More on whirlpools!

Naruto Strait whirlpool from Mantokun, Wikimedia

 

"Whirlpool" is a general term for any swirling body of water. Whirlpools on many scales are common in nature, and they are easily seen in almost any flowing body of water.  In rafting on the Colorado River through the Grand Canyon, it is not uncommon to have one end of a 16' rubber raft sucked down 6" or more by little whirlpools in the river.  According to Wiki on Whirlpools, the 5 strongest whirlpools in the world are in Norway (2), Maine (USA), Japan and Scotland, and these have speeds that reach up to 37 km/hour (23 mph).

The natural whirlpools in Japan occur in the Naruto Strait, a channel between two smal islands, Tokushima and Awiji.  The straight is less than 1 mile in width, and connects the Pacific Ocean and the Inland Sea, a body of water that separates Honshu and Shikoku. Tides here have a range up to 5.6 feet, creating a difference in water level of nearly 5' between the Inland Sea and the Pacific. Because the strait is so narrow, water rushes through it at 8-9 mph, four times per day, and during spring tides the speed can reach 12 mph.  At that time, whirlpools up to 66' in diameter can occur.

The whirlpool in your bathtub is not a good analog for most natural whirlpools because it is caused by the exodus of water down your drain. However, there was one similar whirlpool in a lake in Louisiana in 1980 when a drilling rig broke through the roof of an underground salt mine.  The lake drained, just like bathwater, down through the salt mine and a whirlpool developed.  Although some boats and semi trailers were caught up in it, no lives were lost.