Studied by 6 people
Destructive waves
responsible for erosional processes
high frequency (10-15 waves per minute)
steep and high, with a circular motion so waves break at a greater height, causing the wave to ‘plunge’ and travel a shorter distance along the beach
removes material from coasts because the swash is less powerful than the backwash
Constructive waves
low frequency (6-9 waves per minute)
long and low
move in an elliptical motion, with waves having little height resulting in them ‘spilling’ and breaking out further along the beach
forms gently sloping beaches by depositing material on coasts because the backwash is less powerful than the swash
Longshore drift
transports material along coastlines when waves approach the beach at an angle
Swash direction
wind approaches the coast at an angle because of a prevailing wind direction
waves are controlled by the wind and so this angle will be the direction the swash moves up the beach
Backwash direction
Gravity is the only force that acts on the backwash, so it falls back to the sea at right angles to the coastline
Swash and Backwash effect
because of the difference between the angle of the swash and the angle of the backwash, sediment repeatedly moves in the shape of a right-angled triangle.
over time, sediment is carried along a beach
Erosion: Attrition
pieces of bedload (material carried in the water) are hit against one another causing them to break apart and become smaller and more rounded
Erosion: Hydraulic power
causes the breakdown of cliffs due to the force of the water being compressed into the cracks of the rock
the repeated action of the water forced in and out of the cracks in the rock leads to the breakdown of the surrounding cliff
Erosion: Abrasion
pieces of rock are picked up by waves and hit against the bed, the beach or cliffs causing them to wear away over time
Erosion: Corrosion
a chemical reaction between the seawater (which contains a weak acid) and susceptible rocks like limestone
Headlands
made up of resistant rocks with weaknesses (joints and cracks)
Erosion of headlands (1)
destructive waves erode weaknesses in headlands by corrosion and hydraulic action
Erosion of headlands (2)
when the weaknesses in the rock widen, abrasion becomes more important
Erosion of headlands (3)
over time, these erosional processes lead to the formation of coastal landforms such as caves, arches, stacks and stumps
Caves
erosion attacks lines of weaknesses in the headland
when the crack widens into a small hollowed out area, a cave has formed
Arches
when caves are eroded through the headland, an arch is created
E.g., Durdle Door on the Dorset Coast
Stacks
when the top of an arch collapses because of gravity, a column called a stack is left behind
Stumps
continued erosion and weathering cause the stack to breakdown, forming a stump
at high tide, the stump can become submerged
eventually, the stump will erode and there will be nothing left of it
Formation: Wave-cut notch (1)
cliffs are created when erosion, weathering and mass movement processes cause the undercutting and collapse of unsupported rock
destructive waves are responsible for most of the erosion at the base of cliffs
when destructive waves lead to abrasion undercutting the cliff face, a curved indent in the cliff forms and a wave-cut notch is created
Formation: Collapse of wave-cut notch (2)
continued erosion of the wave-cut notch causes the rock above it to become less and less stable, until it eventually collapses
Formation: New wave-cut notch (3)
waves wash away the collapsed material and begin eroding away at the cliff again, causing a new wave-cut notch to form
Formation: Wave-cut platform (4)
over time, multiple collapsing events lead to the cliff retreating, leaving behind a wave-cut platform
Formation of Wave-Cut Platforms summary
erosion causes a wave-cut notch to form
erosion of the wave-cut notch causes the rock above it to collapse
waves wash away the collapsed material and begin eroding the cliff again
multiple collapsing events lead to the cliff retreating, leaving behind a wave-cut platform
Weathering
breaking down of rocks where they are
Mechanical weathering
rocks are broken down without their chemical composition being changed
salt weathering is the main type of mechanical weathering affecting coasts
Mechanical weathering: Salt weathering
seawater gets into cracks in rocks
salt crystals form when the seawater evaporates. These crystals then expand and put pressure on the rock
over time, the repeated evaporation of saltwater widens the cracks in the rock so much that the rock breaks apart
Chemical weathering
rocks are broken down because of their chemical composition being changed
Chemical weathering: Carbonation
takes place when it is warm and wet
carbon dioxide dissolves in rain, making it a weak carbonic acid
the acidic rainwater dissolves types of rock that contain calcium carbonate
Biological weathering
rocks are broken down by living things
e.g., plant roots get into cracks and push rocks apart as they grow
Littoral zone
series of sub-zones to represent the features of the wider coastline from sea to land
key sub-zones: offshore, nearshore, foreshore and backshore
Sediment cell
a closed system operated by sources, transfers and sinks driven by erosion, transportation and deposition processes
How many sediment cells the UK has
11
Sources
subaerial processes, erosional processes (breaking down cliffs) and sediments brought to the coastline by rivers
Transfers
longshore drift, onshore and offshore winds and tides
Sinks
depositional landforms (spits, bars, beaches and sand dunes)
Depositional landform: Spits
when the coast changes direction at an estuary (where a river meets the sea), longshore drift continues to move sediment across the inlet.
the river doesn't let the spit completely join to the coast on the other side because the river has the energy to move the sediment
often have salt marshes behind them
Depositional landform: Bars
formed when a spit grows across a bay
lagoons often form behind bars
Depositional landform: Beaches
made by constructive waves moving and depositing sand or shingle inland
a more gently sloping beach tends to be formed from sand, whereas a steeper sloping beach is formed from pebbles
Depositional landform: Tombolos
when a spit stretches across the mainland and joins an offshore island
Depositional landform: Cuspate Forelands
form when sediment is deposited across a bay caused by longshore drift transporting sediment in two directions
leading to the formation of two spits which eventually meet and this then results in the trapping of sediment until eventually new land is formed
Dynamic equilibrium
balance between inputs and outputs
Littoral zone in/outputs
sediment is the key input and output of the system and is determined by:
input - the action of waves, currents and wind
output - washed out into the sea by erosion
High energy coast
destructive waves, long fetches, high rates of erosion, caves, arches, stacks and stumps, cliffs and wave-cut platform
Low energy coast
constructive waves, shorter fetches, higher rates of deposition, spits and bars, beaches, sand dunes and salt marshes
Concordant coastlines
alternating bands of hard and soft rock parallel to the coast
Concordant coastlines: Dalmatian coasts
made up of offshore islands and coastal inlets running parallel to the coastline
Discordant coastlines
alternating bands of hard and soft rock at 90o to the coast
erosional landforms are more common on discordant coastlines because erosion happens at different rates along their length
Discordant coastlines: Bays and Headlands
the retreating, less resistant rock and the exposed resistant rocks cause a change in the shape of the coastline. This leads to wave refraction
this change in the way in which waves approach the coastline can cause an increased rate of erosion on the headlands
this leads to the formation of headland features like caves, arches, stacks and stumps
Geological structure: Dips
the angle the rock layer forms with the horizontal bedding plane is referred to as the dip.
rocks can dip either towards land or towards the sea
bedding planes that dip towards the sea create a gentler cliff profile (these cliffs are vulnerable to mass movement processes, e.g., rockfalls)
bedding planes that dip towards land tend to create a steeper cliff profile (these cliffs are more vulnerable to erosion processes, e.g., hydraulic action and abrasion)
Geological structure: Joints and Faults
geological structure of rocks (formation of joints, angle of dip, faulting and folding) is caused by the deformation and stress placed on them by tectonic processes
rocks with more joints and faults (e.g., sedimentary rocks) are more susceptible to the processes of erosion and weathering. This is because these processes exert forces on the weaknesses found in the layers of the rocks
Bedrock lithology
physical properties of different rocks
Igneous rocks
e.g., Basalt and Granite, form from the crystallisation of magma (more resistant to erosion and weathering)
this is because igneous rocks contain crystals which increase the strength of the rocks and reduce the number of lines of weaknesses that would be exploited by physical processes
igneous rocks can either be intrusive (formed from magma inside the Earth) or extrusive (formed when magma escapes through vents on the Earth’s surface)
average rate of erosion of igneous rocks: 0.1-0.5 cm per year
Sedimentary rocks
e.g., Limestone and Sandstone, form from the build-up, compacting and hardening of sediments into layers over time by lithification
sedimentary rocks formed in a shorter geological time scale tend to be more susceptible to erosion and weathering and erode at a faster rate compared with those formed over a longer geological time
average rate of erosion of sedimentary rocks: 2-6 cm per year
Lithification
transform a sediment or other material into stone
Metamorphic rock
e.g., Slate and Marble, are formed from the change in the structure of sedimentary and igneous rocks, caused by variations in heat and pressure
Marble is an example of a metamorphic rock that has been formed from the changing structure of limestone caused by the re-crystallisation of calcite
resistant to erosion
Sand dunes
needs continuous supply of sand, powerful winds to transport sand and obstacles to trap the sand, like plants
typical sand dune transect goes from the mobile dunes nearest the sea (embryo, fore and yellow) to the fixed dunes nearest the backshore (grey dunes and dune slack)
dunes contain two types of plants:
Xerophytes
Halophytes
Xerophytes
can withstand periods of dry weather
Halophytes
can withstand high concentrations of salt from seawater
Yellow dunes
colonised by marram grass (long deep roots and are salt tolerant
Embryo and Foredunes
colonised by sea rocket and sea crouch (deep roots and tolerate high concentrations of salt)
Grey dunes
colonised by heathers (higher rates of humus)
Humus
organic material that forms in soil when plant and animal matter decays
Mass movement
when rocks and loose material shift down slopes. This happens when gravity overcomes the force supporting the material. Mass movements can cause rapid coastal retreat and are common when the material is saturated
Mass movement: Rockfalls
when material breaks apart because of erosion and weathering and then rolls down a slope
the fallen fragments at the base of the cliff create talus scree slopes
Mass movement: Slides
when material moves down a slope in a straight line
Mass movement: Slumps
when material moves down a slope with a rotation
happen slower than rockfalls and often happen when unstable permeable rock overlays more stable impermeable rock
combination of heavy rainfall and erosion processes cause the rotational movement of the cliff
Sea level change: Eustatic change
the rising and falling of sea levels, influenced by ice ages
water is stored in the form of ice when the world is experiencing an ice age, which causes sea level to fall
as the world moves out of an ice age, the ice melts resulting in sea level rise again
Sea level change: Isostatic change
refers to the level of the land, which is also influenced by ice ages
during an ice age, the weight of the ice forces the land to sink
when the ice age has finished, the melting of the ice causes the land to rebound back up
Sea level change: Tectonic change
causes land to either rise or sink at the boundaries where tectonic plates meet
a sudden change in the movement of a plate can lead to a rise or fall in the seabed, causing a change in sea level (as well as tsunamis)
Global warming
changes in the world’s atmospheric temperatures are causing thermal expansion of the oceans, melting of glaciers and ice sheets
global warming is largely because of anthropogenic greenhouse gas (GHG) emissions. The concentration of these gases has risen rapidly since industrialisation
Climate change
changing the frequency and intensity of low-pressure depressions and tropical storms
rising global temperatures are causing our oceans to warm, triggering these low-pressure systems
this increases the risk of coastal flooding and creates unusual weather conditions
Increased frequency of storms (due to global warming)
strong winds caused by storms create high energy, destructive waves which have considerable erosional power
increased energy of the sea will mean more material can be transported and for greater distances. This could leave some areas vulnerable to erosion if they are left without much protection
frequency of storm surges will increase. When combined with sea level rise, these surges will reach further inland and cause more damage
Rising sea levels
some of the contributing factors being linked to the melting of glaciers and ice sheets
e.g., the Greenland and Antarctic ice sheets have been decreasing rapidly
higher sea levels could cause higher tides, which would increase the frequency of coastal flooding
higher tides could also remove more material from beaches, leaving cliffs less protected
Emergent coastlines
emergent coastlines cause the formation of raised beaches and fossil cliffs caused by isostatic rebound
a raised beach and fossil cliff are formed when, following an ice age, the land rebounds. This causes the original height of land to increase
this leaves behind a beach and fossil cliff higher than their original position
e.g., in Fife, Scotland
Submergent coastlines
submergent coastlines cause the formation of rias, fjords and Dalmatian coasts.
Dalmatian coasts are formed because of the arrangement of alternating rock types parallel to the coast
Ria
a flooded river valley formed when rising sea levels flood the valley, often creating an estuary
Fjord
a flooded glaciated valley formed when a glacier erodes vertically, creating a u-shaped valley.
e.g., Lysefjord in Norway
Coastal recession: Subaerial processes
weathering and mass movement processes combine to increase the rate of coastal recession
long periods of rainfall weaken rock structure and in turn, leads to mass movement of material
this collapsed material is then eroded and transported away by wave action
Coastal recession: Hard engineering
construction of hard engineering structures at the coastline can disrupt sediment cells
by disrupting one bit of coast, areas further along the coast may be starved of sediment supply, which can then result in the destruction of beaches
Dredging
the removal of sediment for use in construction but has been linked to increased rates of coastal retreat
Coastal recession: Dredging
removal of the sediment causes the depth of the ocean to increase
this can cause an increase in the occurrence of destructive waves at the coast because they can maintain their energy further towards the shoreline
Rate of coastal recession: Tides
tides are linked to gravitational pull. When the pull is at its strongest, there are high tides. When the pull is at its weakest, there are low tides
during periods of high tide, the rate of coastal recession can increase because waves can reach further towards the shore
Rate of coastal recession: Weather systems
influenced by areas of high pressure, creating anticyclones, and areas of low pressure, creating depressions
increased belts of high pressure reduce the rate of coastal recession because this leads to calmer weather
belts of low pressure systems cause unsettled weather condition
seasons - winter recession is higher than summer recession because winter brings stormy weather, linked with higher tides and long wave fetch
Rate of coastal recession: Wind direction
wind direction controls the movement of waves, influencing the rate of coastal erosion
a dominant wind direction causes powerful destructive waves to attack the coastline
this happens because the waves have travelled a long distance, influenced by the dominant wind, which is linked to the fetch of a wave
Coastal flooding
a risk to millions of people today because many continue to live near coastlines for recreation and employment purposes. Low-lying coasts are at risk of flooding from local factors and global rises in sea levels
Bangladesh flooding
storm surges threaten the lives of those living near the coast.
rate of coastal erosion is expected to increase in the future if storm surge events continue to rise.
risk associated with storm surges in the Bay of Bengal is because Bangladesh is so low-lying
Maldives flooding
the removal of mangroves is leading to an increased risk of flooding with increased wave height and less stable cliffs because there's a lack of roots in the soil
several factors, such as waste disposal and logging, have caused the soil to lack roots
the disturbance and removal of the mangroves is leading to increased wave energy and height because the trees would normally act as a barrier, helping to dissipate the wave’s energy before it reaches land
Consequences of coastal recession: Economic and social losses
damage to houses and businesses mean that people are forced to relocate whilst repairs are done and financial support is needed for this
many people in less developed countries have limited financial assets and are reliant on international aid
in more developed countries, many people can't get enough insurance to cover potential damages, and many houses lose value as the rate of coastal recession increases
Maldives economic losses due to coastal recession
one of the lowest lying countries in the world and at serious risk of being completely submerged due to of coastal flooding
the islands rely on tourism for the local economy, but increased coastal flooding events threaten the physical features that cause many people to travel there
coastal flooding also threatens housing and freshwater sources, which has forced many locals to migrate away from the annual flooding
Hard engineering: Rip Rap
a pile of boulders often placed in front of sea walls to dissipate the wave’s energy and support unstable rock structures
long-lasting and relatively cheap
but provide a hazard for people accessing the beach and have gaps between the rocks allowing erosion and weathering to continue
Hard engineering: Groynes
stone or wooden fences that stick out at 90o to the coast, stopping material being transported long distances by longshore drift
create wider beaches, which slows down waves and so reduces erosion and flooding
relatively cheap
but beaches further down the coast get narrower, which means waves are not slowed down and erosion and flooding are more likely
Hard engineering: Sea walls
hard concrete that deflects waves which are often curved to dissipate the wave’s energy and refract it back to the sea
good long-term solution because of the resistance of concrete, leading to less maintenance
but they create a strong backwash that can undercut the wall and they are expensive to build
Soft engineering: Beach reprofiling and nourishment
involves moving material to the upper sections of beaches from elsewhere, slowing down waves by widening beaches reducing the risk of erosion and flooding
it maintains the beach for tourist use, supporting the local economy
but removing sand and shingle from the seabed threatens certain organisms (e.g. corals)
expensive and must be repeated
Soft engineering: Cliff regrading
cliff re-grading and drainage involves restructuring and supporting the cliff to prevent further collapse from weathering and mass movement processes
maintains the cliff and provides a natural environment for plant and wildlife to continue to flourish
but there are risks associated with altering cliff profiles which can lead to further collapsing and unintended changes to the profile
Soft engineering: Dune stabilisation
the creation or restoration of sand dunes to maintain their protective position through nourishment or planting vegetation
This provides a natural barrier to coastal flooding and can support wildlife habitats
But only a small area is protected and it is ineffective in preventing wave action during powerful storm
ICZM - integrated coastal zone management
holistic approach to coastal management
involves careful consideration of the most effective management approach for a stretch of coastline
It considers the social, economic and environmental implications
Stakeholders (factors of consideration for ICZM)
proposed risk to residential, commercial and industrial buildings
implication of coastal recession on the local economy
impact of coastal recession and flooding on the natural environment
ICZM benefits
promotes the careful conservation of the natural environment
encourages the efficient use of resources to reduce unnecessary costs
tries to reduce the potential loss to the various stakeholders that rely on coastal regions for their livelihood
SMP - shoreline management plan
devised by key organisations (e.g., local government/council) to determine the most appropriate management strategies for a stretch of coastline
has 4 key management approaches
SMP: Advance the line
the construction of new engineering techniques to protect the coastline from further recession
Note 
Flashcard (21)