NATURAL DISASTERS

LANDSLIDES

DEFINITION:

Landslides refers to the downward sliding of huge quantities of land mass which occur along steep slopes of hills or mountains. It can be sudden or slow.

CHARACTERISTICS

Large block of soil moves down during the landslide.

The scar above a landslide is easily visible.

They can occur along a slope where the internal resistance of the rocks are reduced or they loose their holding capacity.

Common after earthquakes or after removal of part of the slope due to construction, particularly for construction of roads.

During the movement, landslide can result into the Debris slides which are failure of unconsolidated material on a surface;

Rock slide or Rock Fall – where movement of large rock block rolls.

They are also common along the steep banks of rivers, lakes etc.

Pore Water Pressure is the key to monitoring landslides. Shear strength (a resisting force) decreases and the weight (a driving force) increases.

Cont…

CAUSESNatural causes of landslides include: Groundwater (pore water) pressure acting to

destabilize the slope. Loss or absence of vertical vegetative

structure, soil nutrients and soil structure (e.g. after a wildfire - a fire in forests lasting for 3–4 days).

Erosion of the toe of a slope by rivers or ocean waves.

weakening of a slope through saturation by snow melt or heavy rains.

earthquakes adding vibrational loads to slopes. earthquake-

caused liquefaction destabilizing slopes. volcanic eruptions.

Cont…Landslides are aggravated by human activities,

such as: 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).

Impacts of landslides

Landslides affect the following elements of the environment:

the topography of the earth’s surface. the character and quality of rivers, streams and

groundwater flow. the forests that cover much of the earth’s surface; and the habitats of natural wildlife that exist on the earth’s

surface, including its rivers, lakes, and oceans.

Commuting disturbance due to land slide between villages/towns

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