Coasts Flashcards
What are the main inputs and outputs within coastal systems?
Marine (waves, tides, currents)
Energy (kinetic, thermal, potential)
Geological
Atmospheric
People
What are the four types of erosion?
Hydraulic action
Corrosion
Attrition
Abrasion
What are the four main types of transportation?
Solution
Suspension
Saltation
Traction
What happens during the process of longshore drift?
Swash carries sediment up the beach, parallel to the prevailing wind.
Backwash carries it back down at right angles to the shoreline.
What is a negative feedback loop?
When a change to a system is nullified, taking it back towards equilibrium.
What is a positive feedback loop?
When a change to a system is amplified, taking it away from equilibrium.
What is an example of a negative feedback loop?
Trampling of sand dunes and damage to marram grass can lead to aeolian erosion causing blowouts.
If left alone surrounding marram grass can release seed, recolonise and lower wind speeds, building the dune back up.
What is an example of a positive feedback loop?
Vertical growth of marram grass lowering windspeeds and reducing saltation. This leads to further deposition allowing it to grow taller and encourage further lowering of windspeed, accreting the dune.
What are the main sources of sediment?
Rivers 90%
Onshore sources 5%
Erosion
Offshore sources 5%
Crushed shells of marine organisms
Waves, tides, currents
What are the main sources of energy?
Winds
Waves
Currents
Tides
What are the features of constructive waves?
Low wave height
Long wavelength
Low frequency (6-8/min)
Swash > backwash
Depositional
What are the features of destructive waves?
High wave height
Steep form
High frequency (10-14/min)
Backwash > swash
Erosional
How do waves form?
Wind blowing across the surface of water (frictional drag).
Circular orbital motion of water particles.
Seabed gets shallower orbits become more elliptical.
Wave height increases, wavelength and velocity decrease.
Water backs up behind the wave until it breaks and surges up the beach.
How do tides form?
Gravitational pull of the sun or moon changes the water levels of the seas and oceans.
What is a spring tide?
The Sun and moon align.
Their gravitational forces pull the ocean to them causing high tides.
Lowest possible low tides on opposite side of earth.
Largest possible tidal range.
What is a neap tide?
Sun and moon perpendicular to each other.
Gravitational forces act against each other.
Overall pull minimised at low tide.
Smallest possible tidal range.
What are the characteristics of low energy coasts?
Low input
Small, gentle waves
Short fetches, gentle winds
Sloping offshore zones
More deposition than erosion
What are the characteristics of high energy coasts?
High input
Large, powerful waves
Long fetches, strong winds
Steeply shelving offshore zones
More erosion than deposition
What is a sediment budget?
A coastal management tool used to analyse and describe the different sediment inputs (sources) and outputs (sinks) on the coasts.
What are sediment cells / littoral cells?
Lengths of coastline that are pretty much entirely self-contained for the movement of sediment. Each cell is a closed system.
What are the four types of sub-aerial weathering?
Salt weathering / salt crystallisation
Freeze-thaw
Wetting and drying / pressure release
Chemical weathering
How does the process of salt weathering take place?
Saline water enters pores/cracks in rocks at high tide.
Tide goes out, rocks dry, water evaporates.
Salt crystals form, expand, exert pressure.
Pieces of rock fall off.
How does the process of freeze-thaw take place?
Temperatures fluctuate between above and below freezing.
Water enters crevices and joints in rocks.
Freezes and expands below 0.
Melts above 0.
Repetition weakens the rock and it falls off.
How does the process of wetting and drying take place?
Some rocks containing clay when wet expand.
Pressure caused by this breaks fragments of rock off.
What is chemical weathering?
Breakdown of rock due to chemical change.
For example chelation where acids released by decomposition of plants and organic matter attacks rocks.
What are the five types of mass movement?
Slumping (shift with rotation)
Rockfall (material breaks up and falls)
Mudflows (material falls downslope)
Slides (in a straight line)
What is solifluction?
Flowage of water-saturated soil down a steep slope.
What is wave quarrying?
Energy of a wave as it breaks against a cliff is enough to detach bits of rock.
What is cavitation?
As waves recede, compressed air expands violently, exerting pressure on rock causing pieces to break off.
What is the littoral zone?
The area of land between the cliff’s or dunes on the coast and the offshore
area that is beyond the influence of the waves, covered by the sea at different
points in time.
What three factors affect wave energy?
Strength of wind
Duration of wind
Fetch length
What is the amphidronic point?
Where there is zero tidal amplitude, complete stillness.
What are rip currents?
Strong, localized, and narrow currents of water which move directly away from the shore, cutting through the lines of breaking waves like a river running out to sea.
What are riptides?
Occur when the ocean tide pulls water through a small area such as a bay or lagoon.
How are wave-cut platforms formed?
Macrotidal conditions required.
Weathering and wave erosion create wave cut notch at high water mark.
WCN forms a cave.
Rock above becomes unstable and unsupported and collapses.
Abrasion makes the WCP flat, slanting towards sea at 3-4 degree angle.
What is an example of a WCP?
Walton-on-the-Naze
What is meant by macrotidal?
Tidal range more than 4m
What is meant by mesotidal?
Tidal range 2-4m.
What is meant by microtidal?
Tidal range less than 2m
What happens during the process of wave refraction?
Waves undergo change in direction as they approach headlands and bays.
Depth reduces, friction increases, speed reduces, crest distorted into pattern reflecting shape of coastline.
What are the main landforms of coastal erosion?
Cliffs
WCP
Caves/arches/stacks/stumps
Headlands and bays
How are headlands and bays formed?
Discordant coastline and destructive waves.
Differential rates of erosion erodes softer rock quickly, forming a bay.
Harder rock eroded less forms headlands.
Wave refraction takes places where headlands are significantly sized.
Constructive waves in bays forms beaches.
How are stacks formed?
Weathering makes faults and cracks in headland.
Headland attacked by destructive waves.
Geo forms and grows into a cave.
Cave eroded through to form an arch.
Top of arch collapses leaving a stack.
Stacks collapse leaving stumps.
What is an example of a sea arch?
Durdle Door, Dorset
What is an example of a stack?
Old Harry Stack
What are the main landforms of coastal deposition?
Beaches
Spits
Offshore bars and tombolos
Barrier beaches and islands
Sand dunes
How are beaches formed?
Constructive waves cause a net gain of sediment on shore through deposition.
How are shingle and sand beaches different?
Shingle beaches are steep and narrow, made of larger particles piled at steep angles.
Sand beaches are formed from smaller particles and are wide and flat.
What are the main features of a beach?
Berms
Ridges & runnels
Ripples
Cusps
Storm beaches
What are berms?
Ridges of sand and pebbles 1-2m high found at high tide marks running along beaches.
What are ridges and runnels?
Parallel ‘hills and valleys’ of sand formed due to the interaction of tides, currents, sediments and the beach topography.
What are ripples?
Wave-sculpted ripples formed when low energy waves transfer orbital energy of waves onto sand below.
What are cusps?
Crescent-shaped indentations that form on beaches of mixed sand and shingle.
What are storm beaches?
A ridge of boulders and shingle found at the back of the beach thrown up by high energy waves during high tide, spring tides, or storm events.
How are spits formed?
Drift aligned beach and where coast suddenly changes direction.
LSD deposits sediment across river mouth, leaving bank of sand and shingle sticking out to sea.
Occasional changes to prevailing wind direction cause recurved end.
How do compound spits form from simple spits?
Over time several recurved ends result from several periods of growth and abandonment of recurved ends as waves return to original direction.
How are barrier beaches formed?
Across a bay or river mouth a spit joins two headlands together, a lagoon forming in behind.
How are tombolos formed?
A bar connects the shore to an island, sometimes a stack.
What is an example of an barrier beaches?
Slapton Sands, Torcross, Devon
2.3km long, 150m wide. 1km2 lagoon.
How do scientists think barrier islands are formed?
In areas with good sediment supplies, small tidal ranges and fairly powerful waves.
Either:
At end of last ice age, sea level rise flooded land behind beaches and transported sand offshore, deposited in shallow water forming islands.
Or:
The islands were originally barrier beaches, eroded in sections causing breaches in the bar.
How are sand dunes formed?
Sand deposited by LSD saltated and trapped by driftwood (deposited at spring tide mark) lowering wind speed.
Colonised by marram grass, which stabilises the sand and encourages more sand accretion forming embryo dunes.
What is the sequence of types of dune involved in sand dune formation?
Embryo 1-2m
Yellow 5m
Grey 8-10m
Mature 10-15m
Why are sand dunes dynamic?
They are in a state of constant change.
How did humans impact Camber Sands pre-1900?
1669 Agarian Revolution. Deforestation made way for new farming techniques. Increased: surface runoff, fluvial erosion, river discharge. More sand via River Rother.
1894 Rye Golf Course. Destroyed western sand dunes.
How did humans impact Camber Sands in the 20th century?
1944 D-Day Landings. Tanks and people caused dune destruction during training.
1967 Carry on Follow That Camel. Film production damaged the dunes.
1967 Dungeness Power Station. Sand mining took place for the concrete.
1968 Regeneration. Initial construction of dune fencing.
1970s Housing. Houses to North-east limit sand dune expansion.
How have humans impacted Camber Sands in the 21st century?
2000 Tourism. 25,000 per day during summer months cause blow-outs.
2014 sea level change. Eustatic and isostatic sea level change could result in drowning of sand dunes.