Sub-aerial And Mass Movement Processes Flashcards
What is weathering?
The gradual breakdown of rock, in situ, at or close to the ground surface. It creates sediment which the sea uses to help erode the coast.
What is mass movement?
The movement of weathered material downslope under gravity. It can reshape the coastline.
Describe the process of freeze thaw (mechanical weathering).
Freeze thaw:
Water enters cracks/joints in rocks. As water freezes it expands by about 10%, exerting pressure, forcing cracks to widen. Repeated freezing and thawing causes fragments of rock to break away and collect at the base of the cliff as scree. Must be in an area where the temperature goes below and above 0 degrees.
=Angular rock fragments and a jagged cliff face are created, with scree slopes at the base.
Describe the process of salt crystallisation (mechanical weathering).
When waves break/splash cliffs on coastal rocks, water evaporates, leaving behind sodium and magnesium salt compounds in joints and cracks. These salt crystals grow and exert pressure and force the rocks apart. Seawater may also enter porous rock and the crystals grow inside the rock itself.
=Angular rock fragments are loosened and fall to create scree slopes at the base of cliff; rock faces crumble.
Describe the process of carbonation (chemical weathering).
Rainwater absorbs CO2 from air, forming weak carbonic acid. This reacts with calcium carbonate in rocks to form calcium bicarbonate which is easily dissolved.
Describe the processes of biological weathering.
-Plants grow into cracks in a cliff face. Cracks widen as the roots grow, breaking up the rock.
-Birds/animals dig burrows into cliffs.
=These holes create weak points in the cliff for other weathering processes to act.
What is mass movement caused by?
Gravity once a slope has become unstable: after waves have undercut resistant rocks or when rainwater enters unconsolidated rocks + forces particles apart.
What’s the process of soil creep (flow)?
Very slow downhill movement of soil particles. Slowest form of mass movement.
What’s the process of solifluction (flow)?
Occurs mainly in tundra areas. When the top layer of soil thaws and becomes saturated. It flows over the frozen layer beneath. Averages 5cm-1 metre a year.
What’s the process of earth flows/mudflows (flow)?
And increase in the amount of water can reduce friction, causing earth and mud to flow over bedrock.
What’s the process of rock falls (slides)?
Most likely to occur when strong, jointed, steep rock faces are exposed to mechanical weathering. Material falls to form scree at the foot of the slope/cliff. Block falls are similar - large block of rock falls from the cliff as a single piece due to the jointing of the rock.
What’s the process of rock/debris slides (slides)?
Rocks that are jointed/have bedding planes roughly parallel to the slope are susceptible to landslides. An increase in the amount of water can reduce friction, causing sliding. Slabs of rock/blocks can slide along a slip plane.
What’s the process of slumping (slides)?
Often occur in saturated conditions on moderate/steep slopes. Rotational movement. Common where softer materials overlie more-resistant/impermeable rock. Slumping causes rotational scars and terraced cliff profiles.
