scholarly journals The onset area of Ice Stream D, West Antarctica

2000 ◽  
Vol 46 (152) ◽  
pp. 95-101 ◽  
Author(s):  
Robert Bindschadler ◽  
Xin Chen ◽  
Patricia Vornberger
Keyword(s):  
Strain Rate ◽  
Global Positioning System ◽  
Landsat Imagery ◽  
Surface Flow ◽  
West Antarctica ◽  
The Past ◽  
Ice Stream ◽  
Global Positioning ◽  
Longitudinal Strain Rate ◽  
Streaming Flow

AbstractSurface flow in a 10 000 km2 expanse of the onset area of Ice Stream D, West Antarctica, was measured by repeat, precise global positioning system surveys over a 1 year interval. The pattern of velocity and strain rate shows the development of Ice Stream D, the major flow into which originates south of Byrd station and follows the course of a deep bed channel. Plotting of the driving stress vs the ratio of velocity and ice thickness identifies the onset of streaming flow (roughly 140 km downstream of Byrd station) as a transition between deformation flow and sliding flow. Along the kinematic center line of the developing ice stream, the ice rheology is linear at stresses below 0.6 bar, and appears temperate at the base well before the onset of streaming is reached. The onset corresponds to a maximum driving stress of 0.8 bar. It occurs downstream of a slight increase in longitudinal strain rate where stronger along-flow lineations are apparent in Landsat imagery, and after the ice has passed the center of an overdeepening in the bed channel. No current deviation from equilibrium is detected in this region, but a set of flow stripes misaligned with present flow indicates significant changes in flow have occurred in the past.

scholarly journals The elevation history of ice streams and the spatial accumulation pattern along the Siple Coast of West Antarctica inferred from ground-based radar data from three inter-ice-stream ridges

2001 ◽  
Vol 47 (157) ◽  
pp. 303-313 ◽  
Author(s):  
N. A. Nereson ◽  
C. F. Raymond
Keyword(s):  
Spatial Pattern ◽  
Internal Layer ◽  
Windward Side ◽  
West Antarctica ◽  
Ice Streams ◽  
Amundsen Sea ◽  
The Past ◽  
Ice Stream ◽  
Siple Dome ◽  
History Of

AbstractMeasurements of the surface and internal layer geometry from ice-penetrating radar and global positioning system surveys on three inter-ice-stream ridges in West Antarctica (Siple Dome, ridge DE and ridge BC) are examined with ice-flow models to infer (1) the history of the divide position at each site and (2) the spatial pattern of accumulation across the ridges. We find that the divide position is most steady at Siple Dome, somewhat steady at ridge DE and highly variable at ridge BC. Data from Siple Dome and ridge DE show evidence for steady northward motion of the ice divide for the past few thousand years. The layers beneath ridge BC suggest a 5 km northward shift of the divide position within the past several hundred years. Assuming the divide shifts are all due to changing elevation of the bounding ice streams, we infer the relative elevation history for segments of Ice Streams B–E. The northward displacement of the divide for all ridges implies a progressive relative thinning of the ice streams from E to B, with most dramatic recent thinning (100 m in <103 years) of Ice Stream B relative to Ice Stream C. Analysis of the internal layer pattern across the ridges indicates a south–north accumulation gradient with higher accumulation rates on the northern flanks of the ridges in all three cases. The inferred accumulation distribution is nearly uniform on the northern flanks, decreases sharply within a few ice thicknesses across the divides, and then decreases gradually farther to the south. The north/south decrease is strongest for ridge DE and weakest for ridge BC. This spatial pattern and the reduction in gradient strength with distance from the Amundsen Sea is consistent with the hypothesis that storms from the Amundsen Sea carry moisture first south then west over West Antarctica and deposit more snow on the windward side of ridges due to orographic lifting. This pattern has been stable for at least the past several thousand years.

scholarly journals Sensitivity of the divide position at Siple Dome, West Antarctica, to boundary forcing

1998 ◽  
Vol 27 ◽  
pp. 207-214 ◽  
Author(s):  
N. A. Nereson ◽  
R. C. A. Hindmarsh ◽  
C. F. Raymond
Keyword(s):  
Time Scales ◽  
Steady Increase ◽  
West Antarctica ◽  
Ice Streams ◽  
Accumulation Pattern ◽  
The Past ◽  
Ice Stream ◽  
Siple Dome ◽  
Climate Event ◽  
Short Time

A linearized perturbation about a two-dimensional Vialov-Nyc ice-shect profile is used to investigate the sensitivity of the divide position at Siple Dome, West Antarctica, to small changes in the accumulation pattern and in the elevation of its lateral boundaries at the margins of Ice Streams C and D. Relaxation time-scales for the ice-sheet surface and divide position are derived from the perturbation theory. For Siple Dome, these time-scales are short: 450 800 years for surface adjustment, and 200-350 years for divide position adjustment. These short time-scales indicate that Siple Dome responds quickly to forcing at its boundaries. Therefore, the recent migration of the Siple Dome divide (determined from previous work) is probably a response to an ongoing, sustained forcing rather than a response to a long-past climate event such as the transition from the Last Glacial Maximum to the Holocene. Based on our analysis, the inferred rate of migration of the Siple Dome divide could be attained by: (1) a steady increase in the south north spatial accumulation gradient of 0.1-1.5 × 10−9 a −2, or (2) a steady increase (decrease) in elevation of the Siple Dome lateral boundary adjacent to a relict margin of Ice Stream D (Ice Stream C) of 0.005-0.040 m a−1 over the past several thousand years. The required forcing is quite small, and suggests that major changes in the configuration of Ice Streams C and D associated with major changes in the elevation at boundaries of Siple Dome have not occurred over the past several thousand years.

scholarly journals Editorial for the Special Issue: “High-Precision GNSS: Methods, Open Problems and Geoscience Applications”

2020 ◽  
Vol 12 (10) ◽  
pp. 1602
Author(s):  
Xingxing Li ◽  
Jacek Paziewski ◽  
Mattia Crespi
Keyword(s):  
High Precision ◽  
Global Positioning System ◽  
Positioning System ◽  
Special Issue ◽  
Open Problems ◽  
The Past ◽  
Global Positioning

In the past two decades, the high-precision Global Positioning System (GPS) has significantly increased the range of geoscience applications and their precision [...]

scholarly journals Surge of Bering Glacier and Bagley Ice Field, Alaska: an update to August 1995 and an interpretation of brittle-deformation patterns

1997 ◽  
Vol 43 (145) ◽  
pp. 427-434 ◽  
Author(s):  
Ute Christina Herzfeld ◽  
Helmut Mayer
Keyword(s):  
Global Positioning System ◽  
Brittle Deformation ◽  
Location Data ◽  
The Past ◽  
Ice Surface ◽  
Bering Glacier ◽  
Global Positioning ◽  
Ice Field ◽  
Deformation Patterns

AbstractIn the summers of 1993, 1994 and 1995, video and Global Positioning System location data and 35 mm photographs were collected in a series of systematic survey flights undertaken over the Bering Glacier and Bagley Ice Field system (Alaska) in an effort to characterize surge-crevasse patterns and surge propagation. During survey flights in late August 1995, we observed that the 1993–94. Bering Glacier surge was continuing and still expanding affecting new areas farther up in Bagley Ice Field. New crevasse fields, similar in pattern to the first surge crevasses we had observed in June 1993 below Khitrov Hills and in other isolated areas of central Bering Glacier and in July 1994 near the head of Bering Glacier (near the junction of Bering Glacier and Bagley Ice Field, in both upper Bering Glacier and Bagley Ice Field), were opening in eastern Bagley Ice Field and in the “Stellet” side of Bagley Ice Field. The type of crevasses seen in the new fields suggested that the surge was propagating into these areas. By analysis and interpretation of the brittle-deformation patterns apparent in the crevasse patterns, some aspects of the past kinematic framework of the surge can be deduced. This approach may lead to a more general classification of ice-surface structures and to their linkage to ongoing processes.

scholarly journals Tidal influence on Rutford Ice Stream, West Antarctica: observations of surface flow and basal processes from closely spaced GPS and passive seismic stations

2008 ◽  
Vol 54 (187) ◽  
pp. 715-724 ◽  
Author(s):  
G. Aðalgeirsdóttir ◽  
A.M. Smith ◽  
T. Murray ◽  
M.A. King ◽  
K. Makinson ◽  
...  
Keyword(s):  
Tidal Cycle ◽  
General Pattern ◽  
Surface Flow ◽  
Surface Velocity ◽  
Velocity Variation ◽  
West Antarctica ◽  
Ice Stream ◽  
Grounding Line ◽  
Passive Seismic ◽  
First Time

AbstractHigh-resolution surface velocity measurements and passive seismic observations from Rutford Ice Stream, West Antarctica, 40 km upstream from the grounding line are presented. These measurements indicate a complex relationship between the ocean tides and currents, basal conditions and ice-stream flow. Both the mean basal seismicity and the velocity of the ice stream are modulated by the tides. Seismic activity increases twice during each semi-diurnal tidal cycle. The tidal analysis shows the largest velocity variation is at the fortnightly period, with smaller variations superimposed at diurnal and semi-diurnal frequencies. The general pattern of the observed velocity is two velocity peaks during each semi-diurnal tidal cycle, but sometimes three peaks are observed. This pattern of two or three peaks is more regular during spring tides, when the largest-amplitude velocity variations are observed, than during neap tides. This is the first time that velocity and level of seismicity are shown to correlate and respond to tidal forcing as far as 40 km upstream from the grounding line of a large ice stream.

scholarly journals The marginal shear stress of Ice Stream B, West Antarctica

1997 ◽  
Vol 43 (145) ◽  
pp. 415-426 ◽  
Author(s):  
Miriam Jackson ◽  
Barclay Kamb
Keyword(s):  
Shear Stress ◽  
Strain Rate ◽  
Time Scale ◽  
Shear Zones ◽  
Hot Water ◽  
West Antarctica ◽  
Ice Stream ◽  
Flow Law ◽  
Ice Stream B

AbstractTo ascertain whether the velocity of Ice Stream B, West Antarctica, may be controlled by the stresses in its marginal shear zones (the “Snake” and the “Dragon”), we undertook a determination of the marginal shear stress in the Dragon near Camp Up B by using ice itself as a stress meter. The observed marginal shear strain rate of 0.14 a−1is used to calculate the marginal shear stress from the flow law of ice determined by creep tests on ice cores from a depth of 300 m in the Dragon, obtained by using a hot-water ice-coring drill. The test-specimen orientation relative to the stress axes in the tests is chosen on the basis ofc-axis fabrics so that the test applies horizontal shear across vertical planes parallel to the margin. The resulting marginal shear stress is (2.2 ± 0.3) × 105Pa. This implies that 63–100% of the ice stream’s support against gravitational loading comes from the margins and only 37–0% from the base, so that the margins play an important role in controlling the ice-stream motion. The marginal shear-stress value is twice that given by the ice-stream model of Echelmeyer and others (1994) and the corresponding strain-rate enhancement factors differ greatly (E≈ 1–2 vs 10–12.5). This large discrepancy could be explained by recrystallization of the ice during or shortly after coring. Estimates of the expected recrystallization time-scale bracket the ∼1 h time-scale of coring and leave the likelihood of recrystallization uncertain. However, the observed two-maximum fabric type is not what is expected for annealing recrystallization from the sharp single-maximum fabric that would be expected in situ at the high shear strains involved (γ ∼ 20). Experimental data from Wilson (1982) suggest that, if the core did recrystallize, the prior fabric was a two-maximum fabric not substantially different from the observed one, which implies that the measured flow law and derived marginal shear stress are applicable to the in situ situation. These issues need to be resolved by further work to obtain a more definitive observational assessment of the marginal shear stress.

scholarly journals Crevasse patterns at the onset to Ice Stream B, West Antarctica

2001 ◽  
Vol 47 (156) ◽  
pp. 29-36 ◽  
Author(s):  
S. F. Price ◽  
I. M. Whillans
Keyword(s):  
Satellite Imagery ◽  
Water Production ◽  
West Antarctica ◽  
Ice Stream ◽  
Water Production Rate ◽  
Ice Stream B ◽  
And Storage ◽  
Possible Cause ◽  
Over Time ◽  
Streaming Flow

AbstractSequential satellite imagery and modeling are used to investigate crevasse patterns at the head of Ice Stream B tributary B1b. The crevasses, informally called the “chromosomes”, form at the upstream limit to B1b’s northern shear margin and chaotic crevasse zone. We find that the onset to crevasse formation, and by inference the onset to streaming flow, has migrated upstream over time at a mean rate of 230(16) m a−1. A possible cause for that migration is changes in net basal friction due to changes in basal water production rate and storage.

scholarly journals Ice-core insights into the flow and shut-down of Ice Stream C, West Antarctica

2003 ◽  
Vol 37 ◽  
pp. 123-128 ◽  
Author(s):  
Donald E. Voigt ◽  
Richard B. Alley ◽  
Sridhar Anandakrishnan ◽  
Matthew K. Spencer
Keyword(s):  
Power Law ◽  
Creep Behavior ◽  
Stream Flow ◽  
Ice Core ◽  
High Density ◽  
West Antarctica ◽  
Ice Stream ◽  
Central Regions ◽  
Power Law Creep ◽  
Streaming Flow

AbstractVigorous flow of central regions of Ice Stream C, West Antarctica, near the UpC camp ended about the year 1830, based on analysis of a firn and ice core taken at the camp. Ice-stream flow was characterized by repeated fracturing and healing, probably subsurface, especially near the onset of streaming flow. High longitudinal stresses caused fracturing, recrystallization of the ice and elongation of bubbles, and enhanced densification rates of high-density firn indicating power-law-creep behavior.

scholarly journals SEISMIC STRAIN MAP IN MALAYSIA DERIVED FROM LONG-TERM GLOBAL POSITIONING SYSTEM DATA

2019 ◽  
Vol XLII-4/W16 ◽  
pp. 399-408
Author(s):  
M. S. Mohamad ◽  
W. A. W. Aris ◽  
N. J. Jaffar ◽  
R. Othman
Keyword(s):  
Strain Rate ◽  
Global Positioning System ◽  
Crustal Deformation ◽  
Peninsular Malaysia ◽  
Positioning System ◽  
North Borneo ◽  
Global Positioning ◽  
The Status ◽  
Seismic Strain

Abstract. Series of major earthquakes struck the Sundaland plate as a result of convergence with neighboring plates such as Indian, Australian and Philippine plates. Since then, the Sundaland is experiencing significant crustal deformation that implicate reactivation of local fault and embark question on the status of geohazard and seismic risk. In Malaysia, crustal deformation study by using Global Positioning System (GPS) has been conducted for many years. However, the information of crustal deformation was reported separately and difficult to be archived. In addition, continuous estimation of crustal deformation derived from GPS has to be carried out in order to provide present day seismic status. This study aims at generating a seismic catalog map in Malaysia derived from approximately nine (9) years of GPS data. In this study, derived long-term crustal deformation in the form of coordinate time series (CTS) were converted into yearly strain map. The changes of strain with respect to location of old and active fault line in Malaysia were properly analysed. From the result, the highest changes of strain rate for Peninsular Malaysia happened in 2004 until 2005 and 2012 until 2013 prior to 2004 Acheh earthquake event with the moment magnitude (Mw) and 2012 two strike-slip events in Northern Sumatera with the magnitude of 8.2Mw and 8.6Mw. In North Borneo region, the most significant changes of strain rate happened from 2007 to 2009 and 2011 to 2013. It can be expected that the results will be beneficial in augmenting geohazard mitigation in Malaysia.

scholarly journals Basal melt rates beneath Whillans Ice Stream, West Antarctica

2010 ◽  
Vol 56 (198) ◽  
pp. 647-654 ◽  
Author(s):  
Lucas H. Beem ◽  
Ken C. Jezek ◽  
C.J. Van Der Veen
Keyword(s):  
West Antarctica ◽  
Ice Streams ◽  
Stress Regime ◽  
Basal Resistance ◽  
West Antarctic ◽  
Ice Stream ◽  
Whillans Ice Stream ◽  
Fast Flow ◽  
Insight Into ◽  
Streaming Flow

AbstractBasal water lubricates and enables the fast flow of the West Antarctic ice streams which exist under low gravitational driving stress. Identification of sources and rates of basal meltwater production can provide insight into the dynamics of ice streams and the subglacial hydrology, which remain insufficiently described by glaciological theory. Combining measurements and analytic modeling, we identify two regions where basal meltwater is produced beneath Whillans Ice Stream, West Antarctica. Downstream of the onset of shear crevasses, strong basal melt (20–50 mm a−1) is concentrated beneath the relatively narrow shear margins. Farther upstream, melt rates are consistently 3–7 mm a−1 across the width of the ice stream. We show that the transition in melt-rate patterns is coincident with the onset of shear margin crevassing and streaming flow and related to the development of significant lateral shear resistance, which reorganizes the resistive stress regime and induces a concentration of basal resistance adjacent to the shear margin. Finally, we discuss how downstream freeze-on in the ice-stream center coupled with melt beneath the shear margin might result in a slowing but widening ice stream.

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