Physical Geography Coasts Notes AS Level

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  • Created on: 24-05-13 09:54
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Physical Geography Notes: Coasts
Factors affecting the rate of erosion
Breaking point of the wave: a wave which breaks as it hits foot of the cliff releases more energy
Wave Steepness: steep destructive waves have more erosive power
Amount of beach material: protects the coast by absorbing wave energy
Rock Type: igneous rocks less likely to erode than sedimentary
Fetch of the sea: the longer the fetch the greater the time available for walks to collect energy
from the wind
Coastal Processes
Longshore Drift
When waves approach the shore at an angle, material is pushed up the beach by the swash in the
same direction as the wind. As the water runs back down the beach, the backwash drags material
back at right angles to the beach. Over time, sediment moves in a zig-zag pattern across the beach.
Waves are created by the transfer of energy from the wind blowing over the surface of the sea. As
the strength of the wind increases so too does the frictional drag and the size of the waves. The
energy of the waves is determined by:
Wind velocity
Waves from local winds = SEA (steeper, shorter and high energy)
Waves from large distances = SWELL (less steep, longer and low energy)
Constructive Waves
Constructive waves tend to be:
Long wavelength
Low frequency
Weak backwash as water percolates into the sand
Material is moved up the beach to create berms

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Destructive Waves
Destructive waves are:
High waves with a steep form
High frequency
Have a powerful backwash as they rapidly steepen then plunge down
Erodes a beach as it pulls material away
The force of the wave may create a storm beach
Sediment Cells
Sediment movements occur in distinct areas or cells. They are distinct areas of coastline separated
from other areas or cells by well-defined boundaries.…read more

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Beaches are formed from sand and shingle and represent the accumulation of material deposited
between low spring tides and the highest point reached by storm waves. They are divided into three
sections: backshore (upper), foreshore (lower) and nearshore (based upon the influence of waves).
Sand produces beaches with a gentle gradient as the small particle size, means the sand becomes
compact when wet, and allows little percolation. Most of the swash is returned as backwash and
material is carried down the beach.…read more

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Berms are a series of ridges marking the high tide mark as the cycle goes from spring to neap tides.
Cusps are semi-circular shaped depressions which form when waves break directly on to the beach
and the swash and backwash are strong. Below this, ripples are developed on the sand by wave
action or tidal currents.
Dunes grow when sand is deposited on the beach by longshore drift and are built up by the wind.
Foreshore: where sand accumulates on the beach.…read more

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Wave Terminology
Wave Refraction
When waves approach a coastline that is not as regular shape, they are refracted. As each wave
nears the coast, it tends to drag in the shallow water which meets the headland. This causes the
wave to become higher and steeper with a shorter wavelength. That part of the wave in deeper
water moves forward faster, causing the wave to bend. The overall effect is that wave energy
becomes concentrated on the headland, causing erosion.…read more

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A bar is formed as a spit grows across a bay, joining two headlands
A tombolo is where a spit grows out from the mainland and joins onto an island.
Landforms from Erosion
Headland and Bays
Headlands and bays occur when the sea erodes the soft, less resistant band of rock and doesn't
erode the harder, more resistant band of rock. This leaves the hard rock jutting out into the sea
whilst the soft rock has been eroded away inland.…read more

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Wave Cut Notch
A wave cut notch is created when the power of the sea erodes the bottom of the cliff, leaving part
of the cliff `top heavy' and liable to fall into the sea as it's unstable due to insufficient support. A
wave cut platform is when the cliff eventually collapses and flat surface is left.
Crack, Cave, Arch, Stack, Stump Formation
Hydraulic action and abrasion wear down the cliff and crack is formed. The erosion continues to form
a cave.…read more

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Defence Cost Disadvantages
Sea wall Expensive to build and maintain Strong backwash erodes under
the wall
Wave ramps/revetments Expensive to build but cheap to Strong backwash
Rip Rap Fairly cheap Can shift in storms
Embankments Quite expensive Can be eroded
Groynes Quite cheap Starve beaches further down
the coastline of sediment
Soft Engineering
Sand Dunes
Sand dunes are areas of land which have been replenished with sand and then vegetation has been
planted on top. This is a cheap process which is environmentally friendly.…read more

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Relict Cliff: a sea cliff which is further inland
Submergent Coastline Features
They can form when sea level rises or the land sinks,
usually coastlines are irregular.
Rias: a deep sunken river valley (flooded v-shaped valley)
Fjords: invasion by sea of a u-shaped valley (flooded glacial u-shaped valley)
Fjards: drowned glacial lowlands.…read more

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Barrier Beaches as sea level rises, the beach is left out at sea as the land behind it gets flooded
Dalmatian Coasts: where the sea level has risen and what was higher land before are now left as
islands which are just off the mainland…read more


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