Systems And Processes In Coastal Environments Flashcards
Define Erosion
The wearing away of the earth’s surface by the action of ice, wind and water.
Define weathering
The breakdown or decay of rock at or near the Earth’s surface in its original location (in situ).
Rock fragments will remain until they are removed by erosion processes. Weathering can be mechanical (e.g. freeze-thaw), biological (e.g. tree roots) or chemical (e.g. calcium carbonate in chalk can be dissolved by sea water).
Define mass movement
The sudden or gradual movement of material downhill due to force of gravity and often assisted by rainfall.
What is the main source of energy at the coast?
Waves - mostly formed by wind but can be produced as a result of tectonic activity or underwater landslides, mostly formed by the wind
Waves are the main source of energy at the coast. Outline the formation of waves by the wind
Before reaching our coast, the winds have blown over the Atlantic Ocean.
This means that the wind has blown over 3000 miles of open water.
This distance is known as the fetch and is one factor that affects wave energy.
As wind blows over the surface of the sea frictional drag leads to a transfer of energy and the formation of waves
What are the factors affecting wave energy?
Fetch, strength and the duration of the wind
What are the characteristics of constructive waves?
Low energy
Deposite sediment - Strong swash and weak backwash
Low height and frequency
Long wavelength
Gentle beach profile - but will make it steeper overtime due to deposition
What are the characteristics of destructive waves?
High energy
Erode sediment - strong backwash, weak swash
Steep height
Short wavelength
Short frequency
What is an example of negative feedback? (beaches and waves)
Where constructive waves operate to build up a beach, eventually the beach profile steepens which can encourage destructive waves which then remove material from
the beach and deposit it offshore.
This can result in the beach profile becoming less steep again, encouraging constructive rather than destructive waves to form.
This will continue until a state of dynamic equilibrium is reached.
What is meant by wave refraction and how does it lead to a concentration of wave
energy on headlands?
When waves approach a coastline that is indented, they are refracted and become increasingly parallel to the coastline.
overall effect of wave refraction is that wave energy becomes concentrated on the headland
Around a headland, for example, waves tend to ‘bend’ and have a higher
frequency, wave height and steepness, which gives greater energy to erode.
because waves approaching the headland meet shallower water first, while the part of the wave approaching the bay is still in deeper water.
What are currents?
The permanent or seasonal movement of surface water in the seas and oceans.
What are tides?
Changes in water level of seas caused by gravitational pull (source of energy) of the moon and to a lesser extent, the sun
Identify three different types of currents along with a brief definition.
Longshore currents - occur as most waves approach at an angle
Rip currents - strong, localised underwater currents that occur on some beaches, moving water away from shoreline
Upwelling - movement of cold water deep in the ocean towards the surface
Explain how tides are linked to the gravitational pull of both the moon and the sun.
The moon pulls water towards it, creating high tide and there is a compensatory bulge on the opposite side of the earth
In areas of the world between the two bulges the tide is at its lowest
What is meant by the term ‘tidal range’ and why are tidal currents important in the development of coastal landscapes?
The relative difference in height between high and low tides is called the tidal range.
Tidal ranges determine the upper and lower limits of erosion and deposition and the amount of time each day that the littoral zone (where land meets the sea) is exposed to weathering.
Outline the key difference between a spring tide and a neap tide.
the relative position of the sun and the moon – the highest during the spring tides and the lowest during neap tides.
Spring - sun and moon parallel to earth - strongest gravitational pull - highest high tides and lowest low tides
Near - sun and moon perpendicular to earth - weaker gravitational pull - middle high and low tides
What are the characteristics of high-energy coastlines?
Strong waves
Prevailing wind with long-fetch creating high energy waves
Erosional landforms such as headlands and bays and wave cut platforms
Rate of erosion greater than rate of deposition
What are the characteristics of low-energy coastlines?
Less powerful waves
Rate of deposition greater than erosion
Low wave energy
Beach, spit landforms
What are the sources / inputs of coastal sediment?
Along side energy:
1) Rivers – sediment is transported in rivers and is deposited in river mouths and estuaries where it is
then reworked by waves, tides and currents. Most coastal sediment originates from rivers.
2) Cliff erosion – this can be particularly important along stretches of coastline where rocks are soft.
One example is along the Holderness Coast in Yorkshire where glacial till forms unstable cliffs of boulder clay.
3) Longshore drift – sediment is transported from one stretch of coastline (as an output) to another
stretch of coastline (as an input).
4) Wind – in glacial or arid regions, wind-blown sand can be deposited in coastal regions. Sand dunes
can act as both a sink and source of sediment (sand).
5) Offshore – sediment from offshore can be transferred into the coastal (littoral) zone by waves, tides
and currents.
In the UK, sea levels rose at the end of the last glacial period, resulting in a
considerable amount of coarse sediment being bulldozed onto the south coast of England to form
landforms such as Chesil Beach in Dorset. Storm surges can also result in inputs of sediment into
the coastal system.
How many sediment cells are there along the coastline of England and Wales?
11
What natural features typically form the boundary between one sediment cell and the next?
Headlands and stretches of deep water
Identify the main inputs, transfers, and stores of a sediment cell
Inputs - sediment from rivers, coastal erosion and offshore sources
Transfers - longshore drift and onshore and offshore processes including rip current
Stores - beaches, sand dunes and offshore deposits such as bars.
What is a ‘coastal sediment budget
The balance between sediment being added to and removed from a sediment cell coastal system.
If more material is added to the cell than is removed then there is a net accretion of material.
This leads to a positive budget or a surplus of sediment and, over time, the shoreline builds towards to
sea.
If more material is removed from the cell than is added a negative budget or a deficit in sediment
supply will result. This will cause the shoreline to retreat landwards.
The sediment budget seeks to achieve a state of dynamic equilibrium where erosion and deposition are balanced.
This balance can be upset by events, such as an increase in river sediment as a result of a flood - leads to deposition in river estuary. A severe storm might also upset the balance by eroding a beach and transferring sediment outside the system.
How is the sediment budget for a stretch of coastline calculated?
requires the identification of all the sediment sources and sinks, and an estimation of the amount of sediment added and removed each year.
Calculating budgets is extremely difficult and relies on the use of complex models and estimations.
