Modelling the Seasonal Evolution of Supraglacial Hydrology with Natural Stream Development and Dynamic Topography

Abstract:

Meltwater inputs to the glacier hydrologic system exert a significant control on ice dynamics. During the melt season, surface meltwater flows across the ablation zone in both distributed sheet flow and through supraglacial streams. This meltwater is eventually either captured by moulins or crevasses and is routed to the subglacial drainage system, or flows off the margins and terminus to become proglacial runoff. The timing and spatial distribution of meltwater delivered to the subglacial system is controlled by the supraglacial drainage system. Since the volume and timing of meltwater delivered to the subglacial system modulates the effective pressure of the subglacial network, driving basal sliding and ice velocity, changes in supraglacial hydrology drive changes in ice flow speeds.

In order to quantify the control that supraglacial hydrology exerts on subglacial hydrology, we present a new supraglacial hydrology model that combines sheet flow with flow in supraglacial streams to accurately compute meltwater inputs to the subglacial system. We model the seasonal growth of supraglacial streams by the balance between downcutting due to heat dissipation and melting out due to ablation of the glacier surface, allowing the natural evolution of a dendritic system of supraglacial streams. We drive the sheet model with melt inputs computed using a distributed surface energy balance model, allowing spatially variable melt rates to change the surface slope and therefore alter the routing of runoff throughout the melt season. Meltwater is transferred from the sheet into adjacent streams, and from streams back to the sheet when streams overflow.

The primary model outputs are hydrographs of meltwater transferred to the subglacial system via moulins. Future work will use these supraglacial hydrology model outputs as inputs to a subglacial hydrology model to fully quantify the supraglacial drivers of the evolution of the subglacial drainage network. Such a fully coupled model would allow us to quantitatively predict the dynamic response of glaciers to changes in surface melt rates.