title: Dynamics of glacier calving at the ungrounded margin of Helheim Glacier, southeast Greenland.
abstract: During summer 2013 we installed a network of 19 GPS nodes at the ungrounded margin of Helheim Glacier in southeast Greenland together with three cameras to study iceberg calving mechanisms. The network collected data at rates up to every 7 s and was designed to be robust to loss of nodes as the glacier calved. Data collection covered 55 days, and many nodes survived in locations right at the glacier front to the time of iceberg calving. The observations included a number of significant calving events, and as a consequence the glacier retreated ~1.5 km. The data provide real-time, high-frequency observations in unprecedented proximity to the calving front. The glacier calved by a process of buoyancy-force-induced crevassing in which the ice downglacier of flexion zones rotates upward because it is out of buoyant equilibrium. Calving then occurs back to the flexion zone. This calving process provides a compelling and complete explanation for the data. Tracking of oblique camera images allows identification and characterisation of the flexion zones and their propagation downglacier. Interpretation of the GPS data and camera data in combination allows us to place constraints on the height of the basal cavity that forms beneath the rotating ice downglacier of the flexion zone before calving. The flexion zones are probably formed by the exploitation of basal crevasses, and theoretical considerations suggest that their propagation is strongly enhanced when the glacier base is deeper than buoyant equilibrium. Thus, this calving mechanism is likely to dominate whenever such geometry occurs and is of increasing importance in Greenland.
authors: Glaciology Group, Department of Geography, College of Science Swansea University Swansea UK.
authors: Tavi
authors: T
authors: Murray
authors: Glaciology Group, Department of Geography, College of Science Swansea University Swansea UK.
authors: Nick
authors: N
authors: Selmes
authors: Glaciology Group, Department of Geography, College of Science Swansea University Swansea UK.
authors: Timothy D
authors: TD
authors: James
authors: School of Civil Engineering and Geosciences Newcastle University Newcastle UK.
authors: Stuart
authors: S
authors: Edwards
authors: School of Civil Engineering and Geosciences Newcastle University Newcastle UK.
authors: Ian
authors: I
authors: Martin
authors: Department of Electronic and Electrical Engineering University of Sheffield Sheffield UK.
authors: Timothy
authors: T
authors: O'Farrell
authors: Department of Electronic and Electrical Engineering University of Sheffield Sheffield UK.
authors: Robin
authors: R
authors: Aspey
authors: Glaciology Group, Department of Geography, College of Science Swansea University Swansea UK.
authors: Ian
authors: I
authors: Rutt
authors: Lamont-Doherty Earth Observatory Columbia University New York New York USA.
authors: Meredith
authors: M
authors: Nettles
authors: Thales, Research & Technology Berkshire UK.
authors: Tim
authors: T
authors: Baugé
keywords: Glacier calving; Greenland; Iceberg calving