Waves are caused by wind blowing over the surface of the water. The best waves, swell waves, are caused by winds blowing consistently across the surface of open water. If there is also a moderate wind blowing into the oncoming wave from the short, this creates a barrel or tube wave. Tube waves are considered ideal for surfing. Most surfers long to ride the tube, and consider these the ideal waves.
Waves are classified by their shape and their speed. Depending on its length-to-width ratio, a wave can be square, round or almond. Depending on its speed, a wave can be slow, medium or fast. Popular surfing locations tend to have one particular combination of shape and speed of waves predominate, since a wave's shape and speed are largely determined by the topography of the sea floor beneath it. For example, G-Land, the world-renowned surf break in Indonesia, is known for fast, square waves. Australia's Angourie Point, on the other hand, typically features slow, almond waves.