Geology of Hydrothermal vents

The crust of the earth is not equally thick everywhere. It is constantly being created at areas such as the one we are at (Endeavour segment of the Juan de Fuca Ridge). At these places the crust is very thin and the mantle, the layer of the Earth beneath the crust, is close to the seafloor. Mantle can move under the crust due to the high pressure at the interior of the Earth. At mid ocean ridges, the mantle rises up to a depth close to the seafloor and melt into magma because of a decrease in pressure. It is the magma below the seafloor that provides heat to the hydrothermal vent systems.

The birth of a black smoker (Tivey, 2004)

As the seawater seeps through the fractures on the seafloor into the interior of the earth, it is heated by the underlying magma to a temperature as high as 500 to 700 degree Celcius. Note that the seawater will not boil even at such a high temperature due to the high pressure. Meanwhile, a series of chemical reactions happen between the seawater and the magma. As a result of those reactions, Mg in the seawater is completely taken out by the crust of the earth, while the metal elements Fe, Cu, and Zn and Hydrogen are added to the seawater from the Earth. The superheated seawater then rises up and spurts out of the seafloor through hydrothermal vents.

Chimney made up of polymetal sulfide covered with tube worms 

When hot hydrothermal plumes mix with cold deep seawater, a lot of chemicals in the plumes precipitate out and form suspending particles. A major composition of the particles is metal sulfides like iron sulfide, which makes the plume look black (black smokers). The accumulation of the particles at the base of the vents builds up the chimney gradually and finally forms the magnificent hydrothermal structure.


Goksenin Sen


Marine Educator




Reference:


Tivey, M. K. (2004). The remarkable diversity of seafloor vents. Oceanus, 42(2), 1-6.
Photo Credits: CSSF-ROPOS/NEPTUNE Canada