2.4. Mass movement

Question 1

What is mass movement?

Answer 1

The downhill movement of material under the influence of gravity

Question 2

Where is mass movement common and why?

Answer 2

Common at the coast due to the weight of rainwater and weak geology

Question 3

What does the type of movement depend on?

Answer 3

• angle
• rock type
• vegetation
• how wet the ground is

Question 4

What are the 4 types of mass movement?

Answer 4

• creep
• flow
• slide
• fall

Question 5

What is soil creep?

Answer 5

• An extremely slow form of movement of individual soil particles downhill
• cannot be seen in operation but can be seen by the build up of soil on the upslope side of walls and the bending of tree trunks

Question 6

What are mudflows?

Answer 6

• involves earth and mud flowing downhill, usually over unconsolidated or weak bedrock, often after heavy rainfall
• mudflows are often sudden and fast flowing
• water gets trapped within rock which increased pore water pressure, forcing rock particles apart and leads to slope failure

Question 7

What are landslides?

Answer 7

• A landslide involves a block of rock moving very rapidly downhill along a planar surface
• landslides tend to be very rapid
• moving block in a landslide remains largely intact
• frequently triggered by earthquakes or heavy rainfall

Question 8

What is a rockfall?

Answer 8

• the sudden collapse or breaking away of individual rock fragment at a cliff face
• most commonly associated with steep or vertical cliffs in heavily jointed and quite resistant rock
• often triggered by mechanical weathering or earthquakes
• once broken away from source, rock falls or bounces down slope to from scree at foot

Question 9

What is a landslip or slump?

Answer 9

• differs from a landslide in that its slide surface is curved, rather than flat
• landslips or slumps are characterised by a sharp break of slope and formation of a scare
• often occur in weak, unconsolidated clays and sands

Question 10

What is run-off?

Answer 10

• occurs down a slope or cliff- face and small particles are moved down slope, forming input into sediment cell
• type of flow that transfers water and sediment from one store to another

Question 11

What is solifluction?

Answer 11

• similar to soil creep but specific to cold environments where temps fluctuate around freezing
• in summer, surface layer of soil thaws and becomes extremely saturated and it sits on top of impermeable permafrost
• known as active layer, sodden soil with blanket of vegetation slowly moved downhill by combination of heave and flow