Lake Michigan Coastal Dunes
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Lake Michigan Coastal Dune Home
Introduction to Lake Michigan Coastal Dunes
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Beyond the Basics - Wet sand and wind processes


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 in Hoffmaster State Park.
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.)

Wet sand dries out as water evaporates or drains into the ground. Drying rates depend on atmospheric conditions, the movement of moisture through the sand, and other factors. Strong winds speed up evaporation. When sand grains at the surface dry out (even though the sand beneath them is still wet), they can be moved by the wind. Impacts of moving grains with the wet surface can put other grains into motion.

Wind does move sand from wet surfaces--as long as the right combination of wind velocity, evaporation, sand grain size and moisture content is present. Total amounts of sand transport on wet surfaces are much lower than the effects results of similar winds blowing over loose dry sand grains.


 

 

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Last updated 03/23/10.