Geology Reference
In-Depth Information
4 TRANSFER OF DEEP FLUIDS
Fluid circulation in fractures at the crustal scale allows thermomineral circuit
upwelling, characterized by the high concentration of certain dissolved
compounds and of certain gases (carbon dioxide, radon, carbo-gaseous
springs). This mineral content, the therapeutic properties of which are used
in hydrotherapy, can also be a source of health hazards (arsenic, barium,
fl uoride, radioactivity).
5 THE ROLE OF WATER IN MAGMATISM
Groundwater plays a major role in the dynamics of volcanism. In normal
periods, the infi ltration of meteoric water (rain or snow) on volcanoes, which
are often areas of high relief, and therefore receive more precipitation than
the surrounding foothills, feeds the production of their steam plumes. In
the case of massive groundwater infl uxes at depth (outfl ow of an aquifer
into a chimney, exceptionally high precipitation) this vadose water sets off
volcanic eruptions, as it can vaporise upon contact with hot lava. Explosive
eruptions follow, which pulverise the lava plug blocking the chimney.
Maars and phreatomagmatism are types of volcanic environments in which
water plays an even greater role, by reinforcing the explosive nature of
eruptions.
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