Weathering, Rivers & Coasts Flashcards
What is weathering?
Weathering is the weakening and breakdown of rocks in the place where they are (in situ)
Biological weathering
The weakening and breakdown of rocks by plants and animals.
Roots of plants and burrowing animals get into the cracks and break them up
Chemical weathering
Chemicals in the air and water react with rocks and break them down
Physical/ mechanical weathering
Extreme changes in temperature cause the rocks to break apart. There are two types: freeze-thaw action and exfoliation (onion skin effect).
Freeze thaw action
During the day, water enters the cracks.
At night, the water freezes and expands, this exerts pressure in the crack.
The next day, water thaws (melts).
The constant cycle widens the crack until breaking the rock.
Exfoliation/onion skin effect
During the day, the surface of the rock heats and expands.
At night, the surface of the rock cools and contracts.
This makes the rock crack and peel of like an onion.
Coastal erosion, explain:
Erosion
Transportation
Deposition
The sea wears the rock away.
The sea carries the eroded material.
The sea drops the eroded material.
Hydraulic action
Waves break against the rocks and air is trapped in the cracks. This causes massive pressure which break rocks over time
Abrasion/ Corrasion
Boulders, pebbles and sand are thrown against the bottom of the cliff by waves. This causes the undercutting of the cliff and break up of rocks.
Solution/Corrosion
Chemicals in sea water dissolve rocks and wear them down
Attrition
Pebbles transported by the sea bang each other. This make them smaller and smoother.
How is the eroded material in the coast transported?
Longshore drift:
The waves move towards the coast at an angle (depending in the prevailing wind) and away in straight line.
Bays and headlands
Bays are areas of soft rock where the sea has eroded the material more quickly than in a headland which are bits of harder rock that are not eroded so quickly.
Caves, arches and stumps.
The sea attacks the cracks in a headland forming a cave.
The sea erodes the cave which turns into an arch.
The top of the arch collapses and a stack is left.
The stack is eroded so it turns into a stump.
Evaporation
Water from water stores evaporates and rises because the warm air is less dense.
Condensation
Water vapour cools and is more dense, clouds are formed.
Precipitation
Water vapour is so dense that it falls in rain, snow, sleet etc.
Interception
Some precipitation is intercepted by plants and goes back into the earth by the process of transpiration.
Surface run-off
The earth is saturated so it can’t absorb water. Water flows quickly through the surface until the river.
Through flow
Some water makes its way through the ground by cracks and spaces in the earth until they reach the river.
Percolation
Water finds its way deep into the ground and slowly goes back to the river or the sea.
River basin
Is the land that the water flows across or under on its way to the river. Like a bathtub, it catches all the water until it reaches the river in the middle of the river basin.
Watershed
The edge of the river basin
Source
Place where the river begins
Tributaries and confluence
Small rivers that meet a bigger one
When the tributaries meet the main river.
Mouth of the river
Where the river meets with the sea or ocean.
Coastal deposition
Beaches
Spits
Bars
The sea deposits sand, pebbles and rocks.
Longshore drift moves large amounts of material and suddenly the longshore drift changes direction leaving an arm attached to the land by one end.
The spit gets bigger with eroded material and leaves a bar which separates the lagoon with the sea.
Coastal erosion
Economic impacts
Buildings and land falling Individuals without homes Workers without jobs Less tourism Less facilities
Coastal erosion
Social impacts
Stress related illnesses
Access to local areas reduced
Less facilities
Coastal erosion
Environmental impacts
Habitats of animals being destroyed
Groynes
Are placed along the beach to interrupt movement of sand by longshore drift.
Interrupting the natural movement of the sea could have negative impacts further up the coast.
Sea walls
The walls absorb energy from the waves and prevent erosion as well as flooding.
Expensive to build and can cause environmental problems
Beach rebuilding
Replaces sand taken away by the sea maintaining the natural beauty of beaches.
This is expensive to maintain in long term
Riprap
Concrete blocks that absorb the waves’ energy before they impact the coast. So the waves don’t have so much power to erode the coast.
This is quite cost-effective but makes access to the beach quite difficult.
Name the three stages of a river and their characteristics
Upper stage: v shaped valleys, interlocking Spurs, waterfalls.
Middle stage: wide river valleys, meanders, flood plains
Lower stage: ox bow lakes, levees, deltas
How is eroded material carried down the river?
Rolling: large stones are rolled along the river bed.
Bouncing: smaller pebbles are bounced along the river bed.
Suspension: light material like sand floats around the river.
Solution: dissolved materials are carried by the river.
