wo weeks after the flood, rescuers in Nepal were still drilling toward three hydropower tunnels where dozens of workers were thought to be trapped behind walls of mud and rock. The flood that sealed them in had arrived on the morning of August 26, when a mass of rock and ice broke off the Langtang range and fell more than two kilometres into a river, gathering into a wall of water and debris that ran down the valley at more than 150 kilometres an hour. It killed more than 1,350 people in Nepal and left thousands more missing, among them residents, border staff, pilgrims and the tunnel crews.

Why the mountain gave way is now coming into focus. The answer runs through the climate crisis.

In the days before the collapse, the glacier at 5,200 metres was hotter than in any comparable spell in more than half a century of records. Researchers studying the site attribute the failure to that heat thawing the permafrost that cements high rock faces together, and to fresh snowmelt seeping into the fractures, acting on a slope already close to its limit. By their estimate, without the warming now built into our climate, a heat spell like this at that altitude would occur perhaps once in several thousand years.

The flood struck on a clear day during the monsoon season. It was not caused by rain. It followed a smaller glacial flood in this same Nepali valley in July last year that killed 19 people. The mountains store water for close to two billion people—that store is shrinking. The International Centre for Integrated Mountain Development finds the Himalaya-Karakoram-Hindukush region’s glaciers losing mass around 65 percent faster in the 2010s than in the decade before, with the Karakoram, long an exception, now losing mass as well.

Pakistan sits on the same ground and the same trajectory.

The Indus, which a study in Nature ranks as the world’s most important and most vulnerable water tower, draws about two-fifths of its flow from this snow and ice. In Gilgit-Baltistan and Khyber Pakhtunkhwa, warming has already opened more than 3,000 glacial lakes. 33 of those judged dangerous. More than seven million people live downstream of them.

The toll in Nepal, though, was shaped, above all, by exposure. The Rasuwa corridor had become one of the country’s busiest trade routes; its towns and power projects crowding the riverbanks. Families displaced by the 2015 earthquake had been resettled on the low ground beside the water. One such settlement of 250 households was erased. At least eleven hydropower projects were engulfed; the border posts were destroyed; and long stretches of the only highway to Tibet were torn away.

People here have lived with mountain hazard for generations; the scale of what it is now exposed to has no precedent.

Pakistan is building the same exposure into its own valleys, pushing roads, tourism and hydropower into narrow gorges below unstable ice. In May 2022, a glacial lake outburst from the Shishper glacier, set off by a heatwave, swept away the Hassanabad bridge on the Karakoram Highway and two hydropower plants in Hunza. The communities in those valleys are among the poorest in the country—more than a quarter of Gilgit-Baltistan’s people and a fifth of Khyber Pakhtunkhwa’s live below the poverty line. They are also the closest watchers of the slopes above them.

Pakistan is building the same exposure into its own valleys, pushing roads, tourism and hydropower into narrow gorges below unstable ice. 

A herder or a mountaineer often sees a fresh crack in a hillside, a lake swelling behind a moraine or a glacier beginning to move well before any instrument registers it. On August 22, 2025, in Ghizer district of Gilgit-Baltistan, a shepherd out with his livestock before dawn saw a glacier breaking apart above his village. He used his mobile phone to warn residents and the whole village evacuated in time. Local observations of this kind are an integral part of an early-warning system. Getting the alert back down the valley in time is the harder half of the task.

In Nepal, the collapse began in a remote stretch that no one had marked as dangerous. The flood moved too fast for any warning. The lesson for planners is that no system will catch every event of the kind. Two responses still help. The first is to reduce what is exposed, keeping people and critical infrastructure off the most dangerous ground where the risk is already known. The second is to watch more widely, joining satellite, seismic and river monitoring with the observations of the people who live in the mountains. Cooperation across borders matters as well. The point of impact sat in Nepali territory that drains into China. Pakistan’s own rivers and glaciers reach across contested frontiers, which makes shared monitoring essential.

Pakistan does not need more policies and plans. They are written in Islamabad and the provincial capitals. What they lack is a way down to the communities: money, authority and monitoring placed where the danger is; and a real seat at the decision-making table for people who live with it.

Five priorities follow for policymakers:

Reduce exposure. Keep new settlement, roads and hydropower out of identified high-hazard corridors and assess cryosphere risk, including rock-and-ice avalanches, outburst floods and permafrost failure, before approving fixed works in the mountains.

Fund community-based monitoring and preparedness. Support local observation networks, hazard mapping and evacuation drills. Route resources and authority to district and community institutions to run them.

Give mountain communities their customary water institutions and the women who manage much of the water and food a formal role in the decisions that shape their exposure.

Build layered early warning. Combine satellite, seismic and river-gauge monitoring with local observers and invest in getting alerts back to communities in the minutes that matter.

Cooperate across borders. Invest in shared glacier and lake monitoring and data exchange with neighbours, since the hazards above Pakistan’s communities form beyond its borders.

The crews in the tunnels, the families along the river and the towns along the trade route were living in places shaped by economic growth and climate change. They were under ice that was becoming unstable for reasons they could not see. Some of our communities are at a similar risk. Reducing this exposure and involving these communities in monitoring and decision-making will be important as the climate crisis strengthens.

The writer works at the intersection of climate, water, ecology and society.