Supervisors

Dr John Hiemstra, Glaciology Group, School of the Environment and Society

Professor Mike Webster, Computational Rheology Group, EPSRC Portfolio Partnership in Complex Fluids, School of Engineering

Project and aims

Accurate prediction of future responses of glaciers and ice sheets to climate change hinges on a thorough understanding of processes operating at the glacier-bed interface. Unfortunately, the subglacial environment is poorly accessible, which means that the development of our knowledge so far has relied heavily on inferences from the glacial sedimentary palaeo-record. To date, we know that beds of many glaciers and ice sheets are not rigid, passive substrata but are actually part of a coupled ice-bed system. We know that deformation or flow of unlithified, heterogeneous subglacial sediments (basal tills) and the drainage patterns of subglacial meltwater play a crucial role in the motion of glaciers (see e.g. Boulton, 1986; Piotrowski et al., 2004; Evans and Hiemstra, 2005; Evans et al., 2006).

The aim of this project is to increase our understanding of the subglacial environment through a rheological modelling study of different glacier substrata. In terms of their rheology, basal tills may be considered as complex fluids whose properties lie between the familiar extremes of liquids and solids. For small strains, tills behave as elastic solids, whilst at large stress, above a yield stress, tills move like a liquid (cf. Hindmarsh, 1998; Iverson, 1999). A key aspect of the study is to investigate alternative continuum till modelling, covering compressible viscoplastic (yield stress), viscoelastic and visco-elasto-plastic (yield stress and memory) idealisations. In particular, visco-elasto-plastic till behaviour will be addressed through a combination of theoretical backgrounds, calling upon hybrid viscoelastic models (i.e. White-Metzner and Phan-Thien-Tanner) and visco-elasto-plastic models (Saramito).

The student will collaborate with, and receive supervision from Professor Mike Webster (Computational Rheology Group, EPSRC Portfolio Partnership in Complex Fluids, School of Engineering) and Dr. John Hiemstra (Glaciology Group, School of the Environment and Society) and will be based at Swansea University.

Applicant requirements

We are looking for a candidate with at least an upper second class degree in a scientific or engineering discipline, excellent numerical skills and a strong interest in the glacial environment. An MSc in a related subject, such as fluid flow, numerical methods, or physical processes would be advantageous. The successful candidate is encouraged to direct the research within the broad remit described above and is expected to present at international conferences. For further details, please contact Prof. Mike Webster (m.f.webster@swansea.ac.uk) or Dr John Hiemstra (j.hiemstra@swansea.ac.uk). Applications should be made through the Swansea University Admissions Office, or online via http://www.swan.ac.uk/postgraduate/apply/

Funding

This project is eligible for competitive funding through NERC studentships awarded to the Department. Other funding opportunities are available and self-funded students are always welcome. Contact your potential supervisor for advice and details of how to apply. The closing date for applications to NERC studentships is 18 March 2011.

References

Aguayo, J.P., Tamaddon-Jahromi, H.R. and Webster, M.F. 2008. Excess pressure-drop estimation in contraction flows for strain-hardening fluids. J. Non-Newt. Fluid Mech. 153, 186-205.
Belblidia, F., Haroon, T. and Webster, M.F. 2008. The dynamics of compressible Herschel-Bulkley fluids in die-swell flows. The first African InterQuadrennial ICF conference (AIQ-ICF), Algeria, June 2008 (Sep 2008, extended version paper in press).
Boulton, G.S., 1986: A paradigm shift in glaciology? Nature 322, 18.
Evans, D.J.A. and Hiemstra, J.F., 2005: Till deposition by glacier sub-marginal, incremental thickening. Earth Surface Processes and Landforms 30(13), 1633-1662.
Evans, D.J.A., Phillips, E.R., Hiemstra, J.F. and Auton, C.A., 2006: Subglacial till: formation, sedimentary characteristics and classification. Earth Science Reviews 78(1-2), 115-176.
Hindmarsh, R.C.A. 1998. The stability of a viscous till sheet coupled with ice flow, considered at wavelengths less than the ice thickness. Journal of Glaciology 44(147), 285-292.
Iverson, N.R., 1999. Coupling between a glacier and a soft bed: II. Model results. Journal of Glaciology 45(149), 41-53.
Keshtiban, I.J., Puangkird, B., Tamaddon-Jahromi, H.R. and Webster, M.F. 2008. Generalised Approach for Transient Computation of Start-up Pressure-driven Viscoelastic Flow. J. Non-Newt. Fluid Mech. 151, 2-20.
Piotrowski, J.A., Larsen, N.J. and Junge, F.W., 2004: Reflections on soft subglacial beds as a mosaic of deforming and stable spots. Quaternary ScienceReviews 23, 993–1000.
Webster, M.F., Tamaddon-Jahromi, H.R. and Belblidia, F. 2008. Computational Rheology, UNESCO, Rheology, 1-40 (Research Monograph).
Walters, K., Webster M.F. and Tamaddon-Jahromi, H.R. 2008. The numerical simulation of some contraction flows of highly elastic liquids and their impact on the relevance of the Couette correction in extensional rheology. Chem. Eng. Sci. (extended version SASOR2, Cape Town, 1-6, 2008, CSR 12-2008).
Walters, K., Webster, M.F. and Tamaddon-Jahromi, H.R. The White-Metzner model – then and now. Goa Conf. 2009, Jan 2009.