Author: Sarah Laskow / Source: Atlas Obscura
Walking in the woods, as winter gives way to spring, you might notice a strange phenomenon. The snow doesn’t just melt away uniformly. Across patches of ground and around tree trunks, almost perfect circles melt in the snow, polka-dotting the forest.
These “thaw circles” can be found in deciduous forests where snow accumulates. The sides of the circles are surprisingly even, straight, and vertical. They often look like someone used a cookie cutter to remove a stout cylinder of snow.
The secret of thaw circle formation is heat: As the sun warms the forest, the dark trunks of the tree absorb more heat than white, reflective snow. That heat radiates outwards from the trunks, melting away the snow in a ring around the tree. Sometimes the small-scale topography of a patch of land can also create uneven melting, forming circles without trees at their center.
Last year around this time, a team of biologists was in the woods in southern Quebec, Canada, when the thaw circles caught their attention. “We were immediately struck by circles of bare ground extending about one tank’s width out from the edges of most medium-sized to large trees,” they wrote in a report published…
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