Gulf is a large body of salt water that is partially enclosed by land. Gulfs open onto oceans, and they share many of their characteristics. For example, many gulfs are as deep as oceans. Because of similarities of this kind, such gulfs as the Gulf of Bothnia and the Gulf of Mexico are often called marginal seas.
Gulfs are formed by movements of Earth’s crust along the borders of continents. In some cases, a sinking of the crust causes an area to drop below sea level. In other cases, faulting occurs—that is, the crust fractures, and the land on the seaward side of the break shifts downward. In both cases, seawater floods the sunken area.
The way in which a gulf is formed determines its shape. The Gulf of Mexico, for example, occupies a circular basin that was formed by the settling of a layer of sand and other sediments about 71/2 miles (12 kilometers) thick. During the course of about 150 million years, the weight of the sediments caused the land to sink, producing the basin. In contrast, a long, narrow inlet, such as the Gulf of California, was produced by faulting.
