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Firnspiegel: a thin layer of ice covers the snowpack. Forms on cold days with intense insolation, when the rays are hot but the air remains cold. It makes for terrible skiing.

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Anchor ice: I always wondered if creek beds collected ice by somehow conducting cold from below, and the answer is no. Fast flowing and shallow water may become super-cooled by frigid air, so the creek can actually chill its bed below freezing. Free-floating crystals called frazil form in the water, and when they touch something solid, they are inclined to stick.

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Ghost trees: water molecules can also become super-cooled in the air and remain liquid all the way down to -40 degrees if they don’t find a seed crystal to form around. Sometimes, this seed comes in the form of objects on land–like a tree. Enough droplets can stick to a tree to create a casing around the entire tree that can weigh many tons. Up close, they reveal elaborate fractals, like three-dimensional snowflakes.

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