Mass Wasting
Context:
A recent study on the increased frequency of mass wasting events in the Sedongpu Gully of the Tibetan Plateau since 2017, coupled with the rapid warming of the region—which rarely saw temperatures above 0ºC before 2012—could pose significant risks for India, particularly in the Northeast.
More on news:
- The Sedongpu Gully, located within the catchment of the Sedongpu Glacier and its valley, drains into the Yarlung Zangbo, also known as the Tsangpo River, near the sharp turn known as the Great Bend.
- Here, the river flows around Mt. Namcha Barwa and Mt. Gyala Peri , creating a gorge that is 505 km long and 6,009 metres deep, making it one of the deepest gorges on Earth.
- The Great Bend is situated close to Tibet’s border with Arunachal Pradesh, where the Tsangpo River becomes the Siang River.
- Further downstream in Assam, the Siang meets the Dibang and Lohit rivers to form the Brahmaputra, which later flows into Bangladesh as the Jamuna River.
- The Sedongpu study carries significant implications for the Tsangpo-Siang-Brahmaputra-Jamuna river system, particularly in India and Bangladesh.
- The most immediate effect could be the substantial increase in sediment deposition along the river’s course, which is already one of the most sediment-laden rivers in the world.
About Mass Wasting:
- Weathering, mass-wasting and erosion are degradational processes.
- Mass wasting, known as mass movement, refers to the downslope movement of rock, soil, and debris under the influence of gravity.
- This process is distinct from other forms of erosion, as a moving medium like water, wind, or ice does not transport the materials involved.
Types of Mass Wasting:
- Creep: A slow, gradual movement of soil and rock down a slope, often influenced by freeze-thaw cycles and moisture content.
- Depending on the material involved, various types of creep can be identified, including soil creep, talus creep, rock creep, and rock-glacier creep.
- Landslides: A rapid movement of large masses of earth and rock, often triggered by heavy rainfall, earthquakes, or volcanic activity.
- Debris avalanche: It is characteristic of humid regions, regardless of vegetation, and typically occurs in narrow, steep tracks.
- Debris avalanches can move significantly faster than mudflows and are similar to snow avalanches.
- Solifluction: A specific type of creep occurring in saturated soils, typically in cold climates, where the thawing of frozen ground leads to slow downslope movement.
- Rockfalls: The free fall or bouncing of rock material down a steep slope, often occurring suddenly due to weathering or seismic activity.
- Subsidence: Sometimes considered a form of mass wasting, this involves the sinking of the ground surface, which can occur gradually or suddenly, often due to the collapse of underground cavities or the removal of materials like coal or salt.
Debris avalanches and landslides are common in the Himalayas due to their tectonic activity, steep slopes, and predominance of sedimentary and unconsolidated rocks. In contrast, the Nilgiris and the Western Ghats, which are relatively tectonically stable and consist mostly of hard rocks, experience these events less frequently. However, they are not entirely free from landslides and debris avalanches.
Causes and Triggers: The primary driver of mass wasting is gravity, which pulls materials down slopes. However, several factors can increase the likelihood of mass wasting events:
- Increased slope steepness: Steeper slopes are more prone to failure.
- Water saturation: Water can reduce friction and increase the weight of materials, making slopes more unstable.
- Vegetation removal: Vegetation helps stabilise soil; its removal can lead to increased susceptibility to mass wasting.
- Earthquakes and volcanic activity: These can destabilise slopes and trigger rapid mass wasting events.