The mechanics of the Nepali flash flood | Hacker News Reader

The mechanics of the Nepali flash flood

economist.com

108 pointsvinni284 comments

https://apnews.com/article/climate-change-nepal-tibet-glacie...

CCTV footage is there. Horrific scene. When you see it coming at you it’s already too late.

What was the comment of the form "climate change will manifest as a series of phone videos of disasters that get closer and closer until you're the one holding the phone?"

I have been trying to find the original source of this quip for a long time. It stays in my head but I don’t know quite where I saw it.

Ok, I found these:

https://www.instagram.com/reel/Da3NGbfk6Lo/

https://heated.world/p/another-summer-day-stolen

It's awful to see dozens of people running and knowing they're all gone. It wasn't even close. They were so small compared to that absolute FORCE.

This is true, and, relatedly, is the feeling I have about all of climate change. By the numbers, it won't be close.

Of course, this little preview is itself anthropogenic. This horrific disaster is the thinnest tendril of the monster we have unleashed.

Both figuratively and literally, this experience was the tip of the iceberg. Terrifying. People might think I'm crazy, but I'm choosing my retirement location 100% based on resistance to climate change. Local water, too much humidity for massive fires, too cold for insane heatwaves... you get it.

I've seen recommendations for locations near the Great Lakes. Upper peninsula of MI, for example. Plenty of water. A warming climate should actually make the winters there somewhat less harsh.

Depends on how much warming. Some areas of the UP are colder temperature wise, but because it stays below freezing most of the winter the humidity stays low and it doesn't feel so bad. Where as some lower areas in Michigan now regularly break the freezing line in winter and everything is always a sopping mess with cold high humidity and no snow to act as insulation for buildings.

Wildfire smoke will be the big question there. It's started to be bad for a week or two a year in Minneapolis, and is only worse the closer you are to the boreal forest.

And the failure of basic services like water and power.

Given it took FEMA ten days to get power restored to the super dome, how long will responses be when there are many simultaneous disasters of that size or bigger? With the current admin the answer could be “indefinite”

Wildfires only a problem until the overgrowth is burned off. When there's not enough to sustain a large spreading fire, they will stop happening.

There is a LOT of overgrowth. Expect a decade+ of fires, or an apocalyptic firestorm which burns everything to cinders. Neither is awesome.

Climate change is defined by both wet and dry extremes.

Excess rainfall creates an explosion of brush that during the now annual drought turns to tinder.

Then come the floods because the roots were holding all the soil in place and the soil was managing water movement. What used to be an all year trickle becomes an occasional deatructive deluge.

True, but disingenuous, as "over" growth implies a normative cap, but climate change just is moving the cap lower. The ceiling is falling: more and more growth, in every biome, counts as overgrowth.

Eventually only desert remains viable, and everything above it, including arability, is locked away forever.

canada's forest is growing, not shrinking. the overgrowth will keep growing year over year

Which places have you found? I'm in Canada and figured most of the places are going to suffer more rain falling in the next decades.

Cities in the tropics at high altitude far from the sea like Bogotá, Medellín, maybe even Mexico City.

Maybe some moderately increased risk of extreme rainfall causing localised flooding, mudslides etc, but Bogotá in particular has an incredibly mild climate year round, and you're at 2600m so you aren't too worried about sea level risk.

As far as I'm aware basically no risk from hurricanes, tornados or anything like that. Biggest risk is earthquakes which is nothing to do with climate change and can be mitigated.

In fact Bogotá is a bit chilly so might be nice if it was slightly warmer.

For some reason people assume that climate change means you need to move closer to the poles, but moving to higher elevation is much better

Yeah but then you have drug cartels and corresponding violence, kidnappings etc. Questionable healthcare, nothing social. Its nice for a short visit for some, but long term? You wanna live behind a fancy fence?

Plus its malaric jungle, so mosquitos can kill you day(dengue ones) and night.

Thats not a definition of move to a better place by any means, unless you come from say Bangladesh.

Not unexpectedly, follow real estate prices.

The average value of homes in safe parts of Canada has risen significantly. E.g. Vancouver is devastatingly expensive, while nearby Abbotsford and Richmond are floodplains and reclaimed marsh, respectively, and are cheap. Sometimes uninsurable, but cheap.

The market will price us all out of the safest places and indeed arguably already has. Expect housing values to continue to diverge. A dry hovel is superior to the mightiest of flooded manses, but a home in a dry, safe metropolis, with enough water for all?

Literally invaluable. It will be priced accordingly.

Great Lakes area is probably well positioned.

Everybody is saying that the Great Lakes region is a climate haven, but it's intensely vulnerable to both polar vortex events coming down from Canada and wet-bulb heat waves coming up from the Gulf of Mexico. The middle of America is flat; there is no natural barrier to stop a frigid or sweltering airmass from moving in. This has already happened multiple times within just the last few years.

In terms of death toll, a power outage during a severe deep freeze (with subzero temperatures and -50 wind chills) or a wet bulb event has a far greater lethality potential than wildfires. The most deadly wildfire in California history was the Camp fire that leveled the town of Paradise; it caused 85 deaths. The Oakland Hills firestorm of 1989, immortalized in SimCity and several made-for-TV movies, only caused 25 deaths. By contrast, the 1995 Chicago heat wave caused 740 fatalities, and even the 2024 polar vortex event that barely made headlines killed more people (90) than the Camp Fire.

(Also note the low absolute numbers of even very severe, headline-grabbing natural disasters in developed countries. And that good construction can mitigate almost all of them. You are probably better off, in strict actuarial terms, by settling in a place where you can make a lot of money and then using it to prepare your home for disaster than by settling in a place that is cheaper but where you can't afford the latest building technology.)

I think they have their fair share of snow storms during the winter because of the vortex coming from the West. The vortex goes down from Alaska because the mountains block it, and then it turns east and goes straight to the lake area.

I live in Montreal, but sometimes I see bitter weathers in Toronto during the winter. Ofc we have our share of pain, but I'm fine with snow -- raining is a huge problem in recent years -- I'm installing a French Drain right now, and hopefully it offers enough protection. However, my house is sitting on top of clay, so that could be a big issue.

Snow can be annoying but is rarely catastrophic.

Somewhat more concerning is that tornado frequency is increasing at a ferocious rate, though most are relatively minor (EF-0 / EF-1).

The total for 2026 to date is 207 ground tracks (as of 27 Aug 2026). The previous full year record was 142, and the historical average (again full-year) is closer to 50.

This has knock-on effects to insurance as well as raising home and landscaping repair (downed trees, etc.).

<https://chicago.suntimes.com/environment/2026/08/27/200-torn...>

Flash-flooding is also an increasing concern, though unlike Nepal, water channels tend to be largely flat. Urban creeks, local rivers, retention ponds, and low-lying locations (underpasses, local low spots) may experience flooding, though generally flow strength is low. Basement flooding is the most likely risk.

I have spoken to quite a few real estate agents in Sudbury who mentioned folks are buying property there as a hedge against climate change.

Personally, I'm aiming for Pittsburgh.

Sea levels haven't changed at Martha's Vineyard. I'd recommend that. Obama moved there in his retirement.

Honestly there is no safe haven while humans over-consume continue to waste in the chase of excess. We have seen in the last few years all the supposed climate safe areas get hit hard.

https://www.npr.org/2024/10/09/nx-s1-5137024/climate-haven-h...

birth rates are falling off the cliff in all developed nations, most are below replacement rate already

Most developing nations are below too now!

Pro tip for people moving north; don't buy land in the valleys around Mt. Rainier. This type of flood (also known as a lahar) has occurred there many times. The mudflows reached the harbor of Tacoma in the past. [0] I expect we'll see at least one new one in our lifetime, as the glaciers have been greatly affected by rising temperatures.

[0] https://www.usgs.gov/media/images/mt-rainier-lahar-hazard-ma...

A bit off topic about the word "lahar", we Indonesians use that word to mean "lava", and we use "lahar dingin" (lit: cold lava) to mean volcanic mudflow.

Do you have a source about the Nepalese flood being a Lahar? I've only read that it was caused due to the glacier collapse, which seems like a different thing

Thanks, I see that Lahars are technically associated with volcanoes as another comment noted. They have a variety of causes of which glacial collapse is one. [0] The term jökulhlaup describes a flood originating from a glacier, for example draining of a glacial lake. [1] It now seems the Nepali flood was triggered by a landslide onto a glacier.

As a practical matter the effects are pretty similar. Rainier has had lahars and jökulhlaups in the past.

[0] https://en.wikipedia.org/wiki/Lahar

[1] https://en.wikipedia.org/wiki/J%C3%B6kulhlaup

I can't access the OP article at the moment, but there's a diagram of the the chain of events that caused the disaster here [1].

I believe Lahars are specifically volcanic, this would be better described as a combination flood and landslide at the same time.

[1] https://www.bbc.com/news/live/c6y8mjmnpxv0t?post=asset%3Ac6b...

OP here. This post went from +6 yesterday to -3 overnight.

The implicit HN Forbidden Topics List is beginning to look a lot like an impartial description of a Tuesday.

Deaths from. atrial disasters are the lowest in history: https://www.vox.com/future-perfect/422084/climate-change-nat...

The same argument could have been made about wildfire deaths and damage through the early 2000s in the US.

It turns out that improved forecasting, warning systems, and well-established emergency response, rescue, and recovery systems, can all tamp down risk.

Looking at your article, the subhead reveals a split narrative: "Natural disasters may cost more money, but they claim far fewer lives than in decades past."

What's begun to occur with wildfires is that events are now exceeding the capability of even advanced modern technological societies to address them. Wildfires now regularly enter the urban core, not merely the urban fringe. That's something unheard of in the US from roughly the 1920s, and there wasn't a notable large-scale urban fire until the Oakland Hills firestorm of 1991. Even that was arguably at the wildland-urban interface (WUI). Contrast the Tea Fire (2008, Montecito & Santa Barbara, CA), the Tubbs Fire (2017, Santa Rosa and Sonoma, CA), Camp Fire (2018, Paradise, CA), Carr Fire (2018, Redding, CA), the August 2020 California lightning fires (2020, multiple locations, 3,500+ structures destroyed), the Marshall fire (2021, Marshall, Superior, and Louisvill, CO), the Mountain Fire (2024, Ventura, CA), the Hawaii wildfires (2023, Lahaina, HI), the 2025 Los Angeles wildfires (2025, Pasadena and Altadena CA amongst other locations), and the 2026 Spokane complex (2025, Spokane, WA, ~850 structures).

That's just within the US (an advanced modern technological society), omits wildfires not significantly impacting urban regions, and probably skips a few. There've also been unprecedented urban fires in Canada, Europe, and Australia within the past few decades after nearly a century of no such instances.

(Europe is an exception: for some reason there were numerous urban conflagrations in the period 1939--1945, e.g., Dresden and Hamburg, though climate doesn't seem directly implicated as I recall. Tokyo, Hiroshima, Nagasaki and other Japanese cities had a similar experience at the time.)

As more facts come out about the Nepal-Tibet glacial flood event of 2026, it's pretty clear that many casualties and damage were unavoidable at all once the event itself was triggered. Avoiding casualties would have required extensive evacuations of a nearly 100km stretch of the Trishuli River, possibly for weeks, with an affected population of over 1 million souls.

I've addressed this in a few recent HN comments: <https://news.ycombinator.com/item?id=49473419> <https://news.ycombinator.com/item?id=49473201> <https://news.ycombinator.com/item?id=49460081>

This event has nothing to do with climate change and is pure fear mongering.

This is the same adage used by the Governments with the "think about the children" campaigns, its a distraction. A cop out.

Yeah, the event primarily marked by receding glaciers probably has nothing to do with this glacier that weakened to the point of destroying a village.

This glacier probably melted many times in the past, especially in such a sudden and violent manner.

I'm sure this is in no way anomalous, nor is it something that could predictably result at some point from a warming planet.

The Missoula Floods. This kind of thing has been happening for a good long time.

That doesn’t diminish the tragedy in any way, this event was shocking and brutal. But it wasn’t the first and won’t be the last.

“Guys this isn’t global climate change, this happened once before at the end of the ice age!”

I have no clue what point you’re trying to make, but I don’t think you got it across here.

</sarcasm>

(For the detection-impaired.)

I sympathize with the reaction to the hyperbole, but it's not a binary thing. Better to think in terms of marginal increases in occurrence rate, or in a single case marginal increase in progression of an impending event (glaciers were all gonna be gone in a few thousand years anyhow).

Still plenty of room to debate numbers.

I do not know if I would consider stopping the climate change as a solution for all such events.

Watching the video makes you realize how small you are in front of the nature. It feels painful to even watch it but its an eyeopener at the same time. Its a misconception to think that the climate would always remain same, nature is an constantly moving/changing entity. What might be perceived as destruction is also the mechanism how creation of life or life like conditions happened in the first place. Just makes me feel like appreciating the day even more.

Mt St Helens erupted in 1980. The landslide alone was 3.3 billion cubic yards, that traveled 15mi at speeds of up to 155mph, and buried 23 square miles to an average depth of 150ft, and up to 600ft, within 10 minutes.

The blast flattened 230 sq mi of forest in minutes.

540 million tons of ash fell in 9 hours, affecting 22,000 sq mi.

The mudflow (lahar) was this debris mixing with 170 million cubic yards of glacial ice and snow, moving at 80 mph.

People liked to make smart ass comments about people who took photos "and would soon be dead" - "they were miles away, they could have left". For a lot of them? No.

The sheer magnitude of these events is truly unimaginable, even if you "were there" (nearby).

And MSH was barely a 5 on the VEI 0-8 (roughly) logarithmic scale, though you can't map to death toll easily.

Pinatubo in 1991 was a high 6. Krakatoa too. Tambora is the largest we know, in 1815, VEI 7, and is estimated at eighty times more output than MSH, and triggered the "Year Without a Summer" globally (https://en.wikipedia.org/wiki/Year_Without_a_Summer) that pulled down average -global- temperatures by a full degree over the course of a year. It completely disrupted the monsoon season throughout Asia, leading to flash flooding events like this becoming a very regular occurrence.

I think some of these types of stats are the closest terrestrial things we have at the limits of human comprehensibility (probably only eclipsed by "interstellar distances").

https://www.reddit.com/r/lastimages/comments/1bdrzsh/one_of_...

Truman refused to leave Mt. St. Helens. There is a memorial cross today whereabouts his lodge stood.

Is it correct to say that the video looks far worse than it actually is ?

As in, the dust/mud particles sprayed & floating in the air do not have the force to do harm beyond vision or breathing impairment, similar to the dust from a collapsing building, or the lead shockwave of a nuclear bomb detonation.

Of course, it looks terrible, and certainly somethingbut its not a reason to perish as long as you can stay away from the following water wall and mud current that does strike sometime after.

No, that's not correct.

The length of time between the spray you mention, and the impact of the water wall, is single digit seconds. It doesn't make a difference.

No, it is not.

The camera position is elevated at least 6--8 stories above the valley floor, an elevation of 20--24m or so by my estimate.

Slightly below it is a concrete platform supporting a parabolic dish antenna.

That platform is well above the main debris flow, catches only comparatively minor impacts, and ... is knocked flat just before the video terminates.

More significantly, the three story block structure at the lower left of the frame is seen visibly displaced an instant before it is obscured by the debris flow, at about 30s into the video.

<https://en.wikipedia.org/wiki/File:Mudslide_at_Gyirong_Port_...>

We now have before/after images of the precise location of the port. THere is absolutely no indicate that structures ever existed there:

<https://news.cgtn.com/news/2026-08-28/3D-imagery-reveals-pat...>

From: "How do newly released 3D images explain the Gyirong mudslide?" <https://news.cgtn.com/news/2026-08-28/3D-imagery-reveals-pat...>.

There is no conceivable way that this can be perceived as a minor or generally-survivable incident.

It literally completely wiped from existence hundreds of reinforced multistory concrete buildings.

It's much worse than you seem to think based on the videos.

Clearly you've never felt the full force of a 6' wave crashing down on you and rolling you in the surf, never mind a 100' wave. What a silly comment.

Just hold your breath, bro, no reason to perish, bro.

Exactly what you see on YT clickbait thumbnails but terrifyingly real.

I don't understand why the push so hard on AI and the greenwashing / misleading information about its impact on the natural world.

I haven't yet been able to properly internalize the horror of this scene. Maybe because we're exposed to so many images from disaster and action movies/videogames, I got somewhat desensitized to the "graphics", so to speak. It's like my brain is denial.

At the same time, I know this is real and a tragedy in an unimaginable scale. Every "little walking figure" is a full human being with dreams, fears and a rich life story.

I'm afraid that at one point it will just hit me super hard.

About 18 years ago, some guy at work was laughing at a video of someone being blown to pieces by an explosive device. People kept walking by his desk and laughing, I suppose because it looked so cartoonish that it felt more like looney tunes than real life.

As an experiment, I showed the same video to my 85-year old grandmother, and she cried out in horror and prayed for the people in the video for a solid hour afterwards.

I go around with the general awareness that about 200k people die every day. I know that disasters and tragedies happen around the world on a regular basis. I know that cameras are nearly ubiquitous even in the developing world, so there is a good chance that any sensational event will be recorded and posted on the internet. Armed with these priors it's not a huge surprise or shock to me. It is still impressive, however.

The drone footage out of Ukraine was like this. Some of it is cartoonish or like watching an action movie or video game.

It's when you recognise the humanity of the individual - for example IR footage of a soldier trying to sleep in a foxhole before a drone drops a grenade. The aftermath starkly reminders you that this was a living person a few moments earlier.

Internet desentitization is real and not good. The accumulation of easily accessed horrors dulls the natural empathy.

What scares me about climate change is how frequent these “little figures” are getting wrecked.

In Japan we have had these sudden flood events this year, people just die as their cars are washed away.

Never in my life have I considered checking the weather forecast and flood watch warnings almost every time I get in the car but I do this year.

We have really fucked the climate and this is just the beginning.

You might want to take an intense media break. I went to 4chan to find more videos of the event, something it's rather good for, and even those guys were largely shocked and flabbergasted at the scale of the carnage and destruction

any link or to way how to find it there? I though it will be in the current events but can't find it and search feature doesnt work

edit: seems the only way to search the site is the google, this thread has few videos

https://boards.4chan.org/pol/thread/541442303

https://boards.4chan.org/pol/thread/541527487/nepal-images

I was looking on /gif and you can just search the titles for nepal

About 160,000 people die each day if less dramatically.

We all must die, if we're to have progeny. If we lived forever, we could not procreate.

How we die does matter. No one should be murdered. Many would prefer to die peacefully, in their sleep, unaware. Survivors generally prefer that the dead have died peacefully -- it can be disturbing to think about a loved one's painful and scary final moments.

The number that die naturally and daily is not scarier or more upsetting than the much smaller number that die violent deaths daily.

Tragedy happens every day, this is likely one of those freak events we cannot do anything about. Millions of people die from hunger and malnutrician every year. Perhaps we could focus our energies on that were it not for the media (us by proxy) that prefers the edgier stuff, since we've desensitized ourselves and seek that fix with something new

The CCTV footage was one of the most heartbreaking things I have seen on the internet lately.

It makes me think a bit of the Johnstown flood from 1889:

https://en.wikipedia.org/wiki/Johnstown_Flood#/media/File:Th...

There was a video on threads earlier today (probably long gone now) of some of the bodies they were finding. Just truly horrific what that amount of sheer force can do to a person.

Really helpful on navigating what happened. https://www.youtube.com/watch?v=9ZvUQ7aoehw

Is Switzerland exposed to similar risk, given the amount of glaciers?

Probably not. Most alpine valleys were carved by glaciers and have a characteristic U-shaped profile. When you get a landslide into a glacial valley, it hits the relatively flat floor and breaks itself apart. The valleys themselves are usually wide enough that they don't dam either. The alps also have significantly less relief than the Himalayas.

The valley where the floods occurred in Nepal has a V-shape, and the peaks around it have much more relief. It's much easier for a large landslide to fill the bottom, creating a dam that can burst, or just continue down the valley without wasting all its energy on a broad flat plain at the bottom. The upper valley immediately below the cliff face that toppled was also a glacial U-shaped valley though, so this speculation might need adjustment as more work is done.

It's worth emphasizing just how much less monitored and dangerous Nepal's mountains are though. The (greater) Himalayas are unlike any other mountain ranges I've ever seen.

> The valley where the floods occurred in Nepal has a V-shape

https://earth.google.com/web/@28.34107217,85.43477356,2834.6...

Didn't realize google earth's performance had gotten that bad, but yeah, you can clearly see the V shape there. You can see the U shape in the hanging valleys on the higher slopes as well as further up where the main waterway originates, but whatever form the lower regions might have had after the last LGM has been reshaped by erosion.

It's already happening: Swiss and French Alps, Italian Alps, Dolomites…

Marmolada glacier collapse, Italian Dolomites (2022)

https://www.theguardian.com/world/2022/jul/05/within-five-mi...

https://www.politico.eu/article/climate-change-italy-canazei...

Village buried, Blatten, Switzerland (2025)

https://planetski.eu/2025/05/29/swiss-village-hit-by-landsli...

Evacuations after rockfall (2025)

https://www.theguardian.com/world/2025/jul/30/rockfalls-ital...

Evacuations, mudslides, bridge destroyed (2026 – last week)

https://italien.news/en/chronicle/severe-weather-hits-northe...

Village threatened, Kandersteg Switzerland (2026 – last week)

https://planetski.eu/2026/08/19/monitoring-continues-on-moun...

As someone from the Austrian alps: Of course as the climate is warming the glaciers are collapsing. At this point thst has been observable with my own eyes during my relatively short lifespan.

That of course means the old wisdom in which places to settle is safe no longer holds. However placed like Austria or Switzerland have top notch tech and public serviced, meaning glaciers are condtantly surveiled and such risks have a much bigger chance of getting noticed here than in the relatively poor Nepalese mountain region. But that doesn't mean black swan events are always preventable.

It really hits the most kind and humble people in Nepal as I know from the stories my grandparents (both avid alpinists) told me about being there.

Yes, but apparently they monitor the glaciers stability / Temperature closely and evacuate required

And it is at a smaller scale in the Alpes than in Himalayas. Still devastating:

https://www.youtube.com/watch?v=YisdT5AJobk

France is actively draining some of those glacier lakes to prevent them to build up over time.

https://www.youtube.com/watch?v=3B-xmvYe11U

That and other risks.

There's the 1963 Vajont Dam collapse in northern Italy (just south of the Swiss border).

Nutshell summary: one of the tallest dams ever built (262m / 860ft) created a reservoir in a high valley surrounded by the sedimantary limestone slopes of Mounte Toc. Layers of limestone were separated by clay a few cm thick. As the reservoir filled, the clay was hydrated, effectively becoming a lubrication layer. On 9 October 1963 a 2km long landslide of roughly 260 million m^3 slammed at 110 kph into the reservoir creating a tsunami of 115 million m^3 of water which overtopped the dam itself in a 250m high wave. The primary impact was downstream in the Piave Valley utterly destroying several villages and towns, with 1,900--2,500 deaths. (Other waves washed across the reservoir and upstream causing additional damage.)

There's a detailed Wikipedia article: <https://en.wikipedia.org/wiki/Vajont_Dam>.

Also several good videos detailing the specifics of the disaster on YouTube.

Generally the Alps are at a far lesser scale than the Himalaya, but yes, glacier, flood, and landslide risks exist.

another good article, without paywall: https://www.theguardian.com/world/2026/aug/27/nepal-tibet-fl...

Is there a text of this elsewhere? I'm hard-paywalled (archive.is doesn't seem to capture a copy).

Paywall. I'm not sure how you expect anyone to read this

I agree, paywall makes it literally literally unreadable

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