USAP-DC

This award supports a project to study the effect of liquid, intercrystalline water on the flow resistance of ice and the mobility of this water within ice. Water plays a central role in the flow of ice streams. It lubricates their bases and softens their margins, where flow speeds abruptly transition from rapid to slow. Within ice stream margins some ice is "temperate,” meaning that it is at its pressure-melting temperature with relatively thick water films at grain boundaries that significantly soften the ice. The amount of water in ice depends sensitively on its permeability, values of which are too poorly known to estimate the water contents of ice-stream shear margins or associated ice viscosities. This award stems from the NSF/GEO-UK NERC lead agency opportunity (NSF 14-118) and is a collaboration between Iowa State University and Oxford University in the United Kingdom. The experimental part of the project is executed at Iowa State University and is the focus herein because it has been supported by NSF. Two sets of experiments are conducted. In one set, a large ring-shear device is used to shear ice in confined compression and at its melting temperature to study the sensitivity of ice viscosity to water content. Ice is sheared at stresses and strain rates comparable to those of ice-stream margins, and water content is varied through twice the range explored in the only previous set of experiments that investigated ice softening by water. The second set of experiments required the design, fabrication, and testing of a laboratory ice permeameter that allows the permeability of temperate ice to be measured. Experiments are conducted to study the dependence of ice permeability on ice grain size and water content--the two dependencies required to model grain-scale water flow through temperate ice.

Person	Role
Iverson, Neal	Investigator and contact
Zoet, Lucas	Co-Investigator

Antarctic Glaciology

Award # 1643120

USAP-1643120_1

Data_Management_Plan.pdf

Repository	Title (link)	Format(s)	Status
USAP-DC	Softening of temperate ice by interstitial water	Excel	exists
USAP-DC	Ice permeameter experimental parameters and results	Excel	exists
USAP-DC	Tertiary creep rates if temperate ice containing greater than 0.7% liquid water	Microsoft Word (OpenXML)	exists

1. Adams, C. J. C., Iverson, N. R., Helanow, C., Zoet, L. K., & Bate, C. E. (2021). Softening of Temperate Ice by Interstitial Water. Frontiers in Earth Science, 9. (doi:10.3389/feart.2021.702761)
2. Fowler, J. R., & Iverson, N. R. (2022). A Permeameter for Temperate Ice: First Results on Permeability Sensitivity to Grain Size. Journal of Glaciology, 68(270), 764-774. (doi:10.1017/jog.2021.136)