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A boundary layer model for ice stream margins

Written by Olivier Gagliardini on .

 

haseloff

The majority of Antarctic ice is discharged via long and narrow fast-flowing ice streams. At ice stream margins, the rapid transition from the vertical shearing flow in the ice ridges surrounding the stream to a rapidly sliding plug flow in the stream itself leads to high stress concentrations and a velocity field whose form is non-trivial to determine. In this paper, we develop a boundary layer theory for this narrow region separating a lubrication-type ice ridge flow and a membrane-type ice stream flow. This allows us to derive jump conditions for the outer models describing ridge and stream self-consistently. Much of our focus is, however, on determining the velocity and shear heating fields in the margin itself. Ice stream margins have been observed to change position over time, with potentially significant implications for ice stream discharge. Our boundary layer model allows us to extend previous work that has determined rates of margin migration from a balance between shear heating in the margin and the cooling effect of margin migration into the colder ice of the surrounding ice ridge. Solving for the transverse velocity field in the margin allows us to include the effect of advection due to lateral inflow of ice from the ridge on margin migration, and we demonstrate that this reduces the rate of margin migration, as previously speculated.

Haseloff M., C. Schoof and O. Gagliardini, 2015. A boundary layer model for ice stream margins. Journal of Fluid Mechanics, 781, 353-387, doi:10.1017/jfm.2015.503.

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Two Elmer/Ice courses this fall

Written by Olivier Gagliardini on .

- A 2-days beginner Elmer/Ice course will take place the 2nd and 3rd of November 2015 at the Niels Bohr Institute (Copenhagen, Danmark), the week after the North Branch IGS meeting. This 2-days course is dedicated to students or researchers aiming to start working with Elmer/Ice. It is sponsored by the Center for Ice and Climate at NBI, CSCLGGE and the Labex OSUG@2020. To register, send an email to Olivier Gagliardini. The number of places is limited to 20, and will be given on the basis of the first registered, first served. There will be no registration fees, but students will have to take care of their lodging and attend the course with their own laptop. More information will be given later on the Elmer/Ice website.

- A 3-days advanced Elmer/Ice course will take place the 30th November, 1st and 2nd of December 2015 at LGGE (Grenoble, France). This 3-days course is dedicated to students or researchers having already an experience using Elmer/Ice. It is sponsored by LGGE, CSC and the Labex OSUG@2020. To register, send an email to Olivier Gagliardini. The number of places is limited to 20, and will be given on the basis of the first registered, first served. There will be no registration fees, but students will have to take care of their lodging and attend the course with their own laptop. More information will be given later on the Elmer/Ice website.

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Thermal change of the Taconnaz avalanching glacier

Written by Olivier Gagliardini on .

taconnazHigh-elevation glaciers covered by cold firn are undergoing substantial warming in response to ongoing climate change. This warming is affecting the ice/rock interface temperature, the primary driver of avalanching glacier instability on steep slopes. Prediction of future potential instability therefore requires appropriate modeling of the thermal evolution of these glaciers. Application of a state-of-the-art model to a glacier in the French Alps (Taconnaz) has provided the first evaluation of the temperature evolution of a cold hanging glacier through this century. Our observations and three-dimensional modeling of the glacier response (velocity, thickness, temperature, density, and water content) to climate change indicate that Taconnaz glacier will become temperate and potentially unstable over a large area by the end of the 21st century. The risk induced by this glacier hazard is high for the populated region below and makes observation and modeling of such glaciers a priority.

Gilbert A., C. Vincent, O. Gagliardini, J. Krug and E. Berthier, 2015. Assessment of thermal change in cold avalanching glaciers in relation to climate warming, Geophys. Res. Lett., 42, doi:10.1002/2015GL064838.

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