Harrow and Hillingdon Geological Society
The Lake District
Lake District-Landscape and Evolution
The Quaternary history of the northern Lake District is a very under-researched region. It is a small area rising in part to 1000 metres with a yearly rainfall of 3,000-4,000mm making it the wettest in England. The solid geology includes Skiddaw slates, which are the oldest Ordovician examples. They are sedimentary and show some metamorphosis. The rougher topography is essentially volcanic, shows more variety than in the slates and is centred on Borrowdale. The southern Lake District is an area of Silurian shales, has a more gentle topography and is around Ambleside and Hawkshead.
This whole region is good example of glaciation and has all the text book examples associated with the formation of this landscape : ‘U’ shaped-valleys, lakes, moraines, alluvial fans, corries. Buttermere has post glacial deposits and arêtes and razor back edges. Derwent water is the shallowest lake and has drumlins and eskers. Penrith and Keswick have truncated spurs. The erratics in Thirlmere show the direction of the glacial flow. There are nearly 200 corries, which are difficult to date but probably developed over the last 2 million years during the Quaternery. The moraines are also the result of the last glaciation. The glacial deposit of till or boulder clay was 20,000 years ago during the Devensian glaciation and is therefore recent and gave rise to the drumlins. The deposits below these are heavily weathered and very different from the last glaciation. This is evidence of previous glaciation and is the only site of two-stage glaciation in N. England. The till is quite thick and in places up to 10m thick. The head of Langdale Pike has moraines.
During the Loch Lomond or Stadial advance, there were dramatic climate changes. Summer temperatures were 7-8° C while in winter it was -20° C. This period although only brief was cold and wet enough to form glaciers and occurred 10,700 years ago. Evidence for this had been obtained from the cores of Greenland ice cap. Subsequent temperatures rose by 7 degrees C in 50 years. The rapid melting of the ice cap put cold water into the north Atlantic altering the direction of the Gulf Stream.
There are also a lot of peri-glacial features, including frost shattering, tundra and scree. During the Holocene there was a lot of landscape development. Wastwater has screes, some of which are active while others are vegetative. There is an infill of lakes and even Derwent Water is 1/3 smaller. Dolerite axes dating to the Neolithic period, 5,000 years ago have been found. There is also a stone circle near Hellvellyn Castle ring. There has also been a serious overgrazing by sheep, which has exposed scree.