Geology

geological boundary

Geological Boundary - Borrowdale Volcanic Group on left, Skiddaw Slate Series on right

Have you ever wondered what has made Borrowdale so beautiful? The answer is a combination of nature, weather, time and man – join us as we unravel the geology and see how the story of Borrowdale began.

The beginning

Borrowdale was once in the southern hemisphere. Landmasses are constantly moving and Borrowdale’s journey began over 400 million years ago. Most of the valley south of Derwentwater is made up of ancient volcanic debris formed c.450 million years ago when central Lakeland was an area of immense volcanic activity. This central region is the largest and most dramatic geological band in the Lake District and is called the Borrowdale Volcanic Group (BVG); named after our valley. Grange lies on the dividing line between this band and the gentler and even older Skiddaw Slate series to the North. The picture to the right shows where the craggy, rocky, uneven landscape of BVG, meets the slopes of the Skiddaw Slate Series at a gully between Maiden Moor and High Spy.

 

The Modelling

So, the bare bones have been laid down – now for the modelling. Imagine huge glaciers, like slow moving rivers of ice, hundreds of feet thick, carving out the Lake District valleys more than 10,000 years ago. Look at a Lakeland map and you will see that there is a distinctive radial pattern to them. The poet, William Wordsworth, described the Lakeland valleys as ‘spokes from the nave of a wheel’. Borrowdale is one of these spokes radiating out from the central hub of fells.

The glaciers carved out Borrowdale giving the valley its distinctive U-shaped form (a classic trough). Look for two such troughs coming together at Rosthwaite before they meet with constriction at the Jaws of Borrowdale between Castle Crag and King’s How. As a glacier carved out the Seathwaite valley it chopped off the ends of smaller side valleys and left them “hanging” above the main valley floor. Look for examples at Gillercombe and Styhead from which Sourmilk and Styhead Gills (ravines with streams) flow down these hanging valleys ending in waterfalls.

The Evidence

How many other glacial features can you see? Grange Bridge straddles a ‘roche moutonée’, meaning ‘rock sheep’. Can you see how the glacier (moving south to north) smoothed the area of bedrock but plucked at its northern end to leave a rough edge? This edge overlooks the River Derwent on the north side of the bridge.

surprise view

Surprise View

Rosthwaite sits on a prominent rocky knoll, the How, which has been overridden by ice. The precipitous crags of “Surprise View” show the awesome power of the glacier scraping the valley sides. Terminal moraines (glacial debris) occur just south of Rosthwaite in the form of two ridges. The How would have formed a rock barrier and at one time a glacier moving north came to rest against it. After a time it left a moraine at its front end in the form of a ridge. A slight retreat followed and a second moraine was deposited.

Pick up our walking leaflet and look for the curve close to the River Derwent, opposite Longthwaite, running southwards towards Borrowdale School. The channel (now a popular footpath from Grange to Seatoller) between Castle Crag and the lower slopes of High Spy to the west was caused when water draining from the upper slopes of High Spy met the main valley glacier and was forced to run along its margin in a north south direction. The hummocky landscape on the eastern slopes of Honister Pass and at Stockley Bridge near Seathwaite is evidence of renewed glacial activity after the main ice age had gone.

bowder stone

the Bowder Stone

The famous Bowder Stone, fallen from the crags above, is a result of glacial activity and subsequent weathering. Weighing nearly 1,200 tons it has been a tourist attraction for many years. Here is an account of the stone written by the poet laureate Robert Southey:

Another mile of broken ground, the most interesting which I ever traversed, brought us to a single rock called the Bowder Stone, a fragment of great size which has fallen from the heights. Here, an ugly house has been erected for an old woman to live in who is to show the rock, for fear travellers should pass under it without seeing it. The ground has been cleared around it and it rests upon a narrow base, like a ship upon its keel. A hole has been dug underneath through which the curious may gratify themselves by shaking hands with the old woman. The oddity of this amused us greatly, provoking as it was to meet with such a hideous building in such a place, – for the place is as beautiful as eyes can behold or imagination conceive. The river flows immediately below, of that pale green transparency which we sometimes see in the last light of the evening sky.

To sum up

The basic structure of the landscape of Borrowdale was laid down 100s of millions of years ago and sculptured by ice thousands of years ago. Nature has added her embellishments and human habitation and endeavour have done the rest.  

Pictures sourced by Richard Hyde