6 ms·

It doesn't look particularly fast-moving, so I must be missing something here that accounts for the legendary 100% mortality rate. Unless there's a giant vortex

It doesn't look particularly fast-moving, so I must be missing something here that accounts for the legendary 100% mortality rate. Unless there's a giant vortex of electric eels, this stretch of water looks tamer than what those extreme kayakers were up to in HBO's recent docuseries.

toss1 4y ago
What you are missing is that this is an extremely complex version of a drowning machine — very good read here [0]. Under the water is turbulence that just traps a person and keeps them tumbling underwater. In addition the article points out that there are numerous rock outcroppings underwater against which an unfortunate person's head would likely get bashed, reducing or eliminating consciousness. I also notice that the water is quite frothy and full of air bubbles. This reduces it's net density and thus reduces the buoyancy available to any objects that would otherwise float. It can be enough to sink ships [1]. So, basically, the turbulent water will pull you under, bash you hard against the rocks, give you less-than-normal buoyancy, and hold you under. It's kind of a toss-up whether you lose consciousness first from the head injuries or the lack of air, and after a few minutes of that, you're dead. Have a nice afterlife [0] https://practical.engineering/blog/2019/3/16/drowning-machine-the-dangers-of-low-head-dams https://practical.engineering/blog/2019/3/16/drowning-machin... [1] https://www.newscientist.com/article/dn1350-bubbling-seas-can-sink-ships/ https://www.newscientist.com/article/dn1350-bubbling-seas-ca...
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graeme 4y ago
I heard it described as follows: the full force of the river you see upstream has been turned on its side and the current goes down. You can’t pull against that, especially against curved, mossy, wet rocks So as if an elephant were pulling you down beneath the water and you only had your strength to grip against it. Can’t be done.
- andrewflnr 4y ago
  What I don't understand is how that works from a conservation of mass perspective. The water can't be literally flowing down at every point and keep a stable surface. I assume it's something more complicated, right.
  - steve_adams_86 4y ago
    Part of the difficulty of turbulent water is that it can really whip you and smash you around. It doesn’t necessarily look that violent from outside of the water, but you could be getting broken limbs and brain trauma in that kind of turbulence. The force of the water pressing you into walls and boulders is tremendous. Loads of fatalities in turbulent water occur because the victim rapidly becomes unconscious in the water.
  - throwaway09223 4y ago
    It can. It's an underground tunnel with a small exposed strip at the top. the water can be circulating around the tunnel, flowing back and forth under the rocks. It can be pulling sideways or down at the exposed strip with the water circulating back up in the underground areas out at the sides.
    - andrewflnr 4y ago
      Looking at the underwater footage, I think this is roughly it. You could see bubbles running up the walls.
  - jakeinspace 4y ago
    Of course the flux of water into any volume is equal to the outward flux. But I would imagine the situation is that there are circulating turbulent branching streams of current pulling you down. If you were incredibly lucky, and not killed by impacting the walls, you might pop back up by catching a ride on another section of current.
  - carabiner 4y ago
    I bet it's flowing horizontally but faster the deeper you go. You fall in, the higher speed flow at your feet apparently "sucks" you under due to its higher speed (higher inertia), like being grabbed by your ankles and yanked down.
Quillbert182 4y ago
I don’t know about in a kayak, but I imagine that the current is too strong for a swimmer to hold on. The water will also suck you down deep underneath, almost certainly lodging you into one of the tunnels for the short remainder of your life.
- Exuma 4y ago
  The sides of the rocks are also angled out, so not only do you get sucked down, you get sucked down and out, so there's no chance of even swimming back up.
- scubakid 4y ago
  Ah, I was wondering about the extent to which it might pull you under. Like, is that quantified at all? Consistent or only in a few sections? And how does it compare with some of the world's other most dangerous rivers?
  - dTal 4y ago
    Imagine this filled with churning whitewater: https://upload.wikimedia.org/wikipedia/commons/7/7c/USA_10096-7-8_HDR_Antelope_Canyon_Luca_Galuzzi_2007.jpg https://upload.wikimedia.org/wikipedia/commons/7/7c/USA_1009... You're not coming out alive.
  - HillRat 4y ago
    Don't know about quantified, but some of the underwater videos show bubble entrainment in some kind of shear flow 25+ meters down, which indicates a terrifying amount of velocity and power pushing downwards.
    - robotnikman 4y ago
      Got a link to any of the underwater videos? I'm really curious to see what it looks like underwater.
      - Exuma 4y ago
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maxerickson 4y ago
It's like 100 feet deep. Better hope you are at the surface if you are trying to grab a rock at the surface.
- throw827474737 4y ago
  The guy in the second vid measures 65 meters (210 feet) at one place, 50 meters at another, thats really a wow deep hidden canyon there.
irrational 4y ago
> What is known is that a powerful undercurrent will pull anybody that falls into certain death. > The reason for the dangerous network of caves is just further up above the mouth of the Bolton Strid the river flows 30ft wide and a lot easier giving a more idyllic, romantic and tranquil flow before being disrupted by a geological formation that abruptly funnels hundreds of gallons of water through a tiny six-foot channel. So, the surface appears tranquil, but under the surface is a swift turbulent undercurrent.
carabiner 4y ago
Clearly you should venture forth and swim in it to prove him wrong. Godspeed.
sideshowb 4y ago
I've not seen the documentaries you refer. But kayakers know that danger of a water feature doesn't necessarily correlate with how violent it looks on the surface. Plenty of very quiet weirs are known to be fatal while plenty of noisy ones (though not all!) will spit you out unharmed.

toss1 4y ago

What you are missing is that this is an extremely complex version of a drowning machine — very good read here [0]. Under the water is turbulence that just traps a person and keeps them tumbling underwater. In addition the article points out that there are numerous rock outcroppings underwater against which an unfortunate person's head would likely get bashed, reducing or eliminating consciousness. I also notice that the water is quite frothy and full of air bubbles. This reduces it's net density and thus reduces the buoyancy available to any objects that would otherwise float. It can be enough to sink ships [1]. So, basically, the turbulent water will pull you under, bash you hard against the rocks, give you less-than-normal buoyancy, and hold you under. It's kind of a toss-up whether you lose consciousness first from the head injuries or the lack of air, and after a few minutes of that, you're dead. Have a nice afterlife [0] https://practical.engineering/blog/2019/3/16/drowning-machine-the-dangers-of-low-head-dams https://practical.engineering/blog/2019/3/16/drowning-machin... [1] https://www.newscientist.com/article/dn1350-bubbling-seas-can-sink-ships/ https://www.newscientist.com/article/dn1350-bubbling-seas-ca...

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graeme 4y ago

I heard it described as follows: the full force of the river you see upstream has been turned on its side and the current goes down. You can’t pull against that, especially against curved, mossy, wet rocks So as if an elephant were pulling you down beneath the water and you only had your strength to grip against it. Can’t be done.

andrewflnr 4y ago
What I don't understand is how that works from a conservation of mass perspective. The water can't be literally flowing down at every point and keep a stable surface. I assume it's something more complicated, right.
- steve_adams_86 4y ago
  Part of the difficulty of turbulent water is that it can really whip you and smash you around. It doesn’t necessarily look that violent from outside of the water, but you could be getting broken limbs and brain trauma in that kind of turbulence. The force of the water pressing you into walls and boulders is tremendous. Loads of fatalities in turbulent water occur because the victim rapidly becomes unconscious in the water.
- throwaway09223 4y ago
  It can. It's an underground tunnel with a small exposed strip at the top. the water can be circulating around the tunnel, flowing back and forth under the rocks. It can be pulling sideways or down at the exposed strip with the water circulating back up in the underground areas out at the sides.
  - andrewflnr 4y ago
    Looking at the underwater footage, I think this is roughly it. You could see bubbles running up the walls.
- jakeinspace 4y ago
  Of course the flux of water into any volume is equal to the outward flux. But I would imagine the situation is that there are circulating turbulent branching streams of current pulling you down. If you were incredibly lucky, and not killed by impacting the walls, you might pop back up by catching a ride on another section of current.
- carabiner 4y ago
  I bet it's flowing horizontally but faster the deeper you go. You fall in, the higher speed flow at your feet apparently "sucks" you under due to its higher speed (higher inertia), like being grabbed by your ankles and yanked down.

Quillbert182 4y ago

I don’t know about in a kayak, but I imagine that the current is too strong for a swimmer to hold on. The water will also suck you down deep underneath, almost certainly lodging you into one of the tunnels for the short remainder of your life.

Exuma 4y ago
The sides of the rocks are also angled out, so not only do you get sucked down, you get sucked down and out, so there's no chance of even swimming back up.
scubakid 4y ago
Ah, I was wondering about the extent to which it might pull you under. Like, is that quantified at all? Consistent or only in a few sections? And how does it compare with some of the world's other most dangerous rivers?
- dTal 4y ago
  Imagine this filled with churning whitewater: https://upload.wikimedia.org/wikipedia/commons/7/7c/USA_10096-7-8_HDR_Antelope_Canyon_Luca_Galuzzi_2007.jpg https://upload.wikimedia.org/wikipedia/commons/7/7c/USA_1009... You're not coming out alive.
- HillRat 4y ago
  Don't know about quantified, but some of the underwater videos show bubble entrainment in some kind of shear flow 25+ meters down, which indicates a terrifying amount of velocity and power pushing downwards.
  - robotnikman 4y ago
    Got a link to any of the underwater videos? I'm really curious to see what it looks like underwater.
    - Exuma 4y ago

deleted 4y ago

[deleted]

maxerickson 4y ago

It's like 100 feet deep. Better hope you are at the surface if you are trying to grab a rock at the surface.

throw827474737 4y ago
The guy in the second vid measures 65 meters (210 feet) at one place, 50 meters at another, thats really a wow deep hidden canyon there.

irrational 4y ago

> What is known is that a powerful undercurrent will pull anybody that falls into certain death. > The reason for the dangerous network of caves is just further up above the mouth of the Bolton Strid the river flows 30ft wide and a lot easier giving a more idyllic, romantic and tranquil flow before being disrupted by a geological formation that abruptly funnels hundreds of gallons of water through a tiny six-foot channel. So, the surface appears tranquil, but under the surface is a swift turbulent undercurrent.

carabiner 4y ago

Clearly you should venture forth and swim in it to prove him wrong. Godspeed.

sideshowb 4y ago

I've not seen the documentaries you refer. But kayakers know that danger of a water feature doesn't necessarily correlate with how violent it looks on the surface. Plenty of very quiet weirs are known to be fatal while plenty of noisy ones (though not all!) will spit you out unharmed.