Physical Factors Influence Coastal Landscapes and Systems

Wind and Atmospheric Circulation

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

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

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

Global Circulation

Background

Global wind system that transports heat from tropical to polar lattitudes

3 cells in each hemisphere

Hadley cell

Ferrel cell

Polar cell

In these the air circulates through the depth of the troposphere

  1. Warm moist air from the tropics is fed north by the surface winds of the Ferrel cell
  1. This meets cool dry air moving south in the Polar cell
  1. The polar front forms where these 2 contrasting masses meet
  1. = ascending air and low pressure at the surface
  1. The polar front jet stream drives this area of unstable atmosphere
  1. 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

Largest, calm weather, 30-40 degrees N+S of the equator

Calm weater

  1. Trade winds blow towards the equator and form the Inter-Tropical-Conversion-Zone
  1. 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

Unsettled weather (esp. in UK), 60-70 degrees N+S, moves in oppo. direction to other cells

  1. Air converges at low lattitudes
  1. It ascends along the boundaries between cool polar air and warm sub-tropical air
  1. Air return flow of air at high altitudes towards the tropics joins sinking air from the Hadley 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

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

As they pass the create a tidal bulge on both sides of the planet

Moon has *2.2 the strength because its closer

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

  1. Tidla wave travels northwards up the Irish sea
  1. Deflection to the right = higher tides in Wales + England
  1. Wave travels southwards down the N Sea

Tidal waves appear to advance from the centre of the ocean

Intertidal Deposits: Tidal Rhythmites

  1. Mud deposits in low energy and low current velocity areas
  1. Increase in velocity = mud transported in suspension
  1. Further increase in velocity = sand transported
  1. Energy drops = sand and then mud are deposited
  1. 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

Storm surges

Low pressure - air rises = less pressure on sea surface = sea lifts + winds strengthen

High pressure - air is falling

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

  1. Regular oscillations in water surface of larger water bodies - the smaller chop waves go off in different directions
  1. 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

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

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

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 can provide a range of rock types with lithologies of differential resistance to subaerial and marine processes

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

  1. Marine action breaches the relatively resistant limestone wall
  1. It reaches the relatively weal wealden shales - easy to erode
  1. These are easy to erode into an elongated cove
  1. Erosion inland is slowed by the resistant chalk
  1. 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

  1. Waves converge on headland
  1. Depth of water decreases off the headland
  1. In these shallower waters, the waves lose more energy to friction, causing them to slow down
  1. 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

Formed from cliff recession

Salt crystalisation due to wetting + drying

Mechanical wave erosion

Bio-erosion

Chemical weathering - esp. for limestone platforms

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

  1. The impact of air + water forced into caves will develop vertical shafts + tunnels upwards
  1. Air + water will be forced thru the blowhole with an explosive force by breaking waves
  1. = large pressure changes in cave = further erosion
  1. Blowhole may collapse = geo or inlet

Formation - Option 2

  1. Differential erosion may result in caves adjacent to each other e.g. on either side of a headland, joining together to form an arch
  1. The shape of this arch is structuarlly controlled
  1. Most arches have a short time span (100 years)
  1. Collapsed arches = stacks (but not all stacks were originally arches)
  1. 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

  1. On jointing, the rocks contract + split = regular patterns of fractures (joints)
  1. These form in many directions
  1. They are weaknesses

Fragmentation: Pyroclastic Rocks

  1. Formed during violent eruptions
  1. Are fragments of fine dust/ash, larger materials, bombs + blocks
  1. These materials are lithified into igneous pyroclastic rocks by sedimentary processes (diagneses)

Sedimentary Rocks

Processes

Fragments are lithified by burial + diagneses

  1. Eroded sediments are transported to water + begin to settle - sedimentation
  1. Over time, the layers accumulate + compress the layers below - lithification
  1. 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

  1. Clasts of various sizes form from weathering
  1. These are transported via streams, winds, riers + glaciesr
  1. Deposition - when the velocity of wind/water decreases OR if there is a delta

Chemical

Clay sediment = shale rock

Sand sediment = sandstone rock

Gravel sediment = conglomerate rock

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

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