[thedoc]

Marisa asked the Naked Scientists:
   
I have ice cubes in my freezer at our office that form long, skinny spikes when freezing. Normally, 1 or 2 in the tray of 14 form 1 and 1/2 inch tall spikes. We have three ice cube trays in our freezer and only the tray on the far right forms these ice spikes.

What causes this?

What do you think?

[AllenG]

That was one of the first questions I asked when I joined TNS.

http://www.usatoday.com/tech/columnist/aprilholladay/2005-10-24-ice-spikes_x.htm
^^^
Long answer.

Short answer: your ice cubes freeze from the sides of the container towards the middle.  Since water expands when it freezes the water is pushed through the small hole left in the center of the ice on top of the cube and is extruded out as a spike.