Coasts: Coastal landscape development - Landforms and Landscapes of Coastal Deposition Flashcards
Origin and development of landforms and landscapes of coastal deposition: - beaches - spits - tombolos - offshore bars - barrier beaches and islands - sand dunes Factors and processes in their development.
What are beaches?
The accumulation of sediment deposited between low spring tides and the highest point reached by storm waves.
What are beaches mainly composed of?
Sand and shingle
Where does the material that forms beaches come from?
Offshore sand bars
Wind-blown sand from up the coast
Longshore drift
Mass movement from the cliffs behind the beach
What is the gradient of sand beaches?
Less than 5 degrees
Why are sand beaches gently sloped?
Sand grains are small and easily compacted so little water percolates through. The majority of water moving up the beach therefore also returns through backwash which smooths and flattens the beach.
What is the gradient of shingle beaches?
10-20 degrees
Why are shingle beaches steep?
Larger sediment size means it is less easily compacted, so broken waves percolate through the shingle. The backwash is limited in its ability to transport material back down the beach, so little material is eroded from the beach.
Why does shingle tend to be at the top of the beach?
It takes high energy storm waves to deposit the larger material.
What is a storm berm?
A wide flat area of sediment at the top of a beach, deposited by a strong swash during spring high tides.
What is a berm?
A ridge or plateau on the beach formed by the deposition of beach material through constructive waves.
Why do beaches usually have a series of berms?
Berms will be formed down the beach by successively lower tides as he cycle goes from spring to neap.
What are cusps?
Semi-circular shaped depressions in a beach
When do cusps form?
When waves break directly onto the beach where swash and backwash are both strong?
Where do cusps form?
At the junction where sand and shingle meet
How are cusps deepened?
The curved sides channel incoming swash into the centre of the cusp, creating a stronger backwash flowing out, deepening the centre.
What forms ripples on a beach?
The action of tides moving back and forth across the sand
What are ridges?
Raised areas of the foreshore parallel to the coastline
What are runnels?
Breaks in ridges perpendicular to the coastline that allow water to return to the sea
Where do ridges form on a beach?
At the LWM
What is the berm crest?
The highest point on a berm
Name the 6 beach features in order from land to sea.
Storm berm Berms Cusps Ripples Ridges and runnels
What relief of beach do ridges and runnels form on?
Gently sloping beaches
What is the major factor determining the nature of the beach features that develop?
The angle at which waves approach the coastline
What are the 2 classifications of beaches?
Swash-aligned
Drift-aligned
At what angle do waves approach swash-aligned beaches?
Parallel to the shore
At what angle do waves approach drift-aligned beaches?
Parallel to the direction of dominant longshore drift
Describe the movement of sediment on swash-aligned beaches.
Sediment moved up and down the beach with minimal lateral transfer
Describe the movement of sediment on drift-aligned beaches.
Sediment is transferred along the coast by longshore drift
What type of environments do swash-aligned beaches usually form in? Give an example.
Low-energy environments such as bays
Are swash aligned beaches composed of sand or shingle?
Either:
- High energy waves transport sand leaving behind shingle.
- Low energy waves deposit sand
What landform can drift-aligned beaches often form?
Spits
Why are swash-aligned beaches more likely to have rip currents?
The onshore wind causes water to pile up along the shoreline.
Why is sediment at the bottom of a beach usually more rounded?
The constant action of the waves causes abrasion and attrition
Name 6 landforms of deposition
Beaches Spits Tombolos Offshore bars Barrier beaches and islands Sand dunes
What are the 2 types of spit?
Simple and compound
What 3 factors affect the development of spits?
Climate
Nature of waves
Type of beach
What is a spit?
A long, narrow ridge of deposited sediment joined to the mainland at one end and projecting out into the sea or across an estuary.
What are simple spits?
Straight or recurved spits with no recurved laterals
What are compound spits?
Spits with a series of recurved laterals along their landward edge
How are simple spits formed?
Material is moved along the coast by longshore drift.
A river estuary or mouth causes the coastline to change direction.
Sediment starts to build up in the sheltered lee of the headland,
Storms deposit larger material above the HWM making the spit more permanent.
Finer material continues to be moved deeper into the estuary/bay by longshore drift, extending the spit further.
How do spits recurve?
Secondary winds and wave refraction carry and deposit sediment round the end of the spit.
How do recurved laterals form on spits?
If the end of a spit recurves enough, it presents another change in direction of the coastline, so the spit may continue to grow in the original direction .
Give an example of a spit in the UK.
Spurn Head, Humberside
Give an example of a spit outside of the UK.
Farewell spit, New Zealand
What causes a spit to stop growing?
The strongest river current prevents the spit from growing across an estuary by carrying the deposited material into the sea.
What is a tombolo?
A spit that joins an island to the mainland
What important coastal habitats can form behind spits?
Salt marshes
How do salt marshes form behind spits?
Rivers or low energy waves can deposit fine sediment in the sheltered low energy zone behind the spit. The deposits build up and are colonised by vegetation to form salt marshes.
How can tombolos lead to salt marsh formation?
Tombolos create more sheltered conditions on their lee-side, leading to deposition.
Give an example of a tombolo in the UK.
St Ninian’s, Shetland
Give an example of a tombolo outside of the UK.
The Angel Road, Shodo Island, Japan
What are barrier beaches?
A spit that joins two headlands together.
How are many of the barrier beaches in the UK thought to have been formed?
By the gravel that was deposited in the English Channel when glaciers melted after the last ice age being deposited on the coast by constructive waves.
What 2 ways can barrier beaches be formed?
The extension of a spit across a bay.
The onshore migration of material from offshore as sea levels rose following the last ice age.
What forms behind a barrier beach?
A lagoon
What may happen to lagoons over time?
They may become full of silt and dry up.
What can form in lagoons in tropical locations?
Mangrove swamps
How are barrier islands formed?
The melting ice at the end of the last Ice Age led to sea level rise, leaving barrier beaches separated from the mainland.
Why do some long barrier islands split into a series of shorter barrier islands?
Inlets develop between them to allow tides to rise and fall around the island
Give an example of a barrier beach in the UK
Slapton Ley, Devon
Give an example of a barrier beach outside the UK
Lido of Venice, Italy
Give an example of barrier islands outside the UK
West Frisian Islands, Netherlands
How long to barrier beaches and islands take to form?
Ramge of timescales but many started to form at the end of the last Ice Age - 18,000 years ago
What is an offshore bar?
A ridge of beach material that remains semi-submerged beyond the breaker zone
How are offshore bars formed?
By the deposition of sand offshore by currents
What are coastal sand dunes?
Accumulations of sand shaped into mounds by the wind
What are the 5 important inputs into a sand dune system?
Sand supply Strong onshore winds Large tidal range Obstacle to trap sand Vegetation growth
What process moves sand inland to form a sand dune?
Saltation
How does saltation move sand inland?
Warmer land than sea causes localised differences in pressure between the two during the day, resulting in wind blowing onshore.
How do sand dunes form?
Sand is initially trapped by obstacles, often on the storm berm.
The obstacle grows as sand it trapped, slowing the wind and contributing to further deposition.
These embyro dunes are colonised by pioneer species, stabilising the dune.
The dunes grow out of reach of high tide to form yellow dunes.
As they grow the humus organic content increases until the dunes become fixed and grey.
Why is sand often initially trapped on the storm berm?
This is where driftwood is deposited, providing an obstacle
What pioneer species colonise sand dunes?
Marram grass and sea couch
What are embryo dunes?
The first dunes in sand dune formation.
1m high and 80% exposed sand.
What are yellow dunes?
Mobile dunes out of reach of high tide.
5m high and 20% exposed sand.
What are grey dunes?
Fixed dunes able to support larger plants.
8-10m high and 10% exposed sand.
Give an example of the type of plant grey dunes can support.
Gorse bushes
What are dune slacks?
Depressions within dunes where the water table is on or near the surface and conditions are damp
What can form in dune slacks?
Ponds and subsequent aquatic ecosystems
What can be found inland from grey dunes?
Dune heath
What is dune heath?
The climax vegetation of sand dune succession, where hardy trees and shrubs grows which increase humus and moisture retention.
How does the pH change throughout sand dunes? Give examples.
It decreases:
- Embryo dune = 8.5
- Yellow dune = 7.5
- Dune heath = 6.0
What type of succession is sand dune succession?
Psammosere
Give an example of sand dunes in the UK.
Studland Bay, near Southampton
Give an example of sand dunes outside the UK.
Jaeres dunes, Norway
How long do sand dunes take to form?
100s of years
