The making of the Solway Firth

Why is the Solway Firth - which is shared by Scotland and England, but has its own unique character – such a special, and changeable, stretch of water?

The Firth from Gretna to Maryport (from Google Earth)

Over the years I have talked to many people who live and work along the margins and on the waters of the Firth: lifeboat crews, harbour-masters, skippers, ships’ pilots, geologists, hydrographical surveyors, conservationists, haaf-netters, and people whose families have lived by the shore for several generations. I've also explored the Firth from the air, on the water, along the coasts - and have even walked across it.

Much of what I have learnt is expanded on elsewhere in this website and on my Solway Shore-walker blog, but this 'story' and the next, The re-shaping of the Firth, will, I hope, help to explain why people love - and respect - these waters and the shores.

'Solway Sunset'. Copyright James Smith Photography, and with thanks.

What do people say about the Solway?

Beautiful”, “glorious sunsets”: these are benign and gentle characteristics of the greater landscape. But ask people about the sea itself, and you only hear awed respect:

Tim Morgan, Plant Manager for E.ON's Robin Rigg windfarm calls it “chaotic and unpredictable”.

Colin Sharpe, Development Manager at Port of Workington says it is “one of the most aggressive estuaries in the UK.

Marine biologists at Natural Power refer to it as a “highly dynamic estuarine environment.”

David Smith, Visiting Professor at Oxford University’s Centre for the Environment, told me, “I don't know of another estuary like the Solway where so much sediment is available for distribution”.

'Changeable Depths': Portion of Admiralty chart

Eddie Studholme of Silloth RNLI: "The environment is very, very unpredictable, it’s uncontrollable."

A Joint Nature Conservation Committee document more prosaically describes it as “a natural estuary system substantially unaffected by human activities, such as industrial development and dredging. The Solway is an unusually dynamic estuarine system, with mobile channels and banks.

Admiralty charts show large areas marked as ‘Changeable Depths.

Was it always like this? What was the embryonic Firth like and how did its body and character develop?

'In the beginning ...'

We can try to imagine what this great estuary looked like in its early days. We, humans, would not have been here. Approximately 20,000 years BP (1), there was no Firth – indeed there was no Irish Sea. The whole area was enveloped in ice which flowed southwards through the Irish Sea as far as the Scillies. At that time the level of the sea beyond the ice margin lay a much as 130 metres below its present level.
When the climate warmed, the ice melted, releasing mighty torrents of fresh water that gouged out valleys and flowed down into the oceans. The sea level rose, pushing coastal margins ever further inland, splitting off islands and drowning valleys (there’s a helpful animation, about the ‘birth of the Mersey’ here).

But glaciers are weighty masses of ice and rock and, as they melt, the land is released and it ‘rebounds’, rising out of the sea.

Professor David Smith puts it eloquently: “The subsequent story of the Solway is one of competition between rising sea and rising land, slowing in rate towards the present, so the changes become progressively more subtle.”

This subtlety and complexity has characterised the development of the Solway Firth, as Smith and his colleagues have found during their extensive field work along the Solway’s Scottish coast (2). There, around the rivers Nith and Cree, the remains of raised beaches -  20-25 metres above Ordnance Datum (3) - show the height of the sea’s incursion about 14-15,000 BP.
At that time the Solway Firth would have been very much wider than today, and torrents of grey, gritty meltwater would have flowed into the sea from the melting ice at the head of the Firth and from the Nith and Cree valleys.

An inhospitable climate: no Mesolithic settlers would have ventured so far North to watch.

Glaciers melted; glaciers briefly re-formed.
The climate cooled again – the ‘Loch Lomond Re-advance’: small ice-caps formed world-wide locking up fresh water. There were glaciers in the ‘Galloway Forest Park’ area and in the ‘Lake District’, and the sea-level was much lower than in the present day. Humans had abandoned chilly Britain for Europe.

Between 11700 BP and about 7000 BP, though, renewed warming caused glaciers to melt yet again and the ‘re-bound’ of the land at times outpaced the rising sea level.

Mudflats and saltmarshes

The edge of the saltmarsh near Campfield RSPB Reserve

Thus, land exposed each side of the Solway as the estuary narrowed, became fringed by mudflats. Saltmarshes developed, edged by reed-swamp, then by salt-tolerant shrubs, then trees: cold-climate vegetation at first, but succeeded by alder and willow carr, birch and oak.

David Smith told me, “The saltmarsh areas would have become less steep as tides deposited sediment amongst the vegetation. As sea levels continued to fall, peat developed across the inland margin of the saltmarsh and reed-swamp so that in turn, the vegetation succession migrated seaward.”

How wide was the Solway at this time?

“I would hazard a guess at less than 10km between Southerness Point and Silloth and certainly less than that between Caerlaverock and Silloth, and there would have been areas of saltmarsh across the mid-channel mud and sandflats we see at low tide today," says David Smith. "People could therefore have walked to the edge of the river channels, but still would have had to cross the diminishing mudflats (the slopes there would have been steep because of the tidal range) to cross the channels.”

Tree-trunk in peat, part of the 'submerged forest' on the Beckfoot shore

The Solway was a narrower estuary than before; but still the competition between sea and land continued.
And on land the torrential rain had encouraged the spread of sphagnum moss, the waterlogged trees had died, vegetation was compressed and became peat ...

It would seem that by about 7000 BP the sea had won the competition; the forest and the peat had been submerged.

The sea crept in across the soggy land, bringing its own biosphere, and land-based life retreated from the edges.

Dune face near Allonby, showing changes in the levels of the shore (and sea)

The Firth grew wider, deeper - by 5500-4500 BP, its mean tide level was about 10 metres higher than today. The ‘Twenty-five foot beach’ on which the coast road between Allonby and Silloth has been built, and the faces of eroded dunes, show stages in the story.

Flint artefacts and axe-heads, the remains of hearths, an enclosure with post-holes at Plasketlands near Mawbray, a trackway of birch branches across the Nith just North of Glencaple – these show that people were living and moving around the area on both sides of the Solway, between the shores and rivers. They would have watched the tides, fished the rivers and sea, roamed the sand and shingle and Galloway’s rocky shores.

And each time they returned, generation after generation, they would recount stories from their collective memories how the high-water mark had retreated lower and lower down the shores, exposing more land, building new marshes at its edges.

Gradually, the sea-level dropped to its present height and the Solway began to look something like it does, in outline, today.

Chaotic’, ‘dynamic’, turbid with sediment...
Even if its main design was becoming fixed, the Firth’s internal configuration would still have been changing rapidly. As they do today, tides and storms would have been energetically and continuously redistributing the sediment and gravel, and the rivers would have been shifting their courses.

Today, rivers still seize stones and sediment during every storm and dump it where their fresh water meets the sea. Estuarine ports, part-suffocated by mud, require days of dredging.

The sand and gravel

At Fleswick Bay, between the two red Heads of St Bees’, multi-coloured pebbles are slippery ball-bearings underfoot. On Allonby Bay large rounded granite pebbles, Ennerdale pink and Criffel white, lie next to smooth Skiddaw slate, mica-glittery discoids of New Red Sandstone and irregular lumps of cloudy feldspar.

Elsewhere on the shores, there are slippery grey or rough red clays, fine brown or yellow muds, pale sand grains, small black fragments of coal.

The sand and silt and pebbles are a mix of sedimentary, metamorphic and volcanic rock - stories of the rich history of the land.

These stories have come from all directions: glaciers grinding down rocks to the North and East and South, meltwater torrents and rivers gouging out channels; the sea pounding and fragmenting the rocks along the shores. 

'Hanging Stone' at the edge of Dubmill Scaur

Glaciers have left ‘fossil’ gravel banks by the Rivers Nith and Cree, and the curved peninsula of Grune Point.

Nellie, Pintle, Maston and Hanging Stone - it was the glaciers, too, that abandoned these 'erratics', these huge boulders with their own names and characters that are scattered along Allonby bay.

And there are more recent stories: pebbles, moss-green and pale-sky-blue tell of discarded slag from West Cumbria’s iron- and steel-making past. Stories of storms, and human discards - flotsam thrown up on the shore, pushed into the Firth by longshore drift: even, after 50 years, the propellor of a Lancaster bomber downed in the sea near Millom.

Groynes at Silloth

Wooden groynes  try to contain this north-easterly drift, but as the waves suck and push, the current forms whorls between the barriers. Pebbles are sorted by size, their weight straining against the wood.

The brown flood tide deposits its sediment on the saltmarshes. Rockcliffe Marsh inches outwards between the Rivers Eden and the Esk.. The routes of the centuries-old waths slowly disappear.

(1) BP: Years Before Present, as measured by corrected radiocarbon dating
(2) Holocene relative sea-level change in the lower Nith valley and estuary (2003) David E Smith et al. Scottish Journal of Geology 39, (2), 97–120
Holocene relative sea levels and coastal changes in the lower Cree valley and estuary, SW Scotland (2003) D. E. Smith et al. Transactions of the Royal Society of Edinburgh: Earth Sciences, 93, 301-331
(3) OD, Ordnance Datum, is Mean Sea Level at Newlyn, Cornwall (ie the same as heights on land); CD, Chart Datum, is the level of the lowest astronomical tide, used for navigation purposes

(C) June 2016

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