Contrasting Dynamic Behaviour of Five Lake-terminating Glaciers Draining the Vatnajökull Ice Cap and Links to Bedrock Topography

Abstract Over recent years, the rapid growth and development of proglacial lakes at the margin of many of Iceland’s outlet glaciers has resulted in heightened rates of mass loss and terminus retreat, yet the key processes forcing their dynamic behaviour remain uncertain, particularly at those glaciers which are underlain by overdeepened bedrock troughs. As such, we utilised satellite remote sensing to investigate the recent dynamic changes at five lake-terminating glaciers draining the Vatnajökull ice cap. Specifically, we quantified variations in surface velocity between ~ 2008–2020, alongside datasets of frontal retreat, proglacial lake growth, bedrock topography and ice surface elevation change to better understand their recent dynamics and how this may evolve in future. We observed contrasting dynamic behaviour between the five study glaciers, with three displaying a heightened dynamic response (Breiðamerkurjökull, Fjallsjökull, Skaftafellsjökull), which was likely driven by retreat down a reverse-sloping bed into deeper water and the onset of dynamic thinning. Conversely, one glacier re-advanced (Kvíárjökull), whilst the other remained relatively stable (Svínafellsjökull), despite the presence of overdeepened bedrock troughs under both these glaciers, highlighting the complex nature of those processes that are driving the dynamic behaviour of lake-terminating glaciers in this region. These findings may be important in helping understand the processes driving the dynamics of other lake-terminating glaciers in Iceland so that their future patterns of retreat and mass loss can be more accurately quantified.