Harvey Adams, of Rotary Park Kindergarten, asks :-

What makes the waves in the ocean?

Ross Vennell, an oceanographer at the University of Otago, responded.

The short answer is that ocean waves are caused by the wind. You can make your own waves by blowing over a large flat bowl of water. The fast moving air in your breath causes small ripples on the surface of the water which move in the same direction as the air. These are tiny waves.

The ocean is much larger than the bowl of water, so ocean waves are much larger. They grow even larger as they move into the shallow water near the shore. Some eventually grow large enough to surf!

The longer answer is that waves are initially formed by friction between the wind and the ocean. This friction also causes the ocean surface to deform into ripples you can see in the bowl of water. Ripples then cause tiny changes in the flow of the wind and in air pressure very close to the water's surface. These tiny changes cause the waves to grow larger as they move across the water's surface. Larger waves produce larger changes in wind and air pressure, which cause the waves to grow even higher.

The waves continue to grow, gaining energy from the wind, until they become large enough to break. They lose some of their energy in the cascade of breaking wave crests, which you see as "white caps" on a very windy day. How large waves grow depends on the strength of the wind, how long the wind has been blowing and the distance the wind has been blowing over the ocean. The largest waves in New Zealand are typically seen on the south west coast of the South Island, where strong winds blowing across the Southern ocean for thousands of kilometers grow waves many meters tall.