IV-14 



and its associated channels and marshlands, as well as the 

 combination of barrier island and coastal marshland 

 formation which makes up the majority of the Gulf of 

 Mexico estuarine systems. 



On the Pacific coast of the continental United States, the continen- 

 tal shelf is 2 to 20 miles wide and terminates at depths of 300 to 

 600 feet. Pouring over this narrow, steep shelf is the full force 

 of the Pacific Ocean swell; this makes for excellent surfing, but it 

 also leads to considerable erosion of the shoreline. Shoreline 

 erosion by wave action with the development of a beach and bluff 

 configuration is typical of this part of the coastline (Figure IV. 

 1.2). Strong currents and turbulent waters near the shore tend to 

 remove eroded material rapidly, and extensive shoal areas rarely 

 occur. 



The continental shelf along all the coasts of Alaska is wide; in 

 the Bering Sea it averages 400 miles. The Bering Sea shelf is the 

 flattest area of this size on the face of the earth, primarily 

 because of the fine silt deposited on an irregular rocky platform 

 by glacier- fed rivers. 



OCEAN CURRENTS 



The major ocean currents impinging on or passing close to the 

 continent exert strong, if subtle, effects on the estuarine zone; 



