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Reading about various snow formations in my backpacking book, figured I'd take you on a tour.
Sastrugi. These formations happen when there aren't a lot of barriers, the snow is dry, and there is high wind-- snow gets shaped much like sand does in the deserts. The ridges can be several feet high, making it difficult to pass.
(img src: https://ap-pics2.gotpoem.com/ap-pics/item/13643/971.jpg )
(img src: https://ap-pics2.gotpoem.com/ap-pics/item/13643/971.jpg )
Nieves penitentes. Water on peaks of the formations evaporates & water in the ridges melts-- melting requires 1/7th of the heat required for evaporation, so the melting areas deepen faster. Can get several feet tall and are difficult to pass. (img src: https://s.w-x.co/util/image/w/es_es_nieve_penitente_0.jpg?crop=16:9&width=480&format=pjpg&auto=webp&quality=60 )
Suncups, basically baby versions of nieves penitentes. If you observe a mountain throughout the day you may notice the suncup pattern migrating north as areas melt. They tend to be passable but can be tedious to pass if large or slippery/frozen (img src: https://cdn2.apstatic.com/photos/climb/117621051_medium_1566323839.jpg )
Cornices. Formed by wind blowing off a peak and gathering snow at the edge, they often look like convincing extensions of a cliff face or ridge. But beware, it is just snow & not on solid ground, and can fall beneath you or lead to avalanches. (img src: https://pixy.org/download/199158/ )
Hoarfrost. Can happen on objects like these branches, on the surface of snow, sometimes called surface hoar. Often is discovered after cold clear nights and is relatively harmless-- just beautiful shapes that are fairly easy to walk through. (img src: https://cdn.britannica.com/63/123863-050-E293BEC2/Hoarfrost.jpg )
Drain channels. On sloped surfaces can look like parallel lines, on flat surfaces more like round patches. If the melted dimples are frozen, can be a good sign of stability, but if still melted it may indicate that snow in the area is dangerous (img src: https://upload.wikimedia.org/wikipedia/commons/thumb/0/07/Vegetation_Induced_Circular_Snowmelt.jpg/220px-Vegetation_Induced_Circular_Snowmelt.jpg )
Verglas. Formed by water (rainfall or snowmelt) that freezes over the surface of rocks. Be careful-- it can look obvious like in this picture, or it can be very much like black ice where you don't realize it's there till you feel the surface. (img src: https://manayunkia.files.wordpress.com/2014/11/the-verglas-of-mountain-brook-denmark-maine-3.jpg )
Sun crust. Happens when sun melts the top layer of snow, then that freezes. Usually thin enough that you can crunch through it, but keep in mind sun crust can get quite thick & can make it very uncomfortable to pass through these areas of snow. (img src: https://lh3.googleusercontent.com/proxy/D4jVXW2asNBdn9Qhev0c8gle5u-_YXc5k8ADMLZnLYQJwGUyl6BtJW95ZeNIz3i9QcpJjArM5940YlapcgP-NW2HSNxOxdkkTRSrqa0EZbHsnlkYtwHWJMrInfaES06chOhTm6O8gQ )
Wind slabs. Wind breaks up snow crystals, blows them, they form compact snow, & that gets hardened further by melting or warming after wind stops. Traveling on a big wind slab can feel fast & easy, but they can also break and lead to avalanches (img src: https://www.mtavalanche.com/sites/default/files/images/wind%20slab%20Beehive%20141231.JPG)
Rime. Frost that can form on objects or the snow surface, and often looks solid & sturdy unlike hoarfrost which is obviously fragile. However, don't be fooled, it usually easily breaks off and shifts around and can be dangerous if you assume it's stable. https://cff2.earth.com/uploads/2018/11/13011759/what-is-hard-rime.jpg
