Coasts Flashcards
what instrument measures changes in sea level
tide gauge
how many people are predicted to be living within 10m elevation of the coast by 2060
over 1 bil people
how much faster is pop. growth in coastal zones in developing countries
3x world average
what region of europe was especially affected by isostasy following the last glaciation
north west europe- land rose relative to the sea (therefore sea level rise has less of an impact now)
4 scales of processes
instantaneous, event, engineering and geological
name 4 ways that energy dissipates at the coast
friction, heat, longshore transport or percolation
why are wide shallow bays dissipative coastlines
the wave breaking process is very drawn out and gradual so the energy is released more slowly
what does v coarse material at the top of the beach indicate
there are events strong enough to carry material all the way inshore (eg, rocky storm beaches)
how do we approach a study of changes at the coast?
segment the coast into chunks and see where the sediment is transported to
3 main anthropogenic coastal sediment controls
climate change, land use change, coastal management and flood protection
what occurs when there is a large amount of sediment in a delta
subsidence can occur, pulling the delta downwards relative to the sea level
how is climate change likely to influence storm events
more intense but less frequent
what percentage of the world’s beaches are eroding
over 30%
difference between sensitivity and resilience
sensitivity is how easily an ecosystem responds to a stimulus and resilience is its ability to bounce back
example of a low resilience low sensitivity ecosystem
hard rock cliff
example of a high sensitivity high resilience coast
beach with dune systems
example of a medium sensitivity high resilience coast
saltmarshes and mangroves
what do the spatial boundaries of the coastal zone represent
the elevational range over which processes have operated during the Quaternary period
examples of submerged coast
drowned river and glacial valleys
example of emerged coast
coastal plain
what is secondary coast
results from marine processes mostly: barrier coasts, coral reefs, mangroves
what is primary coast
result mostly from non-marine processes: drowned river valleys, rocky coasts, deltaic coasts
what are leading edge coasts
adjacent to subducting plate margins, eg. mountain belts with steep erosive rocky coastlines
what are trailing edge coasts
away from subducting plates, older, lower elevation, sediment rich
what major factor influences the global distribution of wave enviros
latitude according to wind patterns
is the tidal range larger at the coast or in the middle of the ocean
coasts
what factors influence tide amplification
gradient and width of continental shelf, location and shape of continents, presence of large embayments
name 3 main environmental conditions driving coastal systems
geology, unconsolidated sediments, external forcing
what source of sediment is most important at the coast
marine sources (rather than atmospheric or terrestrial)
what equation can be used to determine morphological change due to sediment build up or removal
sediment continuity equation
what is relaxation time
the time required to reach equilibrium after disturbance
do big complex systems have longer or shorter relaxation times
longer
what 3 factors impact relaxation time
energy level, sediment mobility and spatial scale
do higher energy systems have long or short relaxation periods
shorter relaxation time due to large sediment transport rates
under what conditions does coastal change take place most dramatically
higher energy conditions
how does relaxation time respond to decreasing sediment mobility?
increases (eg. hard rock cliffs take longer to relax)
what is self-organisation
feedback leads to internal changes in system dynamics that maintain the system in equilibrum
what does it mean that coastal evolution is cumulative
the morphological outputs form the inputs for the next cycle of change (preservation of past inheritance)
what is palimpsest
the sediments or landforms from one time period are preserved overprinted or destroyed by later conditions
by how much is global sea level rising each year
3.2mm
what can enhance resilience to sea level change
ecological buffers like coral reefs and salt marshes, morphological protection
why might salt marshes and tidal flats be able to keep up with rising sea level
they have high deposition rates
what do the gaps in a stratigraphic record indicate
erosion
what is significant wave height
average of the top 1/3 of waves
what is linear wave theory
estimating the behaviour of ocean waves- ratio of water depth to wavelength
3 wave regions
deep water, intermediate water and shallow water
what is the wave base
the point where wave motion ceases and cannot stir the bed sediment
what kind of water motion takes place in shallow water
horizontal movements
how does shoaling occur
waves start to feel the seabed and get steeper, becoming increasingly asymmetrical
wave divergence
waves propagate over a localised area of quite deep water, reduction in wave energy and height, and the spreading out of rays
water convergence
focusing of the wave rays together
3 main types of breakers
spilling, plunging and surging
what parameters can be used to predict breaker type
Iribarren number or surf similarity parameter
wave set-up
rise in mean level of water above the still water elevation of the sea
where do nearshore currents derive their energy
wave breaking
name 3 nearshore currents
longshore currents, bed return flow, rip currents
what intensifies longshore currents
alongshore winds
when are rip currents strongest
low tide
what 3 factors determine the extent of a storm surge
low pressure, onshore wind and coastal topography
what are amphidromes
tidal systems constrained by coastal topography- tide travels around centre as a wave
at what point of the amphidrome is the tidal range 0
the centre
what direction do the tides travel in a Northern hemisphere amphidrome
anticlockwise
where are the largest tidal ranges seen
complex coastal configurations like the irish sea
how does tidal range influence tidal current strength
strength increases with range
3 causes of tsunamis
submarine earthquake, large landslide into ocean, meteorite impact
where do tsunamis shoal
at the edge of the continental shelf
what is the shoreface
an underwater slope seaward of the beach, much larger than the beach area
what features can be found in wave dominated coastal enviros
barriers, beaches, coastal dunes
what feature is found in tide dominated coastal environments
estuaries
what main feature is found in fluvial dominated coastal enviros
deltas
4 types of barriers
swash-aligned, drift-aligned, transgressive and regressive
berms
accumulations of sediment at the top of the beach away from swash influence
beach cusps
rhythmic shoreline features from swash action
what occurs to the beach profile in calm conditions
onshore sediment transport in the nearshore zone to steepen the beach profile, bars can migrate on shore
what occurs to the beach profile during energetic conditions
offshore transport with prolonged high wave conditions- destruction of berm and formation of a flat beach
intermediate beaches
nearshore bar mophology = lots of dissipation due to wave breaking while upper part is quite steep and reflective
what is needed to form dunes
enough sand, energetic wind
what allows sand dunes to begin forming
tidal litter above spring high tide blocks wind and allows accumulation
foredune ridge
where shadow dunes coalesce
blow-outs
damage to veg causes saucer shaped depressions in dunes
when did estuaries begin to develop
when coastal and river valleys flooded at the end of the last ice age, then infilled after stabilisation of sea levels
3 zones in an estuary
inner zone- river dominated, central zone- mixed, outer zone- tidal domination
what accumulates in the centre of wave dominated estuaries
deep central mud basin
what shape ae tide-dominated estuaries
funnel shaped
what can be found in the centre of tidal estuaries
tidal flats and salt marshes
3 types of estuary based on mixing
stratified, partially mixed and well-mixed
tidal prism
the total volume of water entering an estuary on the flooding tide
delta plain
sedimentary platform that covers recent seaward advance
delta front
seaward front of delta in relatively shallow water
pro-delta
toe of delta in quite deep water
when might freshwater flow below seawater
high load makes it denser
delta switching
active region of coastal accumulation switches from 1 location on the delta to another
what factors impact rock breakdown processes
wave energy level climate and rock type
what percentage of the world’s coastlinea re cliffs
80%
angle of repose
the angle of the cliff profile
ICZM
integrated coastal zone management
4 principal management options
no active intervention, managed realignment, accommodation, hold the line
