1.1.4 - Processes of coastal weathering, mass movement, erosion and characteristics and formation of associated landforms and landscapes Flashcards
What is meant by the wave crest?
A crest is a point on a surface wave where the displacement of the medium is at a maximum
What is meant by the wave height?
the difference between the elevations of a crest and a neighbouring trough
What is meant by the wavelength?
the horizontal distance between two crests or troughs.
how are waves created ?
The power of waves is one of the most significant forces of
coastal change. Waves are created by wind blowing over
the surface of the sea. As the wind blows over the sea,
friction is created - producing a swell in the water. The
energy of the wind causes water particles to rotate inside the
swell and this moves the wave forward.
The size and energy of a wave is influenced by
what three things?
The size and energy of a wave is influenced by:
how long the wind has been blowing
the strength of the wind
how far the wave has travelled (the fetch)
What is the fetch and how does it affect the rate of erosion?
Fetch is the length of open sea over which a wind blows to generate waves.
The longer the fetch then the greater is the potential for large waves.
In Cornwall the fetch is to the south-west, and the largest waves approach from this direction.
It is possible therefore that some waves may have originated several thousand kilometres away
What are prevailing winds and how do they affect the UK coastline?
long fetch - south westerly wind will be produce large powerful waves ( fetch up to 800m )
short fetch - south easterly wind will produce small waves ( fetch less than 200m )
The maximum fetch in the British Isles is from the westerly winds blowing onshore from the Atlantic crossing.
The westerly winds are also the prevailing winds, the winds that blow with greatest frequency.
What are the characteristics of both constructive and destructive waves?
desteructive wave tend to occur during storms and in water. destructive wave are steep inform and break at a high frequency, at 13-15waves per min. they have a plunging motion that generates little swash and a relatively more poweful beackwwash this transports sediments down the beach face, rsulting in a net loss of material they create thinner , flatter beach
constructive wave is konws as spilling beaker construcTive wave tend to occur during the summer construcctive wave are low flat and gentle with wavelenghts up to 100m and a low frequency of 6-8 waves per minute. theyre characterised by a relatively more powerful swash, whcoh carries sand and shingle up the beach and a relatively weaker backwash constructive waves contribute to the formaTiion of beach ridges and berms
feautures of a constructive wave ?
samller wave height , and less frequent
weak backwash carries away little sediment
strong swash moves sediment up the beach
gives gentler beach profile
features of a destructive wave
larger wave height and more frequent
strong backwash carries away lots of sediment
weak swash moves little sediment up the beach
How does the sea bed affect wave orientation?
- waves start out at sea and have a circular orbit
- as waves approach the shore friction slows the base of the wave
- this causes the orbit to become eliptical
- untill the top of the wave breaks over
the sea bed is rough and acts as a source of friction
water from a previous wave returns to the sea as backwash
water swashes up the beach
What is wave refraction and how might this impact
the coastline?
It is very rare for waves to approach a regular uniform coastline, as most have bays, beaches and headlands.
Because of these features, the depth of water around a coast varies and as a wave approaches a coast, its progress is modified due to friction from the seabed, halting the motion of waves
As waves approach a coast they are refracted so that their energy is concentrated around headlands but reduced around bays.
Waves tend to approach coastline parallel to it,and their energy decreases as water depth decreases
sediment seabed creates friction
when waves hit the headland more energy concentrtion is higher the refraction goes to the bay but with a weaker force
waves are refracted to the bays and theyre weaker as tehy have ehit friction from the sea bed .
shallow water causes low velocity and shorter wavelength
deeper water allows steeper waves and greater velocitites
What is wave reflection and how might this impact
the coastline?
At some coastlines where the offshore has deep waters, the waves can reflect back from the cliffs.
The interaction of reflected and incoming waves create a standing wave.
Also known as the clapotis effect – French for lapping of water
What is rock lithology?
Lithology is the physical and chemical make-up of
the rock.
It includes:
the hardness of the rock (igneous and metamorphic rocks are
harder rocks than sedimentary)
its chemical composition (how prone is the rock to chemical
weathering)
its permeability (rock pores, joints, faults).
Lithology is based on the rock type. The three
major rock types are igneous, metamorphic
and sedimentary.
Geology describes the structure of a rock and
the processes that have shaped that rock.
How does the hardness of the rock affect the rate of erosion?
Hard rock cliffs, e.g. basalt and granite, will erode slowly and tend to produce steep, high cliffs.
Softer rocks and glacial material will be weathered more quickly and mass movement processes will dominate, resulting in less steep slopes.
what do joints and bedding determine ?
Joints and bedding planes determine cliff form and the amount of movement of material to the cliff foot.
Which rocks erode faster and slower?
igneous - granite/ basalt / dolerite
very slow
sedimentary - sandstone lime stone
moderate to fast
metamorphic - slate/marble schist
slow
