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 the 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)