Environmental Studies(ES)

ENVIRONMENTAL STUDIES

Lesson 7: Land resources

Landslide

A landslide (or landslip) is a geological phenomenon which includes a wide range of ground movement, such as rock falls, deep failure of slopes and shallow debris flows, which can occur in offshore, coastal and onshore environments. Although the action of gravity is the primary driving force for a landslide to occur, there are other contributing factors affecting the original slope stability. Typically, pre-conditional factors build up specific sub-surface conditions that make the area/slope prone to failure, whereas the actual landslide often requires a trigger before being released.

Causes of landslides
Landslides are caused when the stability of a slope changes from a stable to an unstable condition. A change in the stability of a slope can be caused by a number of factors, acting together or alone.

• Natural causes of landslides include:
  
  1. Groundwater (pore water) pressure acting to destabilize the slope
     
  2. Loss or absence of vertical vegetative structure, soil nutrients, and soil structure (e.g. after a wildfire)
     
  3. Erosion of the toe of a slope by rivers or ocean waves
     
  4. Weakening of a slope through saturation by snowmelt, glaciers melting, or heavy rains
     
  5. Earthquakes adding loads to barely-stable slopes
     
  6. Earthquake-caused liquefaction destabilizing slopes (see Hope Slide)
     
  7. Volcanic eruptions
     

• Human causes include:
  
  1. Vibrations from machinery or traffic
     
  2. Blasting
     
  3. Earthwork which alters the shape of a slope, or which imposes new loads on an existing slope
     
  4. In shallow soils, the removal of deep-rooted vegetation that binds colluvium to bedrock.
     
  5. Construction, agricultural or forestry activities (logging) which change the amount of water which infiltrates the soil.