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- A landslide or Landslip isa geological phenomenon whichincludes a wide range of groundmovement
Landslides occur when thestability 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:
groundwater pressure acting to destabilize the slope. Loss or absence of vertical vegetative structure, soil nutrients, and soil structure (e.g. after a wildfire). erosion of the toe of a slope by rivers or ocean waves. weakening of a slope through saturation by snowmelt, glaciers melting, or heavy rains. earthquakes adding loads to barely stable slope. Earthquake- caused liquefaction destabilizing slopes. volcanic eruptions.
“Landslides areaggravated byhuman activities”
deforestation, cultivation and construction, which destabilize the already fragile slopes. vibrations from machinery or traffic. Blasting. earthwork which alters the shape of a slope, or which imposes new loads on an existing slope in shallow soils, the removal of deep- rooted vegetation that binds colluvium to bedrock. Construction, agricultural or forestry activities (logging) which change the amount of water which infiltrates the soil.
- Sand boils or SandVolcanoes occur when water underpressure wells up through a bed ofsand. The water looks like it is"boiling" up from the bed of sand
Sand boils can be a mechanism contributing to levee failure during floods. This effect is caused by a difference in pressure on two sides of a levee or dike, most likely during a flood. This process can result in piping, whereby the removal of soil particles results in a pipe through the embankment. The creation of the pipe will quickly pick up pace and will eventually result in failure of the embankment.
A sand boil is difficult to stop. Themost effective method is by creating abody of water above the boil to create enough pressure to slow the flow ofwater. A slower flow will not be able tomove soil particles. The body of water is often createdwith sandbags forming a ring around the boil