Context: Study identified 219 hanging glaciers in Uttarakhand’s Alaknanda basin, warning that warming and permafrost thaw are increasing break-off risks, potentially triggering ice-rock avalanches and outburst floods.
About Hanging Glaciers:
What It Is?
- A hanging glacier is a glacier that originates high on a mountain wall or valley flank and terminates abruptly at the edge of a steep precipice or cliff face, rather than flowing down into a main valley floor. Its snout ends high above the valley trough, routinely shedding ice through calving, icefalls, and avalanches.
Global Distribution: Prominently found in high-relief alpine environments worldwide, including the European Alps, the Andes, the North American Rockies, and the Himalayas-Karakoram range.
Indian Context: Heavily concentrated along the steep, glaciated slopes of the Garhwal and Kumaon Himalayas (Uttarakhand), Himachal Pradesh, Ladakh, and Sikkim.
How It Forms?
- High-Altitude Cirque & Ledge Accumulation: Heavy snowfall accumulates in steep niches, high shelves, and cirques on upper mountain faces, compacting into firn and glacial ice under freezing conditions.
- Glacial Retreat and Truncation: During warmer periods, larger primary valley glaciers (trunk glaciers) melt, thin, and recede rapidly. The smaller tributary glaciers feeding into them from steep sidewalls become disconnected and left stranded high up on the mountain walls.
- Thermal Destabilization and Basal Melting: Accelerated climate warming elevates zero-degree isotherms. The permafrost and subglacial ice adhering the glacier to the steep bedrock bed thaw, creating basal meltwater that acts as a lubricant and converts stable ice masses into precarious, dynamically unstable hanging bodies.
Key Features of Hanging Glaciers:
- Extreme Basal Slope Gradient: Typically perched on steep bedrock slopes with inclinations, making them highly sensitive to gravitational shear stresses.
- Dynamic and Geometric Instability: Prone to sudden shifts in ice flow velocity—often changing by an order of magnitude over short periods—causing structural fractures, tension crevasses, and redistribution of ice mass.
- Elevated Cliff Terminus: The snout ends abruptly at a sharp break of slope or vertical drop without extending into a gentler ablation zone; mass loss occurs primarily via mechanical detachment rather than surface melting.
- Thermal Regime Sensitivity: Many hanging glaciers in the Himalayas are cold-based or polythermal. Rising ambient temperatures weaken this frozen bond, significantly raising catastrophic structural failure risks.
- High Break-Off Runout Potential: Due to immense gravitational potential energy, collapsing hanging ice masses can trigger avalanche walls exceeding 50 metres in height.
Significance:
- Hanging-glacier collapse can trigger ice-rock avalanches, GLOFs and LLOFs, as seen in the 2021 Chamoli disaster.
- Glacier failures threaten pilgrimage towns, Char Dham roads and hydropower projects, requiring basin-wide monitoring, early-warning systems and risk-based zoning.
