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Articles 1 - 30 of 526

Full-Text Articles in Glaciology

Carbon Flux And Weathering Processes In Icelandic Glacial-Fed Rivers, Allison Quiroga Apr 2018

Carbon Flux And Weathering Processes In Icelandic Glacial-Fed Rivers, Allison Quiroga

Masters Theses & Specialist Projects

An investigation into the carbon dynamics and weathering processes occurring in Icelandic glacial-fed streams was conducted during the spring to summer seasonal transition in June of 2017. Four major outlet rives were sampled from the glaciers of Gígjökull, Steinsholtsjökull, Sólheimajökull, and Falljökull. Markarfljót, the major river that Gígjökull, Steinsholtsjökull, and many other glaciers drain into, was also sampled. Longitudinal sampling occurred at all sites to capture downstream trends in the hydrogeochemistry and carbon dynamics. Distinct differences in geochemistry between glacier surface meltwater, sub-glacial waters, pro-glacial lake water, and post-mixed downstream samples were evident in the data. Glacier surface streams were ...


Improved Estimates Of Glacier Change Rates At Nevado Coropuna Ice Cap, Peru, William Hardy Kochtitzky, Benjamin R. Edwards, Ellyn M. Enderlin, Jersy Marino, Nelida Marinque Feb 2018

Improved Estimates Of Glacier Change Rates At Nevado Coropuna Ice Cap, Peru, William Hardy Kochtitzky, Benjamin R. Edwards, Ellyn M. Enderlin, Jersy Marino, Nelida Marinque

Faculty and Staff Publications By Year

Accurate quantification of rates of glacier mass loss is critical for managing water resources and for assessing hazards at ice-clad volcanoes, especially in arid regions like southern Peru. In these regions, glacier and snow melt are crucial dry season water resources. In order to verify previously reported rates of ice area decline at Nevado Coropuna in Peru, which are anomalously rapid for tropical glaciers, we measured changes in ice cap area using 259 Landsat images acquired from 1980 to 2014. We find that Coropuna Ice Cap is presently the most extensive ice mass in the tropics, with an area of ...


Rapid Expansion Of Greenland’S Low-Permeability Ice Slabs In A Warming Climate, Michael John Macferrin Feb 2018

Rapid Expansion Of Greenland’S Low-Permeability Ice Slabs In A Warming Climate, Michael John Macferrin

Cooperative Institute for Research in Environmental Sciences Graduate Theses & Dissertations

Recent increases in Greenland’s glacial melt have accelerated runoff and become Greenland’s dominant mechanism of ice loss. More meltwater is being generated in the ice sheet’s lower accumulation zone, which has begun to anneal ice lenses found within the porous firn and form continuous low-permeability ice slabs (LPISs). LPISs are layers of ice meters thick that inhibit water percolating beneath them, extend horizontally for tens of kilometers, and can cause runoff from regions where water previously refroze. LPISs form on decadal timescales and have the potential to quickly increase the extent of Greenland’s runoff zone. I ...


Evidence For Ephemeral Middle Eocene To Early Oligocene Greenland Glacial Ice And Pan-Arctic Sea Ice, Aradhna Tripati, Dennis Darby Jan 2018

Evidence For Ephemeral Middle Eocene To Early Oligocene Greenland Glacial Ice And Pan-Arctic Sea Ice, Aradhna Tripati, Dennis Darby

OEAS Faculty Publications

Earth's modern climate is defined by the presence of ice at both poles, but that ice is now disappearing. Therefore understanding the origin and causes of polar ice stability is more critical than ever. Here we provide novel geochemical data that constrain past dynamics of glacial ice on Greenland and Arctic sea ice. Based on accurate source determinations of individual ice-rafted Fe-oxide grains, we find evidence for episodic glaciation of distinct source regions on Greenland as far-ranging as ~68°N and ~80°N synchronous with ice-rafting from circum-Arctic sources, beginning in the middle Eocene. Glacial intervals broadly coincide with ...


The Impact Of Reduced Arctic Sea Ice Extent On Cryospheric Snowfall, Alexander Carne Dec 2017

The Impact Of Reduced Arctic Sea Ice Extent On Cryospheric Snowfall, Alexander Carne

Dissertations & Theses in Earth and Atmospheric Sciences

Satellite observations show that sea ice extent in the Arctic has been declining from 1979 through present day, reaching record minimum extents in 2007 and 2012. Reduced sea ice extent allows for greater expanses of open water to interact with the Arctic atmosphere, potentially leading to changes in the Arctic climate. The greatest declines in Arctic sea ice extent have occurred in summer and autumn. During these seasons, it is likely that the decrease in Arctic sea ice extent led to an increase in atmospheric sensible and latent heat fluxes, possibly leading to increases in Arctic temperature and moisture. Increases ...


Revealing Our Melting Past: Rescuing Historical Snow And Ice Data, Jack Maness, Ruth Duerr, Michael Dulock, Florence Fetterer, Gloria Hicks, Athea Merredyth, William Sampson, Allaina Wallace Dec 2017

Revealing Our Melting Past: Rescuing Historical Snow And Ice Data, Jack Maness, Ruth Duerr, Michael Dulock, Florence Fetterer, Gloria Hicks, Athea Merredyth, William Sampson, Allaina Wallace

University Libraries Faculty & Staff Contributions

Analog archival data can supplement modern digital research, but only if those data are preserved, described, and migrated to appropriate formats. The National Snow and Ice Data Center (NSIDC) at the University of Colorado Boulder (CU) is responsible for managing, archiving, and disseminating cryospheric and polar data. The clear majority of these data are digital, but the NSIDC also houses a collection of historical archival materials that include measurements related to the earth's glaciated regions prior to the development of modern instrumentation. Their formats, however, are not conducive to contemporary analysis, rendering them ostensibly “lost” to research. This paper ...


Monitoring Tropical Debris-Covered Glacier Dynamics From High-Resolution Unmanned Aerial Vehicle Photogrammetry, Cordillera Blanca, Peru, Oliver Wigmore, Bryan G. Mark Nov 2017

Monitoring Tropical Debris-Covered Glacier Dynamics From High-Resolution Unmanned Aerial Vehicle Photogrammetry, Cordillera Blanca, Peru, Oliver Wigmore, Bryan G. Mark

University Libraries Open Access Fund Supported Publications

The glaciers of the Cordillera Blanca, Peru, are rapidly retreating and thinning as a result of climate change, altering the timing, quantity and quality of water available to downstream users. Furthermore, increases in the number and size of proglacial lakes associated with these melting glaciers is increasing potential exposure to glacier lake outburst floods (GLOFs). Understanding how these glaciers are changing and their connection to proglacial lake systems is thus of critical importance. Most satellite data are too coarse for studying small mountain glaciers and are often affected by cloud cover, while traditional airborne photogrammetry and lidar are costly. Recent ...


Raritan Formation (Upper Cretaceous), Long Island, New York: Sedimentological And Geochemical Assessment, Nazrul I. Khandaker, Arif Sikder, Stanley Schleifer, Xin-Chen Liu, Carlos E. Castano Londano, Joseph B. Mcgee Turner Oct 2017

Raritan Formation (Upper Cretaceous), Long Island, New York: Sedimentological And Geochemical Assessment, Nazrul I. Khandaker, Arif Sikder, Stanley Schleifer, Xin-Chen Liu, Carlos E. Castano Londano, Joseph B. Mcgee Turner

Publications and Research

The lithology of the Upper Cretaceous Raritan Formation (RF) consists of two members: an upper clay member (Raritan clay) and a lower unit, the Lloyd Sand Member. RF is unconformably overlain by upper Pleistocene glacial deposits. The RF consists of stratified white, light- to dark-gray, and red beds and lenses of clay, silt, and sand; lignite and pyrite are common. Variegated, thin to thickly-bedded Lloyd sandstone (LS) is considered to be one of the extensive regional aquifers in Long Island and interpreted to be nearshore, fluvio-deltaic deposit. Proximity to fluvial axes and active deltaic lobes plays an important role in ...


Giovanni Badino (1953-2017), Arrigo Cigna, Paolo Forti Oct 2017

Giovanni Badino (1953-2017), Arrigo Cigna, Paolo Forti

International Journal of Speleology

Short obituary of Giovanni Badino.


Oxygen Isotope Ratios In The Shell Of Mytilus Edulis: Archives Of Glacier Meltwater In Greenland?, E. A. A. Verteegh, M. E. Blicher, J. Mortensen, S. Rysgaard, T. D. Als, Alan D. Wanamaker Oct 2017

Oxygen Isotope Ratios In The Shell Of Mytilus Edulis: Archives Of Glacier Meltwater In Greenland?, E. A. A. Verteegh, M. E. Blicher, J. Mortensen, S. Rysgaard, T. D. Als, Alan D. Wanamaker

Alan Wanamaker

Melting of the Greenland Ice Sheet (GrIS) is accelerating and will contribute significantly to global sea level rise during the 21st century. Instrumental data on GrIS melting only cover the last few decades, and proxy data extending our knowledge into the past are vital for validating models predicting the influence of ongoing climate change. We investigated a potential meltwater proxy in Godthåbsfjord (West Greenland), where glacier meltwater causes seasonal excursions with lower oxygen isotope water (δ18Ow) values and salinity. The blue mussel (Mytilus edulis) potentially records these variations, because it precipitates its shell calcite in oxygen isotopic equilibrium with ambient ...


Odu Scientists Address Antarctic Ice Melt Affecting Sea Levels, Miasia Osbey Oct 2017

Odu Scientists Address Antarctic Ice Melt Affecting Sea Levels, Miasia Osbey

News Items

No abstract provided.


The Geography Of Glaciers And Perennial Snowfields In The American West, Andrew G. Fountain, Bryce Glenn, Hassan J. Basagic Aug 2017

The Geography Of Glaciers And Perennial Snowfields In The American West, Andrew G. Fountain, Bryce Glenn, Hassan J. Basagic

Geology Faculty Publications and Presentations

A comprehensive mid-20th century inventory of glaciers and perennial snowfields (G&PS) was compiled for the American West, west of the 100° meridian. The inventory was derived from U.S. Geological Survey 1:24,000 topographic maps based on aerial photographs acquired during 35 years, 1955–1990, of which the first 20 years or more was a cool period with little glacier change. The mapped features were filtered for those greater than 0.01 km2. Results show that 5036 G&PS (672 km2, 14 km3) populate eight states, of which about 1276 (554 km2, 12 km3) are glaciers. Uncertainty is ...


Investigation Of Wing Crack Formation With A Combined Phase-Field And Experimental Approach, Sanghyun Lee, Jacqueline E. Reber, Nicholas W. Hayman, Mary F. Wheeler Jun 2017

Investigation Of Wing Crack Formation With A Combined Phase-Field And Experimental Approach, Sanghyun Lee, Jacqueline E. Reber, Nicholas W. Hayman, Mary F. Wheeler

Jacqueline Reber

Fractures that propagate off of weak slip planes are known as wing cracks and often play important roles in both tectonic deformation and fluid flow across reservoir seals. Previous numerical models have produced the basic kinematics of wing crack openings but generally have not been able to capture fracture geometries seen in nature. Here we present both a phase-field modeling approach and a physical experiment using gelatin for a wing crack formation. By treating the fracture surfaces as diffusive zones instead of as discontinuities, the phase-field model does not require consideration of unpredictable rock properties or stress inhomogeneities around crack ...


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 Apr 2017

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

Neal Iverson

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, J. M. Amundson, Neal R. Iverson Apr 2017

Testing A Glacial Erosion Rule Using Hang Heights Of Hanging Valleys, Jasper National Park, Alberta, Canada, J. M. Amundson, Neal R. Iverson

Neal 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 ...


Subglacial Clast/Bed Contact Forces, John Byers, Denis Cohen, Neal R. Iverson Apr 2017

Subglacial Clast/Bed Contact Forces, John Byers, Denis Cohen, Neal R. Iverson

Neal Iverson

A laboratory device was built to measure the forces that ice exerts on a 0.05 m diameter rigid plastic sphere in two different configurations: in contact with a flat bed or isolated from the bed. Measurements indicated that bed-normal contact forces were 1.8 times larger than drag forces due to creeping flow past a slippery sphere isolated from the bed. Measurements of forces as a function of the bed-normal ice velocity, estimations of the ice viscosity parameter and observations of markers in the ice indicate ice is Newtonian with a viscosity of ∼1.3 × 1011 Pa s. Newtonian ...


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 Apr 2017

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

Neal Iverson

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 ...


Glacier-Bed Geomorphic Processes And Hydrologic Conditions Relevant To Nuclear Waste Disposal, Neal R. Iverson, Mark Person Apr 2017

Glacier-Bed Geomorphic Processes And Hydrologic Conditions Relevant To Nuclear Waste Disposal, Neal R. Iverson, Mark Person

Neal Iverson

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 ...


Rate-Weakening Drag During Glacier Sliding, Lucas K. Zoet, Neal R. Iverson Apr 2017

Rate-Weakening Drag During Glacier Sliding, Lucas K. Zoet, Neal R. Iverson

Neal Iverson

Accurately specifying the relationship between basal drag on a hard, rough glacier bed and sliding speed is a long-standing and central challenge in glaciology. Drag on a rigid bed consisting of steps with linear treads inclined upglacier—a good idealization for the bedrock morphology of some hard-bedded glaciers—has been considered in sliding theories but never studied empirically. Balancing forces parallel to step treads indicates that drag should be independent of sliding speed and cavity size and set by the limit-equilibrium condition sometimes called Iken's bound. In this study we used a large ring-shear device to slide ice at ...


Sliding Of Ice Past An Obstacle At Engabreen, Norway, Denis Cohen, Roger Leb. Hooke, Neal R. Iverson, Jack Kohler Apr 2017

Sliding Of Ice Past An Obstacle At Engabreen, Norway, Denis Cohen, Roger Leb. Hooke, Neal R. Iverson, Jack Kohler

Neal Iverson

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 ...


Preexisting Fractures And The Formation Of An Iconic American Landscape: Tuolumne Meadows, Yosemite National Park, Usa, Richard A. Becker, Basil Tikoff, Paul R. Riley, Neal R. Iverson Apr 2017

Preexisting Fractures And The Formation Of An Iconic American Landscape: Tuolumne Meadows, Yosemite National Park, Usa, Richard A. Becker, Basil Tikoff, Paul R. Riley, Neal R. Iverson

Neal Iverson

Tuolumne Meadows, in Yosemite National Park (USA), is a large sub-alpine meadow in the Sierra Nevada Mountains. Immediately adjacent to Tuolumne Meadows—and underlain by the same bedrock lithology (Cathedral Peak Granodiorite)—are vertical rock faces that provide exceptional opportunities to climbers. While the presence of a broad meadow suggests bedrock erodibility, the vertical rock walls indicate bedrock durability. We propose that the Tuolumne Meadows’s landscape is the result of variable glacial erosion due to the presence or absence of pre-existing bedrock fractures. The meadows and valleys formed because of concentrated tabular fracture clusters—a distinctive and locally pervasive ...


Glacial Landscape Evolution By Subglacial Quarrying: A Multiscale Computational Approach, Sofie V. Ugelvig, David L. Egholm, Neal R. Iverson Apr 2017

Glacial Landscape Evolution By Subglacial Quarrying: A Multiscale Computational Approach, Sofie V. Ugelvig, David L. Egholm, Neal R. Iverson

Neal 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 ...


Magnetic Fabric Of Sheared Till: A Strain Indicator For Evaluating The Bed Deformation Model Of Glacier Flow, Thomas S. Hooyer, Neal R. Iverson, France Lagroix, Jason F. Thomason Apr 2017

Magnetic Fabric Of Sheared Till: A Strain Indicator For Evaluating The Bed Deformation Model Of Glacier Flow, Thomas S. Hooyer, Neal R. Iverson, France Lagroix, Jason F. Thomason

Neal Iverson

[1] Wet-based portions of ice sheets may move primarily by shearing their till beds, resulting in high sediment fluxes and the development of subglacial landforms. This model of glacier movement, which requires high bed shear strains, can be tested using till microstructural characteristics that evolve during till deformation. Here we examine the development of magnetic fabric using a ring shear device to deform two Wisconsin-age basal tills to shear strains as high as 70. Hysteresis experiments and the dependence of magnetic susceptibility of these tills on temperature demonstrate that anisotropy of magnetic susceptibility (AMS) develops during shear due to the ...


Reply To "Comment On ‘Preexisting Fractures And The Formation Of An Iconic American Landscape: Tuolumne Meadows, Yosemite National Park, Usa,’ By Jeffrey P. Schaffer”, Richard A. Becker, Basil Tikoff, Paul R. Riley, Neal R. Iverson Apr 2017

Reply To "Comment On ‘Preexisting Fractures And The Formation Of An Iconic American Landscape: Tuolumne Meadows, Yosemite National Park, Usa,’ By Jeffrey P. Schaffer”, Richard A. Becker, Basil Tikoff, Paul R. Riley, Neal R. Iverson

Neal Iverson

No abstract provided.


Estimating The Sliding Velocity Of A Pleistocene Ice Sheet From Plowing Structures In The Geologic Record, Neal R. Iverson, Thomas S. Hooyer Apr 2017

Estimating The Sliding Velocity Of A Pleistocene Ice Sheet From Plowing Structures In The Geologic Record, Neal R. Iverson, Thomas S. Hooyer

Neal Iverson

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 ...


Experimental Determination Of A Double-Valued Drag Relationship For Glacier Sliding, Lucas K. Zoet, Neal R. Iverson Apr 2017

Experimental Determination Of A Double-Valued Drag Relationship For Glacier Sliding, Lucas K. Zoet, Neal R. Iverson

Neal Iverson

The contribution of glaciers to sea-level rise and their effects on landscape evolution depend on the poorly known relationship between sliding speed and drag at the ice/bed interface. Results from experiments with a new rotary laboratory device demonstrate empirically for the first time a double-valued drag relationship like that suggested by some sliding theories: steady drag on a rigid, sinusoidal bed increases, peaks and declines at progressively higher sliding speeds due to growth of cavities in the lee sides of bed undulations. Drag decreases with increased sliding speed if cavities extend beyond the inflection points of up-glacier facing surfaces ...


Flow Mechanism Of The Des Moines Lobe Of The Laurentide Ice Sheet, Thomas S. Hooyer, Neal R. Iverson Apr 2017

Flow Mechanism Of The Des Moines Lobe Of The Laurentide Ice Sheet, Thomas S. Hooyer, Neal R. Iverson

Neal Iverson

Rapid flow of the Des Moines lobe of the Laurentide ice sheet may have been related to its unlithified substrate. New reconstructions of the lobe, based on moraine elevations, sediment subsidence during moraine deposition, and flow-direction indicators, indicate that the lobe may have been ~3 times thicker than in previous reconstructions. Nevertheless, implied basal shear stresses are <15 kPa, so internal ice deformation was not significant. Instead, the lobe likely moved by a combination of sliding, plowing of particles through the bed surface, and bed shear. Consolidation tests on basal till yield preconsolidation stresses of 125-300 kPa, so effective normal ...


Distributed Shear Of Subglacial Till Due To Coulomb Slip, Neal R. Iverson, Richard M. Iverson Apr 2017

Distributed Shear Of Subglacial Till Due To Coulomb Slip, Neal R. Iverson, Richard M. Iverson

Neal 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 ...


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 Apr 2017

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

Neal Iverson

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 ...


A Laboratory Study Of Particle Ploughing And Pore-Pressure Feedback: A Velocity-Weakening Mechanism For Soft Glacier Beds, Jason F. Thomason, Neal R. Iverson Apr 2017

A Laboratory Study Of Particle Ploughing And Pore-Pressure Feedback: A Velocity-Weakening Mechanism For Soft Glacier Beds, Jason F. Thomason, Neal R. Iverson

Neal 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 ...