Landslides: A Major Natural Disaster in Central Himalayan Region, Causes and Prevention
Author: A. K. Trivedi
ICAR - National Bureau of Plant Genetic Resources (ICAR)
Regional Station Bhowali (Niglat), District - Nainital - 263 132 (Uttarakhand)


Introduction

CHR stands unique in its rich cultural heritages, diversified geographical and climate conditions. Due to its physiographic conditions, land characteristics and climate conditions, CHR is one of the most disaster prone regions in the country exposed to different kinds of natural hazards. Natural disasters in this region are mainly related to the climate and topography. Landslides are common in lower and mid Himalayans region while cloud burst is of frequent occurrence in the high altitude areas.

Types of Natural Disasters

The degree of potential loss due to natural disaster depends upon the type of disaster and place of its occurrence. The occurrence of any type of disaster depends upon the climate and geographical constituents of the affected area itself. Some common and hazardous natural disasters are as following:

{1} Landslide {2} Earthquake {3} Drought {4} Flood {5} Cyclone {6) Volcanoes {7} El-Nina {8} La-Nina

Landslides:

A landslide occurs when part of a natural slope is unstable and unable to support its own weight. If a slippery material is present below soil then soil can become heavy with rainwater and prone to landslide. It is a downward or outward movement of soil, rock or vegetation due to gravitational force. This movement can be fall, flow, slide, spread or topple. Landslides occur usually at steep slopes but these may occur in areas with low slope gradient. These may occur due to:

1. Weakness in the composition, material or geological structure of rock or soil formation.

2. External factors, which affect the ground water regimes such as heavy rain, snowmelt, changes in ground water level etc.

3. Creation of new site conditions such as changes to natural slope due to construction activities.

4. Earthquakes or volcanic activities

Although, landslide is a natural disaster but it may occur due to man made factors such as:

1. Construction work without proper survey of the site and without designing and engineering inputs

2. Irrational farming technologies, for example, ploughing in a lengthwise direction down the slope, accelerate loss of substances on the slopes that are eroded by weathering. These practices continue to deteriorate the mountain slopes and make these slopes the source regions of landslides.

3. Removal of vegetation cover and deforestation, etc.

Farming activities on slopes involve removal of vegetation cover usually followed by terracing. Burning of vegetation to clear the land is a normal practice in hilly areas adopted by farmers this makes the land more prone to land slides. Similarly there are several natural factors which may cause landslide such as:

1. Intense rainfall or deposition of snow will raise the ground water table; decrease the soil strength and increases weight of associated material.

2. Rapid melting of snow adds water to soil mass on slopes makes it prone to land slide.

3. Erosion caused by continuous runoff over a slope can bring about instability of the soil mass.

4. The removal of support of a soil mass by flow of water in rivers, wave action etc.

4. Deposition of loose sediments in certain areas.

5. Weathering and decomposition of rocks

6. Ground vibrations created during earthquakes.

Types of Landslides:

There are several types of land slides depending on the topography the area such as:

1. Creep: Creep is imperceptibly slow down slope movement of earth cover or regolith. In the creep affected areas utility poles, fence posts and gravestones etc. appear tilted or deformed on the surfaces.

2. Debris fall: When rock as well as overlying sediments and vegetation is free falling, it is known as debris fall.

3. Debris flow: Down slope movement of collapsed, unconsolidated material typically along a stream channel.

4. Rock fall: Free falling of detached bodies of bedrock (boulders) from a cliff or steep slope.

5. Rock Slide: Rockslide is a sudden down slope movement of detached masses of bedrock.

6. Slump: It is a type of slope failure in which a downward and outward rotational movement of rock or soil occurs along a curved concave up surface.

Effects of landslides:

Landslides may affect directly or indirectly to inhabitants, animals and natural resources of whole area. Anything on top of or in the path of a landslide suffers damage. Debris may block roads, supply lines (telecommunication, electricity, water, etc.) and waterways. Intensity of causalities (deaths and injuries to people and animals) may vary from slight to severe. In addition, productivity of agricultural and forest land may be reduced. In the downstream area erosion and flooding will change agricultural land to less productive or barren land.

Indirectly landslides may affect safety dam in the area. The safety of a dam can be severely affected by landslide in the upstream area of the dam or on the slopes bordering the reservoir. It may cause flood surges by movements of large masses of soil into the reservoir. Thus wave formed can overtop the dam causing downstream flooding and possibly failures to the dam. Increased sedimentation in the reservoir results in the loss of water storage and increased likelihood that the dam will be overtopped during periods of excessive runoff.

Additionally, landslides and flooding are associated with each other, both are related to intense rainfall, runoff and ground saturation. Debris increases damage because flow can cause flooding by blocking valleys and stream channels, forcing large amounts of water to backup. Moreover, this causes dual damage i.e., backwater flooding in the upstream area as well as quick downstream flooding, if the blockage gives away. In turn, flooding can cause landslides, due to rapidly moving flood waters. Once support is removed from the base of saturated slopes, land sliding takes place. In the steep landslide prone areas occurrence of earthquake, greatly increases the possibility of shattering mudflows. Damage to electrical wires may start fires which increases damages. Landslides may result in direct or indirect losses.

Direct losses include:

1. Most damaging impact of land slides is loss of life. Landslides may cause death and injury to people and animals. The moving mass can bury people and animals under debris.

2. It may cause loss of property and assets. The force and speed of debris, mud or earth mass generated due to mass movement may destroy houses, buildings and other properties on its way.

3. Landslides damage infrastructure as well as lifeline facilities. Earth mass can block or damage infrastructures such as roads, railway, bridges, telecommunication, electrical supply lines, etc.

4. Earth mass can effect water recourses in the area by blocking rivers, diverting water ways, blocking irrigation channels, reducing storage capacity of tanks, reservoirs, ponds, etc.

5. It may cause production losses to open cast mines, rock quarries, etc.

6. Productive land area may be covered with debris or blocked from access thus it may result in the loss of agricultural land.

7. Landslides may cause loss of places of archaeological, historical and cultural importance.

Indirect losses include:

1. Value of immovable properly will be reduced because people may be unwilling to purchase property in landslide prone area.

2. There will be loss of revenue due to loss of productive area and productivity of available area.

3. Investment will be diverted towards mitigating future landslide damage; in turn it will increase costs of essential commodities.

4. Productivity of agricultural and forest lands will be decreased due to being buried by debris, lack of access or being under flood.

5. Water quality will be adversely affected particularly safe drinking may not be available for some time due to damage of water storage facilities such as streams, reservoirs, storage tanks etc.

6. Deaths of family members and the destruction of personal belongings may have great sentimental value and cause reduction in quality of life.

7. Landslides as a natural disaster can have a deep impact on people's emotional wellbeing affecting their feelings, thoughts, actions, and relationships.


Indicators of landslides which may help to minimize/ avoid problem:

There are certain indicators which should be considered to avoid landslide problem such as:

[i.] Normally, if possible trees grow vertically towards the sun. Bend over or tilted trees indicate a dislocation of the slope. Bowed trees indicate that the ground is moving very slowly, which gives time to trees, to straighten up as they grow.

[ii] Bulging earth is an indicator of new or ongoing movement of a slope which can be easily noticed.

[iii] Cracks, particularly running parallel to a slope, are indicators of stress relief and slight movement of a slope. These cracks may appear in the overlying snow during winter season, if the movement is significant enough.

[iv] In homes slope movements can be seen up as cracks through the foundation or the walls of buildings.

[v] Distortion in is a symptom that they are unable to support the upslope building or area.

[vi] Hummocky grounds are low mounds irregularly spaced around the old or some times recent landslide areas. It indicates that the upslope area (old landslide deposits) could move again.

[vii] If excess water is available in a slope, it will try to find its way to the surface. This indicates that the slope area above the seep is saturated and it may slip any time. Seepage of water will cause the down slope area to become saturated and this will also be prone to slide.

[viii] When new utility poles are typically put in vertical position and in line. Any change in their position indicates movement of ground.

Measures to reduce the chance of landslides:

Vegetation cover protects land from landslides and soil erosion. Therefore, efforts should be made to maintain greenery particularly on slopes. Provisions should be made at community level to prevent people from excavating, removing materials from the soil or cutting trees. Trees should be planted on slopes and slope base to prevent erosion. Records of erosion, landslide masses and falling rocks should be maintained. Before building house information should be gathered about site and history of landslides in the area. During constructing a building on a slope design that suits the natural slope should be adopted. Vegetation and large trees should not be removed while constructing. Natural streams or drainage paths should not be obstructed during construction. Surface water should be diverted towards the natural galley enabling water to quickly drain away from the slope.

Precautionary measures to be followed in landslide prone areas:

Listen to weather forecast on the radio, TV etc. about heavy rains. During nights residents should remain awake of heavy continuous rain and be ready to move immediately to a safer location. Abnormal sounds of soil and rock movement or breaking of trees may be followed by landslides hence, these should be listen attentively and consider seriously. To observe cracks on the slope one should not move closure to slope. If residents have to evacuate place it should be done immediately without wasting time to collect belongings. While evacuating, efforts should be made to avoid possible landslide paths because landslide can occur suddenly. If rocks are falling one should immediately seek cover behind trees and other solid objects. Efforts should be made to stay together and support each other as far as it is possible and useful. Special attention should be paid for very small children, very old people and sick or disabled people.

Precautions during landslide:

Preferable one should stay where people are available around. During disaster children need special attention and comfort than normal situation. Attentively all their questions should be answered up to maximum possible extent even if they ask the same question again and again. One should talk children and assure them that they are safe. In fact, more courage, strength and energy is needed to face the situation successfully so one should conserve energy and postpone unnecessary work and divert the energy to accomplish necessary work only.

Precautions needed after landslide:

After landslide one should not enter the area without permission from the authorities. Although field and buildings may seem to be as before landslide but one should not enter damaged area or buildings until the authorities declare them as safe. Persons engaged in the removal of debris or the digging up of bodies buried in the mass should do their work in an organized manner. If water is available in the debris deposit it should be removed first and all water paths should be diverted away from the affected slope area and the debris. Children should not be allowed to go through the loose and new deposits of debris because the surface may appear to be dry but the wet conditions can prevail within the mass. Damaged area should be replanted on priority during next season of planting to avoid erosion

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