[{"awards": "2418105 Zoet, Lucas", "bounds_geometry": null, "dataset_titles": null, "datasets": null, "date_created": "Thu, 10 Oct 2024 00:00:00 GMT", "description": "Glaciers move in response to gravity pulling them downhill and much of the resistance to this motion is supplied by the bedrock that they sit on. For fast moving glaciers this motion is largely the result of basal ice sliding over and around bedrock bumps, and the specific processes at the ice-bed interface that facilitate this sliding play a dominant role in setting the glacier speed. Sliding atop the ice-bed interface is known to create cavities (pockets of water) downstream of bedrock bumps. These cavities facilitate water flow, control areas of ice-bed contact, regulate basal drag, dictate subglacial erosion, and affect ice mechanics in general. Thus, the length and shape of cavities (geometry) as they separate from the bed is of fundamental importance in glaciology. This project will determine the fundamental processes that set the shapes of those cavities. This work will benefit the scientific community by producing improved estimates to basal sliding and subglacial hydrology which are two of the main uncertainties in glacier-flow modeling. It will also lead to a better understanding of subglacial erosion which effectively controls the basal bump geometries. This in turn will lead to improved understanding of the fundamentals of glacier and ice-sheet dynamics. Therefore, the outcome of the project could ultimately improve future projections of sea-level rise, benefitting society at large. In addition, this project will train a postdoctoral researcher and undergraduate students from tribal institutions. This project will: 1) Use a novel experimental device to generate a cavity geometry data set for a range of independent controls; and 2) Use the results from part one to constrain numerical models that will allow for the exploration of a greater range of parameter space than is possible in the physical experiments alone. Using a novel cryogenic ring-shear device, this project will systematically assess three likely controls on cavity geometry: effective stress, sliding speed, and bump geometry, while simultaneously tracking strain indicators within the ice and the geometry of the cavity through the transparent walls of the device. These experiments will be conducted with the University of Wisconsin-Madison, state-of-the-art ring-shear device and represent the first instance where all three parameters\u2019 effects on the resultant cavity geometry can be measured simultaneously. The lab experiment findings of cavity geometry and strain rates within the ice will be used to help constrain the process-based numerical modeling of cavity formation. The numerical simulations of ice flow around obstacles will provide information about the stress and strain distribution within the ice, and from this data we can explore the ability of existing theories to predict cavity geometry for fast-flowing ice. The physics within the numerical model will be updated as needed to incorporate processes such as a stress dependent ice rheology or changes in the ice-bed contact physics that are currently unaccounted for. Outcomes will be 1) a detailed understanding of the physics that govern cavity geometry and 2) a simple parameterization of the lab and modeling results that can be easily incorporated into glaciological models for improved estimates of subglacial sliding, hydrology, and erosion. This award reflects NSF\u0027s statutory mission and has been deemed worthy of support through evaluation using the Foundation\u0027s intellectual merit and broader impacts review criteria.", "east": null, "geometry": null, "instruments": null, "is_usap_dc": true, "keywords": "GLACIER MOTION/ICE SHEET MOTION; Madison, WI", "locations": "Madison, WI", "north": null, "nsf_funding_programs": "Antarctic Glaciology", "paleo_time": null, "persons": "Zoet, Lucas", "platforms": null, "repositories": null, "science_programs": null, "south": null, "title": "Determining the Controls on Subglacial Cavity Geometry", "uid": "p0010481", "west": null}, {"awards": "1745049 Tyler, Scott", "bounds_geometry": null, "dataset_titles": "Ice Diver Madison Run #1 March 1, 2020", "datasets": [{"dataset_uid": "601368", "doi": "10.15784/601368", "keywords": "Antarctica; North America; Temperature", "people": "Tyler, Scott W.", "repository": "USAP-DC", "science_program": null, "title": "Ice Diver Madison Run #1 March 1, 2020", "url": "https://www.usap-dc.org/view/dataset/601368"}], "date_created": "Mon, 03 Aug 2020 00:00:00 GMT", "description": "Nontechnical Abstract Studies in Antarctica are, at present, severely limited by the costs of placing measurement instruments within and beneath thousands of meters of ice. Our aim is to enable dense, widespread measurement-networks by advancing development of low-cost ice melt probe technology to deploy instruments. Ice melt probes use electrical energy to descend through thick ice with little support structure on the ice surface. We are extending previous technology by using anti-freeze to maintain a partially open melt-hole above a descending probe, deploying as we go a new a new fiber-optic technology to measure ice temperature. Ice temperature measurements will reveal spatial patterns of heat welling up from the Earth beneath the ice, which in turn will contribute greatly to finding ancient ice that contains global climate records, and to understanding how ice flow may raise sea levels. Our immediate objective in this 1-year project is to test and refine our anti-freeze-based method in a 15 meter-tall ice column at the University of Wisconsin, so as to reduce technical risk in future field tests. Technical Abstract The overarching aim of our development is to enable widespread, spatially dense deployments of instruments within and beneath the Antarctic Ice Sheet for a variety of investigations, beginning with observations of basal temperature and geothermal flux at the base of the ice sheet. Dense, widespread deployment requires logistical costs far below current costs for ice drilling and coring. Our approach is to extend ice melt probe technology (which is inherently light, logistically) to allow the progressive deployment of cable for Distributed Temperature Sensing (DTS) from the ice surface as the probe descends, without greatly increasing logistical costs. Our extension is based on arresting refreezing of the melt-hole above the probe (at a diameter a few times the cable diameter) by injecting anti-freeze - specifically, ethanol at temperature near 0C - a few meters above the probe during descent. After thermal equilibration of the liquid ethanol/water column with the ice, DTS measurements yield the depth-profile of ice sheet temperature, from which basal temperature and (over frozen beds) geothermal flux can be inferred. We have carried out initial trials of our approach in a cold-room laboratory, but field work based only on such small-scale tests may still involve unnecessary risk. We therefore propose further testing at a facility of the Ice Drilling Design and Operations (IDDO) facility in Madison, WI. The new trials will test our approaches to melt-hole control and probe recovery in the taller column, will test cable and cable-tension-management methods more nearly approximating those needed to work on ice sheets, and will demonstrate the Distributed Temperature Sensing in its field configuration. This award reflects NSF\u0027s statutory mission and has been deemed worthy of support through evaluation using the Foundation\u0027s intellectual merit and broader impacts review criteria.", "east": null, "geometry": null, "instruments": null, "is_usap_dc": true, "keywords": "GLACIERS/ICE SHEETS; North America; ICE DEPTH/THICKNESS; NOT APPLICABLE", "locations": "North America", "north": null, "nsf_funding_programs": "Antarctic Instrumentation and Facilities; Antarctic Instrumentation and Support", "paleo_time": null, "persons": "Tyler, Scott W.", "platforms": "OTHER \u003e NOT APPLICABLE \u003e NOT APPLICABLE", "repo": "USAP-DC", "repositories": "USAP-DC", "science_programs": null, "south": null, "title": "Collaborative Research: Toward Dense Observation of Geothermal Fluxes in Antarctica Via Logistically Light Instrument Deployment", "uid": "p0010121", "west": null}]

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Determining the Controls on Subglacial Cavity Geometry

2418105

2024-10-10

Zoet, Lucas

No dataset link provided

Glaciers move in response to gravity pulling them downhill and much of the resistance to this motion is supplied by the bedrock that they sit on. For fast moving glaciers this motion is largely the result of basal ice sliding over and around bedrock bumps, and the specific processes at the ice-bed interface that facilitate this sliding play a dominant role in setting the glacier speed. Sliding atop the ice-bed interface is known to create cavities (pockets of water) downstream of bedrock bumps. These cavities facilitate water flow, control areas of ice-bed contact, regulate basal drag, dictate subglacial erosion, and affect ice mechanics in general. Thus, the length and shape of cavities (geometry) as they separate from the bed is of fundamental importance in glaciology. This project will determine the fundamental processes that set the shapes of those cavities. This work will benefit the scientific community by producing improved estimates to basal sliding and subglacial hydrology which are two of the main uncertainties in glacier-flow modeling. It will also lead to a better understanding of subglacial erosion which effectively controls the basal bump geometries. This in turn will lead to improved understanding of the fundamentals of glacier and ice-sheet dynamics. Therefore, the outcome of the project could ultimately improve future projections of sea-level rise, benefitting society at large. In addition, this project will train a postdoctoral researcher and undergraduate students from tribal institutions. This project will: 1) Use a novel experimental device to generate a cavity geometry data set for a range of independent controls; and 2) Use the results from part one to constrain numerical models that will allow for the exploration of a greater range of parameter space than is possible in the physical experiments alone. Using a novel cryogenic ring-shear device, this project will systematically assess three likely controls on cavity geometry: effective stress, sliding speed, and bump geometry, while simultaneously tracking strain indicators within the ice and the geometry of the cavity through the transparent walls of the device. These experiments will be conducted with the University of Wisconsin-Madison, state-of-the-art ring-shear device and represent the first instance where all three parameters’ effects on the resultant cavity geometry can be measured simultaneously. The lab experiment findings of cavity geometry and strain rates within the ice will be used to help constrain the process-based numerical modeling of cavity formation. The numerical simulations of ice flow around obstacles will provide information about the stress and strain distribution within the ice, and from this data we can explore the ability of existing theories to predict cavity geometry for fast-flowing ice. The physics within the numerical model will be updated as needed to incorporate processes such as a stress dependent ice rheology or changes in the ice-bed contact physics that are currently unaccounted for. Outcomes will be 1) a detailed understanding of the physics that govern cavity geometry and 2) a simple parameterization of the lab and modeling results that can be easily incorporated into glaciological models for improved estimates of subglacial sliding, hydrology, and erosion. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

Collaborative Research: Toward Dense Observation of Geothermal Fluxes in Antarctica Via Logistically Light Instrument Deployment

1745049

2020-08-03

Tyler, Scott W.

Ice Diver Madison Run #1 March 1, 2020

USAP-DC

Nontechnical Abstract Studies in Antarctica are, at present, severely limited by the costs of placing measurement instruments within and beneath thousands of meters of ice. Our aim is to enable dense, widespread measurement-networks by advancing development of low-cost ice melt probe technology to deploy instruments. Ice melt probes use electrical energy to descend through thick ice with little support structure on the ice surface. We are extending previous technology by using anti-freeze to maintain a partially open melt-hole above a descending probe, deploying as we go a new a new fiber-optic technology to measure ice temperature. Ice temperature measurements will reveal spatial patterns of heat welling up from the Earth beneath the ice, which in turn will contribute greatly to finding ancient ice that contains global climate records, and to understanding how ice flow may raise sea levels. Our immediate objective in this 1-year project is to test and refine our anti-freeze-based method in a 15 meter-tall ice column at the University of Wisconsin, so as to reduce technical risk in future field tests. Technical Abstract The overarching aim of our development is to enable widespread, spatially dense deployments of instruments within and beneath the Antarctic Ice Sheet for a variety of investigations, beginning with observations of basal temperature and geothermal flux at the base of the ice sheet. Dense, widespread deployment requires logistical costs far below current costs for ice drilling and coring. Our approach is to extend ice melt probe technology (which is inherently light, logistically) to allow the progressive deployment of cable for Distributed Temperature Sensing (DTS) from the ice surface as the probe descends, without greatly increasing logistical costs. Our extension is based on arresting refreezing of the melt-hole above the probe (at a diameter a few times the cable diameter) by injecting anti-freeze - specifically, ethanol at temperature near 0C - a few meters above the probe during descent. After thermal equilibration of the liquid ethanol/water column with the ice, DTS measurements yield the depth-profile of ice sheet temperature, from which basal temperature and (over frozen beds) geothermal flux can be inferred. We have carried out initial trials of our approach in a cold-room laboratory, but field work based only on such small-scale tests may still involve unnecessary risk. We therefore propose further testing at a facility of the Ice Drilling Design and Operations (IDDO) facility in Madison, WI. The new trials will test our approaches to melt-hole control and probe recovery in the taller column, will test cable and cable-tension-management methods more nearly approximating those needed to work on ice sheets, and will demonstrate the Distributed Temperature Sensing in its field configuration. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.