Ice Facts

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Ice Facts

 

    When is ice safe? There is no sure answer. Ice is tricky, and just because a lake or stream is frozen doesn't mean the ice is safe. 

    To understand the factors involved in the strength of ice, it's necessary to understand how ice forms on lakes and streams and a few of its physical properties. Here are points to consider, some based on research by the U.S. Army Cold Regions Research and Engineering Laboratory in New Hampshire.

 

You can't tell the strength of ice just by its appearance, the daily temperature, thickness, or whether the ice is or isn't covered with snow. Strength of ice, in fact, is based upon all four factors  plus the depth of water under the ice, size of water body, water chemistry, distribution of the of the ice, and local climatic factors.

 

  • Generally speaking, new ice is much stronger than old ice. Direct freezing of lake or stream water will be stronger than ice formed by melting snow, refrozen ice, or ice made by water bubbling up through cracks and freezing, on the surface. Several inches of new ice may be strong enough to support you, while a foot or more of old, "rotten" ice may not.

 

  • Ice seldom freezes or thaws at a uniform rate. It can be a foot thick in one spot while, 10 feet away, only an inch thick.

 

  • A layer of snow insulates ice, slowing down the ice forming process. In addition, the weight of snow can decrease the bearing capacity of the ice.

 

  • Ice near shore is weaker. The buckling action of the lake or stream over the winter breaks and refreezes ice continually along the shore.

 

  • If you hear ice "booming" or cracking on cold days or still evenings, it doesn't necessarily mean the ice is dangerous, merely that it's changing shape as the temperature changes.

 

  • Ice formed over flowing water can be dangerous near shore, around inflowing or outflowing streams, or on lakes containing large numbers of springs. River ice is generally about 15 percent weaker than ice on lakes. Straight, smooth flowing stretches are safer than river bends. River mouths are dangerous because the current undermines the ice and creates unsafe pockets. A potential danger spot on lakes is an open portion completely surrounded by ice. Winds will force exposed water beneath the ice and rot it from below.

 

  • Other factors which weaken ice are water level fluctuations and the actions of birds and fish. As an example, schools of carp create thin ice spots or even open water by congregating in one location while circulating the water with their fins.

 

 

 



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