Please enable JavaScript.
Coggle requires JavaScript to display documents.
Key information for Coastal Landscapes - Coggle Diagram
Key information for Coastal Landscapes
Processes of erosion
Hydraulic action
- force of the water hitting the bank, breaking pieces off
Corrosion
- some rocks are dissolved by the acids carried in the water
Attrition
- material carried along in the river bashes into other bits of material and breaks into smaller bits
Abrasion (Corrasion)
- bits of material carried in the water rubs away the banks like sandpaper
Key definitions
Fetch
- an area of ocean or lake surface over which the wind blows, thus generating waves
Erosion
- a geological process where material is being removed
Concordant
coastline - layers of rock run
parallel
with the coastline
Discordant
coastline - layers of rock are
perpendicular
to the coastline
Eustatic changes
- changes in the volume of water in the global ocean stores
Isostatic changes
- changes in land level
Processes of transportation
Traction
- large, heavy particles are rolled along the river bed
Saltation
- pebbles are bounced along the river bed, most commonly near the source
Suspension
- Lighter sediment is suspended within the water, most commonly near the river mouth
Solution
- transport of dissolved sediment, varies along the river as it is dependent on the presence of soluble rocks
Landforms
Tombolo
- a bar of deposited material
linking the mainland to an island
. Example:
Chesil Beach
Bar
- a ridge of sand that
blocks off a bay or river mouth
, will create a lagoon behind it across a non-river bay
Spit
-
Emergent
landforms
Emergent
landforms - shaped by wave processes during times of high sea level are left exposed when sea level falls. As a result, they may be found inland
Raised beaches
- former shore platforms that are at a higher level than current sea level, they are often found inland
Abandoned cliffs
- behind the beach on emergent coastlines, cliffs can be found, They may have wave-cut notches, caves and even arches and stacks
Raised beach
example
: on the southern tip of the
Isle of Portland
, near Weymouth, there is a raised (15m) beach. Thought to be formed around 125,000 years ago. The Portland limestone was eroded by hydraulic wave action, partly through the exploitation of the bedding plane weaknesses
Modification
of emergent landforms
After there emergence, wave processes no longer affected them, however mass movement and weathering still could
On top of the
abandoned cliff
on the Isle of Portland, is a 1m-1.5m layer of frost-shattered limestone debris deposited when the area experienced periglacial conditions during the last glacial period. Simultaneously, the cliff face was being gradually degraded by frost weathering process
In post glacial periods, warmer and wetter conditions led to the development of vegetation cover on many exposures
Continued degradation is likely to occur as climates warm, with
chemical weathering
perhaps becoming more influential
Biological weathering
will be more significant on raised beaches
If sea levels rise again, the landforms may be close enough to the coast for
wave processes
to affect them
Submergent
landforms
Submergent
landforms - when the sea levels rising starts to flood the land and fills up landforms on the land
Rias
- submerged river valleys. The lower cause and the floodplains may be completely drowned, while the upper and middle course may remain exposed in the higher land. They are relatively shallow but become deep at the centre. They tend to be winding, reflecting the original river route. Many are found on the south coast of Devon and Cornwall such as
Salcombe
,
Kingsbridge
and
Fowey
Fjords
- submerged glacial valleys, they have steep (cliff-like) valley sides. The water is uniformly deep (often over 1000m). The
Sognefjord
in Norway is nearly 200km long. Ones in Scotland are less developed as the ice was not as thick in glacial periods. They consist of glacial rock basin with a shallower section at the end (threshold) due to lower rates of erosion at the seaward end of the valley. Examples:
Sognefjord
and
Milford Sound
. They have much straighter profiles than rias as the glacier would have truncated any inter-locking spurs
Shingle beached
- formed when sea level falls (due to increased amount of land ice) and 'new' areas of land emerge from the sea. Sediment accumulates hear as it is deposited by waves and rivers. Then when sea levels rise, wave action pushes this sediment onshore. In some places, they beached at the base of former cliff lines, elsewhere they may form tombolos and bars. The tombolo at
Chesil Beach
was formed this way.
Lyme Bay
accumulated large sediment deposits this way.
Modification
of submergent landforms
Both
rias
and
fjords
may be modified by the
wave processes
acting on them at present-day sea level
Sub-aerial processes
may still impact the valley sides, which may cause the sides to become less steep
As sea levels rise, water depth will increase and marine erosion due to stormier conditions and larger waves will also increase
Shingle beaches are very vulnerable due to being composed of unconsolidated material
Coastal system
Coastal landscapes are
open systems
, meaning energy and matter can enter and leave the system
In theory,
inputs
,
processes (throughputs)
and
outputs
work together to create coastal equilibrium
However, in reality, human actions affect the state of equilibrium within the coastal system
Inputs
: marine, energy, geological, atmospheric, people
Throughputs
: stores (sediment/ beaches), flow (transfers)
Processes
: deposition, erosion, weathering, mass movement
Outputs
: marine and wind erosion, evaporation, landforms of erosion, landforms of deposition
When a system's inputs and outputs are equal, it reaches a state of equilibrium
When the rate of sediment being added to a beach is equal to the rate it is being removed, so the beach will remain the same size
Negative
feedback - A stabilising mechanism acting to oppose changes to coastal morphology and establish equilibrium
Positive
feedback - pushes a coastal system away from equilibrium by modifying its morphology until a threshold is reached, whereby a different type of response occurs
A coastal in
equilibrium
is able to
dissipate
or reflect incoming energy
without
the occurrence of
sediment or output
and
change to morphology
Waves
Wavelength
- distance between two successive crests or troughs
Wave frequency
- number of waves per minute
Wave amplitude
- distance between the trough and crest
Waves are influenced by many factors, such as: the
shape
and
gradient
of the
sea floor
and the
irregularity
of the
coastline
Water molecules
do not move with the wave, they move in a circular motion and return to their point of origin
Energy
moves through the wave
Process of waves breaking
Waves start our at sea and have a circular orbit
As waves approach the shore, friction (from the sea bed) slows down the base of the wave
This causes the orbit to become elliptical
Until the top of the wave breaks over
Destructive
Wave height over 1 metre
Steep wave front
Breaking wave gains much height
Wave plunges onto steep beach, energy
directed downwards so does not travel far up the beach
Weak swash but strong backwash which erodes sand
Offshore bar is formed where sand is deposited
Constructive
Long wave lengths, low frequency (8-10 waves per minute)
Low wave height (under 1 metre)
Wave front is gently sloping
Gains a little height, breaks and spills on the beach
Water spreads a long way up the gently sloping beach
Strong swash but weak backwash
Gently sloping sea floor
Factors that influence the coastline
Tides
Tides
- long-period waves that roll around the planet as the ocean is 'pulled' back and forth by the gravitational pull of the moon and the sun as these bodies interact with the earth in their monthly and yearly orbits
Spring
(king) tide - the 'springing forth' of the tide during the new and full moon
Neap
tide - seven days after the spring tide and refers to a period of moderate tides when the sun and moon are at tight angles to each other
Tidal range
Tidal
range
- the vertical difference in height between consecutive high and low waters over a tidal cycle. The range of the tide varies between locations and also varies over a range of time scales
Enclosed seas (like the
Mediterranean
) have a low tidal range, wave action is restricted to a narrow area of land
Funnelled coasts experience tidal ranges as high as 14m
It influences where wave action occurs, the weathering process and the scouring effect of waves
Geology
Geology
- main aspects that influence coastal landscapes are lithology and structure
LIthology
- describes the physical and chemical composition of rocks. Clay has a weak lithology, little resistance to erosion, weathering and mass movement. It focuses on the bonds between the particles that make up the rock
Structure
Structure
- determines if coastlines are concordant or discordant. Factors include:
jointing
,
permeability
(primary and secondary),
bedding
and
faulting
Jointing
- a joint is a break of natural origin in a layer or body of rock that lacks visible or measurable movement parallel to the surface of the fracture
Permeability
- a measure of the ability of water to move through a rock
Primary
permeability - chalk: pores separating the mineral particles absorb water
Secondary
permeability - limestone: water seeps into joints which are enlarged by solution
Bedding
(stratification) - is one of the most prominent features of sedimentary rocks, which are usually made up of piles of layers (strata) of sediments deposited one on top of another. These beds range from millimetres thick to multiple metres thick
Faulting
- a planar fracture or discontinuity in a volume of rock across which there have been significant displacements as a result of rock-mass movements
Currents
Currents
- nearshore and offshore currents influence coastal landscapes
Rip
currents - calm patches in the surf with waves breaking on either side. Rippled foamy, or choppy water. Areas with a darker water colour (sand suspended in the water). Adjacent sand bars, reefs or onshore holes
Ocean
currents - large scale phenomena. Generated by the Earth's rotation and by convection. Set in motion by the movement of winds across the water surface. Ocean currents transfer heat energy from low latitudes towards the poles. Limited impact on coastal geomorphology, this affects air temperature and therefore sub-aerial processes (weathering and mass movement)
Terrestrial
Rivers
are major sources of sediment input to the coastal sediment budget. Very visible on coasts with steep gradient. Sediment delivery to the shoreline is intermittent - mostly occurs during flooding. Sediment origin is inland erosion (water, wind, sub aerial processes)
Wave
erosion - another source of large amounts of sediment that contributes to coastal sediment budgets
Cliff
erosion can be increased due to sea level rise and storm surge evens. In some areas cliff erosion contributes as much as 70% of material found in coastal management systems
Long-shore drift
moves sediment along the coast to adjacent areas
Rock structure
Structure is a very important influence on the planform
of coasts at a regional scale
Rock outcrops that are uniform, or run parallel to the coast, tend to produce straight coastlines (concordant)
Where rocks lie at right angles to the coast they create a discordant planform. The more resistan rocks form headland the weaker rocks form bays
Rock outcrops are visible exposures of bedrock or other geological formations at the surface of the Earth
Human
Beach nourishment when a coastal
sediment budget is in deficit
Offshore
Constructive
waves
- bring sediment from offshore locations (marine deposits), tides and currents
Wind
- blows sediment from other locations, has less energy than water, so it transports finer sediment and less of it
Sub-aerial processes
Physical weathering
Freeze-thaw
- occurs when water continually seeps into cracks, freezes and expands, eventually breaking the rock apart
Physical weathering
- the process that break rocks apart without changing their chemical composition
Thermal expansion
- the tendency for minerals to expand and contract based on temperature. Rapid temperature fluctuations, such as day-night cycles, cause rocks to expand and contract. This causes stress within the rocks and small cracks form
Pressure release
(exfoliation) - when a rock that forms under great pressure is brought to the surface and overlying rock is eroded away, fractures will form parallel to the outer surface of the rock
Salt crystallisation
- causes disintegration of rocks when saline solutions seep into cracks and joints in the rock and evaporate, leaving the salt crystals behind (also known as salt weathering, salt wedging or haloclasty)
Chemical weathering
Carbonation
- the process of rock minerals reacting with carbonic acid. A weak acid is formed when water combines with carbon dioxide. Carbonic acid dissolves or breaks down minerals in the rock
Hydration
- a type of chemical weathering where water reacts chemically with the rock, modifying its chemical structure. Example: anhydrite to gypsum
Solution
- the process by which certain minerals are dissolved by acidic solutions
Hydrolysis
- the breakdown of rock by acidic water to produce clay and soluble salt
Oxidation
- the breakdown of rock by oxygen and water, often giving iron-rich rocks their red colour
Biological weathering
Tree roots
- trees put down roots through joints or cracks in the rock in order to find moisture. As the tree grows, the roots gradually prize the rock apart. Many animals, such as piddock shells bore into rocks for protection, either by scraping away the grains or secreting acid to dissolve the rock
Organic acids
- the organic compounds have acidifying molecules that corrode rock mineral and as such, makes them weak and prone to disintegration. This biological action usually results in chemical weathering
Mass movement
Rock fall
- a form of mass movement or mass wasting in which pieces of rock travel downward through some combination of falling, bouncing and rolling after they are initially separated from the slope
Slides
- is the downslope movement of a soil or rock mass occurring dominantly on the surface of rupture or relatively thin zones of intense strain
Regolith
- loose layers of rocky material covering the bedrock
Factors that can affect changes in global temperatures and
ocean water volume
Variations in the Earth's orbit around the sun (typically every 400,000 years)
Variations in the amount of energy released by the sun (maximum every 11 years)
Changes in the composition of the atmosphere (due to volcanic eruptions)
Variations in the tilt of the Earth's axis (every 41,000 years)
Climate change (global warming or cooling)