Self-organized criticality and formation of supra-glacial lakes and river networks:
A vital issue in the effort to predict and understand future and past ice sheet evolution in warming (and cooling) climate conditions is the need to predict ablation of the ice sheet surface. Critically, ice sheet ablation is not just a static process whereby water slowly accumulates on the ice sheet surface (by melting) and is then steadily transported towards the ice sheet margins. Instead, high resolution satellite imagery has begun to reveal the complexity of surface processes; the transport of water is a complex, dynamic process and the meltwater may flow in thin sheets over the ice sheet, become channelized and form rivers (or even river networks) on the ice sheet’s surface and/or pond in surface nooks and depressions in the ice sheet surface. We have been developing models of the ice surface erosion process. Amazingly, the physics that describes the formation of river networks on the surface of ice sheets turns out to be similar to that used to describe land-river networks. One big difference however, is that land-river networks have evolved for a long period of time and are close to “steady-state”. On the surface of ice sheets, the melt season where patterns form is finite so these drainage networks are always “immature”. The animation below shows how a river network on the surface of an ice sheet might evolve. Early on, rivers (black lines) are small and terminate in lakes (blue circles). As the melt season progresses, lakes fill and overtop and river erode deeper into the ice and form connections between lakes. If the melt season were to progress long enough, we predict that all lakes would eventually connect to the river network. This simulation, however, ignores the fact that some lakes drain when fractures form allowing water to drain all the way to the bed. This phenomena is not included in the model. Yet.
Energy balance models of the Greenland and Antarctic ice sheets:
I am collaborating the Dr. Doug MacAyeal (University of Chicago) and Mac Cathles (a postdoc at the University of Michigan) to develop energy balance models of the thermodynamic processes that lead to the creation and subsequent drainage of large surface lakes on the Greenland Ice Sheet. These not only contribute to the mass balance of the ice sheet, we now know that these lakes also have the potential to drain through more than one kilometer of ice where it lubricates the bed, causing an increase in the sea-ward discharge of the ice sheet. We have also been funded by NASA to develop surface energy balance models of the Greenland Ice Sheet and couple these models with supra-glacial transport models to study how melt ponds and streams will evolve over time.