The shallow underwater plain that spans from the beach to the outer edge of a continent before the ocean depth suddenly drops off a very deep cliff that plunges abruptly to the ocean floor. The shelf can span anywhere from a few miles to over 200 miles, reaching depths of up to about 450 feet.

The continental shelf collects most of the sand, silt and other sediment that rivers carry to the sea.

The Arctic has the largest continental shelves, while Antarctica has the deepest. The eastern continental shelf of the United States is over three times as wide as the continental shelf on the west coast.