Paper 1) Coastal Environments Flashcards
The coast as a system
The coast is a natural system which means that it is a physical cycle where stores and flows of material and energy are linked together.
Erosion definition
The wearing away of rocks to the sea
How coastal erosions impact the UK
-28% of the UK coastline is eroding at varying speeds
-east - more erosion as rocks are softer
-highest rates up to 3.5 meters a year
Types of erosion processes
-hydraulic action
-corrasion/ abrasien
-solution
-attrition
Hydraulic process
-water is forced into cracks into rock
-air compresses
-wave retreats, compressed air blasts out
-damages rock
Corrasion/ abrasien
-rocks are thrown at the cliff
-when waves are destructive they have enough power to throw materials carried to cliff face
-acts like sandpaper, waves cliff away
Solution (erosion process)
-the sea contains salt. Material broken from cliff are dissolved by salt water in waves
-waves crash at cliff, salt and acids cause the rocks to erode
Attrition
-pieces of rock and pebbles from cliff are thrown around, hit each other
-becomes smooth, round
Swash vs backwash
-Waves towards coast
-waves moving away from coast
Constructive wave characteristics
-low energy
-strong swash
-weak backwash
-low wave height
-wide and flat beach shape
-low frequency (6-8 waves per minute)
Destructive wave characteristics
-high energy
-weak swash
-strong backwash
-high wave height
-steep and narrow beach shape
-high frequency (10-14 waves per minute)
Factors affecting coastal erosion
-rock type
-rock structure
-type of coastline
-type of wave
Factors affecting coastal erosion - rock type
Easily eroded (clay and shale):
-wide beaches
Resistant (limestone and chalk):
-steep cliffs, headlands
Factors affecting coastal erosion - rock structure
-rocks parallel to coastline - concordant
-rocks outcrop at right angles to the coast - discordant
Factors affecting coastal erosion - shape of coastline
-headlands are exposed to full force of the sea
-headlands can protect surrounding bays which can be sheltered from erosion
Factors affecting coastal erosion - type of wave
-Destructive wave
-Constructive wave
Types of transportation processes
-traction
-saltation
-suspension
-solution
Traction
Pebbles, large materials roll along the sea bed
Saltation
Small pieces (shingle, large sand grains) bounced along the sea bed
Suspension
Small particles (silts, clays) suspended in the flow of the water
Solution - transportation process
Minerals in rock (chalk, limestone) dissolved in sea water, not visible
Longshore drift
- The prevailing wind pushes waves up the beach at an 45 angle, picking up beach material in the swash
- As the wave retreats, the backwash drags this material back down the beach at a right angle
- Another wave picks up the material and moves it up the beach again, in the swash
- The backwash moves the material back down the beach
- The process continues and the material is moved along the coastline in a zig-zag motion until it meets a barrier (such as a headland or a groyne) and is deposited
Sediment cell
Sediment moved along the coast by longshore drift appears to form part of a circular cell which leads to it eventually returning updrift.
Dredging of offshore shingle banks can therefore contribute to beach depletion.
Coastal deposition
When material being transported dropped by constructive waves as waves have less energy
Where coastal deposition happens
-swash stronger than backwash
-area of shallow water
-enter a sheltered area (cove, bay)
-little wind
-good supply of material
Weathering definition
The breakdown of rocks by the action of weather such as wind and rain at one place.
-can be chemical, mechanical or biological
-erosion is when that rock can then be transported somewhere else
Mechanical weathering
-where water gets into cracks in the rocks during the day
-at night the temperature drops below freezing and the water turns into ice. It expands by 9-10% and begins to push the rock apart
-during the day, the temperature may rise again and ice in the crack will melt. At night-time the same thing happens
-over time, this repeated process will breakdown the rock
Mechanical weathering - salt crystallization
Salt crystals deposited in cracks and over time it accumulates and applies pressure to crack, crystals expand by 300%
Chemical weathering
-Rainwater mixes with chemicals such as carbon dioxide when it falls through the atmosphere
-this weak acid reacts with rocks containing calcium carbonate such as limestone and chalk
-over many years, the acid dissolves the rock - process called carbonation
Biological weathering
-this weathering is caused by animals and plants
-animals such as rabbits can burrow in cracks, make them bigger, and cause the rock to split over a long time
-lichens and mosses release chemicals that dissolves the rock
Mass movement definition
All downhill movement of material under the influence of gravity. The process causes the cliff to retreat backwards and provides material for the marine process
Slumping
Saturated soil slumps along a curved surface
Landslide
Blocks of rock detach themselves from the cliff and slide downhill along a slide plane
-the rock accumulates at the bottom of the cliff
Rockfall
Fragments of rock break away from the cliff face due to weathering
-A scree slope of falling rock is formed at the bottom of the cliff
Landscapes from deposition
-beaches
-spit
-bars
Beaches
Accumulations of sand, mud and shingle. Material has been eroded and transported from elsewhere, and then deposited by waves in the nearshore, foreshore and backshore zone
Key factors that influence beach profiles
-sediment size - grain size/ percolation rates
-wave energy - constructive/ destructive
-tidal range - storms tend to be more frequent in the winter
Spit definition
A long stretch of sand across a river mouth with one end attached to the mainland
Bar definition
A long stretch of sand stretches across a bay leaving a lagoon behind
Tombolo definition
A long stretch of sand joining an island to the mainland
Barrier definition
Form as waves repeatedly deposit sediment parallel to the shoreline. As waves shift, they can constantly move or disappear
Formation of a spit
- Constructive waves and the swash push sediment up the beach
- Sediment moves along the beach in a zig-zag pattern
- Backwash moves sediment down the beach
- Follows the prevailing wind direction
- Sand and shingle is moved along the coast by longshore drift
- Sediment comes to a change in the direction of the coastline
- Sediment is deposited in sheltered water as the current slows down and there is insufficient energy to carry the sediment
- Coast is sheltered and shallow
- Sediment builds up above the level of the sea
- If a spit grows across the river a bar forms and lagoon
- Saltmarsh and sand dunes build up behind the spit
Sand dune formation
- On shore winds blow sand up the beach to the backshore
- In the backshore, obstacles such as rocks and driftwood block sand movement causing deposits to build over time, creating embryo dunes and foredunes
- Vegetation such as Marram Grass starts to grow and helps to stabilize and binds the sand together
- Over time, the sand dunes migrate inland
Factors needed to sand dune formation
-a plentiful supply of sand
-shallow offshore zone with gentle gradient, where large explosives of sand dry out at low tide
-an extensive backshore area where sand can accumulate
-prevailing onshore winds - vegetation which will help the sand be stable
Concordant coastline
Layers of differing rock types that run parallel to the coast
Discordant coastline
Where bands of different rock type run perpendicular to the coast
What do discordant coastlines form
Have alternating bands of hard and soft rock which form the headlands and bays.
-Hard rocks resists erosion and forms headlands
-soft rock is easily eroded and forms bays
-formation of headlands and bays is called differential erosion