Flashcards in Chapter 2 - Coasts Deck (43):
What 5 conditions are needed to form sand dunes?
Large flat beach, large supply of sand, onshore wind, large tidal range and an obstacle such as driftwood
What is the order of formation of coastal erosional features from a line of weakness to a stump?
Line of weakness, caves, arch, stack and then a stump
What happens to an arch to form a stack?
The arch is eroded so much that leads to the arch not being able to support it's own roof meaning that the roof falls into the sea leaving a stack
What causes a stack to form a stump?
Erosional processes abrasion, solution, corrosion (and attrition) erode the stack down over time to leave only the bottom, a stump
What are the transportation methods in the sea?
Solution, suspension, traction and saltation
What is suspension?
Small particles are carried in water, 'suspended'
What is saltation?
Load bouncing along the bottom of the sea as the see looses and gains energy due to friction, like leaves blowing in the wind
What is traction?
Large pebbles and sediment being rolled along the sea floor
What is solution?
Dissolved chemicals, often from the cliff face, in the sea water
What are the 3 types of mass movement?
Slides, rotational slumps and rockfalls
What do mass movements cause coasts to do?
Coasts to retreat rapidly
Which wave causes erosion? Which wave type causes beaches to form?
Destructive waves cause erosion, constructive waves cause beaches to be formed
What factor makes slides and slumps more likely to happen?
If the material is full of water, which acts as a lubricant
Describe destructive waves
They have a high frequency
They are high and steep
Their backwash is stronger than the swash
Causes material to be removed from the coastline
Describe constructive waves
Long wavelength low height
Swash is more powerful than backwash
It deposits material on beach
What is the definition of a wave?
A body of water moving towards a coastline at a higher than average level
Describe the stages in a formation of a wave
Circular orbit of water particles in open water
Friction with seabed distort circular motion
Top of wave moves faster increasing elliptical orbit
Wave begins to break
Water from previous wave returns
Water rushes up the beach
What causes rockfalls?
Cracks in the cliff face are cracked further by freeze thaw until they fall down as they can’t take their weight any longer, or they are undercut by the sea
The breakdown of rocks at the Earths surface by action of rainwater, extremes of temperatures and biological activity
Give some examples of biological weathering
Roots from plants making their way through cracks in the rock
Animals walking over surface of rock
Give some examples of weather weathering
Wind blows sand grains across rock
Waves and rain hit rock
Give some examples of chemical weathering
Chemical reactions in rock causes it to break down
What factors decide the rate of erosion and cause variation in coasts?
Weather conditions, average wind speed, how acidic rainwater/water is, type of wave, wind direction, type of rock cliff is made from, human activity (coastline defences), shape of coastline, fetch
What is the fetch?
The area of ocean or sea the wind has blown over the sea in that direction forming waves
Name some landforms of coastal erosion
Bays, wave cut platforms, cliffs, caves, arches, stacks,stumps, headlands and coves
Name some landforms formed by deposition
Beaches, spit, bars (where spits cross a bay,lagoons are also formed behind bars) tombolas (where a spit stretches and joins an island to the mainland) and sand dunes
What process moves sand along the coast?
How is a wave cut platform formed?
Cracks are formed in between high and low water marks through erosion, over time it is eroded further to create a wave cut notch, this is eroded further until an overhang of rock is formed which then eventually collapses into the sea due to gravity leaving a platform. This cycle keeps happening and the platform over time gets larger
What is the one time, the one condition, where longshore drift doesn’t occur?
When the wind it blowing the waves at a 90 degree angle to the beach, so the sediment just moves up and down
What is the prevailing wind?
The direction of wind that is most common in a certain area
Which direction is the prevailing wind from which hits the UK? What does this mean for the beaches on the South of the UK?
From the South West
That lots of beaches of the southern side of England will have destructive waves as they have had a long fetch across the Atlantic
What direction does the backwash travel?
At 90 degrees to the sea front
Where does the waves energy concentrate when the coast line isn’t straight?
Most energy hits/ is concentrated at the headlands as that is what they hit first
What are the 2 types of beach? What wave type generally forms them
Pebble beach, destructive wave
Sandy beach, constructive wave
What are the 3 types of sand movement? (Hint: it is similar to rivers but with one key difference)
Suspension, small grains
Saltation, medium grains which bounce
Creep, large rocks that are rolled along (NOT traction like in rivers)
Name the key steps in a sand dune forming
At the back of a beach there is an obstacle (such as drift wood), the side of this facing the wind begins to form a crest, the heavier grains settle against the obstacle the lighter ones in the other side, this repeated movement of material up windward side and down leeward side causes dunes to migrate inland, over time these dunes get bigger until the slopes reach a gradient of 30-34 degrees and the sand becomes to steep and falls under its own weight.
What gradient does sand stops slipping when a slope reaches it?
30 - 34 degrees because the sand can’t build up any higher because then it’s too steep and falls under its own weight
Give an example of a named bay and a headland located in Bournemouth
Swanage Bay, Ballard point
What does concordance mean?
Where bands of different rock type run parallel to the coast line so the rock is eroded at the same speed, unless there is a fault in this rock and the rock behind is softer than that is eroded quicker to wave a cove
What does discordant mean?
Layers of rock run at right angles to the coast so the rock is eroded at different rates, if there is softer rock between harder rock then bays and headlands are formed
Give some key example of a soft rock and hard rocks often found at coasts (in this example Swanage bay)
Clay and sands, soft
Chalk and limestone, hard
How is a cove formed?
Along a concordant coastline where there is a fault in the rock which has been eroded revealing a layer of rock which is softer behind the harder rock. This is eroded quicker than the front rock creating a cove where the entrance/ neck is smaller then the width of the cove. This erosion of the inside of the cove continues until harder rock is met again then the erosion slows down to the same rate of the original coast erosion of hard rock