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Articles 1 - 9 of 9
Full-Text Articles in Physical Sciences and Mathematics
Air Compression As A Mechanism For The Underdamped Slug Test Response In Fractured Glacier Ice, Toby W. Meierbachtol, Joel T. Harper, Neil F. Humphrey, Jeremy Shaha, John H. Bradford
Air Compression As A Mechanism For The Underdamped Slug Test Response In Fractured Glacier Ice, Toby W. Meierbachtol, Joel T. Harper, Neil F. Humphrey, Jeremy Shaha, John H. Bradford
CGISS Publications and Presentations
Artificial perturbations of borehole water levels, known as slug tests, are a useful means of characterizing the glacier hydrologic system. Slug tests were performed on Bench Glacier, Alaska, in 21 boreholes over three field seasons during the transition from a winter to a summer drainage mode. Fifty-four slug tests were conducted, with water level monitoring in up to five boreholes adjacent to the slugged borehole. Seven of the slug tests were performed in conjunction with dye dispersion tests to identify water pathways within the slugged borehole following perturbation. Nearly 60% of monitored adjacent boreholes showed a hydraulic connection to the …
Locating Oil Spills Under Sea Ice Using Ground-Penetrating Radar, John H. Bradford, Lee M. Liberty, David F. Dickens
Locating Oil Spills Under Sea Ice Using Ground-Penetrating Radar, John H. Bradford, Lee M. Liberty, David F. Dickens
CGISS Publications and Presentations
The accelerating level of interest in arctic oil and gas exploration was demonstrated in the overwhelming response to recent lease sales in the Alaskan OCS region. As development increases, the potential for accidental oil spills in the arctic marine environment increases. The need for reliable systems to detect oil trapped in a range of ice conditions remains at the forefront of continued efforts to improve response to ocean spills.
Cancellation Of Spurious Arrivals In Green’S Function Extraction, Kasper Van Wijk
Cancellation Of Spurious Arrivals In Green’S Function Extraction, Kasper Van Wijk
CGISS Publications and Presentations
The extraction of the Green's function by cross correlation of waves recorded at two receivers nowadays finds much application. We show that for an arbitrary small scatterer, the cross terms of scattered waves give an unphysical wave with an arrival time that is independent of the source position. This constitutes an apparent inconsistency because theory predicts that such spurious arrivals do not arise, after integration over a complete source aperture. This puzzling inconsistency can be resolved for an arbitrary scatterer by integrating the contribution of all sources in the stationary phase approximation to show that the stationary phase contributions to …
An Interactive Bayesian Geostatistical Inverse Protocol For Hydraulic Tomography, Michael N. Fienen, Tom Clemo, Peter K. Kitanidis
An Interactive Bayesian Geostatistical Inverse Protocol For Hydraulic Tomography, Michael N. Fienen, Tom Clemo, Peter K. Kitanidis
CGISS Publications and Presentations
Hydraulic tomography is a powerful technique for characterizing heterogeneous hydrogeologic parameters. An explicit trade-off between characterization based on measurement misfit and subjective characterization using prior information is presented. We apply a Bayesian geostatistical inverse approach that is well suited to accommodate a flexible model with the level of complexity driven by the data and explicitly considering uncertainty. Prior information is incorporated through the selection of a parameter covariance model characterizing continuity and providing stability. Often, discontinuities in the parameter field, typically caused by geologic contacts between contrasting lithologic units, necessitate subdivision into zones across which there is no correlation among …
Sediment And Nutrient Delivery From Thermokarst Features In The Foothills Of The North Slope, Alaska: Potential Impacts On Headwater Stream Ecosystems, W. B. Bowden, M. N. Gooseff, A. Balser, A. Green, B. J. Peterson, John H. Bradford
Sediment And Nutrient Delivery From Thermokarst Features In The Foothills Of The North Slope, Alaska: Potential Impacts On Headwater Stream Ecosystems, W. B. Bowden, M. N. Gooseff, A. Balser, A. Green, B. J. Peterson, John H. Bradford
CGISS Publications and Presentations
Permafrost is a defining characteristic of the Arctic environment. However, climate warming is thawing permafrost in many areas leading to failures in soil structure called thermokarst. An extensive survey of a 600 km2 area in and around the Toolik Lake Natural Research Area (TLNRA) revealed at least 34 thermokarst features, two thirds of which were new since ~1980 when a high resolution aerial survey of the area was done. Most of these thermokarst features were associated with headwater streams or lakes. We have measured significantly increased sediment and nutrient loading from thermokarst features to streams in two well-studied locations …
Finding Concealed Active Faults: Extending The Southern Whidbey Island Fault Across The Puget Lowland, Washington, Brian L. Sherrod, Richard J. Blakely, Craig S. Weaver, Harvey M. Kelsey, Elizabeth Barnett, Lee Liberty, Karen L. Meagher, Kristin Pape
Finding Concealed Active Faults: Extending The Southern Whidbey Island Fault Across The Puget Lowland, Washington, Brian L. Sherrod, Richard J. Blakely, Craig S. Weaver, Harvey M. Kelsey, Elizabeth Barnett, Lee Liberty, Karen L. Meagher, Kristin Pape
CGISS Publications and Presentations
The southern Whidbey Island fault zone (SWIF), as previously mapped using borehole data, potential field anomalies, and marine seismic reflection surveys, consists of three subparallel, northwest trending strands extending ~100 km from near Vancouver Island to the northern Puget Lowland. East of Puget Sound, the SWIF makes landfall between the cities of Seattle and Everett but is concealed beneath a thick mantle of young glacial deposits and vegetation. A ~20-km-wide, northwest trending swath of subparallel, low-amplitude aeromagnetic anomalies crosses this region of the Puget Lowland and is on strike with the SWIF. The most prominent aeromagnetic anomaly, the Cottage Lake …
A View Toward The Future Of Subsurface Characterization: Cat Scanning Groundwater Basins, Warren Barrash
A View Toward The Future Of Subsurface Characterization: Cat Scanning Groundwater Basins, Warren Barrash
CGISS Publications and Presentations
In this opinion paper we contend that high-resolution characterization, monitoring, and prediction are the key elements to advancing and reducing uncertainty in our understanding and prediction of subsurface processes at basin scales. First, we advocate that recently developed tomographic surveying is an effective and high-resolution approach for characterizing the field-scale subsurface. Fusion of different types of tomographic surveys further enhances the characterization. A basin is an appropriate scale for many water resources management purposes. We thereby propose the expansion of the tomographic surveying and data fusion concept to basin-scale characterization. In order to facilitate basin-scale tomographic surveys, different types of …
Influence Of Morphology And Permafrost Dynamics On Hyporheic Exchange In Arctic Headwater Streams Under Warming Climate Conditions, Jay P. Zarnetske, Michael N. Gooseff, W. Breck Bowden, Morgan J. Greenwald, Troy R. Brosten, John H. Bradford, James P. Mcnamara
Influence Of Morphology And Permafrost Dynamics On Hyporheic Exchange In Arctic Headwater Streams Under Warming Climate Conditions, Jay P. Zarnetske, Michael N. Gooseff, W. Breck Bowden, Morgan J. Greenwald, Troy R. Brosten, John H. Bradford, James P. Mcnamara
CGISS Publications and Presentations
We investigated surface-subsurface (hyporheic) exchange in two morphologically distinct arctic headwater streams experiencing warming (thawing) sub-channel conditions. Empirically parameterized and calibrated groundwater flow models were used to assess the influence of sub-channel thaw on hyporheic exchange. Average thaw depths were at least two-fold greater under the higher-energy, alluvial stream than under the lowenergy, peat-lined stream. Alluvial hyporheic exchange had shorter residence times and longer flowpaths that occurred across greater portions of the thawed sediments. For both reaches, the morphologic (longitudinal bed topography) and hydraulic conditions (surface and groundwater flow properties) set the potential for hyporheic flow. Simulations of deeper thaw, …
Water, Inertial Damping, And The Complex Shear Modulus, Paul Michaels
Water, Inertial Damping, And The Complex Shear Modulus, Paul Michaels
CGISS Publications and Presentations
The author proposes an alternative to the traditional representation of soil damping. Rather than using damping ratio, this author advocates using viscosity as the specific soil property, especially for saturated permeable soils. Thus represented, the imaginary part of the complex shear modulus will vary directly with frequency. The point is particularly relevant in cases where the water table may change, thus affecting the dynamic design of foundations or structures composed of soils.