What happens when a lake freezes over?

Once an ice film has formed on the surface of the lake and the air above the ice continues to be colder than the ice, the ice will thicken. The cold air above the ice causes heat to leave the lake water under the ice and from the ice itself. This causes the water below the ice to freeze into successively deeper layers.



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Only the top layer of the lake or river freezes. Underneath the frozen upper layer, the water remains in its liquid form and does not freeze. Also, oxygen is trapped beneath the layer of ice. As a result, fish and other aquatic animals find it possible to live comfortably in the frozen lakes and ponds.

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Great Lakes that have completely frozen include Lake Superior, Lake Huron, Lake Erie, and Lake Ontario. Lake Michigan is the only Great Lake to have never frozen entirely.

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Most lakes and ponds don't completely freeze because the ice (and eventually snow) on the surface acts to insulate the water below. Our winters aren't long or cold enough to completely freeze most local water bodies. This process of lakes turning over is crtically important to the life in the lake.

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Based on studies, once a thin layer of ice film forms on a lake, it will add 1 inch of ice for every 15 freezing degree days in a 24 hour period.

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Lake ice freezes first at the surface starting at the edges or shoreline for two reasons. Water near the shore is typically shallower and contains less heat than deeper water so it can reach the freezing point faster than deeper water.

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Do fish die in frozen lakes or in lakes that are partially frozen? Since fish are cold-blooded animals, they can survive because they are able to regulate their body temperature to match their environment. However, they could die if a body of water freezes over completely and remains frozen for an extended period.

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Because of the time required to melt ice that has thickened over the winter, the clearing of lake ice occurs some time after average daily air temperatures rise above freezing. Typically the lag is on the order of one month at latitude 50° N and about six weeks at 70° N.

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Health risks Winter swimming can be dangerous to people who are not used to swimming in very cold water. After immersion in cold water the cold shock response will occur, causing an uncontrollable gasp for air. This is followed by hyperventilation, a longer period of more rapid breathing.

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As a result, close to freezing, colder water floats to the top and the warmer water sinks to the bottom. The density of water as a function of temperature can be seen in the plot on the right. Eventually, the coldest water, which has floated to the top of the lake in wintry conditions, freezes to form a layer of ice.

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Ice formed over flowing water and currents is often dangerous. This is especially true near streams, bridges, and culverts. Also, the ice on outside river bends, and inlets and outlets of lakes and ponds is usually weaker due to the undermining effects of the faster current.

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