Hydraulic Permeability of Temperate Ice

Iowa State University, Ames IA

Investigators

Abstract

Water regulates the fast flow of marine-terminating glaciers and ice streams that affect sea-level rise. Specifically, the flow of glacial ice at depth in the margins of fast-flowing ice, where the ice is near its pressure melting point, depends on the fraction of liquid water stored in the network of veins at ice-grain boundaries. It is therefore critical to understand the permeability of these systems. The goal of this project is to better understand controls on ice permeability through tests on laboratory ice and glacier ice. Experiments with laboratory ice will inform on how grain size and water content affect permeability, while experiments with glacier ice will examine how deformation of the ice affects permeability. Results of these experiments will provide a better understanding of permeability of ice near its pressure melting point as a function of grain size, water content, and deformation. The experiments are not intended to simulate interstitial water flow in a glacier. This project includes graduate and undergraduate participation and seeks to include a participant from the PolarTREC program to engage students in K-12 classrooms. This project will measure for the first time the permeability of temperate ice as a function of its grain size, water content, and foliation. The team will use a falling-head permeameter designed and tested for this application. A disk of ice, 140 mm in diameter and up to 70 mm thick, is kept under pressure and at the pressure-melting temperature while chilled water transiently flows through the disk under a head that is allowed to decrease with time. The rate of head decrease provides the permeability value. Different water contents will be achieved by varying the salinity of the ice and will be measured with a calorimetric method used successfully in prior ice-deformation experiments. Chilled water introduced to ice disks will contain fluorescein dye to allow flow networks to be studied in thin-sections after experiments. Experiments with glacier ice, collected from shallow cores at Athabasca Glacier, Alberta, will evaluate the effect of ice foliation style and orientation on permeability. These measurements may also point to differences between permeability of lab-made and glacier ice that are unrelated to structural anisotropy. Results of these experiments will provide the first test of permeability models based on Poiseuille flow of water though idealized vein networks. These untested models are the primary basis for estimating ice permeability in glacier flow models. New empirically-grounded permeability models resulting from this project will allow the water content of temperate portions of ice-stream shear margins to be estimated, thereby improving models of ice softening by water and associated ice-flow kinematics in shear margins. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.