Coasts Flashcards
What causes waves?
Transfer of energy from the wind to the sea due to the friction of the wind on the water’s surface
What effects the strength of waves?
Speed of wind
Time - how long wind has been blowing
The fetch, maximum distance of open sea the wind can blow over
Characteristic of constructive waves.
Where are they found?
What beaches do they form?
Swash ><Backwash ?
Found: Sheltered bays and spits
Low and long
Form sandy beaches
Waves lose energy when in friction with sand so swash is relatively stronger than the backwash so material is deposited.
Low, long wavelengths and low frequency
Build up beaches.
Characteristics of destructive waves
Where are they found?
What beaches do they form?
Swash ><Backwash ?
Exposed bays
Pebble beach
High and steep with high frequency
Backwash is stronger than the swash so it removes material from the beach
How do the waves wear away the coast
Hydraulic power
Abrasion
Attrition
How does longshore drift occur?
Direction of longshore drift is determined by prevailing wind
The swash travells in this direction transporting sediment.
The backwash however moves back at 90 degrees to the beach due to gravity
Why does deposition occur?
Water carrying sediment loses energy and slows down.
Occurs when:
Constructive waves are dominant
Large expanses of flat beach so swash spreads out, backwash doesn’t have enough energy to carry sediment back to sea
Where engineered structures like groynes trap material.
What are the two different weathering processes?
Mechanical (physical)
Chemical
What is chemical weathering?
Chemical reaction when rainwater hits the rock and decomposes or eats it away
Carbonic acid (rain) reacts with rock containing calcium carbonate - limewater
Rocks are then dissolved
What is mechanical weathering
Breakdown of rock without changing its chemical composition
Freeze thaw: Water enters cracks in the rocks. Overnight temp drops, the water freezes and expands. Exerting pressure on the rock.
During the day it melts again (thaw)
Repetition causes the cracks in the rocks to break up
What are the types of mass movement?
Slumping - A saturated material slumps down a concave slip plane and eotates
Sliding - Material shifts in a straight line along a slide plane
Rockfall - Broken up material along a bedding plane, falls down a slope
What is mass movement?
What factors affect it?
Shifting of rocks down a slope when the force of gravity is greater then the force supporting it.
When wet the water acts as a lubricant and makes the material heavier
What’s left behind is a scarp a steep cut in the side of the slope
What is a concordant coastline?
Alternating bands of hard and soft rock parallel to the sea
What is a discordant coastline?
Alternating bands of hard and soft rock are perpendicular to the coast.
Form headlands and bays. Bays form where the soft unconsolidated material is eroded fast forming a bay with a gentle slope
Headlands form where the hard, consolidated material takes longer to erode so it juts out forming a headland with steep sides.
How does cliffs being eroded form wave cut platforms?
Due to preferential erosion (Hydraulic action and Abrasion) at the base of the cliff, between high tide and low tide mark a wave cut notch is formed.
Due to repeated erosion the rock above the notch eventually collapses. Material is washed away.
REPEAT
What is left behind is a wave cut platform - A rocky level of bed rock gently sloping up towards the bottom of the cliff. Represents the base of the old cliff and marks the retreat of the cliff.
How are caves, arches and stacks formed?
The hard consolidated rock that makes up a headland often has weaknesses. Joints and faults.
Waves crash into the weaknesses and through erosion (HA + AB) Enlargement of these cracks forces a cave to form.
When the same thing happens on the other side the two caves join to form an arch.
Preferential Erosion from waves and mechanical and chemical weathering continues to wear away the rock until the arch collapses. This forms a stack
How are spits formed?
Where the is a sharp bend in the coast line eg. river mouth.
Longshore drift transports sand and shingle past the bend and deposits it in the sea. Over time this builds up forming a spit.
Area behind is sheltered from waves so plants are able to grow due to the accumulated material.
How do bars form?
When two spits join two headlands together this leaves a lagoon behind the bar
How are sand dunes formed?
When sand deposited by longshore drift it carried up the beach by the wind. Obstacles slow the wind down so it deposits the sand forming small embryo dunes.
As plants grow on the dune the roots stabilise the sand encouraging more sand to be deposited
This then forms foredunes and eventually mature dunes.
Hard engineering strategies for coasts
Sea walls
Groynes
Gabions
Rock armour
Soft engineering strategies for coasts
Beach nourishment
Dune regeneration
What is a sea wall
P+C
Concrete wall that reflects waves back out to sea
Prevents erosion and acts as a flood barrier
Expensive to build and maintain
What are gabions?
P+C
Wire cage filled with rocks
Absorb wave energy decrease rate of erosion
Ugly
What is rock armour?
P+C
Big boulders piled against coast
Absorb wave energy so decreases the rate of erosion
They can be moved by waves so need replacing
What are groynes?
Wooden/ stone fences that prevent longshore drift
Wider beaches - absorb more wave energy and slows them down
Starve beaches further down the coast so increases erosion there
What is beach nourishment?
Soft engineering strategy involves adding sand and shingle to the beach.
Wider beaches, slows waves.
Expensive and has to be frequently repeated
What is sand dune regeneration?
Creating or restoring sand dunes by adding sand or plants to stabilise the sand.
Barrier between land and sea. Absorbs wave energy
Protection limited to small area. Nourishment is very expensive
What is managed retreat?
Remove defences to allow sea to flood land behind it. Which overtime becomes marshland protecting land behind from flooding and erosion.
Cheap and easy
Agricultural land destroyed
Why is the Holderness coastline rapidly eroding?
Unconsolidated boulder clay, prone to slumping when wet.
Narrow beaches.
Beaches are being starved by Groynes higher up the coast
Long fetch across north sea - powerful waves.
What are the coastal management strategies in place on the Holderness coast
Hornsea has: Sea wall, Groynes and gabions
Mapleton has groynes however causing conflict in Great Cowden due to increased rate of erosion
What are the conflicts on the Holderness coast
Great Cowden is experiencing increased rates of erosion due to Mapleton’s groynes
Reduced rates of tourism due to the sea defences
Some people disagree with the placement of sea defences. Protecting settlements over agricultural land/
What affects the rate of erosion?
Length of fetch
Strength of winds - destructive waves formed
Area under the cliff to act as a buffer and reduce the energy of the waves
Consolidation of rocks and if it has areas of weakness eg. Joints and faults
