Why are there little stalagmites on my icecubes?

Question

In the freezer, in the ice tray, sometimes there are little projections sticking up after the ice has frozen solid. They are made of ice, of course, and may be as long as 3/4" and can be about 3/16 inch thick. Sometimes they go upward at an angle. I believe that water expands when it freezes, but what causes these stalagmites to form?

Answer 1

Ice cubes freeze from the outside in, as they are grown in a cold (typically -20C) environment. Water expands upon freezing (actually starting to expand below 4 degrees C, but dramatic expansion occurs during freezing). So, if the outside freezes, but the inside is still liquid- then it has to expand into something.

What happens is that a small defect in the top surface of the cube allows some water to escape; water continues to flow from this hole and, being right at the freeing point, turns to ice as it hits the cold environment of the freezer. Due to the small amount of liquid flowing, it is able to remain liquid long enough to keep the interior hollow. These spikes presumably form rather quickly, in a few seconds, although I've never observed them forming.

They seem to form more often with ice cubes made with very pure water, such as distilled water. Reverse osmosis is apparently not enough to do it, at least under my conditions.

Answer 2

Simple condensation.
If you have humidity in your house it enters your freezer when you open it (like a magnet attracts iron filings sometimes) and they condense and freeze on the ice cubes.

Answer 3

self defrosting freezer.