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Sedongpu Mass Wasting

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August 27, 2024

Why in news?

A new study highlighted the impact of high frequency of mass wasting events in the Sedongpu Gully to Northeast India.

What is mass wasting?

  • Mass wasting - A geological event, of gravity-influenced movement of rock and soil down a slope.
  • These events may occur very rapidly and move as a flow.
  • Causes – They are often lubricated by rainfall or agitated by seismic activity.
  • Others includes rapid snowmelt, volcanic eruption, storm waves, rapid-stream erosion, or human activities like grading a new road.
  • Types – It involves the slipping, slumping, falling and flowing of soil or rock down a slope.

               MassWasting

  • Determining criteria - There are various factors which increase the likelihood and rate of different types of mass wasting
  • Steepness of slope gradient – The steeper the slope, the greater the influence of gravity on particles.
  • Rock structure - Bedding planes and faults can increase vulnerability to movements.
  • Rock typeSedimentary and unconsolidated sediments are more vulnerable to movement than igneous rocks.
  • Level of water saturation – The greater the saturation, the lower the friction between particles.
  • Vegetation cover – Plant roots help to hold surface together
  • Human activity – Mining can cause vibrations which trigger movement/poor slope management can lead to undercutting slopes

What is sedongpu mass wasting?

Sedongpu Gully

                      Sedongpu

  • Location – It is located in the catchment of the Sedongpu glacier on the Tibetan Plateau.
  • Its valley, is 11 km long and covers 66.8 sq. km.
  • Gully – It is a landform created by erosion from running water, mass movement or both.
  • Great Bend – Sedongpu river drains into the Yarlung Zangbo, or the Tsangpo River by taking a sharp turn called as great bend.
  • It is close to Tibet’s border with Arunachal Pradesh, where the River Tsangpo flows as the Siang River.
  • Gorges – It creates a gorge 505 km long and 6,009 metres deep while flowing around Mt. Namcha Barwa (altitude 7,782 metres) and Mt. Gyala Peri (7,294 metres).
    • It is one of the deepest gorges on the earth.
  • Sedongpu wasting – More than 700 million cubic metres of debris have been mobilised in the Sedongpu gully catchment since 2017.
  • Patterns of sedongpu wasting - From satellite images, 19 large mass-wasting events were grouped into three sub-patterns
    • Ice-rock avalanche (IRA)
    • Ice-moraine avalanche (IMA)
    • Glacier debris flow (GDF)

             Sedongpuwasting

A moraine is a mass of rocks and sediment deposited by a glacier.

What are causes for Sedongpu mass wasting?

  • Long-term warming - Annual temperature in this area increased at rates of 0.34º to 0.36º C during 1981-2018, which is higher than the global average.
    • Sedongpu basin consists mostly of Proterozoic marble whose land surface temperature ranges from -5º to -15º C, rarely exceeding 0º C before 2012.
  • Thus, there is extensive permafrost degradation occurring in the catchment, resulting in the progressive destabilisation of the slopes.
  • Dams – Big dams such as the Zangmu on the Tsangpo accentuate the threat of mass wasting.
    • China plans to set up a 60-GW project on the Tsangpo, which will have thrice the capacity of the Three Gorges project on the Yangtze, the world’s largest hydropower plant.
  • Steep Topography – Due to its steep topography, it is one of the most landslide-prone locations on the planet.
  • Geographical Instability – It is prone to earthquakes.
  • The 2017 Nyingchi earthquake destabilised the slopes and initiated the current period of instability.
  • Other factors – They have a highly fractured rock mass and the presence of large volumes of sediments from recent glaciations.

What are its impacts in India?

  • The Sedongpu mass wasting has serious transnational implications for the Tsangpo-Siang-Brahmaputra-Jamuna basin, especially in India and Bangladesh.
  • Sedimentation - Addition of major amounts of sediments to the course of the river.
    • River Brahmaputra carries more than 800 tonnes of sediment at Pandu in Guwahati, becoming more than a billion tonnes at Bahadurabad in Bangladesh.
  • River Blockage – Added sediments blocks the river at different locations.

                  MassWastingImpacts

Debris flows have occurred in two adjacent gullies, namely Sedongpu Gully (SDP) and Zelongnong Gully (ZLN), since the 1950s.

  • River bank erosion - Increasing sedimentation may make the river more intensely braided in the Assam plains, which could lead to more bank erosion.
  • Flooding Hazard - The sedimentation can elevate the river beds more, accentuating flood hazards.
  • Glacial Lake Outburst Flood- Breaching of the blockages leads to catastrophic flash floods in the downstream.
  • These floods were triggered by the outburst of a dam created by the glaciated debris and rock materials generated during landslides.
  • Livelihood Impact - The channels of the river in Assam and Bangladesh may get choked with sand and silt in the lean season making navigation difficult and also affects fishing.

What lies ahead?

  • Monitor the status and trends of geophysical events leading to landslides, rock falls and other erosional processes.

Reference

The Hindu| Frequent mass wasting in Tibet could Impact India

 

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