Coasts – geography
What causes cliffs to collapse?
Cliffs collapse because of different types of weathering (the breakdown
of rock where it is).
Weathering is mostly caused by weather factors, like rainfall + temp
changes.
Mechanical (physical) weathering:
The disintegration (break up) of rocks
Where this happens, piles of rock fragments called scree, can be found at
the foot of cliffs
Freeze-thaw (mechanical):
Water collects in rock cracks
At the night, the water freezes + expands, enlarging the cracks
When the temp rises again, the ice thaws (becomes liquid) and the water
seeps deeper into the rock
After repeated freeze-thawing, rock fragments break off, falling into
the foot of the cliff (scree)
Salt weathering (mechanical):
Seawater contains salt, so when the water evaporates, it leaves behind
salt crystals
In the cracks/holes, the salt crystals expand
This puts pressure on the rocks, where flakes may eventually break off
Chemical weathering:
Caused by chemical changes
Rainwater’s slightly acidic, so it slowly dissolves certain rocks + minerals
Carbonation (chemical):
Rainwater absorbs CO2 from the air, becoming slightly acidic
Contact w/ alkaline rocks like chalk/limestone produces a chemical
reaction, causing the rocks to slowly dissolve
Biological weathering:
Due to actions of plants + animals
Plant roots grow in rock cracks
Animals like rabbits, burrow into the weak rocks like sands
, Mass movement: downward movement or sliding of material under the influence
of gravity. In 1993, 60m of cliff slipping onto a beach near Scarborough in
North Yorkshire, taking part of Holbeck Hall Hotel.
Types of mass movement at the coast:
Rockfall: Fragments of rock break away from the cliff face, often due to
freeze-thaw weathering.
Landslide: Blocks of rock slide downhill
Mudflow: Saturated soil + weak rock flows down a slope
Rotational slip: Slump of saturated soil + weak rock along a curved surface
Coastal erosion:
Erosion involves the removal of material + the shaping of landforms.
There are many different types:
Abrasion: Bits of rock + sand in waves grind down cliff surfaces like sandpaper
Attrition: Waves smash rocks + pebbles on the shore, into each other and they
break and become smoother.
Solution: Acids contained in sea water will dissolve some types of rock, like
chalk/limestone
Corrasion: When pebbles carried by waves hit the cliff + scrape off rock pieces
Hydraulic action: Air becomes trapped in the cracks of river beds and banks,
causing the rock to weaken and break apart/erode, because the sheer water
power of waves smash against the river banks.
Coastal transportation:
Solution: Dissolved chemicals, often derived from limestone or chalk
Suspension: Particles carried (suspended) within the water
Traction: Large pebbles rolled along the seabed
Saltation: A ‘bouncing’ motion of particles too heavy to be suspended
Longshore drift (LSD): the movement of sediment along a coastline.
LSD depends on the direction that the waves approach the coast
What causes cliffs to collapse?
Cliffs collapse because of different types of weathering (the breakdown
of rock where it is).
Weathering is mostly caused by weather factors, like rainfall + temp
changes.
Mechanical (physical) weathering:
The disintegration (break up) of rocks
Where this happens, piles of rock fragments called scree, can be found at
the foot of cliffs
Freeze-thaw (mechanical):
Water collects in rock cracks
At the night, the water freezes + expands, enlarging the cracks
When the temp rises again, the ice thaws (becomes liquid) and the water
seeps deeper into the rock
After repeated freeze-thawing, rock fragments break off, falling into
the foot of the cliff (scree)
Salt weathering (mechanical):
Seawater contains salt, so when the water evaporates, it leaves behind
salt crystals
In the cracks/holes, the salt crystals expand
This puts pressure on the rocks, where flakes may eventually break off
Chemical weathering:
Caused by chemical changes
Rainwater’s slightly acidic, so it slowly dissolves certain rocks + minerals
Carbonation (chemical):
Rainwater absorbs CO2 from the air, becoming slightly acidic
Contact w/ alkaline rocks like chalk/limestone produces a chemical
reaction, causing the rocks to slowly dissolve
Biological weathering:
Due to actions of plants + animals
Plant roots grow in rock cracks
Animals like rabbits, burrow into the weak rocks like sands
, Mass movement: downward movement or sliding of material under the influence
of gravity. In 1993, 60m of cliff slipping onto a beach near Scarborough in
North Yorkshire, taking part of Holbeck Hall Hotel.
Types of mass movement at the coast:
Rockfall: Fragments of rock break away from the cliff face, often due to
freeze-thaw weathering.
Landslide: Blocks of rock slide downhill
Mudflow: Saturated soil + weak rock flows down a slope
Rotational slip: Slump of saturated soil + weak rock along a curved surface
Coastal erosion:
Erosion involves the removal of material + the shaping of landforms.
There are many different types:
Abrasion: Bits of rock + sand in waves grind down cliff surfaces like sandpaper
Attrition: Waves smash rocks + pebbles on the shore, into each other and they
break and become smoother.
Solution: Acids contained in sea water will dissolve some types of rock, like
chalk/limestone
Corrasion: When pebbles carried by waves hit the cliff + scrape off rock pieces
Hydraulic action: Air becomes trapped in the cracks of river beds and banks,
causing the rock to weaken and break apart/erode, because the sheer water
power of waves smash against the river banks.
Coastal transportation:
Solution: Dissolved chemicals, often derived from limestone or chalk
Suspension: Particles carried (suspended) within the water
Traction: Large pebbles rolled along the seabed
Saltation: A ‘bouncing’ motion of particles too heavy to be suspended
Longshore drift (LSD): the movement of sediment along a coastline.
LSD depends on the direction that the waves approach the coast
