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How do coastal landforms evolve over time as climate changes (Climate…
How do coastal landforms evolve over time as climate changes
changes in the vol of water in global ocean store known as eustatic changes
these changes are influenced by variations in mean global temps
affecting both amount of water in ocean store + its density
However, it should be appreciated that sea level change is relative as it is also affected by changes in land level
these changes known as as isostatic are not considered here
no. of physical factors that can affect changes in global temp and vol of water in oceans
Variations in the Earth's orbit around the Sun, typically every 400,000 yrs.
Variations in amount of energy produced by the Sun, with a solar maximum ebery 11 yrs. or so
Changed in the composition of the atmo due to major volcanic eruption which reduce incident solar radiation
Variations in the tilt of the Earth's axis, occuring every 41,000 yrs.
Climate change and sea level fall
decrease in global temp leads to more precip being in form of snow
Eventually this snow turns to ice
so water is stored on land in solid form rather that being returned to ocean store as liquid
result is a reduction in the vol of water in ocean store an a worldwide fall in sea level
As temps fall water molecules contract, leading to an increased density and a reduced vol
estimated that a 1 degree fall in mean global temp causes sea level to fall aprox 2 m
About 130,000 yrs. ago global mean annual temp were almost 3 C higher than today
sea levels was about 20m above today's position
Temps then fell reaching a min of about 7C lower than tday (108,000 yrs. ago)
As a result less water was returned to the ocean store and sea levels dropped by over 100m- 83m lower than today
Emergent landforms
landforms shaped by wave processes during times of high sea level left exposed when sea levels fall
As a result they may be found well inland
Raised beaches
are areas of former shore platforms that are left at a higher level than present sea levels
often found a distance inland from the present coastline
behind beach not uncommon to find abandoned cliffs with wave cut notches etc.
E.g.
On southern tip of the Isle of Portland near Weymouth on Dorset is a distinct raised beach
height of about 15m above present sea level
though to have formed around 125,000 yrs ago
Portland limestone was eroded by hydraulic wave action- partly thro the exploitation of the bedding plane weakness
Erosion rates at that time estimated to have been as muh as 1 m/per yr.
Other raised beaches at Portland are thought to date to about 210,000 yrs. ago
Wave-cut notch platforms
narrow flat area often found at the base of a sea cliff or along the shoreline of sea that was created by erosion
most obvious at low tide when they become visible as huge areas of flat rock
Modification of landform
after emergance landforms no longer affected by wave process
However they continue to be affected by weather + mass movement