Abstract

Sand Dunes and Their Interactions

Dunes are coherent sedimentary structures which arise spontaneously due to the dynamical interplay between granular matter and the flow of the overlaying fluid. Natural dunes rarely occur in isolation, but usually form vast dune fields. As of now, the mechanisms which regulate the large scale organisation of such dune fields are poorly understood. In particular it is unclear if the dune configurations we observe are stable or transient. In this talk I will discuss some recent experimental results on quasi-2D dune corridors. In our experiments dune corridors are robust and their structure appears to be stabilised by long-range dune-dune interactions. Indeed, by altering the flow, aqueous dunes strongly affect the shape and the migration rate of their downstream neighbours which leads to an effective dune-dune repulsion. In my presentation I shall discuss the repulsion mechanism in detail and explore its consequences for the system-level dynamics.

Glacial Squeegee: Tidal Effects on Subglacial Hydrology

Glacier speed is sensitive to fluctuations in subglacial water pressure. For marine ice sheets, the tidal cycle is linked to the upstream pressure fluctuations as water enters and exits the subglacial environment across the grounding line. I will discuss a model of grounding line migration based on the propagation of fluids under elastic sheets. Travelling wave solutions exist for the up- and downstream migration. Differences in the dynamical processes governing the fluid flow at a small scale leads to an asymmetry in grounding line migration on a much larger scale. I will discuss the effects of this in relation to observations from the Rutford Ice Stream.