Amanda Maxwell

Dec 14th 2022

Fluid Dynamics, Rotation and Surviving Dangerous Whirlpools


Whirlpools have entranced humans throughout history, with their existence sometimes being credited to mythological sea monsters intent on destruction. However, studying how water flows and understanding the physics behind turbulence, flow and currents has helped us learn how whirlpools are formed and how to survive them. From natural phenomena in the world’s oceans to man-made examples, not all of these spinning marvels are dangerous whirlpools, and in fact, not all of them classify as vortices.

How Are Whirlpools Formed?

Britannica calls whirlpools “rotatory oceanic currents,” but how are whirlpools formed? The science behind their formation is detailed in the branch of physics known as fluid mechanics, which explains the movement of liquids and gases. In the oceans and other bodies of water, whirlpools form when two currents meet each other. As Live Science explains, the interaction between the two currents is rather strange: since neither can continue moving in the same direction and pass through the opposing current, the different streams must circulate around each other.

A whirlpool’s size depends on the speed of the currents that formed it. When a whirlpool forms a downdraft in its center, dragging objects deep below the surface, it’s known as a vortex. This can trap whatever it submerges on the seabed, only spitting it out if it can float and bob back to the surface. You’ll often see these dangerous types of whirlpools referred to as “maelstroms.”

Whirlpools also form when a current runs into an obstacle, so they’re often seen as water rushes through a narrow ocean strait or over disturbances in the seabed. One of the strongest whirlpool systems in the world, the Moskstraumen off the coast of Norway, exists due to fast currents flowing through a narrow and exceptionally deep channel. This is where the kraken of ancient lore supposedly snatched up seafarers. The Corryvreckan, off the west coast of Scotland, forms in a narrow strait where the tides run over an unusually pyramidal seafloor.

Whirlpool Hotspots Around the World

Whirlpools are found all over the world, and probably a lot closer than you think. Every time you empty a bath or a sink, the eddies that accompany the water vanishing down the drain give clues about how whirlpools are formed. You can also find man-made versions; wherever human activity creates water outflows, there’s a possibility that a vortex may appear. For this reason, always be careful near the base of a dam and around any water drainage outflow.

In the natural world, the most powerful whirlpools are found off the coast of Norway. Near the Arctic Circle you can find the world’s strongest maelstrom: Saltstraumen. Saltstraumen forms with each tide, so visitors can watch the whirlpool form four times each day in the narrow channel. Currents here flow as fast as 25 miles per hour (40 kilometers per hour), and ships will only pass through the area during the dangerous whirlpool’s slack times.

For comparison, the Moskstraumen reaches speeds of 20 miles per hour (32 kilometers per hour), while the Corryvreckan runs at just 11 miles per hour (18 kilometers per hour). However, the Corryvreckan is still classified by the UK Royal Navy as “very dangerous,” since waves in the area can reach as high as 30 feet (9 meters). It might also be the world’s loudest whirlpool, with a roar that’s audible 10 miles (16 kilometers) away. The vortex has been known to pull objects down to 862 feet (262 meters) below the surface before spitting them out.

Thanks to the Coriolis effect, you’ll notice that whirlpools in the Southern Hemisphere spin clockwise, while those in the Northern Hemisphere spin counterclockwise. This is due to the effects of the planet’s rotation.

Are Dangerous Whirlpools a Concern?

Yes, whirlpools can be dangerous, but contrary to some exaggerated depictions in various literary sources, they are unlikely to sink large ships. However, smaller craft and swimmers should pay attention. The main danger is being caught up in a strong current and, with vortices, being sucked under the surface. You can view whirlpools safely in most instances from land — or even in your bathtub. If you want to get a closer look, you could check out the gardens at Alnwick Castle in northern England. The Serpent Garden there features not only a vortex but also other examples of fluid dynamics in the shape of artist William Pye’s sculptures.

You can also harness the power of a whirlpool in home brewing. Separating the wort from the trub is managed by whirlpool physics, where solid particulate matter is spun out from the liquid simply by creating a vortex. The debris, which includes hops vital to the brew flavor, simply sink to the bottom of the vessel as the whirlpool subsides.

Whirlpool Survival 101

If you’re not a hop, how can you survive being trapped in a dangerous whirlpool? Avoiding them altogether is one option, but if you’re kayaking near them, remember to wear personal protective gear, including a helmet and a buoyancy aid to help you pop back up to the surface. If your boat gets trapped in a whirlpool, use strong paddle strokes to break free of the current. Swimmers should aim for the outside of the whirlpool to reach calmer water, but don’t let go of your kayak or paddleboard, as it can be a good buoyancy aid.

Buoyancy helped to keep a Chinese submarine afloat when it got trapped by an underwater whirlpool that formed above a deep ocean trench off the city of Hainan. According to The Guardian, making the vessel more buoyant helped prevent it from being pulled beyond its operating range and crushed.