geothermal development and research in iceland - Orkustofnun

From Reykjadalir in the Torfajokull area
Magnús Ólafsson
the surface by atmospheric oxygen, either into elemental sulphur, which is deposited
around the vents, or into sulphuric acid, which leads to acid waters altering the soil
and bedrock.
The internal structure of fossil high-temperature systems can be seen in Tertiary and
Quaternary formations, where erosion has exposed rocks that were formerly at a
depth of 1-3 kilometers. The system’s heat source is generally shallow magma intrusions.
In the case of high-temperature systems associated with central volcanic complexes
the intrusions often create shallow magma chambers, but only dyke swarms
are found where no central volcanoes have developed. It appears that intrusive rocks
are most abundant in reservoirs associated with central complexes that have developed
a caldera. The boiling point for water depends on the hydrostatic pressure.
As the pressure increases with depth the temperature needed to let the water boil
rises along a curve that is called the boiling point curve. Temperatures in active, hightemperature
systems generally follow the boiling point curve. The highest recorded
downhole temperature is 380°C. Hydrological considerations and permeability data
imply that the groundwater in the reservoir is undergoing density driven vertical
circulation. This groundwater is in most cases of meteoric origin. However, in three
areas on the Reykjanes Peninsula it is largely or solely marine.
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