Lake District: Physical Geography Information

Aims

1) To provide students with a basic introduction to the key physical processes that influence the environment

2) To provide students with some basic field skills appropriate for the study of physical aspects of the environment

Learning Outcomes

On completion of these exercises students should be able to:

1) Identify major landform types in the natural environment

2) Understand the key processes that underpin environmental change in the Lake District

3) Perform simple field related tasks such as field sketching/photography, walking and orientation

Introduction

The Lake District has long been regarded as a region of outstanding natural beauty. The ruggedness of the environment and the openness of the landscape is as much a result of the processes of weathering and erosion as well as geology and human influences. It is well understood that the economic success of the region (mainly the result of tourism) is dependent upon the stability and attractiveness of the natural environment.

Local stone is often used in the construction of walls and buildings – a factor which helps to give the landscape its character. The influence of glacial action is most striking in the way the local landscape has been shaped during the last few thousand years.

The bulk of the National Park is made up of three broad bands of rock:

1) The SKIDDAW Group (in the North West of the Park)

2) The BORROWDALE Volcanic Group (in the central zone of the Park) and

3) SILURIAN Flags and Shales (to the South East)

See figures 1 and 2 overleaf


Figure 1 - Geological Map of the Lake District

Figure 2- Geological section through the Lake District


Much of the natural landscape features are due to geological processes that have taken place over a long period of time. Mountain ranges were formed some 400 million years ago – when molten magma produced folding and faulting of rocks as it pushed its way to the surface. These events are known as the CALEDONIAN OROGENY (mountain building episode).

Millions of years of subsequent erosion have worn down these mountains to their present size – but the folds and faults can still be seen, and the igneous intrusions, which cooled and crystallised hundreds of metres below the surface are now exposed around Eskdale, Ennerdale, Shap, Skiddaw and Carrock Fell.

During the DEVONIAN period the high mountains were eroded to low hills and about 350 million years ago most of the land sank below a tropical sea. This sea teemed with life and the sea floor became covered with a thick layer of sediment, made up of the broken remains of shells to form Carboniferous Limestone. Some shells remained intact and can still be seen today as fossils.

During the latter part of the CARBONIFEROUS period this sea filled with mud and was colonised by swampy forests whose remains now form coal.

About 280 million years ago the carboniferous rocks were uplifted and folded into a dome by another orogeny, the VARISCAN OROGENY. A landscape of sand dunes and salt lakes developed, with seasonal rainfall washing rock debris from nearby uplands onto stony plains. These conditions persisted throughout the PERMIAN and TRIASSIC periods and ended about 190 million years ago.

About 2 million years ago the Earth’s climate cooled, allowing the development of glaciers and ice sheets which, at their maximum, covered much of mainland Britain. These cold episodes were known as GLACIALS and were separated by warmer INTERGLACIALS supporting broadleaved forests. There may have been as many as 10 such climate oscillations.

It is the action of glaciers and meltwater, frost conditions and slope action during this period which have shaped most of the surface detail of the Lake District.

Following the last glacial episode the HOLOCENE commenced. This was typified by sea-level changes and the development of soils. In the Lake District, grey-brown forest soils developed beneath mature oak forest at lower levels, whilst at higher altitudes MONTANE soils were formed – known locally as RANKERS.

Many of the lake and estuarine basins were filled with peat. Tree clearance in the 11th Century led to soil erosion and further activity on the alluvial fans and lake deltas of the central Lake District. Since then the land surface has remained largely unchanged.

See Figure 3 overleaf


Figure 3 - Geological succession in the Lake District