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
  -line of weakness eroded to form a geo, 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
- beach cusps, berms and ridges
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
- - spits, bars, saltmarshes,cuspate forelands and tombolos

Question 6

different characteristics of different sediment beach types

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

• a cliff or marked by line of dunes’
• at high water mark may be a berm or shingle ridge (storm beaches)

Question 10

describe foreshore

Answer 10

• exposed at low tide
• often made of sand
• ridges and runnels
• ridges are raised areas of land, runnels are dips
• cusps are crescent-shaped indentations on sand/shingle beaches

Question 11

describe nearshore zone

Answer 11

(breaker zone)
- coastal area that extends from the low tide mark to where waves begin to break
- 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

• first material deposited
• waves touch the seabed, so material may be pushed up as offshore bars

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 resulting in deeper water and so surging waves(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
- lower gradient = shallower water = increased wave steepness and so plunging waves

Question 16

formation of a spit

Answer 16

Conditions:
- abundant material, irregular coastline, increased deposition due to vegetation, estuaries/major rivers
1. prevailing wind comes from the south west and 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 so 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. spits become permanent when the prevailing wind picks up sand from the beach and blows it inland to form dunes and a salt marsh develops in the sheltered water behind the spit

Question 17

difference between simple and compound spits

Answer 17

Simple Spit:
- straight or slightly curved accumulation of sand or shingle extending from the coastline into the sea.
- Lacks complex features.
Example: Spurn Head, England - sand and shingle with some boulder clay: extend southward approx 10cm a year, sediment from Holderness cliffs which erode at 2.5 m a year.

Compound Spit:
- spit with a series of ridges or recurved ends formed by changes in wind direction or wave energy over time.
- May show evidence of multiple phases of growth and reworking.
- Often larger and more complex than simple spits.
Example: Hurst Castle Spit, England. - - flint pebbles and some sand

Key Difference:
Compound spits are** more intricate, showing multiple growth stages,** while simple spits are basic, single structures

Question 18

Tombolos

Answer 18

• formed by longshore drift
• Waves move toward the coastline and are slowed down as they enter the shallower water
• first reach the islands that are close to the shore
• waves are moving at a slower than normal pace, so move around the island instead of over it. As the water moves more slowly around the island, it picks up sediment along the way
• When the waves meet on the other side of the island (the side facing the coast), the sediment is deposited - continues to build up until it forms a bar
• e.g chesil beach connects the isle of portland to dorset, made of flinty pebbles

Question 19

Offshore bar formation

Answer 19

• long ridge of sand/pebbles found short distance out to sea
• forms in boundary between offshore and nearshore
• form from sediment eroded by destructive waves and carried seawards by backwash
• 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

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

• 8 thousand years ago sea level 100m lower than now, beach ridges, or dunes formed along continental shelf by waves/wind
• sea level rose, breaking through ridge and flooding low area behind it, forming a lagoon, causing dune area = island
• constant action by waves and continuing rise in sea level caused island to migrate landward as sand removed from beach and deposited inland

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

Every Family Yells Get Down Micheal
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/fixed:
   - as time goes on, soil develops and becomes damper/richer, marram grass replaced by red fescue grass
5. Dune slack:
   - water-loving plants; willow, moss, reeds
6. mature dune:
   - trees: birch, aider, oak

Question 25

saltmarsh formation

Answer 25

- found **low-energy coastlines, behind spits/barrier islands and in estuaries** **Scolt Head Island**, north norfolk coast: 1. thin layer of mud forms over sand which covered each tide, only plants = ** green algae** 2. more mud deposited and first plants **eel grass (salt-tolerant)** appear which trap more mud/silt, **marsh covered at high tides and channels cut as water recedes** 3. further plants appear higher up march, accelerates mud accretion, **channels deepen as marsh surface rises** 4, more plants ((sea lavender** move into **higher zones and mud deepens**, high tides flood marsh but low tides confined to creeks - further eroded as water runs out 5. marsh now slow growing and mud deep, further plants colonise **sea rush and salt wort most common**

Question 26

zones of a saltmarsh

Answer 26

- **m**y **l**ittle **m**onkey **u**ses **t**oothpaste - - 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

- salt-tolerant trees and shrubs that grow in coastal intertidal zones - limited to where temp > **24 degrees** and rainfall exceeds **1250ml** - **shallow root penetration** but with **extensive lateral spreading**, some have **buttress roots** for stability Conditions: - **high salinity, low oxygen, poor nutrient availability, strong wind and wave action, unstable sediments** - **xerophytic** adaptation, e.g thick cuticle, sunken stomata

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

Eustatic changes

Answer 29

- **eustatic** changes occur when there is a **change in the volume of water** in the oceans - effect **GLOBAL** Main causes: **1.changes in climate:** - increase in temps = melting ice sheets - increases sea level and causes water to expand (increases sea level) - decrease in temp cause more snow = increases volume of water stored in glaciers = less volume in sea = decreases sea level **2. tectonic movements:** e.g sea floor spreading increases volume of basin = lower sea level

Question 30

submergent coastlines and how they are affected by sea levels

Answer 30

Submergent: - occur when **sea levels rise** **Rias**: **river valley** partially submerged, e.g **River Fal** - gentle long and cross-profile - **wide/deep** at mouth, becoming **narrower and shallower** further inland - **Fjords**: - **drowned glacial valleys** - straight/narrow with very steep sides - **shallow mouth** caused by deposition of material by glacier - **very deep further inland** - **Milford Sound**: - **valleys parallel** to coast are flooded leaving islands parallel to coastline

Question 31

Case study - Jurassic Coast

Answer 31

- durdle door (Arch) - Wave action has eroded through the **resistant Portland limestone but means low erosion rate of 1 to 2 cm per year** - Lulworth Cove (bay and Headland): sea broke through a narrow band of resistant limestone and eroded the softer clays and sands behind: **limestone slow at 1-2 cm - clay over 10cm a year** . - Old harrys rocks (stacks and stumps): **chalk: 10 to 30 cm per year** - Chesil Beach (Tombolo): shingle beach connecting the Isle of Portland to the mainland: **18 miles long, advancing at portland end by approx 15 cm year**

Question 32

Spit example

Answer 32

examples **Spurn Head, England** - sand and shingle with some boulder clay: extend southward approx **10cm a year**, sediment from Holderness cliffs which erode at **2.5 m a year.**

Question 33

isostatic changes

Answer 33

- **isostatic** changes occur when there is a **movement of the land** relative to the sea - **LOCALISED** change - downward movement of land = sea level rise locally, uplift of land = sea level fall Main causes: - **uplift/depression of Earth's crust** due to accumulation/melting of ice sheets , also caused by accumulation of sediment at mouths of major rivers - subsidence of land due to **shrinkage after abstraction** of water, e.g drainage of marshland - **tectonic processes**

Question 34

emergent coastline

Answer 34

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

Question 35

swash-aligned beach characteristics

Answer 35

- steep beach profile with steep storm beach, made of large pebbles - large ridges: **berms** may appear at the top of the beach

Question 36

factors affecting cliffs

Answer 36

Resistance: - less resistant at top = sub-aerial weathering and wave undercutting - less resistant at base = undercutting and collapse Dip of bedding places: Strata dipping inland = stable Strata dipping to sea = unstable Permeability: Impermeable over permeable = stable Permeable over impermeable = unstable (due to percolation)

Question 37

how are bevelled cliffs formed?

Answer 37

- vertical cliff formed due to marine processes during last interglacial period when sea levels higher - during subsequent glacial period (cold) sea levels dropped, and solifluction/freeze thaw weathering caused a **bevelled edge** to form - sea levels rose again, renewed wave erosion removed debris from base of the cliff

Question 38

cuspate foreland

Answer 38

two separate spits joining: e.g Dungeness near dover