What Causes Tsunamis
Landslide is of the severe natural disaster in the world. It mostly occurs in mountainous regions, which greatly impacts human settlements.
This natural phenomenon is unlike volcanic eruptions or river flooding. In those natural hazards, there is either a liquid or gaseous flow. Landslides,on the other hand, are more disastrous as it is a case of a solid flow. A large chunk of rock getting displaced!
Landslide is not a direct phenomenon. It,actually, is triggered by other natural disasters such as Earthquakes, Volcanic eruption, Flooding, Hurricanes. All these phenomena triggers or weakens a terrain, which later on, becomes a breeding ground for landslides.
This blog looks at :
1. How to differentiate between landslide sensitive and non sensitive area.
2. Factors behind landslide
Before diving deep into the above mentioned agenda, we define a term safety factor, which is the ratio of the strength of a piece of land on a slope divided by the shear force exertion parallel to the slope. SF=Strength/Shear Force.
If a particular area has a safety factor greater than 1, then, it can be denoted as safe. Off course, in this case the numerator ‘strength’ magnitude is greater than the denominator ‘Shear Force’.
In 2nd case, having a safety factor lesser than 1, makes the piece of land prone to landslide.
What is the term strength in the safety factor?
Terrain that have water concentrated deep down the roots are intrinsically weak in strength than their counterparts.
These wet areas primarily contain clay or mud. The clay behaves as a lubricant or a friction reduction fluid for the piece of sliding land against the nearby stiff lands.
Thus, wet lands are vulnerable to this disastrous phenomenon!
What is the shear force in the safety factor.?
As learned in a secondary level physics, An area of land or, in general, anything placed on a slope would always face two components of the gravitational force of earth. One component forces down perpendicular to the slope while the second component exert force parallel to the slope.
The perpendicular force is the one which actually strengthens the area.
The reason being; increase in the surface perpendicular force/weight results in increase in the upward reactionary normal force by the slope surface.
According to laws of physics, frictional force, which stops/holds a material sliding down the plane, is actually dependent on the normal force by the formula F=UR.
R in the above formula is the normal force, which is directly proportional to the frictional force F.
U, in the formula is defined to be frictional co-efficient, which depends on how easily a piece of material can slide against its stable counterpart. A wet land consisting of clay would definitely be having low U constant!
Thus, increase either in R or U would increase frictional force on the material sliding downwards. This adds to the stability of the material.
On the other hand , the parallel force also called shear force works in sliding down the rock/material . Its magnitude increases with the increase in slope. Therefore, its relative increment diminishes the safety factor value.
Shear force impacting a material can be determined by the formula SF=W COS(THETA) , where W is the weight of the material while theta is the angle of slope.
Similarly a downward surface perpendicular force, as discussed previously, can be calculated by PF=W SIN(THETA).
As can be noted from the above two formulas, which of course is intuitive too, increasing the slope of a plane increases the chances of land sliding.
Now we explain how to differentiate between land slide sensitive and non sensitive locations and the causes and precautions of landslides:
Type of rock layering: a rock either sedimentary or metamorphic is made up of layers. If those layers, by chance, happen to be parallel to the slope direction, then it makes the rock easier to slide. Otherwise the rock is resistant to overcome the shear force.
Rock fracturing: if the piece of land or rock has cracks on its surface, then its vulnerable to land slides. Fractures naturally occur in areas with extreme temperatures having hot summers and cold winters. In such a case rocks undergoing expansion in summer and contraction in winter usually cracks up. In some cases,Mining or human construction activities also fractures up a piece of area. All of this adds to the sensitivities of a piece of land.
Loss of vegetation: a mountainous area full of green pastures, vegetation,trees is anchored strongly to its roots. These strong pillars withstands or resists the sliding activity. There fore, don’t let an area go deforested. deforestation usually occur due to drought or wild fires.
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