The continental shelf – a geological explanation

The concept of the continental shelf is originally a geological or geomorphological concept defined as the continuation of the landmass under the surface of the ocean. When it comes to Article 76 in the United Nations Convention on the Law of the Sea (UNCLOS), the legal concept of the continental shelf means the seabed and below in an area stretching across the territorial sea of the coastal state for the entire natural extension of the land area until the limit of the continental margin or a distance of 200 nautical miles from the baseline.

The area between the geological continental shelf and the deep-sea bed is called the continental slope – here, the depth of the ocean increases considerably over a relatively short distance.

Along some types of the continental margin, material from the continental shelf, such as clay and sand, accumulates below the continental slope and this creates the continental rise, which is a part of the deep-sea bed.

Figure A shows a cross section of a type of continental margin that best corresponds with the conditions in the Atlantic Ocean.

When it comes to other types of continental margins, the regulations of Article 76 should be interpreted so that they suit the relevant conditions. Where the continental crust changes to oceanic crust there is a marked thinning of the earth’s crust, from a thickness of 10-40 km to approx. 7 km.