Coastal landscapes

What processes are used in erosion

• hydraulic action

• Abrasion

• Attrition

• Solution

What are the processes in transportation

• solution

• Suspension

• Saltation

• Traction

What processes are usually contained within sediment cells

Processes of erosion, transportation and deposition

What are sediment cells generally considered as, and why is it technically not correct

• generally classes as closed system (meaning sediment from one cell isn’t transferred to another)

• But unlikely due to variations in wind direction and tidal flows

• There is also smaller sub cells within

What are the boundary of sediment cels determined by

The geography and the state of the coastline and topography

What are costal systems classes as

Open systems where both matter and energy can move in and out

What is an input and give example

• material or energy moving into the system from outside

• Precipitation, wind, introductions of sediment, energy (tidal and current)

What is an output and give examples

• material of energy moving from the system to the outside

• Ocean currents, rip tides, sediment transfer, evaporation

What is a store and give examples

• individuals elements or parts of a system

• Beach, sand dunes, erosional landscapes, depositional landscapes

What is positive feedback

Process tends to increase the change in the system

What is negative feedback

Process seeks to counter the change and maintain equilibrium

What is a ready state equilibrium

• variations in energy and the morphological response don’t deviate too far from the long term average.

• E.g along a coast that experiences consistent wave energy conditions, the gradient of a beach may be steeper or shallower depending on the time of the year. BUT the average annual gradient is similar year or year

What is a dynamic equilibrium

• involves a change in equilibrium conditions but much more gradual

• E.g the response of coasts to the gradual rise in sea levels experienced due to climate change

What are the 4 factors that all beaches in dynamic equilibrium involve

• supply of sand

• Energy of the waves

• Changes in sea levels

• Location of the shoreline

  It is the balance of these factors and how they interact with each other that determine weather of a beach erodes or grows.

How is positive feedback seen in the coasts

• where a transfer leads to increase or growth

• Coastal management can inadvertently lead to increase of erosion elsewhere. Groynes trap sediment, depriving areas further down and can increase erosion.

• Seawalls have same effect by transferring high energy waves elsewhere along the coastline.

• As a spit forms, the rivers velocity is further reduced with increased friction. This leads to an increase in spit head material accumulation and yet further river velocity reduction.

How is negative feedback seen in coasts

• where a transfer leads to decrease or decline

• When the rate of weathering and mass movement exceeds the rate of cliff foot erosion a scree slope is formed. Over time, this apron of material extends up the cliff face protecting the cliff face from sub-aerial processes. This leads to a reduction in the effectiveness of weathering and mass movement.

• Sediment is eroded from the each during a storm, the sediment is then deposited offshore forming an offshore bar. This means waves are now forced to break before reaching the beach dissipating their energy and reducing further erosion when they reach the beach.

• When the storm calms, normal waves conditions rework sediments from offshore bar back to the beach and the loop continues.

How is dynamic equilibrium seen in coasts

• this represents a balance within a constantly changing system

• Constructive waves build up a beach, making it steeper. This encourages the formation of destructive waves that plunge rather than surge.

• Redistribution of sediment offshore by destructive waves reduce the beach gradient which in turn, encourages the waves to become more constructive.

• This state of constant dynamic equilibrium between the type of wave and the angle of the beach.

what’s a sediment cell

• sketch of coastline and its associated nearshore within which the movement of coarse sediment. (Usually closed system)

What determines the boundaries of sediment cells

Topography and shape of the coastline

Explain why sediment cells are unlikely to be completely closed systems

Variations in wind direction and the presence of tidal currents

Why is understanding of sediment cells important

For managing our coastlines and to put in strategies

What are physical factors affecting coastal landscape systems

• currents

• Wind

• Waves

• Tides

• Geology

How do waves break

• when waves enter shallow water the deepest circling water molecules come into contact with the sea floor.

• Friction between the seafloor and the water changes the speed, direction, and shape of waves.

• The deepest part of the wave will slow down more than top of wave, wave begins to steepen as the crest advances ahead of the base.

How does wind create waves

• wave energy generated by drag of winds moving across ocean surface

• Higher wind speed, and the longer the fetch, longer waves and more energy they have

• Offshore winds then drive waves to the coast

Name 3 processes that can be carried out directly by wind without involving waves

Erosion, transportation, deposition

What does aeolian mean

Erosional, transpirational, and depositional processes by WIND

Explain constructive waves

• they are allowed to run their course without interference from those ahead or behind.

• Flat and low in height, their swash carries material up the beach, forming a berm, with the energy consequently dissipated over a wide area so has a weak backwash

• They are associated with the progressive steepening of a gently sloping beach

Explain destructive waves

• destructive waves break more frequently, with the force of the swash reduced by the previous wave’s backwash.

• The steep waves plunge onto a smaller area, concentrating their energy.

• Meaning backwash has little time to infiltrate and will carry shingle and sand to form breakpoint (longshore) bar

What are the different ways waves break

• spilling → steep waves breaking onto gently sloping beaches

• Plunging → moderately steep waves breaking into step beaches; plunges vertically downwards

• Surging → low angle waves breaking onto steep beaches, wave slides forwards and may not break

Features of constructive wave

Height - low (1m)

Wavelength - long (6 to 8 minutes)

Frequency - low (no more than 10 per min)

Swash - strong (builds)

Backwash - weak

Beach profile - wide flat and gentle

Nature of wave break - spilling waves

Movement of material - build up of material (deposition)

Features of destructive waves

Height - high (2m +)

Wavelength - short

Frequency - high (12 a minute)

Swash - weak (due to returning backwash of prev wave)

Backwash - strong

Beach profile - steep and short

Nature of wave break - surging sometimes plunging

Movement of material - erosional so there is removal of sediment

How are tides produced

• both the sun and moon, exert a gravitational pull on the rotating earths surfac.

• This causes a rising and falling motion in the waters of the larger oceans, thus producing tides.

What is the difference in height between high and low tide known as…

• it is known as the tidal range and this will vary from a max spring tide when the sun and moon are in a straight line, and so pull together, to a neap tide when the sun and moon are pulling at right angles

What does the greater influence of the moon dictate

Approx 2 high tides a day with spring tides 2 each lunar month, once every 14 days.

What do tidal currents move

• move sediment to and from a beach, and are much more consistent than rip currents associated with longshore drift.

What will a large tidal range expose

• vast areas of sand that, when dry, can be blown inland to form sand dunes

What will a small tidal range do

It concentrates wave pounding and hence erosion on a narrower section of cliff, increasing its impact

(More erosion and more marine processes)

How may tidal ranges affect aeolian processes

Large tidal range means that there is more wind to actin depositional processes to build sand dunes.

How do tidal ranges vary so much around the world

Due to the shape of the coastline as wide open coastlines have smaller tidal ranges.

Why do ocean currents happen

• wind

• Differences in how dense the water is (density differences due to temp and saltiness)

• Currents can happen in deep and shallow parts of ocean

• Tides also play a large role in it

How do currents have an impact on the earths climate

• they help to move warm water from the equator and cold water from the poles around the earth

• E.g warm Gulf Stream brings milder winters to Bergen, regulating the earths climate and keeping temperatures balanced.

What are the 2 different currents

• nearshore

• Offshore (have les effect on the coastal landscapes)

What are rip currents and what are they caused by

• strong and relatively narrow currents of water that flows seawards against breaking waves

• they are caused by either tidal motion or by waves breaking at right angles to the shore

What is an ocean current

Large scale horizontal flow of ocean water driven by planetary winds and contrasts in wind

What do warm ocean currents do

Transfer heat energy from low latitudes towards the poles (driven by onshore winds)

What do cold ocean currents do

Move cold water from polar regions towards the equator (usually driven by offshore winds)

How do ocean currents influence the climate

• regulating the temperature of the ocean so it directly affects air temperature and, therefore sub aerial processes (weathering and mass movement processes)

Define lithology

Describes the physical and chemical composition of rocks

Define structure

Concerns the properties of individual rock types as jointing, bedding, and faulting

Define permeability

Ability of a material to allow fluids to pass through it

Define porosity

Percentage of the total volume of a rock or sediment that consists of voids or pores

Define bedding planes

Horizontal fractures between layers or sedimentary rock, formed during deposition

Define joints

Vertical cracks in rocks caused by cooling, contraction or tectonic forces

How will a horizontally bedded strata affect the cliff

• more likely to be more rigged and irregular

• May break down more easily along joints and bedding planes leading to rockfall and jagged cliff profile

How will a seaward dipping strata affect the cliff

• increased erosion as bedding planes face towards the sea

• Steeper cliff profile; looking more steeper cliff face and undercutting at base

• Erosion along bedding planes, wave cut notch at base of cliff

How will a landward - dipping strata affect the cliff

• more stable cliffs as they face inwards, less likely undercutting, more stable cliffs

• Gentler cliff profile, fewer rockfalls

• Less erosion at base as it is less affected by erosion

• Potential for landslides, after heavy rainfall

Examples of hard rock

granite, slate

Examples of soft rock

Chalk, limestone, clay

How do the joints and bedding planes of chalk and limestone affect erosion

• the joints are vertical weaknesses and this causes further caves when eroded

• The bedding planes get weaker as they get weaker by erosion

How do hard and soft rock affect landform

• Hard rock is consolidated and also erodes slower, this means that it juts out into the sea and is exposed for longer meaning caves can form.

• Chalk is unconsolidated and soft rock and erodes faster and bays can be made

How does the chemical composition of chalk and limestone affect erosion rates

Limestone is Carboniferous meaning it can be affected by chemical weathering.

This can dissolve the rocks making them weaker.

Differences between concordant and discordant

• concordant coastline is when the same type of rock types runs along the coast

• Discordant coastlines have different rock types along the coastline so they erode at different rates

What is a sediment budget

Balance of sediment volume entering and exiting a particular section of coast

Places where sediment has come from

1) rivers, wave erosion, erosion of weak cliffs (70% of overall sediment)

2) terrestrial → cliff erosion, rivers

3) supplied to the coastal sediment budget offshore by constructive waves (suspension, traction), tides and current do the same, wind also blows sediment from other locations

4) human sources of sediment supply like beach nourishment is used when a beach is in deficit, also pumped onshore by pipeline.

Positive feedback pushes the system even further out of balance after a change (Cycle)

• erosion and deposition rates are in balance (dynamic equilibrium)

• Deposition causes a spit to grow across a river or estuary

• River flow is slowed down which encourages more deposition

• The system is pushed more out of balance as deposition is now faster than erosion

Negative feedback rebalances the system after a change (cycle)

• erosion and deposition rates are in balance (dynamic equilibrium)

• A storm increases erosion in the sediment cell

• Eroded sediment is removed by waves and currents then eventually deposited again within the sediment cell.

What is an open system

Has external interactions; movement of energy, material in and out

What are the different classes of coastal processes

• sub-aerial processes → weathering, mass movement

• Marine processes → erosion, deposition, transportation

What are sub-aerial processes

• existing, occurring or formed in the open on the earths surface, not under water or underground

What is weathering

The in situ breakdown of rocks exposed at, or near, the land surface by physical, chemical and biological processes

What are geomorphic processes

• the formation and shaping of landforms and landscapes by natural processes

What is physical weathering

• happens when rocks are broken into smaller bits (Disintegration)

• 2 types of physical weathering- thermal stress and freeze thaw weathering

• Thermal stress happens when rocks warms up and cools down, surface of rock expands and contracts causing stress within the rock, making it break.

• Free thaw is when water finds its way into a crack in a rock, and freezes, expands and then cracks the rock, making it break into fragments

What is chemical weathering

• happens when minerals in rocks change use to chemical reactions

• Makes the rock decay, carbonation happens when rainfall absorbs co2 from atmosphere to form weak acid called carbonic acid

• Carbonic acid reacts with calcium carbonate in limestone/chalk to dissolve

• Oxidation happens when oxygen reacts with minerals in rocks to form new chemical

• E.g iron turns into iron oxide, rock then changes colour, becoming browner and begins to crumble

What is biological weathering

• happens when plant roots enter cracks into rocks

• Roots force crack to widen and cause rock to break apart

• Small animals, like worms, also help to break up the rocks

• Small plants called lichens grow on surface of rock, produce enzymes that slowly make surface of rock decay

Different examples of physical weathering and explain

• freeze-thaw weathering → water enters cracks, freezes, expansion, exerts pressure, repeated cycle caused pieces to break

• Pressure release → when overlying rocks are removed, (weathering & erosion), pressure is released, allowing rocks to expand and fracture parallel to the surface, called dilation.

• Thermal expansion → outer layers of rocks expand and contract when heated and cooled, repeated cycles caused prices outer layers to crack and flake off, also called insolation weathering/onion weathering.

• Salt crystallisation → saline water enters pore spaces/cracks, water evaporates meaning salt to precipitate out to form crystals, growth of crystals over time stresses within rocks, leading to break up, (effective with sodium sulphate and sodium carbonate at 26-27 degrees)

Different examples of chemical weathering and explain

• Solution → minerals (gypsum) are soluble in water, and easily dissolved and removed by seawater.

• Oxidation → some minerals in rocks, e.g iron reacts with oxygen, in air or water, causes rocks to crumble easily.

• Carbonation → weak carbonic acid is formed when rainwater reacts with co2 in atmosphere, acid then reacts with calcium carbonate in limestone/chalk creating calcium bicarbonate, is soluble in water and so easily removed

• Hydrolysis → reaction between water and group of rock minerals called silicates (feldspar found in granite) reacts with hydrogen in water to form kaolin (china clay)

• Hydration → certain minerals react with water creating new minerals of a larger volume e.g anhydrite reacts with water to form gypsum. Other minerals e.g clay expands when wet and contract when dry, causing many rocks e.g shale to flake at their surface

Type of mass movement, description, and real life example (rockfall)

• rapid free fall of rock from steep cliff, rock fragments fall due to gravity, freeze-thaw weathering loosens the rock, well jointed rock is very vulnerable to rockfall, water enters joints, freezes, expands and cracks the rock

• Scree slope of fallen rock is formed at the bottom of the cliffs

• E.g white cliffs in Dover, march 2012, area size of football pitch fell, thousands of rubble fell 300ft down, rain was absorbed by chalk and then expanded as it freezes.

Types of mass movement, description, and real life example (landslide)

• slides occur of cliffs previously weakened by weathering

• Heavy rain infiltrates the soil and percolates down into the rock

• Heavier, saturated mass falls away long a slip plane

• Mud slides are usually wet, rapid and when slopes are steep

• E.g Lyme Regis in Dorset, 6th may in 2008, landslide occurred after a particular wet period during winter and early spring

Types of mass movement, description, and real life example (rotational slumping)

• slide takes a fairly straight path down a cliff, concave slip plane so material is rotated backwards into the cliff face

• As it slips large pieces of rocks are pulled downwards

• Common at clay cliffs, dry weather makes the clay crack allowing water to get into it

• E.g Evan’s cliff, clay, 14th Jan 2006, 17 trapped, slip meant 200,000 tonnes of mud to fall down

How has mass movement helped to develop coastal landforms

• by supplying sediment into the sediment budget as material is moved onto the shore

• Also supping tools for further abrasion

• Material then mass movement then acts as an input

What 5 physical factors affect mass movement

• geology as the structure of the rock determines the angle of the slope and number of joints and bedding planes

• Steeper slopes result in rock fall

• Lithology determines how consolidated the rock is

• Influences the rate and the type of mass movement

• Porous rocks are more likely to become saturated and weaken

Where does deposition tend to take place in coastal landscape systems

• where the rate of sediment accumulation exceeds the rate of removal

• When waves slow down immediately after breaking at top of swash,, where for brief moment the water is no longer moving during the backwash, when water percolates into beach material

• In low-energy environments, such as those sheltered from winds and waves e.g estuaries

What is known as the settling velocity

• the velocity at which sediment particles are deposited is known as settling velocity

• The larger and heavier particles require more energy to transport them

• As flow velocity decreases, the largest particle being carried are deposited first and so until the finest particles are deposited

Explain deposition in fluvial process

• as rivers enters the sea, there is noticeable reduction in velocity when enters static body of sea

• Tides and currents may be moving in opposite direction to river flow, provides resistance to its forward motion.

• Available energy is reduced so some or all sediment is deposited

• Large particles deposited first then smaller particles carried out further into sea

• Meeting of fresh water and salt water causes flocculation of clay particles

• Fine materials clump together due to electrical charges between them in saline conditions, then become heavier and sink to the sea bed

Explain transportation in fluvial process

• rivers also transport sediment by traction, suspension, saltation and solution

Explain erosion in fluvial process

• upper catchment is the main source of a river sediment load

• Sediment derives from weathering and mass movement processes that result in material moving into river channels from valley sides

Explain deposition in aeolian process

• material carried by wind will be deposited when the wind speed falls, usually due to surface friction

• In coastal areas this will occur inland, where friction from vegetation is much greater than on open sea

Explain transportation in aeolian process

• except of solution, moving air can transport material using the same mechanisms as water moving in rivers and waves

• Only the smallest amount of grains can be carried in suspension

Explain erosion in aeolian process

• wind can pick up sand particles and move them by deflation

• Grains of sand are heavier than silt and clay particles so they are carried by suspension

• Restricts erosion as has limited effect in the erosion of rocky coastlines and cliffs

• Erosive forces increases in wind velocity

• Dry sand is easier for the wind to pick up than wet sand, as moisture increases cohesion between particles, keeping them stick together

• Attraction on land is particularly effective in wind as particles tend to be carried for greater distances than in water

Advantages and disadvantages of chi squared

adv

• can test association between variables

• Identifies differences between observed and expected values

Dis

• cant use %

• Data must be numerical

• Only tells us if the variables are related to each other, doesn’t imply any causal effect of one to another

Advantages and disadvantages of standard deviation

Adv

• shows how much data is clustered around a mean value

• Not as affected as much by extreme values

Dis

• doesn’t give u full range of the data

• Assumes a normal distribution pattern

Advantages and disadvantages of spearman’s rank

Adv

• shows significance of the data

• Proves/disproves correlation

• Doesn’t assume normal distribution

Dis

• can be difficult to work out

• Complicated formula

• Can be misinterprated

Advantages and disadvantages of Mann Whitney U

Adv

• states weather difference is significant or occured by chance

• Shows median between 2 sets of data

• Good with dealing with skewed data

Dis

• doesn’t explain why there’s a difference

• Less accurate when sample size is less than 5 or more than 20

Advantages and disadvantages of T-test

Adv

• easy to calculate

• Easy to gather data- only small number of samples required

• Easy to interpret with the means

Dis

• doesn’t give accurate results on large datasets

• Sample sizes uses for comparing the means has to be approx the same

Explain bays and headlands (erosional coastal landform)

• They usually form due to presence of bands of rocks with alternating resistance to erosion

• If these rocks outcrops lie perpendicular to the coastline, the weaker rocks erode more quickly to form bays, results in formation of a dis concordant coastline.

• Bay depth will depend of different rates of erosion between the rocks of different resistance

• Rocks lying parallel to coastline produce concordant coastline. (If more resistant rock lie seaward, it protects any weaker rock inwards)

What happens when waves approach an irregularly shaped coastline

• wave refraction takes place and develop a configuration parallel to coastline.

• ESP true on coastlines with bay and headlands

• As each eave nears coastline, its slowed down by friction in the shallower water of the headland

• And the part of the wave crest in the deeper water approaching the bay moves faster as its not slowed down by friction.

• Means wave bends or refracts around the headland and the orthogonals converge.

• at bays, orthogonals diverge and energy is dissipated, leading to deposition.

• As waves break on the sides of headland at angle there is LSD of eroded material into bays adding to build up beach sediment.

Explains geo’s and blowholes

• even on coastlines with resistant geology, there may be lines of weaknesses such as joints and faults

• Weak points are eroded more rapidly by wave action than the more resistant rock around them

• Hydraulic action is especially important in forcing air and water into joints and weakening the rock strata

• Sometimes geo’s initially form as tunnel-like coves running at right angles to cliff line, which become enlarged by continuous erosion causing roof to collapse, creating a geo

• If part of the roof of tunnel-like cove collapses along a master joint it may form a vertical shoyt that reaches the cliff top, creates a blowhole.

Explain cave, arch, stack and stump

• due to wave refraction, energy is concentrated on the sides of headlands

• Points of weaknesses such as faults or joints are exploited by erosion processes and a small cave may develop

• Wave attack is concentrated between high and low tide levels and it is where caves form

• If caves enlarge to an extent that is extends to the other side of the headlands, arch is formed

• Weathering and processes, the arch may collapse leaving a stack

• Further erosion at the base of stack may eventually cause further collapse to make a stump

Explain shore platforms

• formed by erosion, weathering, solution, freezethaw weathering and salt crystallisation may take place, depending on the rock type and climate conditions of location.

• Marine organisms can accelerate weathering when platform is exposed at low tide

• At night algae release c02, Mixes with seawater making it more acidic, resulting in higher rate of chemical weathering

• Shore platforms usually slope seawardsat angles, wave erosion can occur anywhere between high and low tide levels.

• But as water levels are constant for longest at high and low tide, erosion is greatest at these points, explains the formation of a ramp at the high tide levels and small clif at the low tide level.

• Features develop best if tidal range is less than 4m.

• If higher, then erosion is spread over a wide area of the platform; the water is at its high and low tide positions for a shorter time and so platform teds to be more uniform and more steeply sloping.

What are beaches formed due to

• cliff erosion (only about 5%)

• Offshore (combed from seabed, during times of rising sea levels 5% only)

• Rivers (90% carried into coastal systems as suspended)