Why have Bikaner and Barmer in Rajasthan reported land sinking in the last month?

Sub: Geography

Sec: Indian Physical geography

Context:

Two incidents of land subsidence occurred in Rajasthan within a month.
In Sahajrasar village, Bikaner district, 1.5 bigha of land collapsed forming a 70-feet deep pit, narrowly missing a passing train.
In Nagana village, Barmer district, two parallel cracks appeared over a 1.5 km area.

Barmer Incident:

Cracks appeared near the wells of a crude oil company.
GSI officer suggests water dissolution of soil causing underground space, leading to cracks.
Residents allege groundwater overexploitation by the oil company, which GSI is investigating further.

Geological Concerns and reason behind the land subsidence:

Both incidents in desert districts raised concerns among geologists and the public.
Preliminary reports suggest water as a common factor.
Excessive groundwater exploitation and reduced rainfall are cited as primary causes.
- Analysis of groundwater, rainfall and other relevant data along with geological field observations showed that the area has been experiencing a high degree of groundwater depletion over the years.
- It may lead to drying up the water-bearing aquifer rocks/sediments at the contact zone of the sub-surface hard rocks and aeolian deposits which may induce compaction of dried-up pore spaces/voids, consequently reducing of volume of sub-surface strata and resultant loose sand bearing land subsidence.
Residents dispute claims of groundwater exploitation, citing minimal borewells and reliance on external sources for agriculture.
The historical context suggests the sinking land in Sahajrasar has precedence dating back decades.

Land subsidence:

According to the National Oceanic and Atmospheric Administration (NOAA), subsidence is the “sinking of the ground because of underground material movement”.
Major causes for land subsidence:
- Natural factors: Land subsidence happens due to gradual or sudden natural compaction or collapse of soils due to reasons like –
  - Tectonic activities (e.g. earthquake and faulting).
  - Volcanic activities.
  - Landslide
  - Formation of sinkholes.
  - Thawing of permafrost.
- Anthropogenic causes:
  - Compaction of aquifer systems due to extensive groundwater withdrawals: When water is extracted from aquifers, the clay between pockets of water collapse gradually, leading to land subsidence.
  - Development of underground infrastructure such as metro, tunnels, etc.
  - Excessive underground mining of minerals, oil, and gas.
  - High load of constructions such as high-rise buildings

Solutions To Reduce Land Subsidence:

Slope stabilization: Using methods like terracing or erecting retaining walls, slopes can be stabilized to prevent landslides and erosion.
Planting vegetation: Vegetation planting on slopes can aid in soil stabilization and erosion prevention. Slope stabilization is particularly effective with trees and other deep-rooted plants.
Control of drainage: In hilly areas, it is crucial to effectively manage and maintain drainage systems since poor drainage can cause the land to sag. Installing culverts or other drainage systems may be necessary to direct water away from slopes and stop erosion.
Strengthening foundations: Buildings in mountainous communities may occasionally need to have their foundations reinforced to stop them from sliding or collapsing. This can entail adding strength to the foundations or underpinning them.
Planning and zoning: With careful planning and zoning, structures can be kept out of locations that are vulnerable to landslides or erosion. To do this, certain regions could need to be declared no-build zones or high-risk areas might need to use special construction methods.

Source: DTE