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Small quantities of liquid water lining triple junctions in polycrystalline glacier ice form connected vein networks that enable material exchange with underlying basal environments. Diffuse debris concentrations commonly observed in ice marginal regions might be attributed to this mechanism. Following recent cryogenic ring-shear experiments, we observed emplacement along grain boundaries of loess particles several tens of microns in size. Here, we describe an idealized model of vein liquid flow to elucidate conditions favoring such particle transport. Gradients in liquid potential drive flow toward colder temperatures and lower solute concentrations, while deviations of the ice stress state from hydrostatic balance produce additional suction toward anomalously low ice pressures. Our model predicts particle entrainment following both modest warming along the basal interface resulting from anticipated natural changes in effective stress, and the interior relaxation of temperature and solute concentration imposed by our experimental protocols. Comparisons with experimental observations are encouraging, but suggest that liquid flow rates are somewhat higher and/or more effective at dragging larger particles than predicted by our idealized model with nominal parameter choices. Diffuse debris entrainment extending several meters above the glacier bed likely requires a more sophisticated treatment that incorporates effects of ice deformation or other processes. [ABSTRACT FROM AUTHOR]

The importance of glacier sliding has motivated a rich literature describing the thermomechanical interactions between ice, liquid water and bed materials. Early recognition of the gradient in melting temperature across small bed obstacles led to focused studies of regelation. An appreciation for the limits on ice deformation rates downstream of larger obstacles highlighted a role for cavitation, which has subsequently gained prominence in descriptions of subglacial drainage. Here, we show that the changes in melting temperature that accompany changes in normal stress along a sliding ice interface near cavities and other macroscopic drainage elements cause appreciable supercooling and basal mass exchange. This provides the basis of a novel formation mechanism for widely observed laminated debris-rich basal ice layers. [ABSTRACT FROM AUTHOR]

Icelenses are formed during soil freezing by the migration and solidificationof premelted water that is adsorbed to ice–particle interfacesand confined to capillary regions. We develop a model of ice lensgrowth that clearly illustrates how the freezing rate dependence onparticle size and soil microstructure changes in response to changesin the relative importance of permeable flow and thin-film flow ingoverning the water supply. The growth of an ice lens in fine-grainedporous media is primarily constrained by low permeability in the unfrozenregion. In contrast, the constraints offered by the film flow decreasethe lens growth rate adjacent to larger particles. The trade-off betweenresistance to permeable flow and film flow causes the growth ratefor ice lenses to be maximized for particles of intermediate size.Moreover, because film flow along particle surfaces adjacent to agrowing lens is not strongly affected by the microstructure of thepore space, our analysis predicts that lensing in coarse-grained porousmedia is insensitive to the pore microstructure and porosity, butthe permeable flow that governs lens formation in fine-grained porousmedia causes their growth to be much more affected by these details. [ABSTRACT FROM AUTHOR]

We examine how frictional heating drives the evolution of temperature, strength, and fracture energy during earthquake slip. For small slip distances, heat and pore fluid are unable to escape the shearing fault core, and the behavior is well approximated by simple analytical models that neglect any transport. Following large slip distances, the finite width of the shear zone is small compared to the thicknesses of the thermal and hydrological boundary layers, and the fault behavior approaches that predicted for the idealized case of slip on a plane. To evaluate the range in which the predictions of these two sets of approximations are valid, we develop a model that describes how frictional dissipation within a finite shear zone drives heat and mass transport through the surrounding static gouge. With realistic parameter values and slips greater than a few centimeters, the subsequent evolution of strength and fracture energy are approximated well by the planar slip model. However, the temperature evolution is much more sensitive to the finite shear zone thickness, and the ultimate temperature rise tends to be intermediate between that predicted for the two simplified cases. We explore the range of conditions necessary for melting to begin and focus in particular on the potential role of fault zone damage in facilitating fluid transport and promoting larger temperature increases. We discuss how the apparent scarcity of exhumed pseudotachylytes places constraints on some of the more uncertain fault zone parameters., Earth and Planetary Sciences, Engineering and Applied Sciences