Wet sand is common in coastal dune environments. Waves on the
beach, rain, and melting snow and ice make surfaces moist. The
moisture is an important control on how much sand moves by wind.
Moist sand has much more resistance to movement by wind than dry
sand. Moisture increases cohesion between sand grains, raising
the threshold wind velocity. In general, the wetter the sand,
the greater the cohesion and the more resistant the sand is to
the forces of the wind. Above relatively low levels of moisture
(roughly 4%), even very strong winds are unable to move the sand
grains. Sand pillars illustrate differences in cohesion between
wet and dry sand. Moisture in the pillars holds the sand grains
together enough to support nearly vertical edges. The pillars
exist because wind removed dry sand and left the moist sand
behind as pillars. Note mechanical pencil in photo for scale.
(Hoffmaster State Park in December 2001.) sand dries out as
water evaporates or drains into the ground. Drying rates depend
on atmospheric c