What coastal features are formed by wave erosion and deposition?

1 Answer

The stronger the waves, the larger are the particles that can be suspended and carried off to other areas, where they get deposited when the wave action weakens.


Small waves can only suspend clay and silt particles in the water. Bigger waves can suspend sand grains, granules, and even pebbles. Very big waves scour away all loose sediment and abrade rock outcrops with the suspended particles, causing a lot of erosion that can eat away the shoreline. Big waves can even carry off cobbles and leave only the heaviest boulders and rock outcrops on the shore.

However, when the waves weaken, the heaviest rocks are deposited first followed by the next smaller-sized particles. These particles are often carried parallel to the shore by a "longshore current" if the waves hit the shore at an angle.

When the waves and current weakens, the particles drop onto the shore and form a beach or sandbars of a single predominant size of sediment. Thus, weak waves form a beach of clay or silt, slightly stronger waves form a beach of sandy-mud, and meter-high waves can form beaches of sand or granules. Sand bars and sand spits are not permanent and can degrade or reform throughout the year.

During storm season, the waves push the sediment further up the beach and these form piles of debris or sediment on the high shore called "berms." Berms can also form from dead seaweed or seagrass pulled off the deeper ocean bottom by the biggest waves. In arid climates, the abundant beach particles can be formed by the wind into dunes.