Subject: GS-01: Geography
Context:
- The reports by central technical and scientific institutions that studied the unprecedented land subsidence phenomenon in Joshimath, Uttarakhand have been made available to the public.
Key observations made by various institutions about Land subsidence in Joshimath:
- Central Ground Water Board: It suggested that trenches along with the retention wall may be constructed at different topographic levels so that groundwater pressure may be dissipated and cracks do not appear in the future.
- It also recommended that construction activities in the spring zone area should be immediately stopped.
Vulnerable Joshimath:
- Joshimath is built on the deposits of an old landslide, which means that the slopes can be destabilized even by slight triggers.
- The town is also in Zone V, which, as per India’s seismic zonation scheme, denotes the highest risk.
- It lies between two thrusts, the Main Central Thrust (MCT) and the Vaikrita Thrust (VT), and thus occupies a seismically active terrain.
- Because of the MCT, the area around Joshimath is highly active in terms of slope mobility.
- Climatologically, Joshimath lies in a region that frequently receives high-intensity, focused rainfall which could trigger landslides, since the slopes are precariously balanced.
- Joshimath is overly burdened with structures built without any regard for the land’s load-bearing capacity.
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- Central Building Research Institute: Joshimath town is situated on Vaikrita groups of rocks overlain by morainic deposits composed of irregular boulders and clay of varying thicknesses, which are less cohesive and susceptible to slow subsidence and landslide subsidence.
- The Indian Institute of Remote Sensing: It outlined that “Land Subsidence phenomenon in Joshimath may be due to a toe-cutting phenomenon, slope instability as a result of seepage of local drainage water in the soil, terrain and edaphic characteristics, loose and unconsolidated moraine materials of the slope (due to old landslide) and flash flood events in and around the area in the recent past.”
- IIT Roorkee: The main reason for the subsidence appears to be internal erosion caused by the subsurface drainage, which may be due to infiltration of rainwater/melting of ice from households and hotels.
- Recommendation: Though subsidence is a continuous phenomenon, it can be minimized by controlling infiltration of water, which helps in minimizing internal erosion.
- National Geophysical Research Institute (NGRI): Subsidence was observed in the middle and western side of the town, although isolated subsidence was observed throughout the Joshimath areas.
- The National Institute of Hydrology (NIH): It studied the water seepage point in the Jaypee colony area of Joshimath from where the water kept flowing with great force for days, causing concern among authorities, it outlined that, an eruption was caused by blockage of sub-surface channels.
Also read: Himalayan Blunders that are Ravaging the Himalayas
Importance of Joshimath
- Strategic importance: Joshimath lies on national highway NH58. It connects Delhi with Badrinath and Mana Pass in Uttarakhand near the Indo-Tibet border and is also en route to Barahoti, a disputed territory along the border.
- Religious importance: Joshimath is one of the four institutions that were established by Adi Shankara.
- Gateway to pilgrimage & heritage sites: The town is also a gateway to noted sites of pilgrimage – Badrinath, Hemkund Sahib; the international skiing site of Auli; and the Valley of Flowers, a UNESCO World Heritage site.
September 26, 2023
