Coast Flashcards
crest
highest surface part of a wave
trough
lowest surface part of a wave
wave height
vertical distance between two crests o
How are waves formed?
waves are created by the wind blowing over the ocean/sea, the speed of the wind blowing over the ocean or sea varies with height being slower near the surface of the water. This is because of the friction between the air and the water. The friction causes turbulence in the air near the surface of the water while transferring some of the air’s kinetic energy to the water. The turbulence and transfer of energy combined produces pertubations or ripples in the surface of the water which eventually becomes waves.
How do waves grow?
controlled by how much energy the wind transfers to them (faster winds>more kinetic energy> larher waves) (longer wind blows.more energy can be transferred>stronger waves) (longer fetch>water had more oppurtunity to transfer kinetic energy >stronger waves)
fetch
stretch of open water over which wind blows and wave travels
Movement of waves
In open water, the water molcules of the wave move in a circular orbit. As the wave approaches the coastline, the depth of the water becomes shallower and it encounters increasing contact with the sea bed. This exerts a frictional drag at the base of the wave and forces it to slow down. AS it flowes, the wavelength decreases and wave height increases (SHOALING) The circular orbit then turns into an elliptical orbitas it gets closer to the coast, The impact of friction increases so the top of the wave moves faster than the base eventually, the wave breaks at a critical point where the top topples over.
swash
the body of foaming water that rushes up the beach
backwash
water returning back tot he sea due to gravity
Characteristics of Constructive waves (8)
low and flat, long wavelenght, long wave period, flat/wide and gentle gradient, spills over when breaking, deposits material and builds up coast, stronger swash and weaker backwash, moves slowly 6-8 waves per minute
Charactersitics of Destructive Waves (8)
high and steep waves, short wavelength, short wave period, moves quickly 10-14 waves per minute, plunges over when breaking, weaker swash and stonger backwash, narrow beaches with steep gradient, erodes coasts
Coastal Process/ Erosianl Process
Hydraulic action, Abrasion/Corrasion, Attrition, Solution/Corrosion
Factors affecting coastal erosion
Rock type- some rocks are easily eroded eg shale and these tend to form wide beaches, some rockas are very resistant to erosion eg chalk and these tend to form steep cliffs and rocky outcrops/headlands
Rock structure- rocks parellel to coastline are CONCORDANT and the amount of erosion depends on the resistance of rock type forming the coastline, rocks outcrops at right angles to the coastline are DISCORDANT and differential erosion occurs due to the bands of hard and soft rock forming the headlands
Type of wave- amount of energy a wava has determine the amount of erosion occurring eg destrcuctive wave has strong backwash and more removal of sediments/beach erosion
Shape of Coastline- headlands are exposed to the full force of wave energy but protect bays which are sheltered from erosion
Feature Formed by Coastal Erosion
- Wave cut Platform- Cliffs in Coastal erosion are subjected to sub- aerial weathering and coastal erosion. Wave action is predominant in the region between high tide and low tide. Over time due to erosional processes such as hydraulic action and abrasion, a wave cut notch is created t the high water mark, further erosion will increase the size of the notch and undercutting of the cliff occurs creating an overhang rock.
- Headland and bays- headlands and bays form along discordant coastlines where bands of hard and soft rock outcrops at right angles to the coastline, differential erosion occurs where less resistant rock is erodes more rapidly then more resistant rock. this leaves rocky outcrops jutting out into the sea (headlands) and bays are the are between the headlands where the soft rock has eroded away.
A cove is a circular area of water with a relatively narrow entrance from the sea. it is created on concordant coastlines where the same type of rock is along its length, there are fewer bays and headlands as the rate of erosion os similar throughout, The outer hard rock protects the soft rock furhter inland from erosion but when this is punctured it allows the sea to erode the softer rocks behind to create a cove.
3.Blowholes and Geos -cavities formed in the inland end of a sea cave
what is wave refraction
process by whichwaves becomes distorted due to differential rates of friction caused by shallower water. depth of water around a coast varies , waves are unaffected in deep water but as they approach the coastin shallow water its progress is modified due to frictional drag from the seabed which slows the motion of waves . waves are refracted such that energy is concentrated on the headland but reduced around bays. headlans usualli sites of sediment deposition. it can create a smooth coastline eventually. when it approaches an irregular coastline they are refracted- the waves become increasingly parallel to the coastline.
