All Weather News

Hey Everybody, Ice Floats!

19 Dec 2017, 7:06 pm

The fact that ice floats on water is widely recognized and easily confirmed.  It floats in a glass of ice water, on frozen lakes, in the ocean as polar ice and icebergs. You may think that because ice is a solid it should be heavier than liquid water and should sink, but fortunately this is not the case. When water freezes the molecular makeup actually makes it less dense than the water it may be floating in.

I’ll go further into the explanation as to why, but first here is a poem I penned to help explain.


Ice on the lakes the ponds or the river

May certainly give you reason to shiver

But the thing about ice that may make you think

Is when water is frozen, it doesn’t sink

Most things when frozen will certainly shrink

But not the world’s number one drink

No water when frozen will actually float

Much like you would in a raft or a boat

If all the ice did sink far below

In no time our lakes would be quite shallow

And besides the fish having nowhere to go

There’d be other problems when temps fell to zero

Like think of the beaver the duck and the otter

If it wasn’t for the unique character of water

So when I think of Ice, I think that it’s nice

That it carries its own flotation device


Water has the unique property of being the most dense at 40° F.  That means that hot water and ice are both less dense than cool water.  We know that substances that are of lower densities will float on top of more dense substances. A tennis ball will float and but rocks not so much.

Water will also expand when frozen which is also unique as most substances will shrink when cooled.
In cold climates, the potholes you try to avoid are created by the water freezing in cracks and gaps in the pavement expanding the imperfections and degrading the surface.  Freezing a glass bottle of water is also not a good idea because the expanding properties of freezing water will most times break the container.  

Back to the topic at hand, the reason ice floats on water. Water of course is made up of one oxygen and two hydrogen atoms.  These atoms form strong covalent bonds and make up the molecules of water. Between water molecules there is also another weaker bond that forms known as a hydrogen bond. This hydrogen bond between water molecules becomes a major player to make ice less dense.

Hydrogen Bonds Not A Factor in Water Vapor

The hydrogen bond is weak and when water is warm the water molecules form and break bonds with other water molecules quickly.

Hydrogen Bonds Break and Reform often – Liquid Water


As water gets below 39° F They don’t have the energy to move and break and form bonds so easily.

Stable Hydrogen Bonds in Frozen Water

At this point the molecules will form more hydrogen bonds with other molecules in a lattice structure with more space between molecules.  This extra space between molecules is what water floats and will expand when frozen.  

The fact that ice floats is very important aquatic life on earth.  If ice sank to the bottom of lakes and streams it could eventually freeze the entire lake completely from the bottom up which would be bad for life in the water.  

Fortunately because of the properties of ice it will form on top of lakes and streams and not impact the creatures below.

Meteorologist Mike Morrison

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