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How did rising sea level after the Wisconsin Glacial Stage form many modern estuaries?

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Diagram showing four main types of estuaries: salt wedge, partially mixed, vertically homogeneous, and fjord. Each panel illustrates river and seawater mixing patterns, with arrows indicating the direction of saltwater and freshwater flow. — estuary Four main types of estuaries: (A) salt wedge estuary, (B) partially mixed estuary, (C) vertically homogeneous estuary, and (D) fjord (black arrows indicate salt water and white arrows fresh).

During the peak of the Wisconsin Glacial Stage, global sea levels were significantly lower because vast amounts of water were locked in continental ice sheets. During this period of lowered sea level, rivers extended their courses across the exposed continental shelf, entrenching and deepening their valleys.12

As the climate warmed and glacial melting began approximately 18,000 years ago, sea levels rose, causing marine waters to flood these entrenched river valleys and other coastal lowlands. This inundation created what are known as drowned river estuaries, such as the Chesapeake Bay. In regions where glaciers had previously carved deep, narrow gorges into the bedrock, the rising seas formed fjords, which are another common type of modern estuary.12