3.a. emergent coastal landscapes form as sea level falls & 3.b. submergent coastal landscapes form as sea level rises Flashcards
What 2 major influences change the world sea level over time?
Eustatic and Isostatic
Is eustatic global or local?
Global
Is isostatic global or local?
Local
What is eustatic sea level change?
Eustatic is the worldwide changes in sea level caused by glacial and interglacial periods. During a glacial period, water is stored on land and sea levels fall. During inter-glacial periods (inbetween) sea levels rise as ice melts.
What factor causes eustatic sea level change?
-Decrease in global temperature leads to more precipitation occurring (snow)
-Snow turns to ice and water is then stored on the land rather than being returned to ocean store
-Leads to global fall in sea levels
What is isostatic sea level change?
Isostatic is the change in sea level caused by the crusts response to loading and unloading of ice. In the UK isostatic recovery is greatest over Scotland because that was where most of ice was.
What factor causes isostatic sea level change?
-Weight of ice sheets and glaciers add weight to earths crust
-Causes crust to sink lower into mantle
-Results in apparent sea level rise
-At end of glacial period, ice melts and weight is lost so crust slowly rises
What are the 4 physical factors that affect changes in global temperature and volume of water in oceans?
-Variations in earths orbit around sun
-Variations in amount of energy produced by sun
-Changes in composition of atmosphere due to major volcanic eruptions which reduce incident solar radiation
-Variations in the tilt of earths axis
What are emergent landforms?
-Emergent landforms are features of coastal erosion that appear to have developed well above current sea level
-They are shaped by wave processes during times of high sea level are left exposed when the sea level falls, they may be found well inland
What are the 3 examples of emergent landforms?
Raised beaches, Marine terraces and Abandoned cliffs
What are raised beaches?
Former shore platforms that are left at a higher level than present sea level
What are marine terraces?
Relatively flat, horizontal or gently inclined surface of marine origin that is now away from wave action. A terrace is originally a wave-cut platform formed by erosion and tend to be small and localised
What is an abandoned cliff?
Cliffs that are now beyond the reach of modern wave action. They are formed when sea level has dropped and it is common to find them with wave-cut notches, caves, arches and stacks.
How have these emergent landforms been modified?
-Emergent landforms continue to be modified by weathering and mass movement
-Cliff face was gradually degraded by frost weathering processes leading to rock fall
-Cryoturbation ocurred on main face of cliff, it is frost churning layers of regolith (loose layers of rocky material overlying bedrock) in periglacial environments
-In post-glacial period (11,700 to present day) warmer and wetter conditions have lead to development of vegetation cover
-If temperature rises in future, sea levels may rise enough that these coastlines are then subject to wave action
What are submergent landforms?
-Opposite of emergent landforms
-Form when eustatic rise in sea level takes place faster than isostaic rebound after an ice age
-The water starts to flood land and fills up landforms on land
What are the 3 examples of submergent landforms?
Rias, Fjords and Shingle beaches
What is a ria and how are they formed?
-A submerged river valley formed as the sea level begins to rise.
-As the sea level rise post a glacial period it will flood the floodplain and lower course of the river
-The upper/middle course and higher valley sides usually untouched -They have relatively shallow water becoming increasingly deeper nearer the centre
What is a fjord and how are they formed?
-Flooded coastal glacial valley which is steep almost like cliff valley sides with the water being uniformly deep often over 1000m.
-Formed during previous glaciated periods when the glaciers have retreated and the rising sea levels have filled the valley they left behind.
-Usually shallower near coastline because there was less erosion due to ice thinning in warmer conditions
What are shingle beaches and how are they formed?
-When sea levels falls, the volume of land-based ice grows
-Areas of ‘new’ land emerges from the sea
-Sediment accumulates on this surface deposited by rivers and low energy waves
-As sea levels rose at the end of the last glacial period, wave action pushed these sediments onshore
-They beach themselves at the base of cliff lines or form tombolos and bars.
Chesil Beach Tombolo - 100 million tonnes of shingle - sediment moved 50km before settling
What is a good example of a shingle beach?
-Chesil beach in Dorset
-Sediment accumulated in Lyme Bay and as sea levels rose, sediment was carried North-East because of prevailing winds
-It became attached to Isle of Portland and the mainland at other end due to longshore drift
How are Ria’s, Fjords and Shingle beaches affected by modification?
Ria’s - Wave processes acting on valley sides , operation of sub-aerial processes on valley sides.
Fjords - Wave processes acting on valley sides, operation of sub-aerial processes on valley sides may lead to reduction in steepness of fjord valley sides so sea levels predicted to rise 0.6m in 100 years causing fjords to deepen.
Shingle Beaches - continue to be effected by longshore drift as they are made of unconsolidated material which makes then vulnerable to modification so Chesil Beach and most other beaches may move north
