Interpretive Geologic Cross Sections Across Lower Platte North Natural Resources District, Nebraska (Ccs-20), 2017 University of Nebraska - Lincoln
Interpretive Geologic Cross Sections Across Lower Platte North Natural Resources District, Nebraska (Ccs-20), Dana Divine
Conservation and Survey Division
No abstract provided.
Using Cross-Sets For Paleodischarge Estimation And Paleocurrent Vectors In The Parthenon Sandstone, Northwest Arkansas, 2017 University of Arkansas, Fayetteville
Using Cross-Sets For Paleodischarge Estimation And Paleocurrent Vectors In The Parthenon Sandstone, Northwest Arkansas, Sean Robert Parry
Theses and Dissertations
In this thesis, set thicknesses are used to estimate the paleohydraulics (paleodischarge and give magnitudes for paleocurrent directions) of the ancient river system which deposited the Parthenon Sandstone in northwest Arkansas. Set thickness is the vertical thickness of a group of strata conformable series (Mckee and Weir, 1953); set thickness represents truncated dunes. The goal of this thesis is to: 1) obtain paleodischarge estimates of the Parthenon sandstone via cross-sets and compare the results with previously calculated discharge estimates which use basin area to discharge collation techniques and 2) use paleodischarge estimates calculated within this thesis to give magnitude to ...
Soft-Bed Experiments Beneath Engabreen, Norway: Regelation Infiltration, Basal Slip And Bed Deformation, 2017 Iowa State University
Soft-Bed Experiments Beneath Engabreen, Norway: Regelation Infiltration, Basal Slip And Bed Deformation, Neal R. Iverson, Thomas S. Hooyer, Urs H. Fischer, Denis Cohen, Peter L. Moore, M. Jackson, G. Lappegard, J. Kohler
To avoid some of the limitations of studying soft-bed processes through boreholes, a prism of simulated till (1.8 m × 1.6 m × 0.45 m) with extensive instrumentation was constructed in a trough blasted in the rock bed of Engabreen, a temperate glacier in Norway. Tunnels there provide access to the bed beneath 213 m of ice. Pore-water pressure was regulated in the prism by pumping water to it. During experiments lasting 7–12 days, the glacier regelated downward into the prism to depths of 50– 80 mm, accreting ice-infiltrated till at rates predicted by theory. During periods of ...
Testing A Glacial Erosion Rule Using Hang Heights Of Hanging Valleys, Jasper National Park, Alberta, Canada, 2017 University of Alaska, Fairbanks
Testing A Glacial Erosion Rule Using Hang Heights Of Hanging Valleys, Jasper National Park, Alberta, Canada, J. M. Amundson, Neal R. Iverson
In most models of glacial erosion, glacier sliding velocity is hypothesized to control rates of bedrock erosion. If this hypothesis is correct, then the elevation difference between hanging and trunk valley floors, the hang height, should be dictated by the relative sliding velocities of the glaciers that occupied these valleys. By considering sliding velocity to be proportional to balance velocity and using mass continuity, hang height is expressed in terms of glacier catchment areas, slopes, and widths, which can be estimated for past glaciers from the morphology of glacial valleys. These parameters were estimated for 46 hanging valleys and their ...
Glacial Landscape Evolution By Subglacial Quarrying: A Multiscale Computational Approach, 2017 Aarhus University
Glacial Landscape Evolution By Subglacial Quarrying: A Multiscale Computational Approach, Sofie V. Ugelvig, David L. Egholm, Neal R. Iverson
Quarrying of bedrock is a primary agent of subglacial erosion. Although the mechanical theory behind the process has been studied for decades, it has proven difficult to formulate the governing principles so that large-scale landscape evolution models can be used to integrate erosion over time. The existing mechanical theory thus stands largely untested in its ability to explain postglacial topography. In this study we relate the physics of quarrying to long-term landscape evolution with a multiscale approach that connects meter-scale cavities to kilometer-scale glacial landscapes. By averaging the quarrying rate across many small-scale bedrock steps, we quantify how regional trends ...
Sliding Of Ice Past An Obstacle At Engabreen, Norway, 2017 University of Minnesota-Twin Cities
Sliding Of Ice Past An Obstacle At Engabreen, Norway, Denis Cohen, Roger Leb. Hooke, Neal R. Iverson, Jack Kohler
At Engabreen, Norway, an instrumented panel containing a decimetric obstacle was mounted flush with the bed surface beneath 210 m of ice. Simultaneous measurements of normaland shear stresses, ice velocity and temperature were obtained as dirty basal ice flowed past the obstacle. Our measurements were broadly consistent with ice thickness, flow conditions and bedrock topography near the site of the experiment. Ice speed 0.45 m above the bed was about 130 mm d–1, much less than the surface velocity of 800 mm d–1. Average normalstress on the panelwas 1.0–1.6 MPa, smaller than the expected ...
Glacier-Bed Geomorphic Processes And Hydrologic Conditions Relevant To Nuclear Waste Disposal, 2017 Iowa State University
Glacier-Bed Geomorphic Processes And Hydrologic Conditions Relevant To Nuclear Waste Disposal, Neal R. Iverson, Mark Person
Characterizing glaciotectonic deformation, glacial erosion and sedimentation, and basal hydrologic conditions of ice sheets is vital for selecting sites for nuclear waste repositories at high latitudes. Glaciotectonic deformation is enhanced by excess pore pressures that commonly persist near ice sheet margins. Depths of such deformation can extend locally to a few tens of meters, with depths up to approximately 300 m in exceptional cases. Rates of glacial erosion are highly variable (0.05–15 mm a−1), but ratesa−1 are expected in tectonically quiescent regions. Total erosion probably not exceeding several tens of meters is expected during a glacial ...
Ring-Shear Studies Of Till Deformation: Coulomb-Plastic Behavior And Distributed Strain In Glacier Beds, 2017 Iowa State University
Ring-Shear Studies Of Till Deformation: Coulomb-Plastic Behavior And Distributed Strain In Glacier Beds, Neal R. Iverson, Thomas S. Hooyer, Robert W. Baker
A ring-shear device was used to study the factors that control the ultimate(steady) strength of till at high shear strains.Tests at a steady strain rate and at different stresses normal to the shearing direction yielded ultimate friction angles of 26.3° and 18.6° for tills containing 4% and 30% clay-sized particles, respectively Other tests at steady normal stresses and variable shear-strain rates indicated a tendency for both tills to weaken slightly with increasing strain rate. This weakening may be due to small increases in till porosity.These results provide no evidence of viscous behavior and suggest that ...
Role Of Transient Water Pressure In Quarrying: A Subglacial Experiment Using Acoustic Emissions, 2017 Iowa State University
Role Of Transient Water Pressure In Quarrying: A Subglacial Experiment Using Acoustic Emissions, Denis Cohen, Thomas S. Hooyer, Neal R. Iverson, Jason Thomason, M. Jackson
Probably the most important mechanism of glacial erosion is quarrying: the growth and coalescence of cracks in subglacial bedrock and dislodgement of resultant rock fragments. Although evidence indicates that erosion rates depend on sliding speed, rates of crack growth in bedrock may be enhanced by changing stresses on the bed caused by fluctuating basal water pressure in zones of ice-bed separation. To study quarrying in real time, a granite step, 12 cm high with a crack in its stoss surface, was installed at the bed of Engabreen, Norway. Acoustic emission sensors monitored crack growth events in the step as ice ...
Coupling Between A Glacier And A Soft Bed: I. A Relation Between Effective Pressure And Local Shear Stress Determined From Till Elasticity, Neal R. Iverson, Robert W. Baker, Roger Leb. Hooke, Brian Hanson, Peter Jansson
To predict the distribution of motion beneath glaciers on soft beds, the strength of the coupling between the ice and the bed and its variation with effective pressure must be known. A record of shear strain, acquired with a tiltmeter emplaced in till beneath Storglaciären, Sweden, indicates that fluctuations in water pressure cause variations in the local shear stress on the bed and that the bed deforms elastically in response to these variations. To estimate the shear stress from the elastic component of the total shear strain, the shear modulus of the till was measured in relaxation tests conducted in ...
Distributed Shear Of Subglacial Till Due To Coulomb Slip, 2017 Iowa State University
Distributed Shear Of Subglacial Till Due To Coulomb Slip, Neal R. Iverson, Richard M. Iverson
In most models of the flow of glaciers on till beds, it has been assumed that till behaves as a viscoplastic fluid, despite contradictory evidence from laboratory studies. In accord with this assumption, displacement profiles measured in subglacial till have been fitted with viscoplastic models by estimating the stress distribution. Here we present a model that illustrates how observed displacement profiles can result from till deformation resisted solely by Coulomb friction. Motion in the till bed is assumed to be driven by brief departures from static equilibrium caused by fluctuations in effective normal stress. These fluctuations result from chains of ...
Estimating The Sliding Velocity Of A Pleistocene Ice Sheet From Plowing Structures In The Geologic Record, 2017 Iowa State University
Estimating The Sliding Velocity Of A Pleistocene Ice Sheet From Plowing Structures In The Geologic Record, Neal R. Iverson, Thomas S. Hooyer
As an ice sheet slides over its sediment bed, some clasts partly embedded in the glacier sole plow through the bed surface. The size distribution of such clasts, if it can be characterized from structures in the geologic record, can be used to estimate the sliding velocity of a past ice sheet. By combining a theory of glacier sliding with a geotechnical theory of cone penetration, sliding velocity can be calculated in terms of clast-size parameters, a fluidity parameter for ice, and the thermodynamic properties of ice and clasts. If frictional properties of the bed are measured, the effective normal ...
Diffusive Mixing Between Shearing Granular Materials: Constraints On Bed Deformation From Till Contacts, 2017 Iowa State University
Diffusive Mixing Between Shearing Granular Materials: Constraints On Bed Deformation From Till Contacts, Thomas S. Hooyer, Neal R. Iverson
Shearing of subglacial till has been invoked widely as a mechanism of glacier motion and sediment transport, but standard indicators for determining shear strain from the geologic record are not adequate for estimating the very high strains required of the bed-deformation model. Here we describe a laboratory study of mixing between shearing granular layers that allows an upper limit to be placed on bed shear strain in the vicinity of till contacts. Owing to random vertical motions of particles induced by shearing, mixing can be modeled as a linearly diffusive process, and so can be characterized with a single mixing ...
Acute Sensitivity Of Landslide Rates To Initial Soil Porosity, 2017 United States Geological Survey
Acute Sensitivity Of Landslide Rates To Initial Soil Porosity, Richard M. Iverson, M. E. Reid, Neal R. Iverson, R. G. Lahusen, M. Logan, J. E. Mann, D. L. Brien
Some landslides move imperceptibly downslope, whereas others accelerate catastrophically. Experimental landslides triggered by rising pore water pressure moved at sharply contrasting rates due to small differences in initial porosity. Wet sandy soil with porosity of about 0.5 contracted during slope failure, partially liquefied, and accelerated within 1 second to speeds over 1 meter per second. The same soil with porosity of about 0.4 dilated during failure and slipped episodically at rates averaging 0.002 meter per second. Repeated slip episodes were induced by gradually rising pore water pressure and were arrested by pore dilation and attendant pore pressure ...
A New Laboratory Device For Study Of Subglacial Processes: First Results On Ice–Bed Separation During Sliding, 2017 Iowa State University
A New Laboratory Device For Study Of Subglacial Processes: First Results On Ice–Bed Separation During Sliding, Neal R. Iverson, Ben B. Petersen
A new ring-shear device allows basal slip and related processes to be studied in laboratory experiments for the cases of hard or soft beds. The device rotates a confined ring of ice (0.9 m outside diameter) across a horizontal bed at a constant velocity or drag, while a vertical stress is applied and basal water pressure is controlled. A bath with circulating fluid regulated to ∼0.01°C surrounds the ice chamber and keeps the ice at its pressure-melting temperature. In a first experiment with a stepped rigid bed and zero basal water pressure, steady lengths of step cavities ...
A Laboratory Study Of Particle Ploughing And Pore-Pressure Feedback: A Velocity-Weakening Mechanism For Soft Glacier Beds, Jason F. Thomason, Neal R. Iverson
If basal-water discharge and pressure are sufficiently high, a soft-bedded glacier will slip over its bed by ploughing, the process in which particles that span the ice–bed interface are dragged across the bed surface. Results of laboratory experiments indicate that resistance to ploughing can decrease with increasing ploughing velocity (velocity weakening). During ploughing at various velocities (15–400 m a−1), till was compacted in front of idealized particles, causing pore pressures there that were orders of magnitude higher than the ambient value. This excess pore pressure locally weakened the till in shear, thereby decreasing ploughing resistance by a ...
Slope, Grain Size, And Roughness Controls On Dry Sediment Transport And Storage On Steep Hillslopes, 2017 Pennsylvania State University
Slope, Grain Size, And Roughness Controls On Dry Sediment Transport And Storage On Steep Hillslopes, Roman A. Dibiase, Michael P. Lamb, Vamsi Ganti, Adam M. Booth
Geology Faculty Publications and Presentations
Existing hillslope sediment transport models developed for low-relief, soil-mantled landscapes are poorly suited to explain the coupling between steep rocky hillslopes and headwater channels. Here we address this knowledge gap using a series of field and numerical experiments to inform a particle-based model of sediment transport by dry ravel—a mechanism of granular transport characteristic of steep hillslopes. We find that particle travel distance increases as a function of the ratio of particle diameter to fine-scale (1m) topographic variability associated with rocky landscapes. Applying a 2-D dry-ravel-routing model to lidar-derived surface topography, we show how spatial patterns of local and ...
Characterization Of Massive Vs. Laminated Texture Of The Coconino Sandstone (Permian), Arizona From The Study Of Thin Sections, Sarah C. Rouse
The Research and Scholarship Symposium
This project seeks to contribute to the work of Dr. John Whitmore and Sarah Maithel on the Coconino Sandstone (Permian) of Arizona. More than one hundred thin sections are available for study from this sandstone. Each thin section was examined both macroscopically and microscopically to determine if the sample is "laminated" or "massive." The purpose of this project is to define what "laminae" are and then develop reliable quantitative criteria that can differentiate between the laminated and massive samples. These criteria might then be applied to distinguish patterns that occur across the deposit, which in turn may provide insight into ...
A Correlation And Stratigraphy Of Detailed Measured Core Sections Of The Waynesville And Liberty Formations (Katian; Richmondian) - Transecting Warren, Clinton, And Fayette Counties Of Ohio, 2017 Cedarville University
A Correlation And Stratigraphy Of Detailed Measured Core Sections Of The Waynesville And Liberty Formations (Katian; Richmondian) - Transecting Warren, Clinton, And Fayette Counties Of Ohio, Mark P. Guilliams
The Research and Scholarship Symposium
The stratigraphy of the Cincinnatian is difficult to understand and interpret which has resulted in various models for deposition ranging from a layer cake model with continuous beds to completely discontinuous beds. The interest of this study is the Liberty and Waynesville Formations (previously part of the Bull Fork Formation); these are Late Ordovician (Katian; Richmondian) units of predominantly limestone and shale. This project assesses the continuity of fine scale beds within these formations across a small area (approx. the size of Ohio’s Clinton County) by correlating measured sections from drill cores. The project involved the study of five ...
Petrographic Analysis Of The Oriskany Sandstone (Lower Devonian) From The Ellisburg Storage Pool, Potter County, Northcentral Pennsylvania, Emily R. Jackson
The Research and Scholarship Symposium
Three Lower Devonian Oriskany Sandstone cores, EW-216 (core 1), EW-415 (core 2), and EW-706 (core 3), were obtained from Dominion Transmission’s Ellisburg Storage Pool, located in Potter County, northcentral PA. The goal of the project was to create a petrographic analysis and description of the cores, with special attention given to any deformational features associated with stress/strain indicators. Extended Range Helium Porosimeter measurements, XRD analysis, and thin section production were completed by Calgary Rock and Materials. The cores were then analyzed using a petrographic microscope; a complete description from the analysis was written for each core. Photographs were ...