Geothermal exploration in eastern Ölkelduháls field, Hengill area, SW-Iceland

Abstract

Ölkelduháls area is a part of the Hengill volcanic massif located in the western branch of the volcanic rift zone in SW-Iceland. It is a high-temperature geothermal field endowed with impressive geothermal manifestations which include warm springs, hot springs, mud pools, steam vents (fumaroles), warm grounds, hot grounds, travertine deposits, extinct clay alterations and slight bedrock alterations. The main rock formations in the area are basaltic compound lavas, hyaloclastites and pillow lavas which are altered to clays and iron oxides in the areas surrounding the active geothermal manifestations. The geothermal exploration carried out in the area involved mapping surface geothermal manifestations and shallow soil temperature measurements around the active manifestations to delineate the 15°C and 50°C isotherms. The results indicate that tectonic features control geothermal activity in the area. Five normal faults and four fractures were mapped based on the topographic features and alignment of the geothermal manifestations. There is a marked NW-SE trend in the geothermal manifestations from Klambragil valley to well HE-20, probably controlled by the suspected regional transform fault zone. However, on closer observation, most of the manifestations locally follow the NE-SW trend coinciding with most of the faults and fractures in the Ölkelduháls area. The feeder dykes of Molddalahnúkar appear to have created several fractures in Ölkelduhnúkur, enhancing the upflow of hydrothermal fluids and the occurrence of numerous manifestations. Most of the springs are carbonated and precipitate calcite and aragonite.....