No two estuaries are the same!  One way that they are grouped is by their geology.  There are coastal plain estuaries, tectonic estuaries, bar-built estuaries, and fjords. 

Coastal plain estuaries formed during the end of the last ice age.  At this time, sea level rose because of melting ice and warming ocean waters.  The rising water flooded coastal river valleys, forming estuaries.  The Cape Fear River estuary is a coastal plain estuary. 

Tectonic estuaries form when the Earth’s crust folds or breaks to make faults.  Part of the land sinks and forms a hollow basin.  When the basin is filled in by the sea, an estuary is formed.  San Francisco Bay is a tectonic estuary. 

Bar-built estuaries are found where sand bars form on a coastline.  The water behind the sand bars are partly cut off from the sea.  The Albemarle-Pamlico Sound behind the Outer Banks is a bar-built estuary. 

Fjords are deeply cut valleys that are formed by the movement of glaciers.  When glaciers moved north at the end of the last ice age, the sea filled in the valleys and formed estuaries.  There are many fjord in the

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