Ice Spikes

Everyone can try their hand at making some ice spikes.  All it takes is a dollar's worth of distilled water, some ice cube trays, and a freezer.  This is an easy overnight project that makes a lasting impression.  Ice spikes are bizarre, which makes them fun to make!

What are Ice Spikes?
Ice spikes are odd ice structures that occasionally grow out of ice cube trays.  Unlike some of the strange things you might find growing in your refrigerator, ice spikes are made of nothing but ice.  Ice spikes are the result of physics, not biology.  They look a lot like the limestone stalagmites found in caves! 
To see your own ice spikes, make ice cubes in an ordinary ice cube tray, in an ordinary household freezer, but using distilled water, which you can buy in most supermarkets for about a dollar a gallon.

How do Ice Spikes Form?
Ice spikes grow as the water in an ice cube tray turns to ice.  The water first freezes on the top surface, around the edges of what will become the ice cube.  The ice slowly freezes in from the edges, until just a small hole is left unfrozen in the surface.  At the same time, while the surface is freezing, more ice starts to form around the sides of the cube.

Since ice expands as it freezes, the ice freezing below the surface starts to push water up through the hole in the surface ice.  If the conditions are just right, then water will be forced out of the hole in the ice and it will freeze into an ice spike, a bit like lava pouring out of a hole in the ground to makes a volcano.  But water does not flow down the sides of a thin spike, so in that way it is different from a volcano.  Rather, the water freezes around the rim of the tube, adding to its length.  The spike can continue growing taller until all the water freezes, cutting off the supply, or until the tube freezes shut.