Study of the dynamic state of ice shelves on the south-western Antarctic Peninsula by an interdisciplinary approach of remote sensing, fracture mechanics and modelling of ice dynamics
Zusammenfassung der Projektergebnisse
The project focused on a remote sensing analysis and a fracture mechanical part. The project was hampered by the move of one of the PIs to the US and back to Germany. However, the overall project goals were successfully achieved: on the one hand the detection and monitoring of recent and near-past changes of the Wilkins Ice Shelf (WIS) and its tributaries based on remote sensing. On the other hand, fracture mechanical modeling of different crack and calving scenarios based on the remote sensing datasets was carried out. The remote sensing products included the mapping and classification of surface structures of the WIS, which helped to reveal e.g., failure zones that weaken the ice shelf. Highly resolved multi-temporal ice flow velocities derived from various Synthetic Aperture Radar sensors revealed increased surface flow close to the ice front due to break-up events and mass loss between 1998 and 2009. Ice flow directions in 2008 at the ice bridge between Latady and Charcot Island illustrated the stress situation, which led to the complete failure of the ice bridge in April 2009. The flow fields derived in this project are a valuable product for complementing generalized, low resolution circum-antarctic flow fields. The ice thickness was sampled applying the hydrostatic equilibrium to freeboard heights based on ICESat GLAS (2003-2007) datasets. The dataset revealed a highly heterogeneous ice thickness over WIS, which led to buoyancy induced bending stresses and hence, fracture formation and break-up. In addition to the original proposal, the remote sensing group included bistatic TanDEM-X data in order to calculate surface elevations. The large advantage of TanDEM-X data is the minimized decorrelation between image acquisitions and the comprehensive spatial coverage. Future break-up events, e.g., between Latady Island and Lewis Snowfield might be caused by similar mechanisms leading to a comparable situation with an ice bridge as in 2008/09. The fracture mechanical analysis of different vertical crevasse scenarios revealed new results for various boundary conditions, material parameters, and geometries. Especially, the influences of the crack opening angle and Poisson’s ratio, ignored in previous studies, have to be pointed out. They revealed the necessity for a better determination of crack geometries and elastic material parameters. The analysis of frost wedging processes demonstrated a new simulation approach for the mechanism of disintegration events in austral autumn and winter seasons. The developed finite element simulation of the boundary value problem with subsequent evaluation of configurational forces represented a reliable method for the computation of stress intensity factors, even for complex geometries subjected to body loads, inhomogeneous material parameters and various crack face loadings. The method was able to reproduce values for stress intensity factors found by Rist (2002). The analysis of multiple interacting rifts propagating in horizontal direction could also be captured to a satisfying extend. In this simulation, velocity fields derived from remote sensing were used to compute the viscous surface stresses in the WIS. The measured velocity data were recomputed in terms of viscous volume forces for the analysis of the linear elastic fracture mechanical problem. Very promising results were achieved for the autumn 2008 crack evaluation on the WIS and two Pine Island Ice Shelf break up events. Further research on rift propagation over longer decades on the WIS will be limited by the amount of available input data. Either high-resolution velocity fields of large areas, obtained from several successive points in time can be processed, or velocity fields from ice dynamical simulations are unavoidable as input for the fracture mechanical simulation of rift propagation.
Projektbezogene Publikationen (Auswahl)
- 2010. Deformation and failure of the ice bridge on Wilkins Ice Shelf, Antarctica. Annals of Glaciology 51(55), 49-55
Humbert, A., Gross, D., Mueller, R., Braun, M., van de Wal, R.S.W., van den Broeke, M.R., Vaughan, D.G., van de Berg, W.J.
- 2011. Fracture Mechanical Analysis of Cracks in Ice Shelves using the Finite Element Method and Configurational Forces. Proc Appl Math Mech, 11(1), pp.169–170
Plate, C., Müller, R., Gross, D., Humbert, A.
- 2012. Analysis of Calving Events in Antarctic Ice Shelves Using Configurational Forces. Proc Appl Math Mech, 12(1), pp.155–156
Plate, C., Gross, D., Humbert, A., Müller, R.
- 2012. Evaluation of the criticality of cracks in ice shelves using finite element simulations. The Cryosphere, 6(5), pp.973–984
Plate, C., Müller, R., Humbert, A., Gross, D
(Siehe online unter https://doi.org/10.5194/tc-6-973-2012) - 2014. Finite Element Simulation of Frost Wedging in Ice Shelves. Proc Appl Math Mech, 14(1), pp.141–142
Plate, C., Müller R., Humbert, A., Gross, D.
(Siehe online unter https://doi.org/10.1002/pamm.201410058) - Changes in dynamics of glaciers and ice shelves derived from remote sensing. PhD Thesis, University of Erlangen, Institute of Geography. 2015
Rankl, M.
- Fracture Mechanical Analysis of Failure Processes in Antarctic Ice Shelves. PhD Thesis, TU Kaiserslautern, Department of Mechanical Engineering. 2015. - X, 149 S. - 978-3-942695-11-4 (Forschungsbericht / Technische Universität Kaiserslautern, Lehrstuhl für Technische Mechanik (11))
Plate, C.
