The Indian and Eurasian plates collided about 65 million years ago to begin the process that ultimately formed the Himalaya, and today, the Indian plate continues to plough into Tibet at roughly 4-5cm a year (that is about the speed at which a human fingernail grows). So, if there’s one word that describes the Himalaya best, it is “friable”. As the youngest and most geologically active mountain range in the world, it is also one of the crumbliest.
While the Himalaya are still growing in height, the range is simultaneously eroding at an average rate of about 2.7mm per year, with the eastern part eroding at a higher rate than the western. A combination of strong monsoon rains and steep-sided valleys are the main reasons for this, but of late, another urgent trigger has been added to this—deforestation. The latter is mainly to build roads and other infrastructure like hydroelectric projects and housing. Whether you take the situation in Uttarakhand and Sikkim in India, or Nepal, it is fair to say that the Himalaya is stressed. Into this mix, add climate change.
Once these Earth systems are tipped over the edge, it is difficult to regain the old equilibrium, especially as the world continues to get hotter, because our economic and political systems just don’t want to be weaned off our fossil fuel addiction. And a steadily warming Himalaya means that the glue that holds the rocks of the highest peaks together—regular snowfall, extensive glaciation, and permafrost—is not-so-slowly vanishing.
UNLEASHING THE MONSTER WAVE
All this brings us to the perfect storm that was the Nepal flash flood on 26 August. Perhaps “flash flood” is too vague a word to describe that violent tsunami that wiped out the upper reaches of the Bhote Koshi and Trishuli rivers that day. Scientists are calling it a glacier failure flood, one of the most violently overwhelming and scarily fast-moving monstrosities that can be imagined in a narrow Himalayan valley.
At around 8.37am (Nepalese time) that day, a large chunk of a hanging glacier on the north face of the Langtang Lirung peak, as well as the rock that it was sitting on, snapped off and fell thousands of feet down to the glacial moraine below. The force of the collapse sent millions of metric tonnes of rock and ice thundering into the Lende Khola Valley and the earth shook under this impact, which the US Geological Survey registered as a 5.2 magnitude earthquake. Geologists are increasingly of the opinion that this break happened because the permafrost holding the rocks together under immense pressure had thawed, rendering the entire structure unstable.
This sent a tidal wave of debris flow down the valley, travelling at about 180kmph. It took just 7 minutes for the flood to reach the China-Nepal Gyriong border checkpoint and dry port, 20km away, which straddles the point where the Lende Khola meets the Bhote Koshi. Hemmed in by steep gorges, the speeding flood, nearly 150ft high, obliterated Gyirong, its extensive infrastructure and hundreds of people in seconds.
Over the next half an hour, the flood wiped out the villages of Timure and Syabru Besi (where the Bhote Koshi joins the Langtang Khola to become the Trishuli), and large parts of Trishuli village further downstream. The more the flood destroyed, the greater was the load of mud and other debris it carried. Imagine being hit by a flood of liquid concrete, travelling at over 100kmph!
Between 9am and 3.20pm—when the flood swept away a part of Devighat, where the Trishuli joins the Narayani river—multiple villages and about 10 hydroelectric projects (HEPs) were washed away, wiping out 10% of Nepal’s electricity generation. Wherever the flood encountered infrastructure obstacles, it became more violent, and this is a point we need to remember.
As of the time of writing, over a 1,000 people have been confirmed killed by the deluge, and it is highly likely that the number of casualties could well rise to 5,000 over the next few days. Even now, nearly a week after that catastrophic day, frantic efforts are underway to rescue 900 trapped workers at the various HEPs. Hope dwindles, even as the risk rises for rescue teams. At the point of the avalanche, two large, debris-dammed lakes have been created, and as the area gets more rainfall, the risk of these lakes bursting remains very high.
A DISASTER FORETOLD
Nobody could have forecast the glacier failure event itself, but Nepalese and Chinese authorities had been worried about the vulnerabilities of the area around Gyirong. Reuters reported that at a 27 May meeting in Kathmandu, officials from Nepal and China had discussed greater cooperation to monitor glacier-related hazards and floods, including an inventory of glacier lakes and hazard mapping. In 2025, a glacier lake in the area had suddenly released a large quantity of water, killing nine people in Nepal, with 12 people missing.
The thing is, it is sheer folly to build busy roads and huge buildings in such areas in the first place. Since Gyirong was a border transit point, a lot of trade passed down the valley, not to mention a steady stream of international tourists and pilgrims passing through that choke point in order to travel to Mt Kailash and the Mansarovar lake. The presence of so many HEPs along this fragile area of deep gorges was another act of hubris. On top of that many villages had expanded down to the very edge of the river, with some neighbourhoods constructed on drier parts of the riverbed.
It is true that Nepal contributes next to nothing in the planet-heating greenhouse gas emissions that are causing climate change, but surely someone, somewhere should have raised the alarm at taking on such unnecessary risk in the name of development. But Nepal isn’t alone in this. We have seen similar scenes in the Indian Himalaya, and for the same reasons.
The flood that swept down Rishi and Dhauli Ganga in early February 2021 was uncannily similar to the Nepal catastrophe. Then too, a glacier and bedrock failure in the upper Rishi Ganga gorge—due to a warm winter, lack of snowfall and permafrost thaw—had unleashed a deadly torrent, which became even more destructive when it encountered HEPs downstream. At the time, when I spoke to affected villagers and climate experts, they all blamed the role played by unscientific infrastructure projects in magnifying Himalayan floods.
Last August, Dharali village was washed away when an accumulating debris field in the upper Kheer Ganga river was eroded by heavy rainfall, unleashing a devastating flood that killed at least 61 people in an instant. Just like Nepal, it was a catastrophe that had been captured on numerous phone cameras. In them, it is quite clear that densely built-up parts of the village lay right on the path of the drainage channel of the Kheer Ganga.
Go even further back and we find the deadly Garhwal flood of 2013, when a lake on the Chorabari Glacier behind the Kedarnath temple burst. The death toll was staggering, with over 5,000 people killed. Even then, one of the main force multipliers of the flood were the dozens of HEP along the Alaknanda and Mandakini rivers, many of which were simply washed away.
In October 2023, one of the worst floods hit Sikkim, when a glacial lake in the South Lhonak Glacier burst, unleashing a wave over 65ft high, that surged down the Teesta river, tearing through roads, bridges and the crucial NH10 connecting Siliguri to Gangtok, while destroying the 1,200MW Teesta III HEP dam at Chungthang. In fact, while driving down NH10 a few months ago, I was struck by how low the highway’s elevation is, and just how close it is to the banks of a highly volatile Himalayan river.
The thing is, we never learn.
It was grimly ironic to hear public officials blaming global warming for the Assam floods of July and August. As an attribution study has since shown, there’s no point in blaming climate change, because the climate has already changed. The equilibrium is now broken. In the case of Assam, we should expect cloudbursts every monsoon. But we shouldn’t exacerbate the impact by building HEPs on the tributaries of the Brahmaputra in Arunachal Pradesh and Nagaland, or by encouraging infrastructure development in exposed areas. In Uttarakhand, every monsoon, when huge crowds overwhelm fragile infrastructure during the Char Dham Yatra, we’re playing Russian Roulette with people’s lives.
Just as Assam’s plight has now receded from view, soon the Nepal catastrophe too will be a thing of the past. But the Himalaya will continue to destabilise, glaciers will shrink, more glacier lakes will form, while existing ones will reach dangerous levels. Maybe even a rogue earthquake will spark a chain of collapse. These things are now inevitable in this warming world we live in. Highly vulnerable countries like Nepal and India have to radically re-think what constitutes development and acceptable risk in this new reality.