Is it possible to get sucked down in a quagmire?

[bzakharin]

Being an immigrant from another country (Russia in my case), I have found many things that my culture believes to be obviously true can actually be proven to be false. This particular case, though, is quite puzzling because it appears to have hard physical proofs in Russian, but seems to be shown or proven false in English.

I'm talking about quagmires. Actually, the terminology is the first problem, because the Russian word can be variously translated as marsh, swamp, bog, moor, and more. However, the crucial part is a body of fluid that appears solid at first glance, but "sucks" a person (or any sufficiently heavy living being) in. Quagmire or mire seems to be the best translation of this aspect, though I've searched in vain to find any discussion of these online in English. In fact, the words are used figuratively in almost all cases. What tends to be discussed is quicksand.

Now, the Russian discussion presented on many websites is as follows (I am not a physicist, so this may be a bit muddled): The mire (or whatever the appropriate term should be) is made up of a non-Newtonian fluid, or, more specifically, a Bingham plastic. It will act as a solid until enough pressure is applied, at which point it acts as a liquid. An inanimate object will not sink as far as it would in water because the buoyant force will turn the liquid back into a solid as soon as it counteracts the weight of the body enough for the pressure to diminish below the level required for the fluid to behave as a liquid. But a human, or other living being, moves continuously, with any movement increasing the downward force, which maintains enough pressure to keep the fluid directly below acting as a liquid, and thus sinking deeper and deeper. In particular, even breathing will require enough movement to sink continuously, though slowly. Assuming the mire is deep enough, it is then impossible to prevent oneself from eventually drowning, absent solid objects within reach to grab on to. The body will then not even float up to the surface, trapped in a now solid mass. So, the only recommendation offered, if the above is not an option, is to move as little as possible, not to take exaggerate breaths, and hope help will reach you before you drown.

Now, all sources I could find in English, seem to contradict this notion. While quicksand is stated to be a non-Newtonian fluid, it is stated to be a myth that it is possible for a human to drown in it, due to it being too dense, and therefore more buoyant than water. In fact, the recommendation for someone sinking in a swamp or quicksand, seems to be to lay one's back and float up to the surface as one would in water and, in fact, to breathe deeply to aid oneself in floating up faster!

So, is the problem here that quicksand is not the same as a quagmire, which has different physical properties or is one version correct and the other wrong?

I should note that sinking without a trace in a mire is not an idea foreign to English culture. "The Hound of the Baskervilles" by Arthur Conan Doyle presents such a scenario, but it is a work of fiction, so I cannot really give it any more credibility than the movies depicting drowning in quicksand, and certainly the physics of the situation are not discussed there.

 

[phinds]

In English, I have never heard the word quagmire used in its literal sense. One would say swamp, or bog, or quicksand or whatever was appropriate. That doesn't answer your question at all, I know. I'm just commenting on the words.

 

[zoobyshoe]

Made me think of the La Brea tar pits. Unfortunately, the article doesn't clearly explain why the fossils are found at varying depths. It suggests sinking doesn't start till the decay to bone is complete, however.

http://en.wikipedia.org/wiki/La_Brea_Tar_Pits

 

[AlephZero]

I should note that sinking without a trace in a mire is not an idea foreign to English culture.

For a long time it was real, not fictional. In historical times there were large low-lying areas in the east of England that were effectively impassable without local knowledge, because of the low level of the land and frequent flooding from tidal rivers many miles from the coast. I'm talking about an area maybe 100 miles north-south by 30 miles east-west.

The biggest recorded "loss without trace" was in 1415, when the king managed to lose all the contents of the royal treasury and about 2000 men in a single day. Some people dispute whether it actually happened, but parts of the story are definitely factual. http://www.edp24.co.uk/norfolk-life/norfolk-history/41_king_john_s_treasure_1_214293

Several of the churches in the larger towns had "lantern towers" where a fire was kept burning all night, as a inland lighthouse to guide travelers.

This is one of the tallest, at 270 feet (80 meters). It took about 60 years to build, between 1450 to 1510. Since the surrounding land is almost perfectly flat (to within a few feet) it is visible from up to 30 miles away.

This is what it looks like in the far distance ...

 

[Borek]

So, is the problem here that quicksand is not the same as a quagmire, which has different physical properties or is one version correct and the other wrong?

I have a feeling the "western" version follows sound physics, while the Russian version follows makeshift explanation invented to follow the fairy tale, not the physics itself.

When you sunk to the point when your buoyancy keeps you on the surface, any movement will make the liquid around you soft both under, and over you, so I don't see how you can be moving only down.

 

[A.T.]

The ultimate scientific authority:
http://www.discovery.com/tv-shows/mythbusters/videos/killer-quicksand-minimyth.htm

 

[CWatters]

It should be very simple... If your body is denser than the quagmire you will sink. Otherwise you will float.

However... I find it difficult to float in water unless I breathe in and float on my back. When I breathe out I start to sink. So I reckon the question becomes... Is there some property of the quagmire that makes it harder to breathe and maintain positive buoyancy?

 

[bzakharin]

I finally tracked down the book that all the Russian websites on the subject seem to be quoting or paraphrasing. It is a school textbook released in 1985 in the (then) Soviet Union, and sets out out to describe physics of unusual situations. Other topics include (but are not limited to) how a bicycle can remain upright, how ice fishing is possible, and how trains can turn without derailing. I think I can follow the equations presented in the relevant chapter, but I fail to see how it follows from the equations that once a body is submerged to a point below where the buoyant force exceeds the downward force (for any reason, let's say someone pushes it in), it will not float up, but remain where it is, absent other movement (which will submerge it further).

The book does not have a bibliography or further reading list and the only thing I can find out about the author (who does not seem to have written any other books) is that he graduated Moscow University in 1975.

 

[vortextor]

I think the magic word is "Thixotropy"

 

[Borek]

I think the magic word is "Thixotropy"

And how does it answer the original question? Magically?

 

[SteamKing]

And how does it answer the original question? Magically?

I don't think vortextor means literally that 'magic' is involved; the 'magic word' is a somewhat idiomatic expression in American English which means the 'key term of interest'.

On the old Groucho Marx TV show from the '50's, if a contestant said the 'magic word' while talking with Groucho, a toy duck would descend from the overhead, holding a card in its beak with the magic word printed on a card. The contestant won $100, big money back then. The 'magic word' was an ordinary word or phrase used in everyday conversation.

 

[Borek]

I don't think vortextor means literally that 'magic' is involved; the 'magic word' is a somewhat idiomatic expression in American English which means the 'key term of interest'.

I know. My post was meant to be sarcastic - what he wrote sounded as if naming the behavior of the mud was somehow explaining the problem. As far as I can tell - it doesn't.

 

[bzakharin]

I think the magic word is "Thixotropy"

If I understand correctly, we're not talking about a thixotropic fluid, which exhibits time-dependent viscosity, but a Bingham plastic, which is time-independent. At least that's what's presented in the book.

 

[bzakharin]

I figured that I could translate some of the chapter verbatim, so one can look at any logic flaws on my part or on theirs:

The previous sections introduce the Bingham Plastic and provide a
graph and definition similar to the ones Wikipedia has on the
subject. See http://en.wikipedia.org/wiki/Bingham_plastic. They also
explain the Archimedes' principle and how it works in Newtonian
fluids.

Let's place a body onto the surface of a Bingham plastic. If the
body is light enough and the pressure it exerts is low, it is
possible that the stress ocurring in the fluid will not exceed the
yield stress, or τ₀, and the fluid will behave as a solid. That

is, the object can stand on the surface and not submerge.
On the one hand this seems to be a good thing. It is because of this
property that specially made vehicles that exert a low pressure on
the ground can traverse bogs impassable to humans. In fact, even a
human with the help of "marsh skis" or other such gear can lower his
pressure on the ground enough to feel relatively safe. But this
phenomenon is a double-edged sword. The very fact that the body's
submersion stops at an inequality between weight and Archimedes
force is alarming: everything is not as it should be. Let's say
that the weight of the body is in fact enough for it to begin to
submerge. When will it stop? Obviously not at the point when the
Archimedes force becomes equal to its weight. During the submersion,
the Archimedes force will partially compensate for the weight, so
pressure will gradually decrease until the stress will once again
drop below τ₀. The Bingham fluid will cease to flow and the body
will stop *earlier* than the Archimedes force becomes equal to its
weight. Such a state is called undersubmergence(*).

And now pay attention; this is the start of the most important part.
If undersubmergence can exist in a fluid, oversubmergence(*), where
the Archimedes force exceeds the weight, but the body does not float
up, must be able to exist as well. Do you remember what happens with
Newtonian fluids? If for whatever reason the person submerges below
the level of normal submergence, the Archimedes force exceeds his
weight and returns him back to it. With a Bingham's plastic
(provided τ₀ is sufficiently high) nothing of the sort takes
place(**). If you are submerged due to some careless act, you will
not float back up, but will remain oversubmerged. The process of
"sinking" in quagmire becomes irreversible. Now we can define
"sucking in" more precisely. It means the tendency of the quagmire
to lower living objects below normal submergence, into
oversubmergence.

All that remains now is to figure out why the quagmire sucks in,
that is oversubmerges, only living objects.

Living objects oversubmerge because having gotten into a quagmire
they move, that is they rearrange parts of their bodies. This causes
oversubmergence for four reasons.

1. Let's say you have a heavy load in your hands and are starting to
lift it. To accelerate it upward, you must provide force exceeding
the lead's weight. Due to Newton's third law of motion, the force
the load exerts on you also exceeds its weight. Therefore, the force
with which your feet push at the ground increases. If you are
standing if a quagmire, the attempt to lift the load causes your
feet to sink deeper. And what if you don't have anything in your
hands? It doesn't matter. Your hand has weight and raising it will
lead to oversubmergence, infinitesmal, but irriversible. And
multiple movements can oversubmerge significantly.

2. The quagmire is highly sticky. Even raising your hand to free
requires and exerts significant force causing oversubmergence.

3. The quagmire is viscous and resists movement, so trying to free
your hand must overcome this force as well, causing oversubmergence.

4. (summary) Viscosity also causes friction between layers, causing
the fluid to flow slowly. When you free up, say, your foot, the
fluid does not immediately fill in the empty space as water would,
leaving a partial vacuum that must be filled in by air, causing
additional force from air pressure, causing
oversubmergence.

Some repition is being skipped here

One might think that if a human tries to act as an inanimate object, ceasing all motion, he will remain on the surface as long as necessary. This hope is for naught; as much as he wants to, a person cannot cease all motion. He must breathe. This requires rearranging body parts (the ribcage expands when breathing in). Therefore, true immobility is impossible for a person.

What follows are recommendations on what to do if you're stuck (not much is the short answer), how to determine ahead of time if a bog is likely to be dangerous, and how to traverse a bog relatively safely.

----
*I made these two words up. They're literal translations of the
prefixes. The Russian words I translated as these are also not
present in any dictionaries

**This is the crucial sentence. If I understand why this makes
sense, I'll understand why irreversible sinking is possible