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An introduction to geology
An introduction to geology

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2.17 Hydrothermal vents

Having very hot rocks, at spreading centres, sitting directly below very cold ocean water leads to interesting geological processes – a hydrothermal (literally, water–heat) system develops. These are, at their very simplest, just systems where you have very hot water in contact with rocks.

Described image
Figure 2.20 Hydrothermal system

This happens in the oceans when seawater which has percolated into the rocks meets rock heated by molten magma at the mid-ocean ridge. This superheats the water, and very hot water has the power to dissolve and transport certain elements from the rocks. Usefully, some of the elements which become dissolved in the hot water are elements that we want, like copper, iron, zinc, silver and gold.

The water travels through fissures in the rocks and moves back towards the cold ocean waters. As it’s only the heat of the water which keeps these elements in solution, when they cool down again, the metals fall out of solution and are deposited along the outside of the fissures through which the fluids are travelling.