2 - Coasts (Distinctively coastal processes) Flashcards
(24 cards)
Where does marine deposition take place?
Where waves are low energy or where rapid coastal erosion provides an abundant supply of material.
The deposition occurs
…as waves slow following breaking,
…as water pauses at the top of the swash before backwash begins,
…when water percolates into the beach material as backwash takes it back down the beach.
What is aeolian deposition?
The entrainment (picking up), transport and deposition of sediment.
Where is aeolian deposition more prevalent?
Areas that have high tidal range because large amounts of sand may be exposed at low tides, so providing a supply of sediment to be entrained (picked up) by the wind.
Describe the 2 ways wind transports sand.
Surface creep: (similar to traction) wind rolls or slides sand grains along the surface.
Saltation: wind is strong enough to temporarily lift the grains into the airflow to heights of up to 1m for distances up to 20-30m.
What can wave and tidal energy that isn’t used for erosion or lost through friction with the seabed be used for?
Transport coastal material.
Define traction and the conditions it occurs in.
Large boulders are rolled along the seabed and beach.
High energy environment.
Define saltation and the conditions it occurs in.
Small stones bounce along the seabed.
High energy conditions.
Define suspension.
Very small particles of silt and sand float in the moving water.
Define solution
Dissolved materials are transported in the water.
Explain longshore drift.
Waves approach the beach at an angle of ten determined by the prevailing winds.
Swash carries material obliquely up () the beach
Backwash carries material directly down (|) the beach under gravity.
What are subaerial processes?
Processes that slowly break down the coastline, weaken the underlying rocks and allow sudden movements or erosion to happen more easily.
Material is broken down in still; remaining in or near to its original position.
It may affect the shape of the coastline and includes weathering, mass movement and run-off
What is weathering?
The disintegration (break-up) of rocks. Where this happens, piles of rock fragments called ‘scree’ can be found at the foot of the cliff.
Explain freeze-thaw (mechanical (physical) weathering).
Rocks are porous (contains holes) or permeable.
Water enters cracks in rock.
Water freezes, expands and widens the crack by about 10%.
Ice melts and water goes deeper into the crack.
The process repeats until the rock is split.
Explain biological weathering.
Plant roots, birds nests in cliffs, and piddock clams drilling and burrowing down into rocks all weaken the structure of the rock until it breaks away.
Explain chemical weathering.
Caused by chemicals.
Rainwater is slightly acidic because it absorbs CO2 from the air.
When this rainwater makes contact with calcium-based rocks, such as chalk or limestone, it produces a chemical reaction causing the rock to slowly dissolve.
Define mass movement.
The downhill movement of cliff material under the influence of gravity. There is a range of different types of mass movement.
What are the 4 main areas of mass movement?
Creeps
Flows
Slides
Falls
What is the type of mass movement dependant on?
Cliff/slope angle
Rock type
Rock structure
Vegetation
Saturation of the ground
Presence of weathering
What are the 5 mass movement processes at coasts?
Landslides
Rockfalls
Mudflows
Rotational slip
Soil creep
What is a landslide?
The rapid movement of detached slabs of rock down a slide plane.
What is a rockfall?
Individual rock fragments fall off a cliff face, often due to freeze-thaw.
What is mudflow?
Saturated soil flows downhill, often triggered by heavy rain.
What is rotational slip?
Common coastal landslips in weak rocks, e.g. sands and clays.
What is soil creep?
Very slow downhill movement of individual rock particles.
