The effect of intrusive activity on the Krafla geothermal system, NE-Iceland: The Krafla fires 1975-84

Young igneous geothermal systems derive their energy from magma in their roots.  Some of them have been utilized for electricity production and other uses of geothermal energy.  Iceland has several young igneous geothermal systems and has been pioneering the harnessing of geothermal energy derived from such systems.  Iceland is ideally located for the occurrence of young igneous systems, being underlain by a mantle plume and sitting on the Mid-Atlantic Ridge. Although the overall structure and temperature distribution of young igneous systems are well known in some areas, the nature of how they are recharged by magma has been poorly constrained.  The Krafla high-temperature geothermal area in North-East of Iceland is one of the best-known such systems.  Between 1975-1984 the so-called "Krafla Fires" took place, associated with the widening of the Krafla fissure swarm by several meters, during episodes of volcanic activity consisting of 20 extrusive and intrusive events.  The effects of this intrusive and extrusive activity on the geothermal system are a subject of ongoing research. The intrusions, injected into the geothermal system, are estimated to have had a volume of 0.12-0.19 km³ and added 4-8 x 10¹⁷ J of heat to the system through the solidification and cooling of these intrusions. This heat is released and transferred within and out of the system as cooling and solidification occur.  After each rifting event, some of which were accompanied with fissure eruptions on the surface, this additional heat input was visible on the surface of the geothermal system as intensive steaming.  This was especially prominent in fissures and fractures along the main axis of rifting.  The intrusive activity may have increased the temperature in parts of the system by several tens of degrees.