scholarly journals Deformation motion tracks sliding changes through summer, western Greenland

2021 ◽  
pp. 1-10
Author(s):  
Nathan Maier ◽  
Neil Humphrey ◽  
Toby Meierbachtol ◽  
Joel Harper
Keyword(s):  
Surface Velocity ◽  
Ablation Zone ◽  
Dense Network ◽  
Bed Topography ◽  
Annual Basis ◽  
Spatial Deformation ◽  
Surface Measurements ◽  
Time Variations ◽  
Velocity Changes ◽  
Measurement Period

Abstract Surface speeds in Greenland's ablation zone undergo substantial variability on an annual basis which are presumed to mainly be driven by changes in sliding. Yet, meltwater-forced changes in ice–bed coupling can also produce variable deformation motion, which impacts the magnitude of sliding changes inferred from surface measurements and provides important context to flow dynamics. We examine spatiotemporal changes in deformation, sliding and surface velocities over a 2-year period using GPS and a dense network of inclinometers installed in borehole grid drilled in western Greenland's ablation zone. We find time variations in deformation motion track sliding changes through the summer and entire measurement period. A distinct spatial deformation and sliding pattern is also observed within the borehole grid which remains similar during winter and summer flow. We suggest that positively covarying sliding and deformation across seasonal timescales is characteristic of passive areas that are coupled to regions undergoing transient forcing, and the spatial patterns are consistent with variations in the local bed topography. The covarying deformation and sliding result in a 1.5–17% overestimate of sliding changes during summer compared to that inferred from surface velocity changes alone. This suggests that summer sliding increases are likely overestimated in many locations across Greenland.

scholarly journals Physics-Based Relationship for Pore Pressure and Vertical Stress Monitoring Using Seismic Velocity Variations

2021 ◽  
Vol 13 (14) ◽  
pp. 2684
Author(s):  
Eldert Fokker ◽  
Elmer Ruigrok ◽  
Rhys Hawkins ◽  
Jeannot Trampert
Keyword(s):  
Pore Pressure ◽  
Seismic Velocity ◽  
Pressure Head ◽  
Groundwater Table ◽  
Surface Velocity ◽  
Seismic Velocities ◽  
Stress Monitoring ◽  
Near Surface ◽  
Velocity Variations ◽  
Velocity Changes

Previous studies examining the relationship between the groundwater table and seismic velocities have been guided by empirical relationships only. Here, we develop a physics-based model relating fluctuations in groundwater table and pore pressure with seismic velocity variations through changes in effective stress. This model justifies the use of seismic velocity variations for monitoring of the pore pressure. Using a subset of the Groningen seismic network, near-surface velocity changes are estimated over a four-year period, using passive image interferometry. The same velocity changes are predicted by applying the newly derived theory to pressure-head recordings. It is demonstrated that the theory provides a close match of the observed seismic velocity changes.

scholarly journals The propagation of a surge front on Bering Glacier, Alaska, 2001–2011

2013 ◽  
Vol 54 (63) ◽  
pp. 221-228 ◽  
Author(s):  
James Turrin ◽  
Richard R. Forster ◽  
Chris Larsen ◽  
Jeanne Sauber
Keyword(s):  
Feature Tracking ◽  
Average Rate ◽  
Surface Velocity ◽  
Ablation Zone ◽  
Ice Surface ◽  
Glacier Terminus ◽  
Bering Glacier ◽  
Landsat 7 ◽  
Ice Velocity ◽  
Recent Activity

AbstractBering Glacier, Alaska, USA, has a ∼20 year surge cycle, with its most recent surge reaching the terminus in 2011. To study this most recent activity a time series of ice velocity maps was produced by applying optical feature-tracking methods to Landsat-7 ETM+ imagery spanning 2001-11. The velocity maps show a yearly increase in ice surface velocity associated with the down-glacier movement of a surge front. In 2008/09 the maximum ice surface velocity was 1.5 ±0.017 km a-1 in the mid-ablation zone, which decreased to 1.2 ±0.015 km a-1 in 2009/10 in the lower ablation zone, and then increased to nearly 4.4 ± 0.03 km a-1 in summer 2011 when the surge front reached the glacier terminus. The surge front propagated down-glacier as a kinematic wave at an average rate of 4.4 ±2.0 km a-1 between September 2002 and April 2009, then accelerated to 13.9 ± 2.0 km a-1 as it entered the piedmont lobe between April 2009 and September 2010. The wave seems to have initiated near the confluence of Bering Glacier and Bagley Ice Valley as early as 2001, and the surge was triggered in 2008 further down-glacier in the mid-ablation zone after the wave passed an ice reservoir area.

scholarly journals Variations of carbon monoxide in the atmosphere of Antarctica according to ground-based and satellite measurements

2019 ◽  
pp. 97-106 ◽  
Author(s):  
V. P. Ustinov ◽  
E. L. Baranova ◽  
K. N. Visheratin ◽  
M. I. Grachev ◽  
A. V. Kalsin
Keyword(s):  
Satellite Data ◽  
Total Content ◽  
Mixing Ratio ◽  
Satellite Measurements ◽  
Average Volume ◽  
Average Deviation ◽  
Average Value ◽  
Surface Measurements ◽  
Good Agreement ◽  
Measurement Period

The results of systematic (2003–2017) measurements of the total content and the volume mixing ratio of CO at Novolazarevskaya station with a spectrometer with a resolution of 0.2 cm– 1 are presented. The inverse problem of determining the total CO content, as well as interfering gases (H2O and N2O), was solved using the SFIT4 software package. Data analysis showed that over the measurement period the average total CO content at Novolazarevskaya amounted to (8 ± 2) 1017 molec/cm2, and the average volume mixing ratio amounted to (37 ± 8) ppb. The obtained data are compared with variations in the total content of CO in Arrival-Heights station, with MOPITT satellite data, as well as with surface values of CO concentration at Syova station. The maximum values of CO are observed in September, the minimum — in January–February. For all the considered series, the trends are insignificant, while there are periods of increased CO content (2010). In recent years (2014–2017) there is a tendency towards an increase in the minimum values of CO. For  Novolazarevskaya and  Arrival-Heights satellite data are characterized by the excess of over ground data, amounting to 19% and 14%, respectively, while there is a seasonal dependence of the deviation with the minimum in December–January. Surface measurements of the total CO content are in fairly good agreement at Novolazarevskaya and Arrival-Heights, and since 2010 the average deviation is 2.4%. The average value of the concentration of CO on Syova 51 ppb is higher than the average volume mixing ratio at Novolazarevskaya. According to the spectral, wavelet and composite analyzes, in all the considered series there are oscillations in the range of 6–45 months with closely coinciding periods and phases.

scholarly journals The Potsdam Parallel Ice Sheet Model (PISM-PIK) – Part 2: Dynamic equilibrium simulation of the Antarctic ice sheet

2011 ◽  
Vol 5 (3) ◽  
pp. 727-740 ◽  
Author(s):  
M. A. Martin ◽  
R. Winkelmann ◽  
M. Haseloff ◽  
T. Albrecht ◽  
E. Bueler ◽  
...  
Keyword(s):  
Steady State ◽  
Dynamic Equilibrium ◽  
Ice Sheet ◽  
Surface Velocity ◽  
Surface Mass ◽  
Ross Ice Shelf ◽  
Bed Topography ◽  
Melt Distribution ◽  
Spreading Rates ◽  
Equilibrium Simulation

Abstract. We present a dynamic equilibrium simulation of the ice sheet-shelf system on Antarctica with the Potsdam Parallel Ice Sheet Model (PISM-PIK). The simulation is initialized with present-day conditions for bed topography and ice thickness and then run to steady state with constant present-day surface mass balance. Surface temperature and sub-shelf basal melt distribution are parameterized. Grounding lines and calving fronts are free to evolve, and their modeled equilibrium state is compared to observational data. A physically-motivated calving law based on horizontal spreading rates allows for realistic calving fronts for various types of shelves. Steady-state dynamics including surface velocity and ice flux are analyzed for whole Antarctica and the Ronne-Filchner and Ross ice shelf areas in particular. The results show that the different flow regimes in sheet and shelves, and the transition zone between them, are captured reasonably well, supporting the approach of superposition of SIA and SSA for the representation of fast motion of grounded ice. This approach also leads to a natural emergence of sliding-dominated flow in stream-like features in this new 3-D marine ice sheet model.

scholarly journals Measurements of Water Pressure in Moulins as Part of a Movement Study of the White Glacier, Axel Heiberg Island, Northwest Territories, Canada

1972 ◽  
Vol 11 (61) ◽  
pp. 53-58 ◽  
Author(s):  
Almut Iken
Keyword(s):  
Northwest Territories ◽  
Atmospheric Pressure ◽  
Total Pressure ◽  
Water Pressure ◽  
Surface Velocity ◽  
Pressure Data ◽  
Measuring Range ◽  
Surface Measurements ◽  
Movement Study ◽  
Different Depths

AbstractIn 1970 water pressure was measured in several moulins on the White Glacier. Pressure variations in some moulin channels extended over the full measuring range of the instruments (0–1 and 0–2 bar above atmospheric pressure), even at depths of less than 50 m below the surface. Measurements at different depths showed that total pressure variations were sometimes greater than this. The pressure data are compared with variations in the surface velocity of the glacier.

scholarly journals Bed topography and lubrication inferred from surface measurements on fast-flowing ice streams

2003 ◽  
Vol 49 (167) ◽  
pp. 481-490 ◽  
Author(s):  
Throstur Thorsteinsson ◽  
Charles F. Raymond ◽  
G. Hilmar Gudmundsson ◽  
Robert A. Bindschadler ◽  
Paul Vornberger ◽  
...  
Keyword(s):  
Measurement Errors ◽  
Synthetic Data ◽  
Ice Thickness ◽  
West Antarctica ◽  
Horizontal Scale ◽  
Ice Streams ◽  
Bed Topography ◽  
Ice Stream ◽  
Flow Disturbances ◽  
Surface Measurements

AbstractObservations of surface elevation (s) and horizontal velocity components (u and v) are inverted to infer the topography (b) and lubrication (c) at the bed of an ice stream, based on a linearized perturbation theory of the transmission of flow disturbances through the ice thickness. Synthetic data are used to illustrate non-uniqueness in the inversion, but also demonstrate that effects of b and c can be separated when s, u and v are specified, even with added noise to simulate measurement errors. We have analyzed prominent short-horizontal-scale (∼2 km) features in topography and velocity pattern in a local 64 km by 32 km area of the surface of Ice Stream E,West Antarctica. Our preferred interpretation of bed conditions beneath the most prominent features on the surface identifies a deep trough in the basal topography with low lubrication in the base of the trough.

scholarly journals Characterizing englacial drainage in the ablation zone of the Greenland ice sheet

2008 ◽  
Vol 54 (187) ◽  
pp. 567-578 ◽  
Author(s):  
Ginny A. Catania ◽  
Thomas A. Neumann ◽  
Stephen F. Price
Keyword(s):  
Simulation Model ◽  
Strong Correlation ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Surface Velocity ◽  
Ablation Zone ◽  
Moderate Correlation ◽  
Supraglacial Lakes ◽  
Infill Material ◽  
Englacial Drainage

AbstractRapid, local drainage of surface meltwater to the base of the Greenland ice sheet is thought to result in surface velocity variations as far inland as the equilibrium zone (Zwally and others, 2002). Ice-penetrating radar surveys throughout this region allow us to characterize englacial drainage features that appear as vertically stacked diffraction hyperbolae in common-offset profiles. These data are used with a radar-simulation model, which allows for variations in geometry, penetration depth and infill material, to understand the characteristics of these hyperbolae and the likelihood that they are produced by moulins. We find only a moderate correlation between the locations of these possible moulins and supraglacial lakes, indicating that many lakes drain over the surface of the ice sheet, or do not contain sufficient water to reach the bed through moulin formation. We find a strong correlation between moulin location in the ablation region and elevated along-flow tension (due to flow over rough bedrock), which generates surface crevassing and provides an entry point for meltwater. Although theory suggests that moulins may form anywhere on the ice sheet given sufficient meltwater input, our data suggest that they are far more common in the ablation zone than near, or inland from, the equilibrium line.

scholarly journals The structure of the lithosphere and upper mantle beneath the Eastern Mediterranean and Middle East

2020 ◽  
Vol 2 (3) ◽  
pp. 311-326 ◽  
Author(s):  
Dan McKenzie
Keyword(s):  
Middle East ◽  
Shear Wave ◽  
Upper Mantle ◽  
Eastern Mediterranean ◽  
Three Dimensional ◽  
Surface Velocity ◽  
Wave Velocities ◽  
Shear Wave Velocities ◽  
Surface Measurements ◽  
Lithosphere Thickness

AbstractSurface velocity measurements show that the Middle East is one of the most actively deforming regions of the continents. The structure of the underlying lithosphere and convecting upper mantle can be explored by combining three types of measurement. The gravity field from satellite and surface measurements is supported by the elastic properties of the lithosphere and by the underlying mantle convection. Three dimensional shear wave velocities can be determined by tomographic inversion of surface wave velocities. The shear wave velocities of the mantle are principally controlled by temperature, rather than by composition. The mantle composition can be obtained from that of young magmas. Application of these three types of observation to the Eastern Mediterranean and Middle East shows that the lithosphere thickness in most parts is no more than 50-70 km, and that the elastic thickness is less than 5 km. Because the lithosphere is so thin and weak the pattern of the underlying convection is clearly visible in the topography and gravity, as well as controlling the volcanism. The convection pattern takes the form of spokes: lines of hot upwelling mantle, joining hubs where the upwelling is three dimensional. It is the same as that seen in high Rayleigh number laboratory and numerical experiments. The lithospheric thicknesses beneath the seafloor to the SW of the Hellenic Arc and beneath the NE part of the Arabian Shield are more than 150 km and the elastic thicknesses are 30–40 km.

scholarly journals Surface-velocity field of the northern Larsen Ice Shelf, Antarctica

1994 ◽  
Vol 20 ◽  
pp. 319-326 ◽  
Author(s):  
R. A. Bindschadler ◽  
M. A. Fahnestock ◽  
P. Skvarca ◽  
T. A. Scambos
Keyword(s):  
Satellite Images ◽  
Surface Velocity ◽  
Ice Shelf ◽  
Limited Region ◽  
Surface Survey ◽  
Degree Of Confidence ◽  
High Degree ◽  
The Antarctic ◽  
Larsen Ice Shelf ◽  
Measurement Period

Three satellite images of the northern Larsen Ice Shelf arc used to derive velocity fields for the periods 1975–86 and 1986 89. Substantial increases in the speed of the ice between these periods are detected to a high degree of confidence. Ice which entered the ice shelf between Fothergill Point and Cape Worsley and ice from Drygalski Glacier has accelerated by approximately 15% over the measurement period. Ice from Bombardier and Dinsmoor Glaciers also exhibits acceleration but by a lesser amount. These accelerations may be the result of either significant retreat experienced by the ice shelf during this period or warming in the Antarctic Peninsula region. Velocities measured by surface survey over a 15 d period in 1991 indicate a slower velocity than the image-derived velocities in the limited region of overlap. These differences appear to be systematic and may be the result of uncontrolled errors in the surface survey. Limited control of one image could also contribute to some of these differences.

scholarly journals Measurements of Water Pressure in Moulins as Part of a Movement Study of the White Glacier, Axel Heiberg Island, Northwest Territories, Canada

1972 ◽  
Vol 11 (61) ◽  
pp. 53-58 ◽  
Author(s):  
Almut Iken
Keyword(s):  
Northwest Territories ◽  
Atmospheric Pressure ◽  
Total Pressure ◽  
Water Pressure ◽  
Surface Velocity ◽  
Pressure Data ◽  
Measuring Range ◽  
Surface Measurements ◽  
Movement Study ◽  
Different Depths

AbstractIn 1970 water pressure was measured in several moulins on the White Glacier. Pressure variations in some moulin channels extended over the full measuring range of the instruments (0–1 and 0–2 bar above atmospheric pressure), even at depths of less than 50 m below the surface. Measurements at different depths showed that total pressure variations were sometimes greater than this. The pressure data are compared with variations in the surface velocity of the glacier.

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