When I was in the Civil Engineering dept. at the U of I in Champaign, one of the geotech grad students built an enormous quicksand tank for the annual engineering openhouse. I volunteered and spent several days in it.
As pointed out, quicksand is basically just fine sand that has lost all ability to support any load due to water pressure applied from underneath (if you know the specific gravity of the sand you can figure out the exact details of the “quick condition” very easily, if anyone wants the math I’ll try and dig up [ha ha] my old notes). Typical source of the water pressure is a submerged spring or water percolating up through a pit of sand from a water supply somewhere higher up.
Anyhow the result is an INCREDIBLY bouyant fluid. With me pushing down on the sides of the tank and the 250-pound Marine who designed the thing applying his weight to my shoulders, we managed to get my chin under. We let go and I bobbed up like a cork. Generally I was floating about waist-deep. We used warm water and it was a very soothing way to spend a few hours. I’ve got some photos somewhere I think.
I can’t speak to anyone else’s experience but if I were to fall into quicksand I’d calm down, relax and then swim slowly to solid ground. There is nothing about quicksand that “sucks you down” (quite the opposite) unless you have something like a subterranean stream underneath that gets you (like undertow at the beach).
OK, CasperQ, I have to admit that at FIRST the very top layer of the quicksand that they showed in the segment looked like sand. But as the guy struggled in it, it looked thick dark and slimy.
I guess quicksand has a variety of disguises. Hell, I’ve never had the misfortune to get stuck in it, so what do I know? LOL
It was interesting to me how the guy described being stuck in it. His feet and legs just sunk and sunk the further he struggled. What kept him in it was the more he struggled, the more pressure the gunk placed around his legs. It seemed like the pressure on the legs and waist were what kept him in the quicksand, like a vice. When he got out (after being stuck for those two days), his calves, ankles, and knees were more swollen than his thighs.
The secret to getting out (says the expert dude who taught him how to get out) was distributing your weight across the quicksand (I likened it to snowshoes). He mentioned carrying a long walking stick, and if you get stuck, bend forward at the waist, spread your hands out at the ends of the stick, and work your way out. But if you have no stick, sit back and distribute your weight with your butt and your hands spread out behind you, and pedal your way out until your legs and feet become free (looks like it took awhile, but it beats two days of struggling), and roll or crawl across the quicksand until you get to solid ground.
Quicksand is real. You can see and feel it for yourself at Morcombe Bay in the UK. There are tours organised where visitors are taken to the edge of the dangeous sands by a guide. I have not seen it for myself, only on telly. The general advice seems to be that it is panic that will make you sink whereas staying calm and spreading your wait will allow you to get out.
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One thing that really bugs me is quicksand in the desert – since quicksand requires an uprush of water you’re not likely to find this in the desert (as in Lawrence of Arabia or the first Brendan Fraser Mummy movie). If here is a comparable phenomenon, it’s probably sort of like a sand sinkhole, but for all I know the movies are making it up.
I read about these once, years and years ago. I think it may have been around the time Mad Max: Beyond Thunderdome came out. IIRC, thse “sinkholes” can occur in dunes when subsurface sand flows downward, but the surface part remains intact. If the void is sufficiently close to the surface, then the surface can give way when someone treads on it. So it’s not really like quicksand, but more like stepping into a hole whose sides are giving way.
Where does quicksand usually turn up? It sorta sounds like it can be anywhere that there is sand and water. I live on the east coast and by many rivers and I’ve never heard of a patch of quicksand forming anywhere near.
The lee side of a side dune can have extremely loose fluffy sand. The right conditions include dryness (so it’s not sticky) and prevailing winds from one direction. A person/camel/whatever crossing such a dune destabilizes it, the sand starts packing down, you start sinking and, most importantly, the sand on the dune upslope from you starts to slump down on you. Very little anyone can do for you once you are trapped in one.
You need sand (IIRC it helps if it’s of a particular gradation - harder with silt or boulders for example) and a source of water pressure underneath the sand deposit. It’s not enough to just have water and sand, without the right hydraulic pressure you just get, well, damp sand - that’s why beaches aren’t covered in the stuff. Dunno if there’s any place on earth that is more prone to it or not.
You can also get a temporary quick condition by sudden ground movement. If the soil is saturated, the movement can alter the water pressure enough that the soil loses strength and you get liquefaction which is familiar to those of us in earthquake country. Anything in the area will behave like it was suddenly in a very dense fluid - buried tanks can pop to the surface, buildings can tip or sink (or float!), etc. There are some other causes of liquefaction; the Norwegian landslide mentioned that was caused by the farmer trying to expand his barn depended on a particular type of clay and an unusual salt content. I saw the movies in class, it’s pretty incredible to watch chunks of solid earth with a house on them slide around and then suddenly turn fluid, exactly like a big water balloon was just popped. The army had to use high explosives to “collapse” the rest of the dangerous land. The one building left unscathed by all of this belonged to the fellow who started it all, betcha he wasn’t too popular with the neighbors.
IIRC, it is most common in places where you have (a) sand and (b) underground streams - these places also have underground caves, caverns, and other various cavities.