How do beaches and dunes respond to storms and sea-level rise?
Similar to the winter-summer shape variation in beach profiles, beaches undergo changes during storms and in response to sea-level rise. During storms, waves attack the berm and dunes, causing overtopping of the dunes and overwash. At the same time, the berm and dunes are eroded and sediment is transported offshore and deposited in sandbars. This causes waves to break farther offshore, decreasing the wave energy that reaches the beach. As sea level rises, the same process occurs: waves can attack the upper part of the beach profile, pushing sand over the dune in a process called overwash. At the same time, sand is pulled offshore. The barrier beach migrates landward, rolling landward over itself. The initial beach migrates landward over its own marsh into its second position. This is why you can find peat deposits, tree stumps, and oyster shells in the surf zone. Think of the beach as a tread on a tank rolling over itself in a landward direction.
