Geothermal mapping in western Ölkelduháls field, Hengill area, SW-Iceland

Abstract

This paper presents the results of mapping the main structures and surface geothermal manifestations in Western Ölkelduháls area, SW- Iceland which is a part of the active Hengill geothermal and volcanic system. The main objective of this study was to map the manifestations and investigate the relationship between the geothermal manifestations, the tectonic and volcanic structures and rock types. Geothermal activity is widely distributed in the mapped area, the main manifestations being fumaroles and steam vents; boiling mud pots and water pools; hot, warm and cold springs; hot, warm and steaming grounds. The manifestations occur at elevations between 230 and 430 m above sea level and are mainly fault or fracture controlled. The main structures that control these manifestations trend NE-SW and N-S. Northwest oriented faults and fractures also occur. Hyaloclastites, pillow lavas and lava flows predominate the lithological units in the area. These rocks have been exposed to variable degrees of alteration due to reactions with hydrothermal fluid. Two types of hydrothermal alteration are distinguished on the map, slightly altered rocks, and extensively altered rocks characterized by widespread clay alterations, either extinct or grading from active to cold.