I recently discovered The Straight Dope and I have been reading the archives. I have been amazed at Cecil’s remarkable intelligence, but I didn’t feel he answer sufficiently.
There is a sensation of downward suction that Cecil dismisses if you try to pull yourself out (I have experienced this at first hand) As you lift part of your body out of the soup, sand rushes to occupy the space you have vacated, creating a vacuum. This is where the feeling of suction comes from. This is why it is more difficult to escape from than water, and impossible to swim in.
Although not usually deep enough to drown in, there are some notable exceptions, particularly Morecambe Bay on the North-West Coast of England, where well documented in history scores of people and even horses have succumbed crossing the sands.
But he answered that question in 1973, so nobody probably cares!!
Here’s the original article: http://www.straightdope.com/classics/a1_158b.html
Welcome to the board (I’ve always wanted to be the one to do that).
And, BTW, there is no issue so trivial that you can’t find people who care about it on this board.
I have no experience with quicksand, but I have been in mud, and had the experience of getting my feet so stuck that I pulled my foot out of the shoe with the shoe still stuck. They were lace up shoes.
The suction encountered is the same type. The trick is not to pull directly out, but move sideways through/across the quicksand. Although having somebody nearby to throw you a vine (a la Tarzan) is certainly comforting to ensure you won’t keep sinking, and having aid to help get you out is certainly beneficial, it isn’t required if you remain calm.
Note that strictly speaking, the vacuum isn’t created by the mass of inrushing particles. When you go in (or step in the mud), you press the existing material out of the way by displacement. When you try to remove yourself (or your foot), the quicksand (mud) makes an airtight seal around the body part, preventing the air from flowing in to fill the void. Creating the void by trying to pull out without material to flow in behind creates the vacuum. That’s why it’s relatively easy to get out of water. The water flows easily enough to fill the void as you move out of it. Mud being much thicker doesn’t flow back as well, so there is a pressure build up. Same with the quicksand.
One way to relieve the vacuum is to slide an object like a stick down beside your body and then wiggle it to create an open path between the surface and the bottom. Then as you remove your body, air can flow quickly in behind to fill the void and relieve the vacuum. This might be challenging if you are in the middle and suck down shoulder deep. Thus the admonition to lie out lengthwise and spread your weight. Also why sideways motion (rolling) is easier than direct pull out - it opens up a path for air along the side to underneath and thus relieve the suction.
ISTR that the Worst Case Scenario Survival Handbook said to make sure you’re carrying a stick with you when you’re in quicksand country. Then, if you step in, sort of do what Irishman says and lay down on top of the stick. It scared the heck out of me that they don’t tell you what to do if you forget your stick; it gave me the idea that if you don’t have one, you’re doomed.