Coasts

Question 1

Wind

Answer 1

The source of energy for coastal erosion and sediment transport is wave action. This wave energy is generated by the frictional drag of winds moving across the ocean surface. The higher the wind speed and the longer the fetch, the larger the waves and the more energy they possess.
Onshore winds, blowing from the sea towards the land, are particularly effective at driving waves towards the coast. If winds blow at an oblique angle towards the coast, the resultant waves will also approach obliquely and generate longshore drift.
Wind is a moving force and as such is able to carry out erosion, transportation and deposition itself. These aeolian processes contribute to the shaping of many coastal landforms.

Question 2

Swell waves

Answer 2

A wave with a long wavelength, low height and steepness. It has a wave period of up to 20 seconds.

Question 3

Storm wave

Answer 3

A wave generated locally by high wind energy. It has a short wavelength, greater height and a shorter wave period

Question 4

Properties of Atlantic Ocean

Answer 4

Wave height (m): 5.0
Wave period (sec): 8
Energy (kW per m): 200

Question 5

Properties of English Channel

Answer 5

Wave height (m): 0.6
Wave period (sec): 6
Energy (kW per m): 2.16

Question 6

Types of breaking waves

Answer 6

Spilling (Steep waves breaking onto gently sloping beaches; water spills gently forward as the wave breaks)
-Plunging (Moderately steep waves breaking onto steep beaches; water plunges vertically downwards as the crust curls over)
-Surging (Low-angle waves breaking onto steep beaches; the wave slides forward and may not actually break)

Question 7

Spilling waves

Answer 7

Steep waves breaking onto gently sloping beaches; water spills gently forward as the wave breaks.

Question 8

Plunging waves

Answer 8

Moderately steep waves breaking onto steep beaches; water plunges vertically downwards as the crust curls over.

Question 9

Surging waves

Answer 9

Low-angle waves breaking onto steep beaches; the wave slides forward and may not actually break.

Question 10

Constructive waves

Answer 10

Weak backwash
Strong swash
Long in proportion to length

Question 11

Destructive waves

Answer 11

Weak wash
Strong backwash
High wave in proportion to length

Question 12

Tides

Answer 12

The periodic rise and fall of the sea surface and are produced by the gravitational pull of the Moon and, to a lesser extent, the Sun. The Moon pulls the water towards it, creating a high tide, and there is a compensatory bulge on the opposite side of the Earth. At locations between the two bulges, there will be a low tide. As the Moon orbits the Earth, the high tides follow it. The highest tides will occur when the Moon, Sun and Earth are all aligned and so the gravitational pull is at its strongest. This happens twice each lunar month and results in spring tides with a high tidal range. Also twice a month, the Moon and the Sun are at right angles to each other and the gravitational pull is therefore at its weakest, producing neap tides with a low range.

Question 13

Formation of tides

Answer 13

Spring tide aligned with sun and moon
Neap tide moon is right angle to sun

Question 14

Geology

Answer 14

The two key aspects of geology that influence coastal landscape systems are lithology and structure

Question 15

Lithology

Answer 15

Describes the physical and chemical composition of rocks. Some rock types, such as clay, have a weak lithology, with little resistance to erosion, weathering and mass movements. This is because the bonds between the particles that make up the rock are quite weak. Others, such as basalt, made of dense interlocking crystals, are highly resistant and are more likely to form prominent coastal features such as cliffs and headlands. Others, such as chalk and carboniferous limestone (predominantly composed of calcium carbonate), are soluble in weak acids and thus vulnerable to the chemical weathering process of carbonation

Question 16

Structure

Answer 16

The properties of individual rock types such as jointing, bedding and faulting. It also includes the permeability of rocks. In porous rocks, such as chalk, tiny air spaces (pores) separate the mineral particles. These pores can absorb and store water - a property known as primary permeability. The joints are easily enlarged by solution.

Structure is an important influence on the planform of coasts at a regional scale. Rock outcrops that are uniform, or run parallel to the coast, tend to produce straight coastlines. These are known as concordant coasts.
Where rocks lie at right angles to the coast they create a discordant planform: the more resistant rocks form headlands; the weaker rocks form bays.
Structure also includes the angle of dip rocks and can have a strong influence on cliff profiles. Both horizontally bedded and landward-dipping strata support cliffs with steep, vertical profile. Where strata incline seawards cliff profiles tend to follow the angle of the dip of bedding planes.

Question 17

Primary permeability

Answer 17

Pores in rock, such as chalk, that can absorb and store water.

Question 18

The amount of energy in a wave in deep water formula

Answer 18

P = H²T

P is the power in kilowatts per metre of wave front
H is the wave height in metres
T is the time interval between wave crests in seconds, known as wave period

Question 19

Wave periods

Answer 19

The time interval between wave crests in seconds.

Question 20

Inputs of open systems

Answer 20

-Kinetic energy from wind and waves
-Thermal energy from the heat of the Sun
-Potential energy from the position of material on slopes
-Material from marine deposition
-Weathering and mass movement from cliffs

Question 21

Outputs of open system

Answer 21

-Marine and wind erosion from beaches and rock surfaces
-Evaporation

Question 22

Throughputs of open system

Answer 22

Stores:
-Beach and nearshore sediment accumulations
-Flows (transfers), such as the movement of sediment along a beach by longshore drift

Question 23

System feedback in coastal landscapes

Answer 23

When a system’s inputs and outputs are equal, a state of equilibrium exists within it. In a coastal landscape, this could happen when the rate at which sediment is being added to a beach equals the rate at which sediment is being removed from the beach; the beach will therefore remain the same size.
When the equilibrium is disturbed, the system undergoes self-regulation and changes its form in order to restore equilibrium. This is known as dynamic equilibrium, as the system produces its own response to the disturbance. This is an example of negative feedback.

Question 24

Sediment cells

Answer 24

A stretch of coastline and its associated nearshore area within the movement of coarse sediment, sand and shingle is largely self-contained. A sediment cell is a closed system, which suggests that no sediment is transferred from one cell to another. There are 11 large sediment cells around the coast of England and Wales. There are also many sub-cells of a smaller scale existing within the major cells.

Question 25

Closed system

Answer 25

A system with no inputs or outputs

Question 26

Transfer between sediment cells

Answer 26

It is unlikely that sediment cells are completely closed. With variations in wind direction and the presence of tidal currents, it is inevitable that some sediment is transferred between neighbouring cells.

Question 27

RIP currents

Answer 27

An important role in the transport of coastal sediment. They are caused either by tidal motion or by waves breaking at right angles to the shore. A cellular circulation is generated by differing wave heights parallel to the shore. Water from the top of breaking waves with a large height travels further up the shore and then returns through the adjacent area where the lower height waves have broken. Once rip currents form, they modify the shore profile by creating cusps which help perpetuate the rip current, channeling flow through a narrow neck

Question 28

Ocean currents

Answer 28

Much larger phenomena, generated by the Earth’s rotation and by convection, and are set in motion by the movement of winds across the water surface. Warm ocean currents transfer heat energy from low attitudes towards the poles. They particularly affect western-facing coastal areas where they are driven by onshore winds. Cold ocean currents do the opposite, moving cold water from polar regions towards the Equator. These are usually driven by offshore winds, and so tend to have less effect on coastal landscapes. The strength of the current itself may have a limited impact on coastal landscape systems in terms of geomorphic processes, but the transfer of heat energy can be significant, as it directly affects air temperature and, therefore, sub-aerial processes.

Question 29

Terrestrial

Answer 29

Rivers are major sources of sediment input to the coastal sediment budget, and this is particularly true of coasts with a steep gradient, where rivers directly deposit their sediments at the coast. Sediment delivery to the shoreline can be intermittent, mostly occurring during floods. In some locations, as much as 80 per cent of coastal sediment comes from rivers.

The origin of the sediment is the erosion of inland areas by water, wind and ice as well as sub-aerial processes of weathering and mass movement. Wave erosion is also the source of large amounts of sediment and makes a major contribution to coastal sediment budgets.
Cliff erosion can be increased by rising sea levels and is amplified by storm surge events. The erosion of weak cliffs in high-energy wave environments contributes as much as 70 per cent of the overall material supplied to beaches, although typically it contributes much smaller amounts. Some of this sediment may comprise large rocks and boulders, especially if it is derived directly from the collapse of undercut cliffs.
Longshore drift can also supply sediment from one coastal area by moving it along the coast to adjacent areas.