Understanding the elemental forces that create our ocean waves, and the processes that deliver the surf to our beaches, will help you better appreciate the different surf conditions that exist and participate more safely in ocean sports. Wind, weather, tides, and landforms all influence the types of waves we experience along the shoreline. Let’s take a look at the basics of how waves are made.
Ocean Waves Formation: Ocean waves are usually formed by distant winds. Storms generate strong winds that act on the ocean’s surface for several days. The strength of the wind, its duration, and the size of the fetch all influence the waves that are produced. The area over which the wind blows is called the fetch. The larger the fetch, the larger the resulting waves. Initially these waves are confused and disorganized, forming what is known as a sea. As they travel, interference and superposition organize them into a swell. Smaller waves are absorbed by larger ones, faster waves overtake slower ones, and eventually the organized swell travels across the ocean as a wave train. The wave train carries energy through the water, while the water itself moves very little forward.
Swell Period and Wave Sets: Wave energy can travel hundreds or even thousands of miles. Swell height is measured from crest to trough, while the time between crests is called the wave period. Longer wave periods generally indicate more powerful swell. Swells also arrive in groups called sets, with several smaller waves followed by larger ones.
Swell Becomes Surf: When swell reaches shallow water it begins to interact with the seabed. Friction slows the wave, causing it to steepen and gain height. Eventually the wave becomes too steep to support itself and breaks, becoming surf. The character of the breaking wave depends on both the incoming swell and the shape of the seabed.
Waves on a Human Scale: Even small waves can be dangerous. Water is extremely heavy, and moving water carries tremendous energy. Knee-high waves can knock swimmers over, cause neck or back injuries, or sweep people into rip currents. Always match the conditions to your ability.
Wave Size: Larger waves travel faster than smaller ones. Wave faces are commonly described as waist-high, chest-high, overhead, or double overhead. Hawaiian-style wave measurements traditionally refer to the back of the wave, making the reported height roughly half of the wave face.
Respect the Ocean: Always respect the power of the ocean. Never surf beyond your ability. Never turn your back on the sea. Watch for cleanup sets, consult lifeguards and local forecasts, and when in doubt, don’t go out.
Types of Breaking Waves: The three main types of breaking waves are mushy rollers, plunging waves, and surging waves. Mushy rollers break gently and are generally best for beginners. Plunging waves break violently and can create hollow barrels. Surging waves often rush directly up the shoreline without fully breaking and can be dangerous around rocks and steep beaches.
Wind on Waves: Although wind creates ocean waves, it can also spoil surf quality. Surfers usually prefer light offshore winds, which hold the wave face open. Strong onshore winds create choppy, disorganized surf.
Wave-Generated Rip Currents: Breaking waves push water toward the shore. That water must eventually return to the sea, often through narrow channels called rip currents. If caught in a rip current, swim parallel to the beach until you escape the current, then return to shore.
Standing Waves: Standing waves are commonly found in rivers, but can also occur in the ocean where strong currents meet underwater features. Because they are continuously fed by flowing water, they can trap swimmers in powerful recirculating currents.
