Subsurface hydrothermal alteration mapping in the Reykjanes Geothermal area using a combined geoelectrical approach.

The dynamic behavior of volcanic hydrothermal systems (VHS) and associated hydrothermal eruptions remains largely unknown, processes in VHS such as the circulation of hydrothermal fluids and formation of caprock give rise to a range of geophysical signals. Here we explore the combined use of three geo-electric methods: electrical resistivity tomography (ERT), induced polarization (IP), and self-potential (SP), to characterize a VHS, known to be sensitive to temperature, saturation and mineral precipitations. We conducted a shallow (<50m) geo-electric survey on the Reykjanes geothermal area and identified zones of high and low activity, and the presence of shallow sealing structures (<20m) prohibiting the surface expression of hydrothermal activity, demonstrating that shallow structures can act as a proxy for deep processes. Furthermore, We show that the combination of the three methods is invaluable in the study of these complex systems and recommend this for future research.