3.2.2 Sub-aerial Processes Flashcards
Define weathering
Weathering is the breakdown of rock in its place of origin (in-situ)
Outline 3 types of weathering
Mechanical When rocks break up with no chemical changes
Biological Rock breakdown due to organic activity
Chemical Rock breakdown due to a chemical reaction
Explain freeze-thaw physical weathering
This happens in places where nighttime temperatures often reach below freezing
Process: Water finds its way into small cracks in the rock and expands as it freezes exerting force in the surrounding rock. These expands present cracks in the rock. When the temperature rise again, the frozen water thaws. This cycle of freezing and thawing occurs many times, until eventually a fragment of the rock breaks away completely
Explain wetting and drying physical weathering
In warmer climates where the water doesn’t freeze, a similar process called wetting and drying occurs which works in the same way, just without the ice
This often occurs in the inter-tidal zone; the area is exposed at low tide but covered at high tide
Rocks expand when they are wet and contract again when dry
Explain salt crystallisation physical weathering
Salt crystallisation occurs because the salt crystals are bigger than the water molecules
This exerts pressure on the rock, causing it to break down
Process: Water collects in the cracks in the rock when it rains. When the sun shines the water evaporates salt crystals are left behind in the cracks. Salt crystals grow over time and create stress on the rock causing it to break up.
Explain process of vegetational biological weathering
As the plant growth the roots enter cracks in the rock under the soil/ As the plant and roots grow the roots cause the crack to get larger. Rock breaks away.
Outline 3 types of chemical weathering
Carbonation - when rain is slightly acidic and reacts with carbonate rocks like limestone, causing them to dissolve
Oxidation - when iron minerals in the rock react with oxygen in the air to cause rusting and breakdown the rock
Solution - when other salt minerals in the rock are dissolved
Define mass movement
Mass movement is the downhill movement of material under the influence of gravity
What does mass movement include?
Mass movement includes landslides, slumping and rockfalls
Explain the process of coil creep
Common in humid climates with movement of less than 1cm per year
Soil expands when it freezes, gets wet or is heated up in the sun
As the soil expands, it lifts at right angles to the slope
When the soil shrinks, it falls straight back down
Soil creep takes a long time because the soil moves only a millimetre to a few centimetres at a time
Explain the process of mass movement flow
Occurs on slopes between 5° and 15° with speeds between 1 to 15km per year
Usually happens after the soil has become saturated with a flow of water across the surface
Vegetation is flattened and carried away with the soil
Explain the process of mass movement slide
A movement of material ‘en masse’ which remains together until hitting the bottom of a slope
Explain the process of mass movement of fall
Slopes are steep and movement is rapid
Caused by a number of reasons:
Extreme weathering: freeze-thaw action can loosen rocks that become unstable and collapse
Rainfall: too much rain will soften the surface leading to the collapse of the slope
Earthquakes can dislodge unstable rocks
Hot weather can dry out soil causing it to shrink, allowing rocks to fall
Explain the process of mass movement slump
Usually found on weaker rock types (i.e. clay), that become saturated and heavy
This is common at the coast and is also known as rotational slip
It involves a large area of land moving down the slope in one piece
Because of the way it slumps, it leaves behind a curved indented surface
