Coastal Weathering and erosion
Mechanical: the breakdown of rocks without changing its chemical composition.
· It happens when the temperature alternates above and below 0˚C (the freezing point of water)
· Water gets into the cracks of the rock.
· When the water freezes it expands, which puts pressure onto the rock.
· When the water thaws it contracts, which releases the pressure in the rock.
· Repeated freezing and thawing widens the cracks and causes the rock to break up.
Chemical: when weak acids for example rain dissolves the rocks.
· Rainwater has carbon dioxide in it, which makes it a weak carbonic acid.
· Carbonic acid reacts with rock that contains calcium carbonate, e.g. Carboniferous limestone, so the rocks are dissolved by the rainwater.
Mass movement is when material shifts down a slope as one
· Mass movement is the shifting of rocks and loose material down a slope e.g. a cliff. It happens when the force of gravity acting on a slope is greater than the force supporting it.
· Mass movement cause coasts to retreat rapidly.
· They’re more likely to happen when the material is full of water.
On the top is a layer of sandy gravel and beneath is a layer of clay. The sandy gravel is permeable so the water seeps through it however the clay is impermeable and holds water from the sand above and the rain falling directly on it. Soon the clag turns into a soggy slippery mess then helped by the waves it happens and it material shifts down with a rotation this is called rotational cliff slumping.
Waves Wear Away the coast using four processes of Erosion
Hydraulic power: waves crash against rock and compress the air in the cracks. This puts pressure on the rock. Repeated compression widens the cracks and makes bits of rock break off.
Abrasion: eroded particles in the water scrape and rub against rock removing small pieces.
Attrition: eroded particles in the water smash into each other and break into smaller fragments. Their edges also get rounded off as they rub together.
Solution: weak carbonic acid in seawater dissolves rock like chalk and limestone.
Types of waves:
The waves that carry out erosional processes are called DESTRUCTIVE WAVES.
1) Destructive waves have a high frequency (10-14 waves per minute)
2) They’re high and steep
3) Their backwash (the movement of the water back down the beach) is MORE POWERFUL than their swash (the movement of the water up the beach). This means material is removed from the coast by LONGSHORE DRIFT.
Another type of wave is called CONSTRUCTIVE WAVE.
1) They are created in calm weather and are less powerful than destructive waves.
2) Their swash is bigger than their backwash this means they break on…