Have you ever made ice cubes and then found that when you take them out of the freezer
there are spikes on them?
This phenomenon has caused a lot of curiosity and some concern.
The truth is, there is a simple physical process responsible for ice cube spikes.
Ice cubs cool first from their top surface where they are in direct contact with the
cold freezer air and from which evaporative cooling can occur.
So the first ice crystals form on the surface of the ice cube and along its edges.
Now as that ice freezes, it expands by roughly eight percent.
That is due to hydrogen bonding between the water molecules which makes them on average
slightly further apart than they are in water.
So as the ice grows in from all sides, the water in the middle has nowhere to go.
And it is forced up and out through a hole in the ice.
These holes are often triangular in shape because ice crystals tend to meet at 60 degree
angles.
As the water comes up through the hole it freezes around the edges forming a hollow
spike.
And as the ice continues to grow, more water is forced up the spike, making it longer.
This continues until all of the water is frozen, or until the end of the spike freezes shut.
If you want to make ice cube spikes, they can be created in most ordinary freezers and
there are three steps you can take to increase your chances.
Number one, the ideal temperature seems to be not too cold, between minus five and minus
eight Celsius.
That is cold enough to freeze the water, but not so quickly as to freeze off the tip of
that ice cube spike.
Number two, distilled water seems to work better than tap water because even small concentrations
of salt prevent spike formation.
Number three, a fan in the freezer seems to help spike formation by increasing the circulation
of the air and increasing evaporative cooling.
And given just the right conditions, very large ice spikes can form, for example, on
bird baths.
In these cases the spikes are known as ice vases, for obvious reasons.
When looking at this structures, it is interesting to contemplate that they only form because
of water’s unique property of expanding when it freezes.
If water didn’t expand when it froze, the whole earth would be dramatically different,
because, well, since ice is less dense, it forms on the surface and actually insulates
the water underneath, so it remains liquid and allows life to survive in it.
But if, instead, ice were denser than water, it would sink to the bottom allowing for further
cooling of that water and more ice formation.
And the ice would build up from the bottom upwards, giving less and less water for organisms
to live in, until, if cold conditions persisted for long enough, all bodies of water would
completely solidify as ice, meaning that virtually no life could live in them.
And at that point, the earth would also be completely white.
So it would reflect more of the sun’s light into space, leading to further cooling.
So if water didn’t expand when it froze, the whole earth would be a cold, lifeless
snowball.
But it all depends on your starting conditions, because if there wasn’t very much ice on
the earth to begin with, it would all sink to the bottom of bodies of water, including
arctic sea ice and that means the earth’s surface would be less reflective, so it would
absorb more heat from the sun and it would get a lot warmer.
So if ice didn’t float, if ice was denser than water, either the earth would be much
colder than it is now or much hotter than it is now.
And in either case, life on earth might not exist.
But if it did, we wouldn’t be able to make ice cube spikes.