Late last year, I reported in a couple of posts on my visit to Cumbria and the Solway Firth. The first was a description of the appalling floods that had just occurred and the second, following my ramble on the beach with my host, writer Ann Lingard, was a guest post from her. Now, she has recently written a piece for Cumbria, “Lakeland’s favourite magazine,” and it gives me great pleasure – and great memories - to reproduce it here as another guest post.
THE GROUND BENEATH YOUR FEET
THE SANDY SOLWAY SHORE
It's easy to take the Solway's sandy shores for granted: sand, sea, and sometimes sun -- life's a beach, isn't it?
But walk across firm damp sand at Mawbray or Beckfoot, say, and you will see that your footprints have left pale dry treads that quickly darken again with water. Or stand still and stamp your feet up and down, like a seagull 'paddling' for earthworms in a field - and in less than a minute the firm sand turns to 'quicksand' and your feet start to sink as water wells up around them.
Sand mixed with varying amounts of water has strange properties, as sand-sculptors and sandcastle builders know. Sand grains that have settled through the water, like those in the intertidal zone on the beach, become very well-organised and closely packed. When you walk along the beach, you tread on that orderly arrangement and disrupt it and, completely contrary to what you would expect, the spaces between the grains expand. Water drains down into the gaps, so that on the surface your footstep appears paler and drier. Continue paddling in one spot and you enlarge the gaps between the grains, so that more and more water flows in and pushes the grains apart, forming a slurry of quicksand - which may then seize up solid again and cement your ankles in place!
Every time I visit the Solway the shore looks different, as the tides and wind constantly scoop and re-sculpt the sandscape, whether between the tidemarks or higher up, on the edges of the dunes. Longshore drift, the direction in which the tide and waves travel up the coast from Liverpool to the upper Solway, brings animals and objects from further South -- including all kinds of unexpected things washed down by the River Derwent in the terrible November floods. Sometimes the current creates large 'sand-waves' to mark its progress, the hollows between them trapping pools of water when the tide goes out.
But it is in the mid- to lower-shore that the sandscape becomes staggeringly varied and beautiful, the patterns of ripples changing from metre to metre, locked into their patterns until the tide comes in again to re-mould them. Chevrons, fish-scales, dimples: you look around and there doesn't seem to be any logical reason why the ripples near your feet should have a rounded profile but ripples a few metres away are taller and sharper, or closer together. Some ripples, often those nearest pools, have tiny gullies on their faces, perhaps where water drained down and eroded them as the tide went out.
Do the ripple-patterns form when the tide comes in or when it goes out? Do they form and reform all the time they are submerged, according to the ebb and flow of the water? The shore is a good place for stimulating simple questions.
A few years ago, I took some Year 7 and 8 students to look at 'the science of the shore', and a couple of the boys (part of a group who experimented very vigorously with quicksands - to the extreme detriment of their white trainers) became really hooked on trying to find out how sand ripples formed. I thought it would be easy to find an answer -- but was intrigued and even excited to discover that nobody seemed to know. I asked physicist Philip Ball who has written three excellent books on patterns in nature, and geologist Michael Welland who has written a fascinating book called 'Sand, a journey through science and the imagination'; but they both agreed that science has only found partial answers at best.
Michael Welland had been here in West Cumbria to talk to our Cockermouth Café Scientifique, and we had all enjoyed a very entertaining evening with his practical demonstrations of some of the strange properties of sand grains. So I was especially pleased to be able to take him down to Beckfoot the following morning - here, especially, some of the ripple patterns are spectacularly contrasty, the valleys between the ridges being accentuated with a fine black sediment of powdered mussel shell, thrown up from the vast mussel beds on the rocky scars lower down the shore.
And at Beckfoot, too, there is the added delight of walking on the dunes, on sand that was piled and sculpted by the 'aeolian' effect of the wind. Sadly, the seaward side of this nature reserve, part of the Solway Coast AONB, is being continually eroded; the biggest tides in the Solway can rise and fall by as much as 10 metres and if the barometric pressure is low and the wind is strong from the South-west, the waves pound high up on the shore, battering the free edges of the dunes so that large vegetated plates from their margins tumble down onto the sand. But the erosion at least gives you the chance to look at a cross-section through the dunes, to see how they have grown over hundreds of years: the alternating layers of pebbles, sand, dark organic layers of earth and rotted vegetation, more pebbles, more sand -- and the youngest, upper surface bound together by marram grass, silvery sea-holly and other dune vegetation.
If you take a box of muesli and shake it, the biggest heaviest pieces rise to the top - the 'brazil nut effect'. So it is with sand grains of different sizes - they sort themselves out according to size, under the stirring effect of the wind or of water. And the agitation by wind or water has other effects too, a weathering effect so marked that you can tell (with the help of a magnifying lens) whether the grains were deposited in a river-bed or on a dry plain. As we wandered along the beach on that breezy day, Michael took small samples of sand from the shore and from the dunes. A few days later he sent me photographs of the samples as seen through his microscope.
The sample from the dune is full of beautiful rounded and frosted quartz grains, typical of sand blown in the wind; it also contains quite colourful metamorphic rock grains, presumably from the Lake District. The beach sample in contrast is very fine grained and angular, with lots of quartz and colourful rock fragments; sharp-edged and fairly typical of water-borne sand.
So, next time you wander along the beach at Allonby, enjoying one of Twentyman's icecreams, think about the sand beneath your feet. And build a large sandcastle.
[Ann Lingard's latest novel, The Embalmer's Book of Recipes (Indepenpress 2009}, which is set in Cumbria, is available from all good bookshops; see www.annlingard.com for related pictures and reviews. For details of Cockermouth's Cafe Scientifique: www.cafescientifique.org . Sand grain photos by me, others copyright Ann Lingard]