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lower here; the movement of the California current away from the 

 coast is not as pronounced, and heavier rainfall has resulted in some 

 major rivers cutting through the coastal mountains to form deeply 

 embayed estuarine systems. Extensive erosion and sedimentation have 

 caused wide tidal flats, bars, and shoals to be typical of these systems. 



The straits of Juan de Fuca and Puget Sound, which were glacier- 

 formed, do not have as severe sedimentation as exists along the ocean 

 coast, and have retained much of their original configuration. 



Alaska Estuarine Region. — All of Alaska including the Aleutian 

 and Bering Sea Islands. 



The dominant factors in this region are temperature and precipita- 

 tion. Water temperatures are near freezing, and much of the precipi- 

 tation falls as snow. The Continental Shelf is wide all through the 

 region, and tide ranges are very large. The southeast and south coasts 

 have active glaciation and consist primarily of glacier-cut embay- 

 ments and fjords; the west and north coasts are much flatter and 

 have been modified to some extent by sediments eroded from the inte- 

 rior, including glacial silt, and by the grinding action of pack ice dur- 

 ing winter. 



Pacific Islands Region. — The Hawaiian Islands, American Samoa, 

 and Guam. 



This region consists of tropical ocean islands of volcanic origin. 

 Dominating factors are lack of a Continental Shelf, full exposure to 

 oceanic conditions, and pleasantly warm temperatures. Coral reefs 

 and beach and bluff configurations are typical. 



THE LAND AND THE WATER 



Within the general domination of broad-scale environmental factors 

 are smaller scale governing conditions that, through their effects 

 on water movement and circulation, determine what kind of local 

 environment can exist in a particular estuarine system. 



THE LAND 



The shape of the land along the land-sea interface goes far toward 

 determining what water movement and circulation patterns exist in 

 particular local areas and, consequently, how fast a particular estu- 

 arine system will rid itself of pollutants. Within the general compass 

 of the estuarine regions discussed in the preceding section there are 

 different structural types which define patterns of water movement 

 typical of particular structures, no matter what the external environ- 

 ment may be. 



Alaska presents the greatest variety of estuarine form and structure 

 of any of the estuarine regions. Nearly all kinds of systems typical 

 of other regions are found there. In addition, Alaska has the only 

 glaciated coast and most of the fjords found in the United States. 



Characteristic of the North Atlantic region is a very irregular, 

 hilly coastline with deep water close inshore and long, narrow embay- 

 ments with open access to the sea. Estuarine systems within the 

 Chesapeake Bay region consist of a group of branched rivers entering 

 the Chesapeake Bay itself, which is in turn the former valley of the 

 SusQuehanna River. 



