Anybody else might shrug off these ice spikes as a meaningless hiccup in the preparation of a frosty beverage, but not Lenore and Windell at Evil Mad Scientist Laboratories! has a fairly detailed explanation of how these things form, and it’s documented elsewhere as well. (Roughly speaking, supercooled water is pushed up through a hole, somewhat like magma forming a volcano.) It’s relatively easy to form these in your freezer if you start with distilled water, but occasionally– as in our case –they do occur with regular tap water.