Landslides: Movement of a mass of rock, debris, or earth down a slope under the direct influence of gravity.

It is estimated that 30% of the world’s landslides occur in the Himalayan ranges.

In the Nilgiris alone, unprecedented rains in the region triggered about 100 landslides.

The mean rate of land loss is to the tune of 120 meters per kilometer per year and the annual soil loss is about 2500 tons per square kilometer.

Landslide Vulnerability Zones:

• Very High Vulnerability Zone: Highly unstable, relatively young mountainous areas in the Himalayas and Andaman and Nicobar, Western Ghats and Nilgiris, the north-eastern regions.
• High Vulnerability Zone:  All the Himalayan states and the states from the north-eastern regions except the plains of Assam.

Moderate to Low Vulnerability Zone: Areas that receive less precipitation such as Trans- Himalayan areas of Ladakh and Spiti (Himachal Pradesh), Aravali, rain shadow areas in the Western and Eastern Ghats and Deccan plateau.

Types of landslides:

1. Rockfalls: Rapid descent of individual rock fragments. Example: Landslides along mountainous roads, like the Kedarnath landslide in India (2013).
2. Debris Flows: Fast-moving mix of water, soil, and debris. Example: The Oso landslide in Washington, USA (2014).
3. Mudslides: Slurry of waterlogged soil and debris. Example: The Sierra Leone mudslides in Freetown (2017).
4. Landslide Avalanches: Large-scale, fast-moving landslides. Example: The Randa rockslide in Switzerland (1991).
5. Creep: Slow, gradual downhill movement of soil or rock. Example: Ongoing creep on hillsides globally.
6. Earthflows: Sluggish flow of saturated soil and debris. Example: The Vaiont Dam landslide in Italy (1963).
7. Lateral Spreads: Horizontal movement of soil and rock. Example: The Hope Slide in British Columbia, Canada (1965).

Criteria to Declare:

The Indian government typically relies on a combination of criteria and monitoring systems to declare landslides and issue alerts. These criteria may include:

1. Geological Studies: Assessment of factors like soil types, rock formations, and past landslide history.
2. Rainfall Data: Heavy and prolonged rainfall can saturate the soil, increasing the likelihood of landslides.
3. Ground Movement Monitoring: Technologies like inclinometers and GPS are used to detect ground movement or slope instability in vulnerable areas.
4. Remote Sensing: Satellite imagery and aerial surveys are employed
5. Weather Forecasts: Meteorological data and weather forecasts are examined that could trigger landslides.
6. Historical Data: Past landslide events and their impact on specific regions are considered when assessing the risk of future landslides.
7. Early Warning Systems: Many states in India have early warning systems in place to provide alerts to residents in landslide-prone areas when conditions become hazardous.

Causes:

1. Natural
   1. Heavy Rainfall: Prolonged or intense rainfall can saturate the soil, making it more susceptible to sliding.
   2. Steep Slopes: Slopes with steep gradients are more prone to landslides.
   3. Earthquakes: Ground shaking from earthquakes can dislodge rocks and soil, leading to landslides.
   4. Volcanic Activity: By altering the landscape or generating pyroclastic flows.
   5. Erosion: Natural erosion processes, such as rivers undercutting hillsides.
   6. Soil Type: Loose, poorly compacted soils are more likely to fail.
   7. Freeze-Thaw Cycles: In colder climates, freeze-thaw cycles can expand and contract water within rocks and soil, leading to fracturing and landslides.
   8. Wildfires: Fires can destroy vegetation and alter soil properties, increasing the risk of landslides during subsequent rainfall.
2. Anthropogenic:
   1. Deforestation: The removal of trees and vegetation makes slopes more susceptible to sliding.
   2. Human Modification: Changes in land use and urbanization can increase the risk of landslides.
   3. Human Activities: Excavation, mining, construction, and irrigation can alter the natural landscape and trigger landslides.
   4. Lack of Drainage: Inadequate drainage systems can lead to water accumulation in the soil, increasing its weight and instability.

Mitigation:

1. Restriction on the construction and other developmental activities.
2. Limiting agriculture to valleys and areas with moderate slopes.
3. Control on the development of large settlements in the high vulnerability zones.
4. Promoting large-scale afforestation programmes.
5. Constructions of bunds to reduce the flow of water.
6. Terrace farming should be encouraged in the northeastern hill states where Jhumming (Slash and Burn/Shifting Cultivation) is still prevalent.
7. Landslide Risk Mitigation Scheme (LRMS):
   • The Scheme envisages financial support for site specific Landslide Mitigation Projects recommended by landslide prone States, covering “disaster prevention strategy, disaster mitigation and R&D in monitoring of critical Landslides” thereby leading to the development of Early Warning System and Capacity Building initiatives.

NDMA Guidelines:

• Do’s
  1. Move away from landslide paths or downstream valleys quickly without wasting time.
  2. Keep drains clean,
  3. Grow more trees that can hold the soil through roots,
  4. Identify areas of rock fall and subsidence of buildings, cracks that indicate landslides and move to safer areas. Even muddy river waters indicate landslides upstream.
  5. Ensure that the toe of slope is not cut, remain protected, don’t uproot trees unless re-vegetation is planned.
  6. Listen for unusual sounds such as trees cracking or boulders knocking together.
  7. Stay alert, awake and active (3A’s) during the impact or probability of impact.
  8. Try to stay with your family and companions.
  9. Check for injured and trapped persons.
  10. Mark path of tracking so that you can’t be lost in the middle of the forest.
• Don’ts
  1. Try to avoid construction and stay in vulnerable areas.
  2. Do not touch or walk over loose material and electrical wiring or poles.
  3. Do not build houses near steep slopes and near drainage paths.
  4. Do not drink contaminated water directly from rivers, springs, wells but rain water if collected directly without is fine.
  5. Do not move an injured person without rendering first aid unless the casualty is in immediate danger.

Way Forward:

India has a high degree of vulnerability towards the occurrence of Landslides. It is therefore not possible for the government to completely stop their occurrence. Although, it can definitely curtail their adverse impact by developing robust resilience in consonance with the Sendai Framework for Disaster Risk Reduction 2015-2030.