EQ2 Coasts Flashcards
What are waves caused by
The action of wind dragging on the surface of the sea creating friction
Energy transferred from wind to water
What factors does the formation of a wave depend on
Wind velocity
Fetch - distance over which wind blew
Duration - period of time of wind blowing
What are waves characterised by ?
Wave height ( trough to crest)
Wavelength (crest to crest)
Period (time interval between arrival of consecutive crests)
Wave propagation direction
What are swell waves and how do they form
Waves generated by energy beneath the oceans surface - don’t need local wind
Originate in mid ocean
Maintain their energy for thousands of miles
Build up over time so Greater fetch = larger wave
How are tides formed
Formed by gravitational pull of the moon acting on water in earths surface
Cause high tides to happen What are some examples of processes which occur in a high energy coastline twice a day with 12 hour intervals
What is beach morphology
The shape of a beach including width and slope
Includes features such as berms, ridges and runnels, as well as type of sediment
How do beaches vary seasonally
Winter beach :
Berms and some dune eroded
High water
Offshore Bars formed
Summer beach :
Dunes and berms deposited
What are storm beaches
Furthest point of beach from tideline
Happen after severe storms and involve high energy deposition of very coarse sediment
What are berms
Made from shingle or gravel
Formed as a result of summer swell wave deposition
What is abrasion
When waves advance they pick up sand and pebbles from the sea bed
When waves break at base of cliff, transported material is hurled at cliff foot, chipping away at rock
What is hydraulic action
When a wave advances, air is trapped and compressed in joints or between the wave and the cliff
Wave retreats and cliff expands
Process weakens joints and cracks and causes rock to break off
What is corrosion/ solution
Cliffs are formed from alkaline rock, weak acid solution in sea can dissolve them
What is attrition
The gradual wearing down of rock particles by impact and abrasion
Gradually reduces particle size and makes stones rounder and smoother
Ultimately becomes sand
What is erosion rate influenced by
Wave type
Season
Geology and rock type
Lithology
Type of coastline (C or D)
What is a sediment cell
An area of a coast often hemmed by physical barriers
Contains a sediment budget in dynamic equilibrium
Fed by sources of sediment and contains sinks and stores
What are some examples of mechanical weathering
Freeze thaw
Salt crystallisation
What are some examples of chemical weathering
Carbonation
Hydrolysis
Oxidation
What are some examples of biological weathering
Plant roots
Rock boring
how are caves created
cracks at base of headland widened by erosional processes, and weathering such as salt crystallisation and wet and dry weathering
wave cut notches form, are eroded back to form caves
how do caves deepen?
wave refraction distorts wave direction
destructive waves concentrate energy on sides of cave
how are arches formed
wave refraction effects all 3 sides of headland. If 2 caves are aligned, waves can cut through to form arch
base of arch widened by wave cut notches
how do blowholes form
vertical joints exposed by tall destructive waves
joints weathered from above by carbonation in limestone
how do stacks form
arch becomes unstable and collapses under own weight to form pillar of rock
how is stump formed
stack eroded at base, forming wave cut notches
sub aerial processes weaken from above
exposed stack will collapse
Describe freeze thaw weathering
Water expands by 9% volume when freezing which exerts force within cracks and fissures
Repeated cycles force cracks open and loosen rocks
What rocks are vulnerable to freeze thaw weathering
Any rock with cracks or fissures p, especially high up cliffs away from sea spray
Freezing less common at Uk coast though
Describe salt crystallisation weathering
Growth of salt crystals in cracks can exert a breaking force
Less than freeze thaw
What rocks are vulnerable to salt crystallisation
Porous and fractured rocks
Rocks in hotter and drier climates where evaporation more pronounced
Eg sandstone
Describe carbonation weathering
Slow dissolution of limestone due to rainfall which contains weak carbonic acid
Dissolves calcium bicarbonate
Describe hydrolysis weathering
Breakdown of minerals to form new clay minerals
Which rocks are vulnerable to hydrolysis
Igneous and metamorphic rocks containing silicate minerals
Describe oxidation weathering
The addition of oxygen to minerals, particularly iron compounds
Produces iron oxides which increases volume contributing to mechanical weathering
Which rocks are vulnerable to oxidation weathering
Sandstones, siltstones and shales containing iron compounds
Describe biology plant root weathering
Tree and plant roots grow in cracks and force fissures apart
Describe rock boring weathering
Many species of clams and muscles bore into rocks and secrete chemicals which dissolve rocks
Which rocks are vulnerable to rock boring
Sedimentary - especially carbonates
Describe traction
Sediment rolls along and is pushed by waves and current s
Describe saltation
Sediment bounces along, due to force of water or winds
Describe suspension
Sediment carried in the water column
Describe solution as a transport mechanism
Dissolved material is carried in water as a solution
What is a swash aligned beach
Wave crests approach parallel to the coast
Limited long shore movement
What is a drift aligned beach
Crests break at an angle to the coast
Consistent longshore drift and generation of elongated depositional landforms
Describe long shore drift
Sediment carried up beach in direction of the wave
Sand falls back down beach under pull of gravity
Material moved along beach in series of zig zags
What is gravity settling
Occurs when energy of transporting water becomes too low to transport sediment
Large sediment deposited first followed by smaller sediment
What is flocculation
A depositional process that is important for very small particles such as clay which are so small they remain suspended in water
Clay particles clump together due to electrical or chemical attraction and become heavy enough to sink
What is a spit
A long narrow feature made of sand or shingle which extends from the land to the sea
Forms on drift aligned beaches
How is a spit formed
Sand moved along the coast by longshore drift
Coastline suddenly changes direction (eg because of river estuary)
Sediment builds up across estuary, spit forms
Salt marsh can develop behind a spit
How does a recurved spit form
End of spit begins to curve around as wave refraction carries material around into the more sheltered water behind the spit
What is a beach and how is it formed
Wave refraction creates low energy environment where sediment is deposited
What is an offshore bar
Ridges of sand or coarse sediment which are submerged or partially exposed
Created by waves offshore from coast
Destructive waves erode sand from beach with string backwash and deposit it offshore in bars
What is a bar and a barrier beach
Where a beach or spit extends across a bay to join two headlands
Barrier beach is when a beach becomes separated from the mainland, eg on a bar
Can trap lagoons behind them
What is a tombolo
A beach or ridge which has formed between a small island and the mainland
Can be covered at high tide
What is a cuspate foreland
A triangle shaped headland which extends out from the main coastline
Occurs when coast exposed to longshore drift from opposite directions
Sediment deposited at the point where two directions meet, forming natural triangle
Name the dunes from sea to forest
Sea
Embryo dunes
Fore dunes
Yellow dunes
Grey dune
Dune slack
Dune scrub
Woodland
How many sediment cells are there around England and wales
11
Why are sediment cells unlikely to be completely closed systems
Variation in wind speed and presence of tidal currents
Some sediment will be transported between cells
What are sources in sediment cells
Places where sediment is generated
Cliffs, eroding sand dunes, offshore bars
River systems
What are transfer zones in sediment cells
Places where sediment is moving along the shore through longshore drift and offshore currents
Beaches, parts of dunes, salt marshes
What are stores in sediment cells
Locations where the dominant process is deposition
Spits, offshore bars etc
What is a sediment budget
The amount of sediment available within each sediment cell
Remains constant in long term, some changes on short term
How does the sediment budget stay at overall equilibrium
Positive feedback (erosion) and negative feedback (deposition)
What are sinks in a sediment cell
A more permanent store
E.g a submarine canyon
What conditions leads to increased chemical weathering
Temperature increase - more chemical reactions occur
Precipitation increase - more water = more chem reactions
What conditions leads to increased mechanical weathering
Colder climates as more potential for freeze thaw
What conditions leads to increased biological weathering
Warmer environments
Examples of mass movement flows
Solifluction
Earthflow
Mudflow
Debris flow
Soil creep
Examples of mass movement slides
Rotational slip (slumping)
Landslide
Rockfall
What is coastal mass movement
The downhill movement of cliff material under the influence of gravity
Describe rock fall
Rapid
Large blocks of rock dislodged
Via Mechanical weathering and hydraulic action
Describe rock slide
Jointed rocks with bedding plane parallel to slope are susceptible
Slabs of rock slide
Describe rotational slip
Saturated conditions on ,operate to steel slope
Often have softer material over more resistant impermeable rock
Causes rotational slope creating terraced cliff profile
Describe soil creep flow
Slowest form
Very slow downhill movement of individual soil particles
Describe earth and mud flow
Increased water reduces friction causing earth and mud flow over underlying bedrock
Describe soil fluctuation
Permafrost causes saturated upper later to flow
What are rotational scars
Caused by slumping
Scars are the panes along which slumping wedges of earth slip
What is scree and talus slopes, and what is the difference
Accumulation of rock fragments at base of cliff that have fallen off
Scree and talus often used interchangeably but scree gravel sized and talus larger
What are terracettes
Waves of soil caused by soil creep
Looks as if land has been landscaped into a number of level flat areas resembling set of steps
