Geography Revision Notes (Coasts)

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  • Created by: u_william
  • Created on: 11-12-17 11:26

Georgaphy

Harington School 

OCR Geography A Level Revison Cards (Coasts) 

                                                             

By William_U

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Tides

-          The oceans tides are controlled by gravitational effects, mainly the moon but partly of the sun, together with the rotation of the earth and more locally geomorphology of sea basins.

-          Spring tides are caused by the increase in gravitational attraction – which produces the highest tide and lowest tide the maximum tidal range.

-          Spring Tides – When the sun and moon are parallel as if on a line with the earth.

-          Neap Tides - When the sun and moon are at right angles to the earth. 

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Currents

-          Nearshore and offshore currents have an influence on coastal landscape systems.

-          Rip currents play an important role in the transportation of costal sediment. Rip currents form when waves break near the shoreline pulling up water between the braking waves and the beach.

-          Ocean currents are a much larger scale phenomenon, generated by the Earth’s rotation and by convection. They are set in motion by the movement of winds across the water surface. 

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Spearman’s Rank

-          Spearman’s Rank Correlation Coefficient is a technique which can be used to summarise the strength and direction (negative and positive) of a relationship between two variables. 

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Coastal Systems 1

-          The coast: A zone of transition, a barrier between land and sea

-          They store and transfer energy and material which geomorphic processes use to shape the landscape

-          They are open systems (Energy + material and can transferred to other systems as an input)

-          Inputs: Kinetic energy (wind + waves), thermal energy (Sun), and potential energy (material on slopes), material from deposition and weathering.

-          Outputs: Marine and aerial erosion from beaches and rock surfaces, and evaporation

-          Throughputs (stores): Beach and nearshore sediment, flows (transfers), such as longshore drift effects on sediments.

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Coastal Systems 2

-         Equilibrium: “When inputs and outputs are equal in a system”

-          Dynamic equilibrium: “Inputs and Outputs are disturbed, and system self-regulates, by changing its form (e.g. increased erosion), Form of negative feedback mechanism.

-          Physical factors (wind, waves, tides, geology, and ocean current)

-          They vary in terms of their spatial (place to place) and temporal impacts (over time), and are interrelated

-          Sources of coastal sediment: Beach, cliff, dunes, nearshore, glacial

deposition.

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Coastal landforms development - Geomorphic process

-          Weathering: Physical or mechanical? Disintegration of rocks into particles. 

Chemical weathering - decay of rocks using chemical reactions, “van-Hoff’s law (10% temperature = 2.5% increase in weathering), “synoptic link” (Sea is neutral to alkali, more Co2, temperature and water = more acidic).

Biological weathering: Physical actions, such as growth of plant roots or chemical processes, such as “chelation” by organic acids.

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Coastal landforms development - Geomorphic process

-          Mass movement - Occurs when slope becomes unstable (i.e. wave undercutting, growth of flora on cliff or rainwater), provides significant sediment for the sediment budget. (Cliff erosion).

-          Rock Falls

-          Debris

-          Slides

-          Slumps

-          Water weaknesses in clay

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Coastal landforms development - Geomorphic process

-          Simplified Classification Of Mass Movement

-          Rockfall

-          Mudflow

-          Landslide

-          Rotational Slip

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Coastal landforms development - Geomorphic process

-          Fluvial (River effects): Upper course = most erosion, Middle course = some erosion and deposition, Lower course = most of the eroded material deposited.  River transports and deposits sediment at the coast, increasing the sediment budget.

-          Aeolian (Wind effects): Landscapes can be significantly impacted by the wind, as they are very exposed.

Erosion – Moves particles by “deflation”, at 40KMH, sand particles can be moved, attrition of sand grains by wind is more effective than waves.

Transportation – Creep, suspension, satiation.  Depends on grain size.  E.g. too heavy for satiation, move by creep instead.

Deposition – Winds speeds fall, because of surface friction.

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Coastal landforms development - Geomorphic process

 Synoptic Link – Sea water is typically neutral to slightly alkaline, but with climate change and increasing CO2 rainfall, sea water is becoming more acidic.

 

Mass Movement

-          Occurs when forces acting on slope martial (resultant force of gravity) exceed forces trying to keep material on the slope (predominantly friction).

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Erosional Landforms 1

-          Cliffs and Shore Platforms: When destructive waves break repeatedly on relatively steeply sloping coastlines, undercutting can occur between the high and low tide levels where it forms a wave-cut notch. Continuities undercutting weakens support for the rock strata above, which eventually collapses, producing a steep profile and cliff. The regular removal of debris at the foot of the cliff by wave action ensures the cliff profile remains relatively steep and that the cliffs retreat inland parallel to the coast. Cliffs and Shore Platforms experience 3 main different impacts on their geology: they are Horizontally Beaded Strata, Seaward Dipping - Strata and Land – Dipping Strata.

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Erosional Landforms 2

-          Bays and Headlands: Occur on concordant (small coves with narrow inlets) and discordant coastlines (large, sweeping bays).  Discordant are coastlines that are 90° to the sea.  Less resistant rock is eroded, and contains to head inland, forming a bay, while more resistant remains and sticks out, forming headlands.  As waves approach shore, they must refract around the headlands, this means as they get closer to the cliff of the bay, they lose energy, and deposit materials, and this means that beaches often form at the back and sides of bays.

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Erosional Landforms 3

-          Geo’s: Geos are narrow, steep-sided inlets. Even on coastlines with resistant geology, there may be lines of weakness such as joints and faults. These weak points are eroded more rapidly by wave action than more resistant rock around them. Hydraulic action may be particularly important in focusing air and water into joints and weakening the rock strata.

 

-          Blow Holes: If part of the roof of a tunnel-like cave collapses along a master joint it may form a vertical shaft that reaches the cliff top – this is known as a blowhole. In storm conditions large waves may force spray out of the blowhole as plumes of white, aerated water.

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Erosional Landforms 4

-          Caves, arches, stacks and stumps: Although each of these landforms may be seen independently of each other on upland coasts, they also represent a sequence of erosional landforms which often develop around headlands. Due to wave refraction, energy is concentrated on the sides of headlands.

 

-          Wave Refraction: Occurs when waves approach an irregular coastline. Waves are slowed as they approach the coastline by friction in shallow water (headland first). At the same time the part of the wave approaching the deeper bay doesn’t slow down and the wave bends (or refracts) around the headland.

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Depositional Landforms 1

-          Beaches: Are the most common landform of deposition and represent the accumulation of material deposited between the lowest tides and the highest storm waves. Beach material, which consists of sand, pebbles and cobbles, comes from three main sources: cliff erosion, offshore and rivers.

 

-          Spits: Are long narrow beaches of sand or shingle that are attached to the land at one end and extend across a bay, estuary or indentation in a coastline. They are generally formed by longshore drift occurring in one dominant direction which carries beach material to the end of the beach and then beyond into open water. 

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Depositional Landforms 2

-          Onshore bars: Can develop if a spit continues to grow across an indentation, such as a cove or bay, in the coastline until it joins onto land at the other end. This forms a lagoon of brackish water on the landward side.

 

-          Tombolo: Are beaches that connect the mainland to an offshore island. They are often formed from spits that have continued to grow seawards until they reach and join an island.

-          Salt marshes: Are features of low – energy environments, such as estuaries and on the landward side of spits. The UK has 45,500 ha of salt marsh, mainly in eastern and northwest England. 

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Case Study : Flamborough Head

Landform Case Studies (Landforms are interrelated):

Flamborough Head:

-          Coastline is made up of sandstones, shales and limestone, including carboniferous rocks.  Shale and Clay = 0.8m of erosion/year, Sandstone and limestone = 0.1m/year

-          The headland is made of chalk, and topped with “till”, a glacial deposit left from the last glacial period.

-          Dominant winds from North and Northeast, and waves have a fetch of 1500km from the Arctic, the most exposed parts of the coast is around Saltburn, which can be seen, as the coast has been eroded more.

-          Coastline is in Sediment cell 1, and in the sub cell 1D, the cell goes from “St Abbs” in Southern Scotland to Flamborough head.  Sediment in the sub-cell has come from the nearshore and forced onto the land during the last ice age 100,00 years ago.  Sediment budget is supplied by cliff erosion and the only large river along the coastlines: “The Esk”, but only supplies limited material due to Weirs and reinforced river banks.

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Flamborough Head 1

-          Cliffs: Rocks are horizontally bedded, so cliffs tend to have a vertical face.  Cliffs around Flamborough are made of chalk which has strong and tightly bonded particles, the cliffs are about 20-30m high, with overlying tilt lowered due to mass movement processes to an angle of 40°.Steeper segments of Robin Hood’ bay is formed by more resistant sandstone and limestone, while gentler are made up clay and shale.

-          Shore Platforms: Erosion means that cliffs are retreating, leaving a rocky shore platform behind.  An example is “Robin Hood bay’s” as it has eroded into weaker shales.  Have a 1° angle of slope but can reach 15°, and their maximum width is 500m, they think the shore platform was formed 6,000 years ago.  Could have formed during interglacial periods or when sea levels were stable.

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Flamborough Head 2

-          Headlands and Bays: The variation in rock type along this coastline has led to the formation of a series of bays and headlands as part of a disconcertment platform. Robin Hood’s Bay has been eroded into relatively weak shales with more resistant bands of sandstone either dies forming the headland of Ravenscar, to the south and Ness point to the north.

-          Landforms on headlands: As a result of wave refraction, wave energy is concentrated on resistant headlands that project into the North Sea. Weaknesses, schuh as large joints or faults, are then exploited by the erosive action of the waves, enlarging them to form caves and arches. 

-          Beaches: There are very few well-developed beaches along the Flamborough Head stretch of coastline. The best examples are found in sheltered, low energy environments such as Scarborough and Filey Bay.

-          Changes in landforms: Changes in landforms over time have been due to various factors including: Climate change and sea level fall, Emergent / submergent landforms and modifications of landforms. 

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Evolution Of Coastal Landforms - Submergent

-          Fjords: Submerged glacial valley, 1000M deep, u-shaped valleys, rock basin and shallower area at end called “threshold” due to lower rates of erosion as ice melted.  Valley sides affected by erosion, which will decrease the steepness of the valley, marine erosion increase due to rising sea levels.  E.g. Norway (200km long)

-          Rias: Submerged river valley, shallow water at sides, but deeper towards the centre, valley top middle and upper course of the river remains exposed while lower course and floodplains submerged, smooth profile, formed by fluvial erosion in channel + sub-aerial processes on sides, infilling of earlier channels occurred during Flandrian Transgression, at low tide the river channel flows between broad exposed sandbanks which are only submerged at high tide.  Modified by wave process, sea levels rise may make them deeper but less steep, same as fjords.  E.g. Sydney Harbour.

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Evolution Of Coastal Landforms - Emergent 1

-          Shingle beaches: Sediment which has accumulated on new land that has emerged from the sea, deposited by “rivers” “meltwater” and “low energy waves”, as sea levels rose, they are beached at the bases of former cliff lines or they have formed tombolo’s and spits.  An example is Chesil beach in Dorset, sediment was carried into the English Channel by meltwater as glaciers melted during the “wurm glacial accumulation”, the sediment was carried 50km North-East as sea levels rose due to the South Westerly winds until it attached to Isle of Portland forming a tombolo, the beach contains 100 million tons of single, from 1-2cm to 5-7cm, was thought that the tombolo was formed due to a spit but lack of complex gradins on pebbles suggests that it wasn’t just longshore drift.  Shingle beaches are very vulnerable to modification, rising sea levels may lead to shingle being taken away from the beaches, tombolo’s may suffer a breach as storms may get over the barrier and affecting ecosystem’s and pattern of sediment movement.

- 

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Evolution Of Coastal Landforms - Emergent 2

-          Raised beaches: Found a distance inland behind beaches on emergent coastlines, you can find abandoned cliffs with wave cut platforms and even arches and stacks, formed by marine erosion when the sea levels were higher.  On southern tip of Portland there is a raised beach at 15m above sea level, it was formed 125,000 years ago during “Tyrrhenian inter-glacial period” as the limestone was eroded by hydraulic action, erosion rates were as much as 1m/year and some raised beaches were dated about 210,000 years ago.  After sea levels fell they were no longer affected by marine processes, but are affected by sub-aerial processes and mass movements, over time the cliffs will degrade as vegetation and chemical weathering effect the cliff, and if sea levels rise the abandoned cliffs may be affected by marine processes again.

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Case Study : The Nile Delta 1

-          A delta is a large area of sediment found at the mouths of many rivers, and the sediment is deposited by rivers and tidal currents only form when the deposition of sediment is greater than coastal erosion.

-          They typically form where: (1) Rivers entering the sea carry large amounts of sediments. (2) A broad continental shelf margin exists at the river mouth to provide a platform for sediment accumulation. (3) Low-energy environment exists in the coastal area, where tidal ranges are low.

-          The Nile is an arcuate delta, as it has many distributes splitting from the main river

-          The channels have natural “levees” on their banks, in times of flooding they breach, and the water deposits “lobes” of sediment which will deposit in low lying areas between the levees, caused “crevasse splays”.  This lead to the growth and fertility of the delta.

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Case Study : The Nile Delta 2

-          However, the delta has multiple problems: (1) The dams in the upper Nile (such as the Aswan and GERD dams) have stopped silt and sediment getting to the delta, which has caused the sediment output to decrease from 4.6t/ha/yr, to only traces, leading to the shrinking of the delta and reduction in fertility.  (2) Rising sea levels are bringing more energy to the Nile coast, increasing erosion and speeding up the shrinking of the delta (up to 148m of coastal retreat a year), this is due to imbalance between erosion and accretion.  (3) Pollution from humans across the river has led to the Nile becoming filthy and polluted, leading to death of fish stocks.  (4) Rising temperatures has reduced the rain in Ethiopian highlands, and reduced amount of water getting into the Nile, and decreasing the habitable belt around the river where crops can be grown.

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Case Study : Adelaide, South Australia 1

How Human activity changes a coastal landscape:

Physical Factors:

-          Longshore drift

-          Erosion

-          Rising sea levels

Human Factors:

-          Coastal development

-          Dune development

-          Pollution

 

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Case Study : Adelaide, South Australia 2

Consequences:

-          Northern beaches developed, while Southern beaches starved of material

-          Dunes have been built on and rock armour has been constructed

-          (Add Species name here) were harmed over years of polluting

-          The equilibrium of the coast has been disturbed by human interference

Management Strategies:

-          Beach Replenishment (Introduction of “Living Beaches” to more effectively move sand using pipes rather than trucks) and Rock armour (Former)

Effects:

-          Dune growth has been encouraged to try and get the natural equilibrium restored.

-          Contemplating removing rock armour, as it disturbs natural cycle of dune replenishment.

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