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Author Topic: Why do people drown in quicksand?  (Read 6483 times)

Offline graham.d

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Why do people drown in quicksand?
« on: 28/03/2011 11:01:22 »
Is drowning in quicksand common or just something that happens in films and TV dramas? It would seem, at first sight, that a suspension of sand in water would have a net density rather higher than just water and would therfore be reasonably bouyant. I can see that the viscosity of the mix would make it hard to swim in although it should be possible with some modified technique. Or is it the case that the suspension of particles in the water does not behave in the same way as a uniform fluid of the same net density? Are you just displacing the water part so that, somehow, the sand particles, that are also displaced, don't count in providing the Archimedean upthrust?


 

Offline yor_on

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Why do people drown in quicksand?
« Reply #1 on: 28/03/2011 11:31:25 »
As far as I remember it is a myth. But I'm not sure.

But you can drown in water and earth though, if the mix is right.
 

Offline burning

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Why do people drown in quicksand?
« Reply #2 on: 28/03/2011 18:42:28 »
You're right that neutral buoyancy is greater in quicksand than in pure water.  Unless you are particular laden (say with a heavy backpack) it would actually be an effort to submerge yourself completely.  The big danger as I understand it is that once mired it can be difficult to get out.  Since a lot of quicksand occurs in tidal areas, you might not drown in the quicksand but still drown in high tide.  Even if that doesn't happen, death by exposure is a very real danger.
 

Offline chris

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Why do people drown in quicksand?
« Reply #3 on: 28/03/2011 21:48:49 »
Here's a link to an article I wrote about quicksand and its composition.

http://www.thenakedscientists.com/HTML/articles/article/whatisquicksand-1/

Chris
 

Offline graham.d

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Why do people drown in quicksand?
« Reply #4 on: 28/03/2011 23:10:01 »
Thanks Chris. I thought it was more complicated than it first appears and your article explains the apparent paradoxes.
 

Offline JP

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Why do people drown in quicksand?
« Reply #5 on: 29/03/2011 03:00:59 »
So I guess you could drown, but you'd have to go for a swim head-first.   :P
 

Offline Bored chemist

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Why do people drown in quicksand?
« Reply #6 on: 29/03/2011 06:49:25 »
So I guess you could drown, but you'd have to go for a swim head-first.   :P
People generally do.
 

Offline GrapperJ

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Why do people drown in quicksand?
« Reply #7 on: 29/03/2011 13:09:08 »
Here is another article talking about the lethality of quicksand:

<edited out, didn't see it was already posted>

The short version is you rarely "drown" in it, rather, you get stuck and can't get out and die from exposure to the elements.
« Last Edit: 29/03/2011 13:11:07 by GrapperJ »
 

Offline yor_on

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Why do people drown in quicksand?
« Reply #8 on: 30/03/2011 04:15:56 »
So I guess you could drown, but you'd have to go for a swim head-first.   :P
People generally do.

:)

Not after seeing my friend try it.
I wouldn't..
 

Offline CliffordK

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Why do people drown in quicksand?
« Reply #9 on: 03/04/2011 00:28:34 »
http://www.thenakedscientists.com/HTML/articles/article/whatisquicksand-1/
Quote
Well certainly not the way Hollywood would have you do it – by being pulled out by a horse

Actually...  I did it the other way...
I ended up pulling the horse out   [xx(]

It was pretty extraordinary...  and very scary!!!
Riding along the beach.  And suddenly the horse's belly was flat on the ground.  I got off very quickly and coaxed the horse to pull out of it.  I didn't sink, although I did not go back to inspect the hole we made. 

If I managed to get mired in the stuff...  I certainly wouldn't want a horse to get close enough that I could grab its tail as the horse's feet are much smaller with greater weight per unit area than a person's feet.

There may be different types of quicksand.  This was apparently a spring from a lake on the other side of the dune.  The spring would have caused a saturation and rarefication and upwelling of the sand, perhaps no clay or silt involved. 

The force of extraction calculations sounds excessive, although I suppose it is hard to know what to compare it to.  In the case above, the horse was able to regain solid footing, and the whole thing lasted less than 5 seconds or so.  I've been walking in deep mud which can suck a rubber boot right off one's foot, but not to the point of any danger.  Anyway, I doubt you would yank a leg off.  And, one would naturally point one's toes downwards if one was being pulled out by a rope.

There are stories of vehicles (cars and motorcycles) getting mired in the quicksand at the beach...  being virtually impossible to get out, and disappearing quickly.  But, even so, the occupants usually escape unharmed.
 

Offline graham.d

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Why do people drown in quicksand?
« Reply #10 on: 03/04/2011 12:45:11 »
Mud can be dangerous. A few years ago a well known and experienced solo yachtswoman got her yacht stuck on a falling tide in a river. I can't remember the details but it was in Essex or Suffolk I think. She decided to anchor the yacht and wade ashore rather than wait for the next tide. She didn't make it. She probably got stuck, tired and then, ironically, drowned on the rising tide.
 

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Why do people drown in quicksand?
« Reply #10 on: 03/04/2011 12:45:11 »

 

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