Floodwaters surge through a residential area in Nepal’s Rasuwa district on Aug 26
SPECIAL REPORT / Nepal
By M. Riyaz Hashmi
Calling the devastation in Nepal on August 26 merely a sudden flood underestimates the scale of the Himalayan crisis. It was a cascading disaster in which a large section of ice and rock broke off at high altitude, plunged nearly 1,200 meters downhill, and ice, rock, soil and water combined to form a fast-moving debris flow. Its impact was felt nearly 100 km downstream across the Bhotekoshi and Trishuli river systems.
Scientists are comparing the event with the 2021 Chamoli disaster, while its wider downstream impact is being compared with the 2013 Kedarnath tragedy. Dr. Mohammad Farooq Azam, a senior glaciologist at the International Centre for Integrated Mountain Development (ICIMOD), has also described the process as similar to the Chamoli disaster and its downstream impact as resembling Kedarnath.
The devastation, therefore, did not come from water alone. Mountain debris also became a destructive force behind the flood.
And the collapse of the mountain set off an entire chain of destruction.
According to University of Calgary geomorphologist Daniel Shugar, satellite images show a glacial section nearly 600 meters wide breaking away. When such a mass falls from that height, the energy generated by the ice and rock transforms the water, soil and debris below into an extremely fast-moving flow.
ICIMOD scientists are also investigating whether the debris temporarily blocked the Lhende Khola river and created a natural dam. If so, the sudden release of water accumulated behind it could have further increased the force of the flood.
In one line—the mountain broke, debris fell into the river, the river’s course was disrupted, and the water raced downstream carrying that debris with it.
‘Flood of death’—how did ice falling from such a height become several times more powerful than a normal flood after entering the river?
An ice mass falling from a mountain does not come down alone. Rock, soil and water become attached to it along the way. As the mixture becomes heavier, its destructive force increases.
According to ICIMOD, the water level at the Galchhi center on the Trishuli River rose by up to nine meters within about 30 minutes on the morning of August 26, while a rise of around seven meters was recorded at Malekhu over roughly the same period.
Such a rapid rise indicates how little time people living downstream may have had to escape. It also exposes the limits of conventional flood-warning systems in such disasters: when a flood is generated not by rainfall but by the sudden collapse of a mountain, measuring river water levels is not enough.
When was the ground prepared for the disaster?
The disaster arrived within minutes, but the story of a weakening Himalaya is decades old.
The devastation occurred suddenly on August 26, but the process of Himalayan destabilisation is not new. Rising temperatures across the Hindu Kush Himalaya are causing glaciers to shrink, accelerating ice melt and weakening the grip of snow and soil that has remained frozen at high elevations for long periods.
As glaciers retreat, new lakes can form and existing glacial lakes can expand. At the same time, melting ice and soil can affect the stability of rocks and mountain slopes.
ICIMOD has made it clear that it would be premature to determine how significant a role climate change played in this specific event. Therefore, it would not be appropriate to say that “climate change caused this glacier to break.”
But a warming Himalaya is certainly changing the conditions under which glaciers and mountain slopes remain stable. This is the most important backdrop to future risks.
Why was the damage so extensive?
A natural hazard does not become a disaster on its own; human settlements and construction turn it into a tragedy.
A natural hazard becomes a major human tragedy when settlements, roads, bridges, power projects and markets lie in its path.
Several other geologists have also pointed out that traditional Himalayan settlements were often located above rivers and in relatively safer locations, whereas settlements in many areas have now moved extremely close to river channels.
The lesson from Kedarnath is clear: nature creates the hazard, but humans decide what stands in its path.
Scientific studies in Nepal have also shown that landslide risks have been higher around roads. Cutting into slopes, inadequate drainage, and unsafe debris dumping can weaken mountains.
A road built by cutting through a mountain is not merely a road; it can also alter the natural balance of water, soil and slopes.
Why are questions now being raised about China over the Nepal disaster?
The affected area is extremely close to the China-Nepal border, and activities linked to roads, border connectivity, trade routes and power projects have increased across the region. Questions about Chinese construction activity are therefore understandable.
But there is currently no scientific evidence that any Chinese construction project directly caused the collapse of the glacier involved in this particular event. ICIMOD scientists are studying the actual causes of the event and other associated factors.
That, however, does not mean there is no connection between construction and disaster risk. Studies of glaciers and glacial lakes in the China-Nepal border region have already presented a serious picture of the risks. One study identified 28 glacial lakes as highly vulnerable to sudden outburst floods.
Therefore, the real question is not—“Did China cause this flood in Nepal?”
The question is—“Amid a changing climate, is construction beyond the natural capacity of the Himalaya—whether carried out by China, Nepal, or India—further increasing the risk of disaster?”
Where is the danger looming?
Not one valley in Nepal, but the entire Himalaya from China to India is at risk.
According to scientific assessments of the China-Nepal border region, if 28 vulnerable glacial lakes were to burst, more than 3,000 buildings, around 50 bridges, nine power projects and nearly 50 kilometers of roads could be at risk.
Another study found that such potential floods could affect around 103 kilometers of roads, 103 bridges, two major dry ports and 3,301 buildings in China and Nepal.
The danger, therefore, is not confined within the borders of a single country.
Rivers do not recognise borders.
A flood originating in Nepal can affect China, while a glacial lake bursting on the Chinese side can put Nepal in its path. Nepal’s rivers then flow onwards into India.
Himalayan disaster management must therefore be viewed not merely as a matter of national security, but as a matter of shared security for a shared Himalaya.
Could the disaster have been prevented?
Measuring only the river’s water level will not be enough; the mountain’s collapse must be detected first.
Preventing the entire disaster may not have been possible, but the damage could have been reduced.
In such events, a warning signal may come not from rainfall but from the sudden collapse of ice and rock high in the mountains. Future warning systems will therefore need to monitor the entire mountain landscape.
Continuous monitoring is needed of changes in glaciers through satellite imagery, signs of rock movement at high elevations, the size and water levels of glacial lakes, and river water levels. These streams of information will need to be combined so that warnings can reach people living downstream within minutes.
But equipment alone will not be enough. Where the risks are known, construction rules will also have to change.
Before roads and power projects are approved, scientific assessments of mountain stability, slopes, old river channels and potential flood zones should be made mandatory.
What is the biggest danger?
We look for causes after every disaster, while the mountain has often been giving signals beforehand.
The biggest lesson from Nepal’s tragedy is that we must stop viewing disasters as isolated events.
The question is not simply how much rain fell, whether there was a cloudburst, or whether an earthquake occurred. The real question is—
How much has the mountain changed over the past few decades?
Ice is melting across the Himalaya, glaciers are retreating, new lakes are forming, rock stability is being affected, and human activity is increasing in the same valleys.
The Nepal event brings this entire changing picture together.
This was not just a flood. It was a story of a glacier breaking, rocks falling, debris flowing, the river’s course being disrupted, and a sudden flood emerging as one event after another became interconnected.
Kedarnath taught us that development cannot be allowed to block a river’s path.
Chamoli showed that ice and rock can suddenly break away together.
Nepal has delivered a third warning—the next Himalayan disaster may not be a single event but something created when multiple events occur and connect with one another.
If development, climate change and disaster risk continue to be treated as separate problems and policies are framed accordingly, it is possible that by the time the next warning is heard, it may already be too late.
Thousands of ‘water bombs’ are hidden in the Himalaya, more than 200 lakes are dangerous
The Himalayan danger is not limited to mountains collapsing before our eyes. Glacial lakes located thousands of metres above sea level are also potential ‘water bombs’. Natural walls of ice, rock, and soil hold them back.
If these walls develop cracks or a large mass of ice or rock falls into a lake, the entire lake can suddenly surge down towards the valleys below. This is known as a glacial lake outburst flood (GLOF).
According to ICIMOD, more than 25,000 glacial lakes have been recorded across the Hindu Kush Himalaya region. Not all are dangerous, but more than 200 have been classified as high-risk. Rising temperatures are causing glaciers to retreat, leading to new lakes forming and existing ones expanding.
A scientific study of the China-Nepal border region alone recorded 2,377 glacial lakes. Of these, 76 were found to be potentially dangerous, including four that were classified as extremely high-risk. Between 1992 and 2022, the total area of these lakes increased by around 27 percent.
Another study identified 28 lakes in the China-Nepal border region as highly vulnerable. In an extreme scenario, the volume of water released from some of these lakes could be up to ten times greater than that of a normal seasonal flood. Such floods could affect thousands of buildings, bridges, roads and power projects.
The most worrying aspect is that a lake does not always need heavy rainfall to burst. The collapse of an ice mass, a rockfall or the weakening of a natural barrier holding back the lake can also be enough to trigger a sudden outburst.
In other words, some of the Himalaya’s dangers remain invisible—hidden behind snow and rocks in the form of water accumulated in glacial lakes.
