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1 <p>Today, <a href="mailto:ineel@alumni.stanford.edu">Indraneel 2 Kasmalkar</a> had his paper published in <a 3 href="https://agupubs.onlinelibrary.wiley.com/journal/19422466">Journal of 4 Geophysical Research: Earth Surface</a>. Congratulations Neel! He used 5 my software <a href="https://src.adamsgaard.dk/sphere">sphere</a>, and 6 sheared a granular assembledge with a non-trivial forcing in order to 7 learn more about subglacial sediment behavior.</p> 8 9 <p>Here's an example visualization from the study:</p> 10 <center> 11 <video poster="video/neel.jpg" 12 controls preload="none" class="mediaframe"> 13 <source src="video/neel.mp4" type="video/mp4"> 14 <a href="video/neel.mp4">Link</a> 15 </video> 16 </center> 17 18 <h2>Abstract</h2> 19 <blockquote> 20 <b>Shear Variation at the Ice-Till Interface Changes the Spatial 21 Distribution of Till Porosity and Meltwater Drainage</b> 22 <br><br> 23 Indraneel Kasmalkar(1), Anders Damsgaard(2), Liran Goren(3), Jenny Suckale(1,4,5) 24 <br><br> 25 1: Department of Computational and Mathematical Engineering, Stanford University, CA, USA 26 <br> 27 2: Department of Geoscience, Aarhus University, Denmark 28 <br> 29 3: Department of Earth and Environmental Sciences, Ben-Gurion University of the Negev, Beer-Sheva, Israel 30 <br> 31 4: Department of Geophysics, Stanford University, CA, USA 32 <br> 33 5: Department of Civil and Environmental Engineering, Stanford University, CA, USA 34 <br><br> 35 Plain-language summary:<br> 36 The ice at the base of certain glaciers moves over soft sediments 37 that route meltwater through the pore spaces in between the sediment 38 grains. The ice shears the sediment, but it is not clear if this slow 39 shearing is capable of changing the structure or volume of the pore space, 40 or the path of the meltwater that flows through the sediment. To study 41 the relations between the shearing of the sediment and the changes in its 42 pore space, we use computer simulations that portray the sediment as a 43 collection of closely packed spherical grains, where the pores are filled 44 with meltwater. To shear the simulated sediment, the grains at the top 45 are pushed with fixed speeds in the horizontal direction. Despite the 46 slow shear, which is generally thought of as having no effect on pore 47 space, our results show that shearing changes the sizes of the pores 48 in between the grains, where large pores are formed near the top of the 49 sediment layer. If the grains at the top are pushed with uneven speeds, 50 then the largest pores are formed in the areas where grain speeds vary 51 the most. We show that the exchange of meltwater between neighboring 52 pores is faster than the movement of the grains, indicating that the 53 meltwater can adjust quickly to changing pore space. 54 <br><br> 55 Abstract:<br> 56 Many subglacial environments consist of a fine-grained, deformable 57 sediment bed, known as till, hosting an active hydrological system that 58 routes meltwater. Observations show that the till undergoes substantial 59 shear deformation as a result of the motion of the overlying ice. The 60 deformation of the till, coupled with the dynamics of the hydrological 61 system, is further affected by the substantial strain rate variability 62 in subglacial conditions resulting from spatial heterogeneity at the 63 bed. However, it is not clear if the relatively low magnitudes of strain 64 rates affect the bed structure or its hydrology. We study how laterally 65 varying shear along the ice-bed interface alters sediment porosity and 66 affects the flux of meltwater through the pore spaces. We use a discrete 67 element model consisting of a collection of spherical, elasto-frictional 68 grains with water-saturated pore spaces to simulate the deformation 69 of the granular bed. Our results show that a deforming granular layer 70 exhibits substantial spatial variability in porosity in the pseudo-static 71 shear regime, where shear strain rates are relatively low. In particular, 72 laterally varying shear at the shearing interface creates a narrow zone 73 of elevated porosity which has increased susceptibility to plastic 74 failure. Despite the changes in porosity, our analysis suggests that 75 the pore pressure equilibrates near-instantaneously relative to the 76 deformation at critical state, inhibiting potential strain rate dependence 77 of the deformation caused by bed hardening or weakening resulting from 78 pore pressure changes. We relate shear variation to porosity evolution 79 and drainage element formation in actively deforming subglacial tills. 80 </blockquote> 81 82 <h2>Links and references:</h2> 83 <ul> 84 <li><a href="https://doi.org/10.1029/2021JF006460">Publication on journal webpage</a> (closed access)</li> 85 <li><a href="papers/Kasmalkar et al 2021 Shear variation at the ice-till interface changes the spatial distribution of till porosity and meltwater drainage.pdf">Preprint PDF</a> 86 <li><a href="https://src.adamsgaard.dk/sphere">Simulation software</a></li> 87 </ul>