scholarly journals Large-scale force budget of an outlet glacier: Jutulstraumen, Dronning Maud Land, East Antarctica

2000 ◽  
Vol 30 ◽  
pp. 35-41 ◽  
Author(s):  
C. Rolstad ◽  
I. M. Whillans ◽  
J. O. Hagen ◽  
E. Isaksson
Keyword(s):  
Ground Penetrating Radar ◽  
Large Scale ◽  
Force Balance ◽  
Ice Thickness ◽  
Strain Rates ◽  
Ice Flow ◽  
Outlet Glacier ◽  
Grounding Line ◽  
Dronning Maud Land ◽  
Ground Penetrating

AbstractA large-scale force budget was applied using a combination of remote-sensing and field data from Jutulstraumen, Dronning Maud Land, Antarctica. In the grounded area, more than 95 % of ice flow is balanced by basal friction. In a partly floating section near the grounding-line area, on average lateral drag provides 38% of resistance to flow.Measurement uncertainties were propagated through the calculation of forces. The accuracies of strain rates derived from satellite data (Landsat thematic mapper) were found adequate to calculate meaningful force-balance terms. For the floating section, where lateral forces contribute to controlling flow, the main contribution to errors in the force budget is uncertainty in the rate factor for the flow law of ice. For grounded sections, the uncertainty in ice thickness, as measured by ground-penetrating radar, contributes more or less equally to errors in the force budget as does that in the rate factor.

scholarly journals Force-perturbation analysis of Pine Island Glacier, Antarctica, suggests cause for recent acceleration

2004 ◽  
Vol 39 ◽  
pp. 133-138 ◽  
Author(s):  
Robert Thomas ◽  
Eric Rignot ◽  
Pannirselvam Kanagaratnam ◽  
William Krabill ◽  
Gino Casassa
Keyword(s):  
Surface Strain ◽  
Ice Thickness ◽  
Strain Rates ◽  
West Antarctica ◽  
Ice Shelf ◽  
Amundsen Sea ◽  
Ice Flow ◽  
Velocity Increase ◽  
Grounding Line ◽  
Force Perturbation

AbstractPine Island Glacier, flowing into the Amundsen Sea from West Antarctica, thinned substantially during the 1990s, its grounding line receded by several km, and its velocity increased by >10% to values approaching 3 km a–1. Here, we use these observations, together with estimates of ice thickness and surface strain rates, to estimate the perturbation in forces resisting ice flow compatible with the observations. The analysis assumes that such perturbations are transmitted far upstream from where they originate, and that creep response to the perturbations can be described by equations similar to those that govern ice-shelf creep. It indicates that observed acceleration between 1996 and 2000 could have been caused by progressive ungrounding within the most seaward 25 km ‘ice plain’ of the grounded glacier. Earlier retreat and thinning of the glacier’s floating ice shelf may have provided the conditions that initiated ungrounding of the ice plain. Our analysis indicates that continued ice-plain thinning at the current rate of about 2 ma–1 will result in a velocity increase by 1 km a–1 within the next 11 years as the ice plain becomes totally ungrounded.

scholarly journals Ice-dynamic conditions of Shirase Glacier, Antarctica, inferred from ERS SAR interferometry

2002 ◽  
Vol 48 (163) ◽  
pp. 559-565 ◽  
Author(s):  
Frank Pattyn ◽  
Dominique Derauw
Keyword(s):  
Large Scale ◽  
Drainage Basin ◽  
Surface Strain ◽  
Force Balance ◽  
Phase Correlation ◽  
Sar Interferometry ◽  
Surface Velocity ◽  
Sar Images ◽  
Outlet Glacier ◽  
Grounding Line

AbstractThe surface velocity field of Shirase Glacier, a fast-flowing East Antarctic outlet glacier, is determined from ERS synthetic aperture radar (SAR) images by means of speckle tracking using phase correlation, a technique which matches small image kernels of two complex SAR images by maximization of the local coherence. Velocity estimates are used to calculate surface strain rates, which are then used to calculate the large-scale, vertically integrated force balance and to determine the major stress components resisting the driving stress. For the whole glacier system, the driving stress is largely balanced by the basal drag, but with contributions from lateral drag up to 15% of the driving stress at the grounding line. Longitudinal stress gradients have only local importance to the balance of forces, limited to an area of a few square kilometers near the grounding line, where they resist the driving stress. In the grounded part of the glacier, >90% of the total ice velocity is due to basal sliding. Comparison with a balance-flux distribution of the Antarctic ice sheet suggests that the glacier in the downstream part of the Shirase drainage basin is close to equilibrium, showing a slight negative imbalance.

Thwaites and Dotson Ice Shelves: Field Site Selection and Early Results of Field Measurements

2020 ◽  
Author(s):  
Erin Pettit ◽  
Atsu Muto ◽  
Christian Wild ◽  
Karen Alley ◽  
Ted Scambos ◽  
...  
Keyword(s):  
Continental Shelf ◽  
Satellite Data ◽  
Ground Penetrating Radar ◽  
Hot Water ◽  
Ice Thickness ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Grounding Line ◽  
Ground Penetrating

<p>As part of the International Thwaites Glacier Collaboration (ITGC) field activity in West Antarctica for the 2019-2020 season, the Thwaites-Amundsen Regional Survey and Network (TARSAN) team drilled boreholes using hot water, deployed long-term instruments, and gathered several ground-based geophysical data sets to assess the ice-shelf stability and evolution.<br><br>The Thwaites Eastern Ice Shelf is an important buttress for a broad (25 km) section of Thwaites Glacier outflow and is restrained at present by a few pinning points at the northwestern edge of the shelf. The grounding line of this buttress has retreated within the last 5 years indicating instability. Recent imagery shows major new rifting and shearing within the ice shelf.<br><br>In the Dotson-Crosson Ice Shelf (a single ice shelf with a rapidly evolving central region that has thinned and ungrounded over the past 80 years), satellite data show significant ice flow speed and direction changes, as well as retreating grounding lines where tributary glaciers start to float and where ice flows over and around isolated bedrock pinning points. A complex geometry of deep seafloor troughs underlie the central ice-shelf area which lies at the convergence of the two major troughs that extend to the continental shelf edge at two widely separated locations (roughly 103°W and 117°W longitude along the continental shelf break).<br><br>We surveyed the central Thwaites Eastern Ice Shelf (‘Cavity Camp’, 75.05°S, 105.58°W) and central Dotson-Crosson Ice Shelf (`Upper Dotson’, 74.87°S, 112.20°W) to the extent possible considering site safety and scientific interest. Cavity Camp is located approximately 17 km down-flow of the 2011 Thwaites Glacier grounding line. Ground-penetrating radar data show the ice thickness near Cavity Camp to be 300m, which is ~200m thinner than in 2007 estimated from hydrostatic assumption using altimetry analysis by other researchers. The seafloor below Cavity Camp is 816m, based on pressure from a CTD profile (a ~540 m water column and ~40m of firn).   <br><br>Across the central Dotson-Crosson Ice Shelf, a network of basal channels creates variable thinning rates from near-zero to over 30 m/yr (estimated in several previous remote-sensing-based studies). Ice thickness near our camp over a subglacial channel is 390m and the ice has been thinning at ~25 m/yr estimated from satellite data. Seafloor elevation at the Dotson site is estimated at -570 m, but seismic surveys suggest that the seabed topography varies considerably beneath Dotson. <br><br>On each ice shelf, we conducted ~200 km of multi-frequency ground-penetrating radar profiles. We also conducted 46 (Thwaites) and 17 (Dotson) autonomous phase-tracking radio echo-sounding (ApRES) repeat point measurements, as well as 37 (Thwaites) and more than 20 (Dotson) active-seismic spot soundings to characterize the sub-ice-shelf cavity shape, thinning rates, basal ice structures, and ocean circulation. We deployed two Automated Meteorology Ice Geophysics Ocean observation Systems (AMIGOS-III stations) on the Thwaites Ice Shelf that include a suite of surface sensors, a fiber-optic-based thermal profiler, and an ocean mooring. Additionally, we deployed four long-term ApRES on the two ice shelves to monitor temporal variability in ice melt.</p>

scholarly journals Ice thickness distribution of all Swiss glaciers based on extended ground-penetrating radar data and glaciological modeling

2021 ◽  
pp. 1-19
Author(s):  
Melchior Grab ◽  
Enrico Mattea ◽  
Andreas Bauder ◽  
Matthias Huss ◽  
Lasse Rabenstein ◽  
...  
Keyword(s):  
Ground Penetrating Radar ◽  
Thickness Distribution ◽  
Radar Data ◽  
Tourism Industry ◽  
Swiss Alps ◽  
Ice Thickness ◽  
Hazard Management ◽  
Bed Topography ◽  
Ice Volume ◽  
Ground Penetrating

Abstract Accurate knowledge of the ice thickness distribution and glacier bed topography is essential for predicting dynamic glacier changes and the future developments of downstream hydrology, which are impacting the energy sector, tourism industry and natural hazard management. Using AIR-ETH, a new helicopter-borne ground-penetrating radar (GPR) platform, we measured the ice thickness of all large and most medium-sized glaciers in the Swiss Alps during the years 2016–20. Most of these had either never or only partially been surveyed before. With this new dataset, 251 glaciers – making up 81% of the glacierized area – are now covered by GPR surveys. For obtaining a comprehensive estimate of the overall glacier ice volume, ice thickness distribution and glacier bed topography, we combined this large amount of data with two independent modeling algorithms. This resulted in new maps of the glacier bed topography with unprecedented accuracy. The total glacier volume in the Swiss Alps was determined to be 58.7 ± 2.5 km3 in the year 2016. By projecting these results based on mass-balance data, we estimated a total ice volume of 52.9 ± 2.7 km3 for the year 2020. Data and modeling results are accessible in the form of the SwissGlacierThickness-R2020 data package.

Ground-penetrating radar profiles of the McMurdo Shear Zone, Antarctica, acquired with an unmanned rover: Interpretation of crevasses, fractures, and folds within firn and marine ice

Geophysics ◽  
2016 ◽  
Vol 81 (1) ◽  
pp. WA21-WA34 ◽  
Author(s):  
Steven A. Arcone ◽  
James H. Lever ◽  
Laura E. Ray ◽  
Benjamin S. Walker ◽  
Gordon Hamilton ◽  
...  
Keyword(s):  
Shear Zone ◽  
Ground Penetrating Radar ◽  
Ice Accretion ◽  
Ice Shelf ◽  
Ice Flow ◽  
Ross Ice Shelf ◽  
Robotic Vehicle ◽  
Ground Penetrating ◽  
Depth Ranges ◽  
Radar Antennas

The crevassed firn of the McMurdo shear zone (SZ) within the Ross Ice Shelf may also contain crevasses deep within its meteoric and marine ice, but the surface crevassing prevents ordinary vehicle access to investigate its structure geophysically. We used a lightweight robotic vehicle to tow 200- and 400-MHz ground-penetrating radar antennas simultaneously along 100 parallel transects over a [Formula: see text] grid spanning the SZ width. Transects were generally orthogonal to the ice flow. Total firn and meteoric ice thickness was approximately 160 m. Firn crevasses profiled at 400 MHz were up to 16 m wide, under snow bridges up to 10 m thick, and with strikes near 35°–40° to the transect direction. From the top down, 200-MHz profiles revealed firn diffractions originating to a depth of approximately 40 m, no discernible structure within the meteoric ice, a discontinuous transitional horizon, and at least 20 m of stratified marine ice; 28–31 m of freeboard found more marine ice exists. Based on 10 consecutive transects covering approximately [Formula: see text], we preliminarily interpreted the transitional horizon to be a thin saline layer, and marine ice hyperbolic diffractions and reflections to be responses to localized fractures, and crevasses filled with unstratified marine ice, all at strikes from 27° to 50°. We preliminarily interpreted off-nadir, marine ice horizons to be responses to linear and folded faults, similar to some in firn. The coinciding and synchronously folded areas of fractured firn and marine ice suggested that the visibly unstructured meteoric ice beneath our grid was also fractured, but either never crevassed, crevassed and sutured without marine ice inclusions, or that any ice containing crevasses might have eroded before marine ice accretion. We will test these interpretations with analysis of all transects and by extending our grid and increasing our depth ranges.

Model Track Studies by Ground Penetrating Radar (GPR) on Ballast With Different Fouling and Geotechnical Properties

2015 ◽  
Author(s):  
Hamed Faghihi Kashani ◽  
Carlton L. Ho ◽  
Charles P. Oden ◽  
Stanley S. Smith
Keyword(s):  
Ground Penetrating Radar ◽  
Large Scale ◽  
Empirical Studies ◽  
Geotechnical Properties ◽  
Maintenance Cost ◽  
Non Invasive ◽  
Section Area ◽  
University Of Massachusetts ◽  
Ground Penetrating ◽  
The University

In recent years there has been an increase in the knowledge of, and need for, non-invasive monitoring of ballast in order to identify the problematic sections of track and decrease the maintenance cost. Various technologies such as Ground Penetrating Radar (GPR) are becoming accepted for investigating the condition of ballast. However since these techniques were not originally developed for engineering applications, their applicability in ballast evaluations can be sometimes uncertain. Continued empirical studies and condition specific calibrations are needed to demonstrate repeatable and quantifiable results. In this study large-scale track models with trapezoidal section area were constructed at the University of Massachusetts to investigate the effects of breakdown fouling, and the effects of changing geotechnical properties on GPR traces. This paper presents the design and construction of large scale track models, and methods used for GPR data collection. GPR data are presented in this paper that demonstrate sensitivity to the track model properties and variables. In particular, the experiments are being used to evaluate changes in GPR data with changing geotechnical properties of the ballast such as density, water content, grain size distribution (GSD), and fouling percentage.

scholarly journals The stability of a viscous till sheet coupled with ice flow, considered at wavelengths less than the ice thickness

1998 ◽  
Vol 44 (147) ◽  
pp. 285-292 ◽  
Author(s):  
Richard C. A. Hindmarsh
Keyword(s):  
Large Scale ◽  
Flow Instability ◽  
Ice Thickness ◽  
Ice Flow ◽  
Perturbation Amplitude ◽  
Sediment Flow ◽  
Viscous Models ◽  
The Stability ◽  
Parameter Ranges ◽  
Ice Sheet Modelling

AbstractA perturbation method is used to analyse the stability of a thin till layer overlain by a deep ice layer. Ice is modelled as a linearly viscous fluid, while the till viscosity has power-law dependence on stress and effective pressure. A linearized set of equations yields descriptions of the coupling of the ice flow with the sediment flow and reveals parameter ranges where the till-perturbation amplitude can grow. This sheet-flow instability is an essential part of any theory of drumlin formation and shows that viscous models of till have the ability to explain typical deforming-bed features. This is of great significance for large-scale ice-sheet modelling.

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