Lake District - Geology

Geology

The Lake District's geology is very complex but well-studied. A granite batholith beneath the area is responsible for this upland massif, its relatively low density causing the area to be 'buoyed up'. The granite can be seen at the surface as the Ennerdale, Skiddaw, Carrock Fell, Eskdale and Shap granites.

Broadly speaking the area can be divided into three bands, the divisions between which run southwest to northeast. Generally speaking the rocks become younger from northwest to southeast. The northwestern band is composed of early to mid Ordovician sedimentary rocks – largely mudstones and siltstones of marine origin. Together they comprise the Skiddaw Group and include the rocks traditionally known as the Skiddaw Slates. Their friability generally leads to mountains with relatively smooth slopes such as Skiddaw itself.

The central band is a mix of volcanic and sedimentary rocks of mid to late Ordovician age comprising the lavas and tuffs of the Borrowdale Volcanic Group, erupted as the former Iapetus ocean was subducted beneath what is now the Scottish border during the Caledonian orogeny. The northern central peaks, such as Great Rigg, were produced by considerable lava flows. These lava eruptions were followed by a series of pyroclastic eruptions which produced a series of calderas, one of which includes present-day Scafell Pike. These pyroclastic rocks give rise to the craggy landscapes typical of the central fells.'

The southeastern band comprises the mudstones and wackes of the Windermere Supergroup and which includes (successively) the rocks of the Dent, Stockdale, Tranearth, Coniston and Kendal Groups. These are generally a little less resistant to erosion than the rocks sequence to the north and underlie much of the lower landscapes around Coniston and Windermere.

Later intrusions have formed individual outcrops of igneous rock in each of these groups. Around the edges of these Ordovician and Silurian rocks on the northern, eastern and southern fringes of the area is a semi-continuous outcrop of Carboniferous Limestone seen most spectacularly at places like Whitbarrow Scar and Scout Scar.