Effects of geothermal utilisation on groundwater at Bjarnarflag
The inflow at Mývatn is mostly groundwater which flows from all directions until it reaches the lake. The flow is mostly from the southern end and part of the groundwater is heated up by the geothermal system in the Námafjall Mountain, mixing with geothermal water from this source and from Krafla.
Simplified model of the groundwater system at the eastern end of Mývatn. Source: ÍSOR.
Monitoring on the effects of geothermal utilisation in Bjarnarflag has been ongoing in one form or another for over 40 years or since drilling began in 1963. An extensive report was released on the effect of geothermal utilisation at Bjarnarflag on the warm groundwater flow to Mývatn in 2013. The main results were as follows:
- Model calculations show that the warm groundwater flowing to Ytriflói amounts to approximately 11 m3/s, whereas the cold groundwater entering Syðriflói is approx. 17m3/s.
- Extensive changes took place within the groundwater system in Lake Mývatn as a result of volcanic activity and movements in fissure swarms during the Krafla Fires 1975 to 1984 and the Mývatn Fires 1724 to 1729. The temperature of the groundwater increased and the chemistry changed accordingly.
- Based on the chemistry and the isotopic composition of the cold and warm groundwater it is proposed that the warm groundwater is only partly derived by steam heating but mainly derived by mixing with geothermal water from the Krafla geothermal system.
- The percentage of deuterium, chlorine (Cl) and boron (B) in groundwater indicates that geothermal fluid that has mixed with groundwater originates from the Krafla Geothermal System.
Decades of monitoring have not shown any negative effects on Mývatn from current power operations in the area or from the run-off water from the potential power project in Bjarnarflag which will be re-injected.