Coasts - Landforms of Deposition

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Beach

Beaches = are a constantly changing buffer between the coast and the sea. 

They usually have 3 main components:

1. OFFSHORE - The zone beyond the influence of waves 

2. NEARSHORE - The zone in which waves affect the sea bed

3. FORESHORE - This is the lower beach (often under 5 degrees) it is the inter-tidal or surf zone

4. BACKSHORE - This is the upper beach, usually above the waves. The backshore often represents the accumulation of material deposited by storm waves

(SEE NOTES FOR VERY USEFUL DIAGRAMS)

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Beaches - Ridges and Runnels

The spreading out of the waves' energy across a wide area of beach tends to cause ridges and intervening depressions called runnels. They're commonly found on shallow sandy beaches. They are used as a beaches draining system. 

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Beaches - Berms

Small ridges that develop at the position of the mean tide mark resulting from deposition at the top of the swash. Berms are generally created by smaller waves, with less energy, so the material tends to be smaller. 

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Beaches - Cusps

Semi-circular depressions. They're temporary features formed by a collection of waves reaching the same point. The sides of a cusp channel the incoming swash, into the centre of the depression producing a stronger backwash, which drags material down the beach from the centre of the cusp.

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Bars

Bars = A bar extends across the mouth of a bay, sometimes reaching the otherside, and sealing off its entrance. [An offshore bar forms a low ridge of shingle and sand]

Bars occur in highly developed coastal environments where any streams flowing into the bay are small and have weak flows. They follow the same format as spit formation: -Some prevailing winds  -Longshore drift -Large load This allows sediment accumulation to exceed removal rates by river and sea currents.

Favourable conditions for bar formation:

  • Bend or change in the direction of the coastline 
  • Plentiful load 
  • Active longshore drift 
  • Constructive waves

Factors reducing/stopping spits and bars growth:

-Reduction in supply of sand and shingle - less deposition -Deeper water -Stronger river and tidal current = more erosion than deposition -More exposure to storm waves = More energy=More erosion

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Spits

Spit = A spit is a long, narrow piece of sand or shingle that at one end has joined to the mainland and projects out into the sea or part the way across an estuary. 

Formation:

1. All begin when there is a sudden change in the coastline e.g. because of an estuary. The prevailing winds may have generated a particular direction for longshore drift, but the change in the coastline takes the beach sediment out to sea, away from  land.

2. Storms build up more material, making the feature more substantial. Finer material is then carried, extending the spit into deeper water.

3. The river estuary is an obstacle and prevents further development of the spit. Wave refraction carries material into more sheltered waters, causing the spit to curve, giving the spit its hooked shape.                             

A spit provides the sheltered conditions for the development of a saltmarsh and sandunes.

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Unstable Spit case study

Why it formed:

  • Dominant wind direction from the NE which helps keep the alignment parallel to the coast and the distal end back into the Humber estuary 
  • Natural position for the formation of the spit at the Northern side of the Humber estuary
  • Longshore drift from North to South carries a particularly heavy load because of the rapid rates of erosion along the 60km of boulder clay cliffs at the Holderness coast to the North

Why it is unstable:

  • Once longer than 5km it becomes unstable 
  • Vulnerability of narrow points in the section of the spit to storm waves increases from East and SE
  • New growth exists further west, a reflection of retreat westwards of the boulder clay cliffs coastline to the North, which the new formation is inextricably linked
  • There are records of reaches throughout history - after every breach the spit begins to reform, because of all the favourable conditions continue to exist
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Unstable Spit case study continued

SPURN HEAD 

What has been done to protect it:

  • 1850-1950: a concrete wall was built to stop erosion, wooden groynes were intended to trap and hold sand in place
  • At the time it was not realised Spurn Head needed to move for survival, so the wall was collapsed and the groynes are in a state of disrepair
  • Its positioned has remained stationary whilst the rest of Holderness coast has retreated 
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Sand Dune Succession

Sand Dune Succession = the evolution of plant communities at a site over time form pioneer species to climax vegetation.

Sand dune succession:

  • At each stage of succession the plant community alters the soil and microclimate allowing the establishment of another group of species
  • One community of plants is therefore replaced by another as the succession develops.
  • Eventually a climax community is reached where the vegetation is in a state of equilibirum with the environment and there is no further influx of new species. 
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Sand Dune Formation

SAND DUNE FORMATION 

1. Frequent and strong offshore winds (Winds that blow onto the shore)

2. A wide foreshore exposed at low tides, so that there is more chance of the sand drying out and leaving more time for onshore winds to carry sand inland, beyond the mean high tide mark.

3. The presence of a 'trap' for the blown sand to encourage its accumulation will be required. This trap can be shingle, tufts of grass or drifted debris dumped by waves in a storm and sand will accumulate behind it. 

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1. Embryo Dune

HEIGHT: no more than 1m

CONDITIONS: very extreme, alkaline pH 8+, rapid drainage, no humus, high wind speed, LOTS of salt spray, sand constantly moving around top of beach, needs an obstruction to break the force of the wind, so sand can accumulate

PLANT SPECIES: seaweed 

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2. Fore Dunes

HEIGHT: up to 5m

CONDITIONS: The plants here are drought resistant - capable of withstanding burial by shifting sand. Marram grass grows 50-120cm which helps to bind sand with its extensive root system

PLANT SPECIES: ~Lyme grass ~Sea crouch grass ~Marram grass ~Sea rockcet ~Salt wort ~Ragwort 

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3. Yellow Dune

HEIGHT: 5-10m 

CONDITIONS: Greater diversity of plants since conditions are more favourable. Plants decay and die building up a humus layer which traps water and nutrients. pH is slightly alkaline at 7.5. There is more shelter and less salt spray

PLANT SPECIES: ~Creeping fescue ~Sand sedge ~Mosses ~Lichens ~Sea holly ~Sea spurge

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4. Grey dunes

HEIGHT: 10m 

CONDITIONS: Much more stable, shelter from harshest winds, true soil begins to form, acidic conditions and low water content

PLANT SPECIES: ~Marram grass ~Mosses ~Lichens ~Heather ~Red fescue ~Sand sedge ~Sea spurge ~Brambles ~Gorse ~Buckthorn 

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5. Dune Slacks

HEIGHT: 10m 

CONDITIONS: found in between dunes where water table reaches surface causing seasonal/permanent water-logging and surface water. Plants are well adapted to damp, sheltered hollows if decayed slowly a peat soil may develop

PLANT SPECIES: ~Rushes ~Sedges ~Cotton grass ~Creeping willow 

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6. Mature dunes

HEIGHT: 700m from shoreline and 10m 

CONDITIONS: soil which can support shubs and trees. They are undisturbed, humans may plant fast growing conifers. Eventually an oak climax vegetation may develop. 

PLANT SPECIES: ~Hawthorn ~Ash ~Birch ~Oak trees ~Conifers

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Saltmarsh Succession

Saltmarsh Succession:

  • Saltmarshes may occur in sheltered river estuaries or behind spits 
  • In these areas of intertidal mudflats, marsh will develop and in time begin to colonise the silts and muds. Initially the mudflats are colonised by eelgrass. 
  • Pioneer plants that can tolerate these salty conditions (HALOPHYTES), which are submerged at high tide include: ~Grasswort ~Sea Blite ~Spartina (which has a root system that can secure the plant at the surface and anchors it into up to 2m of sediment, at the same time slowing the tidal flow and trapping more sediment, mud and silt)
  • The irregular profile of some areas of the marsh gives rise to creek systems which enable the tidal waters to come in and out
  • Where the hollow are cut of sea water that is trapped may evaporate leaving saltpans
  • Eventually the marsh rises above sea level and is not regulalry drowned by sea water 
  • Reeds and rushes e.g. sea rush become established 
  • When the marsh is more developed, moisture tolerant trees like alder, ash and oak arrive completing the succession which is known as HALOSERE
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Formation of Saltmarshes

Conditions for growth: -Low energy coastline -Sheltered areas - aids deposition -Mositure, nutrients and oxygen

Formation:

1. Exposed at each low tide are thin layers of mud that contain only algae at first.

2. As the mud deepens, pioneer plants establish, which trap more mud. Channels are cut by receeding water at low tide. Grasswort and Spartina established 

3. More plants higher up in the marsh trap more sediment and cause the marsh surface to rise and the channels to deepen. Mannagrass and sea purslane established

4. As the mud deepens further, the marsh slowly grows with more plants colonising in the higher zones until it is largely covered with vegetation. Only the highest tides now cover the marsh and erosion along the channels can cause bank collapse and salt pans to form. Sea rush and red fescue established

5. Although the channel deepens further due to surface runoff the marsh is only covered at high tide now. Sea thrift and sea lavender established

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Saltmarshes

Animal species found in saltmarshes:

~Ribbed muscles  ~Shark tailed sparrows  ~Great blue heron  ~Otters  ~American black duck 

Stresses of a saltmarsh to overcome:

~Filling and drainign them to be built on  ~Sea level rise = flooding = global warming  ~Yard waste is dumped in them  ~Strong storm waves can wipe out the saltmarsh overnight

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Saltmarsh Case Study: Key Haven

LOCATION: Key Haven saltmarhes are located on the south coast of England. The marshes have formed behind Hurst Castle spit - which protects the marshes naturally from strong winds and coastal erosion                                                                                                                         THREATS TO SALTMARSH:

HUMAN: 

  • Key Haven saltmarshes are under threat from construction of groynes down current, which were designed to trap sediment for south coast beaches - they have starved the spit - which protected the saltmarshes 
  • Human activity can lead to sediment being moved in shoes and bags, more sediment is removed as tourism is increases, leading to a greater amount of erosion taking place - saltmarsh is destroyed

PHYSICAL:

  • In 1989 a storm in December pushed part of the shingle onto the top of the saltmarsh, exposing up to 80m of saltmarsh to the sea. Over the next 3 months lots of erosion on this section of the saltmarsh took place.
  • The starvation of sediment for spit has weakened it = less shelter for saltmarsh 
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Saltmarsh Case Study: Key Haven Continued

IMPACTS:

HUMAN:

  • If conditions within the harber continue to deteriorate it could damage tourism and ecommercial activities
  • Increased wave exposure, reaching further into the estuaries has already affected the number and position of yacht moorings safety within marine recreational areas

PHYSICAL:

  • Wildlife lives in a delicately balanced environment, which is easily upset by the loss of species and habitats. Saltmarsh and mudflats provide extremely important and environmentally sensitive habitats for a diverse range of wildlife
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Saltmarsh Case Study: Key Haven Continued

MANAGEMENT STRATEGIES:

  • An experimental technique is intertidal recharge which is used to describe the raising of the area between high and low water, with imported sediment, such as dredged material, which could encourage sediment deposition on the saltmarsh/mudflat.
  • A shoreline management plan was put into place in 1966 which is hoped will stabalise the saltmarsh, flanking will not occur and the spit will be protected 
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Sea Level Change

There are two types: Eustatic and Isostatic 

ISOSTATIC: Local change in sea level resulting from the depression of the Earths crust by increased or decreased weight imposed upon it by a growing or declining ice sheet. (CHANGE IN LAND)

EUSTATIC: Refers to a worldwide fall or rise in sea level due to changes in the hydrological cycle caused by water being held storage on land, in ice sheets, or released following the melting of ice sheets. (CHANGE IN SEA LEVELS)

Sequence of sea level change:

1.Formation of glaciers and ice sheets produces a eustatic change/ fall in sea level and a lowering sea level.                                                                                                                               2. Continued growth of ice sheets depresses the land surface under the ice and produces a relative isostatic rise in sea level, whic may moderate the eustatic fall in some areas.                               3. As ice sheets begin to melt, a rapid eustatic rise in sea level occurs with +VE change in base lvl 4. As the ice sheets and glaciers continue to retreat there is a buoyancy effect and the land springs back upwards in some areas. This isostatic uplift results in a locally negative change in base lvl

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Sea Level Change - Submergence

The rise of sea level allows the sea to flood land masses, especially in areas of low lying land, such as existing river valleys. Drowned river valleys, from post glacial rise in sea levels, include most estuaries, to some extent. 

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Submergence Land formations - Rias

KEY FEATURES: 

Gently sloping valley sides, shallow and narrow valley, in cross section rias become towards middle of the valley 

FORMATION:

  • During the ice age, the rivers that continued to flow were able to cut their valleys down to the lower base valley
  • When the ice melted and sea level rose, the lower parts of the main valley were drowned to produce sheltered, windng inlets called rias or drowned valleys 
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Submergence Land formations - Fjords

KEY FEATURES: 

In cross section V-shaped valley represents original shape of glacial trough, characterised by steep cliff sides, uniformly deep (1000m + in depth). 

FORMATION:

  • Located where glaciers are able to erode below sea level 
  • When ice melted the valleys were flooded by the rising sea to form long, deep, narrlow inlets, with preciptious sides and hanging valleys

(Fjords are drowned glacial troughs)

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Fjards

FORMATION:

  • Rocky, low lying inlets of land which have been previously glaciated and have now been drowned 
  • Although they can be deep like fjords, they are usually more irregular in shape
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Sea Level Change - Emergence

Emergence = In areas of isostatic change, especially following the removal of ice, results is land rising relative to the sea, land forms of marine erosion and depsotion may rise above the influence of waves that originally created them 

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Landforms of emergence - Raised Beach

Formation:

  • As land rose former wave cut platforms and their beaches were raised above the rest of the waves
  • They're recognised by a line of degraded cliffs fronted by what was originally a wave cut platform within the old cliff line may be a relic landform such as a wave cut notch, arch or stack. 
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Coastal Flooding

CAUSES:

1. Severe weather events create meteorological conditions that drive up the water level, creating a storm surge. These conditions include strong winds and low atmospheric pressure that can be caused by hurricanes or by any severe weather conditions.

2. Large waves driven by local winds or swell from distant storms, raise average coastal water levels and can cause large demanding waves to reach land.

3. High tide levels are caused by normal variations in the astrinomical cycle. When a severe storm hits during high tide, the risk of flooding increases significantly.

4. Flooding from storm surge may be combined with river flooding from rain in upland watershed, increasing flood severity.

5.Coastal floods are extremely dangerous and the combination of storm surge, tides, river inflow and waves can cause servere damage.

STORM SURGE = abnormal rise of water generated by a storm 

STORM TIDE = water level rise due to storm surge and astronomical tide

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Coastal Flooding Case Study: UK East Coast 1953

CAUSES:

High spring tide, large depression over the east coast, combined to create a large tidal surge 

CONSEQUENCES:

307 people died, 40,000 people lef homeless, canvery island, Essex was worst affected, failed flood defences and low level housing - 1st story at sea level, 150 acres of land flooded - agriculture, livlhoods destroyed 

RESPONSES: 

Small scale, individual response - within houses other people helping eachother 

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Soft and Hard Engineering

Soft engineering = Holistic approach, working with nature rather than against it

Advantages = cheaper, protects the environment, long term and sustainable and less environmental impact.

Disadvantages = management of natural, dynamic features is complicated, some areas of the coastline will be left unprotected or less protected 

Hard engineering = The use of structures that aim to resist the energy of waves and tides

Advantages = Solid defences allow for large scale development for the coastline 

Disadvantages = creates narrow shrinking beaches, reduction of wildlife, prevents sediment movement 

 

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Soft engineering - Beach Nourishment

Sand is added to the beach, which widens the foreshore. The sand must be the same grain size as eachother or erosion could speed up. It protects mortality of sea organisms. 

Advanatges:

  • Tourism every $1 they spend on beach they reap $700 from tourism (Miami beach)

Disadvantages:

  • could disturb turtles nesting and laying thier eggs in the beach,
  • relatively expensive 
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Soft engineering - Cliff re-grading

Making the slope of the cliff shallower, works by slowing down rates of erosion and mass movement. (HOLDERNESS COAST)

Advantages: 

  • Very cheap - doesn't require anything additional 
  • Very little maintinence
  • Looks very natural 

Disadvantage: 

  • Doesn't stop erosion, just slows it down 
  • Whilst in production it can distrupt habitats and wildlife that lives there
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Soft engineering - Cliff re-grading

Making the slope of the cliff shallower, works by slowing down rates of erosion and mass movement. (HOLDERNESS COAST)

Advantages: 

  • Very cheap - doesn't require anything additional 
  • Very little maintinence
  • Looks very natural 

Disadvantage: 

  • Doesn't stop erosion, just slows it down 
  • Whilst in production it can distrupt habitats and wildlife that lives there
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Soft engineering - Cliff re-grading

Making the slope of the cliff shallower, works by slowing down rates of erosion and mass movement. (HOLDERNESS COAST)

Advantages: 

  • Very cheap - doesn't require anything additional 
  • Very little maintinence
  • Looks very natural 

Disadvantage: 

  • Doesn't stop erosion, just slows it down 
  • Whilst in production it can distrupt habitats and wildlife that lives there
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Soft engineering - Cliff re-grading

Making the slope of the cliff shallower, works by slowing down rates of erosion and mass movement. (HOLDERNESS COAST)

Advantages: 

  • Very cheap - doesn't require anything additional 
  • Very little maintinence
  • Looks very natural 

Disadvantage: 

  • Doesn't stop erosion, just slows it down 
  • Whilst in production it can distrupt habitats and wildlife that lives there
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Soft engineering - Sand Dunes

It widens 

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