Title

Physical models for moulins: conduits to the subglacial world

Speaker

Kristin Poinar, Assistant Profesor, Department of Geology, University of Buffalo

Abstract

Glacier hydrology is a crucial factor in short-term (daily) and long-term (millennial) calculations of glacier mass loss into the ocean.  This is because meltwater influences the flow of glacier ice if it reaches the bed.   On the Greenland Ice Sheet, meltwater can run over bare ice, coalesce into streams, and pool into lakes on top of the ice.  From there, the water is often -- but not always -- directed into moulins, near-vertical shafts that connect to the bed of the ice sheet hundreds of meters below.  Each individual moulin drains a large catchment of surface meltwater -- typically 10-50 km2, similar to the 30 km2 Cascadilla Creek catchment -- and thus has a strong influence on local to regional basal hydrology.

I am developing two models centered around moulins. (1) The Moulin Shape (MouSh) model predicts the radial expansion and contraction of a moulin connected to a subglacial channel and fed by hourly varying meltwater inputs.  We find that the moulin size and shape changes daily by some 20% as it accommodates changing meltwater fluxes.  (2) The Fracture Sites model (FraSM) predicts the likelihood of moulin initiation in space and time.  We find that moulin formation sites are strongly tied to drainages of neighboring supraglacial lakes, and that new moulins can form ~3-5 km upstream of a draining lake.  A new, upstream moulin could then drain an upstream lake, potentially inciting a chain reaction of lake drainage / moulin formation that steps its way upstream toward the vulnerable interior of the ice sheet, where changes to basal hydrology would significantly speed ice flow.

Ultimately, the moulin models connect climate, in the form of surface meltwater, to sea-level rise, via basal hydrology and ice flow.  As Greenland's climate changes, we need to be able to predict the sea-level rise that is coming as a consequence.

Bio

Kristin Poinar is an Assistant Professor in the Department of Geology and the RENEW Institute at the University at Buffalo, New York.  She has worked on glaciers in Greenland, Antarctica, Washington State, and Alaska.  She uses physically-based models and remote sensing to help constrain the likely fate of glaciers in Earth’s uncertain future.