Recently, I have been noticing small vertical spikes in some of the cubes in my ice trays. For those who haven’t seen this before, small (2-30mm) spikes are forming in the center of the cubes. They often tilt in random directions. There is no evident condensation above the cubes.
I wondered about what could be causing them, so naturally I started my research in the SDMB archives. The phenomenon, which I will refer to as “spikecicles,” has been covered in Ice cube stalagmites? (Nov 1999), Ice Stalagmites (Jun 2000), Spikecicles? (Oct 2000), and ice (Feb 2001). There may be others that my search terms didn’t uncover. As tomndeb once stated, the Jun 2000 thread provided some of the better possible explanations.
There is also some discussion of this at Ice cube phenomenon, which has pictures of spikecicles and several reasonable (and some silly) hypotheses. It is also on the web at Freezer Phenomenon #3, MadSci Network, and doubtless many other places.
Some of the ideas proposed on SDMB to explain this phenomenon are given below:
SandWriter: “One wild theory is that it is some sort of reverse sublimation during the defrost cycle of the freezer. Another wild ass guess is that the purified water is compressed in the middle, then breaks through the ice and instantly freezes due to a drop in pressure”
JoeyBlades: “Alternatively, if the defrost cycle is just slightly warmer, the condensation might fall and the small water droplets would refreeze fairly instantly forming stalagmite like structures. These might tend to be mostly vertical, but defrost cycles and air currents from blowers might make them tend to lean once they reach a certain height. Come to think of it, a leaning structure, under the right conditions might take on the shape of the wedges depicted. One way to check out this theory would be to look for smooth bumps directly above the ice trays. This would be indicative of condensation droplets freezing and thawing.”
DJScherr: “As water freezes it expands, as it expands it should start to form a kind of ‘bubble’ on top due to survace tension. (like when you pour water over the top of a glass it domes.”
Cornflakes: “…the ice cubes are freezing inwards from the outside of the tray. Since water expands as it transitions into a solid (aka: ice), the stuff has to go somwhere, namely out the unfrozen area in the middle at the top.”
ZenBeam: “The ice cubes as they are freezing are kept at 32 degrees F, warmer than the rest of the freezer. Air currents are caused by the higher temperature of the ice, which draws air across horizontally across the ice surface toward a point in the middle, causing a small amount of sublimation from the surface. At the middle of the cube, the air currents come together, and deposit the water molecules there. The tilting is caused by pre-existing air currents flowing in the direction of the tilt.”
Personally, I tend to favor the theory that as the water freezes from the outside in, it causes pressure in the center as the water expands. But clearly, although it has been pondered many times by people much more intelligent that me, there seems to be no universally agreed-upon explanation to what causes spikecicles. Could this indeed be a mystery that only The World’s Smartest Human Being can solve? C’mon, Cecil, only you can authoritatively put this one to rest once and for all!