many times have you watched a movie where the hero is sucked down into a pit of
quicksand, only to be saved at the last minute by grabbing a nearby tree branch
and pulling himself out? If you believed what you saw in movies, you might think
that quicksand is a living creature that can suck you down into a bottomless pit,
never to be heard from again. But no -- the actual properties of quicksand are
not quite those portrayed in the movies. |
Quicksand is not quite the fearsome force of nature that
you sometimes see on the big screen. In fact, quicksand is rarely deeper than
a few feet. It can occur almost anywhere if the right conditions are present.
Quicksand is basically just ordinary sand that has been so saturated with water
that the friction between sand particles is reduced. The resulting sand is a mushy
mixture of sand and water that can no longer support any weight. If you step into
quicksand, it won't suck you down. However, your movements will cause you
to dig yourself deeper into it. In this article, you will learn just how quicksand
forms, where it's found and how you can escape its clutches if you find yourself
hip-deep in it.
Quicksand is an interesting
natural phenomenon -- it is actually solid ground that has been liquefied by a
saturation of water. The "quick" refers to how easily the sand shifts when in
this semiliquid state. Quicksand is not a unique type of soil; it is usually just
sand or another type of grainy soil. Quicksand is nothing more than a soupy mixture
of sand and water. It can occur anywhere under the right conditions, according
to Denise Dumouchelle, geologist with the United States Geological Survey (USGS).
Quicksand is created when water saturates an area of
loose sand and the ordinary sand is agitated. When the water trapped in the batch
of sand can't escape, it creates liquefied soil that can no longer support weight.
There are two ways in which sand can become agitated enough to create quicksand:
1. Flowing underground water - The force of
the upward water flow opposes the force of gravity, causing the granules of sand
to be more buoyant.
2. Earthquakes - The force of the shaking ground
can increase the pressure of shallow groundwater, which liquefies sand and silt
deposits. The liquefied surface loses strength, causing buildings or other objects
on that surface to sink or fall over.
Vibration tends to enhance the quickness, so what
is reasonably solid initially may become soft and then quick, according to Dr.
Larry Barron of the New South Wales Geological Survey.
Quicksand forms when uprising water
reduces the friction
between sand particles, causing the sand to become "quick."
The vibration plus the water barrier reduces the friction
between the sand particles and causes the sand to behave like a liquid. To understand
quicksand, you have to understand the process of liquefaction. When soil liquefies,
as with quicksand, it loses strength and behaves like a viscous liquid rather
than a solid, according to the Utah Geological Survey. Liquefaction can cause
buildings to sink significantly during earthquakes. While quicksand can occur
in almost any location where water is present, there are certain locations where
it's more prevalent. Places where quicksand is most likely to occur include:
Near underground springs
The next time you're at the beach, notice the difference
in the sand as you stand on different parts of the beach that have varying levels
of moisture. If you stand on the driest part of the beach, the sand holds you
up just fine. The friction between the sand particles creates a stable surface
to stand on. If you move closer to the water, you'll notice that the sand that
is moderately wet is even more tightly packed than the dry sand. A moderate amount
of water creates the capillary attraction that allows sand particles to clump
together. This is what allows you to build sand castles. But beach sand could easily become quicksand if enough
water were thrust up through it. If an excessive amount of water flows through
the sand, it forces the sand particles apart. This separation of particles causes
the ground to loosen, and any mass on the sand will begin to sink through it.
In the next section, you will find out how to save yourself if you happen to fall
into a pit of quicksand.
How to Escape
If you ever find yourself in a pit of quicksand, don't
worry -- it's not going to swallow you whole, and it's not as hard to escape from
as you might think. The human body has a density of 62.4 pounds per cubic foot
(1 g/cm3) and is able to float on water. Quicksand is denser than water -- it
has a density of about 125 pounds per cubic foot (2 g/cm3) -- which means you
can float more easily on quicksand than on water. The key is to not panic. Most
people who drown in quicksand, or any liquid for that matter, are usually those
who panic and begin flailing their arms and legs.
It may be possible to drown in quicksand if you were
to fall in over your head and couldn't get your head back above the surface, although
it's rare for quicksand to be that deep. Most likely, if you fall in, you will
float to the surface. However, the sand-to-water ratio of quicksand can vary,
causing some quicksand to be less buoyant. "By the same token, if the quicksand
were deep, as in up to your waist, it would be very difficult to extract yourself
from a dense slurry, not unlike very wet concrete," said Rick Wooten, senior geologist
for Engineering Geology and Geohazards for the North Carolina Geological Survey.
"The weight of the quicksand would certainly make it difficult to move if you
were in above your knees."
The worst thing to do is to thrash around in the sand
and move your arms and legs through the mixture. You will only succeed in forcing
yourself farther down into the liquid sandpit. The best thing to do is to make
slow movements and bring yourself to the surface, then just lie back. You'll float
to a safe level. "When someone steps in the quicksand, their weight causes them
to sink, just as they would if they stepped in a pond," Dumouchelle said. "If
they struggle, they'll tend to sink. But, if they relax and try to lay on their
back, they can usually float and paddle to safety." When you try pulling your leg out of quicksand, you are
working against a vacuum left behind by the movement, according to The Worst-Case
Scenario Survival Handbook. The authors of the book advise you to move as slowly
as possible in order to reduce viscosity. Also, try spreading your arms and legs
far apart and leaning over to increase your surface area, which should allow you