Mark Scheme for Coastal Qn 2003-2009

8/11/2019 Mark Scheme for Coastal Qn 2003-2009

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J033 With the aid of diagrams, describe the nature of fringing reefs, barrierreefs and atolls. (10)

Coral reefs

Fringing reef Barrier reef Atoll

1. It consists of a platform

of coral which is

connected to and which is

built out from a coast.

2. The surface of the

platform is usually flat or

slightly concave and its

outer edge drops away

steeply to the surrounding

sea floor.

3. A shallow lagoon

usually occurs between

the coast and the outer

edge of the reef, e.g.fringing reef off the coast

of the Eilat, Israel.

1. A ring shaped coral atoll

with a central lagoon is all

that remains after

seamount is submerged.

(volcanic island)

2. Atolls are particularly

common in pacific and

indian oceans.

3.Some Atolls are very

large, eg. Suvadiva in the

Maldives.

1.This is similar to

fringing reef except

that it is situated

several miles off the

coast and is separatedfrom it by deep water.

2. The coral of a

barrier reef is joined to

the coast although the

water above is too

deep for coral to grow

on the bed, .e.g Great

Barrier Reef Australia

Diagrams


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b) Describe the processes of marine erosion. Using examples,

explain how marine erosion can affect cliffed coastlines. (15)

Marine erosion

Hydraulic action Attrition Abrasion Solution

Formation

(a) Wave cut

platforms Cliff, stack, stump

Is the force of water

and air on rocks

(30 000kg/m2)

Is the wearing

away of base-rich

rocks, especially

limestone, by an

acidic water &organic acids aid

the process.

Is the wearing

away of

shoreline by

material carried

by the waveswhich is hurled

against the cliff.

Wave

attrition

affects the

debris within

the wave.The particles

reduce in

size and

angularity as

they collide

with each

other within

the wave.


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Cliff profile:

Cliff profiles owe their form to the geology (Lithology andstructure), sub-aerial processes and wave energy along a given

stretch of coastline. It takes thousands of years for the cliffs profileto form from complex processes, there are many complicatedprocesses taking place on coasts that affect the profile of a cliff.

Wave action causes three erosional processes, abrasion, hydraulicaction and corrosion. These processes are most effective whenhigh energy waves, associated with storm conditions strike coastprofiles made of less resistant rocks. Concentrated wave action oncliff leads to undercutting. The three types of wave erosionprocesses play an important part in forming cliff profile. A wavealso trims the front of a cliff. These erosional processes take a longtime and are very complex.

4 Fig. 2 shows a spit and salt marshes.


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(a) Describe the main features of the spit and salt marshes and

explain their formation. (10)

SPIT SALT MARSHES

An accumulation of sand

and shingle that is attached

to a coastline.

Behind the spit are accumulations

of silt and mud that are anchored

by vegetation to produce marsh and

creek areas.

FORMATION

1. As the fetch and prevailing winds are from the south-west,

material will be moved eastwards along the coast by longshoredrift.

2. After headland X the direction of the original coastline changes

and larger material (shingle) is deposited in water sheltered by

the headland (B).

3. Further deposition of finer material (sand) enables the feature

to build up slowly to sea-level (C) and to extend its length (D).

4. Occasionally the wind changes its direction (e.g. comes from the

east). This in turn causes the waves to alter their direction (e.g.

approach from the south east. During this time some material at

the end of the spit may be pushed inland to form a curved end

(E). When the wind returns to its usual direction the spit

resumes its growth eastwards (F).

5. Spits become permanent when sand is blown up the beach, by theprevailing wind, to form sand-dunes. 6 Salt marsh is likely to

develop in the sheltered water behind the spit. 7 The spit is

unable to grow across the estuary as the river current carries

material out to sea. Should there be no river, the spit may grow

across the bay to form a bar.


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(b) Explain why spits and saltmarshes are subject to change and are

considered fragile environments. Suggest ways in which they can be

protected. (15)

Spits & saltmarshes

Growth/lateral Erosionchanges

Why subjected to changes

Storms or removal of sediment supplies can have

severe impacts such that these features can beconsidered fragile. Salt marshes are equally

responsive if the shelter of the spit is removed or

pollution affects the estuarine or river silts and mud.

Development or changes of sea level can also have

severe consequences.

How to protect?

Protection can be afforded by trapping

sediment (groynes) or guaranteeing

continuous sediment supplies


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J04

3. (a) How can changes in sea level affect the formation and

continued existence of coral reefs and atolls? (10)

Coral is sensitive to heat and light it is also sensitive to changes insea level as reefs cannot survive long periods of subaerial exposure.

Falls in sea level can lead to the death of coral and to the emergence

of the reef above high water forming low lying land such as keys.

The islands become colonized by vegetation. To a certain extent

reefs can contend with sea level rise leading to the growth of thick

reefs (Darwins model). However rapid rise consequent upon global

warming may result in inundation and destruction.

(b) With reference to coastal environments, explain the termsustainable management. To what extent has sustainable

management been achieved in a coastal area you have studied?(15)

Sustainable management

encouraging improvement of coasts but

within the capacity of the supporting

physical systems i.e. minimisingenvironmental degeneration.

In coastal terms this can mean

the preservation both of the

coastal environment and its

exploitation.

Do nothing

Similarly a do nothing approach may also

have repercussions for the long term coastal

environment ( loss of fishing, tourism

landforms etc).


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4. (a)Fig.2 shows some stores and transfers of sediment in a coastal

zone.Show how the stores and transfers of sediment have

contributed to the formation 'of beaches. (10)

Case study

Barton on Sea

Stores

Source of sediments for

beaches

Cliff erosion

provide material

Materials form rivers

& estuaries

Sea bed

How transported tobeaches

Longshore drift & tidal currents

Form of beaches

Depend on

Three types of

material

Location of area

deposited


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Using examples, explain how wave action and geology can influence

the rate of coastal erosion. (15)

Loss of material from

beaches

wind

Dunes

Wave

erosion &

offshore

Sea bed

Rate of coastalerosion

Wave action Geology

Wave erosion occur

in high energy

wave, e.g. hydraulic

action, abrasion,

solution & attrition

Cliff profile, wave cut

platform, stumps,

stack & caves.

formation

Remove

materials

from beaches

Unconsolidated rocks &

granite

Rate at which it occur

depend balance between

wave erosion processes and

geology

Examples


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J05

3 (a) How do waves influence the shape of beaches? [10]

Wave

influence

Beaches

constructive Destructive

-Constructive wave often forms where the fetch

distance is long.

- They are small wave, flat in form with long

wave length (100m) & a low frequency wave

(wave period 6 to 8 per minutes)

-On approaching the beach, the wave front

steepens relatively slowly until the wave gently

spills over.

-As the resultant swash moves up the beach, it

rapidly losses volume and energy due to waterpercolating through the beach material.

-The result-backwash is weak & has insufficient

energy to transport sediment back down the

beach or to impede the swash from the

following wave.

-Consequently sand and shingle is slowly, but

constantly moved up the beach, this gradually

increases the beach gradient and leads to

formation of BERMs at its crest and especiallyon sandy beaches, ridges and runnels.

-Destructive wave are more common

where the fetch distance is shorter.

- they are often large/ high waves, steep in

form and with short wave length (20m)

and high frequency (10 to 14 per min)

-on approaching the beach, steepen

rapidly until they plunge over.

- The near vertical breaking of the wave

creates a powerful back wash which can

move considerable amounts of sedimentsdown the beach.

-At the same time reduce the effect of

swash form the following waves.

-Although some shingle may be thrown up

above the high water mark by very large

waves forming a storm beach, most

material is move downwards to form

longshore (break point)


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(b)(i) Explain the operation of the marine processes of hydraulic

action, wave quarrying and abrasion (corrasion).

Hydraulic action is the pressure of water hitting a cliff base and the

sudden release of energy which breaks down incoherent rocks.

Wave quarrying is the entrapment of air in cracks, joints etc. anddecompression as water retreats.

Abrasion is the result of materials carried by waves striking cliff

base giving rise to undercutting and notches.

Different types of beaches

Barrier beach

A long and narrow beachofsandand/orgravelthat runs parallel to thecoastline

and is not submerged by thetide.

Pocket beach Bay head
http://www.physicalgeography.net/physgeoglos/s.html#sandhttp://www.physicalgeography.net/physgeoglos/s.html#sandhttp://www.physicalgeography.net/physgeoglos/s.html#sandhttp://www.physicalgeography.net/physgeoglos/g.html#gravelhttp://www.physicalgeography.net/physgeoglos/g.html#gravelhttp://www.physicalgeography.net/physgeoglos/c.html#coastlinehttp://www.physicalgeography.net/physgeoglos/c.html#coastlinehttp://www.physicalgeography.net/physgeoglos/c.html#coastlinehttp://www.physicalgeography.net/physgeoglos/t.html#tidehttp://www.physicalgeography.net/physgeoglos/t.html#tidehttp://www.physicalgeography.net/physgeoglos/t.html#tidehttp://www.physicalgeography.net/physgeoglos/t.html#tidehttp://www.physicalgeography.net/physgeoglos/c.html#coastlinehttp://www.physicalgeography.net/physgeoglos/g.html#gravelhttp://www.physicalgeography.net/physgeoglos/s.html#sand


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(ii)Briefly describe the factors, other than marine erosion, that can

affect the shape of rocky coastlines. [15]

4 (a)

Fig. 2 shows a theory of the development of a coral atoll. Describe

the coral reefs shown and give an explanation of the theory shown.

[10]

Factors affecting shape of

coastline

Rock lithology &

structure

Sub aerial

rocesses

relief Human

activities

Climate

change

Darwinian Theory of

FormationCondition for coral

develo ment


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Using examples, describe the threats that may affect coastlines and

evaluate the actions that are being taken to protect coasts from them.

[15]

June 2006

3 (a)Describe the processes of wave erosion and demonstrate how

they can produce a wave cut platform. [10]

Same as above.

(b) Describe how sediment is transported along coasts and explain,

with the help of diagrams, how the deposition of sediment canproduce simple and compound spits. [15]

Threats

Erosion Rising sea

levels

Human activities

Interfere

sediment supply,

e.g. sand dredging

Protective measures

Evaluate method use

Examples;

Threats on depositional landforms;

dune, salt marshes, spits

Sediment transported

along coastline

Longshore drift

by


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The transport of sand and pebbles along the coast is called

longshore drift.

Theprevailing wind (the direction the wind ususally blows from)

causes waves to approach the coast at an angle. The swash carries

the sand and pebbles up the beach at the same angle (usually 45).

The backwash, however carries the material back down the beach at

right angles (90)as this is the steepest gradient.

if a pebble was placed in the water it would be carried along the

coastline in a zig-zag motion and would eventually be deposited

when the waves lose energy.

The general direction of longshore drift is decided by the prevailing

wind. In the diagram below the prevailing wind is approaching from

the south-west. Therefore longshore drift is moving material from the

west to the east.

Landforms :Spits

Coastal spits are formed sediment transported by lst accumulate at

changes in coastal direction or where drift is held up by a river

mouth or estuary. The shingle and sand is then fashioned into aprojecting beach ridge which will extend to the point where


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sediment is removed as rapidly as it arrives (a simple spit)

compound spits are those experiencing long periods of growth where

the main active beach ridge is met by inactive ridges (laterals) more

or less at right angles. Recurves are modified by secondary waves.

4 Fig 2 shows the refraction of waves as they approach a coast.

(a) Explain the refraction of the wave crests and suggest the effects

of refraction upon the headland cliff and the bayhead beach.

[10]

1. As the waves approach the coast, they travel in a straight line,parallel to each other, as they travel in the same speed.

2. However as the front of the headland is shallower than thefront of the bay, the waves encounter more friction and it slow

down. (shallower more friction-slow down)

3. As the front of the bay is deeper than the front of the headland,the wave encounter less friction and its speed remains. (Near

bay, deeper thus less friction, speed remains)

Wave refraction

What?


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4. This cause the wave to refract, where the waves bend towardsthe headlands and bends away at the bay.

5. If the wave were to bend towards the headlands, energy willbecome concentrated thus eroding the headland. At the bay

wave energy become less concentrated thus deposition occurat the bay forming pocket beach or bayhead beach.

(b) Explain the extent to which the natural characteristics of coastal

dunes and salt marshes can be changed by human activities. [15]

Dune environments and salt marshes can be considered as fragile,

as they can be relatively easily destroyed by both natural and human

activities. Dunes represent a fine balance between erosion, transport

and deposition. Thus interruptions to sediment supply or the

destruction of anchoring vegetation will result in blow outs and

decline. Human activitieswalking, quad biking etc. can beinstrumental as well as storm surges etc. Salt marshes rely on both

natural protection (e.g. spits) and the unpolluted flocculation of silts

as well as salt loving vegetation. Again destructive elements can

stem from natural causes (storms) or from human activities such as

pollution or reclamation. Level 3: Good appreciation of fragility in

terms of the balance of natural processes. Thus there will be some

attempt to see human activities as destructive balanced by natural

phenomena. [1215]

J07


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3 (a) Describe the nature of a coastal sediment cell. How do these

cells contribute to the formation of coastal landforms?

(b) To what extent do rock type and structure influence the

development of landforms along cliffed coasts?

Rock type and structure have a major role in shaping cliffed

coastlines. This can be demonstrated by reference to different types

of cliff profile, plan of coastal form as well

as the landforms ofstump, stacks, arches etc. Thus the type of rock, its dip, bedding

planes, vulnerability to erosion can all be developed. Of course, rock

type is not the

only influence and high energy environments with

active marine and sub-aerial weathering all have a contribution to

make. [15]

Level 3

Good appreciation of the influence of geology with

exemplification from cliff profiles, coastal plans etc. The

contribution of marine processes will be considered and the answermarked by appropriate exemplification. (1215)

4 (a)

Fig. 2 shows a coastal zone with its tide and wave environments.

Describe the wave activities occurring in the breaker surf and swash

zones. What impact do these activities have upon the shape of

backshore and nearshore zones?

A somewhat different context in which candidates can develop wave

Coastal sediment cell

-It is a system by which sediments are sourced,

transported and deposited within a part of a

coast and offshore area.

-They appear as a coastal system, thus sediments

are derived from estuaries and coastal erosion,

transported by longshore drift and deposited in

the form of beaches, bars, spits etc.

-The nature of the landform thus depends upon

the nature of the cell and also the shape of the

coastline.


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action that they normally associate with constructive, destructive,

plunging waves. Breaking waves

send pulses of water shorewards

until they run out of momentum and gravity draws the water back to

the sea. The surf zone is between the breaking waves and the point

of maximum run up and is thus an area of turbulent activity as thebackwash meets the forward spilling waves (swash). The swash zone

will be associated with the forward movement of constructive

waves, whilst the breaker zone may be associated with plunging

waves. Candidates will see the swash zone as one of accumulation of

beach sediments whilst the other zones may be associated with the

development of a bar at

the edge of the breaker zone and the

combing down of materials into the trough area. [10]

(b) What are the principal threats to the continued existence of coralcoasts? To what extent can these threats be overcome?

Coral coasts are predominantly threatened by human activities,

which disturb the required conditions for growth and development.

Hence, pollution can affect the light sources and the requirement for

clear water with no sediment. Also the oxygen content of the water

could be affected. Tourism can produce erosion as well as pollution

and fishing and other activities can be harmful. Quarrying and

souvenir hunting are equally destructive. Global warming and sealevel rise could lead to long term destruction as the growth of coral

would not be fast enough to compensate for the relatively rapid

rise in sea levels. Rising temperatures and carbon emissions may

also affect the chemical balance of the oceans again acting as threat.

Some natural processes such as storms can also erode reefs, as can

long term changes such as uplift. Any coral exposed above sea level

for long periods becomes blanched. Some assessment can be

made

of attempts to overcome these threats although these will bemost effectively achievedby use of examples or a case study. [15]

Level 3 A good appreciation of the operation of the threats by

reference to the conditions required for coral growth. Good use of a

case study and/or examples. Evaluation of efforts to overcome

threats will be set within the case study or exemplars. (1215)

J08

3 (a) Outline the contribution of wave refraction and longshore drift


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to coastal deposition. [10]

Diagrams can be effective in this question. LSD will be seen as a

combination of littoral or beach drift and longshore currents to

produce the familiar zig-zag movement of sediment along coasts.Where the current slackens then sediment is deposited. Refraction

has a role to play in this, although many will see this as only a means

of reshaping sediment e.g. in recurves.

(b) Explain and assess the theories concerning the formation of coral

atolls. [15]

4 Fig. 2 shows some processes operating on cliffs in a temperate

location.

(a) Explain the processes that are affecting the cliffs shown on Fig.

2. [10] The processes shown are the saturation of the cliff by

groundwater from percolating rainfall leading to large scale

rotational slumping. The cliff slope fails along a glide plane. The

processes of marine erosion and longshore transportation then act

upon the toe of the slump. The other example is produced by direct

undercutting of the cliff face by marine erosion (hydraulic, quarrying

etc) and the removal of the undercut material by transportation. This

then allows the cliff to slump along lines of weakness exploited by

sub-aerial weathering.

(b) Describe and evaluate the success of methods that might be

employed to protect coastlines. [15]

Darwinian Theories

Compare to Daly

theor

Protecting cliff

Barton on Sea

Hard

En ineerin

Removal of materialsErosion

Gabions sea

walls, etc

Restrict sub-

aerial weathering


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J09

3 (a)How might changes in sea level affect the formation and types

of coral reefs found today? [10]

Coral is sensitive to sea depth in terms of the light and temperatures

required for its growth and development.

Thus sea level change has been important in the past for the

development of fringing reefs, barrier reefs and atolls.

Darwins theories regarding sea level change and the development

of coral can be cited and Daly theories should be included.

Use groynes to

protect beaches

Others

Manage retreat

Evaluate

method used

Hard

engineering

disadvantages

Pollution of coral reef

Other examples

Evaluate method to

overcome problems


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(b) To what extent is the building of sea defences (hard engineering)

a more effective method of sustainable management than allowing

coasts to revert to a natural state (managed retreat)? [15]

Managed retreat involves. It is commonly used in areas of deposition

such as salt marsh and creeks where the defences (hard engineered

sea walls, groynes etc) are removed allowing the drained land to

revert to marsh. Although there is a loss of arable land and indeed

settled areas, the result often leads to lower levels of coastal erosionas the marsh is very effective at absorbing storm conditions. There is

also a benefit in maintenance costs. It could thus be regarded as

sustainable coastal management. It can be argued that it is not

suitable in all areas, particularly fast eroding coastlines where

expensive infrastructure has been placed. It also could be deemed

inappropriate where large areas have been reclaimed for use such as

in Holland or Singapore. There is ample opportunity for the use of

examples or case studies of sustainable coastal management.

Level 3 A clear indication of managed retreat and its implications

for coastal management. This is then set against the results of hard

engineering and some assessment made of the advantages and

limitations of both strategies. Well exemplified. [1215]

4 (a)

Fig. 2 shows some factors influencing wave formation.

Using Fig. 2, describe how wind and fetch affect wave height and

Manage retreat

the removal of coastal defences andallowing the area to revert to a

natural balanced state


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suggest other factors which might affect the form of a wave. [10]

Wave height is seen in the diagram as a function of wind velocity

and fetch Generally the longer the fetch the smaller the velocity

required to generate a wave of the same height. Hence a wave of 1min height requires a wind speed of over 17 at 10 km but at a fetch of

100 km only a velocity of c 8. Good candidates will note the

logarithmic scale of fetch. Fetch allows a longer duration for wind to

blow as waves are a product of friction produced by the wind. Good

answers should use the data shown. Other factors affecting wave

form are the depth of water and the shape of the coast. Wave height

will increase as depth decreases. The coast can also refract waves.

(b) How does wave action contribute to both the erosion anddeposition on coasts? [15]

Wave action can be seen as occurring in high energy environments

characterized by high and frequent waves due to long fetch and high

winds. Here marine erosion will be prominent through claptosis and

the other forms of marine erosion. Some might see these as

destructive waves. Conversely in low energy environments where

there is a lower frequency of waves more swash and less backwash

then waves can have constructive functions in building beaches andwhen associate with LSD can bring about other sedimentary

landforms such as spits bars etc.

Level 3. A well organized answer that relates marine erosion and

deposition directly to wave action, providing examples of the types

of processes in operation which can be illustrated by landforms

produced. [1215]

Wave refraction. When a wave approaches a headland, it mustrefract around the headland. This has several effects. The first of theseis that the wavelength shortens. The wave depth decreases, and heightincreases. The energy is focused on to specific points either side of theheadland, and it is in these points that caves often begin to form. Theconcentration of energy is accompanied by a rise in wave height. Sinceenergy is proportional to wave height, then the power of the waves isgreater on the headland. As waves approach the shoreline and enter


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progressively shallower water, the speed at which they move no longerdepends on the size of the wave, but becomes entirely dependent onthe depth of water. In the shallower water commonly found offheadlands, a wave crest moves more slowly than it would in the deeperwater of adjoining bays. The wave crest in the bay, therefore, movesahead of the wave crests approaching the headlands on either side,and the wave appears to be bent into the bay. This phenomenon isknown as refraction. Because of refraction, waves commonly approachthe coast with their crests closely paralleling the line of the shore,although the actual plan shape of the wave will depend on the contoursof the seabed close to the shore. Wave refraction also tends toconcentrate wave energy on headlands, at the expense of adjoiningbays; material eroded from the headlands washes into the bays.

Coastal Weathering; (1) Salt Crystallisationis effective where thereis a high evaporation potential, and the growth of chloride slats derivedfrom the salt in sea-water attacks a wide variety of rocks. It loosensfragments of rocks for erosion (2) Solutionon the coast is notable onlimestones. Sea-water is often saturated with calcium carbonate, and itis hard to see why it is so effective. This is particularly true if the tropics,where CaCO3 levels decrease with temperature increase. It is possiblethat photosynthesis in plants oxygenates the water during daylight, butreleases carbon dioxide in to the water at night, increasing the acidityand effectiveness of solution. The morphological effect is to produce

sharp fretted pinnacles of limestone called lapies, low down in the inter-tidal zone. When wave attack is less prevalent, solution may cutnotches at the edge of pools and leave overhanging lips. In tropicalseas with microtidal or mesotidal ranges, these features become verylarge and are called visors. (3) Biological activityassists solution.Other rock types besides limestone are attacked by secretions,particularly from the blue-green algae which live between the tide lines.Seaweed firmly attaches itself to rocks, which effectively increases theexposed surface area.

Mark Scheme for Coastal Qn 2003-2009

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