Continental Shelf

The continental shelf is the submerged edge of a continent, the part of the landmass that continues under the ocean before dropping away into the deep sea. It is not open ocean; rather, it is covered by relatively shallow seas and gulfs that sit on top of this extended margin. Think of it as the continent's underwater doorstep — the shallowest part of the entire ocean floor.

Because it is so shallow, its slope is extremely gentle. The average gradient of the shelf is about 1° or even less, meaning it descends almost imperceptibly. This gentle incline does not continue forever. The shelf typically ends at a very steep slope called the shelf break, the point where the sea floor suddenly plunges down toward the deep ocean basins.

The width of continental shelves is not uniform; it varies considerably from one ocean to another. The average width is about 80 km, but this figure hides enormous extremes. Along some margins, the shelf is almost absent or very narrow — the coasts of Chile and the west coast of Sumatra are examples where the land drops off quickly into deep water. At the other extreme, the Siberian shelf in the Arctic Ocean is the largest in the world, stretching an extraordinary 1,500 km in width.

Depth also varies, just as width does. In some areas the shelf is as shallow as 30 m, while in others it reaches depths of 600 m before the shelf break occurs. So the shelf is not a flat, uniform platform; it is a gently sloping zone whose dimensions shift from place to place. …