Using stable isotopes and continuous meltwater river monitoring to investigate the hydrology of a rapidly retreating Icelandic outlet glacier

Virkisjökull is an outlet glacier draining the western flanks of Öræfajökull on the southern extremity of the Vatnajökull ice cap in SE Iceland. The glacier is highly sensitive to environmental change and has been shown to be in rapid retreat since 2005. Since 2011 there has been continuous measurements of flow in the proglacial meltwater channel, daily photographs of the snout and regular campaigns to sample water chemistry and stable isotopes from the meltwater, ice and groundwater. Ice- and snowmelt dominate the summer flows, but significant flow is also observed in winter due to periodic snowmelt and winter storms. The data indicate a highly efficient glacial drainage system, which makes use of a series of permanent englacial channels within active and buried ice throughout the year. Groundwater contributions to river flow can also be distinguished using stable isotopes and forms an important source of baseflow to the river at low flows. The efficient and year round drainage network may be a contributory factor to the grounding and subsequent rapid retreat of the glacier.