glaciology, fluid dynamics, applied mathematics
Office: EOS-South 356 Phone: 604-822-6482 Office2: ESB 1007 Phone2: 604-822-5891
MPhys (Physics), Oxford University, 1998
DPhil (Applied Mathematics), Oxford University, 2002
Postdoctoral Fellow (Earth and Ocean Sciences), UBC, 2002-2005
Research Associate (Earth and Ocean Sciences), UBC, 2005-2007
Assistant Professor (Tier 2 Canada Research Chair) , UBC 2007-2012
Associate Professor (Tier 2 Canada Research Chair), UBC, 2012-present
About my work
I am a mathematical / physical glaciologist whose main interest is the dynamics of ice sheets, such as those found in Antarctica and Greenland. My work focuses on fundamental aspects of ice sheet dynamics. Some of the questions that motivate my work are: what drove the retreat of the West Antarctic Ice Sheet following the Last Glacial Maximum? How can large ice sheets such as the Laurentide disintegrate as quickly as they are known to have done? What caused the massive discharges of sediment-laden ice known as Heinrich events? What is the likely future behaviour of West Antarctica and Greenland?
In order to answer these questions, the flow behaviour of ice sheets must be understood. Ice sheets accumulate snow in their interior where surface elevations are high. They lose mass at their margins, either through melting or through calving. Ice is transported between these regions by ice flow, and generally, the faster the rate of flow, the greater the rate of mass loss. Much of my work has concentrated on processes that can speed up ice flow and can potentially contribute to the rapid and irreversible disintegration of ice sheets.
Mountain glaciers also motivate much of my work. Glaciers do a number of fascinating things that are interesting to theorize about and even more fascinating to observe directly. I am particularly interested in glacier surges, where a glacier switches from a slow to a fast flow state and then continues to flow fast even though it thins and the stresses acting on it become smaller, as well as the flow of melt water under glaciers and the dynamics of lakes dammed by glacier ice.
Much of my work, especially more recently, has been done in collaboration with students, postdocs and collaborators at UBC, Simon Fraser University and elsewhere.
A word about mathematics...
Some of the methods I use are mathematical. In the mathematical sphere, I have a particular interest in partial differential equations, free boundary problems, applied complex analysis, nonlinear dynamics, perturbation methods and scientific computing, and in fluid dynamics in general.
A word about field work...
I also conduct field work on glacier dynamics. This is motivated in part because mountain glaciers are a fascinating natural laboratory in which to confront theoretical ideas with reality. Mountain glaciers also allow processes that are likely to affect ice sheets to be observing in a logistically simpler setting, which often allows more detailed data to be collected. In collaboriation with Gwenn Flowers at Simon Fraser University I have been developing a project in the St Elias Mountains, Yukon Territory, aimed at understanding the dynamics of a small valley glacier.
Prospective graduate and undergraduate research students
I currently have three graduate students and one co-supervised student outside of UBC, several of whom are in the later stages of their PhDs. I am currently looking for one or two new graduate students to work on the evolution of subglacial drainage systems or outburst floods from glacial lakes, ideally combining observational work already underway with modelling. I will post any openings I have for undergraduate assistans.
The Canadian funding system makes supporting graduate students financially difficult, so external funding through NSERC or similar sources is a bonus. Note that NSERC funding applications for graduate studies are ideally submitted in October of your last year as an undergraduate (you have to be Canadian or a permanent resident to qualify for most NSERC programs). In addition, there are internal scholarships at UBC; these are awarded competitively so a strong performance in your most recent degree is essential, as is an early application to the EOS graduate program (for a scholarship application to get full consideration, your application to EOS usually has to be complete with references by mid-February).
That said, the most important qualities I look for in a graduate student are inquisitiveness, a willingness to explore (and therefore to admit that there is something still to be learnt!) and initiative (e.g., can you come up with a research idea of your own? Find something out about the field you want to study? Or maybe fix a propane-powered pump on a glacier with whatever tools and spare parts are on hand?).
For the theoretical side, strong mathematics and physics skills are also essential. My publications page gives a good impression of the type of work you may find yourself involved in if you are interested in taking that route, and supervision through the Institute of Applied Mathematics is possible.
For the fieldwork-oriented side of research in my group, experience with instrumentation, experimental work and / or practical engineering are ideal, as are strong quantitative skills in the physical sciences. The ultimate aim is to generate hig-quality data that can be used to test and further develop quantitative models of glaciological phenomena. Also essential is a willingness to spend weeks living and working in a cold and often wet (though arguably beautiful) place while most likely never getting to climb any of the surrounding peaks. The reality is that fieldwork consists of often repetitive tasks that require a lot of attention to detail under physically demanding conditions. Basic outdoor and mountaineering skills (glacier travel, backcountry travel) are also very useful, but bear in mind that we don't go into the field in order to climb! And above all, common sense and an ability to get on with others are great assets in the field.
Marine ice sheet dynamics
The Western half of Antarctica contains enough ice to raise sea levels by about 6 m. It also rests on bedrock below sea level, which leaves it vulnerable to irreversible shrinkage if the rate of ice flow from the grounded ice sheet into the surrounding ice shelves were to increase, causing partial flotation and hence retreat of the grounded ice sheet. Key to the behaviour of marine ice sheet is that they are susceptible to such irreversible shrinkage if its grounding line rests on an upward-sloping bed, because a small retreat in grounding line position should lead to increased discharge, which leads to further retreat and so on.
This positive feedback occurs because discharge through the grounding line - where grounded ice lifts off the bed to become an ice shelf - generally increases with water depth there. This is something I studied in detail three theoretical papers (Marine ice sheet dynamics. Part 1: the case of rapid sliding, Marine ice sheet dynamics. Part 2: a Stokes flow contact problem, Marine ice sheet stability). The general idea behind the positive feedback had been around since the 1970s, but had somehow remained contentious. I got interested in the problem because there was a neat way of using boundary layer theory to show that the positive feedback is indeed mathematically robust,, at least in one horizontal dimension. Another paper on the subject (Ice sheet grounding line dynamics: steady states, stability and hysteresis) explores the implications of this for large-scale ice sheet dynamics, and demonstrates that the behaviour of West Antarctica can be understood in simple terms as a hysteresis loop driven for instance by sea level changes, providing a teleconnection to ice sheets in the Northern Hemisphere: a transition to a large ice sheet in West Antarctica occurs when sea levels drop below a critical level, while the reverse transition occurs when they rise again beyond a second critical level that is higher than the first. Such variations in sea level can of course be driven by the growth and shrinkage of the Laurentide or Fennoscandian ice sheets.
The main outstanding issues in marine ice sheet dynamics are to understand the effect of lateral confinement of ice shelves on the dynamics of the grounding line (which can suppress the positive feedback) and to incorporate ice stream dynamics (see below) into the picture. The activation of ice streams could cause a marine ice sheet to destabilize. Conversely, a marine ice sheet can potentially be stabilized if it is fringed by a confined ice shelf, as is the case in West Antarctica. Recent work (Grounding line movement and ice shelf buttressing in marine ice sheets) shows that the precise geometry of the shelf becomes important if stabilization is to occur, a point also made but many others who have made interesting numerical progress in this area recently. In order to understand the evolution of ice shelf geometry through calving and basal melting, a better understanding of ice shelf-ocean interactions and of fracturing processes will be required. Recent observations of ocean warming and ice shelf collapse around Antarctica make this a topic of pressing concern.
Richard Hindmarsh, Frank Pattyn and I devised an early intercomparison exercise aimed at exploiting advances in marine ice sheet modelling. The results of this intercomparison are written up in the following paper. Full details can also be found on the MISMIP website. The intercomparison is now into its third version, with a new generation of organizers.
Ice stream dynamics and glacier sliding
Ice streams are the main arteries through which ice can flow rapidly in an ice sheet. They are narrow bands of rapidly flowing ice in an ice sheet whose high velocities are caused by sliding at the bed, and this sliding motion is often unsteady on a wide range of timescales, to the extent that ice streams can shut down completely and subsequently re-activate. Much of the physics driving ice stream flow is poorly understood.
Closely related to ice stream motion is the broader field of fast glacier flow. Glacier flow is a combination of viscous deformation of the ice and slip at the contact between ice and bed. While there are unresolved questions about the viscous creep of ice, we know much less about sliding than we do about creep. This is partly because sliding happens in a difficult-to-access part of glaciers, so there is a relative scarcity of data. More important, however, is that there are more dynamical variables involved in sliding than in creep - apart from ice temperature, we also need to know about water pressure at the base of the ice (which affects the strength of ice-bed contact) and possibly about evolving mechanical properties of the underlying substrate. Sliding at the bed is also a process that can speed up ice motion much more abruptly than shearing of the overlying ice, so improved models of sliding would be helpful in understanding rapid changes in glaciers and ice sheets.
My work has focused on
- using first-principles physics to derive friction parameterizations (e.g. The effect of cavitation on glacier sliding, Bed topography and surges in ice streams)
- incorporating modern understanding of sliding into large-scale ice sheet models (A variational appraoch to ice-stream flow, Variational methods for glacier flow over plastic beds)
- Higher order glacier flow models as means of representing fast and slow sliding in a single mathematical description (Thin film flows with wall slip: an asymptotic analysis of higher order glacier flow models,Coulomb friction and other sliding laws in a higher order glacier flow model)
- improving models of subglacial meltwater drainage, and relating these to temporal changes in ice stream geometry and flow velocities (see below)
- Understanding the thermomechanics of ice stream shear margins, and tracking them as an internal free boundary in ice sheets (On the mechanics of ice-stream shear margins, Thermally driven migration of ice-stream shear margin)
- Thermomechanical and hydraulic feedbacks driving glacier and ice stream surges (Thermally driven surging of ice streams)
The ultimate goal of this work is to explain the spatial patterning and likely oscillatory behaviour of ice streams, and to incorporate ice stream physics into predictive ice sheet models. I also have an observational angle to my work on subglacial sliding and glacier hydrology: our field program is providing data for testing of some of our theoretical work (see below)
The sliding of glaciers and ice sheets is critically dependent on the pressure exerted by melt water flowing at the base of the glacier on the ice above. This water pressure is controlled by the configuration of drainage conduits at the base of the ice as well as on the nature of water input into the drainage system. This is a focus of ongoing work in my group (Drainage through subglacial water sheets, ice sheet acceleartion driven by melt supply variability, a distributed drainage model accounting for partial filling of cavities as well as ice flotation, the same but with channels); in addition to a focus on interactions between drainage and ice flow, I am also interested in outburst floods from glacier-dammed lakes (so-called jokulhlaups). Part of my field research targets a glacier-margininal lake dammed by the Kaskawulsh Glacier in the St Elias.
Glaciology is a wonderfully active research area. There is a great variety of complementary approaches, of which I am engaged in two (field studies and modelling). I am happy to say that mathematically-oriented researchers do appear to be welcome in the field, which is generally very collegial. I have collaborated (and in many cases still do!) with a number of people outside of UBC, including Tim Creyts, Gwenn Flowers, Dan Goldberg, Ian Hewitt, Richard Hindmarsh, Alex Jarosch, Frank Pattyn, Eli Tziperman and Mauro Werder.
My current graduate students at UBC are Marianne Haseloff, Camilo Rada and Arran Whiteford, and I also work with Alex Robel at Harvard and Elisa Mantelli in Torino.