What Is a Swell in the Ocean?

What Is a Swell in the Ocean?
The ocean world is a vast, restless wilderness ceaselessly roiled by waves. A swell born in featureless brine might travel hundreds of miles to break against a shore.

Birth of a Wave

Wind creates most of the waves on the ocean. Friction between the air and the sea surface, transferring energy from wind to water, typically generates wave motion.

Chaotic Waves

Heavy wind, as in a storm, creates a confused bed of superimposed waves called a "sea." The size of a wind-blown wave depends basically on how much energy the air transfers to the water; this is impacted by factors like wind velocity and distance.


Waves flow from the "generating area"--the wind source--in the same direction the air was blowing. Even after the winds die, the waves continue sloughing where they were directed and become more regular as they travel. These long-distance, stable waves are "swells."


Swells can travel great distances across the ocean. Because waves don't lose much energy traveling over deep water, they can move mostly unchanged unless countered by a stronger swell from another direction or until they hit the shore.

Other Swell Sources

While wind is the main generating force for swells, long-distance waves can also be prompted by seismic activity, volcanic eruption and tidal activity. These waves can sometimes be very big indeed, especially when they encounter shallow waters. Tsunamis, or seismic sea waves, are not particularly noticeable as swells in the open ocean--they have a low crest and a long wavelength--but can sometimes approach 100 feet in height when hitting a coastline.


Article Written By Ethan Schowalter-Hay

Ethan Schowalter-Hay is a writer and naturalist living in Oregon. He has written for the "Observer," the Bureau of Land Management and various online publishers. He holds a Bachelor of Science in wildlife ecology and a graduate certificate in geographic information systems from the University of Wisconsin.

Don't Miss a Thing!

All our latest outdoor content delivered to your inbox once a week.



We promise to keep your email address safe and secure.