Antarctica’s perennially ice-covered Lake Hoare bears the scars of sand and dirt that have worked their way from the surface down into the ice. Soil blows onto the lake from a nearby dry valley, warms in the sun, and melts downward, leaving a bubble column in its trail.

(Text adapted from and photograph shot on assignment for, but not published in, "Timeless Valleys of the Antarctic Desert," October 1998, National Geographic magazine)