8.2 Characteristics and formation of coastal landforms

Question 1

formation of wave-cut platform

Answer 1

• hydraulic action/abrasion erode the base of the cliff, creating a wave-cut notch
• as the wave-cut notch grows deeper, it undercuts the cliff, leaving the rock above unsupported
• eventually, the overhanging section of the cliff becomes unstable and collapses under gravity
• the eroded material is removed by wave action, leaving a flat, gently sloping wave-cut platform

Question 2

Headland and bay formation

Answer 2

• on discordant coastline, e.g swanage bay
• different bands of different resistant rock, less resistant rock quicker toe rode, whereas more resistant rock slower to erode
• results in headland
• wave refraction around headland, means erosion heading in all directions around that headland
• likely to get arches, stacks and stumps as a result of wave refraction

Question 3

Succession of a headland

Answer 3

• wave refraction concentrates the erosion around the headland
• large crack, opened up by hydraulic action
• crack grows into a cave by hydraulic action/abrasion
• cave become larger and breaks through to form an arch
• arch eroded/collapses leaving stack and then finally form a stump
• only on sedimentary rock (rock type important feature (sedimentary))

Question 4

blowhole

Answer 4

• sedimentary rock with large joints
• sea exploits cracks
• sea fills the hole in rock, exerting huge amounts of air pressure
• causing bits of the rock to fall away, results in a channel up to the top of the rock
• during a very high tide, water may come out of the channel

Question 5

different kinds of beaches

Answer 5

swash-aligned:
- wave crests parallel to coast, so limited longshore drift
- sediment doesn’t travel far along beach, wave refraction may reduce speed of high energy waves, leading to formation of shingle beach with larger sediment

• drift-aligned
• waves approach at a significant angle, so longshore drift causes the sediment to travel far along the beach, which may lead to the formation of a spit at the end of a beach
• generally larger sediment is found at start of beach and weathered sediment moves further down the beach through longshore drift, becoming smaller as it does, so the end of beach is likely to contain smaller sediment

Question 6

role of sediment in formation of the beach

Answer 6

Sandy beach:
- small sediment size
- lower infiltration rates = greater backwash
- material removed, so flatter gradient
- waves dissipate over a wider area - less focused erosion

Pebble beach:
- large sediment size
- greater infiltration rates = less backwash
- material built up, so steeper gradient

Question 7

what are neap and spring tides

Answer 7

• neap to spring - flat beach (tide coming in)
• spring to neap - berms (tide going out)

Question 8

different zones of the beach

Answer 8

back shore zone
foreshore
nearshore zone
offshore zone

Question 9

whats backshore zone?

Answer 9

• consists of storm beach made up of fairly large sediment
• breaking wave has enough energy to throw pebbles up the beach but backwash too weak to pull back down the beach
• berms formed fortnightly by spring tide and two/three slightly lower high tides that follow

Question 10

describe foreshore

Answer 10

• often made of sand
• low ridges running parallel to coastline formed by constructive waves at different stages of the tide and ridges are separated by runnels
• flatter areas of beach small-scale sand ripples can form as backwash runs back into sea

Question 11

describe nearshore zone

Answer 11

(breaker zone)
- longshore bars - ridges of sand that run parallel to the coastline but are bigger/more permanent than the fuels
- on beaches with low tidal range, often form at point that waves break and known as breakpoint bars

Question 12

describe offshore zone

Answer 12

• always underwater
• longshore bars also found in this area, produced when the circular movement of water in the waves start to touch the sea bed
• friction slows the wave, changes in motion of water within the wave can sweep up sediment to form these bars
• in places with very gently sloping beaches and low tidal range, bars can become substantial features and contribute to formation of barrier beaches/islands

Question 13

characteristics of a constructive wave

Answer 13

• long wavelength so low frequency
• gently sloping wave front and low wave height
• water spreads a long way up the gently sloping beach
• strong swash and weak backwash

Question 14

characteristics of a destructive wave

Answer 14

• short wave length so high frequency (10-14 waves per minute)
• steep wave front
• breaking wave gains much height and so wave plunges onto steep beach, energy directed downwards so does not travel far up the beach
• weak swash and very strong backwash

Question 15

compare summer/winter beach

Answer 15

Summer beach: constructive
- constructive waves move material up the beach as have stronger swash than backwash
- helps to create berms
- increase gradient of the beach (through the addition of material)

winter beach: destructive
- destructive waves comb material down the beach, so reducing gradient of the beach
- remove material creates offshore bars

Question 16

formation of a spit

Answer 16

1. prevailing wind comes from the south west
2. material is carried eastwards by longshore drift
3. where the coastline changes direction, sand and shingle are deposited in the water sheltered by the headland
4. material builds upwards and outwards, forming a spit
5. occasionally, strong winds blow from a different direction
6. waves approach the land from the south east, causing the end of the spit curve round
7. when the wind returns to its usual direction, the spit will continue to grow eastwards, developing further hooked ends during times of changed wind direction
8. the spit cannot grow across the estuary due to the speed of the river carrying material out to sea
9. spits become permanent when the prevailing wind picks up sand from the beach and blows it inland to form dunes
10. a salt marsh develops in the sheltered water behind the spit

Question 17

difference between simple and compound spits

Answer 17

Simple spit:
- can be straight but usually has curved ends either due to wave refraction/changeable winds e.g spurn head in yorkshire

Compound spit:
- narrow base attaching it to mainland - widens into a broad re-curved end with a series of ridges
- ridges often have sand dunes on the

Question 18

Tombolos

Answer 18

• formed by longshore drift
• after LSD carries sediments across a gap between the mainland and an island, forming a narrow long ridge of sand and pebbles
• where two beaches extend to an island they create a cuspate tombolo - wave refraction causes LSD to operate in opposite directions, altering the pattern of deposition
• e.g chesil beach connects the isle of portland

Question 19

Offshore bar formation

Answer 19

• long ridge of sand/pebbles found short distance out to sea
• forms in shallow water, where destructive waves break before reaching the beach
• waves scour the seabed and throw material forward into a heap, currents in sea will also supply sediments for this
• sometimes exposed at low tides but when submerged at high tide can be a hazard to ships
• these shallow areas used for wind farms, e.g Scroby sands, also sometimes used for beach nourishment or dredged for building material

Question 20

Bar formation

Answer 20

• form when a spit joins together two headlands
• bar particularly obvious at low tide when exposed
• can happen where there is no powerful river current to stop the spit growing all the way across the inlet
• lagoon forms between bar and original coastline

Question 21

Barrier beach formation

Answer 21

• long sandy beaches detached from but parallel to the coastline
• form where there is a plentiful supply of sand, shallow nearshore and offshore areas, waves and winds with enough energy to move sand and a rising sea level so that waves move sand towards the shore
• also where the tidal range is low and where the sea bed and the adjacent coastline are very gentle sloping with no cliffs

Question 22

conditions for growth of sand dunes

Answer 22

1. wide, flat, sandy beach (supply of dry sediment above the tide mark)
2. strong onshore winds
3. an obstacle - e.g a stone, shell

Question 23

formation of sand dune

Answer 23

• sand bounces along, due to pressure differences through saltation and piles up in zone of no wind, as high levels of friction
• sand bounces over obstacle and builds up on sheltered side (in zone of no wind)
• when wind direction changes, builds up more on sheltered side

Question 24

Different sand dunes along beach

Answer 24

1. Embryo dune:
   - most hostile envt
   - pioneer species
   - halophytic - salt tolerant
   - mainly sand and some marram grass
2. Fore dune:
   - marram grass and sea rocket
   - sand and plants
3. yellow dune:
   - more humus
   - 80% plant cover dominated by marram grass
4. Grey dune:
   - more sheltered, less acidic dune heath, red fescue, gorse
5. Dune slack:
   - water-loving plants; willow, moss, reeds
6. mature dune:
   - trees: birch, aider, oak

Question 25

saltmarsh succession

Answer 25

1. Algal stage: gut weed and blue green algae establish as they can grow on bare mud, which their roots help to bind together
2. Pioneer Stage: cordgrass and glasswort grow, their roots begin to stabilise the mud allowing the estuarine to grow
3. Establishment stage - saltmarsh-grass and sea asters grow, creating a carpet of vegetation and so the height of the salt marsh increases
4. Stabilisation - sea thrift, scurvy grass and sea-lavender grow and so salt rarely ever gets submerged beneath the marsh
5. Climax vegetation - Rush, Sedge and red fescue grass grow since the salt marsh is only submerged once or twice a year

Question 26

zones of a saltmarsh

Answer 26

• influence of tide decreased further inland (period of inundation reduces)

1. mudflats:
   - inter tidal - only a few hours a day exposed to air
   - the only plants are algae growing on the mud
   - vegetation is halophytic (salt tolerant) because it can tolerate being submerged by the sea
2. Lower marsh:
   - the marsh is covered at each high tide and channels known as creeks are cut as the water receded
   - typically characterised by spartina, salicornia
3. Middle Marsh:
   - as more mud is deposited, the first plants appear which help trap more mud and silt, building up the marsh
   - salt pans can be related by impeded drainage
   - water evaporates, making them extra saline
4. upper marsh:
   - level of the marsh is higher so period of inundation is reduced
   - these can be tolerated by a variety of plants, so diversity increases
5. Terrestrial vegetation:
   - eventually land builds up until it is always above the level of the tide, so shrubs and woodland can grow
   - vegetation is no longer affected by the sea, so not halophytic

Question 27

Mangroves

Answer 27

• stilt roots that anchor the plant into the mud
• slow down wave movement, encouraging further deposition
• halophytic and well adapted to live in salt water
• prop roots for stability
• pneumatophores: suck air down into root system, due to low oxygen levels in the mud, grow from roots vertically
• similar to salt marshes but develop salt tolerant forests and shrubs and cover 25% of tropical coastlines

Question 28

tidal sedimentation in estuaries

Answer 28

• in tidal estuaries the incoming freshwater flow of a river will be opposed by both the mass of the seawater and the tide
• short period of time between the rising and falling tides when the flow comes to rest and turbulence of the water in the estuary is at a minimum
• gives heavier sediment particles a chance to settle at the bottom
• as tide current increases again, the particles are lifted in into the water column again
• but unlike river water which continues to flow through the estuary in the upper layer, the sediment particles are now in the lower layer of the estuarine circulation where the mean water movement is from the ocean towards the head of the estuary
• means large part of the sediment will therefore never make it to sea but accumulate in estuary
• sediment may eventually leave the estuary during flood events

Question 29

when do saltmarshes form?

Answer 29

• low-energy wave environments which encourages the deposition of fine silts and clays
• large tidal range that produces strong tidal currents which can transport large quantities of silt and clay around
• large, constant supply of silts and clays - can come from coastal erosion of cliffs

Question 30

what causes a salt marsh to form?

Answer 30

• when fine-sized clay material mixes with salts in seawater, chemical reaction causes clay particles to come together (flocculation) to form larger, heavier particles which fall to the sea bed
• the accumulated mud is then colonised with pioneer halophytic plants which can tolerate being covered during tide cycles where there is lack of oxygen/high pH value
• these plants trap sediment and lead to inter-tidal mudflats developing further

Question 31

role of sea level change in formation of coastal landforms (eustatic and isostatic changes)

Answer 31

• eustatic changes occur when there is a change in the volume of water in the oceans
• affect sea level across whole planet and may be due to thermal expansion/contraction or changes in glacial processes
• isostatic changes occur when there is a movement of the land relative to the sea
• localised change
• often result of isostatic subsidence (glaciers weigh down the land beneath and so the land subsides)
• melting of glaciers after last ice age has led to isostatic recovery causing coastline to rebound and rise again in areas that were covered by ice

Question 32

emergent and submergent coastlines and how they are affected by sea levels

Answer 32

Emergent:
- form due to fall in sea level
- where land has been raised in relation to the coastline
- arches, stacks and stumps may be preserved
- wave cut notches

Submergent:
- occur when sea levels rise or coastline sinks in relation to the sea
Rias: formed when rising sea levels flood narrow winding inlets and river valley
- Fjords: formed when rising sea levels flood deep glacial valleys to create natural inlets and harbours
- Dalmatian Coasts:
- occurs when valleys running parallel to the coast become flooded due to sea level change
- leaves series of narrow, long and rugged islands

Question 33

Case study - Jurassic Coast

Answer 33

• durdle door (Arch) - Wave action has eroded through the resistant Portland limestone
• Lulworth Cove (bay and Headland): sea broke through a narrow band of resistant limestone and eroded the softer clays and sands behind.
• Old harrys rocks (stacks and stumps)
• Chesil Beach (Tombolo): shingle beach connecting the Isle of Portland to the mainland.