Features Resulting from Crustal Deformation

1. Elevations. The large-scale elevations of the ocean bottom are termed ridges, rises, or swells.

   1. Ridge (F, Dorsale; G, Rücken). A long and narrow elevation with sides steeper than those of a rise.

   2. Rise (F, Seuil; G, Schwelle). A long and broad elevation which rises gently from the ocean bottom.

      Isolated mountain-like structures rising from the ocean bottom are known as seamounts. Where the ridges are curved, and particularly if parts of them rise above sea level, they are sometimes termed arcs. The broad top of a rise is termed a plateau. The expression sill is applied to a submerged elevation separating two basins. The sill depth is the greatest depth at which there is free, horizontal communication between the basins.

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2. Depressions. The terms trough, trench, and basin are those most commonly applied to the large-scale depressions on the ocean bottom.

   1. Trough (F, Dépression; G, Mulde). A long, broad depression with gently sloping sides.

   2. Trench (F, Fossé; G, Graben). A long and narrow depression with relatively steep sides.

   3. Basin (F, Bassin; G, Becken). A large depression of more or less circular or oval form.

      The terms defined above are used rather loosely and are applied to features of a wide range in size.

      For those parts of a depression which exceed 6000 m in depth, the term deep (F, Fosse; G, Tief) is used. As originally suggested by Murray, the term designated areas where the depths exceeded 3000 fathoms (5486 m), but it is now generally restricted to those depressions of greater depth (Vaughan et al, 1940). The term depth (F, Profondeur; G, Tiefe), prefixed by the name of the vessel concerned, may be used to designate the greatest sounding obtained in any given deep.