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t013-neel.html (4803B)
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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>