Sub-Ariel processes

• what is a sub ariel process


  processes above the sea level that erode cliffs, including weathering, mass movement and surface run off
• definition of weathering


  breakdown of rock in situ
• three types


  -biological

  -mechanical

  -chemical
• what is biological weathering

  -plant roots grow into faults or bedding planes in the rock they bind with the soil and widen them which destabilises the rock

  -animals such as rabbits can burrow into a crack and widen it

  -even tiny bacteria can secrete chemicals to break down rock and access nutrients
• how can biological weathering be seen

  when green vegetation grows on the top of a cliff
• what is mechanical weathering


  The breakdown of rock without changing its chemical composition
• two types of mechanical weathering

  Freeze-thaw weathering

  salt weathering
• how does freeze thaw weathering work

  water enters fault

  water freezes and expands by 9%

  water thaws and joint is widened

  process repeats until rock splits completely
• how does salt weathering work


  -salt water enters cracks in rock

  -when salt water evaporates, salt crystals are formed which put pressure on rock
• three types of chemical weathering


  oxidation, hydrolysis, carbonation
• what rocks can be affected by carbonation

  chalk and limestone (white rocks)

  or any rock that contains calcium carbonate/caco3
• how does carbonation work


  when acidic rainwater reacts with calcium carbonate/caco3 the calcium carbonate becomes calcium bicarbonate which is soluble so removes by surface run off
• how can oxidation be seen


  red dots or markings on the rock
• how does oxidation work

  iron in sedimentary rock reacts with the oxygen in air so it rusts. when it rusts it expands as new iron compounds are formed, thus putting pressure on the rock causing faults
• which rock normally contains iron


  sedimentary
• what mineral causes hydrolysis


  feldspar which can be found in granite
• how does hydrolysis weathering occur

  acidic rainwater reacts with feldspar to form clay and slats that can be removed by rainwater
• 4 things that can affect weathering


  geology

  lithology

  precipitation

  temperature
• is rainwater acidic or alkali

  acidic
• what is mass movement

  downhill movement of rock due to gravity
• what are the 3 types of mass movement

  slides, slumps and rockfall
• explain how a slump occurs

  -when a permeable layer of rock lies above an impermeable layer of rock (eg) clay

  -permeable rock becomes saturated with rainwater, so it becomes have which causes a curved plane

  -the top layer of the impermeable rock becomes lubricated

  -due to gravity, the saturated rock slumps down the curved plane
• explain how a landslide occurs

  -when rock becomes saturated due to rainfall, it falls along the flat plane
• what are the features of a cliff that cause a slide to occur

  -steep gradient

  -where there are faults or bedding planes that get exploded by water
• what is the difference between the plane at a landslide and slump

  curved plane at a slump

  linear slip plane at a slide
• explain how a rockfall occurs


  -the cliff is exploited by mechanical (freeze thaw) weathering

  -rocks break off and fall down the steep cliff face rapidly
• what are the features of a cliff where rockfall occurs

  -steep/verticle strata (cliff face over 45 degrees) - high angle of seaward dip

  -many faults that can be exploited by freeze thaw weathering
• what are the 3 landforms caused by mass movement

  rotational scars, talus scree slope, terraced cliff profiles
• what landform does a rockfall cause

  talus scree slopes
• what is a talus scree slope

  angular rockfall debris that forms at the foot of the cliff face
• what landform does a slump form

  rotational scars
• what is a rotational scar


  a fresh, curved, unweathered and unvegetated rock surface on the cliff after a slump has occurred
• what is a terraced cliff profile

  where the cliff profile is stepped
• what causes a terraced cliff profile

  slumps/fractures in the rock