An "ice shelf" is a floating ice sheet of considerable thickness that is attached to the coast. It usually extends far out over the water - which gives it a gently undulating surface.

The shelf is nourished by snow falling on the top, water freezing at the bottom, and often also by the seaward extension of land glaciers. The seaward edge is termed an "ice front" and new icebergs can break away, or "calve", from the front of the shelf.

Lying along the northern coast of Ellesmere Island in northern Canada, the Ward Hunt Ice Shelf is the biggest ice shelf in the Arctic. This vast region of ancient ice floating on the water is however, starting to break apart.

Comparisions with the early 20th-century records of Arctic explorer Robert Peary show that there was much more ice than today. It is estimated that the ice has now retreated by about 90% since Peary made his observations.

Retreating ice shelves may provide indications of climate change and the Ward Hunt Ice Shelf breakup comes at the same time as news of increased melting of sea ice in the Northern Hemisphere.