Abstract
AbstractWe developed a tilt sensor for studying ice deformation and installed our tilt sensor systems in two boreholes drilled close to the shear margin of Jarvis Glacier, Alaska to obtain kinematic measurements of streaming ice. We used the collected tilt data to calculate borehole deformation by tracking the orientation of the sensors over time. The sensors' tilts generally trended down-glacier, with an element of cross-glacier flow in the borehole closer to the shear margin. We also evaluated our results against flow dynamic parameters derived from Glen's exponential flow law and explored the parameter space of the stress exponentnand enhancement factorE. Comparison with values from ice deformation experiments shows that the ice on Jarvis is characterized by highernvalues than that is expected in regions of low stress, particularly at the shear margin (~3.4). The highernvalues could be attributed to the observed high total strains coupled with potential dynamic recrystallization, causing anisotropic development and consequently sped up ice flow. Jarvis'nvalues place the creep regime of the ice between basal slip and dislocation creep. TuningEtowards a theoretical upper limit of 10 for anisotropic ice with single-maximum fabric reduces thenvalues by 0.2.
Highlights
Accelerated melting of glaciers and ice caps has raised serious concerns about sea level rise
To accurately project sea level rise, future models will require careful treatment of shear margins. This necessitates a deeper understanding of the flow dynamics at shear margins and how streaming flow relates to the constitutive flow law for ice (Glen, 1955, 1958)
To obtain kinematic measurements of streaming ice, we developed an inexpensive tilt sensor built from accessible parts that can be installed at multiple depths in a borehole
Summary
Accelerated melting of glaciers and ice caps has raised serious concerns about sea level rise. To accurately project sea level rise, future models will require careful treatment of shear margins. This necessitates a deeper understanding of the flow dynamics at shear margins and how streaming flow relates to the constitutive flow law for ice (Glen, 1955, 1958). There remains a lack of systematic in-situ studies in natural settings of streaming flow, and most in-situ (e.g. Faria and others, 2014) and in-lab (Nye, 1953; Glen, 1955) studies of natural ice have focused on bodies of ice with frozen beds that experience minimal shear strain across planes normal to both the bed and margins, and where the viscosity at the base of the ice controls most of the velocity field
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