Cliffs

They result from the interaction of a number of processes:o Geological.o Sub-aerial.o Marine.o Meteorological.o Human activity.

Hard rock cliffs:

o Examples include granite and basalt cliffs.

o They exhibit a slow rate of erosion and tend to be stable.

Soft rock cliffs:

o Examples include cliffs comprised of glacial till and clay, such as

those found at Fairlight Cove in Hastings.

o These cliffs often erode rapidly. In these cliffs, sub-aerial processes

can contribute more to erosion than marine processes, leading to

mass movements such as sliding, slumping and falls.

Reasons for cliff erosion at Holderness:

The cliffs at Holderness have an average speed of retreat of 2m per year.

1. Cliffs are made of soft glacial till.

2. Till is easily eroded at base by waves, resulting in instability.

3. Rainwater from above enters the till easily, adding to its weight and

instability.

4. Massive slumps and slides occur.

A similar situation exists at Baton on sea in Hampshire and Beachy Head.

Headlands and bays

Usually found where less resistant and more resistant rock alternates. The

less resistant rock is attacked, first forming bays, and the stronger rock

remains as headlands. As wave refraction later occurs, energy becomes

concentrated on headlands, leaving them more liable to erosion.

Wave cut platforms

o Gently sloping features, often found extending from the base of a

cliff

o They consist partly of material removed from the cliff (wave cut

notch) as a result of continual undercutting by waves. 

As undercutting increases, the cliff slowly retreats, leaving a

platform with an angle of less than 4 degrees.

The platform widens to a point, but due to the cliff being attacked

less frequently by waves, it is thought that they can only reach a

maximum of 0.5km.

Caves, arches, stacks and blowholes

o Secondary features occurring during cliff formation

o They originate due to lines of weakness such as joints or faults

being attacked and made larger by marine erosion

o Caves occur where the weakness is at the base of the cliff

o can become a blowhole if the crack extends all the way to

the surface.

1. Caves formed on either side of a headland may form an arch if the 2

caves join together.

2. Stacks are collapsed arches.

3. Stumps are stacks that have been eroded and lost height

Spits

Narrow, long stretches of sand/shingle that extend out to sea, or partway across a river estuary. One end is more protected than the other,

and mud flats/salt marshes may develop in sheltered areas behind them. One of the most famous examples is Chesil Beach in Dorset:

Sandy spits form as a result of dominant constructive swell waves.

Shingle spits are a result of dominant destructive waves.

Why do spits develop hooked ends?

Two explanations are offered:

1. A change from the prevailing wind direction, coinciding with the direction of second most dominant fetch and wave direction.

2. Wave refraction occurs at the end of the spit which carries some material into more sheltered areas.

Tombolos

This is where a spit or bar connects the mainland to an island.

Barrier beaches and islands

Such features are uncommon in the UK, but are the most common feature of coastal deposition in the world, shown by their presence on the Eastern

Seaboard of the USA from New Jersey south to Florida. They are a number of sandy beaches that are totally separate to the main land, but run parallel to it,

meaning that lagoons may develop behind them.

Cuspate forelands

Can be described as triangular beaches. Their origin is due to longshore drift operating on a coastline from two different directions. The two sets of storm

waves build up a series of ridges, each protecting the material behind it, creating the triangular feature.

Explanations for erosion

Abrasion/corrasion:

When waves approach the coastline they are carrying material such as sand, shingle, pebbles and boulders. Abrasion occurs when this material is hurled against cliffs as waves hit them, wearing the cliff away.

Hydraulic pressure:

Cliffs and rocks contain many lines of weakness in the form of joints and cracks. A parcel of air can become trapped/compressed in these cracks when water is thrown against it. The increase in pressure leads to a weakening/cracking of the rock.

Corrosion/solution:

Seawater contains carbonic acid, which is capable of dissolving limestone. The evaporation of salts in seawater produces crystals and their formation can lead to the disintegration of rocks.

Sub-aerial:

Coastal erosional processes that are not linked to the action of the sea. Erosion occurs via rain, weathering by wind and frost. Its impact is often seen in soil creep, slumping and landslides.

Human activity:

Much building and recreation occurs at the coast, and this increases pressure on cliff tops, making them more liable to erosion and subsidence. The building of sea defences upsets the dynamic equilibrium of the coastline.

Berms are formed as sand/shingle is slowly moved up a beach by successive incoming tides

o They are more common on shingle beaches

Whilst ridges and runnels are found more on sandy beaches.

Both form 'crests'.

Constructive waves

o Depositional waves

o Most common where a large fetch exists

o They tend to have a low gradient

o A larger swash than backwash, low energy

o The wave period is long, with 6-8 waves breaking in a

minute.

Destructive waves

o These act as agents of erosion, because backwash is greater than

swash

o They are most common where fetch is short

o A steep gradient, and 'plunge' onto the beach

o The wave period is short, with 12-14 waves breaking per minute.

Wave definitionsWave fetch:  The distance of open water over which a wave has passed. Maximum fetch is the distance from one coastline to the next landmass, it often

coincides with prevailing wind direction (South West in the UK).

Wave crest:  Highest point of a wave.

Wave trough: Lowest point of a wave.

Wave height:  Distance between trough and crest.

Wave length:  Distance between one crest/trough and the next.

Swash:  Water movement up a beach.

Backwash:  Water movement down a beach.

Sand Dunes

Conditions for formation

Strong onshore winds

Large expanses of dry sand

Obstacles to limit sand movement

Sand movement is effected by

Wind velocity

Grain size and shape

Damp sand

Obstacle where deposition of sand occurs, eg Vegetation

Embryo duneThe first part of the dune to develop. Stabilisation occurs via marram and lyme grass, which act as traps for sand. Conditions are dry and plants adapt to this via long roots, or thorny leaves to reduce evapotranspiration.

Yellow duneColour is due to a lack of humus, but with distance inland they become increasingly grey due to greater amounts of humus. Heights can reach 5m and plants include sand sedge, sea holly, and red fescue.

Fixed grey dunesLimited growth due to distance from beach. Far more stable as shown by existence of thistle, evening primrose, bracken, bramble and heather.

Dune slacksDepressions between dune ridges, which will be damp in summer and water-filled in winter. Species include water mint, rushes, and weeping-willow.

Blow outsOften evidence of over use by humans. Large 'holes' that appear in the dunes.

Salt marshes and mud flatsFormed from a shelter, usually provided by estuaries, barriers, and spits.Fine sediment e.g. silt and clay grains that is the main input into the system. Sediment is deposited and is not easily removed due to low velocitiesAlgae has an ability to withstand being underwater and high salinity.

ShoreBackshoreNot usually reached by wavesUnless stormy

ForeshoreSediment transport takes place (longshore drift)Wave energy is dissipated here

NearshoreSimilar to foreshoreBut only at low tide

OffshoreLimited direct sediment movementTidal current > wave action