This type of shelf is relatively broader. Some of the continental shelves in East Asia were formed in this way. In the distant past these shelves were surrounded by island areas which, after being eroded, got submerged under the sea water. These are called the depositional shelves. Hard rocks are found along their seaward margins. Thus, the enclosed basins offer ideal conditions for the deposition of sediments, and the shelf created in this manner would be one of deposition, and it will be flanked by a rim of solid rocks (fig. 7).
Delta growth is also an important factor in the formation of the continental shelf. However, this is found in certain localities only. Example may be cited of the Mississippi delta where there is a huge accumulation of debris. Moreover, this delta, as it grows at a fast rate, helps in the formation of a shelf, though on a local scale.
Even the convectional currents are supposed to be one of the factors that help in the formation of continental shelf. Wherever, because of the unequal distribution of sial and sima near sea coasts, the convectional currents arise, there is subsidence of the land along the coast. The direction of movement is from sima beneath the oceans, towards the sial, the base of the continents. Eroded material derived from the land is deposited in the subsided submarine depression just for compensation. It results in the gradual uplift of the continents and subsidence of the continental shelf.
According to some other oceanographers, the origin and growth of the continental shelves in certain areas of the oceans is attributed to the falling of the sea-level by about 38 fathoms during the Pleistocene period. Due to the lowering of the sea-level, the submerged parts of the coastal regions became dry land areas. The processes of glacial erosion and deposition were operative on these newly emerged land areas. This resulted in the creation of various types of land forms. With the subsequent rising of the sea-level at the end of the Pleistocene period, these land areas adjoining the sea coasts were again submerged under the sea water. This type of shelf is found along the Norwegian coast.
However, all these views regarding the origin of continental shelf are open to criticism. But it is undoubtedly true that continental shelves in different areas were formed by different processes. Thus, it is unlikely that any one explanation accounts for all the continental shelves of the world.