A megaplume is a giant plume. In its geological sense, plume is defined as “An upwelling of molten material from the earth’s mantle.” But the term can also be used to describe a column of hot water ascending from the ocean floor, and a megaplume is an exceptionally large pocket of unusually hot ocean water. Precisely what heats the water is the subject of some debate, but one way or another; the heat does clearly come from tectonic activity.
The first megaplume was discovered in 1986 on the Juan de Fuca Ridge, which runs roughly parallel to the coast of the U.S. Pacific Northwest, about 300 miles (450km) west of Oregon. Since then, only handfuls have been observed. They do bring with them a wide variety of interesting creatures, including some rare microbes that flourish in the superhot waters of hydrothermal vents. Moreover, megaplumes can transport both minerals and animal life to areas far outside the range where they would normally be found, giving researchers no end of unusual things to.
Although hydrothermal vents—discharges of a hot, mineral-rich water solution from the ocean floor—are well known, megaplumes have been likened to a huge initial “belch” of hot water that may occur when such a vent forms. The hot water forms itself into a free-floating lens like shape that can be more than 12 miles (about 20km) in diameter and more than half a mile (about 1000m) deep. When the water closer to the surface—which is now colder than the water beneath—begins to sink, it contributes to the formation of powerful but slow-moving whirlpool-like currents. But the whirlpool is not anchored in one spot; like a tornado, the entire megaplume can move horizontally—sometimes hundreds of miles over a period of months—before dissipating. However, because the ocean is relatively deep in areas in which megaplumes are known to exist, the whirlpool is far below the surface, making it difficult to detect