around objects such as rocks or headlands

Wind blowing over the surface of a body of water forms waves. The friction between air and water caused by a gentle breeze on a pond causes ripples to form. A strong blow over the ocean causes larger waves as the moving air pushes against the raised ridges of water. The waves reach their maximum height when the rate at which they travel nearly matches the speed of the wind. The waves form at right angles to the direction from which the wind blows. In open water, if the wind continues to blow, as happens in the Roaring Forties in the southern hemisphere, long, organised masses of water called swell roll across the ocean. If the wind dies down, the wave formation is reduced, but already-formed waves continue to travel in their original direction until they meet land. Small waves form in small areas of water with islands and other land masses, but large waves form in open stretches of sea where the wind blows steadily and strongly. When waves meet other waves coming from different directions, interference between the two can produce broken, irregular seas.[24][25]

The top of a wave is known as the crest, the lowest point between waves is the trough and the distance between the crests is the wavelength. The wave is pushed across the surface of the sea by the wind, but this represents a transfer of energy and not a horizontal movement of water. When a wave approaches, the water molecules at a point rise up and when it retreats, they go down, moving in a roughly circular pattern each time a wave passes. Those near the surface make a larger movement than those lower down, and deep molecules are completely unaffected by the passage of a wave. A floating object rises up and down as a wave passes but is not moved along by the wave (only by the wind). When waves approach land and move into shallow water, they change their behaviour. If approaching at an angle, the waves may bend or wrap around objects such as rocks or headlands. When the deepest circling molecules in a wave come into contact with the seabed, friction between the water and the beach slow the wave down and the crests become closer together. The height of the wave increases as the energy in it is unable to move downwards and is forced upwards instead. The wave changes profile as the crest moves faster than the base. Eventually, the wave "breaks" as it topples forward and is converted into a tumbling mass of foamy water. This rushes in a sheet up the beach before retreating back into the sea under the influence of gravity