Alabama Landscapes

The Coastal Plain

The Origin of Mobile Bay

 Mobile Bay is one of the largest estuaries in the United States, with about 20,300 acres of open water.  In this estuary, the city of Mobile and its port has flourished.  Situated on the Mobile River north of I-10, the Alabama State Docks is 29 miles from the Gulf of Mexico.  Mobile Bay has an average depth of 10 feet, so a 40-45 feet deep channel has been dredged to connect the docks with open water.  The port is the 14th busiest in the nation, handling 19.4 million short tons of goods in 2003.  The main imports were coal(!), aluminum, iron and steel, lumber, wood pulp and chemicals, whereas the main exports were coal, forest products, iron, steel and chemicals.  It's 2003 revenues were $566.4 million.

According to some geologists, the bay may have formed as a result of relatively recent (geological) faulting that developed a graben (downthrown block of rock between two normal faults).  Figures MB1 shows a possible scenario for the formation of the bay.

Figure MB1.    Origin of Mobile Bay. Sequence from top to bottom shows the possible recent geologic history of Mobile Bay for the last 2 million years.  Red lines: normal faults.

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