A whirlpool is a rotating current of water which creates a characteristic vortex. Many myths and legends of the sea have featured whirlpools, typically in situations involving great peril to shipping, and there are a number of famous whirlpools around the world which form consistently and frequently. An especially powerful whirlpool is known as a maelstrom; one of the more notable maelstroms is the Moskstraumen, an immense network of eddies and whirlpools off the coast of Norway.
Several things can lead to the formation of a whirlpool. Most commonly, whirlpools are caused by the meeting of opposing currents. When the currents are strong enough, they can start to wrap around each other, creating a spiral of rapidly swirling water. Whirlpools can also be caused by winds, which may cause surface currents to switch direction, and consistent whirlpools are sometimes caused by geographical features which determine the flow of water currents in a region.
When people hear the term “whirlpool,” they usually visualize a swirling vortex of water which is powerful enough to swallow up ships. In fact, most whirlpools are not nearly powerful enough to destroy ships, and many appear almost invisible, with the currents in the whirlpool moving below the surface of the water. In order for a ship to be damaged in a whirlpool, the flow must be especially strong, and the ship unusually small or flimsy.
Some notable whirlpools around the world can be found in places like Scotland, where the Gulf of Corryvreckan often develops a whirlpool, along with Japan, where visitors can see the famous Naruto Whirlpool. A number of smaller whirlpools come and go along the coastlines of the world, and occasionally emerge in rivers, lakes, and streams as well.
Because any change in current can influence navigation, many mariners like to avoid whirlpools, especially if they are in charge of small boats. While large ships can often pass through a whirlpool without major issue, small boats may find themselves buffeted about in the whirlpool, and they could suffer damage or be thrown off course. Major recurrent whirlpools are typically marked in navigational charts for this reason.