Under the microscope the sandgrains are amber, gold, and white, and others are clearly tiny fragments of speckled granite; many are spherical, all are smooth, and their surfaces are opaque and abraded. In the second sample, the grains sparkle, sharp-edged, and are mainly of glinting transparent quartz, some stained ruby with iron salts. The samples were collected from the Solway coast at Allonby within perhaps 50 metres of each other, by my friend, the late Dr Michael Welland, a geologist who seemed to know everything about sand . The first sample was of aeolian – wind-blown – grains from the dunes at the top of beach; the second sample was of water-borne grains from the shore.
The very high spring tides of the past month, encouraged by low atmospheric pressure and strong onshore winds, have sliced into the faces of some of the dunes, causing the overlying mats of marram grass, sea holly and other salt-tolerant plants that stabilised those rolling, jumping sandgrains, to tumble onto the shore. And now the stories of the Solway’s geological past are revealed: a thick band of slippery grey glacial clay at the dune’s base, on top of which lies a dark band of peat in which, if you look carefully, are embedded the twigs and branches of the forest that covered much of this area 8000 years ago. Higher up the dune-face are more recent stories, layers of shingle separated by sand, the evidence of former beaches. I wish now that Michael and I had been able to take sand samples from these older shores, but their profiles were not yet visible on the day we visited.
On the computer screen Chris, a hydrographic surveyor, brings up and overlays coloured charts to show how the depth of water in the channel leading to the port of Silloth has changed between 2014 and 2015: the red and yellow blocks that indicate shallow water – sandbanks – shifted eastwards, almost obliterating the green and blue of the deeper channel, then moved back West again. The pilots who navigate ships to the port on the Upper Solway have to be very aware of the likely dangers. In autumn 2015 and further West on the Firth a giant jack-up barge has extended its legs onto the sea-floor; the upper sections of two wind turbines from the large Robin Rigg windfarm have already been removed and today its huge crane will lift out one of the remaining bases – now like an artificial reef, encrusted with sea-anemones and starfish and mussels. The turbines were unsafe because one side of the Robin Rigg sandbank has been eroded by the currents and the adjacent channel has deepened. The following year, and to the entertainment of ship-spotters, the molasses-bearing tanker, Zapadnyy, is grounded on an enlarged sandbank just West of the difficult entry to Silloth. (The ship is eventually pulled off that night during high tide.)
When I flew along the Cumbrian shore of the Solway in a gyroplane a few years ago – I wanted to get an aerial view at low tide of some important named stones and possible ancient fishtraps – I had not expected that over-flying the water itself would be so revealing and that so much of the Firth’s underlying structure would be visible: deep currents had braided greenish channels in the sandy sea-bed; huge sub-sea sand-waves were zebra-stripes of light and dark; the tops of sandbanks newly-exposed by the low tide rose glistening like surfacing whales. Of course I knew that the sea-bed was being constantly sculpted and re-sculpted, by the interaction of the tides and wind and the rivers that feed into the Firth; the Admiralty charts mark areas of ‘changeable depths’ and I’d felt it myself, in a minor but still unnerving way, when being guided across one of the ancient ‘waths’ or crossing places in the Upper Firth – the suck of the current, scouring away the previous solidity beneath each hesitant footstep. Now, though, to see the wide sweep of the patterns and colours of this mutability from above was humbling. I had long respected this huge estuary but that day I felt that I might have also begun – just a little – to ‘understand’ the Solway. For the Firth is nearly always referred to by its name, ‘the Solway’: it has such a powerful character that descriptions by those who work on its waters often use the words “aggressive”, “powerful” and “unpredictable”. The Solway makes the decisions about what will happen on its waters and along its margins.
Not only the dunes and the sea-bed, but also the present-day shore, are always changing. One Spring morning last year the normally smooth dome of the beach was patterned with broad horizontal lines, ochre and blue. Large sandwaves about half-a-metre high, looking as though they had been frozen in the act of rolling along the shore, had trapped water, now still, that reflected the blue of the sky. A curious mirage shimmered in the distance, a line of stick-like Lowry people floating above the sand. As I approached, the black forms resolved themselves into the periscope-like heads and necks of barnacle geese who had settled in a trough between the sandwaves. They watched me, then rose in a black-and-white sheet and beat away towards the dunes.
Beneath my feet the sandwaves were themselves embossed with sand ripples, their symmetry punctuated here and there with the holes and coiled excreta of lugworms. The varied patterns of the ripples are very photogenic and over the years I have photographed dozens of them. There are straight, evenly-spaced lines; bifurcating ripples that form small ‘cells’; ripples that overlap each other like fish-scales; ripples that are contrast-y stripes of black and gold, where finely-powdered sea-coal and mussel shells have accumulated in the hollows; there are places where the ripples have been smoothed away as though by the sweep of a mighty hand. Do ripples form when the tide flows in, or on the ebb? Can they tell us what was happening when the tide was inundating the shore? Experiments in labs, and observations, (see Solway Shore-walker) suggest reasons for the patterns – regular, straight ripples indicate quieter, more stable, conditions while others, for example, indicate a waning storm or changing wave frequencies as a storm arrives. The angles, the lengths, the height, all hint at the arguments between the water and the wind.
Even a rippled sandy beach might seem as though it’s a desert, empty and devoid of life, for how could anything that is alive make this shape-shifting and apparently inhospitable place its home? The intertidal zone especially is a challenging neighbourhood where organisms, animal or algal, are left exposed to the air and weather, then covered by the ebb and flow of a column of water – twice each day. Imagine living there on the sandy shore where, unlike on rocky shores, there are few places to hide. Sun, desiccation, rain, snow or ice; then salt water, containing suspended sediment, food, parasites and predators: there is so much uncertainty to contend with in this changeable physical landscape.
So, for many organisms, the answer is to live within the sand, or to move freely on top of it when the tide is in, or to engineer it to make a home. A fisherman is digging for bait, and he shows me the thick red lugworms writhing in the bottom of his bucket; he is using a fork because a spade would most likely bisect the worms he seeks, and some of the worms’ U-shaped burrows are still intact. Later I show a small group of 12-year-old boys an easy way to burrow. Despite the school’s advice they are wearing jeans and two are wearing white trainers but they gleefully imitate how I paddle my (welly-booted) feet up and down, turning the firm sand into a pool of slush. My feet sink in and I stand still, the sand setting firmly around my feet. The boys’ white trainers are now scarcely visible, and the bottoms of their jeans are wet and heavy with sand, but surely they will explain that ‘we were learning about thixotropy’ when they return home? In this way, by shoogling their bodies, the lugworms soften the sand to create their burrows, the walls of which they stabilise with a sticky layer of protein and carbohydrate. In contrast, the related and voracious ragworms with their busy ‘feet’ and sinuous bodies live mainly on the surface when the tide flows in, scurrying over the surface after small crustacea and other prey, then slipping beneath pebbles to sit out the ebb tide. The tracks they leave on the sandy surface are like those of mountain bikes, betraying a snap-shot of their earlier behaviour beneath the water.
And down towards the low-tide mark the honeycomb worms, Sabellaria alveolata, for which Allonby Bay is famous, use the sandgrains on the shore to create their own fine dwellings: high-rise blocks, tenements and crowded estates, constructed by creatures without eyes and using tentacles for hands. When the tide covers them, each tiny worm reaches out and selects sandgrains of the right size, and glues them edge to edge to form a delicate tube; side by side, the worms build their tubes to form strong and sculptural reefs. They extend their crowns of tentacles and trap food from the passing currents – and when the tide ebbs, each retreats to the bottom of its tube. Together, they are eco-engineers, stabilising their unstable surroundings. Their reefs trap the outgoing tide to form shallow lagoons where other animals and sea-weeds flourish; half-buried mason worms, Lanice, protect themselves in messy tubes of sandgrains and broken shells; sea-anemones, Urticina, burrow in the sand and hide their exposed surfaces with sand and débris (but the symmetry of the disguise gives away their secrets); tiny flatfish change colour to mimic the patterns in the sand.
The recent storm surges that sliced the dune faces and exposed the Solway’s past also churned and re-distributed the sand on the shores. Parts of the Sabellaria reef have disappeared beneath new deposits, and the tubes of many have been fractured – but those worms that have not been suffocated by sediment will repair and rebuild, and next Summer new planktonic larvae will arrive on the tide and join the construction site. The sand that has been scoured from Allonby’s shore has been swept up the Firth; the sandbanks off Silloth are growing, and the saltmarshes will have received new deposits to increase their height. Whether the shipping channel has changed will be checked by the ships’ pilots as they navigate up to the Port, but more accurate, computerised charts from the hydrographer’s echo-sounder will have to await calmer weather. Local people worry about the economic and social losses due to erosion of the dunes that protect the narrow coast-road. Meanwhile, the dwellers in the sandy shores and the animals and micro-algae of the mudflats, move home, multiply or succumb to the loss of their shelters – unnoticed by the humans who share their neighbourhoods.
Ann Lingard is a former scientist, and a novelist, and writer of non-fiction. She runs a small-holding in north west Cumbria within sight of the Solway Firth and in non-Covid years leads low-tide walks on the Solway shore. She blogs about the Solway here and her latest non-fiction book is The Fresh and the Salt. The Story of the Solway, published by Birlinn Books in September 2020. Follow her on twitter.
The photograph at the head of this essay is by Andrew Lysser. The remaining photographs are by the author.