10 August 2024 : Daily Answer Writing
Q1) Discuss the natural and anthropogenic factors behind incidents of land subsidence. Suggest counter-measures to contain such incidents.
(150 Words/10 Marks)
ANS
Land subsidence is a gradual settling or sudden sinking of the Earth’s surface because of underground material movement. Land subsidence may happen owing to various natural and anthropogenic factors:
- Natural causes:
- Activity along geographical faults may result in subsidence of ground. E.g., reported role of reactivated geographical fault in Joshimath land subsidence (2023).
- Volcanic activities: Volcanic activities lead to collapse of underlying magma chambers, ground shaking etc., which leads to land subsidence.
- Liquefaction associated with earthquakes may result in severe subsidence of land. E.g., subsidence in Urayasu city in Japan.
- Frequent landslides, especially in the young fold mountains, may also result in land subsidence.
- Anthropogenic causes:
- Decline of groundwater: Over/unplanned extraction of ground water resources is one of the prominent factors behind land subsidence. It is seen in areas of underground karst topography. E.g., as per a study, a 9 m decline in the groundwater showed a subsidence rate of 18.23 mm/year.
- Unplanned development:
- Lack of proper drainage in tandem with unplanned/illegal construction led to the blocking of the natural flow of water, resulting in frequent landslides and land subsidence.
- Infrastructure development without the proper vulnerability mapping of the area is also a leading cause behind subsidence. E.g., As per experts, construction over landslide debris may have aggravated subsidence problem in Joshimath; infrastructure projects in fragile Himalayas
- Unbridled mining activities done in an unsustainable manner may also lead to land subsidence. E.g., subsidence in Raniganj due to underground coal mining; land subsidence due to coal fires (void is created as the underground coal is burnt) in Jharia. region.
Counter-measures to contain the incidents of land subsidence can be seen as:
- Infrastructure:
Construction work in the fragile ecosystem should be done using low impact techniques.
E.g., In case of Joshi math, M C Mishra committee (1976) warned against blasting the hill side for removing the boulders.
The load bearing capacity of the ground/land should inform the choice of construction material.
E.g., using cow dung, wood, mud, tin etc., for construction of houses.
- Deep soil mixing (injecting stabilising agents deep into the ground) can prevent land subsidence caused by soil compression.
- Maintaining and replenishing ground water resources may ameliorate the challenge of land subsidence.
- Afforestation activities readily reduce soil erosion and can check landslides, countering the problem of land subsidence in the long run.
Land subsidence presents itself as a seminal challenge having environmental, economic, and social consequences. Therefore, it is an imperative to adopt a multipronged stakeholder approach to arrest this menace.
