Surf zones are the most dynamic parts of the beach. These zones form when water flows on loose sedimentary material. There are varying conditions that cause these bedforms, and some of these patterns remain stationary. Ocean currents can also cause beach erosion. The wind blows sand dunes in the desert in the direction of the wind. The currents can be either longshore or offshore. Sand can be found at any of the three ends of the beach in both cases.
During spring and summer, sand grains move parallel to the shore. Waves that break at an angle and wash up the beach at a certain angle create a zigzag pattern. These patterns occur on both the north and south coasts. In fact, the sand on the beach can move several miles along the coast within a few hours. The waves can move the sand up to three feet per second depending on how strong they are.
Wind affects sand’s ability to form waves. These patterns are formed more often depending on the strength of wind and how large the waves are. Wind-blown sand creates ripples that travel in waves with a period of three seconds to several days. However, when the wind blows strongly over a beach, waves with periods of three to 15 seconds form. Large waves can also create berms which eventually transform into undulating dunes.
Sand also moves in different directions. Sand flows from rivers during floods, from hillside and rockside erosion, and then it moves out to sea via submarine canyons. Wave action is what re-suspends the sand in oceans and washes it ashore. In addition to beaches, sand is blown inland into sand dunes and blown into submerged canyons, which effectively close the littoral cells.
Sandwaves are waves of sand that migrate in the direction of the prevailing flow. They are usually short-lived and travel no more than ten centimeters per hour. Sandwaves larger than a metre don’t migrate at more than ten centimetres each day, although some types can travel faster than 10 cm/day. Sandwaves move at different rates depending on their size, flow speed and other factors.
Wave action is also important for sediment transport. Wave action is responsible to the large amount of sand that covers many coastlines. Sand beaches are dynamic environments because of these processes. The beaches we see today are formed by the interaction of sand, waves, tides, and sand. Short (1999) and Komar (1998) are useful references for learning more about beach characteristics. There are many types of beaches, and how they develop.
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