- Created by: wilsonmatthew2000
- Created on: 07-04-19 11:28
Beaches, Berms and Beach Cusps
Beaches are landforms where there is an accumulation of sediment which is reworked by the action of waves and tides.
Berms are formed through the transport and subsequent deposition of sediment up the beach by the swash of waves during high tides - the ridges at the back of the beach represent the section highest up the beach where the material was deposited in a particular tidal cycle. Storm berms near the cliff line are ridges where sediment is thrown by swash during extreme conditions and thus, is above the level of high spring tides.
Beach Cusps form where different sized sediments (sand and shingle) meet. As the gradient begins to steepen sediment transport by the swash moves the smaller sediment up the beach whilst sediment transport by the stronger backwash removes the material, especially from the centre of the semi-circular depression creating the cusp. Runnels are depressions in the sand between ridges left as tidal scour causes sediment to be removed.
Spits are long, narrow ridges of sand and/or shingle that are attached to the land at one end known as the proximal end. The distal end is in the sea and often extends partly across an estuary. This end can be hooked and is likely to change its position over time.
Salt marshes often develop behind the spit and sand dune succession is often key in their stabilisation. These are created through sediment transport caused by the process of longshore drift.
They form due to the presence of a surplus of sediment combined with the process of longshore drift, the dominance of constructive waves and an appropriate coastal configuration – the presence of an estuary or a change in direction of the coast.
Example: Spurn Head on the Holderness Coast
Double spits are formed when there are two dominant directions of wind creating spits either side of a harbour. A bar is stopped from occurring as either the daily action of the tide scours away any deposits or the supply of sediment is not great enough to create a bar.
Double spits can also be formed when a bar ponds freshwater and creates a lagoon. This subsequently breaches the bar and forms two ‘spits’ on either side of the breach.
Example: Chichester Harbour
Recurved spits can be formed when there are two dominant directions sediment transportation–either through two dominant directions of wind causing two directions of longshore drift or due to longshore drift and tidal action.
They can also be formed when wave refraction ‘bends waves’ around the tip of the spit and so causes the spit to become recurved.
Example: Castle Hurst Spit, Hampshire
Bars are formed where sediment transport caused by longshore drift elongates a spit from one side of the river channel to the other. This also creates a lagoon behind the bar such as at Lady’s Island Lake, Ireland.
Other bars are formed when rising sea levels associated with the end of the last ice age have pushed or overwashed sediment landwards and so trapped a freshwater lagoon such as at Slapton Sands.
Example: Chesil Beach, Dorset
Tombolos are features when a beach or bar connects two landmasses.
They are formed when an offshore island refracts approaching waves so that there is then a convergence of two directions of longshore drift on the opposite side of the island creating a beach/bar that connects the island to the mainland.
Example: St Ninian's Tombolo
Fall and Topple
- Blocks of rock can be dislodged by mechanical weathering or by hydraulic action.
- Undercutting of cliffs by the creation of wave-cut notches can lead to large falls.
- Forms scree
- Where rock strata have a very steep seaward dip, undercutting by erosion will quickly lead to instability and blocks of material toppling seaward.
Translational and Rotational Slide
- A very low angle seaward dip in strata will prevent falls.
- In this case, the material will tend to slide down the dip slope towards the sea.
- Bedding plane between the impermeable and impermeable clay and permeable sand dips seaward.
- Cracks develop in the cliff top during dry weather as soil and sediment dry out; these later become routes for water.
- Heavy rain saturates the permeable sands, loading the cliff material and water percolates through creating high pore pressure.
- Erosion undercuts the cliff and curved failure surfaces develop in the sand and the whole cliff rotates around a pivot point.
Slumps and Solifluction
- The difference between sliding and slumping is that there is a rotational movement in slumping.
- Movement of one material over another different one.
- Slumping causes rotational scars and repeated Sumping creates a terraced cliff profile.
- Occurs mainly in tundra areas, where the ground is frozen.
- When the top layer of soil thaws in the summer- the permafrost below remains frozen- the surface layer becomes saturated and flows over the frozen subsoil and rock.
Submergent Coastline Landforms
Rias e.g. Kingsbridge Estuary
- Sheltered winding inlets with irregular shorelands.
- They form when valleys in a dissected upland area are flooded.
Dalmatian Coasts e.g. Croatian coastline
- Similar to rias, but rivers flow almost parallel to the coast.
Fjords e.g. New Zealand
- Formed when deep glacial troughs are flooded by a rise in sea level.
- They are long and steep-sided, with a U-shaped cross-section and hanging valleys.
Emergent Coastline Landforms
Examples: Fife and Ayrshire, Scotland
Headlands and Bays
Different strength rock types exposed to the coast, erode at different rates.
- Headlands force the incoming waves to refract- concentrating their energy at the headlands. This increases the wave's erosive power, which leads to a steepening of their eventual erosion into arches and stacks.
- By contrast, when waves enter a bay, their energy is dissipated and reduced. This allows for deposition of sand and shingle.
Caves, arches, stacks and stumps
- The erosion of rocks like limestone and chalk tends to exploit any lines of weakness- joints, faults and cracks.
- When joints and faults are eroded by hydraulic action and abrasion, this can then create caves. If the overlying rock then collapses, a blowhole will develop as the cave opens up at ground level.
- If two caves on either side of a headland join up, or a single cave is eroded through a headland, an arch is formed. The gap is then further enlarged by erosion and weathering- becoming wider at the base.
- Eventually, the top of the arch will become unstable and collapse- leaving an isolated pillar of rock, called a stack.
- The stack itself will continue to be eroded by the sea, as it collapses and is eroded further, it may only be visible during low tide- stump.
Wave-cut notches and platforms.
- Marine dominated erosion at the base of the cliff between the high and low water mark.
- A wave-cut notch is formed by erosional processes such as abrasion and hydraulic action.
- As the notch increases in size, the cliff becomes unstable and collapses, leading to the retreat of the cliff face.
- The backwash carries away the eroded material, leaving a wave-cut platform.
- The process repeats. The cliff continues to retreat.
- The wave will break earlier and its energy will be dissipated before it reaches the cliff- reducing the rate of erosion.
- Rock strata run parallel to the coastline
- Different rock strata intersect the coast at an angle, geological variation.
- The transition from land to sea is abrupt
- At low tide, the foreshore zone is exposed as a wave-cut platform.
- Flamborough Head, Yorkshire
- At high tide, the sandy beach is inundated, but the vegetated dunes are not.
- Dune vegetation plays a crucial role in stabilising the coast and preventing erosion.
- Extensive mudflats, cut by channels, are exposed at low tide but inundated at high tide.
- Closer to the backshore the mud flats are vegetated forming a salt marsh.
- Lymington, Hampshire
- Pioneer species stabilise the mobile sand with their root systems, reduce wind speed at the sand surface, allowing more sand to be deposited and add dead organic matter to the sand.
- Embryo dunes alter the environment allowing new species to colonise creating a foredune.
- Embryo and Fore Dunes
- Yellow Dunes
- Fixed Dunes
- Salt Crystallisation
- Plants Roots
- Rock Boring
Erosion and Sediment Transport
- Hydraulic Action