Geothermal exploration of Saudá Valley North of Hveragerdi, SW-Iceland

Abstract

The present study area is a part of the extinct Hveragerdi central volcano. It is categorized as a high-temperature area in line with measured and inferred temperature greater than 200°C at less than 1 km depth. Cold water springs in the area are located above the geothermal alteration zone at 300-400 m altitude. In many cases it is observed that cold ground/surface water passes through geothermal manifestations like hot ground and steaming ground and is heated up. The distribution of geothermal manifestations shows normally two sets of faults/fractures almost in NE-SW and NW-SE strike direction. In the areas covered by rock slides and alluvium, the linear arrangement of the manifestations has been obscured. Most of the geothermal manifestations lack native sulphur but silica sinter could be observed in the shape of platforms, particularly in the southern part of the study area near Reykir, and is related to outflow of high-temperature water. The extinct hydrothermal alteration has probably reduced the porosity and permeability of the rocks in the core of the volcano. This affects the present surface geothermal activity, most of which appears to be related to structural features like faults and dykes. Deep reservoir silica-rich water emerges only at low elevations in the south. Two types of geothermal activity are observed: a) Extinct alteration which is evidenced by greenish altered hyaloclastites where the alteration is most intense. The altered minerals are smectite-chlorite and chlorite. b) Present geothermal activity, represented by areas of hot geothermal manifestations and characterized by grey or dark brown to reddish brown smectitic clays.