Coasts

geography

What is weathering?

Breakdown of rocks, soils and minerals through contact with the Earth's atmosphere, waters and biological organisms.

What are the 3 types of weathering?

Chemical, biological and mechanical.

What is mechanical weathering?

Breakdown of rock without changing its chemical composition (freeze-thaw) – affects coasts.

What is the first step of the mechanical weathering process?

Water infiltration – seeps into cracks in the rock

What is the second step of the mechanical weathering process?

Freezing and expansion – temperature drops below freezing; water freezes and expands in volume.

What is the third step of the mechanical weathering process?

Pressure generation – ice acts as a wedge; tensional force of surrounding rock widens the crack.

What is the fourth step of the mechanical weathering process?

Thawing, repeated cycle – temperature rises and ice melts.

What is the fifth step of the mechanical weathering process?

Fragmentation – forces rock to split into smaller fragments

What is biological weathering?

Breakdown of rock by living organisms – plants, animals and microbes.

What is the first step of the biological weathering process?

Roots enter small cracks in rock.

What is the second step of the biological weathering process?

Seed grows, plant root grows into rock, fuelled by water and nutrients.

What is the third step of the biological weathering process?

Root grows thicker, stronger, pressure on surrounding rock.

What is the fourth step of the biological weathering process?

Crack widens, rock breaks away, splits apart, creating angular fragments.

What is chemical weathering?

Breakdown of rock by changing its chemical composition – carbonation – only happens in warm and wet conditions.

What is the first step of the chemical weathering process?

Water introduction – enters fractures in rock – brings dissolved oxygen or acids.

What is the second step of the chemical weathering process?

Chemical reaction – oxygen reacts with iron-rich minerals causing them to rust and weaken.

What is the third step of the chemical weathering process?

Breakdown and transport – rock weakens, crumbles and dissolves; minerals are carried away, often forming soil.

What is hydraulic action?

Force of the water into cracks in cliff.

What is abrasion?

Rocks carried by the current into bank/cliff.

What is attrition?

Rocks hit each other making them smaller.

What is corrosion?

Chemically breaks down rock (dissolve).

What are discordant coastlines?

Have alternating layers of rock at right angles to the coast.

What is longshore drift?

It is the primary process of transportation of sediment along a coastline in a zig-zag pattern driven by prevailing wind.

Where does longshore drift occur?

Inshore and offshore.

What does the zig-zag movement cause?

Particles to move in a saw tooth pattern along the coast.

How do waves approach the beach?

At oblique angles.

With swash how do waves approach the beach?

At oblique angles.

What does swash do in longshore drift?

Carries material up the beach following the angle of the waves.

With backwash what happens to waves?

Waves lose energy, water returns to the sea, pulled by gravity, moves straight down the beach at 90° angle to the shoreline.

What does backwash do in longshore drift?

Takes material straight down the beach under gravity.

In longshore drift waves approach the beach at an angle that is?

Similar to that of the wind.

What does longshore drift create?

Coastal landforms like spits, bars and beaches.

4 environmental impacts of longshore drift

Landform creation, sediment redistribution, coastal erosion and deposition, impact of human inference.

2 impacts on ecosystems from longshore drift?

Habitat changes, destruction of ecosystem (plants).

What are the 4 methods of sediment movement?

Traction, saltation, suspension, solution

What is traction?

Large boulders roll along the seabed by powerful waves.

What is saltation?

Smaller pebbles and shingle are bounced along the seabed.

What is suspension?

Fine particles like silt and clay are carried within the water flow (making it look cloudy).

What is solution?

Certain minerals dissolve in the water and are carried as an invisible load.

An advantage of groynes?

Create wider beaches (naturally dissipate wave energy).

A disadvantage of groynes?

Starves areas further down coast of sediment. Must be repeated frequently – making it costly (long-term).

What is soft engineering?

These techniques work naturally with the environment to absorb wave energy and maintain coastal stability.

What is beach nourishment?

Replacing sand or shingle that has been eroded by the sea to widen the beach.

An advantage of beach nourishment?

Blends naturally with environment and widens beach to slow waves.

A disadvantage of beach nourishment?

Must be repeated frequently (making it costly – long-term).

What is sand-dune regeneration?

Planting marram grass or adding fencing to stabilise sand dunes, which act as a natural barrier to absorb wave energy.

An advantage of sand-dune regeneration?

Looks natural and provides good wildlife habitats.

A disadvantage of sand-dune regeneration?

Expensive – requires restricting public access until vegetation takes root.

What is the Holderness Coast?

One of Europe's fastest-eroding coastlines, losing about 2m of land per year due to soft, easily eroded boulder clay and powerful waves.

What strategies are used?

Sea walls and groynes.

How do they protect?

Local businesses and residential properties, but trap sediment leaving areas further south without natural beach protection.

Which statistic shows how it was protected?

In 1991 area protected with £2 million worth of groynes to protect the village and main road.

What are wave cut platforms?

Massive wave energy hits the base of the cliff between the high and low tide mark.

What happens to the cliff after?

The cliff becomes unstable and collapses.

What happens after repeated cycles?

The cliff retreats back leaving a wave cut platform at the base.

How do headlands and bays form?

Discordant coastline – alternating bands of hard and soft rock at right angles to the coast.

What does wave energy do to the soft rock?

Rapidly erodes the soft rock (e.g. clay) forming a bay.

What happens to the hard rock?

Erodes much slower, sticking out into the sea as a headland.

What is the first step of the crack, cave, arch, stack, stump process?

Hydraulic action and abrasion widens joints/cracks in the headland.

What is the second step?

Over time the crack widens to form a cave.

What is the third step?

Wave energy cuts through the cave to form an arch.

What is the fourth step?

Weathering (sub-aerial) weakens the roof of the arch causing it to collapse.

What is the fifth step?

Leaving an isolated pillar of rock called a stack.

What is the final step?

The stack is eroded at the base by waves, collapsing to leave a stump.

How do beaches form?

Low energy, constructive waves deposit sediment (sand/shingle) in sheltered areas like bays.

What is a spit?

An elongated ridge of sand/shingle extending out into the sea, attached to the land at one end.

How do they form?

Longshore drift moves sediment along the coast. When the coastline changes direction, sediment is deposited.

What happens when the wind changes direction?

Causes the end of the spit to curve, forming a recurved lateral hook.

What forms behind the spit?

A salt marsh forms in the sheltered, low-energy water behind the spit.

What is a bar?

A ridge of sand/shingle that joins two headlands together, cutting off a body of water.

What is formed behind the bar?

A lagoon.

How do sand dunes form?

Wind blows sand inland, which gets trapped by obstacles (e.g. driftwood/rocks) on the beach.

What is the first stage of a sand dune called?

Embryo dunes.

What plant grows on dunes to stabilise them?

Marram grass – its long roots bind the sand together.

What is a sea wall?

Concrete wall placed at the foot of a cliff to reflect wave energy back out to sea.

An advantage of sea walls?

Highly effective at protecting the coast from flooding and erosion.

A disadvantage of sea walls?

Very expensive to build and maintain, and can look unnatural.

What is rock armour?

Large boulders piled up at the base of a cliff or sea wall to absorb wave energy.

An advantage of rock armour?

Relatively cheap and quick to construct.

A disadvantage of rock armour?

Boulders can be expensive to transport and can look out of place with local geology.

What are gabions?

Wire cages filled with rocks placed at the foot of cliffs to absorb wave energy.

An advantage of gabions?

Cheap and easy to construct; eventually blends into the environment as vegetation grows.

A disadvantage of gabions?

Wire cages can rust and break, making them dangerous and visually unattractive.

What is mass movement?

The downhill movement of sediment or rock under the force of gravity.

What are the 3 types of mass movement?

Rockfalls, slumping, sliding.

What is slumping?

A type of mass movement where material moves down a slope with a rotation, typically occurring after heavy rain saturates the soil.

What is managed retreat?

Allowing the sea to naturally flood or erode an area of low-value land (e.g. farmland) to protect higher-value areas elsewhere.

An advantage of managed retreat?

Very cheap, creates new natural habitats (like salt marshes), and acts as a natural defence against future erosion.

A disadvantage of managed retreat?

Landowners lose their land, which can cause conflict and require financial compensation.

What is a constructive wave?

A wave with a low frequency (6–8 per minute) and a strong swash, but a weak backwash.

What does a constructive wave do?

It builds up the beach by depositing sediment.

What are its characteristics?

Low height, long wavelength, and a gentle spill onto the shore.

What is a destructive wave?

A wave with a high frequency (10–14 per minute) and a powerful backwash, but a weak swash.

What does a destructive wave do?

It removes sediment from the beach, eroding the coastline.

What are its characteristics?

High height, short wavelength, and a steep plunge onto the shore.

Where is Old Harry Rocks located?

On the Isle of Purbeck in Dorset, southern England.

What type of rock forms Old Harry Rocks?

Chalk, which is a hard, resistant rock but still prone to erosion along joints.

How did Old Harry Rocks form?

It is a classic example of headland erosion forming a cave, arch, stack and stump sequence.

What process formed the original cave?

Hydraulic action and abrasion exploited weakness/cracks in the chalk headland to create a cave.

How did it become an arch?

Waves broke all the way through the cave.