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Physical Factors Influence Coastal Landscapes and Systems (Physical…
Physical Factors Influence Coastal Landscapes and Systems
Wind and Atmospheric Circulation
Basics
Equator =
low pressure
= air rises
Poles =
high pressure
= air sinks
Subtropics =
high pressure
= air sinks
High pressure
= low precipitation + deserts
Low pressure
= unsettled conditions + storms
Background
Source of energy erosion and transport is wave action
Generated by frictional drag of winds moving cross the ocean
Higher wind speed = longer fetch = larger waves + more energy
Onshore winds
Blow form the sea towards land
Effective at driving waves towards the coast
LSD
Generated when winds blow at an oblique angle to the coast
Waves will also approach obliquely
Wind carries out
aeolian processes
Erosion, transportation, deposition
Contributes to the shaping of coastal landforms
Global Circulation
Background
Global wind system that transports heat from tropical to polar lattitudes
3 cells in each hemisphere
Hadley cell
Largest, calm weather, 30-40 degrees N+S of the equator
Calm weater
Trade winds blow towards the equator and form the Inter-Tropical-Conversion-Zone
From the tops of these storms, the air flows towards higher lattitudes
At high latitudes air sinks = high pressure regions over the sub-tropical oceans + deserts
Ferrel cell
Unsettled weather (esp. in UK), 60-70 degrees N+S, moves in oppo. direction to other cells
Air converges at low lattitudes
It ascends along the boundaries between cool polar air and warm sub-tropical air
Air return flow of air at high altitudes towards the tropics joins sinking air from the Hadley cell
Polar cell
Smallest and weakest cells, 60-70 degrees N+S to the poles
Air sinks over the highest latitudes and flows out towards the lower latitudes at the surface
In these the air circulates through the depth of the
troposphere
Warm moist air from the tropics is fed north by the surface winds of the
Ferrel cell
This meets cool dry air moving south in the
Polar cell
The polar front forms where these 2 contrasting masses meet
= ascending air and low pressure at the surface
The polar front jet stream drives this area of unstable atmosphere
The unstable atmosphere here causes unsettled weather e.g. around the latitude of Europe
The unsettled weather in the UK + Europe is caused by travelling areas of low pressure which form when moist air rises along the polar front
Jet Stream
Guides the low pressure systems with unsettled conditions across the Atlantic regularly
Summer - Jet Stream is N to the UK - drags low pressure away = settled conditions
Runs W-E and pushes weather systems through quickly
Meridional - sometimes it curves N and S = zonal flow (a more linear W-E flow)
Meridional flow - areas of law pressure may linger over UK = long periods of rain and strong winds
The 3 circulation cells and the Coriolis effect = global circulation. Net effect is to transfer energy from the tropics to the poles in a conveyor-belt-like motion
Physical Factors
Influence development of coastal landscapes
Influence operation of landscapes as systems
Influence the way that processes work + therefore shape of the landscape
Wind, waves, tides, geology, ocean current circulation
Vary in terms of spatial and temporal impcts
In a given location and time, some factors will have a greater impact that others
Marine Factors
Wind, waves, tides, salt spray, currents
Tectonics
Coastal uplift, volcanic activity
Climatic Factors
Winds generate waves + currents, weathering affects cliffs, climate change, glaciation changes sea level (eustatic/isostatic)
Geology
Structure, lithology
Human
Pollution, conservation management, buildings, recreation
Biotic Factors
Vegetation, coral reefs
Subaerial Factors
Temperature, weather e.g rain, snow, frost, wind, sun
Ocean Currents
Driven by winds
Mimic wind patterns (on a global scale) = gyres
Cold water is moved from the poles, warmed and then transported back tot he poles
Surface current movement can cause upwelling
Circular process
Normally on the W coast of continents bc of the Coriolis effect
Surface waters moving towards the equator are replaced by deeper cooler water that moves up to the surface
Thermohaline Circulation
The largest circulation of water is due to temperature and salinity
When water moves N it cools and freezes = salinity increases
Movement and temperature of oceans affects climate + sub-aerial processes
Thermohaline circulation = circulation of ocean currents due to salinity and temperature
Wave Energy and Landform Development
Cliff-foot Processes
Hydraulic action
Abrasion
Corrosion
Sub-aerial Processes
Above water
Rotational slip processes e.g. slumping
Constant erosion low cliffs
Jurassic Coast: Purbeck Coast - CASE STUDY?????
Tides
Background
Are waves with extremely long wavelengths
Result from gravitational attraction of the sun + moon
Moon has *2.2 the strength because its closer
As they pass the create a tidal bulge on both sides of the planet
The oceans are pulled towards the sun + moon
The earth moves slightly
when the bulge hits the coast it causes a higher tide; the trough produces a low tide
Factors: moon, sun + earth
Moon is an elliptical cycle
Sun is at different points in the sky
Classification and Landforms
Mcrotidal - <2m of open ocean costs - WAVE DOMINATED
Macrotidal - >4 m of open ocean costs - TIDE DOMINATED
Mesotidal - 2-4m of open ocean coasts - BOTH
Low energy, depositional
coastlines = high tidal ranges - TIDE DOMINATED
Tidal flats, wetlands, saltmarshes, mangroves, sabkhas
High energy, erosional
coastlines = high energy + low sediment input
Barrier islands, tidal deltas, coral reefs, shore platforms, cliffs, beaches, tombolos, shingle ridges
Coriolis Effect
Effect of Earth's rotation on air and water
= deflation to the right in the N hemisphere
Tidla wave travels northwards up the Irish sea
Deflection to the right = higher tides in Wales + England
Wave travels southwards down the N Sea
Tidal waves appear to advance from the centre of the ocean
Intertidal Deposits: Tidal Rhythmites
Mud deposits in low energy and low current velocity areas
Increase in velocity = mud transported in suspension
Further increase in velocity = sand transported
Energy drops = sand and then mud are deposited
Repeated cycles = deposits - rhythmites
Wave Energy
Background
Generate currents
Waves + currents generate, erode, transport and deposit sediment
Wave energy influences the balance of the processes
Factors of wave size
Wind strength, wind duration, fetch
Greater fetch = greater distance between waves = greater wavelength + lower frequency
Extreme latitudes = short-lived storm waves
Closer to the equator are conditions affected by tropical storms
Low Pressure Systems
Heating + pressure differences = convective air cells
High pressure
areas
Descending limb of pressure cells -
cold air descends
Rising limb of pressure cells -
warm air rises
Low pressure
areas
Are
depressions
Strong winds, precipitation and unstable conditions
Typical UK winter storms
Winter
Low pressure in N hemisphere = storm conditions = lots of coastal erosion
Low-pressure systems travel towards UK from SW
= less pressure on the sea surface so sea will lift = strong winds + winter storms
Summer
High pressure in N hemisphere
Low pressure moves further N, being replaced by the high-pressure = dry, settled conditions
Wave Types
Swell Waves
Form in deep water
Molecules spin in a circular motion
Water movement is up + down
Translatory Waves
Form in shallow water
Wavelength shortens and height steepens
The orbit of the molecules becomes elliptical
Constructive Waves
Build and break over longer distances
Regular profile beaches + wave energy is absorbed by the beach
Longer wavelength + less violent
Swash is stronger than backwash
Do not reach the foot of the cliff
Berms deposited
Destructive Waves
More violent, shorter wavelength + higher frequency
Both swash and backwash is stronger than constructive waves - but backwash is strongest
Beach is flatter but steeper at the back
Upper part attacked by spray
Little wave energy absorbed by the beach
Factors
Width of swell window
Wind speed + strength
Fetch
Steepness + width of beach
Flatter beaches absorb more energy
Local weather conditions - affected by low + high pressure
Low pressure
- air rises = less pressure on sea surface = sea lifts + winds strengthen
High pressure
- air is falling
Storm surges
Intense areas of low pressure
On warm water surface, warm air molecules rise = less pressure on sea surface = sea bulges
Rushing air + high winds = even larger waves
Waves are further enlarged with a high tude
Wave Refraction
Occurs when coastline is not even
Waves are concentrated and refracted towards headlands
Destructive waves at the headlands
Less sheltered from winds + erosion
Waves have shorter length - energy is concentrated at headlands
Shore platform = friction at bottom of wave = higher + steeper - same effect as when waves enter shallow water
Constructive waves at headlands
Sediment is deposited = beaches
Ocean Waves
Factors
Low pressure systems
Deep low pressure systems = a low, moving ridge of water + strong, sustained anti-clockwise winds = high energy waves
Fetch
Maximum length of the swell window
Maximum sea distance across which winds blow without interruption
Sea floor gradient
Shallow offshore gradients absorb wave energy by friction and decrease the height of waves reaching the shore
Size of swell window
Amount of open ocean facing a stretch of coastline
Making Waves
Regular oscillations in water surface of larger water bodies - the smaller chop waves go off in different directions
Waves in the direction of the prevailing wind will combine = one large swell wave
Geology
Background
Lithology and structure influences coastal landforms because they influence the rate of erosion
Rock = mass of mineral matter - consolidated or not
Igneous, sedimentary, metamorphic
Combined impacts of lithology + structure effect
The coastline in plan (map)
Coastline in profile (cliffs, shore platforms)
Distribution of micro-features (caves, arches, stacks)
Structure
Arrangement of rocks can increase likelihood of erosion
Weaknesses let water into the rocks
Bedding planes, joints + faults
Increases permeability + susceptibility to weathering (weakens the rock = erosion)
Cementation - poorly cemented rocks are porous and permeable along weaknesses
Area exposed to weathering is increased
Plan-form (ariel view) - arrange of geological outcrops
Concordant
coastlines - rock outcrops run parallel to the coast - fewer lines of weaknesses exposed to wave action
Discordant
coastlines - rock outcrops are perpendicular to the coast - waves can actively select lines of weaknesses = differential erosion
Structure can provide a range of rock types with lithologies of differential resistance to subaerial and marine processes
Composition + Arrangement of Grains
Sedimentary
Limestone
Grains of CaCO3 - soluble in acidic solutions
Can be strong if grains are cemented
Sandstone
Grains of quartz - very hard mineral = very resistant
Poorly cemented grains = weak haematite cement
Clay
Tiny grains of clay minerals + mica
Chemically bonded but rarely cemented = weak
Chalk
CaCO3 + fine fossils (coccoliths)
Weakly cemented = soft
Igneous
Granite
Interlocking crystals of resistant minerals e.g. quartz, fledspar
Very resistant
Metamorphic
Mix of grain sizes that are poorly cemented = weak
Planar fabric formed by alignment of mica
Importance of Structure + Lithology
Certain aspects combine to make neighbouring rocks more/less susceptible to weathering + erosion =
differential erosion
Hardness of rock types
Igneous + metamorphic rocks are harder + therefore more resistant
Bc of heating + compression during their formation
Unconsolidated sands, clays of tertiary age + deposits of glacial boulder clay + gravels
S + E Brtain
Easily eroded
Erosion if quickened if cliff bases are poorly protected by beaches by 3-6m/year
Higher cliffs are harder to erode - collapse of cliff face due to recession = greater amounts of debris to be transported away before new erosion can occur
Permeability
Pores, fissures, cracks, joints
As surface water seeps through the cliff, it increases resistance to subaerial processes, adding strength of relatively soft rocks
Hence chalk forms relatively high, vertical cliffs + has stacks + arches
Permeable rock is underlain by impermeable rock = zone of lubrication
= cambering + extensive mass movement
Physical Make-up
Amount of joints, bedding planes + faults
Impacts rate of physical + chemical weathering
High density of joints + bedding planes weakens rock = increased subaerial + marine erosion
Exploitation of faults + isolated master joints by the sea = range of micro-featuers
Folds + faults can become shattered zones + easily exploited by the sea = inlets+ bays
Chemical Composition
Silica
Most sandstones made from this
Chemically inert = little chemical weathering = high resistacne
Iron compounds
Oxidise in some sandstones
Feldspars
Altered into clay minerals by hydrolisis in some rocks e.g. granite
These rotted zones increase vulnerability to subaerial + marine erosion
Salt water can quicken rate of erosion
Increase the chemical decomposition of limestone by carbonation = increased disintegration of some shore platforms
Weathers basalt *4 quicker than under freshwater conditions
Coastline in Plan
Concordant Coastlines
Form straight coastlines
Bc the different rock types are all parallel to the sea
Coves can still form if the sea breaches the hard rock
Differential erosion results from the exploitation of a master joint or fault line
These act as weaknesses for the sea to develop into a beginning cove e.g. Stair Hole, W of Lulworth
Marine action breaches the relatively resistant limestone wall
It reaches the relatively weal wealden shales - easy to erode
These are easy to erode into an elongated cove
Erosion inland is slowed by the resistant chalk
Residual parts of the original limestone = stacks
Discordant Coastlines
Headland + bay formation
Geology alternates between bands of hard + soft rock which hav eone side exposed to the sea
Erosion of headland is quickened by erosion of bay is reduced die to loss of energy
Waves converge on headland
Depth of water decreases off the headland
In these shallower waters, the waves lose more energy to friction, causing them to slow down
As the wave changes speed, it also changes direction -
refracts
Coastline in Section
Rock Types
Hard rocks e.g. granite erode slowly = high + steep cliffs
Soft rocks e.g. glacial boulder clay weathers quickly with mass movement e.g. slumping = less steep cliffs
Influence the nature of subaerial processes
Boulder clay can be weathered away to expose sandstone
Joints and bedding planes
Determine the cliff form and amount of movement at cliff foot
Seaward dip of rocks = slabs of rocks slide into sea = low angle profile
Bc of underlying soft clay, zone lubrication + wave attack = land slips and cliff is temporarily protected by recent mass movement
Very large rocks with widely spread master joints, chemical weathering + hydraulic action = various micro-features
Coal seams = rapid undercutting of cliffs by formation of a deep wave-cut notch
Other factors
Deep offshore water - so waves don't directly erode the coast, but adre reflected back -
claptotis effect
Aspect of coast in relation to dominant winds
Fetch
Wave-Cut Platforms
Relatively flat, gently sloping expanses of rocks at the cliff foot, extending out to sea
Intertidal (between high + low water mark)
Processes of Formation
Salt crystalisation due to wetting + drying
Mechanical wave erosion
Bio-erosion
Chemical weathering - esp. for limestone platforms
Formed from cliff recession
Structure + Lithology
Influences effectiveness of the processes
Widest platforms occur near the horizontal, unresistant rocks
Narrow + ridged platforms occur where the rocks are steeply dipping + resistant
Micro-Features
Conditions of Formation
Sufficient thickness of uniform rock type which is relatively resistant to erosion + has strength to support tunnels + caves
A massive rock - well-spaced joints + bedding-planes that can be exploited by hydraulic action
Formation - Option 1
The impact of air + water forced into caves will develop vertical shafts + tunnels upwards
Air + water will be forced thru the blowhole with an explosive force by breaking waves
= large pressure changes in cave = further erosion
Blowhole may collapse = geo or inlet
Formation - Option 2
Differential erosion may result in caves adjacent to each other e.g. on either side of a headland, joining together to form an arch
The shape of this arch is structuarlly controlled
Most arches have a short time span (100 years)
Collapsed arches = stacks (but not all stacks were originally arches)
Stacks are eroded into stumps
Rock Types
Igneous Rocks
Background
Formed from molten magma
Extrusive
Eurpted on Earth's surface as lava flows
Or composed of rock fragments
(
pyroclasts**) if eruptions are violent
Small interlocking crystals bc they cool quickly
Intrusive
Cool within earth
Form intrusions/intrusive bodeies
Large interlocking crystals bc they cool slowly
Hardest rock type
Examples
Granite, Gabbro, Dolerite, Basalt
Jointing
On jointing, the rocks contract + split = regular patterns of fractures (
joints
)
These form in many directions
They are weaknesses
Fragmentation: Pyroclastic Rocks
Formed during violent eruptions
Are fragments of fine dust/ash, larger materials, bombs + blocks
These materials are lithified into igneous pyroclastic rocks by sedimentary processes (
diagneses
)
Sedimentary Rocks
Processes
Fragments are lithified by burial + diagneses
Eroded sediments are transported to water + begin to settle -
sedimentation
Over time, the layers accumulate + compress the layers below -
lithification
More layers (
strata
) are further compaction forces water out of the layers
Beds = different layers
Bedding planes = boundaries between the beds
Classes
Clastic
Basic sedimentary rock
Clastic rocks are accumulations of clasts
Clasts = small pieces of rock that have accumulated + been lithified by compaction + cementation
Clasts of various sizes form from weathering
These are transported via streams, winds, riers + glaciesr
Deposition - when the velocity of wind/water decreases OR if there is a delta
Clay sediment = shale rock
Sand sediment = sandstone rock
Gravel sediment = conglomerate rock
Chemical
Result form changing conditions e.g. temperature, pressure + water chemistry
Most form from sea water but also warm watesr
Most form from when standing water evaporates, leaving dissolved minerrals behind
Common in arid lands
Thick deposits of salt and gypsum form due to repeated flooding over long periods of time
Biochemical/Organic
Any accumulation of sedimentary debris caused by organic processes
Form mostly from precipitation of marine organisms
Form in marine environments
Many animals use calcium for shells, bones + teeth
These pieces of calcium accumulate on the sea floor = a thick enough layers for organic sedimentary rock
Metamorphic Rocks
Rock enters an environment where its minerals become unstable + out of equilibrium with the new environ. conditions
Normally involves burial + = a rise in temperature + pressure
Formed by burial + heating of any pre-existing rock
Transformation
Rocks are deformed (compressed) by increasing pressure - burial
Heated as a result of burial and new minerals grow
Rocks contain new fabrics + mineralogy
The changes in minerals always move in a direction designed to restore equilibrium
Bc of compression + parallel alignment of new mats, the rock develops planar structures (
foliations
) e.g. slate