Temperature dependence of ice-on-rock friction at realistic glacier conditions

Abstract

One contribution of 11 to a theme issue 'Microdynamics of ice'. Using a new biaxial friction apparatus, we conducted experiments of ice-on-rock friction in order to better understand basal sliding of glaciers and ice streams. A series of velocity-stepping and slidehold-slide tests were conducted to measure friction and healing at temperatures between −20°C and melting. Experimental conditions in this study are comparable to subglacial temperatures, sliding rates and effective pressures of Antarctic ice streams and other glaciers, with load-point velocities ranging from 0.5 to 100 µm s −1 and normal stress σ n = 100 kPa. In this range of conditions, temperature dependences of both steady-state friction and frictional healing are considerable. The friction increases linearly with decreasing temperature (temperature weakening) from μ = 0.52 at −20°C to μ = 0.02 at melting. Frictional healing increases and velocity dependence shifts from velocity-strengthening to velocityweakening behaviour with decreasing temperature. Our results indicate that the strength and stability of glaciers and ice streams may change considerably over the range of temperatures typically found at the ice-bed interface. Subject Areas: glaciology KeywordsThis article is part of the themed issue 'Microdynamics of ice'.

Slow‐slip events on the Whillans Ice Plain, Antarctica, described using rate‐and‐state friction as an ice stream sliding law

“…In this setting, friction transitions from rate‐weakening to rate‐strengthening behavior as temperatures rise above −15°C. This transition may occur due to the onset of pressure melting at highly stressed microscopic asperity contacts, although further work is necessary to confirm this hypothesis [ McCarthy et al , ]. This mechanism for rate‐weakening friction seems unlikely to occur on the WIP, however, due to the WIP having basal temperature near the pressure melting point [ Kamb , ].…”

“…We use frictional parameters (Table ) in our simulations that are consistent with experimentally determined values [ Thomason and Iverson , ; Rathbun et al , ; Rathbun and Marone , ; Schulson and Fortt , ; Zoet et al , ; McCarthy et al , ]. We use a = 0.02 and b − a = 0.005 in rate‐weakening regions.…”

“…This framework has been shown to encompass a wide range of different physical processes across a diversity of systems, both natural and experimental. With respect to glaciology, these include experimental studies of ice sliding against ice [ Schulson and Fortt , ], ice sliding against rock [ Zoet et al , ; McCarthy et al , , ], sliding within a layer of glacial till [ Thomason and Iverson , ; Rathbun et al , ; Rathbun and Marone , ; Iverson , ], and ice sliding against a rigid‐stepped [ Zoet and Iverson , ] and a rigid sinusoidal [ Zoet and Iverson , ] bed. We discuss the physical processes that give rise to rate‐and‐state friction in greater detail in section 3.1.1.…”

Ice microstructures and microdynamics

“…Three papers in this theme issue address friction. McCarthy et al [9] use an empirical approach of rate and state friction, with parameters derived from laboratory ice-rock friction studies to arrive at a constitutive relation applicable to glacier motion over bedrock. Sammonds et al [10] test a microphysicsand micromechanics-based constitutive friction law against intermediate-scale experiments on saline ice floes conducted in an environmental basin.…”

Microdynamics of ice

“…Sammonds et al [6] discuss this in the context of experiments on saline ice floe friction and the scaling involved. McCarthy et al [7] examine ice-on-rock friction for realistic glacier conditions, while Seymour-Pierce et al [8] discuss the context of microstructures in relation to friction in winter sports. The next group of papers concerns sea ice.…”