Lake Michigan Coastal Dunes
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Environment - Frozen ground


The ground freezes when soil temperatures go below 0°C (32°F) and water freezes in the pore spaces between sand grains.

Freezing temperatures may occur any time between September and May, but they are most common from mid-December through mid-March (see Temperature).

Ground freezing occurs from the surface down. As freezing temperatures continue, the layer of frozen ground thickens. Because temperatures change very slowly at greater depths, the frozen layer is rarely more than 0.5 m (1.5 feet) deep. Frozen ground may last for weeks or months, but conditions are often variable at the surface. A surface layer may go through many freeze-thaw cycles during the winter in response to changing temperatures.


Before coastal ice forms, Lake Michigan waves erode frozen beach sand. The results are small vertical scarps, undercut features, and chunks of frozen sand scattered on the beach. (Hoffmaster State Park in January 2005.)

 



Frozen ground halts wind erosion because sand grains resist wind forces when they are cemented to the ground by pore ice. The effect is not permanent--when the pore ice is removed (by sublimation) or broken (by impacts of moving sand grains), wind can move the sand.

Frozen ground affects sand transport by wind by providing a solid surface for sand to travel on. Wind-blown sand travels further on hard surfaces because grains in motion keep more of their kinetic energy; loose sand surfaces absorb some of the energy of moving grains.

Loose sand deposit on frozen beach.
A small deposit of loose sand (with ripples) lies on top of the frozen beach. (Hoffmaster State Park in January 2003.)

 

 


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Last updated 03/23/10.