# NEW PAPER OUT ON SUBGLACIAL SHEAR SIMULATION

Today, [1]Indraneel Kasmalkar had his paper published in [2]Journal of
Geophysical Research: Earth Surface. Congratulations Neel! He used my software
[3]sphere, and sheared a granular assembledge with a non-trivial forcing in
order to learn more about subglacial sediment behavior.

Abstract

   Shear Variation at the Ice-Till Interface Changes the Spatial Distribution
   of Till Porosity and Meltwater Drainage

   Indraneel Kasmalkar(1), Anders Damsgaard(2), Liran Goren(3), Jenny Suckale
   (1,4,5)

   1: Department of Computational and Mathematical Engineering, Stanford
   University, CA, USA
   2: Department of Geoscience, Aarhus University, Denmark
   3: Department of Earth and Environmental Sciences, Ben-Gurion University of
   the Negev, Beer-Sheva, Israel
   4: Department of Geophysics, Stanford University, CA, USA
   5: Department of Civil and Environmental Engineering, Stanford University,
   CA, USA

   Plain-language summary:
   The ice at the base of certain glaciers moves over soft sediments that
   route meltwater through the pore spaces in between the sediment grains. The
   ice shears the sediment, but it is not clear if this slow shearing is
   capable of changing the structure or volume of the pore space, or the path
   of the meltwater that flows through the sediment. To study the relations
   between the shearing of the sediment and the changes in its pore space, we
   use computer simulations that portray the sediment as a collection of
   closely packed spherical grains, where the pores are filled with meltwater.
   To shear the simulated sediment, the grains at the top are pushed with
   fixed speeds in the horizontal direction. Despite the slow shear, which is
   generally thought of as having no effect on pore space, our results show
   that shearing changes the sizes of the pores in between the grains, where
   large pores are formed near the top of the sediment layer. If the grains at
   the top are pushed with uneven speeds, then the largest pores are formed in
   the areas where grain speeds vary the most. We show that the exchange of
   meltwater between neighboring pores is faster than the movement of the
   grains, indicating that the meltwater can adjust quickly to changing pore
   space.

   Abstract:
   Many subglacial environments consist of a fine-grained, deformable sediment
   bed, known as till, hosting an active hydrological system that routes
   meltwater. Observations show that the till undergoes substantial shear
   deformation as a result of the motion of the overlying ice. The deformation
   of the till, coupled with the dynamics of the hydrological system, is
   further affected by the substantial strain rate variability in subglacial
   conditions resulting from spatial heterogeneity at the bed. However, it is
   not clear if the relatively low magnitudes of strain rates affect the bed
   structure or its hydrology. We study how laterally varying shear along the
   ice-bed interface alters sediment porosity and affects the flux of
   meltwater through the pore spaces. We use a discrete element model
   consisting of a collection of spherical, elasto-frictional grains with
   water-saturated pore spaces to simulate the deformation of the granular
   bed. Our results show that a deforming granular layer exhibits substantial
   spatial variability in porosity in the pseudo-static shear regime, where
   shear strain rates are relatively low. In particular, laterally varying
   shear at the shearing interface creates a narrow zone of elevated porosity
   which has increased susceptibility to plastic failure. Despite the changes
   in porosity, our analysis suggests that the pore pressure equilibrates
   near-instantaneously relative to the deformation at critical state,
   inhibiting potential strain rate dependence of the deformation caused by
   bed hardening or weakening resulting from pore pressure changes. We relate
   shear variation to porosity evolution and drainage element formation in
   actively deforming subglacial tills.

Links and references:

 • [4]Publication on journal webpage (closed access)
 • [5]Preprint PDF
 • [6]Simulation software
 • [7]Visualization of example simulation


References:

[1] mailto:[email protected]
[2] https://agupubs.onlinelibrary.wiley.com/journal/19422466
[3] https://src.adamsgaard.dk/sphere
[4] https://doi.org/10.1029/2021JF006460
[5] https://adamsgaard.dk/papers/Kasmalkar%20et%20al%202021%20Shear%20variation%20at%20the%20ice-till%20interface%20changes%20the%20spatial%20distribution%20of%20till%20porosity%20and%20meltwater%20drainage.pdf
[6] https://src.adamsgaard.dk/sphere
[7] https://adamsgaard.dk/video/neel.mp4

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