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.


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.


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.