Why Do Waves Increase in Height As They Approach the Shore?

As waves approach the shore, their interaction with the sea floor causes bunching, compressing them into shorter horizontal distances and increasing their height. The bunching of waves is an effect oceanographers call shoaling. Eventually, gravity overcomes the height of the wave, causing them to break.

The way the wave breaks depends on the shape and slope of the ocean floor. They generally break as "a spilling, plunging or surging breaker," according to Coastal Care. Wide flat beaches form spilling breakers that appear to crumble as they move. A slightly steeper slope causes the crest to curl in a plunging breaker. This curling wave is the type surfers seek. When there is a very steep coastline, waves do not have the opportunity to break before hitting the shore and reflect back into the water, causing surging waves of water.

Waves do not cause water to travel. Instead, they move energy through the ocean toward the shore in a wave form. The water does not move as a current, but the energy moves in a circular motion. The wave crest is the top of the orbital and the trough is the bottom of the orbital. Breaking waves expend energy as they break, which moves sand and shapes the beach.