coasts Flashcards
compare constructive and destructive waves in terms of physical appearance
constructive: larger wavelength and smaller amplitude
destructive: smaller wavelength and bigger amplitude
compare constructive and destructive waves in terms of swash and backwash
constructive: powerful swash, weak backwash
destructive: powerful backwash, weak swash
how and when do constructive waves form
formed by storms often hundreds of kilometres away
common in summer
how and when do destructive waves form
formed by local storms close to the coast
common in winter
what are the three types of weathering with basic descriptions
mechanical - disintegration of rock
chemical - chemical changes
biological - actions of flora and fauna
description of example of mechanical weathering
freeze thaw
water collects in cracks of rock and expands as it freezes. cracks and collects as scree at foot
description of example of chemical weathering
carbonation
rainwater is slightly acidic because it absorbs co2. contact with alkaline rocks e.g limestone causes slow dissolve
description of example of biological weathering
plant roots and animals burrow into weak rocks/sand
what is mass movement and three examples
downward movement of material under influence of gravity
sliding, slumping, rockfall
what is sliding
rock sliding down the slide plane of a cliff due to rainfall or an earthquake
what is slumping
collapse of saturated/weak rocks along curved slip plane (scarp) due to unstable base
what is rockfall
rocks falling down cliff face due to freeze thaw. collects as scree
what is hydraulic action
power of waves and air that gets trapped by them causes erosion
what is abrasion
sandpapering effect of rocks against rocky platform
what is attrition
rocks knocking against each other and becoming smaller/more rounded.
does not contribute to coastal erosion
what is solution (transportation)
dissolved chemicals from limestone or chalk
what is suspension
particles carried within water
what is traction
large pebbles rolled along sea bed
what is saltation
bouncing motion of particles too heavy to suspend
what geological structure is required for headlands and bays
discordant coastline: bands of stronger and weaker rock perpendicular from the coastline
how do headlands and bays form
on discordant coastline, weaker rock erodes faster (bay). sheltered and low energy waves - deposition.
harder rock sticks out (headland). high energy waves - wcn & no deposition
how do caves form and which erosion/weathering processes occur
weaknesses e.g faults or joints in cliff face start to erode.
ABRASION AND HYDRAULIC ACTION
how do arches form and which erosion/weathering processes occur
back to back caves connect
ABRASION AND HYDRAULIC ACTION
how do stacks form and which erosion/weathering processes occur
roof of arch is weakened and collapses
WEATHERING PROCESSES
how do stumps form and which erosion/weathering processes occur
wave cut notches form at bottom of stack and collapses
HYDRAULIC ACTION
how do faults form in cliffs
hydraulic action
what is a wave cut notch
hydraulic action and abrasion processes between the high and low wave zones erode the base. material removed by destructive waves. notch formed
why do cliffs retreat
once wcn become to large for the overhanging cliff to defy gravity, it falls onto the beach, aided by weathering.
processes repeats
what is a wave cut platform
former base of cliff is left. continuously smoothed by abrasion.
features of a sandy beach
shallow and flatter
low energy constructive waves
wider
sometimes dunes at back
strong swash
features of pebble beach
steep profile
destructive waves
not wide
larger pebbles at back
stronger backwash
why do beach profiles change
berms (ridges of sand caused by deposition in calm weather) are moved up beach by storms and spring tides.
in winter, berms dragged down beach, forming offshore bars, lowering beach.
how are dunes formed
• embryo dunes form around obstacles
• develop and stabilise by vegetation, eg marram grass, forms fore dunes
• rotting vegetation makes sand fertile and creates wider range of plants
• wind can form depressions called dune slacks, in which ponds form
how do spits form
- on coastlines with longshored drift, if coastline bends sharply, sediment continues to be pushed in same direction, out to sea
- changes in strong winds and waves can curve spit (recurved end)
- may be multiple from previous positions of spit
how do saltmarshes form
the area behind spit is sheltered. mud is deposited and causes vegetation. these are vital wildlife habitats
what is a bar
when spits grow across a bay.
freshwater lagoon trapped behind it
three advantages of sea walls
• very effectively deflects wave energy, preventing erosion & flooding
• provides promenade in seaside town
• long lasting
three disadvantages of sea walls
• unattractive and unnatural
• £5000 per metre and high maintenance
• restrict access to beach
four advantages of groynes
• wider beach - popular with tourists
• useful structures for fishers
• less expensive, 150 000 per 200m
• windbreakers
two disadvantages of groynes
• terminal groyne syndrome - interruption of longshore drift deprives beach further down - increasing erosion elsewhere
• unnatural & unattractive
three advantages of rock armour
• relatively cheap, £200 000 per 100m
• used for fishing
• provide services e.g climbing, sunbathing to beach
two disadvantages of rock armour
- expensive to transport rock
- rocks from elsewehere - doesn’t fit into local geology - obtrusive
three advantages of gabions
• cheap, £50 000 per 100
• can become vegetated and merge into landscape
• even if cages erode, rocks inside form makeshift body armour
three disadvantages of gabions
• rocks taken from elsewhere
• unnatural and unattractive when first built
• cages only last 5-10 years
what is beach nourishment/re profiling?
adding local sand or shingle to existing beach to heighten or widen it
two advantages of beach nourishment / re profiling
• increases tourist potential
• added shingle blends into beach
two disadvantages of beach nourishment/reprofiling
would not be effective on coastlines with longshort drift - hard engineering would be needed (groynes)
* 500 000 per 100m
what is dune regeneration
using dunes as buffers to sea, preserving them using marram grass and fences
two advantages of dune regeneration
- habitat to rare bird, reptile, and dragon/damsel fly species
- cheap 200-2000 per 100m of boardwalk
three disadvantages of dune regeneration
• time consuming to plant grass and boardwalks
• people do not always respond well to being prohibited from natural areas
• damaged by storms
what is dune fencing/conservation
planting fences to encourage dune formation and protect existing dunes
three advantages of dune fencing
• minimal impact on habitats
• restricted access preserves dunes
• cheap, 400-2000 per 100m
two disadvantages of dune fencing
damaged by storms - moudly & broken - unsightly
what is managed retreat
deliberately allowing sea to flood or erode area of low value land
three advantages if managed retreat
• more sustainable than spending money and effort on building and maintaining defences
• soft engineering
• important for future as seas rise
disadvantages of managed retreat/ do nothing
• people may be rehoused
what is no active intervention
no plans for defences
what is hold the line
maintain current defences
what is advance the line
increase defences to extend coastline
where is medmerry
south coast of uk
in west sussex
why was management needed in medmerry
• 300 homes, waterworks and roads
• constant heavy machinery work on beach
what were the objectives of medmerry
• create natural saltmarsh (natural buffer to sea)
• protect surrounding farmland and caravan parks from flooding
• create intertidal wildlife habitat and encourage visitors to sea o
description of scheme and things needed for medmerry
• 7 km of banks
• 450 000 tonnes of clay
• 60 000 tonnes or rock, just to barricade ends
• ditches created to encourage ponds
6 advantages of medmerry
• leisure
• habitats
• natural buffer for erosion
• protects local towns & industry
• investment: no maintaining defences
• salt in wanter gives grazing cows desirable taste
3 disadvantages of medmerry
• 28 million
• loss of farmland
• hard engineering still required
where is lyme regis
small coastal town, south coast of england
reasons for management in lyme regis
• built on unstable cliffs
• fastest eroding cliffs in all if europe
• sea wall breached many times, damaging property
aims of management in lyne regis
• long term protection
• no controversy as public informed and meetings held
phase 1 and 2: 4 key features of lyme regis scheme
• new sea walls and promenades
• rock armour extended
• sand dredged from english channel for nourishment
• £1.4 million for cliff stabilisation: hundred of nails hold rocks tg
phase 4 lyme regis
• 340m sea wall in front of existing wall
• further cliff stabilisation to protect 480 homes
phase 3 lyme regis
proposed to prevent landslips
costs outweighed benefits
3 advantages of lyme regis scheme
• new beaches = tourism
• new defences have withstood recent stormy winters
• harbour protected, benefitting fishermen and boat owners
2 disadvantages of lyme regis scheme
• tourism led to litter and congestion
• natural landscape spoiled
2 disadvantages of lyme regis scheme
• tourism led to litter and congestion
• natural landscape spoiled
