Geography 4.2.1 Coastal Landscapes

What are the 2 categories for coastal processes?

• Marine processes: Offshore (water-based)

• Terrestrial processes: Onshore (land-based)

What are the 5 main coastal processes?

• Wave action

• Erosion

• Transportation

• Weathering

• Mass movement

What are the effects of rock type on coastline

	Hard Rock	Soft Rock
Shape of cliff	High and steep	Generally lower and less steep
Cliff face	Bare rock and rugged	Smoother; evidence of slumping
Foot of cliff	Boulders and rocks	Few rocks; some sand and mud

What are concordant coastlines?

• Concordant coastlines are made up of the same rock type, running parallel to the sea, these coastlines produce coves 

What are discordant coastlines?

• Discordant coastlines have alternating bands of rock perpendicular to the sea, these types of coastlines form headlands and bays

What are the 4 types of erosion?

• Hydraulic Action 

• Attrition

• Corrosion 

• Abrasion 

Hydraulic Action

Attrition

Corrosion

Abrasion

What are Headlands and bays?

• Occur where there are alternating bands of hard and soft rocks run perpendicular to oncoming waves (discordant coastline)

• At first, the soft rock (e.g. clay) is eroded backward, forming an inlet

• As the inlet continues to erode it curves inwards, and a bay is formed, usually with a beach

• The hard rock (e.g. limestone) is left protruding out to sea as a headland

What are cliffs?

• Cliffs are shaped through erosion and weathering processes

• Soft rock erodes quickly and will form sloping cliff faces

• Steep cliffs are formed where there is hard rock facing the sea

What are wave cut platforms?

• A wave-cut platform is a wide gently sloped surface found at the foot of a cliff:

  • As the sea attacks the base of a cliff between the high and low water mark, a wave-cut notch is formed

  • Abrasion, corrosion and hydraulic action further extend the notch back into the cliff

  • The undercutting of the cliff leads to instability and collapse of the cliff

  • The backwash of the waves, carries away the eroded material, leaving behind a wave-cut platform

  • The process repeats and the cliff continues to retreat, leading to a coastal retreat

What is a cave and how are they formed?

• These form in a headland because of wave action and sub-aerial weathering

• As waves approach the shore, their speed is reduced as they move along the sea floor

• This changes the angle of the waves, and they will turn so the crest becomes parallel to the coast - known as wave refraction

• This refraction concentrates erosive action on all sides of the headland

•  The erosional processes of hydraulic power, abrasion and some corrosion begin to attack any weaknesses in the headland

• As the crack begins to widen, abrasion will begin to wear away at the forming cave

What is an arch and how are they formed?

• The cave will become larger and eventually breaks through the headland to form an arch

• The base of the arch continually becomes wider and thinner through erosion below and weathering from above

What is a stack and how are they formed?

• Eventually, the roof of the arch collapses, leaving behind an isolated column of rock called a stack

• The stack is undercut at the base by wave action and sub-aerial weathering above, until it collapses to form a stump

What is the UK’s overall climate?

• The UK has a temperate maritime climate

• This means a mild, seasonal climate-cool, wet winters and warm wet summers

How does this factor affect the UK climate?

• Continentality:

• Continentality:

  • Coastal areas are warmer in winter and cooler in summer 

  • Seas take up the heat in the summer, cooling the surrounding land

  • During the winter, the heat is released, keeping the coastal land warmer

How does this factor affect the UK climate?

• Ocean currents bringing warm waters from the Caribbean to the west coast of the UK

• This keeps the west coast of the UK warmer than other regions of the UK

How does this factor affect the UK climate?

Air masses

• Large volumes of air with similar water content and temperatures

• Classified by the region where they form: 

  • Arctic or Polar cold air

  • Tropical warm air

  • Maritime wet air

  • Continental dry air

• Five types of air masses that bring different weather to the UK:

The UK's Air Masses

Air Mass	Weather
Polar Maritime	Cold and wet
Arctic Maritime	Very cold and wet
Polar Continental	Cold and dry
Tropical Continental	Warm and dry
Tropical Maritime	Warm and wet

What is the impact of this factor on coastal erosion?

Seasons

• The UK's climate impacts coastal erosion in the following ways:

  • Th UK seasons affect the rate of weathering and erosion

    • Cold temperatures lead to freeze-thaw weathering on cliff faces, increasing rock falls

    • Winds are stronger in winter than in summer and stronger winds give energy to waves

What is the impact of this factor on coastal erosion?

• Prevailing winds

• Prevailing winds in the UK are from the south-west

  • This brings frequent rainfall and increases the rate of weathering

How does this factor affect the UK climate?

• Storm frequency

• Storm frequency is high in many areas of the UK

  • Coasts are exposed to strong winds which increases destructive wave power 

  • Rainfall is heavily leading to flooding and increases in the mass movement

What are destructive waves?

• Destructive waves erode the beach

  • They have a short wavelength, high-frequency rate and a steep wave gradient

  • Their backwash is stronger than their swash, which scours the beach, dragging material out to sea 

What are constructive waves?

• Constructive waves are beach builders

  • They have a long wavelength, low-frequency rate and a shallow wave gradient

  • The swash is stronger than its backwash, which carries material up onto the beach and deposits it there  

Comparison of Wave Type

	Constructive	Destructive
Swash	Strong	Weak
Backwash	Weak	Strong
Wavelength	Long with low height	Short with high height
Frequency	Low (6-8 per minute)	High (10-12 per minute)
Type of beach	Sandy - depositional	Shingle - erosional

What is wave action?

• Waves are marine processes that erode, transport and deposit material

• Waves are formed as winds blow over the surface of the sea 

• The height and strength of a wave is dependent on 3 factors:

  • The fetch 

  • The amount of time the wind blows

  • The strength of the wind

• The greater the strength, time and fetch of the wind, the larger the wave

• As a wave enters the shallow water of the coast, friction from the seabed causes the wave to lean forward and eventually will crest and break onto the beach 

• The movement of water up the beach is called the swash, and the return movement is the backwash

What is weathering?

• Weathering is best defined as:

The break-down of rock in-situ

• Weathering does not involve the movement of the material; this is what makes it different from erosion

• Sub-aerial weathering describes coastal processes that are not linked to the action of the sea

• It includes freeze-thaw weathering (mechanical) and chemical weathering

• Weathering weakens cliffs and makes them more vulnerable to erosion

What is mechanical weathering?

• Mechanical weathering physically breaks up rock

  • Freeze-thaw or frost shattering is where:

    •  Water gets into cracks and joints in the rock

    •  When the water freezes it expands and the cracks open a little wider

    • When the water thaws, the crack contracts, releasing pressure on the crack

    •  Over time, repeated freezing and thawing, widens the crack until pieces of rock split off the rock face, whilst big boulders are broken into smaller rocks and gravel

What is chemical weathering?

• Chemical weathering occurs when rocks are broken down by a chemical process:

  • Rainwater is slightly acidic through absorbing carbon dioxide from the atmosphere

  • This reacts with minerals in the rock creating new material

  • Rock-type affects the rate of weathering e.g. limestone chemically weathers faster than granite

  • The warmer the temperature, the faster the chemical reaction

What is biological weathering?

• Biological weathering takes place when rocks are worn away by living organisms:

  • Trees and other plants can grow within the cracks in a rock formation

    • As the roots grow bigger, they push open cracks in the rocks making them wider and deeper

    • Over time the growing tree eventually prizes the rock apart

  • Burrowing animals, such as rabbits, disturb the ground above the burrow, which puts pressure on any cracks, eventually leading to pieces falling off the rock

What is mass movement?

The downhill movement of material under the influence of gravity

• Throughflow and runoff caused by heavy rain can also make cliffs more unstable and increase the likelihood of mass movement

• It includes landslides, slumping and rockfalls

What is mass movement determined by?

• The type of movement is determined by:

  • Angle of slope (the steeper the slope the faster the movement)

  • Nature of regolith

  • Amount and type of vegetation

  • Water

  • Type and structure of rock

  • Human activity

  • Climate

What is soil creep?

• Common in humid climes with the movement of less than 1cm per year 

• Soil expands when it freezes, gets wet or is heated up in the sun

• As the soil expands, it lifts at right angles to the slope

• When the soil shrinks, it falls straight back down

• Soil creep takes a long time because the soil moves only a millimetre to a few centimetres at a time

What is flow?

• Occurs on slopes between 5° and 15° with speeds between 1 to 15km per year

• Usually happens after the soil has become saturated with a flow of water across the surface

• Vegetation is flattened and carried away with the soil

What is slide?

• A movement of material 'en masse' which remains together until hitting the bottom of a slope

What is Fall?

• Slopes are steep and movement is rapid

• Caused by a number of reasons:

  • Extreme weathering: Freeze-thaw action can loosen rocks that become unstable and collapse

  • Rainfall: Too much rain will soften the surface leading to the collapse of the slope

  • Earthquakes can dislodge unstable rocks 

  • Hot weather can dry out soil causing it to shrink and allowing rocks to fall

What is Slump?

• Slump:

  • Usually found on weaker rock types (i.e. clay), that become saturated and heavy

  • This is common at the coast and is also known as rotational slip

  • It involves a large area of land moving down the slope in one piece

  • Because of the way it slumps, it leaves behind a curved indented surface

Describe the process of longshore drift?

The process of longshore drift

• It is the main process of deposition and transportation along the coast 

• Influenced by the prevailing wind, waves approach the beach at an angle

• As the waves break, the swash carries material up the beach at the same angle

• As the swash dies away, the backwash carries the material down the beach at right angles (90°) 

• The process repeats, transporting material along the beach in a zig-zag movement

What are depositional landforms?

• Deposition will happen when transported material is dropped from the sea water

• This occurs when the velocity (speed) of the water flow slows down

• This means there is not enough force to hold/suspend the material in the water anymore, and it is dropped onto the ground

• Beaches are formed of sediment deposited in bays

• Saltmarshes and mudflats are formed in sheltered estuaries, usually behind spits

What are beaches?

Sediment deposition

• Beach formation usually occurs in the summer months when the weather is calmer

• Form in sheltered areas such as bays through deposition via constructive wave movement, where the swash is stronger than the backwash

• Blown sand can create sand dunes at the backshore of a beach

• When a constructive wave carries sediment up the beach, the largest material is deposited along the upper reach of the swash

• As the backwash moves back down the beach, it loses water and therefore energy as it travels due to the porosity of the sand

• Consequently, the deposition of sediment gets progressively smaller, and the beach is therefore, sorted by wave deposition, with the smallest mud particles settling in the low-energy environment offshore

• If a destructive wave forms due to a storm, then large shingle is thrown above the usual high tide level to form a ridge at the top of the beach called a berm

What are spits?

• An extended stretch of sand or shingle that extends out to sea from the shore

• Spits occur when there is a change in the shape of the coastline

• Or the mouth of a river, which prevents a spit forming across the estuary

• A spit may or may not have a 'hooked' end, depending on opposing winds and currents

• A good example is Spurn Point, which stretches for three and a half miles across the Humber Estuary in the northeast of England

How do spits form?

Spit formation

• Sediment is transported by the action of longshore drift

• Where the coastline changes direction, a shallow, sheltered area allows for the deposition of sediment

• Due to increased friction, more deposition occurs 

• Eventually, a spit slowly builds up to sea level and extends in length

• If the wind changes direction, then the wave pattern alters and results in a hooked end

• The area behind the spit becomes sheltered

• Silts are deposited here to form salt marshes or mud flats

What are Bars and how do they form?

Image showing how longshore drift contributes to spit and bar formation

• When a spit grows across a bay, and joins two headlands together

• A bar of sand is formed (sandbar)

• Sandbars can also form offshore due to the action of breaking waves from a beach