Penitentes

These unusual snow formations are most often found high in the Andes Mountains and are named for their similarity to the tall white hats of the Procession of Penance. At high elevations, the air is so cold and dry that sublimation can occur (where the phase changes directly from ice to vapor). When dirt gets blown onto the snow, the dirty spots absorb more heat and melt, creating valleys. Solar radiation is trapped in the valleys, reflecting off the valley walls. This allows the valleys of snow to melt much faster than the clean white peaks where sublimation occurs.