Coastal Landscapes Flashcards
Physical Process 1
The coastline is shaped by the interaction of the different physical processes of weathering, mass movement and erosion. You need to understand how each process causes change along coastlines.
Weathering on the Coast
Weathering helps wear away but leaves weathered material in situ. There are three types of weathering: chemical, mechanical and biological.
Chemical Weathering
Rocks reacting with slightly acidic water, e.g. limestone dissolved by carbonation.
Mechanical Weathering
Water falls into the cracks in rocks and freezes, causing it to expand; over time the repeated thawing and freezing causes the rock to break apart.
Biological Weathering
Action of plants and animals (e.g. tree roots widen in cracks in rocks), causing the rock to split apart.
Mass Movement on the Coast
Mass movement is the downhill movement of material under the influence of gravity. Types of mass movement vary according to:
- Material involved
- Amount of water in the material
- Type of movement, e.g. sliding, slumping.
How Waves Erode the Coast
There are four types of erosional processes:
- Abrasion
- Hydraulic Action
- Attrition
- Solution
Abrasion
Breaking waves throw sand, pebbles and boulders against the coast, during storms.
Hydraulic Action
The sheer weight and impact of water against the coastline, particularly during a storm, erodes the coast. Also waves compress air in joints in rocks, forcing them apart.
Attrition
Rocks and pebbles carry by waves rub together and break into smaller pieces.
Solution
The chemical action of seawater dissolves some rocks.
Explain how slumping occurs
Slumping happens when the rock is saturated. Loose, wet rocks slump down under the pull of gravity along curved slip planes.
Explain how sliding occurs
Sliding happens when loosened rocks and soil suddenly slide down the slope. Blocks of material may all slide at once.
Physical Processes 2
Waves transport eroded material along the coast and deposit it when they lose the energy to carry it further.
Longshore Drift
This is the process by which beach sediment can be transported along the coast by waves.
- Sediment is transported along the beach. This process is called longshore drift (LSD).
- The action of swash forces the sediment up the beach at a 45º angle.
- The action of the backwash will bring the sediment back down the beach at a 90º angle.
- The direction of the prevailing wind will dictate the angle and direction in which beach sediment will move.
- As waves hit the beach, this ‘zigzag’ process continues.
Transportation Methods
Waves transport material by:
- Traction
- Saltation
- Suspension
- Solution
Traction
Large boulders are rolled along the seabed by waves.
Saltation
Smaller stones are bounced along the seabed.
Suspension
Sand and small particles are carried along in the flow.
Solution
Some minerals are dissolved in seawater and carried along in the flow.
Deposition
The load carried by waves is deposited by constructive waves. Different factors influence deposition, for example:
- Sheltered spots (e.g. bays)
- Calm conditions
- Gentle gradient offshore causing friction
All reduce the wave’s energy.
Influence of Geology
The geological structure of coasts, rock type and wave action all influence coastal landforms.
Geological Structure
Geology affects how fast coastal erosion occurs. Soft rock is eroded much faster than hard rock. Particular landforms are created when soft rocks and hard rocks occur together.
Soft Rock (e.g. clay)
- Soft rock is easily eroded by the sea.
- Cliffs will be less rugged and less steep than hard rock coasts.
- Soft rock landscapes include bays.
Hard Rock (e.g. granite)
- Hard rock is resistant to all types of erosion.
- Cliffs will be high, steep and rugged.
- Hard rock landscapes include wave-cut platforms and headlands where caves, arches and stacks are formed.
Concordant Coasts
Concordant coasts are made up of the same rock type.