COASTS PT.2 (climate + humans) Flashcards
what is a eustatic change?
A change in volume of water in global ocean stores
what are eustatic changes influenced by?
Variation and mean global temperatures affecting amounts of water in ocean stores and its density
what two things change sea levels?
-Land level
-Temperature
what is isostatic?
When sea level changes is affected by land levels
What four physical factors affect volume of ocean water
- eccentricity.(400,000 years.)
- Variation and amount of energy from sun (solar maximum every 11 years)
- Changes in earths atmospheric composition due to major volcanic eruptions, which reduce solar radiation.
- Variation in tilt of us axis (obliquity)(41,000y)
why do sea levels fall?
-Decrease in global temps= more precipitation form of snow which turns to ice so water is stored on land
-Results in a reduction of water volume in ocean stores so sea levels fall
what happens as temperature fall to water
water molecules contract leading to increased density and a reduced volume of water
-Estimated 1° C fall in global temps= sea levels fall 2 m
when did sea levels rise(period)
-130,000 years ago during the tyrrhenian inter glacial global temperatures were 3° C higher than today’s and sea levels were 20 m above today’s
when did sea levels fall? (period)
-during the riss glacial 108,000 years ago, temperatures were 7° below today and sea levels dropped by over 100 m which is 83 m below today
what are emergent landforms?
They’re shaped by wave processes during times of high sea level and are left exposed as a seafood. As a result they are found well in land.
what are three examples of emergent landforms
-Raised beaches
-Marine terraces
-Abandoned cliffs
what are raised beaches?
Areas of former Shaw platforms that are left at a higher level than the present sea level. They are found in land far from the current coastline.
How are raised beaches formed?
At the highest sea level waves pound against the cliff edge and create a normal beach below when the sea drops the original beach is left high and dry, and the new lower beach is formed
Where are abandoned cliffs found?
Behind beaches on emergent coastlines
what are abandoned cliffs often found with?
-wave cut notches
-caves
-arches
-stacks
what are marine terraces?
Largest scale landscape features
how are marine terraces formed?
The same as a raised beach, so marine erosion during periods of high sea level
what can be found on the southern tip of Isle of Portland? (how long ago was it formed and how)
Raised beach, 15 m above the current sea level
-was formed 125,000 years ago during tyrrhenian interglacial period
-Portland limestone, eroded by hydraulic action through exploitation of the bedding planes weaknesses
-Erosion rates at this time=1m/year
What happens to landforms after they emerge?
They are no longer affected by wave processes, and now affected by mass movement and weathering
what is cryoturbation
Evidence of contortions and fragmented limestone as a result of freeze thawing of permafrost
what happens to the emergent landforms if there is further warming
-Predicted, continued degradation with chemical weathering, and biological weathering on raised beach becomes more significant with the colonisation of surface by increasing numbers of marine of organisms, such as an limpets
What would be the effect of rising sea levels to emerging landforms?
Would lead to these emergent landforms being found much closer to the coastline, where they are subject to more wave processes
what is modification of emergent landforms PSD?
-on top of abandoned cliff on Isle of Portland is a 1-1.5m layer of frost shattered limestone debris deposited when it experienced periglacial conditions during the last glacial period
what is a submergent landform?
Where coastline is submerged and landforms shaped by rises in sea levels
what are two submergent landforms
-rias
-fjords
what are rias?
Submerged River valleys formed a sea level rises
what parts of rivers course remain exposed on rias
-valley sides
-middle
-upper part
what’s the shape of a ria
exposed valley sides are gently sloping
-Plainview= winding, and reflecting the original route of the rivers and its valley
what is a ria formed by?
fluvial erosion within the channel and sub aerial processes on Valley sides
what are rias typically underlain by and what happened when sea levels rose
Alluvial deposits in channels that were eroded by rivers that flowed down low sea levels of pleistocene glacial periods
-When sea levels rose, further deposition would ever occurred, as rivers, had less surplus energy for erosion.
What are fjords?
Submerged, glacial valleys that have steep cliff like valley sides
what is the water depth of a fjord?
water is uniformly deep often reaching over 1000 m
two examples of PSD for fjords
-sogne fjord - Norway = 200 km long
-Milford sound-New Zealand
what reflects the original shape of the glacial valley on a fjord?
the U-shaped cross-section
what features does a fjord have
-glacial rock basin with a shallow section at end, known as a threshold which results in lower rates of erosion at sea ward end of valley, where ice thinned in warmer conditions
why are fjords straighter than rias?
They have straight planforms as glacier would have truncated any interlocking spurs present
why did Marine erosion rates remain high in fjords
-due to depth of water that occupied fjords in flandrian transgression
PSD- a fjord that has been infilling
-south coast of new zealand have been infilling with sediment
Why do you sea levels rise?
an increase in global temperatures= Higher rates of melting ice stored on land, or in ice sheets, caps or valley glaciers
-So there’s a global increase in volume of water in the oceans, causing sea levels to rise
-Temperature rise, causes water, molecules to expand so increase volume of water in oceans
what were the conditions during the würm period and what was this period called
-9° C lower than today
-Sea levels = 90 m lower than today
-flandrian transgression= sea level rise from 25,000 years ago during the würm glacial period
how are shingle beaches formed?
-When sea level fall areas of new land emerge
-Sediment accumulates on this surface deposited by rivers, melt water streams and low energy waves
-As sea levels rose at end of last ice age wave action pushed sediment on shore
-some places sediment was beached at the base of cliffs elsewhere. They formed Tombolos or bars.
PSD of shingle beaches
-Tombolo at Chesil Beach
-Thought to informed during flandrian transgression
-lyme Bay beach contains hundred million tons of shingle varying from 1-2 cm to 5-7 cm.
what modification will happen to rias in the future?
-modified by wave processes, acting on sides at present day sea level
-Also affected by sub aerial processes
-Water depth will increase
-Increase in marine erosion due to more storm action
how will fjords be modified in the future?
-Modified by wave processes, acting on sides at present day sea level
-Also affected by sub aerial processes, which will eventually lead to a reduction in steepness of the valley side
-Water depth will increase
-Increase in marine erosion due to more storm action
how will shingle beaches be modified in the future? PSD
as they are made of loose material, they are vulnerable to modifications
-PSD- Chesil Beach Tombolo is affected by longshore drift and is likely to be affected in the future
-With sea levels, rising shingle may be moved further north east, with a current rate of 17 cm per year
-Breach of Tombolo is likely storm events
-In 2009, 1 m sizes of Shelly clay were eroded from in front of the beach and washed up onto the west bexington in a winter storm. sediment addition will become more common in the future with high sea levels and more storms 
what is hard engineering?
Working against natural systems and processes
what is soft engineering?
Working with natural systems and processes
what are hard engineering management strategies?
CLIFF FOOT + BEACH STRATEGIES
-offshore breakwaters
-Embankments
-gabions
-revetments
-rip rap
-sea walls
CLIFF FACE STRATEGIES
-cliff drainage
-Cliff fixing
-Cliff regrading
What is soft engineering beach management strategies?
-Beach nourishment
-Beach reprofiling
-Dune regeneration
-Vegetation planting
-Encouraging natural defences(reefs/mangroves)
-Offshore reefs
how does a seawall work?
As a layer between vulnerable coastline and ocean
-It reflects energy back to sea
-Helps insulate communities from flooding. However, high waves can still breach the seawall.
-Several lower barriers may be used to help break up wave energy before the waves hit the wall
-The wall will eventually breakdown and require repair
