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What Is the Difference Between a Bay & a Gulf?

The terms "bay" and "gulf" are used interchangeably, and they both refer to bodies of water that have worked their way inland. Although there is no standard of measurement, a gulf typically describes large bays and bays connected to oceans. These geologic formations form important economic areas and are often the location of important harbors and cities.

Water Body Definitions
- A bay or gulf is a sheltered body of water that is nearly enclosed by land but opens up into a larger body of water. Bays can form in rivers, lakes, inland seas or oceans, but the term "gulf" typically refers to a large, baylike indentation that connects to an ocean. Because of their sheltered formation, bays and gulfs often have calm waters that form ideal locations for harbors and shipping traffic. In general, gulfs have proportionally smaller openings than bays.
Sizing Things Up
- The term "gulf" is usually denotes a larger area like the Gulf of Mexico, and bay is a term reserved for smaller indentations like Elliott Bay, where Seattle, Washington, is located. The names on some bodies of water, however, can seem arbitrary. For example, the National Geographic website points out that the Persian Gulf in the Middle East is actually smaller than Hudson Bay, Canada.
Geological Forces
- Gulfs and bays are basically formed in three ways. Rifts or breaks in tectonic plates can allow large bodies of water to flow inland. Gulfs can also be formed when softer rocks erode on shorelines, allowing for water to make its way inland; the harder-to-erode deposits, meanwhile, will jut outward, creating headlands. In addition, large rivers help bays and gulfs form by inundating land at their mouths. These estuaries, which have both fresh water and saltwater, erode shorelines and, along with tidal action, work to widen and form a bay. An example of this is seen in the relationship between the Susquehanna River and Chesapeake Bay on the Atlantic Coast.
Famous Formations
- The largest gulf in the world is the Gulf of Mexico, which opens up into the Atlantic Ocean. It encompasses an area of over 1.5 million square kilometers, or 600,000 square miles. A very large bay is Hudson Bay in Canada, covering over 1.23 million square kilometers, or 475,000 square miles. This important bay connects much of inland Canada with the Atlantic Ocean. Many of the major cities of the world are located along bays and gulfs, such as New York, San Francisco, Houston and Tokyo.

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