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Ice Formation Demystified | Ponds & Lakes Q&A


Ice Formation Demystified

Ice Formation Demystified

Ice is cool. It’s fun to play on. And, to some, it’s a mystery. How in the world does ice form on your pond? Why does it expand when it freezes? Why does it float? And how is it possible that ice can actually support the weight of a vehicle?

Don’t glaze over just yet. Unlike lessons from those boring middle school science classes, this explanation will be simple—and as interesting as possible.

Lesson #1: Cold Water is Heavy Stuff

When the air temperature cools, the water on the surface of your lake or pond loses its heat and becomes heavier. This cold, heavy water sinks to the bottom while the warmer water from the bottom rises to the top and cools. The cycling process continues until the overall water temperature reaches 39 degrees Fahrenheit (or about 4 degrees Celsius). Before long, the water on top cools enough to freeze.

Lesson #2: Water Crystals Need Their Space

As the water in your pond freezes, the liquid molecules transform into solid ice crystals—and those things expand and space themselves out when they form, which is why ice takes up more room than liquid. Think of how freezing water can cause a pipe to burst when temperatures dip below freezing, or how expanding ice can crack a rock in two.

Lesson #3: Ice Floats

The spaced-out ice crystals are also less dense than liquid, which is why ice floats. As mentioned in Lesson #1, cold water is heavier than warmer water—but ice is lighter than them both. Confusing? Consider the ice cubes in your glass of lemonade: The crystallized water molecules float on the surface, the lemonade that’s cooled by the ice becomes more dense and sinks to the bottom, and the warmest liquid in the glass rises to the top where it’s cooled by the cubes.

Lesson #4: It’s Strong Stuff

When given enough time to form, the ice layer formed by this crystallized frozen water thickens—and becomes strong enough to support critters, humans and even vehicles! An inch of ice can hold a small animal without cracking, 3 inches of ice can bear the weight of an average person, and 6 to 8 inches of ice can host a hockey team or even a snowmobile. Once the ice layer grows to 8 to 12 inches, it can support a slow-moving vehicle—but we don’t recommend it!

Pond Talk: What burning questions do you have about ice formation and safety?

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10 Responses

  1. We have a “newer” 3/4ac. pond,and has been frozen for 3 weeks at least 5-7 ” thick.
    I do knock a big 4’X4′ hole in the ice to with the backhoe “maybe to help with some fresh air” for our fish…..Am I doing any good?
    And if Lake Superior freezes over, how do the fish live…there’s no fresh air there.

    • Hi Ralph – In order to keep a hole open in the ice, we would recommend an aerator or circulator. Winter fish kills happen if there is a lot of decaying organic matter in the pond. The difficult part about using a backhoe is with the cold temps, the hole will freeze back up rather quickly.

      You cannot compare large lakes, like Lake Superior, to a small backyard pond. The Great Lakes still have water movement under the ice. The fish have a lot more depth and room to move about to depths with more oxygen.

  2. Anyone know if the pump is shut off during the winter will your fish servive???

  3. Hey, if you are in Minnesota or any other northern state, we drive cars and trucks on the ice all winter. House have even been moved across Lake Superior in the winter.

    • Hi Tim – That is quite true! We just urge caution before walking or driving out onto the ice. Make sure that you or a local authority has verified ice thickness.

  4. Why is the water along the shore still soft when the water towards the center is frozen solid?

    • Hi June – The edges are some of the shallowest areas in your pond and can quickly change with weather conditions. Edges tend to both freeze and melt first. Think about a hot summer day, the edges are probably fairly warm compared to diving into the center of your pond.

  5. My question is, how do I or what do I use to determine the thickness of the ice?

    • Hi Narda – You would want to use a drill to cut samples of the ice. Make sure you do so in multiple locations as you work your way toward the center of the pond as the water won’t necessarily freeze evenly. Here’s a recent blog we did on Ice Safety.

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