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.