Weathering And Mass Movement Flashcards
What are subaerial processes?
Erosion above the high water mark. It involves weathering and mass movement
What is weathering?
The gradual breakdown of rock, in situ, at or close to the ground surface
What are the types of weathering?
Mechanical
Chemical
Biological
What are the types of mechanical weathering?
Freeze-thaw
Salt-weathering
Wetting and drying
What is freeze-thaw weathering?
Occurs when water enters a crack or joint in the rock when it rains - and then freezes in cold weather.
When water freezes it expands in volume by about 10%. This expansion exerts pressure on the rock, which forces the crack to widen
When this processes is repeated fragments of rock break away and collect at the base of the cliff.
What is salt-weathering?
When salt water evaporates, it leaves salt crystals behind. These can grow over time and exert stresses in the rock, just as ice does - causing it to break up.
Salt can also corrode rock, particularly if it contains traces of iron.
What is wetting and drying?
Rocks rich in clay expand when they get wet and contract as they dry. This can cause them to crack and break up.
What is biological weathering
It can occur when plant roots start to grow into small cracks, which widen as the roots grow, breaking up the rock.
Water running through decaying vegetation becomes acidic, which leads to increased chemical weathering.
Birds and animals dig burrows into cliffs
Marine organisms are also capable of burrowing into rocks, or of secreting acids.
What is chemical weathering?
E.g. carbonation - rainwater absorbs CO2 from the air to form a weak carbonic acid.
This reacts with calcium carbonate in rocks such as chalk and limestone, to form calcium bicarbonate, which is easily dissolved.
The cooler the temperature of the rainwater, the more CO2 is absorbed, increasing the effectiveness of carbonation in winter.
What is mass movement?
The movement of weathered material down slope, as a result of gravity.
What can affect the type of mass movement?
The angle of the slope or cliff
The rock type and its structure
The vegetation cover
How wet the ground is
What are the types of mass movement?
Flows
Slides
What are the types of flows?
Soil creep
Solifluction
Earth flows and mudflows
What are the types of slides?
Rock falls
Rock/debris slides
Slumps
What is soil creep?
A very slow downhill movement of individual soil particles
Slowest form of mass movement
Almost continuous processes
What is solifluction?
When the top layer of soil thaws in the summer, but the layer below remains frozen, the surface layer becomes saturated and flows over the frozen subsoil and rock.
Occurs mainly in tundra areas
What are earth flows/mudflows?
An increase in the amount of water can reduce friction, causing earth and mud to flow over underlying bedrock.
What’s the difference between a slide and a flow?
In a slide the material remains intact (moves ‘en masse’).
In a flow, the material becomes jumbled up.
What are rock falls?
The material once broken away from the source either bounces or falls vertically to form scree at the foot of the slope/cliff.
Most likely to occur when strong, jointed and steep rock faces/cliffs are exposed to mechanical weathering.
Rock falls occur on slopes over 40°.
What are rock/debris slides?
An increase in the amount of water can reduce friction - causing sliding. In a rock or landslide, slabs of rock/blocks can slide over underlying rocks along a slide or slip plane.
Rocks that are joined, or have bedding planes roughly parallel to the slope or cliff surface, are susceptible to landslides.
What are slumps?
Often occur in saturated conditions. There is a rotational movement. Occur on moderate to steep slopes. Common where softer materials overlie more resistant or impermeable rock. Causes rotational scars
Repeated slumping creates a terraced cliff profile
