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article imageDefying the laws of gravity: ice spikes

By Bart B. Van Bockstaele     Sep 13, 2010 in Science
This morning, while checking my freezer, I discovered a 4.1 cm long ice spike on an ice cube. It was the very first in nearly 15 years. Millions of ice cubes are made every day, yet only a few will develop spikes. Little is known about this phenomenon.
A spike on an ice cube in the freezer is a rare sight for most of us, although for reasons as of yet unknown, a small minority of us sees them on a regular basis.
The phenomenon is not limited to ice cubes in freezers, it can also be observed outdoors, usually during a cold snap when the temperature drops very rapidly. A good bet is to observe water freezing in bird baths.
Ice spikes are often thought to be the stalagmite version of icicles, but they are a very different beast. Icicles form when water flows along them, on the outside. A tiny amount of the water freezes and thickens and lengthens the icicle. In contrast, ice spikes form by water that flows inside them.
What happens, is this: liquid water freezes first at the surface and at the sides of the vessel in which it sits, and grows inward from there. Since ice expands when it freezes, the ice exerts some pressure on the remaining water. Eventually, water is pushed through a small unfrozen patch or a weak spot on the surface. Some of the water freezes, first creating a volcano-like shape.
After a while, a drinking-straw type of structure is created. Water will continue to flow upwards and freeze at the top, extending the spike further and further until all the water is frozen or until the tip is frozen, effectively capping the spike.
So, while ice spikes may seem to defy the laws of gravity, they do not. They are simply created by upward pressure created by the expanding ice.
Very little is known about the mechanisms behind ice spikes. A handful of people have researched the phenomenon in recent years, but their conclusions -while similar- are not identical and even though the general mechanism is well understood, much remains to be discovered.
More about Ice spikes, Freezer, Stalagmite ice
 
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