Physical Geography – How Salt Has Shaped Our Landscape
How does salt shape and change our physical landscape? Salt not only plays an incredibly important role in sustaining our daily lives but it has done much to shape the landscape around us – and continues to do so today.
Naturally formed salt pans are expanses of flat land, found in deserts, where the surface is covered in salt and other minerals.
A salt pan is created when pools of seawater evaporate at a rate faster than it is replenished by rainfall. As the water evaporates, it leaves behind the minerals precipitated from the salt ionsdissolved in the water.
Salt is typically the most abundant of these minerals, accumulating over many thousands of years, giving the surface its hard white crust.
Natural salt pans should not be confused with the man-made salt pans used in solar salt production, or smaller pans which are heated to evaporate the water from the brine and produce salt.
Notable Salt Pans Around the World
The Salar de Uyuni in Bolivia is the world’s largest salt pan. It contains between 50% and 70% of the world’s lithium reserves – a mineral essential to the production of mobile phones.
The Bonneville Salt Flats in Utah, United States of America is a well-known salt pan where many land speed records have been set.
The Makgadikgadi Pan is a salt pan in north-eastern Botswana and is another of the world’s largest salt flats.
Salt marshes are areas of vegetation often found in sheltered water areas, such as estuaries or behind land-spits. An estuary creates perfect conditions for salt marshes – a wide, shallow area of water where a river meets the sea. It contains both fresh water entering from a river, and salt water replenished twice daily as a result of flooding by the tidal actions.
As the tide rises and falls, it leaves behind deposits of fine silts and muds. As plants begin to grow in these areas the amount of mud and silt left behind increases eventually forming mud flats. These are important feeding areas for sea birds.
Where there are hollows and troughs in the mud flat, sea water will be left behind as the tide falls. During these periods of low tide, the water in the pools partially evaporates – leaving behind highly concentrated areas of salty water, known as salt pans.
Some recent research has found that salt marshes are an effective defence against coastal erosion as they reduce the impact of waves on the shore line.
European Rock Salt Formations
The rock salt deposits in the UK are found at Cleveland, County Antrim and below the Cheshire town of Winsford. They were formed some 220 million years ago during the Triassic geological period.
At this time the United Kingdom was still attached to Europe by a land-bridge, and central England consisted of a series of inland seas that were regularly replenished by the surrounding oceans. The combination of the inland seas and the desert environment led to slow evaporation over many millions of years, resulting in the formation of the salt beds which today lie beneath these areas. During this evaporation, substantial quantities of sand blew in from eastern deserts, helping to create the pink tinge which is a feature of UK rock salt.
Although the original salt bed is now fragmented, it can be traced from its starting position in Carrickfergus, Northern Ireland, from where it dips below the Irish Sea before reappearing around central England to then dip under the North Sea. The final part of the salt bed lies across much of Europe. Scandinavia is the only European country without its own natural salt supply.
Winsford’s Rock Formation
The rock formation at Winsford has four distinct rock salt seams – known as ‘halite’ (from the Greek word ‘hals’ – meaning salt). The remaining strata consist of rock salt with Keuper Marl either in separate bands or intermixed with the rock salt.
Due to many of the influencing geological aspects, the colour of Winsford’s salt varies greatly – it can range from clear to pink through to dark brown, although a mixture of dark brown and pink is most commonly found. While the Keuper Marl is usually amber or brown in colour – it can on occasions be blue or green.
Whilst Marl is impervious, over time water has penetrated the exposed salt beds, dissolving the salt and creating a’ wet rock head’ above the Mine. This resulted in wild brine springs presenting themselves on the surface in many areas, particularly in Cheshire. These were used as the source of brine for white salt production from ancient times up to the early 20th Century.
The overuse of these wild brine springs over many years led to subsidence in some areas. This led to the banning of wild brine pumping and the development of ‘solution mining’.