It defines the term ‘landslide’ as “the slippery masses of rock, earth or debris which move by force of their own weight down mountain slopes or river banks.”
Landslides are a major natural disaster in terrains like the Himalaya’s Western Ghats and in the north-eastern parts of the country and destroy life and property almost and cause devastating damage to transportation and communication network.
CAUSES OF LANDSLIDES
There are several causes of landslides. Some major causes are:
Geological weak material: Weakness in the composition and structure of rock or soil may also cause landslides.
Erosion: Erosion of slope toe because of cutting down vegetation;The construction of roads might increase the vulnerability of the terrain to slide down.
Intense rainfall: Storms that produces intense rainfall for periods as short as several hours or have a more moderate intensity lasting several days triggered abundant landslides. Heavy melting of snow also results in landslides.
Human factors: include mining, deforestation, irritation, vibration/blast, and water leakage from services.
Earthquake: Earthquake shaking has triggered landslides in many areas. Rock falls, soil-slides and rock-slides aggregated soils, or rock, or both have been the most abundant types of landslides triggered by earthquakes.
Volcanic Eruption: Deposition of loose volcanic ash on hillsides follows by sped up erosion.
TYPES OF LANDSLIDES
It describes the common landslides below:
Falls: These are abrupt rolling movements of materials that become detached from steep slopes or cliffs, moving by free fall, bouncing, and rolling.
Flows: This is a general term including many types of mass movements such as debris flow, debris avalanche, lahar and mud flow.
Creep: It is a slow, steady downslope movement of soil or rock which often showed by curved tree trunks, bent fences or keeping walls, tilted pole fences.
Debris Flow: It is rapid mass movement in which loose soils, rocks and organic matter combine with untrained air and water to form the slurry that then flows downslope and associates with steep gullies.
Debris Avalanche: A variety of rapid debris avalanche.
Lahar: It is the mudflow or debris flow that originates on the slope of a volcano, triggered by heavy rainfall eroding volcanic deposits, sudden melting of snow and ice because of heat from volcanic vents or the breakout of water from glaciers, crater lakes or lakes dammed by volcanic eruptions.
Mud-flow: flowing mass of wet material that contains at least 50% sand, silt, and clay-sized particles.
Lateral spreads: These often occur on gentle slopes and result in the horizontal movement of earth materials. Lateral spreads cause liquefaction, where saturated sediments (sands and silts) transformed from a solid into a liquefied state triggered by an earthquake.
9. Topple: A block of rock that tilts or rotates forward and falls, bounces or rolls down the slope.
EFFECTS OF LANDSLIDES
The effects of landslides are:
1. The most common elements at risk are the settlements built on the steep slopes, built at the toe and those built at the mouth of the streams emerging from the mountain valley.
2. Buildings constructed without foundation for a soil and in sloppy areas are also at risk. Roads, communication lines are also vulnerable.
Structural mitigation :
Built in keeping walls helps to stop land from slipping. Such walls are often present along roads in hill stations.
Increasing vegetation cover is the cheapest and most effective way of reducing landslides. Vegetation helps in binding the top layer of soil with layers below and prevents excessive water run-off and soil erosion.
The natural way of preventing landslide is reducing water infiltration and allowing excess water to move down without hindrance. Therefore, proper maintenance of natural drainage channels is another mitigation strategy of the landslide.
Engineered structures having flexible underground installations like pipes can withstand forces caused by landslides.
Non-structural Mitigation :
Hazard mapping will locate areas prone to slope failures. This will permit identifying avoidance of areas for building settlements.
Land use practices must adopt to reduce landslides. Land use practices involve :
- Areas covered by degraded natural vegetation in upper slopes and afforested with suitable species.
- Existing natural vegetation must preserve.
- Any developmental activity started in the area must have taken up only after a detailed study of the region. During the construction of roads, irrigation canals, etc., proper care is necessary to avoid blockage of natural drainage.
- Buildings must construct in an area beyond a certain slope.
It must educate the public about signs that a landslide is imminent so it may take personal safety measures.