2B.6bc

• what is mass movement?

  the movement of weathered material down slope, as a result of gravity
• what does mass movement depend on?

  the angle of slope --> cliff profile (steeper=faster)

  the rock type and its structure e.g. areas of weakness

  the vegetation cover

  how wet the ground is (porous rocks will become saturated)

  shear strength vs shear stress: particles with high friction stay together e.g. crystallisation = more stable
• what are the 3 types of flow mass movement?

  soil creep

  solifluction

  earthflow
• what is soil creep + its rate?

  slow downhill movement of individual soil particles caused by wetting and drying of the ground causing it to absorb water which reduces the friction between soil particles - it then expands and contracts when it dries causing it to move

  rate: slowest continual process
• what is solifluction + its rate?

  occurs mainly in tundra areas: top layer of soil thaws in summer, but the soil layer below is still frozen (permafrost) - the surface layer becomes saturated and flows over

  rate: 5cm-1m per year
• what is earthflow?

  when increased rainfall reduces friction between soil/ earth so earth and mud flows over underlying bedrock
• what are the 3 types of slide mass movement?

  rock fall

  rock slide

  slump
• what is rock fall?

  occurs on slopes of angle >40° --> a rock fragment breaks away and drops vertically or bounces downslope and becomes scree: this occurs when strong, jointed, steep rock faces are exposed to mechanical weathering
• what is rock slide?

  when increased rainfall reduces friction in rock causing slabs of rocks to slide over underlying rocks along a slide plane

  occurs to rocks that are jointed or have bedding planes roughly parallel to the slope
• what is slumping?

  when increased rainfall causes rocks to become saturated, causing rotational movement that occurs on moderate to steep slopes --> causes rotational scars

  its common when softer rock overlies more resistant or impermeable rock
• how does mass movement affect the coast?

  it increases erosion as there's more loose sediment to remove and contributes to the sediment supply
• how is mass movement affected by geology?

  porous rocks are more likely to become saturated as they have a higher water retention and therefore more vulnerable
• what is a rotational scar + cause?

  Its a scar that is curved, un-weathered and has no vegetation

  Forms as a result of rotational slumping
• what are talus scree slopes + cause?

  a mound of small loose scree that covers a slope on a mountain due to rock fall - they have a concave upwards form
• what are terraced cliff profiles + cause?

  Where the cliff profile is stepped due to lithology or fractures in the rock.
• what is rock slide?

  when increased rainfall reduces friction in rock causing slabs of rocks to slide over underlying rocks along a slide plane

  occurs to rocks that are jointed or have bedding planes roughly parallel to the slope
• case study of rock fall?

  St Oswalds Bay, Dorset (Jurassic coast):

  date: 2013

  what: a 90m area of cliff failed and removed part of a coastal path, leaving a talus scree slope (caused by rockfall) which extended out to sea

  rock type: porous chalk became saturated due to antecedent conditions (rainfall)
• case study of slump?

  where: Hollbeck Hall hotel, North Yorkshire

  when: 1993

  what: cliff failed cutting the cliff back by 70m, caused by antecedent conditions (rainfall)

  rock type: glacial tilt resting on Mudstone and sandstones

  --> destroyed Holbeck Hill hotel at the top of the cliff
• case study of earthflow?

  where: Nefyn Bay, North Wales

  when: 2001

  what: mud flow caused by antecedent conditions (rainfall) and weak geology --> less resistant sands overlying less permeable clay layer

  rock type: clay and silt

  --> caused 1 death