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- Keyword
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- Bench Glacier (2)
- Geochemistry (2)
- Hydrology (2)
- Snow (2)
- Accumulation (1)
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- Acid mine drainage (1)
- Albedo (1)
- Aluminum (1)
- Annals of Glaciology (1)
- Aquatic communities (1)
- Astrobiology (1)
- Atmospheric dynamics; precipitation; global change (1)
- Balance (1)
- Basal water-pressure sensors (1)
- Bench Glacier; subglacial water-pressure (1)
- Boreholes (1)
- Burial (1)
- Catchment (1)
- Central-Western Spain (1)
- Connectivity (1)
- Cover (1)
- Dehesas (1)
- Detection of life (1)
- Diurnal changes (1)
- Diurnal fluctuations; diurnal meltwater input (1)
- Flume (1)
- Geomorphology (1)
- Geothermal (1)
- Glaciology (1)
- Greenland (1)
Articles 1 - 30 of 42
Full-Text Articles in Physical Sciences and Mathematics
Helium In Stream Water As A Volcanic Monitoring Tool, W. Payton Gardner, David D. Susong
Helium In Stream Water As A Volcanic Monitoring Tool, W. Payton Gardner, David D. Susong
Geosciences Faculty Publications
We show that synoptic sampling of streams can be used to characterize volcanic volatiles in groundwater over large spatial scales. Synoptic sampling of dissolved noble gases, 222Rn, major ions, and stream discharge was carried out along a 30 km reach of the Gibbon River, near Norris Geyser Basin in Yellowstone National Park, USA. Groundwater discharge location, volume, and composition were estimated by constrained calibration of a stream flow and solute transport model. Estimated groundwater composition from stream modeling was compared to shallow groundwater concentrations measured in nearby springs. 3He, 222Rn, and Cl− aq signatures in the Gibbon River are indicative …
Metal Contamination And Food Web Changes Alter Exposure To Upper Trophic Levels In Upper Blackfoot River Basin Streams, Montana, Jack E. Landers, Sean Sullivan, Lisa Eby, Andrew C. Wilcox, Heiko Langner
Metal Contamination And Food Web Changes Alter Exposure To Upper Trophic Levels In Upper Blackfoot River Basin Streams, Montana, Jack E. Landers, Sean Sullivan, Lisa Eby, Andrew C. Wilcox, Heiko Langner
Geosciences Faculty Publications
Reduced invertebrate abundance and diversity are common responses to metals contamination in mining-impacted streams. The resulting changes in community composition may have implications for metals accumulation and transfer through the food web. We investigated how changes in invertebrate community composition (abundance, species richness, and food web complexity) influence metals bioaccumulation and exposure risk to upper trophic levels along a contamination gradient in the upper Blackfoot River Basin, Montana. Invertebrate species richness exhibited the strongest decline with increasing sediment metals concentrations, driven by the loss of metals-sensitive taxa. These changes in invertebrate community composition resulted in a decline in the proportion …
Coarse Bedload Routing And Dispersion Through Tributary Confluences, Kurt Imhoff, Andrew C. Wilcox
Coarse Bedload Routing And Dispersion Through Tributary Confluences, Kurt Imhoff, Andrew C. Wilcox
Geosciences Faculty Publications
Sediment routing fundamentally influences channel morphology and propagation of disturbances. However, the transport and storage of bedload particles in headwater channel confluences, which may be significant nodes of the channel network in terms of sediment routing, morphology, and habitat, is poorly understood. To characterize routing processes through confluences of headwater channels, we investigate how sediment routing patterns through headwater confluences compare to those described in low-gradient gravel bed river systems, and how confluences affect the dispersive behavior of coarse bedload particles compared to non-confluence reaches. We address these questions with a field tracer experiment using passive-integrated transponder and radio-frequency identification …
Flow And Scour Constrainst On Uprooting Of Pioneer Woody Seedlings, Sharon Bywater-Reyes, Andrew C. Wilcox, John C. Stella, Anne Lightbody
Flow And Scour Constrainst On Uprooting Of Pioneer Woody Seedlings, Sharon Bywater-Reyes, Andrew C. Wilcox, John C. Stella, Anne Lightbody
Geosciences Faculty Publications
Scour and uprooting during flood events is a major disturbance agent that affects plant mortality rates and subsequent vegetation composition and density, setting the trajectory of physical-biological interactions in rivers. During flood events, riparian plants may be uprooted if they are subjected to hydraulic drag forces greater than their resisting force. We measured the resisting force of woody seedlings established on river bars with in situ lateral pull tests that simulated flood flows with and without substrate scour. We quantified the influence of seedling sizes, species (Populus and Tamarix), water-table depth, and scour depth on resisting force. Seedling …
The Science And Practice Of River Restoration, Ellen E. Wohl, Stuart N. Lane, Andrew C. Wilcox
The Science And Practice Of River Restoration, Ellen E. Wohl, Stuart N. Lane, Andrew C. Wilcox
Geosciences Faculty Publications
River restoration is one of the most prominent areas of applied water-resources science. From an initial focus on enhancing fish habitat or river appearance, primarily through structural modification of channel form, restoration has expanded to incorporate a wide variety of management activities designed to enhance river process and form. Restoration is conducted on headwater streams, large lowland rivers, and entire river networks in urban, agricultural, and less intensively human-altered environments. We critically examine how contemporary practitioners approach river restoration and challenges for implementing restoration, which include clearly identified objectives, holistic understanding of rivers as ecosystems, and the role of restoration …
Temperature Distribution And Thermal Anomalies Along A Flowline Of The Greenland Ice Sheet, Joel A. Harrington, Neil F. Humphrey, Joel T. Harper
Temperature Distribution And Thermal Anomalies Along A Flowline Of The Greenland Ice Sheet, Joel A. Harrington, Neil F. Humphrey, Joel T. Harper
Geosciences Faculty Publications
Englacial and basal temperature data for the Greenland ice sheet (GrIS) are sparse and mostly limited to deep interior sites and ice streams, providing an incomplete representation of the thermal state of ice within the ablation zone. Here we present 11 temperature profiles at five sites along a 34km east-west transect of West Greenland. These profiles depict ice temperatures along a flowline and local temperature variations between closely spaced boreholes. A temperate basal layer is present in all profiles, increasing in thickness in the flow direction, where it expands from about 3% of ice height furthest inland to 100% at …
Quantifying Meltwater Refreezing Along A Transect Of Sites On The Greenland Ice Sheet, C. Cox, N. Humphrey, Joel T. Harper
Quantifying Meltwater Refreezing Along A Transect Of Sites On The Greenland Ice Sheet, C. Cox, N. Humphrey, Joel T. Harper
Geosciences Faculty Publications
On the Greenland ice sheet, a significant quantity of surface meltwater refreezes within the firn, creating uncertainty in surface mass balance estimates. This refreezing has the potential to buffer seasonal runoff to future increases in melting, but direct measurement of the process remains difficult. We present a method for quantifying refreezing at point locations using in situ firn temperature observations. A time series of sub-hourly firn temperature profiles were collected over the course of two melt seasons from 2007 to 2009 along a transect of 11 sites in the accumulation zone of Greenland. Seasonal changes in temperature profiles combined with …
Thermal Boundary Conditions On Western Greenland: Observational Constraints And Impacts On The Modeled Thermomechanical State, Toby W. Meierbachtol, Joel T. Harper, Jesse V. Johnson, Neil F. Humphrey, Douglas John Brinkerhoff
Thermal Boundary Conditions On Western Greenland: Observational Constraints And Impacts On The Modeled Thermomechanical State, Toby W. Meierbachtol, Joel T. Harper, Jesse V. Johnson, Neil F. Humphrey, Douglas John Brinkerhoff
Geosciences Faculty Publications
The surface and basal boundary conditions exert an important control on the thermodynamic state of the Greenland Ice Sheet, but their representation in numerical ice sheet models is poorly constrained due to the lack of observations. Here we investigate a land-terminating sector of western Greenland and (1) quantify differences between new observations and commonly used boundary condition data sets and (2) demonstrate the impact of improved boundary conditions on simulated thermodynamics in a higher-order numerical flow model. We constrain near-surface temperature with measurements from two 20mboreholes in the ablation zone and 10m firn temperature from the percolation zone. We constrain …
Ecogeomorphic Feedbacks And Flood Loss Of Riparian Tree Seedlings In Meandering Channel Experiments, Li Kui, John C. Stella, Anne Lightbody, Andrew C. Wilcox
Ecogeomorphic Feedbacks And Flood Loss Of Riparian Tree Seedlings In Meandering Channel Experiments, Li Kui, John C. Stella, Anne Lightbody, Andrew C. Wilcox
Geosciences Faculty Publications
During floods, fluvial forces interact with riparian plants to influence evolution of river morphology and floodplain plant community development. Understanding of these interactions, however, is constrained by insufficient precision and control of drivers in field settings, and insufficient realism in laboratory studies. We completed a novel set of flume experiments using woody seedlings planted on a sandbar within an outdoor meandering stream channel. We quantified effects on local sedimentation and seedling loss to scour and burial across realistic ranges of woody plant morphologies (Populus versus Tamarix species), densities (240 plants m-2 versus 24 m-2), and sediment …
Rapid Reservoir Erosion, Hyperconcentrated Flow, And Downstream Deposition Triggered By Breaching Of 38 M Tall Condit Dam, White Salmon River, Washington, Andrew C. Wilcox, Jim E. O'Connor, Jon J. Major
Rapid Reservoir Erosion, Hyperconcentrated Flow, And Downstream Deposition Triggered By Breaching Of 38 M Tall Condit Dam, White Salmon River, Washington, Andrew C. Wilcox, Jim E. O'Connor, Jon J. Major
Geosciences Faculty Publications
Condit Dam on the White Salmon River,Washington, a 38m high dam impounding a large volume (1.8 million m3) of fine-grained sediment (60% sand, 35% silt and clay, and 5% gravel), was rapidly breached in October 2011. This unique dam decommissioning produced dramatic upstream and downstream geomorphic responses in the hours and weeks following breaching. Blasting a 5 m wide hole into the base of the dam resulted in rapid reservoir drawdown, abruptly releasing ~1.6 million m3 of reservoir water, exposing reservoir sediment to erosion, and triggering mass failures of the thickly accumulated reservoir sediment. Within 90 min …
Climate And Topographic Controls On Simulated Pasture Production In A Semiarid Mediterranean Watershed With Scattered Tree Cover, J. Lozano-Parra, Marco P. Maneta, S. Schnabel
Climate And Topographic Controls On Simulated Pasture Production In A Semiarid Mediterranean Watershed With Scattered Tree Cover, J. Lozano-Parra, Marco P. Maneta, S. Schnabel
Geosciences Faculty Publications
Natural grasses in semiarid rangelands constitute an effective protection against soil erosion and degradation, are a source of natural food for livestock and play a critical role in the hydrologic cycle by contributing to the uptake and transpiration of water. However, natural pastures are threatened by land abandonment and the consequent encroachment of shrubs and trees as well as by changing climatic conditions. In spite of their ecological and economic importance, the spatiotemporal variations of pasture production at the decadal–century scales over whole watersheds are poorly known.We used a physically based, spatially distributed ecohydrologic model applied to a 99.5 ha …
Changes To Snowpack Energy State From Spring Storm Events, Columbia River Headwaters, Montana, Zachary M. Seligman, Joel T. Harper, Marco P. Maneta
Changes To Snowpack Energy State From Spring Storm Events, Columbia River Headwaters, Montana, Zachary M. Seligman, Joel T. Harper, Marco P. Maneta
Geosciences Faculty Publications
The generation and release of meltwater during the spring snowmelt season can be delayed because of spring storm episodes with snow accumulation and/or sustained subfreezing temperatures. The delayed release of snowmelt often extends beyond the particular storm event because of changes to the internal state of energy in the snowpack that prevents transmission of meltwater. Following a storm, two energy deficits internal to the snowpack must be overcome before surface melt can drain and exit the snowpack: 1) cold content created by heat lost during the episode must be removed and 2) dry pore space must be filled with liquid …
Understanding Greenland Ice Sheet Hydrology Using An Integrated Multi-Scale Approach, A. K. Rennermalm, S. E. Moustafa, J. Mioduszewski, V. W. Chu, R. R. Forster, B. Hagedorn, Joel T. Harper, T. L. Mote, D. A. Robinson, C. A. Shuman, L. C. Smith, M. Tedesco
Understanding Greenland Ice Sheet Hydrology Using An Integrated Multi-Scale Approach, A. K. Rennermalm, S. E. Moustafa, J. Mioduszewski, V. W. Chu, R. R. Forster, B. Hagedorn, Joel T. Harper, T. L. Mote, D. A. Robinson, C. A. Shuman, L. C. Smith, M. Tedesco
Geosciences Faculty Publications
Improved understanding of Greenland ice sheet hydrology is critically important for assessing its impact on current and future ice sheet dynamics and global sea level rise. This has motivated the collection and integration of in situ observations, model development, and remote sensing efforts to quantify meltwater production, as well as its phase changes, transport, and export. Particularly urgent is a better understanding of albedo feedbacks leading to enhanced surface melt, potential positive feedbacks between ice sheet hydrology and dynamics, and meltwater retention in firn. These processes are not isolated, but must be understood as part of a continuum of processes …
Dynamically Downscaled Winter Precipitation Over Complex Terrain Of The Central Rockies Of Western Montana, Usa, Nicholas Loren Silverman, Marco P. Maneta, S.-H. Chen, Joel T. Harper
Dynamically Downscaled Winter Precipitation Over Complex Terrain Of The Central Rockies Of Western Montana, Usa, Nicholas Loren Silverman, Marco P. Maneta, S.-H. Chen, Joel T. Harper
Geosciences Faculty Publications
We evaluate the results of dynamically downscaled winter precipitation over Western Montana using the weather research and forecasting (WRF) model through comparison with estimates from the observationally based parameter-elevation regressions on independent slopes model (PRISM). Seven years (six winters) from 2000 to 2006 are simulated at 4 km resolution to assess the similarities and differences between the two models as well as the implications for hydrologic modeling. Inherent biases in both approaches are apparent, highlighting the difficulty in climate model validation. Results show general agreement between the two models in the spatial distribution of winter precipitation. A principal component analysis …
Compressional And Em Wave Velocity Anisotropy In A Temperate Glacier Due To Basal Crevasses, And Implications For Water Content Estimation, John Bradford, Joshua Nichols, Joel T. Harper, Toby W. Meierbachtol
Compressional And Em Wave Velocity Anisotropy In A Temperate Glacier Due To Basal Crevasses, And Implications For Water Content Estimation, John Bradford, Joshua Nichols, Joel T. Harper, Toby W. Meierbachtol
Geosciences Faculty Publications
We have conducted a series of experiments designed to investigate elastic and electromagnetic (EM) velocity anisotropy associated with a preferentially aligned fracture system on a temperate valley glacier in south-central Alaska, USA. Measurements include a three-dimensional compressional wave (P-wave) seismic reflection survey conducted over a 300 m x 300 m survey patch, with uniform source grid and static checkerboard receiver pattern. Additionally, we acquired a multiazimuth, multi-offset, polarimetric groundpenetrating radar (GPR) reflection experiment in a wagon-wheel geometry with 94 degrees of azimuthal coverage. Results show azimuthal variation in the P-wave normal-moveout velocity of less than 3% (3765 and 3630 ms …
Influences Of Lithology On Water Quality: A Study Of The Ngam And Mou Watersheds In West Cameroon (Central Africa), E. Kemayou Tchamako, Rv Tsinkou Fotsing, Jp Tchouankoue, Jr Ndam Ngoupayou, B Ngounou Ngatcha, Nancy W. Hinman
Influences Of Lithology On Water Quality: A Study Of The Ngam And Mou Watersheds In West Cameroon (Central Africa), E. Kemayou Tchamako, Rv Tsinkou Fotsing, Jp Tchouankoue, Jr Ndam Ngoupayou, B Ngounou Ngatcha, Nancy W. Hinman
Geosciences Faculty Publications
The Ngam and Mou Rivers belong to the river system of the central part of the Cameroon Volcanic Line. The Ngam River watershed comprises 51 Ma old basalts, while the Mou River watershed comprises younger, < 5 Ma pyroclastic basalts. The physico-chemical characteristics of water samples from both watersheds indicated pH between 4.2 and 8.2, and 4.2 to 7.5, and very low mineralization between 11 and 246 μS/cm and 45 to 165 μS/cm, respectively, for the Ngam River and the Mou River. Chemical data showed that waters from old, highly weathered plateau basalts (Ngam River watershed) were dominated by calcium and sodium (signatures of feldpars from syenites and orthogneisses), while waters in the Mou River watershed were dominated by magnesium (signature of olivines and pyroxenes from basalts). Mineralizations in the two watersheds are thus primarily controlled by lithology rather than anthropic activities. These results are promising for identifying potential potable water resources in these areas.
Aluminum In Silica Phases Formed In Hot Springs, Nancy W. Hinman, J. Michelle Kotler
Aluminum In Silica Phases Formed In Hot Springs, Nancy W. Hinman, J. Michelle Kotler
Geosciences Faculty Publications
Sinters are difficult to characterize with traditional methods and are often described by their chemical composition alone. Yet information about the depositional environment and possible diagenetic processes is available in atomic structure. This study probes the atomic structure of siliceous sinters from two geothermal areas using nuclear magnetic resonance (NMR) spectroscopic techniques. Specifically, this study demonstrated that Al is present in tetrahedral coordination with or without octahedral coordination in geyserites from Yellowstone National Park, WY, USA and Geyser Valley, Kamchatka, Russia.
Water-Rock Interaction And Life, Nancy W. Hinman
Water-Rock Interaction And Life, Nancy W. Hinman
Geosciences Faculty Publications
Water-rock interactions play a critical role in the origin, existence, and prospects of life. Minerals are sources of energy and nutrients. Life uses aqueous chemical gradients to access and use minerals. Chemical disequilibrium, therefore, represents one type of biotic signature. Life also controls other types of disequilibrium, including isotopic disequilibrium and morphology. Water is a fundamental contributor to all of these biosignatures, acting as a medium for mass transfer and a reservoir for components. Distinguishing biosignatures from abiotic signatures challenges instrumental capabilities. Finally, the ubiquity and heterogenous distribution of life on Earth challenges the ability to interpret different types of …
Monitoring Glacier Surface Seismicity In Time And Space Using Rayleigh Waves, T. D. Mikesell, K. Van Wijk, M. M. Haney, J. H, Bradford, H. P. Marshall, Joel T. Harper
Monitoring Glacier Surface Seismicity In Time And Space Using Rayleigh Waves, T. D. Mikesell, K. Van Wijk, M. M. Haney, J. H, Bradford, H. P. Marshall, Joel T. Harper
Geosciences Faculty Publications
Sliding glaciers and brittle ice failure generate seismic body and surface wave energy characteristic to the source mechanism. Here we analyze continuous seismic recordings from an array of nine short-period passive seismometers located on Bench Glacier, Alaska (USA) (61.033N, 145.687W). We focus on the arrival-time and amplitude information of the dominant Rayleigh wave phase. Over a 46-hour period we detect thousands of events using a cross-correlation based event identification method. Travel-time inversion of a subset of events (7% of the total) defines an active crevasse, propagating more than 200 meters in three hours. From the Rayleigh wave amplitudes, we estimate …
Thermal Tracking Of Meltwater Retention In Greenland’S Accumulation Area, Neil F. Humphrey, Joel T. Harper, W. Tad Pfeffer
Thermal Tracking Of Meltwater Retention In Greenland’S Accumulation Area, Neil F. Humphrey, Joel T. Harper, W. Tad Pfeffer
Geosciences Faculty Publications
Poorly understood processes controlling retention of meltwater in snow and firn have important implications for Greenland Ice Sheet’s mass balance and flow dynamics. Here we present results from a 3 year (2007-2009) field campaign studying firn thermal profiles and density structure along an 85 km transect of the percolation zone of west Greenland. We installed one or two thermistor strings at 14 study sites, each string having 32 sensors spaced between 0 and 10 m depth. Data from our network of over 500 sensors were collected at 15-60 min intervals for 1-2 years, thereby recording the thermal signature of meltwater …
Georadar-Derived Estimates Of Firn Density In The Percolation Zone, Western Greenland Ice Sheet, Joel Brown, John Bradford, Joel T. Harper, W. Tad Pfeffer, Neil Humphrey, Ellen Mosley-Thompson
Georadar-Derived Estimates Of Firn Density In The Percolation Zone, Western Greenland Ice Sheet, Joel Brown, John Bradford, Joel T. Harper, W. Tad Pfeffer, Neil Humphrey, Ellen Mosley-Thompson
Geosciences Faculty Publications
Greater understanding of variations in firn densification is needed to distinguish between dynamic and melt-driven elevation changes on the Greenland ice sheet. This is especially true in Greenland’s percolation zone, where firn density profiles are poorly documented because few ice cores are extracted in regions with surface melt.We used geoader to investigate firn density variations with depth along an about 70 km transect through a portion of the accumulation area in western Greenland that partially melts. We estimated electromagnetic wave velocity by inverting reflection travel times picked from common midpoint gathers. We followed a procedure designed to find the simplest …
High-Resolution Study Of Layering Within The Percolation And Soaked Facies Of The Greenland Ice Sheet, Joel Brown, Joel T. Harper, W. Tad Pfeffer, Neil Humphrey, John H. Bradford
High-Resolution Study Of Layering Within The Percolation And Soaked Facies Of The Greenland Ice Sheet, Joel Brown, Joel T. Harper, W. Tad Pfeffer, Neil Humphrey, John H. Bradford
Geosciences Faculty Publications
Within the percolation and soaked facies of the Greenland ice sheet, the relationship between radar-derived internal reflection horizons and the layered structure of the firm column is unclear. We conducted two small-scale ground-penetrating radar (GPR) surveys in conjunction with 10 m firm cores that we colleced within the percolation and soaked facies of the Greenland ice sheet. The two surveys were separated by the distance of about 50 km and about 340 m of elevation leading to about 40 days of difference in the duration of average annual melt. At the higher site (about 1997 ma.s.l.), which receives less melt, …
Hydraulics, Morphology, And Energy Dissipation In An Alpine Step-Pool Channel, Andrew C. Wilcox, Ellen E. Wohl, Francesco Comiti, Luca Mao
Hydraulics, Morphology, And Energy Dissipation In An Alpine Step-Pool Channel, Andrew C. Wilcox, Ellen E. Wohl, Francesco Comiti, Luca Mao
Geosciences Faculty Publications
To investigate the relationship between hydraulics and channel morphology in step‐pool channels, we combined three‐dimensional velocity measurements with an acoustic Doppler velocimeter and topographic surveys in a steep step‐pool channel, the Rio Cordon, Italy. Measurements were organized around step, pool, and tread units and occurred within a range of 36%–57% of bankfull discharges. As flow moved from steps to their downstream pools in our study reach, an average of approximately two thirds of the total energy was dissipated, as measured by relative head loss through step‐pool sequences. Much of this head loss was achieved by elevation (potential energy) loss rather …
Timing Of Present And Future Snowmelt From High Elevations In Northwest Montana, Bonnie Jean Gillan, Joel T. Harper, Johnnie N. Moore
Timing Of Present And Future Snowmelt From High Elevations In Northwest Montana, Bonnie Jean Gillan, Joel T. Harper, Johnnie N. Moore
Geosciences Faculty Publications
The sensitivity of snowmelt-driven water supply to climate variability and change is difficult to assess in the mountain west, where strong climatic gradients coupled with complex topography are sampled by sparse ground measurements. We developed a model which ingests daily satellite imagery and meteorological data and is suitable for areas >1000 km2, yet captures spatial variability of snow accumulation and melt in steep mountain terrain.We applied the model for the years 2000–2008 to a 2900 km2 snowmelt-dominated watershed in NW Montana. We found that >25% of the basin’s snow water equivalent (SWE) accumulates above the highest measurement station and >70% …
Complex Dielectric Permittivity Measurements From Ground-Penetrating Radar Data To Estimate Snow Liquid Water Content In The Pendular Regime, John H. Bradford, Joel T. Harper, Joel Brown
Complex Dielectric Permittivity Measurements From Ground-Penetrating Radar Data To Estimate Snow Liquid Water Content In The Pendular Regime, John H. Bradford, Joel T. Harper, Joel Brown
Geosciences Faculty Publications
Monitoring the snow water equivalent (SWE) is critical to effective management of water resources in many parts of the world that depend on the mountain snowpack for water storage. There are currently no methods to remotely sense SWE with accuracy over large lateral distances in the steep and often forested terrain of mountain basins. Previous studies have shown that measurements of ground-penetrating radar (GPR) velocity can provide accurate estimates of SWE in dry snow. Introduction of liquid water into the snowpack results in a three-phase system that cannot be accurately characterized with GPR velocity alone. We show that measuring the …
Continuous Profiles Of Electromagnetic Wave Velocity And Water Content In Glaciers: An Example From Bench Glacier, Alaska, Usa, John H. Bradford, Joshua Nichols, T. Dylan Mikesell, Joel T. Harper
Continuous Profiles Of Electromagnetic Wave Velocity And Water Content In Glaciers: An Example From Bench Glacier, Alaska, Usa, John H. Bradford, Joshua Nichols, T. Dylan Mikesell, Joel T. Harper
Geosciences Faculty Publications
We conducted two-dimensional continuous multi-offset georadar surveys on Bench Glacier, south-central Alaska, USA, to measure the distribution of englacial water. We acquired data with a multi channel 25 MHz radar system using transmitter-receiver offsets ranging from 5 to 150 m. We towed the radar system at 5-10 kmh-1 with a snow machine with transmitter/receiver positions established by geodetic-grade kinematic deferentially corrected GPS (nominal 0.5 m trace spacing). For radar velocity analyses, we employed reflection tomography in the pre-stack depth-migrated domain to attain an estimated 2% velocity uncertainty when averaged over three to five wavelengths. We estimated water content from …
Air Compression As A Mechanism For The Underdamped Slug Test Response In Fractured Glacier Ice, Toby W. Meierbachtol, Joel T. Harper, Neil Humphrey, Jeremy Shaha, John Bradford
Air Compression As A Mechanism For The Underdamped Slug Test Response In Fractured Glacier Ice, Toby W. Meierbachtol, Joel T. Harper, Neil Humphrey, Jeremy Shaha, John Bradford
Geosciences Faculty Publications
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 …
Diurnal Fluctuations In Borehole Water Levels: Configuration Of The Drainage System Beneath Bench Glacier, Alaska, Usa, T. J. Fudge, Neil Humphrey, Joel T. Harper, W. Tad Pfeffer
Diurnal Fluctuations In Borehole Water Levels: Configuration Of The Drainage System Beneath Bench Glacier, Alaska, Usa, T. J. Fudge, Neil Humphrey, Joel T. Harper, W. Tad Pfeffer
Geosciences Faculty Publications
Water levels were measured in boreholes spaced along the entire length of Bench Glacier, Alaska, USA, for a period in excess of 2 years. Instrumented boreholes were arranged as nine pairs along the center line of the glacier and an orthogonal grid of 16 boreholes in a 3600 m2 region at the center of the ablation area. Dirunal fluctuations of the water levels were found to be restricted to the late melt season. Pairs of boreholes spaced along the length of the ablation area often exhibited similar fluctuations and diurnal changes in water levels. Three distinct and independent types …
Significance Of Trends Toward Earlier Snowmelt Runoff, Columbia And Missouri Basin Headwaters, Western United States, Johnnie N. Moore, Joel T. Harper, Mark C. Greenwood
Significance Of Trends Toward Earlier Snowmelt Runoff, Columbia And Missouri Basin Headwaters, Western United States, Johnnie N. Moore, Joel T. Harper, Mark C. Greenwood
Geosciences Faculty Publications
We assess changes in runoff timing over the last 55 years at 21 gages unaffected by human influences, in the headwaters of the Columbia-Missouri Rivers. Linear regression models and tests for significance that control for ‘‘false discoveries’’ of many tests, combined with a conceptual runoff response model, were used to examine the detailed structure of spring runoff timing. We conclude that only about one third of the gages exhibit significant trends with time but over half of the gages tested show significant relationships with discharge. Therefore, runoff timing is more significantly correlated with annual discharge than with time. This result …
Two Modes Of Accelerated Glacier Sliding Related To Water, Joel T. Harper, Neil Humphrey, W. T. Pfeffer, Brian Lazar
Two Modes Of Accelerated Glacier Sliding Related To Water, Joel T. Harper, Neil Humphrey, W. T. Pfeffer, Brian Lazar
Geosciences Faculty Publications
We present the first glacier-wide detailed measurement of basal effective pressure and related observations including bed separation to elucidate the role of water in sliding. The hard bedded glacier instrumented in our study exhibited two phases of accelerated sliding motion apparently driven by separate mechanisms. The first acceleration phase (up to 5 fold increase in speed) was closely tied to an increase in bed separation. The faster second phase (up to 9 fold increase in speed) was related to an unusually high level of connectivity of subglacial waters. We infer the first mode was related to cavity opening and the …