The continental shelf is a shallow ocean. It varies in depth, up to 140 metres deep. It varies greatly in its width. At the leading edge of a moving continental plate there will be little or no shelf. The western edge of the Americas are an example. The shelf on a passive edge of a plate will be wide and shallow. The widest shelf is the Siberian shelf in the Arctic Ocean: it is 1500 km (930 miles) in width.