Controls on short-term calving glacier dynamics

The global retreat and thinning of mountain glaciers and ice sheet margins is a well-documented consequence of recent climate changes, impacting both downstream hydrology and freshwater availability and eustatic sea-level rise. Alongside recent reductions in ice volume, proglacial lakes observed at the termini of many glaciers have increased in both number and areal extent as glacier overdeepenings become ice-free and fill with meltwater. The size and number of such lakes is projected to increase in future.

The presence of an ice-marginal lake has been observed to change the dynamics and behaviour of a glacier via a number of thermo-mechanical processes and positive feedbacks. While calving fluxes are mostly a function of ice velocity, the retreat of a glacier margin into progressively deeper water alters the longitudinal stress distribution of a glacier. Moreover, the lake itself can decouple glacier mass loss from climate forcing as heat absorption by the lake and seasonal fluctuations in water temperature, depth and circulation patterns influence the calving regime

Remote sensing data indicates that the flow velocity and retreat of lake-terminating glaciers is substantially faster than nearby land-terminating glaciers. These changes provide an insight into ablation mechanisms at a local scale that have hitherto been poorly quantified in mass balance and surface energy models because of the difficulty of acquiring data at the necessary temporal and spatial scale. Indeed, despite these important contributions to overall glacier mass loss, there is a paucity of field data documenting and quantifying "frontal ablation" (including calving, subaqueous and subaerial frontal melt) of lake-terminating glaciers and ice sheets.

Advances in field sensors and monitoring/survey techniques, coupled with developments in remote sensing platforms have created a step-change in the quantity, quality and availability of data. Such advances have opened up new opportunities to better understand the rates, controls and mechanisms of glacier frontal ablation at a nested range of space and time scales These data are urgently needed to better represent lake-glacier interactions in numerical models of mountain glacier and ice sheet evolution).

The aim of this project is to constrain the short-term dynamics of glaciers calving into ice marginal lakes. An array of novel field monitoring techniques will be deployed as part of data acquisition. High resolution, short-term repeat Structure-from-Motion (SfM) glacier surveys will be undertaken from a packraft, boat or Uncrewed Aerial Vehicle (UAV) and differenced to provide information on calving volumes, timing and mechanisms. A weather station, trail cameras and networks of pressure sensors and thermistor strings will provide information on weather and lake conditions.

The final field site(s) will be chosen in discussion with any successful candidate. The project team have an established history and experience of working on these questions at a range of field sites including the Himalayas, West Greenland, Arctic Sweden and New Zealand. Owing to the logistical advantages and number of such proglacial lakes, we anticipate initial fieldwork to be conducted on outlet glaciers of the Vatnajökull Ice Cap, Iceland. Moreover, at this site there is the potential opportunity to examine the impact of large-scale additions of debris onto the glacier surface on the monitored relationships.

Objectives
(1) To intensely monitor glacier calving processes alongside environmental/lake data collection at one site for a season/year;
(2) To partition mass loss between surface melt and calving volumes at that site (or multiple sites nearby);
(3) To determine the controls on that mass loss partition from a wider light touch monitoring campaign/analyses of other data sources and analysis of the longer-term remote sensing data archive.