Quasi-static granular flow of ice mélange

We use Landsat 8 imagery to generate ice mélange velocity fields at Greenland’s three most productive outlet glaciers: Jakobshavn Isbræ, Helheim Glacier, and Kangerdlugssuaq Glacier. Winter velocity fields are generally steady and highly uniform. Summer velocity fields, on the other hand, tend to be much more variable and can be uniform, compressional, or extensional. We rarely observe compressional flow at Jakobshavn Isbræ or extensional flow at Helheim Glacier, while both are observed at Kangerdlugssuaq Glacier. Transverse velocity profiles from all three locations are suggestive of viscoplastic flow, in which deformation occurs primarily in shear zones along the fjord walls. We analyze the transverse profiles in the context of quasi-static flow using continuum rheologies for granular materials and find that the force per unit width that ice mélange exerts on glacier termini increases exponentially with the ice mélange length-to-width ratio and the effective coefficient of friction. Our estimates of ice mélange resistance are consistent with other independent estimates and suggest that ice mélange may be capable of inhibiting iceberg calving events, especially during winter. Moreover, our results provide geophysical-scale support for constitutive relationships for granular materials and suggest a potential avenue for modeling ice mélange dynamics with continuum models.From acknowledgments: Funding for this project was provided by the U.S. National Science Foundation (DMR-1506446 and DMR-1506307). Digital elevation models were provided by the Polar Geospatial Center under the U.S. National Science Foundation (OPP-1043681, OPP-1559691, and OPP-1542736)Ye

The Amisk site : a multi-component campsite in south-central Saskatchewan

The Amisk site is a stratified archaeological site containing the remains of at least eight and possibly nine occupations over the past five millennia. A variety of subsistence activities occured at the site during these occupations such as food processing and preparation, tool making and tool repair. This combination of activities is characteristic of a habitation area. The Amisk site, therefore, represents a series of campsites adjacent to a small meandering stream. In this respect the Amisk site can be seen as analogous with other archaeological sites in Saskatchewan such as the Long Creek site, the Mortlach site, the Garratt site, the Oxbow Dam site as well as a number of sites in the Tipperary Creek valley including the Newo Asiniak site and the Tipperary Creek site which are presently being studied. Artifactual and chronological evidence supports and strengthens our understanding of the cultural chronology of southern Saskatchewan with projectile points and radiocarbon dates which coroborate existing data from the Oxbow complex and the Late Side-Notched series

Third Interger Resonance Slow Extraction Using RFKO at High Space Charge

A proposal to search for direct {\mu}-->e conversion at Fermilab requires slow, resonant extraction of an intense proton beam. Large space charge forces will present challenges, partly due to the substantial betatron tune spread. The main challenges will be maintaining a uniform spill profile and moderate losses at the septum. We propose to use "radio frequency knockout" (RFKO) for fine tuning the extraction. Strategies for the use of the RFKO method will be discussed here in the context of the Mu2e experiment. The feasibility of this method has been demonstrated in simulations.Comment: 3 pp. 2nd International Particle Accelerator Conference: IPAC 2011. 4-9 Sep 2011. San Sebastian, Spai

Involving Older Volunteers, in Public Schools

Each day, 5,000 Americans celebrate their sixty-fifth birthday. As this age group becomes larger, it will also become more powerful. As voters, seniors make up the most conscientious of the voting group in our society

An economic comparison of high moisture feedstock biofuel production

This study compares final fuel production costs of multiple biomass-to-liquid production facilities. Process economics are estimated for four different high moisture feedstocks, four different biomass supply chain pathways and three different conversion and upgrading technologies. Two biorefinery capacities are examined, small (200 tonne per day) and large (2000 tonne per day). Corn stover, corn silage giant miscanthus and sweet sorghum are the feedstocks considered for conversion via hydrothermal liquefaction (HTL) and anaerobic digestion (AD). Final product finishing is done by hydroprocessing of the HTL biocrude and either Fischer-Tropsch (FT) synthesis or methanol-to-gasoline (MTG) conversion of the AD biogas. Water footprints are estimated for blue, green and grey water consumption during the entire biofuel production process for each scenario. In efforts to decrease the production costs, moisture and size reduction steps are omitted during the biomass supply chain stage. Multi-pass and single pass harvesting scenarios are considered along with wet and dry storage techniques. These steps lead to an estimated delivered feedstock cost ranging from $63.84-$86.19 per tonne; comparable with recent literature. Conversion and upgrading pathways were chosen based on ability to handle high moisture feedstock. Capital investments were estimated for each technology scenario and ranged from $424-$538 MM for the 2000 tpd biorefinery, within a degree of uncertainty; HTL resulted in the lowest estimated capital costs. Final fuel production costs ranged from $2.04-$6.39 per gallon for all feedstocks and all conversion pathways, with stover and sorghum resulting in the lowest. The total water footprints were estimated to range from 5.92-23.21 Lw/Lb and 5.58-14.89 Lw/Lb for the conservative and optimal blue water scenarios, respectively. The green and grey water footprints ranged from 232.30-2,568.27 Lw/Lb and 296-526 L, respectively

Quantifying flow and stress in ice mélange, the world’s largest granular material.

Tidewater glacier fjords are often filled with a collection of calved icebergs, brash ice, and sea ice. For glaciers with high calving rates, this “m ́elange” of ice can be jam-packed, so that the flow of ice fragments is mostly determined by granular interactions. In the jammed state, ice m ́elange has been hypothesized to influence iceberg calving and capsize, dispersion and attenuation of ocean waves, injection of freshwater into fjords, and fjord circulation. However, detailed measurements of ice m ́elange are lacking due to difficulties in instrumenting remote, ice-choked fjords. Here we characterize the flow and associated stress in icem ́elange, using a combination of terrestrial radar data, laboratory experiments, and numerical simulations. We find that, during periods of terminus quiescence, ice m ́elange experiences laminar flow over timescales of hours to days. The uniform flow fields are bounded by shear margins along fjord walls where force chains between granular icebergs terminate. In addition, the average force per unit width that is transmitted to the glacier terminus, which can exceed 107N/m, increases exponentially with them ́elange length-to-width ratio. These “buttressing” forces are sufficiently high to inhibit the initiation of large-scale calving events, supporting the notion that ice m ́elange can be viewed as a weak granular ice shelf that transmits stresses from fjord walls back to glacier termini.Ye

Seismic Tremor Reveals Spatial Organization and Temporal Changes of Subglacial Water System

©2019. American Geophysical Union. All Rights Reserved.Subglacial water flow impacts glacier dynamics and shapes the subglacial environment. However, due to the challenges of observing glacier beds, the spatial organization of subglacial water systems and the time scales of conduit evolution and migration are largely unknown. To address these questions, we analyze 1.5‐ to 10‐Hz seismic tremor that we associate with subglacial water flow, that is, glaciohydraulic tremor, at Taku Glacier, Alaska, throughout the 2016 melt season. We use frequency‐dependent polarization analysis to estimate glaciohydraulic tremor propagation direction (related to the subglacial conduit location) and a degree day melt model to monitor variations in melt‐water input. We suggest that conduit formation requires sustained water input and that multiconduit flow paths can be distinguished from single‐conduit flow paths. Theoretical analysis supports our seismic interpretations that subglacial discharge likely flows through a single‐conduit in regions of steep hydraulic potential gradients but may be distributed among multiple conduits in regions with shallower potential gradients. Seismic tremor in regions with multiple conduits evolves through abrupt jumps between stable configurations that last 3–7 days, while tremor produced by single‐conduit flow remains more stationary. We also find that polarized glaciohydraulic tremor wave types are potentially linked to the distance from source to station and that multiple peak frequencies propagate from a similar direction. Tremor appears undetectable at distances beyond 2–6 km from the source. This new understanding of the spatial organization and temporal development of subglacial conduits informs our understanding of dynamism within the subglacial hydrologic system.Raw seismic data described in this paper are available through the Incorporated Research Institutions for Seismology Data Management Center (http://ds.iris.edu/mda/ZQ? timewindow=2015‐2016; Amundson et al., 2015). The raw weather data used in this paper can be found through the Arctic Data Center (https://doi.org/ 10.18739/A2H98ZC7V; Bartholomaus & Walter, 2018). Python code developed to carry out the analyses presented here is available at https://github.com/ voremargot/Seismic‐Tremor‐Reveals‐ Spatial‐Organization‐and‐Temporal‐ Changes‐of Subglacial‐Water‐System and https://github.com/ tbartholomaus/med_spec. This study was made possible with support from the University of Texas Institute for Geophysics and the University of Idaho. We thank Ginny Catania for the loan of weather stations. J. P. W.'s and J. M. A.'s contributions to this work were supported by the U.S. National Science Foundation (OPP‐1337548 and OPP‐ 1303895). T. C. B. thanks Dylan Mikesell for an early conversation, which inspired the analysis presented here.Ye