"On any glacial ice, but more especially on any part of the Antarctic continental glacier, a traveler lives constantly under the Damoclean threat that a crevasse may be under him. Without warning, the snow that has bridged over the yawning maw, rendering it indistinguishable, may give way. Men and machines may be instantly swallowed down forever, down perhaps hundreds of feet of undulating, ice-blur depths." --Commander Standish Backus