Coasts Flashcards
What is a coastal landscape?
A coastal area where you get a combination of geomorphological processes
You also get specific coastal landforms
What are the 4 types of geomorphological processes?
Erosion, Weathering, Transportation/deposition , Mass movement
What type of system do coasts operate as, and what does it mean?
Open- inputs and outputs can change.
What are the sources of energy in a coastal system?
Wind, Waves, Currents, Tides, Low/high energy coasts.
What are wind and waves?
- Wind is created by air moving from areas of high pressure to areas of low.
-It is the primary source of energy for other processes, and is important for erosion/transportation.
-Waves are created by the transfer of energy from wind blowing over sea surface (frictional drag)
-Energy gathered by waves depends on the strength of the wind, length of time it is blowing, and the distance travelled (fetch)
- The further the wind has blown, the more destructive waves created. - creates a high energy coastline
What is a high energy coastline?
What are the characteristics?
-When a coast is exposed to strong, powerful prevailing winds it creates high energy waves.
-The rates of erosion are greater than the rates of deposition.
-It is open and uninterrupted, with a large fetch
-Greater exposure to tropical storms
-erosional landforms form (headlands, cliffs, wave-cut platform)
-Processes tend to straighten the coastline as material eroded from headlands gets deposited as beaches which smooths the coastline
What is a low energy coastline?
What are the characteristics?
-Waves are not powerful
-rates of deposition greater than erosion
-creates constructive waves
-includes depositional landforms (beaches ,spits)
What are characteristics of destructive waves?
-Short wavelength
-High amplitude-high vertical height
-stronger backwash than swash
-Results in a steep beach profile
-high frequency (10/14 per minute)
What are characteristics of constructive waves?
-Build up the beach
-long wavelength
-low amplitude
-strong swash weak backwash
-low frequency (6-8 per min)
What are the 4 factors affecting energy on a coastline?
1- coastal geomorphology
2-tides
3-tidal surges
4-currents
Coastal geomorphology
Headlands attract wave energy, and the waves concentrate there - known as wave refraction
Tides
The periodic rise and fall of the ocean surface, caused by gravitational pull of the moon and sun (although moon has more influence as its nearer)
-Moon pulls tide towards it, creating a high tide
- Spring tide is when you get the highest monthly tidal range - due to the sun, moon, earth being in a straight line
-Neap tide is when twice a month the sun and moon are positioned at 90 degrees to each other- resulting in the lowest monthly tidal range
Tidal surges
-Occasions where weather conditions create much stronger winds which can produce much higher water levels than those at high tide
-Areas affected: East coast of Britain
-Depressions (intense low air pressure systems) over the North sea produce low air pressure conditions that can raise sea levels.
-Strong winds push sea water against coastline
Currents
The general flow of water in one direction, which moves material along a coastline
- caused by wind/ variation in temp
3 types of currents:
1- Longshore drift:
waves hit at an angle and create a general flow parallel to the shoreline
2-RIP currents:
strong currents moving away from the shoreline
3-upwelling:
The movement of cold water from the deep ocean to the surface.
Dense cold water replaces the warm surface water and creates a nutrient rich cold ocean current
What are the 6 types of erosion ?
1- hydraulic action
2-wave quarrying
3-corrosion/abrasion
4-wave cavitation
5-solution
6-attrition
What is hydraulic action?
On a high energy coastline, waves hit the cliff and air gets into the cracks- compresses it. The force of the water exerts pressure and the rocks break off. This is known as wave pounding
What is wave quarrying?
Energy of a wave as it bangs against a cliff is enough to detach bits of rock.
what is corrosion/abrasion?
Bits of rock and sediment being transported by waves which hit the cliffs and rocks, and break bits off and smooth surfaces.
What is wave cavitation?
as waves retreat, the compressed air expands and exerts pressure, causing bits of rock to break off.
what is attrition?
Rocks bang in to eachother and break down
what is solution?
soluble calcium based rocks gradually dissolve by sea water.
Doesn’t happen in fresh water as it has a stable pH, but can occur in areas where both saltwater and fresh water interact
What is the rate of erosion affected by?
-wave steepness
-fetch
-geology
-human activity
-coastal configuration eg. headlands -wave refraction
-sea depth
What are the 6 different types of transportation?
1-traction
2-saltation
3-suspension
4-solution
5-longsore drift
6-aeolian
what is traction
large boulders that roll along a sea bed
what is saltation?
small rocks that bang along the sea bed
what is suspension?
small material that floats in the water
what is solution?
material that gets dissolved in the water
what is longshore drift?
the movement of sediment along a coastline due to the prevailing wind coming in at a zig zag motion
(comes in at 45 degrees (swash that moves material up the beach), leaves at 90 degrees (backwash that moves material down the beach))
what is aeolian transportation?
transportation by wind
can happen in 2 ways:
1-surface creep- wind rolls sand grains along surface
2-saltation- wind is strong enough to lift grains into the air at heights up to 1 metre
what is deposition?
when the velocity of wind and water decreases due to a decrease in energy so material eroded gets deposited.
In high energy environments:
-sand is easily transported away so leaves behind larger pebbles and rocks (shingle beaches)
In low energy environments:
-small clay particles fall to the sea bed and form mudflats
what is sub-aerial weathering?
the break down of rock which weakens the cliff and makes it vulnerable to erosion
what is physical weathering?
Freeze thaw: on hard rock coastline
when water enters the joint of a rock and freezes. when frozen, it expands by 10%
Overtime, repeated freeze-thaw weakens the cliff and fragments of rock break off
What is chemical weathering?
salt crystallisation:
-when waves refract, the water splashes back onto the top of the cliff. When the water evaporates it leaves behind salt crystals . These corrode the rock and exert pressure and it breaks off.
The salt crystals can also dissolve in rainwater to form acid rain
What is biological weathering?
when plants grow on top of a cliff, the roots can cause parts of the rock to break off
-if animals burrow on top of cliff, it weakens the rock structure
What is mass movement?
the movement of material down a coastline (which is influenced by gravity)
-can be slow(soil creep) or fast (weak geology)
-at a cliff, the weight of the rainfall or weak geology is the main cause of collapse
What is slumping?
occurs on weak, unconsolidated clay, where permeable rock lies on top of impermeable rock.
-The bedding plane is curved, not flat.
-heavy rainfall saturates the soil, lubricates the bedding plane and leads to the rock slumping.
-leaves a scar
What is a landside?
-rock moving rapidly down a planar surface (where the bedding plane is parallel to the ground and not curved)
-rainfall lubricates it and reduces friction, and the force of gravity pushes material down a slope.
What is rockfall?
Happens along a hard rock coastline,
-rock at the top of the cliff are weathered (freeze-thaw) and break off
What is mudflow?
mud flows downhill, usually over unconsolidated rock after heavy rain
what is soil creep?
the slow movement of individual soil particles downhill.
What is runoff?
Where overland flow occurs down a slope and takes along small material
What are the 3 erosional landforms?
1- cliffs
2-wavecut platforms
3-caves, arches, stacks