LANDSLIDE SUBSIDENCE ZONE - GEOGRAPHY

News: Joshimath declared landslide-subsidence zone

 

What's in the news?

       Joshimath has been declared a landslide-subsidence zone and over 60 families living in uninhabitable houses in the sinking town have been evacuated to temporary relief centers.

 

Key takeaways:

       There are a total of 4,500 buildings in Joshimath and 610 of these have developed huge cracks, making them unfit for habitation.

 

Land Subsidence:

       According to the National Oceanic and Atmospheric Administration (NOAA), subsidence is the “sinking of the ground because of underground material movement”.

 

Causes:

The causes may be man-made or natural.

       Man Made causes:

       Removal of water, oil, or natural resources

       Mining activities.

       High load of constructions such as high-rise buildings.

       Development of underground infrastructure such as metro, tunnels, etc.

       Compaction of aquifer systems due to extensive groundwater withdrawals.

 

       Natural Causes:

       Earthquakes

       Soil erosion

       Soil compaction.

       Landslide.

       Formation of sinkholes.

       Thawing of permafrost.

 

What can be the reasons behind Joshimath subsidence?

The exact reason behind Joshimath land subsidence is still unknown but experts suggest that the incident might have occurred due to variety of factors such as

       Unplanned and unauthorized construction

       Over-population

       Obstruction of the natural flow of water and hydel power activities

       Active Seismic Zone.

       Lack of a proper drainage system

       Built on ancient landslide materials:

       According to experts, Joshimath city has been built on an ancient landslide material - meaning it rests on a deposit of sand and stone, not rock, which doesn’t have high load-bearing capacity.

       This makes the area extremely vulnerable to ever-burgeoning infrastructure and population.

       Reactivation of a geographic fault:

       It is defined as a fracture or zone of fractures between two blocks of rock - where the Indian Plate has pushed under the Eurasian Plate along the Himalayas.

 

What's with NTPC's Tapovan Vishnugad Hydro Power Plant?

       As per the reports, residents have also blamed NTPC’s Tapovan Vishnugad Hydro Power Project for the incident.

       They allege that the tunnel had water seepage “from a punctured aquifer, leading to the drying of water sources in Joshimath.”

 

Impacts of Land Subsidence:

       It is estimated that by 2040, land subsidence will affect approximately 8% of the world’s top layer and approximately.

       In India areas other than Mumbai like Kolkata and Delhi are also witnessing land subsidence.

       Areas where the earth matter is made up of thin soil particles, like the alluvial deposits of fertile Gangetic plains, are more vulnerable.

 

M. C. Mishra Committee:

       It cautioned against “unplanned development in this area, and identified the natural vulnerabilities.”

       It suggested following measures to sustain land subsidence.

 

1. Imposition of restrictions on heavy construction:

       Construction should only be allowed after examining the load-bearing capacity of the soil and the stability of the site, and restrictions should also be imposed on the excavation of slopes.

2. Keeping the boulders:

       In the landslide areas, stones and boulders should not be removed from the bottom of the hill as it would remove toe support, increasing the possibility of landslides.

3. Sealing of cracks:

       Cracks which have developed on the slopes should be sealed. The toe of a landslide is its bottom-most point.

4. Conserving of trees:

       It has also advised against cutting trees in the landslide zone, and said that extensive plantation work should be undertaken in the area, particularly between Marwari and Joshimath, to conserve soil and water resources.

5. Agriculture on the slopes must be avoided:

       Activities like ploughing loosens the soil thereby triggering the scope for landslides.

6. Preventing water seepage:

       To prevent any more landslides in the future, the seepage of open rain water must be stopped by the construction of a pucca drainage system.

7. Cobbled roads:

       Roads should be metalled and without scuppers, that drain away the water from the road surface.

8. River training:

       The construction of structures to guide the river’s flow should be carried out.

       Hanging boulders on the foothills should be provided with appropriate support.

 

WAY FORWARD:

1. Technological support:

       Using advanced satellite technology to accurately identify hotspots afflicted by land deformation, can prompt local authorities to carry out ground measurements.

2. Regional Study:

       Understanding the geophysical properties of the subsiding areas to tackle causes.

       For instance, in regions with high groundwater extraction, stricter measures for rainwater harvesting, punishing illegal groundwater mining, etc.

3. Judicious use of groundwater:

       Implementing solutions to offset the over-extraction of groundwater like- recharging groundwater by rainwater harvesting, managed aquifer recharge, pond revival, curbing illegal groundwater pumping, and planting native species that can help in groundwater conservation.

4. Sustainable planning:

       Evaluating building conditions in hazard zones to undertake necessary repair and maintenance.

       Incorporating land subsidence in the assessment and modeling of flooding and inundation in urban areas.

       Systematic and continuous monitoring of land subsidence to avoid widespread disasters, especially in areas that are highly populated and prone to other hazards like earthquakes, floods, etc.

       Time-bound reconstruction plan must be prepared.

       Continuous seismic monitoring must be done.

       A risk sensitive urban development plan for Joshimath should also be developed.