cliff profiles

• what is a cooling joint

  fractures in igneous rocks caused when magma contracts as it looses heat
• what is an unloading joint

  when overlying rock is removed, underlying strata expand and stretch (release of pressure) which creates joints parallel to the surface
• how do joints form in sedimentary rocks

  when rock is subject to compression or stretching by tectonic forces or the weight of overlying rock
• what is a fold

  a bend in rock strata, produced by tectonic forces of compression
• how can rates of erosion be increased

  faulting significantly increases rates of erosion

  folding increases rates of erosion indirectly

  jointing increases rates of erosion
• what is a ria

  an unglaciated river valley being flooded due to a rise in sea levels
• how does folding indirectly increase rates of erosion

  -folding increases the angle of dip

  -folding causes major jointing as rock is stretched along an anticline and compressed in a syncline
• how does jointing increase rates of erosion

  creates small openings which marine erosion rates and weathering can exploit
• how does angle of dip affect cliff profiles

  horizontal dip 🌲---- 🌊

  produces a vertical cliff profile as blocks loosened in overlying strata by weathering can still be supported and kept in place by underlying layers of strata

  
  

  seaward dip 🌲 \ 🌊

  produce a sloping cliff profile, as bedding planes between strata are weakly bonded, they are easily loosened by weathering so when overlying strata are loosened by sub-aerial processes the rock slides into the sea

  
  

  landward dip 🌲 / 🌊

  produces steep cliff profiles as the downslope gravitational force pulls loosened blocks towards the land and not sea, these are very stable and have few rock falls
• two main cliff profile types

  steep, unvegetated cliffs

  shallow angles, vegetated cliffs
• how are steep unvegetated cliffs created

  -produced where marine erosion dominates

  -have little debris at the bottom due to constant attrition
• how are shallow angled vegetated cliffs created

  -little active marine erosion

  -sub aerial processes move sediment downslope but marine erosion is unable to move it from the base = debris at the bottom
• how are complex cliff profiles formed

  -where cliffs are composed of rock strata with different lithology (different rock type)

  -less resistant strata erode + weather quickly so will be cut back rapidly

  -resistant strata erode + weather slowly so retreat less rapidly, they form overhanging sections until they collapse due to mass movement
• how is the rate of recession measured in a complex cliff profile


  determined by the weakest rock layer
• what is a porous rock


  a rock witch has voids/air spaces
• define a permeable rock


  a rock which allows water to flow through

  -could be permeable due to being porous or having lots of joints
• how does a spring form on a cliff profile

  where permeable rock overlays impermeable strata, groundwater can't percolate down to lower layers

  -water then accumulates in the permeable layer

  -this produces a saturated layer with pores full of water

  -a spring will then form on the cliff face at the top of the saturated layer
• what does a spring cause

  fluvial erosion

  - this attacks both the saturated and unsaturated strata which reduces the angle of the cliff profile
• what does fluvial erosion cause

  -increased water pressure in the pores of saturated rock

  -this pushes rock particles appart

  -this reduces friction between the grains of unconsolidated material and increases lubrication in weakness areas such as bedding planes

  -saturation promotes mass movement due to added lubrication and weight : slumping in unconsolidated material and sliding in consolidated strata