Slow Geophysical Flows of Complex Particulate Matter Open Access
Nissanka, Kavinda (Spring 2024)
Abstract
The Earth’s surface is continuously shaped by the flow of materials. From microns to kilometers, seconds to millennia, geophysical process exist across a vast range of spatial and temporal scales. Seemingly quiet hill slopes and roaring volcanoes are both extremely complex non-equilibrium systems, which intersect with and impact our lives. Understanding the fundamental physics at play in geophysical flows is crucial to predicting, controlling, and responding to these natural phenomenon. This dissertation reports the suite of experiments I have conducted to understand and examine two geophysical flows: the sedimentation of mass-polar spheroids, and the quasistatic flow of the world’s largest floating granular material, ice mélange. These systems both contain complex particle shapes and exist in non-inertial regimes, but are driven externally far from equilibrium. Sedimentation is a process that occurs in low Reynolds number flows, and is important in controlling many industrial and terrestrial processes of micron to millimeter sized particles. I report on experimental observations of sedimenting objects which deviate from uniform spheres in such a way as to mimic realistic geophysical particles. I show that a center-of-mass offset changes individual particle dynamics, interparticle interactions, and the distribution of many particles in suspension. On the opposite side of the length scale, ice mélange is a floating conglomeration of icebergs, dirt, and sea ice that sits at the interface between tidewater glaciers and the open ocean in narrow fjords. Because of confinement and jamming, ice mélange can impact the total ice mass flux out of tidewater fjords. I study ice mélange using scaled down laboratory experiments to extract the most salient parameters and features controlling its behaviour. By examining surface velocity fields, thickness profiles, and its buttressing strength, I showcase the importance of friction and particle shape for ice mélange. Importantly, I demonstrate that
the force the mélange exerts on the terminus scales as F ≈ H_0^2 , which is the thickness at the terminus. I also show the importance of fluctuations, and the limitations of continuum model’s ability to capture these fluctuations. Integration of this knowledge into models of the cryosphere can improve the accuracy of sea level rise predictions. Overall, the phenomena I studied here showcase a wealth of non-equilibrium dynamics, complex particle interactions, and unexpected behaviors.
Table of Contents
1 Introduction 1
1.1 Earth’s geophysical flows . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Non-inertial flow regimes . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.3 Complex particles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2 Sedimentation of Mass Polar Spheroids . . . . . . . . . . . . . . . . . 17
2.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.2 Experimental Methods and Particle Fabrication . . . . . . . . . . . . 22
2.3 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 25
2.3.1 Single Particle Dynamics . . . . . . . . . . . . . . . . . . . . . 25
2.3.2 Sedimenting Particle Pairs . . . . . . . . . . . . . . . . . . . . 34
2.4 3D Particle Suspensions . . . . . . . . . . . . . . . . . . . . . . . . . 41
2.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
2.5.1 Future Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . 45
3 Experimental Investigations of Ice M ́elange and the Flow of Floating
Granular Materials . . . . . . . . . . . . . . . . . 49
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
3.2 Experimental Design and Methods . . . . . . . . . . . . . . . . . . . 52
3.2.1 Experimental Methods . . . . . . . . . . . . . . . . . . . . . . 52
3.2.2 Glaciological Scaling . . . . . . . . . . . . . . . . . . . . . . . 56
3.2.3 Friction in dense ice mélange . . . . . . . . . . . . . . . . . . . 58
3.2.4 1D Depth-Averaged Model of Ice Mélange Thickness . . . . . 60
3.3 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 65
3.3.1 Experimental Mélange Thickness Profiles . . . . . . . . . . . . 65
3.3.2 Surface Velocity Fields . . . . . . . . . . . . . . . . . . . . . . 70
3.3.3 Buttressing Strength and Fluctuations . . . . . . . . . . . . . 73
3.3.4 DEM Simulations of Ice Mélange . . . . . . . . . . . . . . . . 77
3.3.5 Modifications of the Continuum Model . . . . . . . . . . . . . 83
4 Summary . . . . . . . . . . . . . . . . . 87
4.1 Sedimentation of Mass-Polar Spheroids . . . . . . . . . . . . . . . . . 87
4.2 Quasistatic Flow of Ice Mélange . . . . . . . . . . . . . . . . . . . . . 88
4.3 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
Bibliography 91
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