A wide and shallow river flows over the sandy beach at Ventry Bay on the Dingle Peninsula in Ireland. I do not know its name. Characteristic ripple marks are made in the wet sand around the margins of its wandering channels, showing the influence of the freshwater currents modified by the sea water tides. As you walk away from the fast flowing water, the overlapping ‘leaf’ patterns made by the river currents gradually transition into the parallel ridges of wave-induced ripples that are more typical of the intertidal shore .
Patterned Sand 8 – 14: Naturally formed patterns of black sediment on yellow sand were photographed on the beach at Rhossili Bay, Gower, in April 2017. The black sediments were mainly composed of minute pieces of rotten wood, coal dust, and miniscule fish bones, with a small proportion of seeds. The images have been digitally colour-enhanced to emphasise the patterns of this natural abstract art.
Patterned Sand 1-7 – Naturally formed patterns of black sediment on yellow sand were photographed on the beach at Rhossili Bay, Gower, in April 2017. The black sediments were mainly composed of minute pieces of rotten wood, coal dust, and miniscule fish bones, with a small proportion of seeds. The images have been digitally colour-enhanced to emphasise the patterns of this wonderful natural abstract art.
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.
As my walk continued from Hill End northwards on Rhossili beach, the dark drift patterns and fine strandline debris covering the sand eventually faded away to be replaced by dry sand ripple and swash/backwash patterns before arriving at the extreme north-east corner of Rhossili beach. This is the place where much of the flotsam ends up. It is not that Gower visitors are careless with their trash. Most of this stuff comes from far afield – sometimes as far away as South America. It does get periodically cleared away but is difficult to manage because the rubbish arrives and leaves with each tide, and can get buried or revealed from one high water to the next. Bicycle wheels, brightly coloured plastic pieces, fishing net and ropes, toothbrushes, balloon stoppers, and flip flops are common items along with the driftwood. The pile of organic and plastic rubbish lies adjacent to Spaniard Rocks which connect the tidal island of Burry Holms to Llangennith Burrows.
The geology here is interesting but on this occasion I focussed on the seaweeds which attach to the rocks along the water-filled channel between Burry Holm and Spaniard Rocks. There are many types intermingled. They include amongst others the brown Fucoid algae such as Toothed Wrack (Fucus serratus) , Spiral or Flat Wrack (Fucus spiralis), and Egg or Knotted Wrack (Ascophyllum nodosum). Bladder Wrack or Pop Weed (Fucus vesiculosus) was also present but not in its typical form. The numerous small, paired, almost spherical air bladders typical of the species were few and far between on specimens in the area where I was looking – so that there is confusion in my mind as to the identity of some of the weed I have named as Spiral Wrack.
There were also some red algae of the thin bladed type that dry out between tides into blackened streaks on the rocks (of the kind to which the lavabread seaweed belongs). Another red alga was the Sand Binder seaweed (Rhodothamniella floridula) which forms small humps of fine filaments trapping sand grains on rocks low on the shore; it is often found beneath the taller stalked fucoids. Finely branching red Polysiphonia lanosa was epiphytically attached to the Egg Wrack.
Of special interest this visit was the fact that the seaweeds were getting ready to reproduce. The Spiral Wrack had swollen receptacles on the forked frond tips that were not fully ripened yet. However, the Egg Wrack was ready to go. It has separate males and females. The male receptacles are bright golden green studded with orange pustules (conceptacles) that release a colourful fluid containing the sperms. I had seen these and reported on them before. This time I also saw the female receptacles which were dull green and covered with minute darker almost black blisters (conceptacles) containing the eggs. It almost seems as if you can see the eggs when you zoom in on the picture – actually just the light bouncing off the ripe eggs within the pustule.
As I walked further along the beach from Hill End to Spaniard Rocks, I realised that there were maybe four or five strandlines lying parallel to each other and to the water line. Each line of mainly organic debris was slightly different in its constituents. Similarly, there were changes in the make up and proportions of the animal and plant debris in the strandlines in a linear way as I walked from south to north along the shore. The starfish became less numerous and the numbers of bivalve molluscs and their shells increased,
Most noticeable was the way in which the darker particle component of the strandlines became separated out on the up-shore side of the lines, and formed patterns contrasting with the yellow sand on which it lay. Sometimes there were branching lines of clear spaces, like rivulets running through the black stuff. Sometimes, the black pieces followed and echoed the shallow ripple marks in the sand – either as parallel lines or cross-hatching designs full of beautiful natural abstract compositions. In other places, small obstacles such as seashells had formed little dams to impede the flow of lighter, darker, material as the water that carried it swashed and backwashed over the beach, and this had created distinctive patterns as the water flowed around the barriers.
I was curious about what made up the fine black material responsible for the patterns. I took some samples to look at under the microscope when I got home.
Some more images showing the subtle colour transitions and delicate branching patterns that characterise the low relief natural sculptures in the fine clean sand on the shore near Picquerel Point at Grand Havre in the Channel Island of Guernsey. The dendritic patterns have been created by sea water draining down the beach as the tide recedes; and this has led to a sorting out of particles by size, weight, and colour. The darker sediments that outline and emphasise the design may be organic remnants or different darker minerals. These patterns are the best of their type that I have seen – perhaps due to the very fine sand. The patterns are so delicate they could almost be drawings.
Click on any image to view in larger format in a gallery.
Subtle colour transitions and delicate branching patterns characterise the low relief natural sculptures in the fine clean sand shown in this photograph. It was one of many taken on the shore near Picquerel Point at Grand Havre in the Channel island of Guernsey. The dendritic patterns have been created by sea water draining down the beach as the tide recedes; and this has led to a sorting out of particles by size, weight, and colour. The darker sediments that outline and emphasise the design may be organic remnants or different darker minerals. These patterns are the best of their type that I have seen – perhaps due to the very fine sand. They look like pencil sketches. I am definitely going to frame some of the images.
The shape of natural abstract sand sculptures, like these ripples on the seashore, result from complex interactions of water and substrate which are the subject of much research in the field of fluid mechanics. They are described as “small-scale three-dimensional bedforms due to interactions of an erodible bed with a sea wave that obliquely approaches the coast, being partially reflected at the beach” (Roos & Blondeaux 2001). Different combinations of three main perturbation agencies create different ripple designs.
Roos, P.C. and Blondeaux, P. (2001) Sand ripples under sea waves. Part 4. Tile ripple formation, J. Fluid Mech. vol. 447, pp. 227-246.