Surface and geometry changes during the first documented surge of Kverkjökull, central Iceland.

Glacier surges are events of enhanced ice flow during which ice previously stored at elevation is rapidly discharged down glacier. Surges are important agents of erosion and deposition, they affect the timing and magnitude of meltwater runoff and in areas where surging is common, e.g. Iceland and Svalbard, they represent an important mechanism of glacier mass transfer. Glacier surges may usually be recognised by their distinctive surface morphological expression, and where appropriate data are available, by changes in terminus position, surface velocity and glacier surface elevation. However, many surge-type glaciers remain unrecognised because surge events can be short-lived and are rarely captured by satellite or field data. This study reports the first documented surge of Kverkjökull, central Iceland, adding a relatively short, narrow, steep and alpine outlet glacier from the Vatnajökull ice cap to the known surge-type glaciers in Iceland. The surge occurred after decades of persistent and recently accelerated terminus retreat. The surge initiated after 2008 and immediately preceded drainage of the Gengissig geothermal lake and the subsequent jökulhlaup in 2013. The surge was still in progress in 2013. It caused vertical surface displacements of up to 20 m that were most prominent in parts of the glacier >100 m thick. The magnitude of surface elevation changes, terminus advance and ice surface velocity changes probably reflect only a single surge phase. Asymmetry in the response of the glacier terminus to the surge front suggests interaction with near-stagnant ice but otherwise the trigger and mechanism of the Kverkjökull surge remain unexplained.