Building trust is key in warnings on melting glaciers

Why in the News

The disaster that unfolded in Nepal and Tibet began with a rock-ice avalanche that transformed into a devastating debris flow. First reports read the event as an earthquake and possibly a glacial lake outburst flood (GLOF), a flood released when a lake held back by glacial ice or debris gives way. The shaking was in fact the force of the rock-ice avalanche hitting the valley floor. There was no glacial lake in the valley at all. The same sequence produced the Chamoli disaster in 2021, from a rock-ice avalanche off Ronti Peak, and the Dharali disaster in 2025. Himalayan warning systems are organised around glacial lakes whose location is known. The hazard that killed at Rasuwa can begin on any of hundreds of thousands of thawing slopes.

What is a rock-ice avalanche hazard cascade?

1. Rock-ice avalanche: A mass of rock and ice detaches from a steep, deglaciating slope and falls to the valley floor.
2. Transformation into a debris flow: The impact converts the avalanche into a debris flow, which then travels down the valley and destroys what stands in its path.
3. Hazard cascade: One process sets off the next, so the damaging flood has no single identifiable source waiting to be watched.
4. Disaster rather than natural event: Many rock avalanches and thousands of debris flows occur every year, and they become disasters only where they strike lives and surroundings.

Why is a hazard cascade harder to plan for than a glacial lake flood?

1. Known water source in a GLOF: For a glacial lake outburst flood, the origin of the water is the glacial lake itself.
2. Three interventions available at a lake: A lake can be modelled to forecast flood behaviour, drained where it is judged dangerous, or fitted with real-time monitoring.
3. No lake at Rasuwa: There was no large lake in that valley, so none of those three options was available and the event was as difficult to plan for as Chamoli.
4. Number of possible sources: Rock-ice avalanches could originate from many hundreds of thousands of steep, rapidly deglaciating slopes with thawing permafrost in the Himalaya.
5. Limits of failure prediction: Detecting slopes that are already moving is perhaps possible, and working out which of them will fail catastrophically is not yet reliable.

Who is exposed to these hazards, and where did the deaths occur?

1. Global GLOF exposure: 15 million people worldwide live with glacial lake outburst flood danger.
2. Concentration in High Mountain Asia: Over 9 million of those people are in High Mountain Asia, and nearly 3 million are in India alone.
3. Hydropower workers among the dead: In both Chamoli and Rasuwa, a significant number of the dead and missing were workers at hydropower infrastructure standing in the path of the flows.
4. Decisions downstream: The open questions are where people can and cannot live below such slopes, and what the benefits and risks of hydropower development in these environments are.

What would a denser seismic station network deliver?

1. Detection of landslide-generated earthquakes: Seismic stations can detect and locate the earthquake that a landslide itself generates.
2. Seismic signature of the flood: Extreme flood events produce continuous seismic noise as they move down a valley, in the same way glacial lake outburst floods do.
3. Technically possible, not yet built: The denser network is achievable with existing science and has not been done.
4. Cost and cross-border requirement: It would need co-operation across the Himalaya’s international borders and tens of millions of dollars.

Challenges to early warning for Himalayan hazard cascades

1. Instrumenting every valley is impractical: River gauges or monitoring in every single high mountain valley cannot realistically deliver warning in time. Eg. At Rasuwa the cascade began where there was no lake and no instrumented source to watch.
   The Fix: Concentrate instruments on the valleys that carry settlements or hydropower works below a rapidly deglaciating slope.
2. No usable lead time near the source: Warning shrinks to nothing for people living close to where the cascade begins. Eg. The system in place during the Rasuwa event gave enough warning for those further downstream and not enough for those upstream.
   The Fix: Pair instrumented warning with pre-agreed evacuation routes for the upstream valley, where no alert will ever arrive early enough.
3. Warning as a communication problem: Detection has to be followed by the news reaching people, by the speed at which they respond, and by what they actually do. Eg. Workers at hydropower sites in the flow path died in both Chamoli and Rasuwa.
   The Fix: Embed the warning system in the communities expected to act on it, so an alert is trusted and attached to a rehearsed response.
4. Cost of a wrong call: Naming a slope as dangerous, and failing to name one, both carry high consequences. Eg. Identifying which moving slopes will catastrophically fail is not yet reliable science.
   The Fix: Publish slope hazard assessments with their stated uncertainty, so the confidence attached to a warning travels with the warning.

Conclusion

Himalayan risk planning is built around a hazard whose source can be located, and the events now killing people begin on slopes nobody is watching. The science to close that gap exists and the network to carry it does not, because it requires money and agreement between countries that share the range. A warning that communities do not trust, or do not know how to act on, saves nobody, which makes trust part of the engineering rather than an afterthought. Lives can be saved on those terms, and the places cannot, which turns the harder question into where building should be permitted at all.

Matching Previous Year Question

“[2020, GS1, 10 marks] How will the melting of Himalayan glaciers have a far-reaching impact on the water resources of India? (हिमालय के हिमनदों के पिघलने का भारत के जल-संसाधनों पर किस प्रकार दूरगामी प्रभाव होगा ?)”