Flooding in Nepal - Glacier Collapse

[Point Conception]

TL;DR

Hundreds of Trekkers Missing in Nepal Flooding

https://www.yahoo.com/news/world/articles/foreign-tourists-missing-nepals-flash-155744585.html.

 

[gmax137]

The videos are terrifying.

 

[256bits]

You might want to factual check for sensationalism in this one paragraph:

Equations
1. Potential Energy of 1 kg of water at height
E = m g h --> mass 1 kg, g = 9.81 m/s/s, h = 1200 m ( Assuming 1200m as height, and not glacial path length )
E = 11.8 kJ

Temperature rise of 1 kg water from heat addition Q
dt = Q / ( m Cp ) Q = 11.8 kJ, , = 1 kg, Cp = 4.2kJ / ( kg C )
dt = 2.8 C

Edit:
dt = Q / ( m Cp ) Q = 11.8 kJ, , = 1 kg, Cp = 2.050 kJ / ( kg C )
dt = 5.76 C


I would take the 2.8 C 5.76 C temperature increase due to conversion of potential energy to heat energy to mean that the chunk of glacier ice had already approached melting temperature, lost its cohesive strength and broke away, travelled down the glacial valley on the incline ( not straight down ) and completely liquified into a slush ( ie disintegrated into a mixture of ice particles and water ) during decent.

Reaching warmer temperatures along the path 50 km further down the valley, all of the slush would become water.

 

[Greg Bernhardt]

The videos are terrifying
https://www.nytimes.com/2026/08/26/world/asia/nepal-flood-glacier-ice-avalanche.html

Unfortunately I think we'll see more of this with glaciers continuing to melt.

 

[Andy Resnick]

TL;DR: Hundreds of Trekkers Missing in Nepal Flooding

https://www.yahoo.com/news/world/articles/foreign-tourists-missing-nepals-flash-155744585.html.

The videos are terrifying.

The videos are terrifying
https://www.nytimes.com/2026/08/26/world/asia/nepal-flood-glacier-ice-avalanche.html

Agreed- I have never seen anything like that.

 

[Point Conception]

You might want to factual check for sensationalism in this one paragraph:

View attachment 373873

If the mass of the glacier that fell is estimated to be 5 000 000 000 kg from 1200 m then v =153 m/s. And with KE = 1/2 mv^2 . joules at impact= 58x10^9. The phase change from ice to water=334000 joules/kg. So only about 173,653 kg of ice converted to water at impact.

[Mentor Note: Some AI content has been deleted out of this post since the thread is in the technical forums]

 

[256bits]

If the mass of the glacier that fell is estimated to be 5 000 000 000 kg from 1200 m then v =153 m/s. And with KE = 1/2 mv^2 . joules at impact= 58x10^9. The phase change from ice to water=334000 joules. So only about 173,653 kg of ice converted to water at impact.

Right. I incorrectly used the Cp for change in degree for water, instead of that for ice.

Equations
1. Potential Energy of 1 kg of water at height
E = m g h --> mass 1 kg, g = 9.81 m/s/s, h = 1200 m ( Assuming 1200m as height, and not glacial path length )
E = 11.8 kJ

Temperature rise of 1 kg water from heat addition Q
dt = Q / ( m Cp ) Q = 11.8 kJ, , = 1 kg, Cp = 2.050 kJ / ( kg C )
dt = 5.76 C

The chunk of ice would have risen in temperature of 5.76 degrees C from the drop.

And then there is the phase change to water, as you have expressed.

Post #3 edited

 

[sbrothy]

The videos are terrifying
https://www.nytimes.com/2026/08/26/world/asia/nepal-flood-glacier-ice-avalanche.html

Unfortunately I think we'll see more of this with glaciers continuing to melt.

It sounds so bad I serioulsy don't want to look!

 

[256bits]

Some discussion from Jakob Steiner, a geoscientist at the University of Graz in Austria
and Glaciologist Simon Cook, University of Dundee, Scotland.




Satellite image at the 1:42 mark.

 

[256bits]

Some video of the deluge. Viewer beware.
( I find she babbles a bit much, but that's just me, 229 subscribers she has )



1. Question of where all the water came from.
2. Blocked lake upriver posing a risk of secondary water cascade
3. Seismic recordings were that of the deluge ( not an earthquake in the normal sense )

 

[Point Conception]

If the mass of the glacier that fell is estimated to be 5 000 000 000 kg from 1200 m then v =153 m/s. And with KE = 1/2 mv^2 . joules at impact= 58x10^9. The phase change from ice to water=334000 joules/kg. So only about 173,653 kg of ice converted to water at impact.

[Mentor Note: Some AI content has been deleted out of this post since the thread is in the technical forums]

Correction the joules at impact with 5000000000 kg ice falling 1200m: KE = 1/2 mv^2 = mgh = 5.8 x 10^13 joules. So with 334000 joules/kg ice to water phase change. About 176 000,000 kg ice converted to water at 0 degrees C at impact. Out of 5000,000,000 kg ice in glacier. *** Of course all this is kind of hand wavy since the glacier contains other material in the total mass . And some of the kinetic energy at impact is going to displace material at impact location

 

[Astronuc]

Affected river: Trishuli River, Syapru Besi, Nepal; Bhotekoshi River

Affected districts/towns/villages: Nuwakot, Nepal; Rasuwagadi, Nepal - Gyirong, China (Tibet) border crossing; Dhading, Nepal; Chitwan, Nepal

Nuwakot (Nepali: नुवाकोट) is a town in central Nepal, serving as the namesake of the district of the same name. The town is located on the bank of Trishuli and Tadi Rivers. It is located around 60 kilometres west of Kathmandu, . . .

Ref: https://en.wikipedia.org/wiki/Nuwakot,_Bagmati_Province
https://en.wikipedia.org/wiki/Nuwakot_District

Floods kill more than 500 people in Nepal and Tibet, with 90 Americans [and 30 Canadians] among the missing
https://www.npr.org/2026/08/27/nx-s1-5946309/nepal-tibet-deadly-floods

https://abcnews.com/International/h...issing-massive-nepal-tibet/story?id=136022919

Bhotekoshi River Flood Devastates Rasuwa, Nuwakot, Dhading, and Chitwan
https://english.ratopati.com/story/...floods-sweep-away-settlements-increasing-fear

Apparently, there is also flooding in Gyirong county, China.


Multi-story buildings (looks like ~20 m) overtopped by flood (mudslide with rocks) at Nepal-China (Tibet) border checkpoint. It looks like a 5 or 6 story building south (downstream) was inundated. I would guess the water/mud/rock flood was perhaps 30+ m.

 

[Point Conception]

Amazing

 

[Astronuc]

I looked for the mountain where the glacier collapsed. It appears to be near Langtang Lirung (7,234-m. peak, the highest in the Langtang Himal range) or Tsangbu Ri (6,781 m, or 22,247 feet), also known as Kimshung, which is east of LangTang Lirung. It appears probable that one of the glaciers on Langtan Lirung or nearby in the Langtang Himal range let loose, mainly based on the comment that it was at about 5000 m near a peak of about 7000 m. Several valleys run downhill to the NW toward the Rasuwagadi, Nepal - Gyirong, China (Tibet) border crossing.

https://en.wikipedia.org/wiki/Langtang_Lirung
https://en.wikipedia.org/wiki/Tsangbu_Ri

https://phys.org/news/2026-08-satellite-images-bedrock-glacier-collapsed.html

https://www.cnn.com/2026/08/28/worl...lirung-peak-nepal-china-flood-hnk-vrtc-digvid

Prof. Steiner from U of Graz mentioned a similar event happened last year (2025) in the same location!


Other sources point to glacier on the north side of Langtang Lirung.
https://www.bbc.com/news/videos/c07l9ggx8m7o

https://www.reuters.com/graphics/NEPAL-FLOODS/MAP/byvrdywwlve/

Update/Edit - Graph shows Lende Khola and Bhote Koshi Rivers merge at Rasuwagadi, Nepal - Gyirong, China (Tibet) border crossing and the outflow is the Trishuli River

 

[Hornbein]

One is reminded of the landslide into an Alaskan fjord that caused a wave five hundred feet high. A father and son in a sailboat battened down the hatches and survived.

After a year stuck in the ice, the Shackleton Antarctic expedition dispatched enclosed lifeboats to beg for rescue at a distant island. On the way they sighted what they at first believed to be mountains in the distance but was actually an enormous wave. It must have shaken them like the seeds in a maraca. The crew survived but they said after that Shackleton was never again quite the same.

Scientists denied the existence of such waves until one was recorded at an oil platform in the North Sea.

The largest wave that attracts surfers is in Portugal. The impact of the falling water can be so great that the falling wave bounces off of the surface. The mass bounces so high that it bounces again. And again for a total of three times. A surfer was struck upward by the first rebound, which broke his back. He survived. This is not the most dangerous surfable wave.

 

[nsaspook]

 

[Astronuc]

I saw a reel (short-video) compiled from three surveillance cameras at three locations along the Trishuli River. Muddy water was flowing ahead of the flood; one could then see a high slope of water build up, and over top three story buildings that were already meters above the bottom of the river.

I have not yet found the video except for a facebook post. There is water in the river (ostensibly from melt water), which is probably a meter or so in depth, but the flood upstream would be collecting that water and carrying it downstream.


Meanwhile, some other videos:







The flood knocks down buildings build along the river bank, so one would conclude that the locals probably never experienced such flooding in recent memory, otherwise it would be insane to build a structure (home or otherwise) in a flood plain subject to such catastrophic flooding.


Edit/update: I just watched a video in which the commentator/presenter mentioned the flood was up to 30 m high and traveling at up to 75 km/h. Teacher(s) rapidly evacuated 1643 students from Tribhuvan-Trishuli Higher Secondary School (in Trishuli Bazar, Nepal) and took them to higher ground as the flood approached. The three story school buildings have been obliterated!

 

[Astronuc]

Video purporting to show a secondary landslide apparently caused by the flood up the Lende Khola River (Donglin Tsangpo River).




I don't know if this is the same landslide, but in the same drainage system, it will complicate matters going forward.

https://news.cgtn.com/news/2026-08-...Gyirong-mudslide-in-Xizang-1PYx0bgPkxG/p.html

The Trishuli River (Nepali: त्रिशूली नदी) is one of the major tributaries of the Narayani River basin in central Nepal. The river is formed by the merger of the Gyirong Tsangpo (Kerung Khola) and the Lende Khola (Donglin Tsangpo) originating in Gyirong County of Tibet, which join together near the Rasuwa Gadhi on the Nepal–Tibet border. The valley of the river used to be the traditional trade route between the Kathmandu Valley and Tibet.

Ref: https://en.wikipedia.org/wiki/Trishuli_River
See also - https://en.wikipedia.org/wiki/2026_Nepal_floods

The flash flooding occurred along a course of 160 km (100 miles) of the Trishuli River (I don't know if the distance also includes the Lende Khola (Donglin Tsangpo) River.

According to CBS news, as many as 12,000 people have been reported missing.


Edit/update: It was reported that there was a flooding event last year (2025).
Indeed, there was damage done to the same border crossing!

Rasuwagadhi flood: A severe flash flood on 8 July 2025, caused by monsoon rains and a likely glacial lake outburst, swept away the Friendship Bridge over Nepal’s Trishuli River at Rasuwagadhi.

https://en.wikipedia.org/wiki/2025_Nepal_floods

There was a flash flood in Tilgau, or Til Gau, in Humla District in Karnali Province, located in northwestern Nepal. The recent flood along the Trishuli River began in the Nepal-China border area almost directly north of Kathmandu. Humla District is much further west and close to the border with Uttarakhand State in northern India.

Humla’s Tilgaun residents decide to leave ancestral land for good
https://kathmandupost.com/karnali-p...dents-decide-to-leave-ancestral-land-for-good

 

[Astronuc]

Nepal-Tibet floods death toll tops 1,100 as missing tourists found safe
https://www.yahoo.com/news/articles/nepal-tibet-floods-death-toll-093159512.html

Police in Kathmandu buried dozens of bodies in multiple trenches as Nepal’s disaster agency said 1,003 deaths had been counted there and 3,916 people still missing, including 583 foreigners.

https://www.itv.com/news/2026-09-01...ses-1000-as-hundreds-still-trapped-in-tunnels

Chinese authorities reported 16 deaths and 546 missing in their most recent update on Sunday.

 

[Astronuc]

Everything We Know About Nepal's Flood - And What Everyone Got Wrong​

How scientists unraveled the cause of the devastating flood in Tibet and Nepal​

Global cooperation revealed a landslide, not a glacial collapse, likely initiated the cascade of events
https://www.science.org/content/art...veled-cause-devastating-flood-tibet-and-nepal

The first accounts, including from the U.S. Geological Survey (USGS), indicated the event was a magnitude 4.4 earthquake, which might have shaken rock and ice loose in a landslide that sparked the flood. A dam break was also touted as a possibility. But within 15 minutes of waking up, Cook, who has been conducting research on the Lhende Khola, had downloaded publicly available seismic data from a Nepali station located north of Kathmandu to see for herself. “I could already see that some of the initial attribution was wrong,” she says. Rather than the quick, intense seismic jolt typical of an earthquake, the data showed low-frequency, long-period waves characteristic of prolonged rumblings: a giant landslide, which itself generated the seismic signal.

On the opposite side of the Atlantic Ocean from Cook, Ekström was using data from the Global Seismographic Network, a collection of about 200 seismometers operated by many countries, to come to the same conclusion. He fed the seismic data into algorithms developed at Lamont-Doherty to find that a more accurate magnitude was 5.7—equal to a significant earthquake. It soon became “clear that [the Lhende Khola landslide] was one of the largest in the last decade or two in the world,” he says.

Cook, Ekström, and a smattering of other top natural hazard researchers soon created a Slack group to share data, discuss interpretations, and argue. (As of this publication, the group has more than 85 scientists.) It was here that the next useful observations got shared: satellite imagery from Planet Labs, which takes daily images of Earth’s surface at a resolution of 3 to 5 meters. But there was a problem: In the few available images of the mountains where the seismic signal originated, there were “very strategically placed inconvenient clouds,” Cook says. What could be clearly seen was a sharp edge, at about 5200 meters above sea level, where a glacier that blanketed the mountain had snapped off.

The imagery soon led to reports that the explanation was a glacial collapse: A thick layer of ice had slid off the underlying rock, potentially because of warming at its bottommost layer, until it crashed into the valley below. There, the shattered ice and rock flowed down the Lhende Khola valley at speeds approaching 150 kilometers per hour, kicking off a flood that caused water levels to rise as much as 9 meters in 30 minutes.