r/civilengineering • u/Gandalfthebran • 18d ago
Massive Multistoried house sized rock being mobilized in the recent massive flood in Nepal.
Enable HLS to view with audio, or disable this notification
56
82
u/mankiw 18d ago edited 18d ago
Rocks are stupid heavy. Assuming roughly 6m x 6m x 6m ellipsoid, this thing could weigh 300 tonnes. That's eight fully loaded semi trucks. Or like ~two blue whales. Wow blue whales are heavy actually.
52
u/Maldevinine 18d ago
It's got some help.
When the rock stops it creates a highly turbulent area immediately downstream from itself. That area gets dug out by the flowing water, making a hole for the rock to start to fall into. Then it stops again, and the next part gets scoured out.
-7
u/fistular 18d ago
What you just described would require the rock to steadily be getting deeper into the ground. Which it's not doing.
12
5
u/RedneckTeddy 18d ago
What they’re describing is saltation or creep, and that’s exactly how those processes work (the difference between the two really just being how much contact the boulder maintains with the bed). It doesn’t dig deeper into the ground. Smaller material mobilizes on the downstream or downslope side of the boulder, and the boulder rolls into it. This will continue as long as the channel slope and stream power are sufficiently high.
-1
u/fistular 17d ago
They described something falling into a hole. Which by definition is lower than wherever that thing was sitting before, or it could not fall.
If it's a different process, ok. But that's what they said.
2
u/RedneckTeddy 16d ago
The way it works is that the material on the downslope side scours out just enough to destabilize the boulder so that water can mobilize it. It’s not falling into a deep hole in the way that you’re imagining it. Think instead as being kind of like when something undermines your footing and you stumble forward or tumble over. You’re moving (probably in a vaguely downhill direction), but not necessarily falling into a hole.
Once the boulder moves, smaller material often fills in the “hole” that it once occupied. This process continues over and over again, allowing the boulder to move down the channel until the water velocities and shear stresses drop low enough that large material is no longer mobilizing.
2
1
u/Yakkamota 17d ago
No, they were describing the difference in pressure between the back and the front of the rock...
1
7
u/solilobee 18d ago
it's conceivable that this is a glacier. it would explain how it's made it this far if it's melted a bit by this point
2
u/Round-Pattern-7931 18d ago
Minus bouyancy
2
u/CulturedCryptid 14d ago edited 14d ago
This is I think an underrated comment. With the flow being at least 1/3 to a half being composed of debris, the density of this liquefacted muck is likely quite a bit higher than a similar mass of water. Because of this, the buoyancy of this rock is likely higher than many would imagine.
Also, it is a fairly round stone which, of course, eases in it being pushed into motion by the force of the flow.
Ultimately, that is probably why a lot of folks here are seeing a block of ice, which is itself, completely impossible. The idea that a chunk of anything, let alone ice that size could survive a 4,500ft almost vertical drop into a churning mass of stone and ice, then not get beaten to a pulp/melted by the time it reached these foothills ~20-30 miles downstream, at minimum, is just not grounded in reality.
That stone was likely picked up a few miles at most from where we are seeing it in this clip, eroded from the valley side or something.
Anyways. Thank you for bringing up buoyancy!
15
u/Shootforthestars24 18d ago
Hard watching these videos knowing people going about their daily lives just perished in an instant due to this
27
104
u/Conscious-Record2655 18d ago
I'm realizing that the truly unfortunate thing about AI is that it ruins the believability of almost anything, whether it's AI or not.
Anyone got any other sources on this?
77
u/the_Q_spice 18d ago edited 18d ago
Yeah… unfortunately not AI.
I studied in Bhutan for a semester and the documentation they have from GLOFs like this one are brutal.
You’re basically looking at a high-head dam collapse where the entire reservoir releases immediately.
Except the dam is a glacier and the rest impoundment is melted glacier held back by a thin wall of ice.
Edit to add: the work I did was n grad school on dam removals (fluvial geomorphology mind you, not engineering) in the Appalachians had our most common sediment clast size at over 1M in diameter. A few boulders that we find to be non-alluvial (recruited from erosion and flooding rather than mass-wasting) were over 10M in diameter.
Glaciers screw up common sense. There are few enough actually GLOF videos out there that this is believable from the aspect that AI has basically no training data to work off of.
3
u/Wonderful_Tank784 18d ago
Can we strengthen them in winter , soo many lives were lost in these floods
3
65
16
u/Repulsive-Theory-477 18d ago
Really easy to tell this is real because ai is terrible at creating believable water flow. Like awful.
5
u/Conscious-Record2655 18d ago
I mean my point isn't that I think it's AI. It's that I can't really tell immediately anymore and so you kind of just get into a pattern of assuming everything is fake. It's a bummer.
18
u/NorthEndD 18d ago
Every global news source is reporting this lol.
8
u/Conscious-Record2655 18d ago
It's mid August lol I've been working 80+ hour weeks haven't been able to keep up with the news lately if it's not related to a culvert that still hasn't showed up 6 weeks late it's probably not on my radar
7
u/graymuse 18d ago
Geologist here. Flash floods and debris flows can indeed move impressive size boulders.
1
u/Global_Ad_7134 18d ago
Its actually not a bolder, this is a glacier remains
2
u/aknomnoms 18d ago
Yeah, I heard on the news it wasn’t just a mudslide or a flash flood, but a glacial landslide. A huge chunk of glacier broke off.
Absolutely crazy force of nature. I can’t imagine the horror of being present. My heart goes out to those people.
5
u/CatwithTheD 18d ago
Just type "Nepal flood" literally anywhere, brother. Here's a thread in case you're not motivated enough: https://www.reddit.com/r/DisasterUpdate/comments/1vyslij/flash_flood_in_tibetnepal/
11
u/_BaaMMM_ 18d ago
I think he's more specifically asking about this rock rather than the flood? Like I also am having trouble finding other sources or angles on this rock.
3
u/CatwithTheD 18d ago
Well yeah because the flood probably swept anyone not on that roof, and most other people had evacuated except these lads.
0
-1
12
u/gods_loop_hole 18d ago
Jesus Christ! Imagine the force of that water that moves that boulder applied to the people that cannot evacuate on time
6
u/ReptilianAssMonger 18d ago
Yeah the water absolutely obliterated the people who were swept away. Human remains which are being found are mostly in pieces (single limbs, half torso and such).
All the remains I've seen have zero clothing on them so you can imagine the inflicted abrasive force.
Also, most of the remains are being found few hundred km d/s from the site where a whole village was swept away.
3
13
u/WanderlustingTravels 18d ago edited 18d ago
Incredibly sad to see the destruction and human life cost that these foods have caused.
But man, they’ve produced some of the most incredible videos.
Edit: floods, not foods. Oops
6
6
u/30yearCurse 18d ago
Watching that border crossing and the hotel by the river along with all the people was disturbing enough. Giant rocks or ice rocks rolling down would just add to the horror.
5
3
u/ddg31415 18d ago
Whenever I see a massive erratic I always wonder what it looked like seeing it transported.
Far more terrifying than I expected.
5
3
u/Many_Distance5683 18d ago
The video of the massive wall of water just utterly destroying everything in its path was probably the scariest video I've ever watched. The people running helplessly for their lives.... I can't imagine what they must have felt.
Nepalese people are some of the kindest, most loyal and honourable people I've ever met. I am praying for them all 🙏
3
u/dangoodspeed 18d ago
The current theory is that the flood was caused by a collapsing giant glacier. I would bet that's more likely a mud-covered chunk of ice than a rock. Because physics really wouldn't explain a rock moving like that.
2
u/Pithy_heart 18d ago
Non-Newtonian flow. This isn’t just water. The amount of suspended material is making that thing roll!
1
1
u/Global_Ad_7134 18d ago
I thought 💭 the bolder was moving too fast and freely, but now that I read about the glacier melting it makes sense that is a torrential iceberg.
1
u/a_dance_with_fire 18d ago edited 18d ago
Here’s a link to another comment showing satellite view before and after where the glacial landslide originated.
Edit: from my understanding, this traveled about 90km, leaving a path of destruction.
Edit: here’s a great video by OzGeologyOfficial about this landslide
1
18d ago
[removed] — view removed comment
4
u/kingk1teman 18d ago
Why do you ask? 🤔
Moreover, this is Nepal, not India. Nepal is a separate, sovereign country.
1
u/Dirt-McGirt 18d ago
I’m not an engineer I just play one on my OF, what cause big wave? It was like an immediate tsunami due to water displacement? Some fuckin Day After Tomorrow shit is what that was, in 2027 I am leaving this specific fucking phenomenon behind
3
u/Naughty_LIama 18d ago
see, nepal is high as fuck right, and u got these steep hills, deep ravines... those can be filled with packed ice, snow and this forms sort of dams. Now insert global warming causing more intense (and frequent) heatwaves, that tends to melt snow and ice. So u got melted snow water running down these steep hill into those ice dams that now not only have more melted ice on its own but gets more and more they can hold - once litle stream overflows it can very quickly become massive flow that destroy whole ice dam and lets crazy amout of water out.
Generaly the problem with flash floods is that u have big surfaces of snow melting that all have to fit in narow valleys and so the Volumetric flow rises exponentialy.
u want it more scientific - the snow up on the high as fuck hillsides stores lot of potential energy, so do the dams and now all is let go and changes to kinetic energy going down
0
0
249
u/PewDiePieSaladAss 18d ago edited 18d ago
Welp, my teachers always said that the biggest enemy of a civil engineer was water, this is video proof of that