Ice patches on melting glaciers greater threat than thought: ISRO scientists

Why in the News

A new study by scientists from the Indian Space Research Organisation has identified exposed ice patches on retreating Himalayan glaciers as a key precursor to flash floods. The study examined the August 5, 2025 Dharali flash flood in Uttarakhand that killed nine people and devastated settlements along the Bhagirathi river valley. Satellite imagery revealed exposed ice patches in the nivation zone of the Srikanta glacier shortly before the disaster. (Nivation is defined as the erosion of the ground beneath and around a snow bank, primarily resulting from the processes of alternate freezing and thawing.) This indicates accelerated deglaciation and unstable cryosphere conditions. This finding marks an important shift in understanding Himalayan hazards: disasters may originate not only from glacial lake outburst floods (GLOFs) but also from smaller, previously overlooked cryospheric instabilities linked to warming temperatures.

What are exposed ice patches?

1. Exposed ice patches are areas of ancient, stable ice that have become visible on the surface of a glacier or mountain slope after their protective covering of seasonal snow and firn (intermediate ice) has thinned or melted away. 
2. Unlike the main body of a glacier, which flows like a slow-moving river, these patches are often stationary and act as “prehistoric freezers”

Reasons for their formation are as follows:

1. Thinning Insulation: Warmer temperatures reduce the layers of snow and firn that normally insulate the deeper ice.
2. Ablation: During the ablation period (when a glacier loses more ice/snow than it gains), these patches may emerge on steep, shaded slopes, particularly in nivation hollows where snow traditionally lingers year-round.
3. Wind Scouring: In some regions, like Antarctica, strong winds can strip away top layers to reveal bright blue patches of older, denser ice.

How do exposed ice patches signal accelerated glacier retreat in the Himalayas?

1. Deglaciation indicator: Exposed ice patches in the Srikanta glacier’s ablation zone indicate thinning seasonal snow and firn cover due to rising temperatures.
2. Satellite evidence: Pre-event satellite imagery showed persistent exposed ice patches on north-northeast facing slopes where snow normally accumulates.
3. Cryosphere instability: Loss of insulating snow layers accelerates melting and structural weakening of glaciers.
4. Regional warming effect: Similar processes have been documented in other warming cryosphere regions including the Canadian Arctic and Greenland.

What role did nivation processes play in triggering the Dharali flash flood?

1. Nivation process: Erosion of ground beneath snowbanks caused by alternate freezing and thawing cycles.
2. Formation of nivation hollows: Repeated snow accumulation creates depressions which deepen over time.
3. Structural instability: In steep Himalayan terrain, nivation hollows accumulate ice, meltwater, and debris.
4. Trigger mechanism: Collapse of an exposed ice patch within the nivation zone of the Srikanta glacier released meltwater and debris.
5. Result: Sudden downstream debris flow triggered the Dharali flash flood.

Why are Himalayan glaciers increasingly vulnerable to cryosphere hazards?

1. Rapid glacier retreat: Himalayan glaciers are losing ice due to rising regional temperatures.
2. Snow and firn thinning: Seasonal snow cover that stabilizes glaciers is shrinking.
3. Steep mountain terrain: High relief areas amplify instability and debris flow risks.
4. Glacier fragmentation: Smaller unstable ice masses form as glaciers shrink.
5. Emerging hazard types: Hazards now include not only GLOFs but also ice collapses, debris flows, and cryosphere mass movements.

How do satellite observations improve early warning systems for glacier disasters?

1. Pre-event detection: Satellite imagery identified exposed ice patches before the Dharali flood.
2. Landscape monitoring: Remote sensing helps track glacier retreat and unstable cryosphere zones.
3. Hazard reconstruction: Earth observation data reconstructs sequences leading to disasters.
4. Early warning potential: Monitoring exposed ice patches could provide advance signals of possible cryosphere hazards.

Why must disaster monitoring extend beyond glacial lakes to smaller cryosphere instabilities?

1. Focus shift: Traditional monitoring emphasizes glacial lake outburst floods.
2. Overlooked hazards: Small-scale cryosphere instabilities can trigger similar destructive floods.
3. Regional prevalence: Similar geomorphological conditions exist across much of the Himalayan arc.
4. Policy implication: Disaster risk assessment must include nivation zones and exposed ice patches.

Conclusion

Rapid glacier retreat in the Himalayas is generating new cryosphere hazards beyond traditional glacial lake outburst floods. The Dharali flash flood demonstrates how exposed ice patches and nivation-zone instability can trigger sudden disasters in high-mountain regions. Strengthening satellite monitoring, hazard mapping, and climate-resilient disaster management systems is essential to reduce risks and protect vulnerable Himalayan communities.

PYQ Relevance

[UPSC 2024] What is disaster resilience? How is it determined? Describe various elements of a resilience framework. Also mention the global targets of the Sendai Framework for Disaster Risk Reduction (2015-2030).

Linkage: The Dharali flash flood from glacier ice-patch collapse highlights the need for disaster resilience in fragile Himalayan regions facing climate-induced hazards. It underlines the importance of Sendai Framework goals like risk monitoring, early warning systems, and satellite-based glacier surveillance.