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Coasts - Coggle Diagram
Coasts
Lessons 3 and 4
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Small Scale
geological structure of the rock includes:
- strata = layers of rock
- bedding planes = horizontal cracks
- joints = vertical cracks
- folds = formed by pressure during tectonic activity causing the rocks to buckle and crumple
- faults = formed when the stress/pressure to which a rock is subjected, exceeds its internal strength causing it to fracture
- dip = the angle at which rock strata lie
Joints:
- wave erosion - exploits lines of weakness
- mechanical erosion - weathering can further exploit joints
Dip of the Strata
horizontally bedded strata:
- undercutting wave action leads to the development of wave-cut platforms and notches
- main form of mass movement = rock fall
- leads to vertical profile
- cliff retreats parallel to the coast
seaward-dripping strata:
- cliff face slopes to the sea
- large loosened rock slide off easily along bedding planes
- sub-aerial processes have a greater influence than marine
- leads to steep, shelving cliffs
landward-dripping strata:
- loosened rocks from weathering and wave action are hard to dislodge
- the slope profile gradually lowers by weathering and mass movement
- cliff is rugged and uneven
Large Scale
Discordant coastlines: coasts where the cliffs are structured so that the geology alternates between bands of more-resistant and less-resistant rock at right angles to the coast
- resistant rock is harder/slower to erode meaning that headlands are formed
- less resistant rock is easier/quicker to erode meaning that bays are formed
Concordant Coastlines: coastlines where the cliffs are structured so that the geology alternates between bands of more-resistant and less-resistant rock parallel to the coast
- bands of resistant rock on the coastline which is eroded forms steep cliffs
- when resistant rocks are eventually eroded, the sea can break through to the less resistant rocks behind, resulting in quicker erosion
Types of concordant coastlines:
Dalmatian coasts:
- limestone cost has been folded by the collision of tectonic plates into a series of anticlines (folded ridges) and synclines (folded down valleys) parallel to the coast.
- as sea level rose, the synclines were flooded, leaving the anticlynes projecting and a coastline of long, narrow islands
Haff coasts:
- form in low energy environments where there is deposition of muds and sands in unconsolidated structures parallel to the coastline
- long ridges of sediment topped by sand dunes run parallel to the coast, creating lagoons between the ridges and shoreline
Lessons 1 and 2
Transportation
- traction = large materials such as boulders are rolled along the sea bed (because they are heavy, the waves do not have the energy to carry them)
- saltation = pebbles or small stones are lifted by the sea when it has enough energy, but dropped when it loses energy. As a resul, pebbles are bounced along the sea bed
- suspension = smaller particles such as sand float in the sea
- solution = particles such as clay are dissolved in the sea, and constantly moves with the water
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Deposition
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Flocculation: clay particles clump together due to chemical attraction, gain mass then sink due to their high density
Sub-Aerial processes
land based processes which alter the shape of the coastline. a combination of mass movement and weathering
- mechanical weathering - freeze-thaw weathering and salt cracking
- biological weathering - tree roots and burrowing animals/birds
- chemical weathering - acid in rainwater and seawater erodes the rocks/cliffs
Mass Movement
Slumping: slumps occur on weak, unconsolidated cliffs such as clay
weak cliffs are eroded quickly at the base - destabalising the cliff
rainwater enters the cliff, increasing the weight of the soil and lubricating the slip plane
the material then slides down the slip plane
rock fall/block fall: erosion at the base of the cliff creates an overhang. doesn't happen on unconsolidated cliff
well jointed rocks allow mechanical weathering to exploit the cracks and joints
eventually rock fragments fall from the cliff due to gravity