The Hengill High-Temperature Area SW-Iceland: Regional Geophysical Survey

Abstract

The Hengill high temperature geothermal area is situated within the Neovolcanic zone in SW Iceland 40 km east of Reykjavik. The geology is characterized by the active Hengill central volcano, an major fissure swarm and the extinct Hveragerdi volcanic center. The area of surface geothermal manifestations is about 40 km2. The geothermal area is characterized by a resistivity low, some 110 km2 in areal extent at 200m depth below sea level. Its central part contain a high resistivity body below the resistivity layer, caused by dense intrusion, change in alteration minerals and transition form water dominated to two phase system at depth. A negative magnetic anomaly caused by hydrothermal alteration of the magnetite in the basaltic rocks correlates well with the outlines of the geothermal area. A good correlation is observed between gravity data, P-velocity data and geologic structure. The geophysical survey outlines a major geothermal area and locates the most promising geothermal fields. Only three small subfields have been explored by drilling so far.