Have you ever filled up an ice tray put it in the freezer and come back to see an ice spike? Here is how they form.
The water in the ice tray cools very rapidly and begins to freeze at the surface. The water freezes first around the edges of the tray first then moves inward. As water freezes it expands. The water can not go in any other direction than up. The ice continues to grow and move inward at the surface and a small hole forms. The water is forced through the small hole and freezes around the edge leaving a small opening for more water to move through it. The spike grows until all of the water is frozen and you are left with an ice spike.