Why does the ocean have waves?

The ocean is constantly in motion. Whether we watch it from the shoreline or from a boat, waves are almost always visible moving across the horizon. Waves form when energy moves through water, causing the water particles to move in a circular pattern. However, the water itself does not travel forward with the wave. Instead, waves carry energy across the ocean rather than transporting the water. When nothing interrupts their movement, waves can travel across an entire ocean basin.

Wind-Driven Waves

Wind is the most common source of ocean waves. Wind-driven waves, also known as surface waves, develop because of friction between moving air and the water at the surface. As wind travels across an ocean or lake, it continually disturbs the water, gradually producing wave crests.

These waves occur throughout the world's oceans and can be found both in the open sea and near coastlines. Their size and strength depend on factors such as wind speed, how long the wind blows, and the distance over which it moves across the water.

Storm Surge and Other Dangerous Waves

Some of the most hazardous waves are associated with powerful weather systems such as hurricanes. The intense winds and changes in atmospheric pressure produced by these storms can generate storm surge. Storm surge consists of long waves that develop offshore in deeper water and become stronger as they approach the coastline.

Other dangerous waves can result from sudden disturbances beneath the ocean. Earthquakes, underwater landslides, and volcanic eruptions can rapidly displace enormous quantities of water, producing extremely long waves known as tsunamis.

Storm surge and tsunamis are different from the breaking waves normally associated with beaches. Instead of forming a typical crest that crashes onto the shoreline, these waves can move inland much like an enormous and rapidly advancing rise in sea level. Their effects can therefore extend well beyond the immediate coast.

Tides and Tidal Waves

The gravitational forces exerted by the moon and the sun on Earth also produce movements in ocean water. These movements are known as tides and are sometimes referred to as tidal waves.

However, the expression “tidal wave” is often misunderstood. A tidal wave is not another name for a tsunami. Tsunamis are not produced by the gravitational forces responsible for tides. Instead, they result from sudden underwater disturbances such as earthquakes, landslides, or volcanic activity.

A tsunami can occur regardless of whether the tide is high, low, rising, or falling. Its relationship to the tide is therefore unrelated to the mechanism that creates it.