The origin of the warm groundwater near Lake Mývatn, NE Iceland, traced by stable isotopes

The origin of the warm groundwater which feeds Lake Mývatn is unknown, but it has been affected by volcanic episodes as well as geothermal activity and utilisation. In this contribution stable isotopes of hydrogen ( 2 H), oxygen ( 18 O), sulphur ( 34 S), chlorine ( 37 Cl) and strontium ( 86 Sr and 87 Sr) in 20 groundwater and effluent samples from the Lake Mývatn area are used to constrain the origin of the warm groundwater. The results suggest that the warm groundwater is partly formed by mixing with geothermal effluent water and partly by mixing with geothermal steam.