Coastal Landforms

When destructive waves break repeatedly on relatively steeply sloping coastlines, undercutting can occur between high and low tide levels where it forms a wave cut notch. Continued undercutting weakens support for the rock strata above, which eventually collapses, producing a steep profile and a cliff. The repeated process of the collapse of the cliff and then the undercutting of the cliff is often referred to as the “retreat” of the cliff. As the cliff retreats, a gentle platform (with a gradient less than 5˚), referred to as a wave cut platform, is left behind. As the platform grows, the waves have to travel further to reach the cliff and they’ll lose more and more of their energy. Once the platform reaches a certain size (big width), the waves will become small and shallow water will be produced. Friction from the platform slows down approaching waves causing them to break on the platform rather than the cliff and undercutting slows and eventually ceases. Solution, freeze thaw and salt crystallisation may also help to develop shore platforms.

- is an oval shaped bay with a narrow opening to the sea.

1. Cliffs of resistant limestone.

2. Erosion by the sea.

3. Cuts through to resistant limestone.

4. Forms a break in the cliff.

5. Less resistant sand and clays are eroded.

6. Cove forms.

7. Sea cannot erode resistant chalk.

8. Cove is widened.

Bays and headlands form adjacent to each other, usually due to the presence of bands of differing resistance to erosion. Weaker rocks such as boulder clay are eroded more rapidly to form bays and more resistant rocks such as chalk remain between the bays as headlands.

Due to wave refraction, energy is concentrated on nthe sides of the headlands. Lines of weaknesses in the cliff such as faults or joints are exploited by erosional processes such as hydraulic action and weathering processes such as freeze thaw or crystallisation. This means a cave will develop. If erosion continues, the cave may enlarge to the other side of the headland, forming an arch. Further weathering and erosion will make the arch collapse forming a stack. Finally, with additional erosion a stump will form.

- Is a narrow, steep inlet.

Action of destructive waves and hydraulic action will erode a joint/ fault in a lower portion of the cliff to weaken rock strata. Sometimes, geos initially form tunnel-like caves running at right angles to the coatline. As erosion continues the cave will become enlarged, finally, the roof will collapse forming a geo.

Tunnel like cave created from line of weakness in a cliff as hydraulic action and freeze thaw exploit it to form a cave. If part of the roof of the tunnel-like cave collapses along a master joint, it may form a vertical shaft that reaches the cliff top, this is a blowhole.

In storm conditions, waves may force water out of the blowhole.

Constructive waves help to build up beaches. Beaches represent the accumulation of material deposited between the positions of the lowesr tides and highest storm waves.

Beach material is the form of sand, shingle,pebbles and cobbles come from cliff erosion, rivers and offshore.

SHINGLE= steep gradient 10-20 degrees. Rapid percolation-larger air spaces so little backwah occurs.

SAND= gentle gradient- greater than 5 degrees. Small particle size- becomes compact when wet, little percolation during backwash.

-are long, narrow beaches of sand or shingle that are attached to the land at one end and extend acriss a bay, estuary or indentation in a coastline.

1- Longshore drift occurs in dominant direction, carrying beach material beyind open water.

2- As storms build up more, larger material is deposited making the feature more substantial.

3- End of spit becomes recurved due to wave refraction.

4- If the sheltered area behind the spit, wave energy is reduced, so silt and mud will be deposited and salt-tolerant vegetation may colonisw.

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

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

-are smaller ridges that develop at the position of the mean tide mark, they result from deposition at the top of the swash.

-form on beaches with a shallow gradient as a drainage route for tides.

They are formed due to interation of tides, sediment and beach topography form parallel to the shore.

-are small, semi- circular depressions.

They are formed temporarily when a collection of waves reach the same point, with the swash and backwash at a similar strength.

Salt marshes are vegetated areas of deposited silt and clays. Salt tolerant plant species such as eelgrass and spartina trap sediment and their roots stabilise the sediment.

Form in a low energy environments, where there is shelter from prevailing wind and waves. Deposition will occur where the energy is reduced.

Flocculation also helps deposition of salt to occur.

-are large areas of sediment found at the mouths of many rivers.

Deltaic sediments are deposited by rivers and tidal currents at are deposited by rivers and todal currents at a faster rate then the waves and tides can remove it.

Deltas are criss-crossed by a branching netwrok of ditrubutaries.

- are submerged glacial valleys which have steep, almost cliff like valley sides and the water is around 1000m deep.

They consist of a glacial rock basin with a shallower section at end- threshold- straighter platforms than rias.

Due to the depth of the water , marine erosion rates remained high, deepening the fjord.

-are submerged river valleys, formed as sea level rises.

Rias are typically underlain by alluvial deposits in buried channels that were eroded by the rivers that flowed down to the lower sea levels during glacial floods.

During interglacial periods, when sea levels rose, further deposition would have occured as the rivers have less surplus energy for erosion, so infilling of the channels occured.

When sea level falls as the volume of land- based ice grows, large areas of 'new' land emerge from the sea.

Sediment accumulates on this surface, deposited by rivers, meltwater streams and low energy waves.

As sea levels rose at the end of the Devensian Period, wave action pushed these sediments onshore.