- Created by: Marainesthai
- Created on: 07-12-18 17:59
Characteristics of landscapes in the UK - 1
Geology is about rocks and their formation, structure, and their composition. There are three types of rock: sedimentary, igneous, and metamorphic.
Igneous rocks form from magma that has cooled on the surface (extrusive) or below the ground (intrusive). They are tough and resistant to erosion, and often form uplands like Dartmoor (granite).
Sedimentary rocks form from the accumulation and compaction of sediment, usually in the ocean, and have variable resistace to erosion; limestone is resistant, whereas weaker clays and sands form lowlands eg in southern England.
Metamorphic rocks are existing rocks that have undergone change due to heating or pressure, and are resistant to erosion, forming uplands eg Snowdonia.
Geology also influences the location of built landscapes - some rocks are valuable sources of energy, or contain raw minerals. This has encouraged urbanisation eg in the northeast of England, the development of Middlesbrough was based on nearby mineral resources, supplying the chemical industry.
Characteristics of landscapes in the UK - 2
Climate is the long-term average weather conditions, whereas weather is the day-to-day conditions of the atmosphere.
The UK's climate is a maritime climate, with prevailing winds blowing across the Atlantic from the southwest, accounting for the high rainfall and moderate temperatures throughout the year.
The uplands receive a high proportion of rain, with the lowlands tending to be drier. The moist air from the Atlantic is forced to rise and cool over uplands, forming relief rainfall, whereas lowlands are in the rain shadow (has little rainfall due to being sheltered from relief rainfall).
Temperatures tend to be lower in the uplands than lowlands, with frost and snow being common hazards in the winter, because temperature falls by 0.6 degrees Celsius per 100 metres of altitude.
In upland areas, freeze-thaw is very active, resulting in jagged surfaces and accumulation of scree. Rivers are fast-flowing and erosive due to high rainfall, creating V-shaped valleys.
Characteristics of landscapes in the UK - 3
Uplands are sparsely populated due to the harsh climate and steep relief, so human activity is limited to sheep rearing, forestry, and reservoirs.
Lowlands are more densely populated due to the moderate climate and gentle relief. Human activity involves commercial farming, and much of the landscape is urbanised and criss-crossed by transport and service infrastructure.
Geomorphic processes are responsible for shaping landscapes.
Weathering is the decomposition and disintegration of rock in situ, including chemical and mechanical weathering.
Chemical weathering involves carbonation - carbon dioxide dissolved in rainwater forms a weak carbonic acid, reacting with limestone to form calcium bicarbonate. Hydrolysis is acidic rainwater reacting with feldspar in granite, turning it to clay and causing it to crumble. Oxidation is oxygen dissolved in water reacting with iron-rich minerals, causing it to crumble.
Mechanical weathering involves freeze-thaw (repeated cycles of freezing and thawing cause water trapped in rocks to expand and contract, causing rock fragments to break away) and salt weathering (salt crystals grow in cracks and holes and expand, causing rock fragments to break away).
Biological weathering is weathering done by the actions of living organisms eg plant roots expanding in cracks.
Geomorphic processes - 2
Mass movement is the movement of material caused by gravity. Sliding involves loose material sliding downhill along a slip plane, often triggered by earthquakes or heavy rain (when sediment becomes saturated and heavy). Slumping is the collapse of weak rock, resulting from heavy rainfall when sediment becomes saturated and heavy.
Erosion is the wearing away and removal of material by a moving force, including abrasion, hydraulic action, attrition, and solution. Abrasion is when loose particles are scraped or flung against a surface, also known as corrasion. Hydraulic action involves compressing air into cracks, causing rocks to break away. Attrition is when rocks that are being transported bump into each other and break up into smaller pieces. Solution is the dissolving of soluble rocks.
Transportation is the movement of eroded sediment from one place to another. Traction involves large particles rolling along the seabed, saltation is the hopping motion by pebbles too heavy to be suspended, suspension involves particles being suspended in the water, and solution involves chemicals being dissolved in the water.
Deposition occurs when the material being transported is dropped due to a reduction in energy, perhaps in areas of low energy, where velocity is reduced eg bays or river banks.
Formation of river landforms
A V-shaped valley is formed by river erosion as the river cuts down vertically into the landscape. Weathering and mass movement on the valley sides broaden the top of the valley profile. Interlocking spurs are common in the upper course of a river.
Waterfalls form where flast-flowing water plummets over a vertical cliff into a plunge pool. A river flows over a hard, resistant band of rock, and unable to erode the tough rock, a step is formed in the long profile of the river. Hydraulic action and abrasion erode the plunge pool.
A gorge is formed by the upstream retreat of a waterfall. Hydraulic action and abrasion undercut the hard rock forming the waterfall to create an overhang, which eventually collapses into the plunge pool, causing the waterfall to retreat upstream. This process continues until a gorge is formed downstream.
Meanders are found in the middle and lower course. The fastest flowing water swings around the outside bend of a meander, eroding the banks to form a river cliff. On the inside bend, velocity is lower, and deposition occurs to form a slip-off slope. The meander develops an asymmetrical cross-profile. Meanders are associated with gentle gradients, fine sediment, and steady precipitation regime throughout the year.
Formation of river landforms - 2
Oxbow lakes are seen in the middle and lower course. The neck of the meander narrows due to lateral erosion on opposite sides of the meander, and during floods, the neck is broken through, and the river now adopts a short route bypassing the old meander. Deposition occurs at the edges of the new straight section, cutting off the old meander, which now forms an oxbow lake. The oxbow lake silts up to form marshland.
Levees are raised water banks found in the lower course of a river. As water overtops the banks, there is a sudden localised reduction in the velocity of water, causing sediment in suspension to be deposited at the river bank, with coarse sediment being deposited first, trapping finer sediment. With each flood, the deposited sediment raises the river banks by as much as a few metres.
Floodplains are seen in the middle and lower course. During a flood, water containing alluvium pours out over the valley floor, and the water slowly soaks away, leaving the deposited sediment behind. Over time, flooding repeats to form a thick alluvial deposit that is fertile.
Floodplains can become wider due to the lateral erosion of meanders. When the outside bend of a meander meets the edge of a river valley, erosion will cut into it, widening the valley. Meanders slowly migrate downstream, also widening the valley.
Headlands and bays are features of a discordant coastline (rocks of different resistance to erosion). Headlands form resistant promontories jutting out into sea, separated by bays of less resistant rock where the land has been eroded back by the sea. Weaker rocks are eroded more readily than the harder rocks to form a sequence of alternating headlands and bays. Erosion at the headlands creates cliffs and wave-cut platforms.
Joints in a cliff are eroded and enlarged by hydraulic action to form a wave-cut notch, further eroded by hydraulic action and abrasion to form a cave, which is eroded through the headland to form an arch, and over time, erosion widens the arch and weathering weakens the roof. The roof collapses to form a stack, which will be eroded and collapse to form a stump.
A beach is formed from deposition and is made up of shingle. Constructive waves, which are low-energy and have a higher swash than backwash, deposit sediment over time to create sandy beaches.
A spit is a shingle ridge commonly formed by longshore drift (zig-zag movement of sediment along a stretch of coastline as a result of wave action). At the end of the spit, it is more exposed to variations in the wind and waves, and curves to form a hook or recurved tip.
Case study: A UK river basin (River Wye) - 1
River Wye is over 210km long, and is the fifth longest river in the UK. Its source is in the Plynlimon Hills, then flows south-east to join the River Severn at Chepstow. Geomorphic processes operate at different scales, both spatially and temporally - processes of erosion, transportation, and deposition are active along Wye, producing V-shaped valleys, meanders, floodplains, and levees. Weathering and mass movement are common in the upper course at Plynlimon Hills, but occur on a more localised and smaller scale.
River Wye, for much of the upper course, flows across impermeable shales and gritstones, accounting for the large number of tributaries joining the river. High rates of flow occurring after rainfall enable the river to carry out significant erosion, to form V-shaped valleys and waterfalls. Near Rhayader, alternating bands of soft and hard rock result in a series of rapids. South of Hereford, weak mudstones and sandstones have been eroded to form a flat valley with meanders. Between Goodrich and Chepstow, the river cuts through carboniferous limestone, forming the gorge known as Wye Valley.
The average annual rainfall of Wye is 725mm, but in Plynlimon Hills, this exceeds 2500mm! This leads to rapid river flows, allowing higher rates of erosion. Winter temperatures can be low, resulting in active freeze-thaw on the valley sides to form V-shaped valleys. This also promotes mass movement.
Case study: A UK river basin (River Wye) - 2
V-shaped valleys are found in the upper course of Wye and along its tributaries. Waterfalls like Cledon Falls are formed on some of the tributaries. Levees and floodplains have formed in the middle and lower courses of the river, with extensive alluvium deposition.
Wye flows through several large settlements like Rhayader, Hereford, and Chepstow - over 200,000 people live in the Wye and Usk river valleys. Much of the valley is used for farming, in the middle and lower courses (due to floodplains being fertile - alluvium deposits). The Wye Valley gorge attracts canoeing, climbing, and kayaking activities.
Flooding is a serious issue in settlements like Hereford, so to reduce the risk, flood walls have been constructed to protect 200 properties in the Belmont area for £5 million. Storage lakes like Letton Lake are constructed above to store surplus water.
Tree planting (afforestation) in the upper course helps to stabilise the slopes, reducing mass movement and the amount of sediment in the river, which can increase the risk of flooding. There will be a reduction in deposition further downstream, so depositional landforms will be less. Planting trees reduces the height of floods by 20% as they increase the amount of water that can be stored.
Case study: a UK coastal landscape (North Norfolk)
The North Norfolk coast is located in East Anglia. It is exposed to powerful waves from the north-east, the direction of maximum fetch (over 4000km), meaning that the coast is exposed to the most powerful waves. Longshore drift operates from east to west, although opposing currents transport sediment southwards along the east coast of England, around The Wash. Mechanical weathering and mass movement (slumping in particular) is very active on the cliffs in the east, between Overstrand and Happisburgh, on a smaller scale. Erosion is dominant in the east; deposition dominates the west.
The entire region is underlain by sedimentary rock chalk, which is overlied by thick glacial sediment (drift and till) that spread south from Scandinavia during the last glacial period. Cromer Ridge is a 100m rmoraine ridge marking the furthest extent of ice advance. Sand and gravel deposited by glacial meltwater streams are found along parts of the coast to the west of the region, alongside till, forming thick deposits along much of the coast. These glacial sediments are susceptible to mass movement and coastal erosion. Cliffs retreat by 1m per year.
Case study: a UK coastal landscape (North Norfolk)
During the last glacial period, ice advanced over the area, depositing thick sediment. After being exposed to geomorphic processes, this was rapidly eroded in the east and redistributed in the west. The climate is relatively dry, with warm summers and occasional cold winters. Till dries and cracks in dry conditions, making it more vulnerable to geomorphic processes. Cold spells in the winter promote freeze-thaw, especially if the clay has deep cracks.
The northeast coast between Overstrand and Happisburgh is dominated by actively eroding till cliffs. Powerful waves undercut the cliff, causing them to collapse, and the limited beach causes them to be exposed to the full force of waves - the long fetch from the northeast, over 4000km! The north coast to the west of Sheringham is dominated by deposition. Longshore drift operates from east to west, forming the Blakeney Point spit, and salt marshes (Stiffkey), features of a spit.
The coast is widely used by people - villages and small towns on the coast, with activities like forestry, farming, and fishing. Much of the area is popular with tourists who enjoy the landscapes. In fact, tourism is the largest sector in the Norfolk county, supporting 65,000 jobs and contributing £3 billion to the local economy, and in North Norfolk, the total value of tourism in 2017 was £505 million.
Case study: a UK coastal landscape (North Norfolk)
Several threats face North Norfolk coast, like the high rates of erosion and occasional storm surges (most recently in 2013), as well as sea levels rising due to climate change. At Holkham, the Holkham Estate have planted pine trees to stabilise the sand dunes and constructed boardwalks to enable visitors to access the dunes without disturbing wildlife or habitats.
At Wells-next-the-Sea, groynes have been constructed to protect the beach huts, and gabions protect the National Coastwatch Institution (NCI) lookout station. These methods of hard engineering trap sediment, building up the beach to protect the coastline from the especially powerful waves. However, this could starve beaches of sediment further along the coast.
Sea walls and rock armour have been built at Cromer, Sheringham, and Overstrand. Sea walls deflect high-energy waves (destructive waves) along the coast. Some people consider these defences to be ugly and ruining the natural landscape. Groynes increase the size of the beach, which could attract more tourists, causing the local economy to grow.