Danger from Above: On the Nepal Flood

UPSC Syllabus: Gs Paper 3- Disaster, and disaster management

Introduction

The devastating flash floods along the Nepal-Tibet border show the growing danger of disasters originating in the high Himalayas. The event was initially linked to an earthquake or rainfall, but satellite evidence pointed towards a glacial collapse or ice-rock avalanche, followed by destructive downstream flooding. It highlights the risks from unstable glaciers, debris blockages, glacial lakes and vulnerable infrastructure in a rapidly warming Himalayan region.

Nepal Flood Disaster: Causes and Sequence of Events

1. Glacial collapse as the trigger: Satellite imagery and scientific assessments indicate that a glacier collapse or ice-rock avalanche triggered the destructive flood, while the seismic event resulted from the collapse.
2. Possible river blockage and breach: Ice, rock and sediment may have temporarily blocked the river before accumulated water broke through, intensifying downstream flooding.
3. Rapid spread through river valleys: The flood entered the Lhende Khola, flowed into the Bhote Koshi, and then travelled south through the Trishuli river system.
4. Sudden rise in water level: Water in the Trishuli River reportedly rose by about 9 metres within 30 minutes, showing the extreme speed of the flood.
5. Human and infrastructure losses: The disaster caused hundreds of deaths and many missing persons, while settlements, hydropower and monitoring infrastructure suffered extensive damage.
6. Continuing secondary flood risk: A newly formed barrier lake upstream created fears of another breach and further flooding in downstream areas.

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1. Meaning of glacial collapse: It involves the detachment of a large mass of glacier ice, often carrying rock, sediment and water, from its bed.
2. Different forms of failure: Such gravity-driven events can include glacier detachments, ice avalanches and rock-ice avalanches on steep mountain slopes.
3. Transformation into debris flows: The collapsed material can move rapidly downhill as an ice-rich avalanche or a highly destructive debris flow.
4. High-altitude fall: Satellite observations suggested that part of the glacier broke off at about 5,200 metres and fell roughly 1,200 metres into the valley.
5. Role of melting snow: Available imagery indicated that a substantial amount of snow may have melted during the 24 hours before the disaster.
6. Barrier lake formation: Landslide and avalanche debris can block mountain rivers, creating temporary lakes that store large volumes of water.
7. Sudden barrier failure: When such blockages fail, stored water, mud, rock and debris can surge downstream as a catastrophic flood.
8. Difficulties in escape: High-speed flows of mud and water leave very little time for evacuation and can overwhelm roads and vehicles.

Glacier-Related Disasters: Evidence from the Himalayas and Beyond

1. South Lhonak Lake disaster: In October 2023, a Glacial Lake Outburst Flood in Sikkim released water, debris and rock, severely damaging the State’s largest hydropower project.
2. Long-term build-up of risk: Subsequent analysis showed that the South Lhonak disaster had developed over several years rather than appearing suddenly.
3. Aru glacier collapses in Tibet: In 2016, two major glacier collapses released about 68 million and 83 million cubic metres of ice, killing people and animals.
4. Sedongpu Basin events: Ice-rock avalanches in 2018 blocked the Yarlung Tsangpo River, creating a dangerous temporary lake and downstream flood threat.
5. Bukadaban Feng collapse: In 2022, around 40 million cubic metres of glacier ice detached and generated a 13-metre-high wave after entering a lake.
6. Ronti Peak disaster: In 2018, about 27 million cubic metres of rock and glacier ice collapsed in Uttarakhand, killing more than 200 people.
7. Rare but serious events: Glacial collapses remain unusual and site-specific, but Tibet has emerged as a location of several major documented collapses.
8. Risk beyond the Himalayas: The Blatten collapse in Switzerland also showed how combined rock, soil and ice failures can destroy settlements.

Climate Change and Increasing Himalayan Cryosphere Risks

1. Rapid glacier loss: Glaciers across the Hindu Kush Himalaya lost ice 65% faster between 2011 and 2020 than during the previous decade.
2. Shrinking glaciers in Nepal: Nepal’s glaciers lost close to one-third of their ice volume in roughly three decades, according to United Nations estimates.
3. Glacial retreat and instability: Rising temperatures can increase glacier retreat, alter mountain slopes and contribute to conditions favourable for glacier-related hazards.
4. Permafrost reduction: Warming can reduce permafrost, weakening high-altitude slopes and increasing the possibility of landslides and ice-rock failures.
5. Growing danger of glacial lakes: Melting glaciers can create or enlarge glacier-fed lakes, increasing the risk of Glacial Lake Outburst Floods (GLOFs).
6. More heat-related pressures: There is high confidence that increasing heatwaves, glacier retreat and permafrost loss will raise Himalayan hazard risks.
7. Hazards are location-specific: Even under a warming climate, the immediate causes of individual glacial collapses must be examined separately for each site.

Challenges in Monitoring and Predicting Himalayan Disasters

1. Large monitoring challenge: The Indian Himalayas contain nearly 7,500 glacial lakes and about 15,000 glaciers, making comprehensive monitoring extremely difficult.
2. Limits of remote sensing: Satellites can detect changes and reconstruct disasters, but they cannot fully determine the stability of every glacier or lake.
3. Need for field assessment: Accurate assessment often requires site visits, but remote terrain makes access difficult and limits the period for expeditions.
4. Short fieldwork window: High-altitude expeditions are generally feasible only from July to September, restricting detailed on-ground observations.
5. Difficulty of precise forecasting: Even with satellite data, predicting exactly when and where a glacier will collapse remains extremely difficult.
6. Limits of conventional flood warnings: The absence of rainfall before the Nepal disaster shows that rainfall-based warning systems may fail to detect such sudden events.
7. Risk of ineffective warnings: Warnings may also have limited value when residents cannot relocate because of habit, livelihood needs or lack of alternatives.
8. Role of advanced technology: Satellites, drones, unmanned aerial vehicles and thermal imaging can help assess damage, locate survivors and identify high-risk areas.

Way Forward

1. Improve glacier health monitoring: Governments should invest in better tracking of glaciers, glacial lakes and unstable mountain areas through remote sensing and field studies.
2. Identify vulnerable zones: Scientific monitoring should be used to map areas exposed to glacier collapse, GLOFs, landslides and debris-blocked rivers.
3. Integrate risk into development: Disaster assessments must become part of long-term development planning instead of being considered only after a disaster.
4. Restrict construction in high-risk areas: Settlements and large infrastructure projects should be discouraged in zones already identified as vulnerable to major natural outbursts.
5. Strengthen construction standards: Governments should enforce appropriate construction codes to reduce damage to roads, bridges and other infrastructure.
6. Protect hydropower infrastructure: Dams and hydropower projects in Himalayan valleys require greater attention because they are often among the first assets damaged.
7. Prepare for cascading hazards: Disaster planning must consider secondary risks, including temporary barrier lakes, river breaches and repeated downstream flooding.
8. Go beyond relief and rescue: Long-term prevention, continuous monitoring and safer development are necessary to address disasters worsened by passive neglect.

Conclusion

The Nepal flood shows how a disaster high in the Himalayas can quickly turn into a major downstream crisis through glacial collapse, debris flow and river blockage. Climate change is increasing the wider risks, even if its direct role remains uncertain. Better monitoring, safer construction and risk-based development can reduce future losses and prevent natural hazards from becoming larger human disasters.

Question for practice:

Discuss the causes, growing risks and challenges associated with glacier-related disasters in the Himalayan region, with special reference to the Nepal flood.

Source: The Hindu