The Coastal Zone Flashcards
What is mechanical weathering?
The breakdown of rock without changing its chemical composition.
What is chemical weathering?
The breakdown of rock by changing its chemical composition
What happens during freeze thaw weathering?
- Water gets into cracks in the rock
- It freezes and expands, putting pressure on the rock
- The water thaws and contracts, releasing the pressure
- The process repeats and widens the cracks
What is carbonation weathering?
- Rainwater has carbon dioxide dissolved in it which makes weak carbonic acid
- Carbonic acid reacts with rock that contains calcium carbonate
What is mass movement?
When material shifts down a slope as one, under the force of gravity
What are slides?
Material shifting in a straight line
What are slumps?
Material shifts with a rotation
Mass movement causes coasts to…
…retreat rapidly
When is mass movement more likely to happen?
When the material is full of water, as it acts as a lubricant
What are the 4 processes of erosion?
Hydraulic action, abrasion, attrition and solution
What is Hydraulic action?
Waves crash against the rock and compress the air in the cracks. This puts pressure on the rock. Repeated compression widens the cracks and bits of rock break off
What is abrasion?
Eroded particles in the water scrape and rub against the rock, removing small pieces
What is attrition?
Eroded particles in the water smash into each other, and break into smaller fragments. Their edges also get rounded off.
What is solution?
Weak carbonic acid in seawater dissolves rock like chalk and limestone
What are the features of a destructive wave?
- High frequency (10-14 a minute)
- They’re high and steep
- Their backwash is more powerful than their swash
- They remove material from the coast
Waves erode cliffs to form…
…wave cut platforms
How are wave cut platforms formed?
- Waves cause most erosion at the foot of a cliff.
- This forms a wave cut notch, which is enlarged as erosion continues
- Undercutting occurs
- The rock above becomes unstable and collapses
- Repeated collapsing causes the cliff to retreat
- A wave cut platform is left behind
How are Headlands and Bays formed?
- Headlands and bays form where there are alternating bands of hard and soft rock along a coast
- The less resistant rock is eroded quickly and this forms a bay
- The resistant rock is eroded more slowly so is left protruding into the sea, forming a headland
How does longshore drift occur?
- Waves follow the direction of the prevailing wind
- The hit the coastline at an oblique angle
- The swash carries material up the beach, in the same direction as the waves
- The backwash then carries material down the beach at right angles
- Material zigzags along the beach over time
What is deposition?
When material being carried by the sea is dropped on the coast
When are coasts built up?
When the amount of deposition is greater than the amount of erosion
When is the amount of material deposited increased?
- There’s lots of erosion elsewhere on the coast
- There’s lots of transportation of material into the area
Which waves give a lot of deposition but not much erosion?
Low energy waves
What are the features of a constructive wave?
- They’re low in frequency (6-8 per min)
- They’re low and low
- The swash is powerful and carries material up the coast
- The backwash is weaker and it doesn’t take a lot of material back down the coast
Beaches are formed by…
…deposition
Which marks are beaches found between?
The high water mark and the low water mark
What type of waves are beaches formed by?
Constructive
Sand beaches are…
…flat and wide - sand particles are small and the weak backwash can move them back down the beach
Shingle beaches are…
…steep and narrow - shingle particles are large and the weak backwash can’t move them back down the beach
How are spits formed?
- The from at sharp bends in the coastline
- Longshore drift transports sand and shingle past the bend and deposits it in the sea
- Strong winds and waves can curve the end of the spit
- The sheltered are behind the spit can accumulate material, forming a salt marsh
How are bars formed?
- A bar is formed when a spit joins two headlands together
- The bar cuts off the bay from the sea
- This means a lagoon can form
What is a sea wall?
A wall made out of hard material like concrete that reflects waves back into the sea
What is rock armour?
Boulders that are piled up along the coast
What are Groynes?
Wooden or stones fences that are built at right angles to the coast. They trap material transported by long shore drift.
What are the advantages and disadvantages of sea walls?
- They prevent erosion of the coast and act as barriers against flooding
- They create strong backwash which erodes under the wall. They are expensive to build and maintain
What are the advantages and disadvantages of rock armour?
- The boulders absorb wave energy and so reduce erosion and flooding
- Boulder scan be moved around by strong waves, so need to be replaces
What are the advantages and disadvantages of groynes?
- Groynes create wider beaches which slow the waves. This gives greater protection from flooding and erosion. Also fairly cheap.
- They starve beaches further down the coast of sand, making them narrower, leading to greater erosion and floods
What is beach nourishment?
Sand and shingle from elsewhere is added to beaches
What is dune regeneration?
Creating or restoring sand dunes by either nourishment or by planting vegetation to stabilise sand
What is marsh creation?
Planting vegetation in mudflats along the coast
What is managed retreat?
Removing an existing defence and allowing the land behind it to flood
What are the advantages and disadvantages of beach nourishment?
- Creates wider beaches which slow the waves
- Taking material from the seabed can kill organisms and is a very expensive defence which has to be repeated
What are the advantages and disadvantages of dune regeneration?
- Sand dunes provide a barrier between land and sea. Wave energy is absorbed which prevents flooding and erosion
- The protection is limited to a small area. Nourishment is very expensive
What are the advantages and disadvantages of marsh creation?
- The vegetation stabilises the mudflats and helps reduce the speed of waves, preventing flooding and erosion
- Marsh creation isn’t useful where erosion rates are high because the marsh can’t establish itself
What are the advantages and disadvantages of managed retreat?
- Over time the land will become marshland, creating new habitats. Flooding and erosion are reduced behind the marshland. Also cheap.
- People may disagree over what land is allowed to flood.
