Geology Reference
In-Depth Information
To move sand-sized particles, wind first pushes them along the surface. If the particle is
too heavy to be lifted, it continues to move forward along the ground in a movement
called
creep.
Smaller or lighter sediments are picked up into the wind flow when the speed (or
velo-
city
) of the wind flow is great enough to lift them up. But even after they're lifted, the
particles are still subjected to the pull of gravity, so after a short period of suspension
they fall back to the surface.
This type of particle motion is called
saltation:
The particle jumps along the
surface, being repeatedly lifted and dropped as it moves in response to the force
of the wind flow.
As the particles land, they bounce farther along and bump other grains, which may be-
gin to
saltate
or move forward in the same manner. In this way, the bed load of a wind
current is filled with sand-sized sediments bouncing along in the direction of the wind
flow. If the surface is very hard, the bed load may extend up to 2 meters (about 6.5 feet)
above the surface because objects bounce higher off a more compact surface. For ex-
ample, if you drop a marble onto grass, it will not bounce or move very far. But if you
drop the same marble onto pavement, it will bounce and move much farther.
The bed load of a wind current is illustrated in Figure 14-1.
Figure 14-1:
Creep,
bed load, and sus-
pended load layers
in a wind current.
