Caves in the Ross Ice Shelf, Antarctica. An ice shelf is an extensive sheet of floating ice, on the margin of & attached to a coastline. The Ross Ice Shelf covers approximately 160,000 square miles of sea. In time (geological), caves on the edge of an ice shelf collapse & the broken mass floats free as an iceberg. Icebergs formed in this way, as opposed to those formed at the end of a glacier, are usually rectangular in shape with a plateau or tabular top.