Weathering And Mass Movement

Question 1

What are subaerial processes?

Answer 1

Erosion above the high water mark. It involves weathering and mass movement

Question 2

What is weathering?

Answer 2

The gradual breakdown of rock, in situ, at or close to the ground surface

Question 3

What are the types of weathering?

Answer 3

Mechanical
Chemical
Biological

Question 4

What are the types of mechanical weathering?

Answer 4

Freeze-thaw
Salt-weathering
Wetting and drying

Question 5

What is freeze-thaw weathering?

Answer 5

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.

Question 6

What is salt-weathering?

Answer 6

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.

Question 7

What is wetting and drying?

Answer 7

Rocks rich in clay expand when they get wet and contract as they dry. This can cause them to crack and break up.

Question 8

What is biological weathering

Answer 8

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.

Question 9

What is chemical weathering?

Answer 9

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.

Question 10

What is mass movement?

Answer 10

The movement of weathered material down slope, as a result of gravity.

Question 11

What can affect the type of mass movement?

Answer 11

The angle of the slope or cliff
The rock type and its structure
The vegetation cover
How wet the ground is

Question 12

What are the types of mass movement?

Answer 12

Flows

Slides

Question 13

What are the types of flows?

Answer 13

Soil creep
Solifluction
Earth flows and mudflows

Question 14

What are the types of slides?

Answer 14

Rock falls
Rock/debris slides
Slumps

Question 15

What is soil creep?

Answer 15

A very slow downhill movement of individual soil particles

Slowest form of mass movement
Almost continuous processes

Question 16

What is solifluction?

Answer 16

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

Question 17

What are earth flows/mudflows?

Answer 17

An increase in the amount of water can reduce friction, causing earth and mud to flow over underlying bedrock.

Question 18

What’s the difference between a slide and a flow?

Answer 18

In a slide the material remains intact (moves ‘en masse’).

In a flow, the material becomes jumbled up.

Question 19

What are rock falls?

Answer 19

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°.

Question 20

What are rock/debris slides?

Answer 20

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.

Question 21

What are slumps?

Answer 21

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