and blues and overall reminding me of sugared almonds. A total delight. Many rock types are represented. Some have interesting patterns.

I like the way that the numbers of beach stones seem to increase or decrease depending on how they are pushed around the shore between one visit and the next, and how the sand changes its level and distribution throughout the year and the transition from season to season. This time the wooden ribs and keel of the shipwrecked ketch Anne were only just visible above the sand and pebbles. I like the way that pebbles are arranged partly buried in the damp sand that quickly dries to a different hue and texture. The pebbles underlie the tall sand dunes of the Llangennith Burrows. The dunes have been scooped out by stormy seas and footsteps in many places to demonstrate that even wind-blown sand is stratified; and marram grass roots exposed to air show how deep they penetrate the soft fine sediments to bind them together and stabilise the dunes.

Sand Dune Erosion at Whiteford

Sand dune erosion at Whiteford Sands on the north Gower coast in South Wales

Shorelines evolve. Changes happen – sometimes slowly and sometimes quickly. The winter of 2013 to 2014 brought severe storms and winds that impacted on all our British coastlines. Whiteford Sands on the north shore of the Gower Peninsula in South Wales was no exception. By May 2014 a dramatic change in the long line of dunes bordering the sands was clear to see. The dunes have been fixed for a long time with the outer slopes stabilised with marram grass, and a turf covering further inland. Small changes had been occurring steadily for many years with a gradual wearing away of the dunes.  High tides and extreme weather events had been nibbling at the seaward faces. The erosion process has not been continuous but interspersed with periods of accretion both by water-borne and wind-borne sand.

The sand was originally deposited by a melting ice sheet in Carmarthen Bay, including the Loughor estuary on which Whiteford Sands is situated, and at Pendine Sands and Rhossili Bay. The first direct evidence for glaciation on Wales dates to 480,000 years ago in the Anglian Stage of the Pleistocene in the Quaternary Period when ice sheets enveloped Wales and the adjacent sea. The last ice coverage in the region was the Late Devensian Era about 24,000 years ago. There seem to be only minimal additions to the sand deposits from local sources since then because the Carboniferous limestones of the area dissolve rather than disintegrate into particles or grains. The sand is a therefore a finite resource albeit one that is controversially exploited locally by dredgers on the Helwick Bank just off the tip of Gower.

The sand is basically mobile within the area on the shorter and longer timescales. A useful and interesting research report on this subject is that by V J May on Carmarthen Bay in the Geological Conservation Review in which the sediment transport around the region is discussed. Figure 11.12 presents a sketch map of the key geomorphological features and sediment transfers of Carmarthen Bay. Figure11.13 depicts variations in accretion and erosion since 1950 in Carmarthen Bay. Figure 1.17 illustrates geomorphological features of Rhossili bay and Whiteford Burrows. The report records how and in which directions the sand is being shifted by river/estuarine currents, onshore and longshore drift; and where attrition and accumulation of sand is most marked. It is an intriguing read and gives much to elucidate the field observations I have been making in the area over the last decade.

Shoreline Changes at Llangennith Burrows – Part 1

Sand dunes at Rhossili in May 2012

When there are especially dramatic events, like the severe winds and storms of last January and February, that destroyed coastal railway lines, caused major landslips, created disastrous flooding, and removed entire beaches of shingle and sand, everyone becomes aware of how vulnerable our coastline is to extreme weather events. However, visiting the same seashore locations many times over the past ten years, and making a detailed photographic record of animals, plants, sediments and rocks, has enabled me to see changes gradually and steadily taking place as well as resulting from these recent extreme events.

This is the first in a series of posts about changes in shoreline topography, sometimes due to accretion of sediments, sometimes resulting from erosion, that have been changing the way the seashore looks. These changes have an impact on the whole coastal ecosystem, affecting plant communities, the invertebrates that colonise the seashore, and the people who use and enjoy the shorelines.

I have been trying to find among the many images in my collection, those which show recognisably the same place, to illustrate what the location looked like originally, some of the details of the transition if any, and what the location looks like now. In this post, the location is the seaward-facing sand dunes belonging to Llangennith Burrows, at the north end of Rhossili Beach, approaching the tidal island of Burry Holms. The position is “fixed” by a vertical wooden sign indicating one of the designated footpaths that cross the Burrows.

In the first photograph, shown above, the wooden post has had some bright orange plastic flotsam tied to it with rope, to increase its visibilty from low on the sandy beach. The picture was taken on the 16th May 2012. Wind-blown dry sand forms a continuous and gradual incline from the shore to the top of the dune. The dune is stabilised by marram grass. Pebbles at the base of the dune are only just visible beneath the layer of sand. The footpath passes to the right of the signpost, forming a shallow depression on the sky-line.

The image immediately below shows the same location two years later on 6th May 2014. The signpost lacks the orange flotsam now but the footpath can still be seen to the right of it, forming a steep gouge in what remains of the dune. The seaward face of the dunes has been reduced in places to a near vertical surface showing stratification of the established dune. Mobile sand deposits are almost entirely absent. Much of the marram grass has fallen down as turf clumps or disappeared. Pebbles are clearly exposed at the base of the dunes.

Sand dunes at Rhossili in May 2014

Of course, the changes started long before May 2012. The sea has been nibbling at the compacted sand of the dunes for a while, and in between times, the loose sand moves in, out, and all around the beach, sometimes from day to day, and even from tide to tide. However, the hard stratified sand in the dunes has been steadily and inexorably receding. The following pictures show in a bit closer detail what the same area of the Llangennith/Rhossili dunes was looking like at one point (12th December 2012) in the interim period between the times that photographs 1 & 2, and 3 & 4  were taken.

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