Coasts

• What are the 6 types of Marine Erosion?

  1. Abrasion
  2. Hydraulic Action
  3. Cavitation
  4. Pounding
  5. Corrosion
  6. Attrition
• What is Abrasion?

  Abrasion is bits of rock and sediment which smash and grind against the base of the cliff by waves.
• What is Hydraulic Action?

  Hydraulic Action is air which is forced into joints and compressed when waves crash in. The pressure of this breaks the rock off.
• What is Cavitation?

  As waves recede, the compressed air expands violently causing pressure to break off rocks.
• What is Pounding?

  Pounding is the energy of a wave being able to erode the sediment and rock off of a cliff.
• What is Corrosion?

  Corrosion is soluble rocks dissolving in the sea water as it's slightly acidic (e.g. Limestone and Chalk).
• What is Attrition?

  Attrition is bits of rock in the water smashing against each other and breaking off into smaller bits, resulting in more smooth shapes like pebbles.
• What is Longshore Drift?

  Longshore Drift is the process which transports sediments along the coastline. The swash carries the sediment (e.g. shingle, pebbles) up the beach, parallel to the prevailing winds at 45 degrees. The backwash then carries the sediment back down the beach at right angles to the shore line (90 degrees) due to gravity. Over a period of time, sediment moves along the coastline in this zig-zag pattern where it will be deposited further along.
• What are the 5 main methods of Transport?

  1. Longshore Drift
  2. Traction
  3. Saltation
  4. Suspension
  5. Solution
• Traction

  Traction is very large particles (e.g. boulders) being pushed along the seabed by the force of the water.
• Saltation

  Saltation is large particles (e.g. pebbles or gravel) that bounce along the seabed as they are too heavy to be carried in suspension.
• Suspension

  Fine material (such as silt and clay) are whipped up by the turbulence and carried along in the water.
• Solution

  Solution is substances that can dissolve and are carried in the water (e.g. limestone dissolves in slightly acidic water).
• What factors effect the rate of erosion?

  • Beach presence
  • Human Activity
  • Coastal Configuration
  • Sea depth
  • Fetch
  • Wave steepness and Breaking Point
• How does Wave Steepness and Breaking Point affect the rate of erosion?

  Steeper waves are high energy waves and have greater erosive power than low energy waves.

  Waves that break at the foot of the cliff release more energy which can have a larger erosive power than those break some distance from the shore.
• How does fetch affect the rate of erosion?

  Fetch refers to the distance a wave has travelled by wind. The larger a wave has travelled, the more energy generated creating larger erosive power.
• How does Sea Depth affect the rate of erosion?

  A steep shelving seabed at the coast will create higher and steeper waves.
• How does Coastal Configuration affect the rate of erosion?

  Headlands attract wave energy through wave refraction which leads to more erosion due it being a high wave energy zone.
• How does Human Activity affect the rate of erosion?

  People remove protective material from the beach which can allow for more erosion further down the coastline.

  Hard engineering, such as groynes, can prevent Longshore Drift from carrying sediment along the beach. This results cliffs down the coastline receiving little material which makes it easier for waves to erode the cliff.
• How does Beach Presence affect the rate of erosion?

  Beaches absorb wave energy and can therefore provide protection against marine erosion.
• What are the 5 types of Mass Movement?

  1. Rotational Slip/Slumping
  2. Soil Creep
  3. Landslides
  4. Rock falls
  5. Mudflows
• The difference in height between the tides is known as the tidal range and tends to be largest in channels such as river estuaries.
• What is a Spring Tide and how is it formed?

  The highest high tide and the lowest low tides occur when the sun and the moon are in alignment. Both of their gravitational forces combine to effectively pull the oceans towards the 2 planets to cause the highest high tides. On the other side of the planet, this creates the lowest possible low tides. This creates a 20% higher tidal range.
• What is a Neap tide and how is it formed?

  The lowest high tide and the highest low tides occur when the sun and the moon are perpendicular to each other. Both of their gravitational forces act against each other , so the overall pull is minimised at high tide, but therefore creates a higher low tide. This creates a minimal tidal range as the gravitational pull is counterbalanced.
• Gravity is another key source of energy in coastal environments and is responsible for tides which occur when the gravitational pull of the sun or moon changes the water levels of the seas and oceans. The high and low tides and therefore the tidal range are all impacted by the positioning of the moon and the sun.
• What are features of Constructive Waves?

  • tend to have a low wave height but a long wavelength (up to 100m)
  • low wave frequency: 6-8/min
  • wide area to cross energy which soon disputes leaving a weak backwash
  • sand and shingle slowly move up the beach
  • gradually increasing the gradient of the beach and creates berms
• What are features of Destructive Waves?

  • high wave height and a low wave length
  • high wave frequency: 10-14/min
  • associated with increased energy available in storms
  • steep sloping shingle beaches
  • steep waves plunge over breaking so energy is concentrated on small area
  • most material is carried down by backwash to create an offshore bar
  • as material is constantly combed downwards, the gradient becomes more gentle
• What is Soil Creep?

  The slowest but most continuous form of mass movement involving the movement of soil particles downhill. Particles rise and fall due to wetting and freezing and in a similar way to longshore drift, this causes the soil to move down the slope.
• What is Runoff?

  Runoff is an example of a link between the water cycle and the coastal system , as the water in the form of overland flow may erode the clifface and coastal area or pick up sediment, that then enters the littoral zone, when it is transported in the water via suspension. It may also be responsible for increasing pollution in coastal areas if it picks up waste or excess chemicals.
• Negative feedback is a response to a change in a system which brings about a nullification/diminishes the effect of the change.
• The coast is a narrow zone where the land meets the sea/ land and sea overlap.
• Positive feedback is a response to a change in a system which leads to an amplifying effect, it increases the output.
• Positive feedback on coast: vegetation on a sand dune is trampled → sand becomes exposed → sand is eroded by the wind → vegetation struggles to re-grow and hold the dunes together.

  
• • Offshore - area beyond the point where waves don't interact with the seabed
  • Nearshore - area between the low water mark and where waves begin to break
  • Foreshore - area between high water mark and low water mark
  • Backshore - area above high water mark, far in land for no marine activity to occur

  
• A sediment cell is a stretch of coastline within which the processes of erosion, transportation and deposition operate and the movement of sediment is self contained (only moved within the cell but not to another cell). This is a closed system.
• Larger sediment cells divided into sub cells for easier management (e.g. Holderness Coastline between Flamborough Head and Humber Estuary).
• Sediment cells are separated from each other by well defined boundaries such as headlands and stretches of deep water.
• The inputs of sediment to the Holderness coastline sub cell is chalk from Flamborough Head, alluvium from Humber Estuary, boulder clay.
• Deposits of sediment are called sediment sinks e.g. beaches, spits, bars, tombolos, offshore bars, sandbanks.
• Sediment budget

  • The sediment budget is the balance between inputs (usually from erosion) and outputs (usually from deposition)
  • Where inputs exceed outputs there is a positive budget and a surplus of sediment, leads to shoreline builds toward the sea
  • Where outputs exceed inputs there is a negative budget and a deficit of sediment, leads to shoreline retreating landward.