slopes

• Slope


  An open system that can be commonly found in steep gradients, where weak rock is present, common areas of heavy rainfall, and basal undercutting
• How slopes are formed


  1. Tectonic (fault scarps)

  2. Depositional (volcanoes, dunes, alluvial fans, glacial moraines)

  3. Erosional (glacial, fluvial valleys)

  4. Human activity (blasted rock slopes, hydraulic mining)
• Paleoslopes


  • Formed under a different climatic regime e.g. glacial troughs (U-shaped valleys) in Snowdonia, North Wales
• Physical factors affecting slope processes

  • Rock type
  • Tectonic activity
  • Geological structure
  • Permeability and porosity
  • Climate
• Rock type


  Tougher rock (igneous/metamorphic) = steep slope Sand/gravel = gentle slope
• Tectonic activity


  Earthquakes may trigger slope failure
• Geological structure


  Rock slabs detached along joints and bedding planes promote rockfalls and landslides
• Permeability and porosity


  An impermeable rock will be liable to surface water flow, deep gullies may form
• Climate


  Affects weathering type. Physical weathering e.g. frost shattering produce angular, bare rock surface and chemical weathering tends to dissolve and produce fine clay and more rounded slopes
• Human factors affecting slope processes

  • Vegetation
  • Basal excavation
  • Altering slopes
• Vegetation


  If a slope is forested/vegetated it helps to protect slopes from direct effects of rainfall and help bind rock and soil particles
• Basal excavation


  It takes place in the form of river undercutting of slope/sea cutting into notch of cliff. Road construction has the same effect → this leads to a steep slope which makes it unstable
• Altering slopes


  By mining or quarrying, road construction, housing estates and terracing land for farming. Deforestation can cause soil erosion
• Processes acting on slopes

  • Mass wasting (e.g. creep, flow, fall)
  • Action of water (e.g. Rainsplash, Slope wash, Channelised flow, Subsurface flow)
• Rainsplash


  Rain may move soil directly: this is known as 'rainsplash erosion' (or just 'splash erosion'). Splash is only effective if the rain falls with sufficient intensity. If it does, then as the raindrops hit bare soil, their kinetic energy is able to detach and move soil particles a short distance. Because soil particles can only be moved a few centimetres (at most) by this process, its effects are solely on-site. Although considerable quantities of soil may be moved by rainsplash, it is all merely redistributed back over the surface of the soil (on steep slopes, however, there will be a modest net downslope movement of splashed soil). Thus a more descriptive term might be 'rainsplash redistribution'. Because rainsplash requires high rainfall intensities, it is most effective under convective rainstorms in the world's equatorial regions. Rainsplash is relatively ineffective where rain falls with a low intensity (e.g. because the rainfall is of frontal origin), such as in the north-west of the USA or in northern Europe.
• Slope wash


  Hortonian overland flow describes the tendency of water to flow horizontally across land surfaces when rainfall has exceeded infiltration capacity and depression storage capacity.
• Channelised flow


  Rills are caused by concentrated runoff in rivulets, cutting several inches deep into the soil surface. These grooves are called rills. Gullies may develop in unrepaired rills or in other areas where a concentrated flow of water moves over the soil.
• Subsurface flow

  1. Eluviation: Removal of dissolved or suspended material from a layer or layers of the soil by the movement of water when rainfall exceeds evaporation.

  2. Throughflow: water moving through the subsurface

  3. Solute transport: As water moves through the soil, it carries any substance dissolved in it.
• Inputs that can affect slope processes

  • Biotic
  • Climatic
  • Gravitational
  • Groundwater
  • Tectonic
• These inputs may vary in terms of time & scale
• Movement of a slope

  The more severe the failure, the more impact it has on the movement characteristics of the slope
• Inputs before regolith

  • Soil depth & type
  • Types of surface & vegetation
  • Gravity
  • Precipitation
  • Angle of slope
  • Geology (rock type & structure)
  • Frost
• Inputs in regolith

  • Vegetation type & amount of cover
  • Human influences (Infrastructure/waste tips)
• Processes before regolith

  • Infiltration of water into ground
  • Interception
  • Rainsplash
  • Surface runoff
  • Heave
  • Channel flow
• Outputs at the top of regolith

  • Evapotranspiration temp/insolation radiation
• At the end, the river removes material at the foot of the slope