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How lake ice forms.

Field Science--Does it thicken from the top or bottom? Although making ice can be described as a simple process of freezing it can actually be quite detailed when the physics of water and ice are considered. Inspecting a cross section of on ice hole yields cities as to how it formed.

After the entire water column reaches 4[degrees]C (file temperature when water is at its greatest density), cold air eventually cools less dense surface water to the freezing point or below, resulting in the formation of plate-like crystals that freeze together to form skim ice.* This process occurs on calm, still waters and is quite different from the way ice forms on rivers or wind-blown waters.

Once a laver of skim ice is established, lake ice can continue to thicken from both the top and bob tom. As long as the ice is cold enough so heat can be transferred tip through the ice from the water immediately below, ice continues to thicken from the bottom surface. This is known as congelation ice. When water changes from liquid into ice, the crystallization process releases heat, which is transferred up through the ice column.

Congelation ice is often referred to as black ice. This clear laver allows high transmission of light to the water below, hence its dark appearance. Sometimes you see air bubbles and bubble trails that were trapped in this ice layer, and cracks are easily spotted as well.

Lake ice also thickens from the top. Referred to as snow ice, it can form when the weight of fresh snow pushes down on the ice sheet, forcing liquid water to rise through cracks to the surface where it freezes. Snow cover also melts on warmer days, the water or slush refreezing to add thickness. The snow-ice laver appears white or ,grayish due to the many of micro air bubbles trapped within it.

* Ashton, G. D., editor. 1986. River and lake ice engineering. Water Resources Pub., Littleton, Colorado.

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Title Annotation:Bits & Pieces: Blending Fishery Science with Everyday Fishing
Author:Neumann, Rob
Date:Dec 1, 2009
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