The mysterious icy figures who haunt the Andes

These mysterious ice figures form only at high altitudes, and only under very specific conditions. In the Andes, they're called "penitentes," and fields of them can stretch for miles.

If you're an astronomer (as no doubt many of you will be) and walking through the high terrain in the Andes (as hardly anyone can avoid), you may one day come upon a huge crowd of white-robed figures, standing quietly and facing the sun. Don't freak out. They're called "Los Penitentes," in the Andes, after the spiky white hats that certain holy people wear during Easter processions.

We don't know exactly how the penitentes form, but we know a little about the processes that shape them. The high Andes is, in some places, so dry that melting ice doesn't go through a water phase. It engages in a process called "sublimation," instead, going directly from ice to steam. Since there's no water to pool and refreeze, little dry pits form in the snow. These pits grown and grow. Once the pits get deep enough they have their own little microclimate, which is humid enough to allow ice to melt into water and refreeze, depending on the temperature. The combination of sublimation of open areas and small pits, and melting in deep pits, causes these shapes to grow.

They can be anything from tiny little pilgrims a few inches high to giants five meters tall. Either way, they're cool.

Image and Information: ESO.