Penitentes

Photographed at 19,300 feet on Ojos del Salado, the highest volcano in the world, January 7, 2010.

According to Wikipedia, Penitentes "are a snow formation found at high altitudes. They take the form of tall thin blades of hardened snow or ice closely spaced with the blades oriented towards the general direction of the sun. Penitentes can be as tall as a person."