Weahering And Mass Movementt Flashcards
What is weathering?
Weathering is the breakdown of rocks (mechanical, biological or chemical) over time, leading to the transfer of material into the littoral zone, where it becomes an input to sediment cells.
What is mechanical weathering?
Mechanical (Physical) Weathering: the breakdown of rocks due to exertion of physical forces without any chemical changes taking place
Examples of mechanical weathering?
● Freeze-thaw (Frost-Shattering): Water enters cracks in rocks and then the water freezes overnight during the winter. As it freezes, water expands by around 10% in volume which increases the pressure acting on a rock, causing cracks to develop. Over time these cracks grow, weakening the cliff making is more vulnerable to other processes of erosion
● Salt Crystallisation: As seawater evaporates, salt is left behind. Salt crystals will grow over time, exerting pressure on the rock, which forces the cracks to widen. Salt can also corrode ferrous (materials that contains iron) rock due to chemical reactions
● Wetting and Drying: Rocks such as clay expand when wet and then contract again when they are drying. The frequent cycles of wetting and drying at the coast can cause these rocks and cliffs to break up
What is chemical weathering?
The breakdown of rocks through chemical reactions
Examples of chemical weathering?
Carbonation: Rainwater absorbs CO2 from the air to create a weak carbonic acid which then reacts with calcium carbonate in rocks to form calcium bicarbonate which can then be easily dissolved. Acid rain reacts with limestone to form calcium bicarbonate, which is then easily dissolved allowing erosion.
● Oxidation: When minerals become exposed to the air through cracks and fissures, the mineral will become oxidised which will increase its volume (contributing to mechanical weathering), causing the rock to crumble. The most common oxidation within rocks is iron minerals becoming iron oxide, turning the rock rusty orange after being exposed to the air.
● Solution: When rock minerals such as rock salt are dissolved.
What is biological weathering?
The breakdown of rocks due to the actions of plants, bacteria and animals
Example of biological weathering?
Roots if plants growing into the cracks of rocks, which exerts pressure, eventually splitting the rocks
What does the type of mass movement depend on?
The type of mass movement that occurs depends on:
- the angle of the slope/cliff
- the rock’s lithology and geology
- the vegetation cover on the cliff face
- the saturation of the ground/ previous weather patterns
What is the difference between a slide and a flow?
For a slide, sediment keeps its same place within the whole material, simply moves downhill. However, for a flow, all the material flows downs and mixes.
Types of flows?
Solifluction - Occurs mainly in tundra areas where the land is frozen. As the top layers
thaws during summer (but the lower layers still stay frozen due to permafrost) the surface
layers flows over the frozen layers.
● Mudflows - An increase in the water content of soil can reduce friction, leading to earth and
mud to flow over underlying bedrock.
Types of slides?
Rock falls - Occur on sloped cliffs (over 40o ) when exposed to mechanical weathering.
● Rock slides - Water between joints and bedding planes (which are parallel to the cliff face) can reduce friction and lead to more sliding.
● Slumps - Occur when the soil is saturated with water, causing a rotation movement of soft materials (such as clay and sand) forming rotational scars and terraced cliff profiles.
What influences cliff profiles?
The resistance of the rock to the erosion
The dip in rock strata in relation to the sea
