A wave is made up of two main parts—crests and troughs
When waves crash on the beach head-on, the water they moved through flows back to the ocean underneath new incom ing waves. This movement of water, which carries sand, rock particles, and plankton away from the shore, is called an undertow
Sometimes waves called whitecaps form in the open ocean. Whitecaps are white, foaming waves with very steep crests that break in the open ocean before the waves get close to the shore.
These waves usually form during stormy weather, and they are usually short-lived. Winds that are far away from the shore form waves called swells. Swells are rolling waves that move steadily across the ocean
A local rise in sea level near the shore that is caused by strong winds from a storm, such as a hurricane, is called a storm surge.