coasts Flashcards
What are high energy coastlines?
High energy coastlines in the Uk are stretches of alantic-facing coasts, where waves are powerful for much of the year (eg.cornwall) where rate of erosion exceeds rate of deposition. Erosional landforms are formed here.
What are low energy coastlines?
Found in low energy enviroments in stretches of less powerful waves where coast is sheltered from large waves (Northumberland) and where the rate of deposition> rate of erosion.
What are areas in the UK are of different resistance?
Wash is an area of low falt relief known as a coastal plain. At 20km wide and 30km long is the largest eustary sytem in the uk with a range of habitats such as salt marshes. However mostof the coast of of Eastern UK consists of low lying sandy beaches such as bamburugh beach whilst the sout west of cornwall cosnsits of igneous and metamorphic froming a rocky coastline able to withstand winter storms north as well like this. In reality many coasts are a mixture of high and low-energy enviroments eg some may be predominatly low energy such as holderness coast but still sufferr from einter storms creating a high energy erosional enviromernt.
What are inputs into the littoral system/
marine: waves,tides, storm surges
Atmospheric: weather/climate, climate change
Land:rocky type, tectonic actvity
People:human activity, coastal management
What are the processes in the littoral zone?
> Weathering
mass movement
Erosion
Transport
deposition
What are the outputs in the littoral zone?
Erosional landforms
>depositional landforms
>Different types of coasts
What is the littoral zone?
Stretches out into sea onto the shore and is constantly changing due to the dynamic interation betweeen processes seas and land. Varies due to :
>Short term factors- seasonal storms and daily tides
>Long-term factors- sea level change and climate change.
Divided into 4 zones
Backshore- area above influence of the waves (storm beach)
Foreshore- intertidal/ surf zone. (ridges)
Nearshore- breaker zone (breakpoint bar of breaking waves)
Offshore- beyond the influence of waves.
How is sediment supplied?
Weathering and erosion produce output in the form of sediment which is then transported producing coastal landform. For example in the wash sediment originates from
> cliffs eroding between west Runton and weybourne east of the wash these cliffs have retreated 1m per year and as sandstone 60% of their sediment consists of sand.
> some sediment comes from tidal currents picking up glacial deposits of the sea floor.
> Erosion of holderness cliffs further north also provides some sediment, which is carried southward in suspension
> 4 rivers also bring
sediment into the wash.
How are coasts classified?
> Their geology- which create rocky sandy and estuarine coasts as well as concordant and disconcordant coasts
> their level of energy- low/high energy coasts.
> the balance between erosion & deposition creating erosional/ depositional coasts.
> changes in the sea level- submergent/ emergent
No classification system is definitive- Cornwall is mostly rocky but has long stretches of sand.
What is lulworth crumple?
Example of limestone folding. Here thin beds of Purbeck and limestone fold in response to tectonics.
What are geological characteristics?
Strata-layers of rock
Bedding planes(horizontal cracks)- natural breaks in strata caused by gaps in time during periods of rock formation
Joints- vertical cracks caused by uplift and time and sediment contraction.
Folds- formed by pressure and tectonic activity.
Faults- formed when stress or pressure which a rock is subjected too exceeds internal stength causing rock to slip on a fault plane.
Dip-angle at which stata lie
What different types of cliff profiles are there?
> horizontal strata produce steep cliffs
> rocks can have a gentle dip towards the sea with hortizontal joints
> Rocks slabs slide down bedding planes in a steep dip
> Rocks dipping inward produce steep cliff profiles.
> rocks can dip inland but with well developed joints at 90 degrees to bedding planes.
What are concordant coasts?
Where bands of more resistant and less resistant rock run parallel to the coast. Lulworth bay is an example, formed by purbeck limestone being eroded at entrnce of cove and the rapid erosion of less resitant clays behind the limestone leading to the formation of a cove or bay.
What are dalmation and haff coasts?
Type of concordant coasts formed as a result of a rise in sea level where the valleys are flooded resulting in ridges remaining above sea level, tops of ridges remained above sea level creating a series of off shore parallel islands example is the dalmation islands in croatia.
Haff coasts are long spits of sand and lagoons parallel to the coast.
What is a disconcordant coast?
Geology alternates between bands of more resistant and less resistant rock 90 degrees to the coast. Isle of perbeck eastern coast is disconcordant. Runs south from studland bay to Durlston head. More resistant are headlands and less are bays. Geology has infuenced morphology considerably.
> Bangshot and tiertary beds consist of unconsolidated sands and clay exposed to studland and forming a large bay as a result.
> Chalk strong and resistant to erosion, so formed cliffs and headland at the coast (foreland)
> Wealden beds consist of unconsolidated clay leading to bay at swange bay
> Purbeck beds consist of limestone forming headlands durlston head and preveril point but limestone is jointed creating lines of weaknesses that can be easily eroded.
What processes act to create headlands and bays?
> Headlands, such as Foreland and peveril point , jut out into the sea, with bays (swanage) lying between them. Headlands and bays are commonly formed when rocks of different strengths are exposed to the coast. More resistant rock such as chalk and limestone tend to form headlands whilst weaker rocks are eroded to form bays.
Headlands force the waves to refract and bend as headland becomes shallower or higher so velocity increases concentrating their energy at the headlands and increasing their erosive power leading to steeper cliffs and eventual erosion of inot arches and stacks.
When waves enter a bay their energy is dissapaited as water is deeper so less steep waves leading to deposition of sediment- forming beach.
What causes waves?
Most waves orginate locally- forming when wind blows over water, size is related to wind speed and can build up over time, so storm waves increase in size over several days. Wind creates frictional drag, which produces movement in the upper surface of the water which move in circular orbit as waves move along the surface.
When wave approaches :
> Water becomes shallower and the circular orbit of the water particles changes into an elliptical shape.
> Wavelength and velocity decrease as wave height increases- causing water to push from behind
> Forcing wave higher so it becomes steeper before spilling and breaking onshore
> as water rushes up the beach as swash, and flows down as backwash.
What are swell waves?
Not all waves originate locally, some originate in mid ocean and maintain their energy for thousands of miles. The sistance of open water over which they move is called the fetch- the greater the fetch the larger the wave. On the UK coast these mid ocean waves appear as large waves amongst smaller local waves. Called swell waves.
What are the differences between constructive waves and destructive waves?
Constructive waves have low surging waves with a long wave length, weak backwash and a strong swash, beach gain landforms include a ridge of sediment (berm) and wave energy to be absorbed by the beach with wave not reaching the foot of a cliff.
Destrucctive waves have high plunging waves with a short wavelength, weak swash and a strong backwash and results in beach loss.
What is the winter profile of a beach?
> Destructive waves occur at a higher frequency (11-16 per min) causing berms to be eroded by plunging waves and high energy swash, this strong backwash then transports sediment offshore ( depositing it as offshore bars)
What is the summer profile of a beach?
Beach profiles are steeper in the summer where con>des waves, constructive waves are less frequent (6-9 per min) so wave dissipates and deposits over a wide area weakening back wash, swash of constructive wave deposits larger material at the top of the beach creating a berm. As berm builds up, backwash becomes weaker with only enough energy to move smaller material.
What is abrasion?
When rocks and sediment hurled at cliff foot from sea bed size of sediment and type of wave experience determine the importance of this process.
What is hydraulic action?
When a wave advances, air can be trapped or compressed in joints. Wave retreats and air expands in cracks exploding outwards and widening joints. This continous proccess causes pieces of the rock to break off. Wave can also hammer cliff as at high velocities then form bubbles which collapse like a hammer.
What is corrosion?
Alkaline rock such as limestone dizzolved by acid in sea water
What is attrition?
Gradual wearing of rocks making rocks smoother and rounder.
How do waves and lithology influence erosion?
Most erosion occurs during winter storms where des waves are at most powerful. This is where hydraulic action and abrasion are at their most powerful. Attack differences in the rock resistance. Lithology affects erosion weaknesses geologically are eroded more quickly and results in a range of dif landforms. Bands id more resistant rock between weaker joints and cracks erode more slowly, Selective erosion of areas of weakness as opposed to resi is called differential erosion.
Erosion faster where rocks are weaker for example in holderness weak bolder clay have eroded inland by 120meters in a century compared to resistant granites at lands end only eroded by 10meters.
What landforms are created as a result of erosion?
Headlands,cliffs,stacks and stumps, shoreline platforms .
How are wave cut notches and shoreline platforms formed?
A wave cut platform is a flat rocky platform formed when waves break against the foot od a cliff erosion concentrated at high tide line forming a wave cut notch which undercuts the cliff. As it becomes bigger rock becomes unstable and collapses. As procceses are repeated the notch migrates inwards and cliff retreats leaving SL platform. Gentle slope of 4 degrees so only exposed at low tide reduces rate of erosion and can spread to 100+m so wave breaks earlier reducing energy.
How is a stump formed?
When weaknesses such as joints are eroded by Hydraulic action a cave is created. A blowhole then also develops as cave opens up at ground level. when 2 caves or 1 caves eroded this forms an arch ,gaps then largened by weathering and erosion until the top of the arch collapses leaving behind a stack until a stump forms.
