Weathering is the breakdown of rock in situ, with two types:
Mechanical weathering: breakdown of rock without changing its chemical composition
Chemical weathering: breakdown of rock by changing its chemical composition
Example of mechanical weathering: Freeze-thaw weathering
Water enters rock through a crack, freezes, expands, and puts pressure on the rock
When water thaws, it contracts, releasing the pressure and widening cracks, causing rocks to fall and break
Example of chemical weathering: Carbonation
Rainwater with carbon dioxide dissolved in it forms weak carbonic acid
Carbonic acid reacts with rock containing calcium carbonate, dissolving the rock
Mass movement is the shifting of rocks and loose material down a slope, such as a cliff, when gravity's force is greater than the force supporting it
Three types of massmovement:
Sliding: materials shift in a straight line along the side plane
Slumping: material rotates along a curved slip plane
Rockfall: material breaks up along bedding planes and falls down a slope
Waves created when wind blows over the sea:
Destructive waves erode the coast and destroy the beach
Constructive waves deposit material at the coast, building the beach
In destructive waves, the backswash (water moving down the beach) is more powerful than the swash (water moving up the beach)
In constructive waves, the swash is more powerful than the backwash, depositing material
Three types of erosion:
Hydraulic power: waves crash against rock, compress air within cracks, putting pressure on the rock and widening cracks causing bits of rock to break off
Abrasion: eroded particles in the water scrape and rub against the rock, removing small pieces of the seabed
Attrition: eroded particles in the water collide, break into smaller pieces, and become more rounded
Longshore drift:
Water moves in a specific direction following the prevailing wind direction
Waves hit the coast at an angle, shown by arrows of the swash
Swash carries material up the beach in the same direction as the waves
Backswash carries material down the beach at right angles back towards the sea
Over time, material zigzags along the coast
Five steps to describe longshoredrift:
Waves hit the coast at an angle
Swash carries material up the beach
Backswash carries material down the beach
Material zigzags along the coast
Diagram is helpful for understanding
Four processes of transportation:
Traction: large particles like boulders pushed along the seabed by the force of water
Saltation: pebble-sized particles bounce along the seabed by the force of water
Suspension: smaller particles like silt and clay carried along in the water
Solution: soluble materials dissolve in the water and are carried along
Transported materials move in four different ways based on size, from largest to smallest
Deposition:
Happens when water carrying sediment loses energy and slows down
Material is let go when the rate of erosion elsewhere provides material and the amount of material transported into the area affects the rate of deposition
Rock types and geological structures influence the erosional landforms that develop on a coastline
Discordant coastlines are made of altering bands of hard and soft rock at right angles to the coast
Concordantcoastlines have altering bands of rock that are parallel to the coast
Headlands and bays form along discordant coastlines
Headlands and bays form when there are altering bands of resistant and less resistant rock along a coast
The less resistant rock erodes faster, forming a bay with a gentle slope
The resistant rock erodes more slowly, jutting out to form a headland with steep sides
Headlands create caves, stacks, and stumps
The resistant rock of headlands often has weaknesses like cracks
Waves crash into the headlands and enlarge these cracks mainly by hydraulic power and abrasion
Repeated erosion and enlargement of the cracks cause a cave to form
Continued erosion deepens the cave until it breaks through the headland to form an arch
Erosion continues to wear away the rock supporting the arch until it collapses, forming a stack - an isolated rock separate from the headland
Wave cut platforms:
Waves cause most erosion at the foot of a cliff, forming a wave cut notch
Repeated erosion causes the rock above the notch to become unstable and eventually collapse
Collapsed material is washed away, and a new wave cut notch starts to form
After repeated collapse, the cliff retreats, leaving a wave cut platform
Beaches:
Found on coasts between high and low water marks
Formed via constructive waves depositing material
Two types of beaches: sandy and shingle
Sandy beaches created by low energy waves, flat and wide with small sand particles
Shingle beaches created by high energy waves, steep and narrow with large shingle particles
Spits:
Form 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 forming a recurved end
Sheltered area behind the spit accumulates material and flats are able to grow over time
Bars:
Form when a spit joins two headlands together, cutting off a bay from the sea to form a lagoon
Offshore bars can form if the coast has a gentle slope, where waves slow down and deposit sediment offshore
Sand dunes:
Formed when sand deposited by longshore drift is moved up the beach by the wind
Obstacles cause wind speed to decrease, leading to sand deposition and formation of small embryo dunes
Embryo dunes are colonized by plants, stabilizing the dunes
Hardengineering:
Man-made structures built to control the flow of the sea and reduce flooding and erosion
Examples include seawalls, gabions, rock armor, groins
Soft engineering:
Schemes set up using knowledge of the sea and its processes to reduce the effects of flooding and erosion
Seawall:
Built at the edge of the coastline to protect the base of cliffs, land, and buildings against erosion
Aims to prevent coastal flooding
Expensive to build
Curved sea walls reflect wave energy back onto the sea, maintaining powerful waves over time
High cost of maintenance
Groins:
Wooden barriers built at right angles towards the beach to prevent the movement of beach material along the coast (Longshore drift)
Allow the build-up of a beach, acting as a natural defense against erosion
Can be seen as unattractive and costly to build and maintain
Rockarmor and boulder barriers:
Large boulders piled up on the beach to absorb wave energy and allow the build-up of a beach
Expensive to obtain and transport
Beachnourishment:
Replaces beach or cliff material removed by erosion or Longshore drift
Beaches act as a natural defense against erosion and coastal flooding
Relatively inexpensive but requires constant maintenance
Managedretreat:
Areas of the coast allowed to erode and flood naturally, usually low-value areas
Encourages the development of beaches, natural defenses, and salt marshes
Low cost but requires compensation for loss of buildings and farmland
The path of a river as it flows downhill is called its course
Rivers have a steep upper course near the source, a gently sloping middle course, and an almost flat lower course
The long profile of a river shows how the gradient changes