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What is the difference between swell & waves?

A blog by our intern, Toni Zill

Waves are caused by winds within the surrounding area, while swell is the increase in wave height due to a storm or bad weather further out at sea. (Follow this link to watch a video that explains waves in more detail)

The ocean is never still. Whether observing from the beach or a boat, we expect to see waves on the horizon. Waves are created by energy passing through water. However, water does not actually travel in waves. Waves transmit energy, not water, across the ocean and if not stopped by anything, they are able to travel across an entire ocean.

Waves are most commonly caused by wind. Wind-driven waves, or surface waves, are created by the friction between wind and surface water. The gravitational pull of the sun and moon on the earth also causes waves. These waves are tides or tidal waves.

Waves travel for a short distance, they are very irregular, meaning they might occur 5 to 10 seconds apart. They are affected by local winds which means if the wind in the local area is calm then the wave will be calm and gentle. Speed and power from a wave disappears over time.

Swell is formed in a similar way. Swell appear in the ocean when the wind transfers its energy from air into the water. Every swell starts as small ripples on the surface and as they travel their energy builds and that means the swell becomes bigger over time.

When a storm occurs out at sea there are strong winds that over time generate surface waves, after a long period of time those waves change into swell. Swell is smooth long waves that travel in groups away from the storm that generates them. Swell travels on the surface of the ocean and unsettles the wave underneath as they pass by.

If we have to swell out at sea it might look like water moving with each wave but as we know it is actually energy being transferred rather than moving water. Once swell is formed it is very hard to stop it. Swells travel across great distances, sometimes for days covering thousands of kilometres. As the swell is traveling they have little to no interaction with waves, weak winds and currents.

When swell moves pass areas that are calm. The surface water of the swell moves the air just above the smell and this generates a little wind coming off the water. In scientific terms we can say the water passes the energy to the atmosphere.

As the swell draws closer to the shore, it is an indication to Meteorologists, who study the weather, that a storm had taken place somewhere. The swell finally dies once it reaches the shore because the shore creates friction and the swell breaks forming waves along the shore.

Waves and swells are also influenced by the different seasons. Waves that are generated by storms will lose energy quickly as they move away from the storm, sometimes they combine with other swells and pick up more energy, and over time they will dissipate.

Over the past few weeks South Africa has experienced an extreme pulse of swell and huge waves generated by the type of weather we've been having. Keep an eye out for our next set of swell and waves, and watch from a distance.


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