Up to the waist
What is it about the stories in which desert travelers suddenly sink into the sand, irretrievably lost, unable to be freed, especially not on their own? Since field experiments are out of the question, laboratory experiments bring light into the grain darkness. And relief before the next Sahara tour.
Mannis Bluff fails: Although he stops the fast-paced hunt of the gay rhino couple in the film "Ice Age", the sloth Sid, of all people, unmasks the supposed quicksand as solid ground. This leaves the question unanswered: How deep would the two disgruntled odd-toed ungulates have sunk?
Just to the waist, Daniel Bonn of the Ecole Normale Supérieure in Paris and his colleagues would reassure all rhino lovers. But the good news was followed by bad news: the two Ice Age contemporaries would have gotten stuck. Without external, far more powerful help than Manni, they would have had to look at the approaching glaciers from below.
The scientists don't, of course, lure rhinos into quicksand fields to make such statements, they study the behavior of the strange sands in the laboratory. With a special mixture of sand, clay and s alt water, they simulate the properties of the treacherous underground and explore the danger of sinking with balls of different densities. If the vessel is left alone, the viscosity of the mixture will increase over time, as the clay slowly forms a colloidal, albeit extremely fragile gel. However, as soon as the slightest shock occurs, the system loses its composure and immediately liquefies. So the more a prisoner tries to flail his arms, the deeper he sinks.
And why is it so hard to get out? Because the liquefaction of the loose mixture creates two phases: one - below - rich in sand, now more densely packed, the other - above - correspondingly richer in water and significantly less dense than before. In order to free a trapped person, water would have to be pumped into the sand layer with its high viscosity so that it becomes more permeable again. It is, however, a complex undertaking: In order for the rescuing liquid to penetrate the ground at one centimeter per second, you would need ten bar with the average pore size of sand - i.e. ten times the air pressure. It would take tens of thousands of Newtons to pull a foot out of the trap at the same speed. Entire mid-size cars can be lifted with such forces.
In their laboratory quicksand experiments, the researchers now wanted to test whether a person could sink helplessly and unsupported up to their heads - the stuff of numerous desert stories. They therefore determined the speed at which an aluminum ball with a density of 2.7 grams per milliliter and a radius of two millimeters disappears into the mixture. Again it turned out that in calm conditions absolutely nothing happens: Despite its greater density – the laboratory quicksand has two grams per milliliter – the ball remained on the surface. However, if the scientists shook their quicksand bowl only slightly, the ball would rush down so quickly that it would even hit the bottom before the slowing sand layer formed.
Bonn and his team calculated from the test results that an object with a density of only one gram per milliliter would not sink, but would remain "floating". Such objects include humans and animals. So if you get caught in quicksand, you should do one thing above all, despite the panic: keep still and hope that powerful help will come quickly.
