Buzz
Main Insights
- Prevailing winds on the West Coast drive waves toward the shoreline, amplifying their energy, whereas East Coast winds often oppose wave movement, diminishing their size.
- The West Coast's narrow continental shelf forces waves to rise sharply and break near the shore, while the East Coast's wider shelf results in more gradual wave breaks.
- The vast expanse of the Pacific Ocean provides a longer fetch, enabling West Coast waves to travel greater distances and grow larger, unlike the Atlantic Ocean's shorter fetch impacting East Coast waves.
Some of the globe's top surfing destinations are found along the U.S. West Coast and Hawaii, and the explanation is clear: the waves! But what causes West Coast waves to be larger than those on the East Coast? Three main factors influence wave height:
- the direction and strength of prevailing winds
- the width and slope of the continental shelf
- the distance over which wind blows across the ocean (fetch)
As defined in the Encyclopedia of the Sea, a wave is described as "the rhythmic rise and fall of the sea surface driven by wind moving across it in the same direction as the wind." A key point to note is that the water itself doesn't travel—instead, the wind's energy propagates through it (distinct from tides, which are influenced primarily by the moon). On the West Coast, the prevailing winds align with the waves, boosting their energy. Conversely, on the East Coast, these winds oppose the waves, reducing their energy.
The United States is bordered by a continental shelf on both coasts. To visualize this, picture the ocean drained away. The submerged terrain resembles the Grand Canyon, featuring cliffs, valleys, plateaus, and ridges. On the West Coast, the continental shelf is narrower, meaning the transition from beach to steep underwater drop-off is quick, akin to a cliff. On the East Coast, the shelf is wider, offering a gentler slope that extends farther, like a lengthy ramp.
Beneath the water's surface, particles rotate in alignment with the wind's direction. These particles are largest near the surface and diminish in size with depth. As waves approach the East Coast and encounter the gradual incline of the continental shelf, friction slows the particles, causing the wave to collapse gradually. On the West Coast, the shelf rises abruptly near the shore, allowing waves to maintain their size and energy until they crash dramatically onto the coastline.
The Pacific Ocean on the West Coast spans a much larger area than the Atlantic Ocean on the East Coast. This results in a longer fetch (the distance wind travels over water) on the West Coast. Think of a wave like a snowball: the farther it rolls, the larger it becomes. West Coast waves originate far out in the Pacific, giving them ample distance to grow in size and strength before reaching the shore.
Dr. Ernie Knowles, an associate professor of oceanography at NC State University, summarizes this phenomenon: "The West Coast's steep shelf leads to a sharper buildup of shoaling waves, making them 'steeper' upon breaking. Additionally, the Pacific's extensive fetch allows waves to absorb more wind energy, resulting in larger swells. West Coast waves typically have periods of 10 to 17 seconds, while East Coast waves range from six to 10 seconds."
Here's a simple way to demonstrate how wind generates waves at home:
- Fill a bowl roughly three-quarters full with water.
- Allow the water to become completely still.
- Place a small piece of Styrofoam into the water.
- Position yourself beside the bowl and gently blow across the water's surface.
Your breath acts as the wind, pushing the water in the direction of the airflow. Notice how the Styrofoam (representing a water particle) barely moves as the wave passes over it. Congratulations—you've just made a miniature wave in your kitchen!
