The Scottish coast is renowned for the wealth of its rocky features. And if you can’t abide Geology, you can while away the hours with the local marine biology. It’s dead quiet and if you’re lucky on a clear day, you might even see Arran magically emerge from the mist across the waters of the Clyde estuary.
The Firth of Clyde encloses the largest and deepest coastal waters in the British Isles. It is an inlet of the Atlantic Ocean, off the southwest coast of Scotland, named after the River Clyde which empties into it. The firth enjoys the climatic benefit of the Gulf Stream from America.
Around the Clyde’s estuary, Ayrshire is a large farming region located directly on the Scottish west coast, directly adjacent to Arran, an island popular with visitors, famous for its food delicacies, walking, golf and geological pursuits.
Indeed the local geology is erm… pleasingly complicated.
Rocks contain a narrative of the Earth’s history. They contain information on past climatic conditions, fossils that reveal the story of life and evolution.
Over hundreds of millions of years, the surface of the Earth is rearranged by the slow grind of geological processes. Given enough time, the powerful results include the generation and destruction of mountain ranges stretching across the continents, and the opening and closing of oceanic basins.
About 400 million years ago, a huge mountain range formed, similar in size to the Himalayas, which covered the northwest of Britain. Wind, weather, ice and rivers eroded the mountains, and formed sediments: sand and mud that gathered at the bottom of the sea and lakes over 40 kilometres thick.
During the Late Tertiary Period, between 52 and 2 million years ago, the ongoing effect of lava pressure from below was to push the Earth’s crust upwards along the west of Scotland.
Over the next 50 million years, the powerful forces of erosion removed much of the surface layer of young rocks from Ayrshire. Sediments were washed away swiftly by powerful river systems. Jumbled chunks of relatively young Jurassic rocks and chalk are found in the ‘Central Complex’ of Arran, unusually protected from erosion by the older rocks there.
A few curious reminders to help geologists work out what happened here…
Land of Ice
From the Quaternary on, Scotland continued drifting northwards to arrive at its present position. By this time, the climate had entered repeated cycles of warm and cool periods, each lasting about 100,000 years.
These cycles were becoming more pronounced. About 20 cycles in the last 2 million years have plunged Scotland into successive ice ages.
A cold spell meant that snow falling on the Grampian Highlands and the Southern Uplands in winter could not melt before the snows came the following winter. Snow began to compact under its sheer weight, and built up to huge thicknesses. Much of it moved eastwards into the North Sea.
The entire area of the Firth of Clyde was buried beneath ice estimated to have been about 5,000 feet thick here when at its maximum extent between 22,000 and 18,000 years ago.
On the west side of Scotland, Ayrshire was in the front line, because ice from both north and south converged here, before heading in a south-westerly direction.
The now uninhabited Ailsa Craig island stands in the outer Firth of Clyde. It is formed from the volcanic plug of an extinct volcano. The special nature of its rock – an unmistakable blue hone granite – was useful in tracing these ice movements. Indeed boulders of the Craig have been found in parts of England and Wales, and at Cork harbour in south-west Ireland, having been carried there by the ice.
Fourteen thousands years ago, rapid warming caused most of the ice disappeared. Then, 11,000 years ago, it got colder again, just for a thousand years: the Loch Lomond re-advance.
One possible explanation for this is very relevant to us today. Huge amounts of freshwater from melting ice may have lain over salty water and blocked off the Gulf Stream, which keeps the west coast a couple of degrees warmer than the east. As the Ayrshire region relies on that warm Atlantic ocean current to prevent it from freezing up every winter, there are fears that today’s global warming could once again switch off the current, tipping us here in Scotland into another Ice Age!
Submergent and Emergent Coastlines
Glaciers and ice sheets fundamentally changed the landscape 20,000 years ago, profoundly affecting what lies beneath our feet and underwater. The evidence is the deep rock basins that were cut into the sea bed around Arran.
Both land and sea level fell. The enormous weight of ice pushed the crust of Scotland downwards. Sea level also dropped as huge amounts of water became trapped in ice. But the land dropped a little farther and the waves started pounding at a higher level along the coast during periods of Ice Age.
The result has been a series of wave-cut platforms, ‘raised beaches’, hollowed caves and sea stacks visible all along the Firth of Clyde and Ayrshire coast, indicative of a previously higher sea level.
Formation of Drumlins
As glaciers moved from highland areas across Ayrshire, billions of tons of rock debris was picked up and then dumped across the lowlands. Much of the soils of Ayrshire are predominantly glacially deposited sediment. Some contains marine shells, indicating that some ice must have moved from the sea onto the land.
Ultimately, these glacial sediments were pushed by the remaining ice into low mounds called ‘drumlins’. These rounded hills occur all over Ayrshire.
Drumlins (or ‘rôches moutonnées‘, because they look like sheep lying down) are geological formations, created by the passing of a glacier. The passage of glacier ice over underlying bedrock often results in asymmetric erosional forms, as a result of abrasion on the “stoss” (upstream) side of the rock, and plucking on the “lee” (downstream) side. These erosional features are seen on scales of less than a metre to several hundred metres.
Soon after the retreat of the ice, the surface of Ayrshire was covered by birch forest. Temperatures kept on rising, and oak, ash and elm trees took over the land. These forests helped to make the material deposited by the ice more fertile, by adding humus.
Less than an hour away from the bustling Glasgow, the beaches of Ayrshire are within easy reach. And you don’t have to be a geologist to enjoy the craggy and raw beauty of the coast. Nor do you need to be a botanist or a marine biologist to appreciate the abundance of natural features present on the seashore.
Between Ardrossan and Largs, the villages of West Kilbride, Seamill and Portencross make up a ‘small town’. Each one with its own unique charms and history.
Portencross and its medieval 14th-century castle, lies to the northwest along the Clyde coast. It is the location of a Scottish Site of Scientific Interest (SSSI).
The rocks here are made of brown and chocolate-brown sandstone, a sedimentary rock. Sandstone comes from sediments and is made up of grains of sand. Earth scientists call this type of rocks ‘Lower Old Red Sandstone’.
At the time of their formation, Scotland was in a different part of the World, south of the Equator – the same latitude where we find countries like Malawi today. The climate was warm and dry. But flash floods stormed down valleys, scraping the mountainsides.
The layers in the rocks are visible around Portencross. Originally horizontal, you can see that the rocks are tilted on a slope on the shoreline. The slopes show the many cracks (or faults) and folds that formed in the layers over millions of years.
A major fault has broken the rocks at Farland Head with great force. Where this has occurred, a wedge of grey/green mudstone, called Sandy’s Creek Mudstone, is visible.
The rock type to the south of the Inlet looks similar to the rocks near the castle, except that they dip more steeply. To the north of the Inlet, however, the rock is different. It has a more gentle dip.
A crack or fault in the Earth’s crust caused the changes to the rock type that you see here. Geologists call this second type of rock a conglomerate. Locals call it ‘pudding stone’ because it is a mixture of coarse gravel, cobbles and occasional boulders all set in a solid sand mix. This rock was formed about 380 million years ago.
The Machair and the Sea
During high and low tides the approximate distance to the water’s edge from the beach can vary between 20-200 metres. Around High Spring Tide, you may be delayed for 1-4 hours by the rising tide at several points of the Ayrshire coast.
Between Seamill and Portencross, the coastline provides uninterrupted, panoramic views of the Clyde and Arran. The fields bordering the ocean around Portencross are similar to the unique ecosystems of the coastlines of Western Scotland and north-west Ireland.
The machair is a fertile dune grassland environment, where the sea plays a major role.
The North Ayrshire Ranger Service carried out a survey in 2014 of the plants growing on the rocky shore, whinstone dyke, saltmarsh and ‘machair-like’ seaside vegetation, according to a Wikipedia article.
The calcareous sandy terrain can house rare wild flowers, including orchids, such as Irish lady’s tresses (Spiranthes spiralis) and the Hebridean Spotted Orchid (Dactylorhiza fuchsii subsp. hebridensis).
Many other plant specimens are found there, such as the Japanese rose (Rosa rugosa), meadow cranesbill (Geranium pratense), milk thistle (Silybum marianum), ragged-robin (Lychnis flos-cuculi), scurvy-grass (Cochlearia officinalis), sea ivory (Ramalina siliquosa), sea plantain (Plantago maritima), silverweed (Potentilla anserina) and yellow rattle (Rhinanthus minor)…
Both flora and fauna are strongly influenced by red sandstone substrate and calcium carbonate shells washed up on the beach.
Next to the machair, kelp softens the impact of sea waves, reducing erosion.
When washed ashore by storms, algae bundles form a protective barrier on the beach. If covered with sand, it will compost to form the fertile bed where the annual coastal flowers and marram grass (Ammophila arenaria) thrive.
As algae rot, the sand flies abound and this provides a rich feeding ground for the many varieties of birds, such as the black guillemot (Cepphus grylle), oystercatchers, cormorants, and the local flocks of starlings, wintering waders, gulls and other passerines, that inhabit the region.
Common seals (Phoca vitulina) and grey seals (Halichoerus grypus) abound in the Firth of Clyde. Occasionally, you can spot them sun-bathing or swimming near the shoreline.
Harbour porpoises (Phocoena phocoena) are also common.
Dolphins (Stenella frontalis) are much less so, but were spotted in the upper reaches of the estuary in Summer 2005.
Whales (Eubalaena glacialis) do not favour the Clyde, though there have been instances of larger whales beaching themselves or becoming stranded in the upper firth. Only smaller pilot whales or minke whales seem to visit with any kind of regularity.
In 2005, the Firth of Clyde was listed as having the second highest incidence of basking shark sightings in Scotland. These huge sharks favour the warm, shallow waters surrounding Pladda.
Although at one time the Firth of Clyde was heavily fished from the many coastal towns, the only catches remaining in Clyde waters today of commercial interest are prawns, lobsters and herrings.
Mussel and crayfish harvesting remains important to the economy.
During Summer, there is a possibility of increased numbers of jellyfish in the water. Although there are a few stinging species common to the UK, most of them are harmless.
Nevertheless, the Marine Conservation Society‘s advice is to: ‘Look but don’t touch!’
Of course, such an ecosystem relies heavily on a very fragile environmental balance.
Threats to the Ecosystem
Most natural waters will be affected to some extent by rainfall, as pollutant loads may be increased due to run-off from agricultural or urban land in the catchment area.
At some locations, waste water discharges from combined sewer overflows, which then drain into the bathing water, can reduce the water quality. Pollutants can enter coastal waters via:
- direct discharges into the marine environment at, or near, the beach,
- the freshwater network draining into a bathing water, which can be prone to elevated bacterial levels as a result of diffuse pollution and/or point source inputs upstream.
The principal risks and source of wet weather-driven short term pollution arise from surface water urban drainage, agricultural run-off, combined sewage overflows and treated sewage effluent. These events are expected to last 1-2 days depending on the duration of the rainfall and may result in elevated bacteria levels compared to dry conditions.
Under the right conditions, accumulated seaweed can rot producing grey/black fluid. Rotting seaweed can also generate offensive odours, even though this is an entirely natural process.
Marine waters are not at risk of cyanobacteria (blue-green algae) overproduction. Current information suggests that the bathing water at Seamill, near West Kilbride, is not at risk of overproduction of macroalgae (seaweed) or phytoplankton. At any time of the year, however, particularly after storms, a considerable amount of seaweed can become stranded on the beach.
There is a Marine Biological Station run by the Universities of Glasgow and London on Great Cumbrae.
In September 2008, Scotland’s first No Take Zone (NTZ) was introduced in Lamlash Bay, Isle of Arran. This was instigated by a community effort driven by the Community of Arran Seabed Trust (C.O.A.S.T).
The NTZ was specifically introduced to protect delicate communities such as ‘maerl’.
Maerl (or Rhodolith) is a very slow-growing (1 mm per year) coral-like calcareous red algae and is an important Scottish species. Maerl beds are reservoirs of biodiversity, important both as nursery grounds for young scallops and young fish.
The environmental dangers are two-fold:
- Studies show that organic waste from fish farms significantly reduces live maerl.
- Scallop dredging has profound and long lasting impacts on a maerl bed. It has been found to kill over 70% of live maerl, with no discernible recovery over the following four years. Recovery of maerl beds take many years of being left without disturbance.
Arable and fallow machair is threatened by changes to land management, whereby the original system of crofts has been reduced in number and the use of “modern” techniques has been introduced.
Changes to Common Agricultural Policy subsidies reduced the amount of grazing taking place in many crofting areas, leading to some areas being under-grazed or abandoned.
A lack of native seed increases the need for fertilisers and herbicides.
Rare species are at stake. Bird species including the corn crake (Crex crex), twite (Linaria flavirostris), dunlin (Calidris alpina), common redshank (Tringa totanus) and ringed plover (Charadrius hiaticula).
And rare insects, such as the northern colletes bee (Colletes floralis), the great yellow bumblebee (Bombus distinguendus) and the moss carder bee (Bombus muscorum).
Whatever the weather, the Earth and the sky meet the sea to make for some glorious sights.
But as time goes by, the jagged coast keeps changing. And the sea is winning.
The average winter wave heights along the Atlantic coast of Western Europe have been rising for almost 70 years. In fact, the waves have grown by more than 0.7 metre (2.3 ft) in total since 1948.
A recent study by UK and French scientists suggests the coastlines of Scotland and Ireland have seen some of the largest increases.
Naturally, these rising sea levels come as a long-term consequence of global warming. But they do pose a serious threat to low-lying areas, and lead to increasing coastal erosion.
The 1968 Scotland Storm tracked north up the west coast of Scotland. In Glasgow, some 20 people were killed, 40 injured and 2,000 people made homeless. Both Ayrshire and Argyll were affected.
In January 1993, the Braer storm eroded 3 metres (9.8 ft) of machair along the entire length of Uist and Barra in the Shetlands. And over the past 20 years, it is plain to see that high waves washed away part of the Ayrshire coastal path leading to Portencross and Hunterston (Ardneil Bay). It now takes a muddy trek across the fields to get to Portencross, and further North to Largs.
On 11-12 January 2005, Storm Gero, with consistent winds in excess of hurricane force 12, destroyed hectares of machair, as well as killing a family of five South Uist residents. Stormy seas combined with high spring tides and caused flooding in low-lying coastal areas.
The study used actual data and a combination of weather and mathematical wave modelling, or hindcasts, to estimate the changes in wave height and variability along coastlines from Scotland to Portugal. The results were correlated against two climate indices, the North Atlantic Oscillation (NAO), long-known to have affected climate variability in the Northern Hemisphere, and the West Europe Pressure Anomaly (WEPA).
Continuity in Change
As the last Ice Age subsided, the weight of the ice was lifted, and the Scottish landmass started rising back slowly out of the molten mantle below. This uplift provided rivers with extra energy and cutting power, and its effect are seen along the River Ayr, which has cut deeper into its bed to form a gorge…
The geological process is continuing now, and the land is still rising at the rate of about half a millimetre a year.
Nevertheless, it is slowing.
According to the study on Increased Winter‐Mean Wave Height, Variability, and Periodicity in the Northeast Atlantic, the results showed that all coastal areas had seen an average rise in winter wave heights during the period of 69 years (1948-2017), although it varied from 10 millimetres (0.4 inches) per year in Scotland, compared to 5 mm (0.2 inches) per year in France and 1 mm (0.04 inches) per year in Portugal.
Clearly, if human-made climate change is indeed responsible, we must begin to reduce our coastal vulnerability to extreme winter storm events. We must adapt proactively and be prepared for a more energetic wave climate future.