Creep Buckling of Ice Shelves and the Formation of Pressure Rollers

AbstractMuch of the surface of an ice shelf is covered with series of undulations. These undulations or “pressure rollers” are particularly noticeable in the neighbourhood of ice rises or ice streams. To date, there is no satisfactory theoretical model explaining the formation of these waves. As a contribution to understanding this phenomenon, this paper investigates the stability of ice shelves to perturbations in the background stress and strain-rate distributions.The perturbation analysis is based on Glen’s creep law and leads to a continuous eigenvalue problem for the wavelength of the disturbance as a function of growth-rate. It is shown that, provided these strain-rates are sufficiently compressive, waves of the type observed can be expected to form. It is shown that lateral extensional strain-rates have a destabilizing effect and pressure rollers are more likely to form when these are present. Comparison of predicted wavelengths is made with available field data.

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On the Disintegration of Ice Shelves: The Role of Fracture

Journal of Glaciology ◽

10.3189/s0022143000005177 ◽

1983 ◽

Vol 29 (101) ◽

pp. 98-117 ◽

Cited By ~ 4

Author(s):

T. Hughes

Keyword(s):

Sea Level ◽

Local Strain ◽

Ice Shelf ◽

Ice Streams ◽

West Antarctic Ice Sheet ◽

Ice Shelves ◽

West Antarctic ◽

Shear Rupture ◽

Fatigue Rupture ◽

The Stability

AbstractCrevasses can be ignored in studying the dynamics of most glaciers because they are only about 20 m deep, a small fraction of ice thickness. In ice shelves, however, surface crevasses 20 m deep often reach sea-level and bottom crevasses can move upward to sea-level (Clough, 1974; Weertman, 1980). The ice shelf is fractured completely through if surface and basal crevasses meet (Barrett, 1975; Hughes, 1979). This is especially likely if surface melt water fills surface crevasses (Weertman, 1973; Pfeffer, 1982; Fastook and Schmidt, 1982). Fracture may therefore play an important role in the disintegration of ice shelves. Two fracture criteria which can be evaluated experimentally and applied to ice shelves, are presented. Fracture is then examined for the general strain field of an ice shelf and for local strain fields caused by shear rupture alongside ice streams entering the ice shelf, fatigue rupture along ice shelf grounding lines, and buckling up-stream from ice rises. The effect of these fracture patterns on the stability of Antarctic ice shelves and the West Antarctic ice sheet is then discussed.

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On the Disintegration of Ice Shelves: The Role of Fracture

Journal of Glaciology ◽

10.1017/s0022143000005177 ◽

1983 ◽

Vol 29 (101) ◽

pp. 98-117 ◽

Cited By ~ 53

Author(s):

T. Hughes

Keyword(s):

Sea Level ◽

Local Strain ◽

Ice Shelf ◽

Ice Streams ◽

West Antarctic Ice Sheet ◽

Ice Shelves ◽

West Antarctic ◽

Shear Rupture ◽

Fatigue Rupture ◽

The Stability

AbstractCrevasses can be ignored in studying the dynamics of most glaciers because they are only about 20 m deep, a small fraction of ice thickness. In ice shelves, however, surface crevasses 20 m deep often reach sea-level and bottom crevasses can move upward to sea-level (Clough, 1974; Weertman, 1980). The ice shelf is fractured completely through if surface and basal crevasses meet (Barrett, 1975; Hughes, 1979). This is especially likely if surface melt water fills surface crevasses (Weertman, 1973; Pfeffer, 1982; Fastook and Schmidt, 1982). Fracture may therefore play an important role in the disintegration of ice shelves. Two fracture criteria which can be evaluated experimentally and applied to ice shelves, are presented. Fracture is then examined for the general strain field of an ice shelf and for local strain fields caused by shear rupture alongside ice streams entering the ice shelf, fatigue rupture along ice shelf grounding lines, and buckling up-stream from ice rises. The effect of these fracture patterns on the stability of Antarctic ice shelves and the West Antarctic ice sheet is then discussed.

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Climatic conditions, mass balance and dynamics of Larsen B ice shelf, Antarctic Peninsula, prior to collapse

Annals of Glaciology ◽

10.3189/172756404781814573 ◽

2004 ◽

Vol 39 ◽

pp. 557-562 ◽

Cited By ~ 17

Author(s):

Pedro Skvarca ◽

Hernán De Angelis ◽

Andrés F. Zakrajsek

Keyword(s):

Mass Balance ◽

Antarctic Peninsula ◽

Satellite Image ◽

Climatic Conditions ◽

Strain Rates ◽

Ice Shelf ◽

Ice Flow ◽

Ice Shelves ◽

Additional Information ◽

Significant Acceleration

AbstractFollowing the collapse of Larsen A in 1995, about 3200 km2 of Larsen B ice shelf disintegrated in early 2002 during the warmest summer recorded on the northeastern Antarctic Peninsula. Immediately prior to disintegration the last field campaign was carried out on Larsen B. Measurements included surface net mass balance, velocity and strain rate on a longitudinal transect along Crane Glacier flowline and over a remnant section confined within Seal Nunataks that survived the collapse. In addition, an automatic weather station located nearby allowed derivation of melt days relevant to the formation and extent of surface meltwater. Repeated surveys allowed us to detect a significant acceleration in ice-flow velocity and associated increasing strain rates along the longitudinal transect. It may be possible to use this acceleration as a predictor of imminent ice-shelf collapse, applicable to ice shelves subject to similar climatic conditions. Additional information on recent ongoing changes was provided by a visible satellite image acquired in early 2003.

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Ice shelf internal reflection horizons reveal ice provenance, dynamics, surface accumulation and oceanic melt

10.5194/egusphere-egu21-15794 ◽

2021 ◽

Author(s):

Inka Koch ◽

Reinhard Drews ◽

Daniela Jansen ◽

Steven Franke ◽

Vjeran Visnjevic ◽

...

Keyword(s):

Shear Zones ◽

Ultra Wideband ◽

Internal Layers ◽

Ice Shelf ◽

Ice Streams ◽

Catchment Scale ◽

Ice Dynamics ◽

Ice Shelves ◽

Wideband Radar ◽

Narrow Belt

<p>Ice shelves are widely known to slow the transfer of Antarctic grounded ice to the ocean, especially if their flow is decelerated by local pinning points. Their longevity is influenced by variations in ice dynamics, surface accumulation and oceanic conditions in the ice shelf cavity. This is reflected in the ice shelf structure, which can be characterized by the shape of internal radar reflection horizons.</p><p>We aim to map the internal ice shelf stratigraphy of ice shelves, starting with the narrow belt of ice-shelves in the Dronning Maud Land area. The final goal will be to evaluate these as a spatiotemporal archive of ice provenance and ice dynamics. The bulk of the data presented here were collected with AWI&#8217;s airborne multi frequency ultra-wideband radar and we combine these new observations with airborne and ground-based radar surveys from previous years. We present a consistent set of internal radar isochrones on a catchment scale for the Roi Baudoin area including the Ragnhild ice streams, the grounding-zone, the iceshelf and multiple ice rises. &#160;Using pattern matching technique we can link isochrones across different ice rises in the area, and hence provide first observational constraints on how ice rises jointly react to changes in atmospheric and oceanographic forcings. We also find a number of interesting features including dynamically induced dips in shear zones, truncating layers at the ice-shelf base, and the development of a meteoric ice layer distinguishing advected from newly accumulated ice in the iceshelf. The time series provided by radar observations over the last 10 years also offers the potential to map temporal changes. We use ice-flow modelling to provide age constraints for some internal layers and delineate portions within the shelf as a function of their advection history, hence marking areas of differing rheologies within the shelf. Taken together, this case study on a catchment scale is a primer to unravel the information stored in the isochronal stratigraphy of coastal Antarctica and contributes to international efforts (e.g., SCAR AntArchitecture)&#160; of mapping stratigraphy on ice sheet scales.</p>

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Significant submarine ice loss from the Getz Ice Shelf, Antarctica

10.5194/tc-2018-163 ◽

2018 ◽

Author(s):

David M. Rippin

Keyword(s):

Mass Loss ◽

West Antarctica ◽

Ice Shelf ◽

Ice Streams ◽

Ice Shelves ◽

Warming Climate ◽

Circulation Patterns ◽

Direct Measurements ◽

Radio Echo Sounding ◽

The Impact

Abstract. We present the first direct measurements of changes taking place at the base of the Getz Ice Shelf (GzIS) in West Antarctica. Our analysis is based on repeated airborne radio-echo sounding (RES) survey lines gathered in 2010 and 2014. We reveal that while there is significant variability in ice shelf behaviour, the vast majority of the ice shelf (where data is available) is undergoing basal thinning at a mean rate of nearly 13 m a−1, which is several times greater than recent modelling estimates. In regions of faster flowing ice close to where ice streams and outlet glaciers join the ice shelf, significantly greater rates of mass loss occurred. Since thinning is more pronounced close to faster-flowing ice, we propose that dynamic thinning processes may also contribute to mass loss here. Intricate sub-ice circulation patterns exist beneath the GzIS because of its complex sub-ice topography and the fact that it is fed by numerous ice streams and outlet glaciers. It is this complexity which we suggest is also responsible for the spatially variable patterns of ice-shelf change that we observe. The large changes observed here are also important when considering the likelihood and timing of any potential future collapse of the ice shelf, and the impact this would have on the flow rates of feeder ice streams and glaciers, that transmit ice from inland Antarctica to the coast. We propose that as the ice shelf continues to thin in response to warming ocean waters and climate, the response of the ice shelf will be spatially diverse. Given that these measurements represent changes that are significantly greater than modelling outputs, it is also clear that we still do not fully understand how ice shelves respond to warming ocean waters. As a result, ongoing direct measurements of ice shelf change are vital for understanding the future response of ice shelves under a warming climate.

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An improved bathymetry compilation for the Bellingshausen Sea, Antarctica, to inform ice-sheet and ocean models

The Cryosphere Discussions ◽

10.5194/tcd-4-2079-2010 ◽

2010 ◽

Vol 4 (4) ◽

pp. 2079-2101 ◽

Cited By ~ 3

Author(s):

A. G. C. Graham ◽

F. O. Nitsche ◽

R. D. Larter

Keyword(s):

Ocean Circulation ◽

Ice Sheet ◽

West Antarctica ◽

Ice Shelf ◽

Ice Streams ◽

Ice Shelves ◽

Sea Floor ◽

Bellingshausen Sea ◽

Warm Deep Water ◽

Basal Melting

Abstract. The southern Bellingshausen Sea (SBS) is a rapidly-changing part of West Antarctica, where oceanic and atmospheric warming has led to the recent basal melting and break-up of the Wilkins ice shelf, the dynamic thinning of fringing glaciers, and sea-ice reduction. Accurate sea-floor morphology is vital for understanding the continued effects of each process upon changes within Antarctica's ice sheets. Here we present a new bathymetric grid for the SBS compiled from shipborne echo-sounder, spot-sounding and sub-ice measurements. The 1-km grid is the most detailed compilation for the SBS to-date, revealing large cross-shelf troughs, shallow banks, and deep inner-shelf basins that continue inland of coastal ice shelves. The troughs now serve as pathways which allow warm deep water to access the ice fronts in the SBS. Our dataset highlights areas still lacking bathymetric constraint, as well as regions for further investigation, including the likely routes of palaeo-ice streams. The new compilation is a major improvement upon previous grids and will be a key dataset for incorporating into simulations of ocean circulation, ice-sheet change and history. It will also serve forecasts of ice stability and future sea-level contributions from ice loss in West Antarctica, required for the next IPCC assessment report in 2013.

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Can Relict Crevasse Plumes on Antarctic Ice Shelves Reveal a History of Ice-Stream Fluctuation?

Annals of Glaciology ◽

10.3189/s0260305500006364 ◽

1988 ◽

Vol 11 ◽

pp. 77-82 ◽

Cited By ~ 3

Author(s):

D. R. MacAyeal ◽

R. A. Bindschadler ◽

K. C. Jezek ◽

S. Shabtaie

Keyword(s):

Numerical Model ◽

Ice Shelf ◽

Ice Streams ◽

Ice Shelves ◽

Stream Discharge ◽

Ice Stream ◽

History Of

Configurations of relict surface-crevasse bands and medial moraines that emanate from the shear margins of ice streams are simulated, using a numerical model of an ideal rectangular ice shelf to determine their potential for recording a past ice-stream discharge chronology.

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On the Disintegration of Ice Shelves: the Role of Thinning

Annals of Glaciology ◽

10.1017/s0260305500002676 ◽

1982 ◽

Vol 3 ◽

pp. 146-151 ◽

Cited By ~ 11

Author(s):

T. J. Hughes

Keyword(s):

Weak Links ◽

Ice Melting ◽

Ice Shelf ◽

Ice Streams ◽

Ice Shelves ◽

Ross Ice Shelf ◽

Tidal Pumping ◽

Grounding Line ◽

Converging Flow

It is proposed that an ice shelf disintegrates when its calving front retreats faster than its grounding line. This paper examines the role of ice thinning in grounding-line retreat. Thinning occurs as a result of creep spreading and ice melting. Thinning by creep is examined for the general regime of bending converging flow in an ice shelf lying in a confined embayment, and at the grounding lines of ice streams that supply the ice shelf and ice rises where the ice shelf is grounded on bedrock. Thinning by melting is examined at these grounding lines for tidal pumping and for descent of surface melt water into strandline crevasses, where concentrated melting is focused at the supposed weak links that connect the ice shelf to its embayment, its ice streams, and its ice rises. Applications are made to the Ross Ice Shelf.

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Equilibrium Profile of Ice Shelves

Journal of Glaciology ◽

10.1017/s0022143000014453 ◽

1979 ◽

Vol 22 (88) ◽

pp. 435-460 ◽

Cited By ~ 73

Author(s):

T. J. O. Sanderson

Keyword(s):

Strain Rates ◽

Ice Shelf ◽

Ice Shelves ◽

Glacier Tongue ◽

Flow Parameters ◽

Starting Point ◽

Equilibrium Profile ◽

Hinge Zone ◽

General Method ◽

Equilibrium Thickness

AbstractUsing expressions for ice-shelf creep derived by Weertman (1957) and Thomas (1973[b]) a general method is developed for calculating equilibrium thickness profiles, velocities, and strain-rates for any ice shelf. This is done first for an unconfined glacier tongue and the result agrees well with data for Erebus Glacier tongue (Holdsworth, 1974). Anomalies occur within the first 3 km after the hinge zone and these are too great to be the result of local bottom freezing; they are probably due to disturbance of the velocity field. Secondly, profiles are calculated for bay ice shelves. Thickness gradients are largely independent of melt-rate or flow parameters but are inversely proportional to the width of the bay. Data from Antarctic ice shelves agree with this result both qualitatively and quantitatively. The theory is readily extended to ice shelves in diverging and converging bays. An ice shelf in a diverging bay can only remain intact if it is thick enough and slow enough to creep sufficiently rapidly in the transverse direction. If it cannot, it will develop major rifts or will come adrift from the bay walls. It is then likely to break up. The presence of ice rises or areas of grounding towards the seaward margin can radically alter the size of the ice shelf which can form. The theory could be used as a starting point to study non-equilibrium behaviour.

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