Migrating petal-shape lakes on the George VI Ice Shelf: A new kinematic wave?

The George VI Ice Shelf supports supraglacial meltwater lakes exhibiting a variety of morphologies including one represented by a strikingly uniform series of petal-shaped lakes aligned en echelon along the boundary between the ice shelf and Alexander Island (as first described by Reynolds, 1981). What sets these lakes apart from others in the interior of the ice shelf is the fact that they propagate along the boundary from distinct source points along the boundary toward sinks where they disappear or interleave with other features. Propagation velocity differs in both direction and speed from ice flow. We thus hypothesize that the petal-shaped lakes are a form of kinematic wave. Our observations of migrating petal-shaped lakes are intended to document their morphology and establish a quantitative measure of their propagation. The two main data sources are repeat Landsat satellite imagery (which we assembled into time-lapse animations that show the migration along the boundary) and surface elevation from the ICEsat satellite laser altimeter. The petal-shaped lakes seem to originate at two points on the ice-shelf boundary where ice flow is directed perpendicular to the boundary, i.e., stagnation points. The lakes then propagate away from these points toward two types of sinks. One type, located between two source points, is where the lakes collide and change morphology. The other type, located at distal ends of the boundary where ice flow is less compressive into the boundary, the lakes cease to be visible. We have observed propagation speeds of the lakes ranging from less than 100 m/a to above 700 m/a. Presently, we do not know the mechanism for the formation and propagation of these lakes; however, we speculate that they are associated with pressure waves where the ice shelf compresses against the coast of Alexander Island.