‘Discuss the factors that have shaped the landscape of the Lake District, Cumbria, UK’
Abstract (150)
Five Key Words
Intro (320) 296
The Lake District, Cumbria, falls into a location of the UK which has experienced the greatest levels of glaciation, figure 23.29 (Holden, 2017) It is no surprise therefore that it is characterised by a distinct landscape. As would be expected, there are landscape features – these being specific geographical definable imperfections in an archetypal basic landscape – which can directly be attributed to processes consistent with glaciation. This, however, cannot describe all the features found in the Lake District. It is also the case that a basic archetypal landscape cannot easily be defined and arguably does not exist. Thus, to correctly understand the nature of the park, an investigation using solely glacial and interglacial processes would not suffice. It is with this predication that this essay will discuss why there is mountainous topography in the first place, the major time frame which have been used to build it in the first place, and the interdependent role this topography has with its features. It is through understanding discussed in this essay that comparisons can be made between the Lake districts past and current environments. Consequentially this will allow a greater understanding to be modelled when predictions can be made how climates are likely to change.
The discussions making up this essay will firstly attempt to establish why there is topography in the lake district in the first place. From this premise the essay will discuss why the possible features seen in the study area are there and why they are not characterised differently; this being features created through the glaciation itself, through processes active after glaciation, and currently occurring reasons for change in the North West of England. Finally, having established what change might be currently occurring it will highlight the implications which this has on the established society.
Landscape are influenced by the underlying rocks and the natural processes shaping their surface. The district is a low relief mountain environment (McDougal, 2013) which is broadly comprised of three bands of rock trending from North West to South West with completely different characteristics.
The Skiddaw bedrock forms a broadly triangular, mountainous zone in the northern third of the National Park, reaching maximum heights of 931m on Skiddaw. Formed from muds and sands on the seabed about 500 million years ago during the Ordovician period, the rock was subjected to uplift and faulting during the Caledonian and Devonian orogenies. Generally, Skiddaw group mountains are typically smooth in outline; examples include the fells of the Newlands valley. The brittle rocks break down easily resulting in features such as streams and deep gorges such as Trout Beck.
The central Lake district is Dominated by rugged mountains, formed from hard rocks of the Borrowdale volcanic group (BVG). 450 million years ago, subduction of the lapetus Ocean under Avalonia caused melting of the Earth’s mantle; magma rose forming a volcanic arc across Cumbria centred near the Scafell mountain range. Eruptions of lavas and latterly explosions of copious ash and pyroclastic flows over a few million years formed a layer of rock estimated at 8km. The BVG rocks are mainly andesites with basalts and rhyolites; such rocks are almost as hard as granite and very resistant to external forces, tending to break down into large blocks. Landscapes formed on such rock contrast with the earlier Skiddaw rock; their resistance to erosion results in extensive areas of the highest and craggiest upland – Scafell (964m). On a smaller scale, variations in detailed form of the individual lakes is controlled by local geology, e.g. Derwent water’s shape being the result of a valley glacier widening rather than deepening the valley due to the bedrock of less resistant Skiddaw rocks which compares with the ribbon shape of the other BVG lakes (Smith, 2008).
The Volcanic fells tend to be much rougher, with rugged, crag slopes reflecting the resistant nature of the rock. The nature of the volcanic bedrock impacted upon the erosive capacity of the glaciers; water at the base of the glaciers on the impermeable rocks leads to propagation of cracks and loosening of blocks of rock. Rock type is thus important in explaining the detailed form of the trough; the BNR were heavily influenced by the nature of successive periods of glaciation. It is because of this that valley sides are therefore rugged; steep crags rim these valleys and irregular knolls and striated knobs of rock remain where the ice overrode them. Such steep crags are fewer over the Sliddaw valleys; the rocks broke down more easily producing a fine debris with valley sides smoother and closer to a v shape than would perhaps be anticipated. It is partly because of this that the Skiddaw rock debris has formed an isthmus separating Bettermere and Crummock water (Smith, 2008)
Troughs scoured by glaciers on impermeable BVG bedrock gives rise to contemporary landscapes are also impacted by the impermeability; the rapid runoff in such areas resulting in higher erosive capacity of streams and storm damage in areas such as Cockermouth on the small band of BVG between Cockermouth and Uldale. It comprised hard lava beds interspersed with softer bands of ash and boulders called tuffs. Some rick remains in the original deposits bet elsewhere ash was eroded and redeposited by rivers.
In the southern third of the Lake District, the Windermere group comprises a zone of less resistant slates, siltstone, sandstones, and limestones, formed in Silurian seas about 420 million years ago and results in gentler foothills stretching from the Duddon estuary to Kendal which include Windermere and Coniston water.
About 350 million years ago, during submergence, carboniferous rocks were laid down; evidenced by a long-curved limestone cuesta around the northern edge of the Park and two prominent west-facing scarps: Whitbarrow Scar and Scout Scar. Throughout the Permian and Triassic uplift periods, sand dunes and salt lakes developed resulting in the gentle hills and till covering undulating plateaus to the west and north of the region; dune bedding and rounded grains in the Penrith and Lazonby sandstone ridges are Aeolian in origin, whilst the St. Bees and Kirklington sandstones result from debris deposited by flash flooding. Such erosive rocks underlie areas of lowlands upon which subsequently have had glacial transport deposited on them.
Over the last 200 million years, periods of uplift and submergence occurred; during uplift, extensive erosion over several hundred million years exposed the Silurian slate and wore the rock down to low-profile hills. During the Alpine orogeny, a batholith of granite, 10km below the surface, buoyed up an area centred on ‘central massif’; subsequent erosion exposing it in the Eastern Skiddaw Fells. The granite batholith combined with hardness of the BVG bedrock has determined the topography and altitude of this system (Mcdougall, 2013) which when combined with previous fault systems formed the distinctive drainage system whereby valleys radiate from a point centred on Dunmail Raise north of Grasmere. The impermeability of the underlying BVG bedrock has ensured that meltwater and latterly rain water is held in place forming Britain’s longest lakes. The resistant nature of the BVG rocks has further relevance when considering the effect of glaciations. During glaciations, the most efficient and from such the most common method of ice flow were the valleys (Smith, 2008). The ice used and modified such fault line valleys, deepening their floors and in places straightening their alignments.
Underlying geology and rock characteristics have had a significant impact upon the landscape of the Lake District. The consequential mountainous nature of the area has resulted in high precipitation, which during glacial events resulted in high accumulation of ice and erosive glaciers with resulting landforms.
Furthermore, the established topography has influenced the effect that the glaciers have had in ways as simply put as the altitude they are found at. The lower level glaciers of the west and north west are more effective at lower altitudes (Smith, 2008). The glaciers in the east, whilst still being highly erosive were standomg at higher levels.
Glacial (650)
2.6 million years ago, during the Quaternary period, climatic conditions worsened, resulting in a possible 21 distinct glacial periods separated by, equally distinct regularities, nominally interglacials and interstadials (Figure 1). Whilst landscapes evidence such repeated cycles, the previse geological timeline for such events is derived from ocean floor and ice cores along with C14 dating of pollen. (XXXX). Most deposits in the Lake District relate to the Devensian cycle. The Woolstonian Glacial period lasted 160,000 years until 128KaBP; clays and glacial debris found in boreholes near Sellafield data from this period; XXX to XXX whilst, vegetative evidence in Scandale peat deposits dates from the Ipswichian interglacial; XXX to XXX. The Devensian glacial occurred 118KaBP to XXX with maximum ice coverage circa 18 KaBP; average temperatures declined progressively over the first few thousand years with eventual, rapid ice build-up and intense glacial condition (Smith, 2008).
Whilst the surface of the area and low lying topography would all have been encased in ice sheets, there is evidence to suggest that outside the limits of the ice some peaks remained untouched. This evidence comes from trimlines found at sporadicly located but in concrescence in altitude – these peaks are known as Nuntaks. It is the nature of these peaks that information is provided on the three-dimensional attributions of the Devinsian ice masses. Erosional evidence suggests that valley glaciers in the West and South West Lake district were larger and more active than those further East – it is theories that this is because of an increased level of precipitation (Smith, 2008). It is from this that an understanding into the weather patterns active in the Devensian period could be found. With this being said however there is still altitudes of the mountains – this seen on High Street ridge and on Great Gable – that a maximum ice height didn’t reach; this being around 870m (Paterson and Cuffey, 2013). Furthermore, on some of the Central Fells frost shattered rock outcrops indicate that the summits were exposed peaks (Smith, 2008). This contrast with previous models. The existence of other Devinsian icecaps impacted upon the three-dimensional character of the Lake District. This is evidenced in drumlins length to width rations in different locations. The more rounded drumlins with ratios of 4.6:1 found near Wigton indicate faster ice moving unimpeded into the Irish Sea Basin, whilst ratios of 1.9:1 found near Carlisle are indicative of ice blocked by other masses.
Drumlin location Length:width ratio Characteristic Indication
Appleby
2.5:1 Slow moving Escaping up valley SE through Stainmore Gap
Penrith 3.1:1 Fast moving Travelling N
Carlisle 1.9:1 Slow moving Ice impeded by Scottish ice
Wigton 4.6:1 Very fast Ice streaming into Irish Sea
Throughout most of the glacial undulation period the polar front was around 40 degrees latitude off Northern Portugal, but by 15KaBP it receded to a position within the currently established arctic circle. The impact of such change was dramatic. By 14.5 KaBp the climate of Britain was comparable with present day. This period was known as the Windermere Interstadial (Bell and Walker). Between 13 and 11.5 KaBp, during the Loch Lomond Stadial (LLS), polar waters spread southwards at a rate of 5km yr-1 evidenced in sea corers with the polar front reaching south of Ireland. Renewed glacier activity occurred in mountainous regions; valley glaciers developed in the Lake district and woodland that had re-established during the warm periods was replaces by tundra in Northern and Western Europe. This meant that the areas previously being eroded directly through glaciation was now able to be eroded through other forms of weathering along with a change in climate and its associated landscape evolution.
Amelioration occurred in the early Holocene; an increase of 15 degrees from the LLS took around 1500 year. The initial increase of 10 degrees was rapid and was accompanied by increased snow accumulation, a decline of wind-blown materials and the rapid expansion of wetlands. Evidence in Icelandic sea cores shows that climatic optimum occurred 9KaBP to 4KaBp, with temperatures in the order of 1 – 3 degrees above present. Pollen analysis shows the northwards migration of woodland in Europe and advancement of the treeline to above present-day levels. It is true that this change in climate, along with environmental change will establish different soil mineral components (Ashman and Puri, 2015) which would eventually contribute to the current environment and wildlife seen in the area.
Circa 6KaBP In the late Holocene, a decline in temperatures occurred with an accompanying trend towards wetter conditions around 4.5 KaBP. A slight climatic recovery followed during the historic period with fluctuating but generally warmer conditions, but with slightly cooler and wetter conditions during the middle of the first millennium (Lamb). The medieval warm period followed; AD 800 to AD1200, which allowed the advance of cultivation.
During a period known as the Little Ice Age from AD 1400 up to circa 1850, slow cooling, colder, and winters with higher levels of precipitation occurred which resulted in vegetation changes, crop failures, and the abandonment of settlement.
Such a glacial time line would clearly create a large number of glacial landforms and process features. This is the case with the land scape of the lake district. The main geomorphic process which can be attributed to the subglacial processes of erosion and deposition. Firstly, erosion is the process by why material which comes into contact with the glacier is removed. Largely this is done from the pressure of the glacier – 44MPa (Holden, 2017) – and the force which such a large pressure excerpts on the landforms. The pressure could directly pluck or crush the rock in weaknesses and in faults. Erosion is also likely to happen through rock particles scouring the bed during subglacial transport called abrasion; consequentially this results in such features as striations on the rock. A further method of erosion found in glaciers is that of N-channels (sub glacial streams protruding into the rock surface) and the mechanical action of the water or chemical action from the water. Whilst, N-channels will create features during their active phase, during the end period of glacial recession and at time of high accumulation they will become features of deposition – the other major geomorphic process. Deposition is the act of a glacial laying down its transported material. Normally, because glacial streams will gradually decrease competence the glacial till will have been laid down in accordance with the calibre of the particle. It is from such that the features of deposition in the lake district are stratigraphically sorted; larger particle object sub-setting smaller, more easily entrained particles. Conversely, when a glacier directly deposits it material from either a massive change in momentum or total recession this is done without sorting. The nature of where the material has come from can be deduced through the angularity of it – if it is rounded and finer it has been suspended whilst in contact with rock: normally basal material.