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.
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.
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.
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
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.