Steam devil

A steam devil is a small, weak whirlwind over water (or sometimes wet land) that has drawn fog into the vortex, thus rendering it visible. They form over large lakes and oceans during cold air outbreaks while the water is still relatively warm, and can be an important mechanism in vertically transporting moisture.

Smaller steam devils and steam whirls can form over geyser basins even in warm weather because of the very high water temperatures. Although steam devils are generally quite a rare phenomenon, hot springs in Yellowstone Park produce them on a daily basis.

These phenomena have only been reported and studied since the 1970s.

Naming

Steam devils were first reported by Lyons and Pease in 1972 concerning their observations of Lake Michigan in January 1971. This month was a particularly cold one for Wisconsin (one of the coldest in the 20th century) which, combined with Lake Michigan staying mostly ice-free, produced good conditions for steam devil formation. Lyons and Pease named steam devils by comparison to the dust devils on land to which they have a comparable size and structure. They were also motivated by the need to distinguish steam devils from the much more powerful water spout whose land equivalent is the tornado. Lyons and Pease wrote their article with the aim of persuading the National Oceanic and Atmospheric Administration to include steam devils in the International Field Year for the Great Lakes which was imminently to occur in 1972-3.