Northern England district - Lake District and surrounding areas

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This area includes the upland area of the Lake District and the surrounding coastal lowlands to the west and south where the main settlements include Workington, Whitehaven, Barrow-in-Furness and Kendal.

Sedimentary Bedrock

On the flanks of the Lake District layered sedimentary rocks occur at or near the surface across much of west and south Cumbria.

The youngest bedrock in this area comprises red sandstones and mudstones, around 250 million years old and forming undulating lowlands to the west of the Lake District and south of Whitehaven. For example, the spectacular cliffs at St Bees Head are formed of reddish sandstone laid down by a massive, northward flowing river system. These rocks are referred to as the Sherwood Sandstone and provide substantial quantities of groundwater from both the water-filled pores between the sand grains and from fractures cutting the rock. Deposits like this are known as aquifers and the Sherwood Sandstone is the second most important aquifer in England. The water quality has been affected by the invasion of saline water in areas of heavy extraction near Barrow-in-Furness and this probably occurs all along the Cumbrian coast. In south Cumbria, the sandstones are overlain by red mudstones, known as the Mercia Mudstone. Locally these contain layers of rock salt and these have been worked in the past by brine pumping on Walney Island.

Beneath the Sherwood Sandstone are older sediments, comprising Coal Measures and the underlying Carboniferous Limestone. The most widespread of these layers is the Carboniferous Limestone, deposited in warm, clear seas and occurring from Caldbeck west almost to Maryport where it is up to 270 m thick. To the south, bordering Morecambe Bay, the limestone is widespread at or near the surface and is encountered at depths to around 500 m. Locally, it contains substantial deposits of iron ore which have been mined extensively in the past. In west Cumbria, between Maryport and Whitehaven, the limestone lies at depths of 70 to 640 m and is overlain by alternating beds of mudstone and sandstone, and in higher layers there are many seams of coal present in the Coal Measures. The limestones formed in relatively shallow seas, with vast quantities of sand and mud gradually building up to form large river deltas. When the tops of these deltas were exposed, massive swampy forests grew up and the vegetation from these forests was later buried and compressed to produce layers of coal. Mining of coal in West Cumbria dates from the 16th century. The mines reached depths up to 400 m and extended out beneath the Irish Sea for up to 6.5 km. Together, the resources of iron ore and coal supplied the former heavy industries of Workington, Whitehaven and Barrow-in-Furness.

Basement rocks

Volcanic rocks forming Scafell and Bowfell in the English Lake District. P005109.

Carboniferous Limestone rests on the basement rocks of the Cumbrian fells, the oldest rocks in Northern England. At the heart of the Lake District lies Scafell Pike which, at 977 metres above sea level, is England’s highest mountain. The craggy mountainous terrain surrounding Scafell (Plate P005109) is formed by rocks that were originally ash deposits and lavas erupted from volcanoes about 450 million years ago (Borrowdale Volcanic Group). This part of the Lake District is associated with extensive base metal mineralisation and was once one of the world’s principal copper producing areas.

To the north, the smoother, more rounded mountains around Skiddaw are formed of dark slates derived from older sandstone and dark grey mudstone (Skiddaw Group), while the southern Lake District is characterised by undulating hills and rocky crags made up of layers of limestone, mudstone and sandstone of the Windermere Supergroup and Reston Group, that are younger than the volcanic rocks. Each of these basement rock units is known to extend to several kilometres below the surface. As well as the deformed sediments and volcanic rocks, the basement includes a number of intrusions of granite, originally emplaced as molten rock or magma. The main examples are at Ennerdale, Eskdale and Shap.

Generally, the basement rocks are impermeable, meaning that they do not let water pass through them and therefore they do not supply large amounts of groundwater. However, the Lake District’s hills form an important gathering ground for rainwater and some of the large lakes on the valley floors, such as Thirlmere, have been dammed to form reservoirs that supply water to nearby towns and cities such as Manchester.