When the thermometer reads below zero, even the river’s breath turns foggy. If the rivers are large enough to have open water still during a freeze, ethereal plumes of mist can cloak the waterway, shrouding the trees above in hazy cloaks. The mist would look just like steam rising off a boiling pot if not for the ice and snow contrasting with the dark pockets of open water. As it rises over the water, the mist clings and freezes to overhanging tree branches, creating chilly ice sculptures that drip back down when the sun comes out.
This phenomenon can be seen anywhere there are rivers and freezing temperatures, creating magical, living beings from the winding rivers as they appear to exhale plumes of steam. As it turns out, this mist results from the same process of condensation that causes our breath to fog on cold days.
According to Dr. Lyle Ford, professor, and chair of the UW-Eau Claires Department of Physics and Astronomy, the mist we see over rivers on cold days is a form of evaporating moisture, which then condenses into mist. How does the water evaporate when it’s below zero?
As Dr. Ford describes it, when the very cold air comes in contact with the surface of the water (which is above 32 degrees, remember), it cools down the water’s surface quickly. This causes a loss of energy in the form of heat. The lost energy then heats the water surface (paradoxical but true), allowing some of the water molecules to gain enough energy to escape the liquid. Of course, the air above the water is absolutely frigid, causing energy loss and forcing those escaped water molecules to condense with other escapees. This forms the millions of tiny water droplets we perceive as mist.
Maia is an environmental science student at the Community College of Vermont. Living on a windswept hilltop farm in Walden, Vt, she is an avid writer and reader, spending as much time as possible in the garden, or gaining inspiration from the beautiful outdoors.
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