Quiescent-phase evolution of a surge-type glacier: Black Rapids Glacier, Alaska, U.S.A.

AbstractBlack Rapids Glacier, a surge-type glacier in the Alaska Range, most recently surged in 1936–37 and is currently in its quiescent phase. Mass balance, ice velocity and thickness change have been measured at three to ten sites from 1972 to 1994. The annual speed has undergone cyclical fluctuations of as much as 45% about the mean speed. Ice thickness and surface slope did not change enough to cause the speed fluctuations through changes in ice deformation, which indicates that they are being drinven by changes in basal motion. The behavior of Black Rapids Glacier during this quiescent phase is significantly different from that of Variegated Glacier, another well-studied surge-type glacier in Alaska. The present medial-moraine configuration of Black Rapids Glacier indicates that a surge could occur at any time. However, ice velocity data indicate that the next surge may not be imminent. We belive that there is little chance that the next surge will cross and dam the Delta River.

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Geometry and ice dynamics of the Darwin–Hatherton glacial system, Transantarctic Mountains

Journal of Glaciology ◽

10.1017/jog.2017.60 ◽

2017 ◽

Vol 63 (242) ◽

pp. 959-972

Author(s):

METTE K. GILLESPIE ◽

WENDY LAWSON ◽

WOLFGANG RACK ◽

BRIAN ANDERSON ◽

DONALD D. BLANKENSHIP ◽

...

Keyword(s):

Ice Sheet ◽

Ice Thickness ◽

Ice Shelf ◽

Ice Dynamics ◽

Ross Ice Shelf ◽

Basal Ice ◽

Grounding Line ◽

Ice Flows ◽

Ice Velocity ◽

The Mean

ABSTRACTThe Darwin–Hatherton Glacial system (DHGS) connects the East Antarctic Ice Sheet (EAIS) with the Ross Ice Shelf and is a key area for understanding past variations in ice thickness of surrounding ice masses. Here we present the first detailed measurements of ice thickness and grounding zone characteristics of the DHGS as well as new measurements of ice velocity. The results illustrate the changes that occur in glacier geometry and ice flux as ice flows from the polar plateau and into the Ross Ice Shelf. The ice discharge and the mean basal ice shelf melt for the first 8.5 km downstream of the grounding line amount to 0.24 ± 0.05 km3 a−1 and 0.3 ± 0.1 m a−1, respectively. As the ice begins to float, ice thickness decreases rapidly and basal terraces develop. Constructed maps of glacier geometry suggest that ice drainage from the EAIS into the Darwin Glacier occurs primarily through a deep subglacial canyon. By contrast, ice thins to <200 m at the head of the much slower flowing Hatherton Glacier. The glaciological field study establishes an improved basis for the interpretation of glacial drift sheets at the link between the EAIS and the Ross Ice Sheet.

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Using surface velocities to calculate ice thickness and bed topography: a case study at Columbia Glacier, Alaska, USA

Journal of Glaciology ◽

10.3189/2012jog11j249 ◽

2012 ◽

Vol 58 (212) ◽

pp. 1151-1164 ◽

Cited By ~ 76

Author(s):

R.W. Mcnabb ◽

R. Hock ◽

S. O’Neel ◽

L.A. Rasmussen ◽

Y. Ahn ◽

...

Keyword(s):

Thickness Distribution ◽

Computational Time ◽

Ice Thickness ◽

Thickness Change ◽

Bed Topography ◽

Surface Data ◽

Direct Measurements ◽

The Mean ◽

Time Required

AbstractInformation about glacier volume and ice thickness distribution is essential for many glaciological applications, but direct measurements of ice thickness can be difficult and costly. We present a new method that calculates ice thickness via an estimate of ice flux. We solve the familiar continuity equation between adjacent flowlines, which decreases the computational time required compared to a solution on the whole grid. We test the method on Columbia Glacier, a large tidewater glacier in Alaska, USA, and compare calculated and measured ice thicknesses, with favorable results. This shows the potential of this method for estimating ice thickness distribution of glaciers for which only surface data are available. We find that both the mean thickness and volume of Columbia Glacier were approximately halved over the period 1957–2007, from 281 m to 143 m, and from 294 km3 to 134 km3, respectively. Using bedrock slope and considering how waves of thickness change propagate through the glacier, we conduct a brief analysis of the instability of Columbia Glacier, which leads us to conclude that the rapid portion of the retreat may be nearing an end.

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Measured Velocities and Ice Flow in Wilkes Land, Antarctica

Annals of Glaciology ◽

10.1017/s0260305500007187 ◽

1989 ◽

Vol 12 ◽

pp. 192-197 ◽

Cited By ~ 14

Author(s):

N.W. Young ◽

I.D. Goodwin ◽

N.W.J. Hazelton ◽

R.J. Thwaites

Keyword(s):

Distance Scale ◽

Ice Thickness ◽

Shear Strain Rate ◽

Horizontal Shear ◽

Ice Flow ◽

Velocity Surface ◽

Wilkes Land ◽

Similar Distance ◽

Ice Velocity ◽

The Mean

Ice velocity, surface elevation, and ice thickness were measured along oversnow traverse routes in the sector of Wilkes Land, East Antarctica, bounded by long. 93° and 131°E, and the coast and lat. 75°S. The velocity measurements show that the ice flow varies smoothly in both direction and magnitude over a distance scale of at least 20 times the ice thickness, and that it is in the direction of the surface slope averaged over a similar distance scale. A comparison of the mean horizontal shear strain-rate with the driving stress supports a power-law relation for the bulk rheology of the ice sheet with an exponent between 3 and 3.2

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Measured Velocities and Ice Flow in Wilkes Land, Antarctica

Annals of Glaciology ◽

10.3189/s0260305500007187 ◽

1989 ◽

Vol 12 ◽

pp. 192-197 ◽

Cited By ~ 3

Author(s):

N.W. Young ◽

I.D. Goodwin ◽

N.W.J. Hazelton ◽

R.J. Thwaites

Keyword(s):

Distance Scale ◽

Ice Thickness ◽

Shear Strain Rate ◽

Horizontal Shear ◽

Ice Flow ◽

Velocity Surface ◽

Wilkes Land ◽

Similar Distance ◽

Ice Velocity ◽

The Mean

Ice velocity, surface elevation, and ice thickness were measured along oversnow traverse routes in the sector of Wilkes Land, East Antarctica, bounded by long. 93° and 131°E, and the coast and lat. 75°S. The velocity measurements show that the ice flow varies smoothly in both direction and magnitude over a distance scale of at least 20 times the ice thickness, and that it is in the direction of the surface slope averaged over a similar distance scale. A comparison of the mean horizontal shear strain-rate with the driving stress supports a power-law relation for the bulk rheology of the ice sheet with an exponent between 3 and 3.2

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Antarctic ice shelf thickness change from multimission lidar mapping

The Cryosphere ◽

10.5194/tc-13-1801-2019 ◽

2019 ◽

Vol 13 (7) ◽

pp. 1801-1817 ◽

Cited By ~ 2

Author(s):

Tyler C. Sutterley ◽

Thorsten Markus ◽

Thomas A. Neumann ◽

Michiel van den Broeke ◽

J. Melchior van Wessem ◽

...

Keyword(s):

High Resolution ◽

Climate Models ◽

Regional Climate ◽

Regional Climate Models ◽

Surface Velocity ◽

Ice Thickness ◽

Flux Divergence ◽

Ice Shelf ◽

Thickness Change ◽

Ice Shelves

Abstract. We calculate rates of ice thickness change and bottom melt for ice shelves in West Antarctica and the Antarctic Peninsula from a combination of elevation measurements from NASA–CECS Antarctic ice mapping campaigns and NASA Operation IceBridge corrected for oceanic processes from measurements and models, surface velocity measurements from synthetic aperture radar, and high-resolution outputs from regional climate models. The ice thickness change rates are calculated in a Lagrangian reference frame to reduce the effects from advection of sharp vertical features, such as cracks and crevasses, that can saturate Eulerian-derived estimates. We use our method over different ice shelves in Antarctica, which vary in terms of size, repeat coverage from airborne altimetry, and dominant processes governing their recent changes. We find that the Larsen-C Ice Shelf is close to steady state over our observation period with spatial variations in ice thickness largely due to the flux divergence of the shelf. Firn and surface processes are responsible for some short-term variability in ice thickness of the Larsen-C Ice Shelf over the time period. The Wilkins Ice Shelf is sensitive to short-timescale coastal and upper-ocean processes, and basal melt is the dominant contributor to the ice thickness change over the period. At the Pine Island Ice Shelf in the critical region near the grounding zone, we find that ice shelf thickness change rates exceed 40 m yr−1, with the change dominated by strong submarine melting. Regions near the grounding zones of the Dotson and Crosson ice shelves are decreasing in thickness at rates greater than 40 m yr−1, also due to intense basal melt. NASA–CECS Antarctic ice mapping and NASA Operation IceBridge campaigns provide validation datasets for floating ice shelves at moderately high resolution when coregistered using Lagrangian methods.

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An unusual jökulhlaup involving potholes on Black Rapids Glacier, Alaska Range, Alaska, U.S.A.

Journal of Glaciology ◽

10.3189/s0022143000005670 ◽

1990 ◽

Vol 36 (122) ◽

pp. 125-126 ◽

Cited By ~ 1

Author(s):

Matthew Sturm ◽

Dawn M. Cosgrove

Keyword(s):

Alaska Range ◽

Black Rapids Glacier

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Tensile, Torsional and Bending Strain at the Adhesive Rupture of an Iced Substrate

Volume 5: Polar and Arctic Sciences and Technology; CFD and VIV ◽

10.1115/omae2009-79458 ◽

2009 ◽

Cited By ~ 5

Author(s):

Caroline Laforte ◽

Jean-Louis Laforte

Keyword(s):

Adhesion Strength ◽

Ice Thickness ◽

Stress And Strain ◽

Substrate Roughness ◽

Mean Values ◽

Time Deformation ◽

Bending Strain ◽

Load Cells ◽

The Mean ◽

Major Factors

In order to develop an effective deicing device using mechanical deformation of substrates, the adhesive and/or cohesive strains of ice at rupture were measured for three different modes of solicitation: tensile, twisting and bending. A total of 108 icing/deicing tests were conducted with aluminum and nylon samples covered with hard rime ice deposits 2, 5, and 10 mm thick strained at various strains rates in brittle regime at −10°C. Real time deformation was precisely monitored using a strain gage fixed to the A1 interface, and force by means of load cells and a torque-meter. Deicing strain was determined at the time of ice detachment, which corresponds to a visible, instant change in the slope of stress-strain curves. The mean values of deicing strains, ε %, measured in tensile, torsion and bending experiments are respectively, 0.037 ± 0.015%, 0.043 ± 0.023% and 0.004 ± 0.003% As for adhesion strength, the highest values were obtained in tension, 4 MPa ± 50%, and the lowest in bending, 0.014 MPa ± 36%. In torsion, the value was intermediary, at 1.26 MPa ± 67%. Measurements also showed that deicing stress and strain tended to increase with substrate roughness, whereas they decrease with increasing ice thicknesses. In summary, this work points out the effects of two major factors on ice adhesion strength, the solicitation mode and the ice thickness. Finally these results suggest that the first criteria for a mechanical deicing device has to satisfy to be effective is to have the capacity to generating a strain at around 0.04% ice/substrate interface.

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ICESat observations of seasonal and interannual variations of sea-ice freeboard and estimated thickness in the Weddell Sea, Antarctica (2003–2009)

Annals of Glaciology ◽

10.3189/172756411795931480 ◽

2011 ◽

Vol 52 (57) ◽

pp. 43-51 ◽

Cited By ~ 52

Author(s):

Donghui Yi ◽

H. Jay Zwally ◽

John W. Robbins

Keyword(s):

Sea Ice ◽

Weddell Sea ◽

Ice Thickness ◽

Sea Ice Extent ◽

Sea Ice Thickness ◽

Earth Observing System ◽

Pack Ice ◽

Snow Water ◽

The Mean ◽

Seasonal And Interannual Variations

AbstractSea-ice freeboard heights for 17 ICESat campaign periods from 2003 to 2009 are derived from ICESat data. Freeboard is combined with snow depth from Advanced Microwave Scanning Radiometer for Earth Observing System (AMSR-E) data and nominal densities of snow, water and sea ice, to estimate sea-ice thickness. Sea-ice freeboard and thickness distributions show clear seasonal variations that reflect the yearly cycle of growth and decay of the Weddell Sea (Antarctica) pack ice. During October–November, sea ice grows to its seasonal maximum both in area and thickness; the mean freeboards are 0.33–0.41m and the mean thicknesses are 2.10–2.59 m. During February–March, thinner sea ice melts away and the sea-ice pack is mainly distributed in the west Weddell Sea; the mean freeboards are 0.35–0.46m and the mean thicknesses are 1.48–1.94 m. During May–June, the mean freeboards and thicknesses are 0.26–0.29m and 1.32–1.37 m, respectively. the 6 year trends in sea-ice extent and volume are (0.023±0.051)×106 km2 a–1 (0.45% a–1) and (0.007±0.092)×103 km3 a–1 (0.08% a–1); however, the large standard deviations indicate that these positive trends are not statistically significant.

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The Parallaxes of U Gem Variables

International Astronomical Union Colloquium ◽

10.1017/s0252921100076442 ◽

1979 ◽

Vol 53 ◽

pp. 494-494

Author(s):

Karl W. Kamper

Keyword(s):

Confidence Level ◽

Absolute Magnitude ◽

Weighted Mean ◽

Quiescent Phase ◽

A Value ◽

The Mean ◽

The Absolute ◽

Absolute Magnitudes

An Allegheny parallax series of SS Cyg, consisting of 52 exposures obtained on 15 nights, was recently measured on the PDS microphotometer at the David Dunlap Observatory, and a value of (m.e.) derived for the absolute parallax. This is close to the mean of the two previous discordant measures for this star given in the table below. The weighted mean of the three determinations implies that the absolute magnitude, at quiescent phase, of the star is between 7.0 and 9.0 formally at a 90% confidence level. Recent parallax determinations made at Lick by Vasilevskls et al. (1975) for three other stars, listed below along with the Mt. Wilson value for U Gem, imply even fainter absolute magnitudes.

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