Hydrothermal Vents

The earth’s crust (also known as the lithosphere) is composed of large rocky plates (tectonic plates) that are constantly in motion. They float on a bed of magma (mantle) within which are convection currents which circulate throughout , initiating the motion of tectonic plates. Thus, there are regions on the crust where plates are converging or diverging. Regions of convergence are known as subduction zones, as one plate slides beneath another. The heat generated from the friction between the two plates causes the subducted region of the plate to melt into magma, which subsequently rises to the surface to form volcanoes (Seyfert et al., 1979).

When oceanic plates diverge, a gap (rift) is formed. Magma rises into this space from the mantle and cools into basaltic rock as it encounters oceanic water.This exchange of heat and chemicals between the magma and water contributes to the formation of hydrothermal vents (Xi-wu, 2004).

Summary of tectonic processes (courtesy of www.enchantedlearning.com)

At the divergence zone, water circulates throughout pores in the rock surface, absorbing metal ions and inorganic compounds that leach from the surrounding rocks. The water is heated to >400°C as it comes into contact with magma and subsequently shoots upward. The ambient hydrostatic pressure at this depth in the ocean is so great that the water cannot enter the gas phase. This is known as superheating. Dissolved minerals are deposited around the site where the water exits the rock matrix and over time structures known as chimneys or smokers develop (Xi-wu, 2004).

Smokers can be classified according to the content of their effluent. There are two types of smokers: black and white. ‘Black’ smokers expel water with high concentrations of heavy metals and sulphides; their plume is therefore black. The first black smoker was discovered in 1977 by DSV Alvin. ‘White’ smokers expel water containing lighter-coloured metal ions such as Ca2+; their plume is white in appearance (Baker and German, 2004).

Hydrothermal vent dynamics (courtesy of Wikipedia)

The landscape of the geothermal deep-sea benthos is varied and diverse. Due to the constantly evolving state of geological formation inherent to this environment, colonizing organisms can be found to inhabit a complex yet ephemeral 3-dimensional habitat with extremes of heat and halinity.


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