Most of us have seen “needle ice” but are unsure of how it is formed. James Carter, former professor of geology and geography at Illinois State University, describes its formation in the following way. “On cold nights at the beginning of winter, when temperatures just barely sink below freezing, the ground will stay slightly warmer than the air above. That means that any water in the ground… will remain liquid. In certain soils, though, water that’s in the ground gets sucked upward rather than sinking down. This is a result of capillary action: the adhesion of water molecules to the walls of a very narrow tube will cause the liquid to be drawn upward despite the pull of gravity.“
Certain soil contains particular kinds of pebbles that contain pores just wide enough to allow capillary action to occur. Water in the ground is drawn upward through the pores until it hits the air. Then it freezes. As more water is drawn up, it freezes as it hits the air and pushes the newly formed needle of ice outward, resulting in the curls of ice growing out of the ground at this time of year.
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