Geography Paper 1 Section C Coasts and Rivers

How are waves caused?

By transfer of energy from the wind to the sea due to friction.

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Speed of the wind:

Stronger winds = stronger waves because more energy is transferred.

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Constructive waves

Have a wave height under 1 meter; are less frequent with less than 10 waves per minute; the swash is stronger than the backwash; this means that constructive waves build up beaches

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Destructive waves

Have a wave height over 1 metre, they are more frequent with more than 15 waves per minute, the backwash is stronger than the swash; this means that they move beach material back into the sea, therefore are capable of destroying beaches in the winter

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Mechanical weathering (physical weathering)

Causes rocks to be disintergrated and usually happens due to extreme weather changes.

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Freeze-thaw weathering

Water enters a crack in a rock, the water freezes at night which increases its volume by 9%, then in the daytime if the temp is above freezing then the ice thaws. This leads to repetitive weathering of the rock.

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Chemical weathering - Hydrolysis

When acidic rainwater breaks down the rock, causing it to rot

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Biological weathering

Animals burrowing into rock or plants growing through cracks, this can break rocks apart.

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Rockfalls

The rock breaks away from the cliff face, often due to freeze-thaw weathering. The rocks lose contact with the cliff face and form a scree slope at the base of the cliff

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Sliding

This is when blocks of rock / mud slide downhill. They maintain contact with the cliff, but slide down it. At the base of the mudslide the saturate soil spreads into a lobe.

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Slumping

This is when material is rotated as it slips downhill, the saturated soil and weak rocks move along a curved surface; the leading edge of the slump is called the toe.

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Hydraulic Action

Due to the sheer power in (destructive) waves, they hit against the cliffs and erode them. This causes repeated changes in pressure as their power forces water (h.p. air) into the cracks, when the wave retreats, the pressure is released-explosive ef.

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Abrasion / Corrasion

When rocks smash and collide into each other. Destructive waves have enough power to carry rocks and sand in them, being hurled at the cliff with the waves, scratching and scraping the rock surface. Can happen a lot in high-energy storm conditions.

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Attrition

When sand and pebbles within the water collide with each other They break apart and become smaller and more rounded.

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Longshore drift

Movement of sediment across the coast

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Headlands and bays

Created when there is a discordant coastline, they bay being eroded quicker than the headlands because they are made of softer rock, e.g. clay.

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Discordant coastlines

Alternating layers of hard and soft rock which run at right angles to the shore.

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Wave cut platform

An area of bedrock visible at the base of some cliffs. Slopes into the sea at a very gentle angle, and is generally only visible at low tide. Hydraulic action and abrasion erode the base of the cliff as they slope down into the sea broken off by fr-t

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Notch and overhang

When the cliff is eroded at the base and the rock breaks away, collected at the base of the cliff. This creates a notch with an overhang, which over time becomes bigger, unsupported and is likely to fall.

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Caves, Arches, Stacks and Stumps

As the headland is reshaped by destructive waves and wave refraction features such as caves, arches and stacks appear.

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Sandy beaches

They have a gentle, flat gradient and are usually wider beaches due to the constructive waves that shape them. The sediment is small (e.g. grains of sand) so even the weak backwash can move them back down the beach.

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Shingle / Pebble beaches

Steep gradient; usually narrow due to destructive waves that shape them, sediment is too heavy to carry, creates a steep slope.

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Berms

Sandy riges towards the back of the beach where waves stop and deposit the material before returning to sea.

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Storm Ridges

In winter, waves can be more destructive and push larger material (shingle and pebble) past the berm to create larger ridges. Then, as the waves leave the beach, they still have a strong backwash so they transport material off beach onto sea bed.

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Offshore bar

If these conditions remain then this can build and build to create a ridge of sand and pebbles found a short way out to sea.

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Sand dunes - what they need to form

To form, needs a large flat beach, large supply of sand and a large tidal range - time for sand to dry, onshore wind to move the sand to the back of the beach and an obstacle for the dune to form against.

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Sand dunes

Formed when sand deposited by longshore drift is moved up the beach by the wind and obstacles cayse wind speed to decrease, so sand is deposited around the obstacle. This sand is then colonised by plants and marram grass eg.

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Sand dunes 2

The vegetation stabilises the sand and encourages more sand to accumularte there, forming small dunes called embryo dunes. Over time, the oldest dunes migrate inland as newer dunes are formed. These mature dunes can reach heights of 10m.

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Spits and bars

Formed by longshore drift depositing material when the coastline suddenly changes shape at the mouth of an estuary.

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Spit

Unstable landform, grows until the water becomes too deep or material is moved faster than it is deposited. A hook can develop if the direction of wind changes, behind forming mud flats or salt marshes.

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Bar

A ridge of sand or shingle which has joined two headlands, cutting off the bay, this bay is then known as a lagoon. There are different types of bars; bay bar, submerged bar and offshore barrier island

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Rivers

Yes

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Upper course

River travelling through mountains and upland areas; very steep gradient; vertical erosion mainly hydraulic action; narrow, shallow channel; low velocity o water; small discharge; rough river bed; large angular rocks on river bed; traction rocks

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Upper course 2

V-shaped valleys, interlocking spurs, waterfalls, gorges

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Middle course

River travelling through hills; gradient less steep; more lateral erosion; mainly attritiona and abrasion, some solution; channel wider and fairly deep; fairly high velocity; quite a high discharge; river bed less rough than in UC.

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Middle course 2

River bed sediments are smaller and smoother than in upper course; more deposition, inside the bends of meanders; LANDFORMS meanders, ox-bow lakes

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Lower course

River travelling through large areas of low-lying land; very broad valley; very gentle gradient; mostly deposition processes here; very little lateral erosion; very wide and deep river channel; high water velocity; high discharge.

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Lower course 2

Smooth river bed covered with alluvium; material moved mostly through suspension and solution. Very small particles but lots of them; LANDFORMS: levees, floodplains and estuaries

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Hard Engineering

Dams and reservoirs; straightening; embankments; flood relief channels.

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Soft Engineering

Flood warnings and preparations; flood plain zoning; planting trees (inc infiltration and transpiration); river restoration

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Get Revising

Geography Paper 1 Section C Coasts and Rivers

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