Geothermal exploration in Gufudalur, Hveragerdi, SW-Iceland

Abstract

The Hveragerdi geothermal field is located on the eastern margin of the western rift zone and the western margin of the South Iceland Seismic Zone (SISZ). Earthquakes with epicentres in the Hveragerdi central volcano are quite common; most of these are smaller than 4 on the Richter scale. The most recent earthquakes in the SISZ occurred on the 29th of May 2008 with two major earthquakes with magnitudes of 6.3 and 5.5 between the towns of Selfoss and Hveragerdi. It is believed that the first earthquake triggered the second one. These major earthquakes affected the Hveragerdi geothermal field. Many sudden changes regarding surface manifestations were observed. Visible fractures on the surface, the appearance of new fumaroles, hot springs, and many surface manifestations in the Hveragerdi geothermal field changed due to these earthquakes. The main purpose of this study on the valley of Gufudalur, Hveragerdi, is to map the surface manifestations, alteration and soil temperatures and correlate the manifestations with structures such as faults, fractures and lineaments. In addition, the results are compared with previous geothermal maps from the same area to pinpoint any changes caused by the earthquakes in 2008. More than 450 GPS locations of geothermal manifestations were taken and divided into 12 separate active areas. Present geothermal activity was compared with studies done in 1995 and soon after the earthquakes in 2008.

The present study reveals that the earthquakes which occurred in 2008 created new geothermal manifestations and the geothermal activity increased. New surface manifestations are still forming in the Gufudalur, Hveragerdi area. Alignment of geothermal manifestations along preferred directions indicates structural features, like lineament expression of underlying geological structures such as faults/ fractures/lineaments. The major structural trends that control the geothermal manifestations are oriented NE-SW, although N-S and NW-SE oriented faults and fractures are also present. On the basis of geothermal mapping, it was concluded that the geothermal manifestations are controlled by the geological structures and topography