Coast and Beach - Submergent Coasts

If sea level rises, or the elevation of the coast falls, formerly exposed topography will be inundated. Valleys carved out by rivers will become estuaries like Chesapeake Bay. Hilly terrains will become collections of islands, such as those off the coast of Maine.

The ability of rivers to transport sediment depends on their velocities. When rivers flow into a deep body of water, they slow down and deposit their sediment in what will eventually become a delta. Thus, the flooding of estuaries causes deposition further inland. As the estuary fills in with sediment, the depth of the water will decrease, and the velocity of the water flowing across the top of the delta will increase. This permits further sediment transport. The delta builds out toward, and eventually into, the sea. The additional load of all the sediment may cause the crust of the earth to deform, submerging the coast further.