I drink a lot of Coke. And along with the Coke, I drink a lot of ice. Some days, it seems like the Coke is just a delivery mechanism for the ice (as my sister once said about hotdogs and condiments).
I notice, from time to time, little spikes or finger of ice growing on top of my ice cube tray. What the heck are these upside-down icicles, these tiny ice phalli, and how did they get there? Well, the The Experimental Nonlinear Physics Group at the University of Toronto knows:
The short explanation is this: as the ice freezes fast under supercooled conditions, the surface can get covered except for a small hole. Water expands when it freezes. As freezing continues, the expanding ice under the surface forces the remaining water up through the hole and it freezes around the edge forming a hollow spike. Eventually, the whole thing freezes and the spike is left.
Hallelujah! Another of life’s tiny mysteries solved. That ice cube spikes page is pretty cool–they’ve even got a couple of videos showing the cubes forming.
DarrenBarefoot.com 
“Tiny Ice Phalli”. Best, band name, ever.
I can honestly say that this is one of those things I’d always wondered about but could never figure out.
Kudos, Darren!
Is it just me, or were there a couple too many “The Experimental Nonlinear Physics Group”‘s in that second last paragraph?
Regardless, neat article! I’m still waiting for someone to use GPS tracking to solve the mystery of missing laundry socks, but every little mystery solved along the way makes me happy.
Ah, thanks for that. I’m using a back-up mouse, and clicking the scroll-wheel = paste, which can result in these sorts of issues.
I thought you were cutting down on the Coke after your “clean and sober” experiment, no?
Rob: True, I drink about half as much Coke as I used to. Which is to say, one every other day. I still think of that as a lot, but it’s all relative.
I’d wondered the same thing when I first moved here:
http://www-us.flickr.com/photos/mussels/1730326/
Had never seen it before, so apparently at least one of water softness, mineral content, or altitude make a difference on whether this occurs or not.
I created a Flickr group (Ice Spikes) on the subject due to its popularity. At one time, I thought I was the only one witnessing this devil-work. I know better now, so I can come out of hiding.