Coasts 🌊 Flashcards
outline a coastal system
open system
inputs - sediment and energy
outputs - sediment washed to sea or another cell
stores - landforms
flows - wind and water transport
inputs in a costal system
sediment
- rivers
- cliff erosion
- longshore drift
- wind
energy
- wind
- waves
- currents
- tides
outputs in a coastal system
sediment
- washed out to sea, deposited further along shore
flows and transfers in a coastal system
erosion
transportation
deposition
wind
LSD
weathering
stores in a coastal system
landforms
- beaches, dunes, spits
negative feedback in coastal system
- beach eroded
- cliffs exposed to wave attack
- sediment eroded
- eroded sediment deposited on beach
- beach grows again
or
- cliff being eroded
- leads to mass movement
- collects at bottom of cliff
- protect base from wave energy
- reduced erosion
or
- cliff eroded
- wave cut platform created
- cliff retreats
- eventually out of reach of waves
- reduced erosion
positive feedback in a coastal system
- beach forms
- slows down waves
- more sediment is deposited (not enough energy)
- beach grows more
sources of energy
- wind
- waves
- tides
- currents
wind
air moving from high to low pressure
responsible for waves and some currents
prevailing wind (consistantly same direction) creates higher energy waves
(than changing winds)
role of wind
source of energy
creates waves and currents
can transport material
agent in erosion - abrasion
waves
created by friction as wind blows over surface of sea
creates circular motion
wave height depends of wind speech and fetch
what is wave refraction?
where waves bend as they approach an indented coastline
- eg a headland
waves approaching headland reach shallower water before waves approaching bay
wave energy becomes concentrated around the headland
waves in bay spread out - less frequent
results in energy concentrated around headland, creates erosional landforms
and constructive impacts in bays, beaches
why do waves break
break as they get close to shore
friction with seabed slows down bottom of waves
motion becomes more elliptical
crest rises and collapses
constructive waves
low frequency
- 6-8 per minutes
long wavelength
low wave height
powerful swash and weak backwash
deposition
destructive waves
higher frequency
10-14 per minute
short wavelength
high and steep height
strong backwash weak swash
erosion
factors affecting wave energy
wind:
- strength
- duration
- fetch (distance)
tides
periodic rise and fall of ocean surface
due to gravitational pull of sun and moon
affects position waves break on beach
high tidal range = energy less concentrated, position wave break varies
low tide range = energy more concentrated on certain areas
NOT caused by wind
spring tides
highest tides
sun and moon in line with earth - stronger gravitational pull
neap tides
lower tides
sun and moon at right angles to earth - weaker pull
currents
general flow of water in one direction
caused by WIND, change in water temperature or salinity
move material along coast
- localised
sources of energy importance
wind most important
creates waves and currents
- localised impacts
tides not generated by wind
- global impacts
low energy coasts
low inputs of energy
small, gentle waves
- light winds (sheltered area)
- short fetch
rate of deposition higher than erosion
creates salt marshes and mudflats
high energy coasts
high inputs of energy
large, powerful waves
- strong winds
- long fetches
rate of erosion higher than deposition
creates rocky landforms, caves, arches etc
sources of sediment (inputs)
- rivers
- cliff erosion
- longshore drift
- wind
sediment budgets
the balance between inputs and outputs of sediment in a system
(difference between them)
can be positive (more enters, beach builds)
or negative (more leaves, beach retreats)
when balanced = dynamic equilibirum
disturbed by climate change and human intervention
sediment cells
lengths of coastline (between 2 headlands or estuaries) that are closed coastal systems
Mostly self contained movements of sediment
(Sediment may move in strong waves)
how does climate change impact sediment cells?
rising sea levels and more frequent storms = more erosion
more inputs of sediment
glacial melt = more inputs
how does traditional management impact sediment cells?
hard engineering prevent natural processes of erosion
reduce outputs of sediment - traps it to build up beaches
therefore reduces inputs of sediment down coast
eg groynes in Happisburgh
how do SMPs impact sediment cells?
focus on individual cells
however advance and hold the line can impact inputs and outputs
managed retreat and do noting can restore dynamic equilibrium
processes of erosion
corrasion
solution
hydraulic action
cavitation
attrition
wave quarrying
corrasion
sediment transported by waves thrown against cliffs
smash and rind against rock
solution
soluble rocks get dissolved in seawater
eg limestone
hydraulic action
air in cracks in cliffs compressed by waves crashing
pressure caused bits to break off, crack widens
cavitation
waves receed, compressed air expands violently
creates pressure
bits break off, crack widens
attrition
rock and sediment in water smash against each other
make smaller particles
wave quarrying
energy of wave breaking on cliff
breaks bits off
how does lithology affect cliff erosion?
seaward dipping bedding planes
- means loose material can slide down the bedding planes
= less stable so more vulnerable
landward dipping bedding planes
= relatively steep and stable, less vulnerable
transportation
solution
saltation
traction
suspension
solution
substances are dissolved and carried in water
eg limestone
suspension
very fine material carried along in water (above seabed)
eg silt and clay
saltation
larger particles (can’t be suspended) bounce along seabed by force of water
eg pebbles and gravel
traction
very large particles pushed along seabed (rolled) by force of water
eg boulders
what is deposition
when material being transported is dropped on the coast
causes of deposition
happens when sediment load exceed the ability of the water to carry it
due to
sediment load increases eg landslide
water loses energy
- friction increases, shallow water, slows
- conflicting currents, slows
sub aerial weathering
gradual breakdown of rocks in situ
weakens cliffs, more vulnerable to erosion
- chemical
- biological
- mechanical. freeze thaw, wetting and drying
chemical weathering
breakdown of rocks by changing its chemical composition
carbonation
- carbon dioxide dissolves in rain to form acid rain
- dissolves rocks containing calcium carbonate eg limestone
solution
- dissolved
oxidation - iron minerals in rock react with oxygen and rust = breakdown
biological weathering
plant roots growing into cracks, widens
animals building burrows
mechanical weathering
freeze thaw
- happens where temperatures fluctuate around 0
- water enters cracks
- freezes as it expands
- overtime, weakens and breaks off
wetting and drying
- rocks that contain clay
- gets wet, expands
- creates pressure causing bits to break off
Salt crystallisation
- water collects in cracks
- sun causes water to evaporate, leaves crystals
- salt crystals bigger and grow = pressure in cracks so break up
what is mass movement?
movement of material downhill due to gravity
unconsolidated rocks prone to collapse, less friction to hold together
heavy rainfall saturates rocks, reduces friction
runoff can also move fine sediment
- creep
- slide
- slump
- rockfall
- mudflow
creep
soil particles get wet
less friction
slowly move downslope
landslide
happens when wet, less friction
downhill movement of material ‘en masse’
moves rapidly
slump
softer material overlies more resistant
material moves downhill
creates a curved indented surface
rockfall
rocks on a vertical cliff face
mechanical weathering, weaken and dislodge rocks
large parts breaks off and collect at bottom as scree
mudflow
mud on a hill slope
rainfall saturated soil, increases pressure and particles heavier
sediment flows downhill
longshore drift
moves sediment along shore
- swash carries sediment up beach at similar angle to prevailing wind
- backwash moves sediment back down beach at right angles to shoreline
= zig zag movement
marine processes
transportation
Erosion
Deposition
sub aerial processes
weathering
mass movement
eustatic sea level change
rise or fall in sea level
caused by a change in the volume of water in ocean basin
- global effects
causes of eustatic sea level change
climate change/ice melt
- increase in temperature
- ice sheets melt
- increases volume - levels rise
- decrease in temperature
- more precipitation falls as snow
- increased storage in cryosphere
- decreased volume - levels fall
thermal expansion of water
- warmer water expands - levels rise
tectonic movements
- alters shape of basin
- mid ocean ridges, new land formed
- displaces water - levels rise
isostatic sea level change
rise or fall in sea level
caused by vertical movements of the land relative to the sea
- effects are local
causes of isostatic sea level change
glaciation causing depression of crust
- weight of glaciers and ice presses down crust into asthenosphere - levels rise
post glacial readjustment
- uplift of earths crust as glaciers melt, asthenosphere rebounds - levels fall
tectonic activity
- causes land to move up or down
coastline of emergence
when sea levels fall relative to coast = emergent landforms
raised beaches - beach above high tide mark, over time become vegetated
marine platforms - exposed wave cut platforms
relict cliffs - cliffs above raised beaches, no longer eroded by sea, exposed to weathering
coastline of submergence
when sea levels rise relative to coast = submergent landform
rias
fjords
Dalmation Coastine
formation of a ria
river valleys are partially submerged
wide and deep at mouth, shallower inand
much wider than natural river mouth
eg Exemouth, River Exe
formation of a fjord
drowned glacial valleys
eroded by glaciers in glacial times
straight and narrow with steep sides
very deep
eg Sognefjorden, Norway
formation of a Dalmatian Coastline
islands parallel to coastline
caused by flooded valleys lying parallel to coast
ridges at different heights, lower areas flooded and higher left exposed
eg Dalmatian Coast, Croatia
sea levels over 10,000 years
glacial period, max 18,000 ya
- more water stored in cryosphere
- sea levels lower
temperature increased, started 12,000 ya
- ice melted
- sea levels rose to current
about 130m higher now
since 1930, levels rising more
- climate change
impacts of climate change on sea levels
global warming - human activities, more greenhouse gases
increased temperature
- more thermal expansion
- more ice melt
(eustatic)
impacts of climate change on coastal areas
warmer tempertures = more frequent and intense storms
- damage to coastal ecosystems and settlements
rising SLs = more frequent and severe flooding
- contamination of bodies of freshwater
- damage to settlements
- salinisation of soils, crop damage
submergence of low lying islands
how does feedback help with management?
ICZM aims to restore equilibrium
climate change = + feedback
needs to be managed
chi squared
if critical smaller than calculated
= null rejected
(there is a significant difference)
if calculated smaller
= null excepted
(no significant difference)
impacts of geology on coastal processes
erosion
- hard rock (granite) more resistant than soft
= discordant coastlines
weathering
- softer rock/ certain types more vulnerable to weathering
- eg limestone and chemical
mass movement
- soft = more unconsolidated so more saturated when it rains
= heavier so mass movement more likely
transportation
- more sediment to move
deposition
- more sediment = increased load
= more deposition
- scree at base of cliffs slows erosion to create deposition
impacts of energy on coastal processes
erosion
- high energy = more erosion as creates destructive waves
- compared to more deposition at low energy
weathering
- more erosion = more cracks so more vulnerable to weathering
mass movement
- high energy = more vulnerable as material losened by erosion and weathering
transportation
- high energy = more movement of sediment
deposition
- high energy = less deposition, strong backwash
- low energy = more deposition as less energy to carry
impacts of management on coastal processes
erosion
- absorbs wave energy to reduce rates
- can increase rates down coast
weathering
- protected from mechanical
- but exposed to chemical and biological
mass movement
- cliffs more stable as eroded less, reduced risk
- but still vulnerable after heavy rainfall, saturation
transportation
- groynes reduce movement by offshore drift
deposition
- some forms encourage deposition to protect cliffs and absorb energy
- eg beach nourishment
impacts of erosion on coastal processes
weathering
- creates cracks so more vulnerable
mass movement
- weakens and loosens material
transportation
- creates more sediment to move
depostion
- more sediment removed by destructive waves
impacts of weathering on coastal processes
erosion
- more weathering = weaker and unconsolidated rocks = more vulnerable
mass movement
- less consolidated = more likely
- means water can infiltrate
transportation
- create more lose material to be transported
deposition
- material collects at base of cliffs, slows waves = deposition
