A model of viscoelastic ice-shelf flexure

AbstractWe develop a formal thin-plate treatment of the viscoelastic flexure of floating ice shelves as an initial step in treating various problems relevant to ice-shelf response to sudden changes of surface loads and applied bending moments (e.g. draining supraglacial lakes, iceberg calving, surface and basal crevassing). Our analysis is based on the assumption that total deformation is the sum of elastic and viscous (or power-law creep) deformations (i.e. akin to a Maxwell model of viscoelasticity, having a spring and dashpot in series). The treatment follows the assumptions of well-known thin-plate approximation, but is presented in a manner familiar to glaciologists and with Glen’s flow law. We present an analysis of the viscoelastic evolution of an ice shelf subject to a filling and draining supraglacial lake. This demonstration is motivated by the proposition that flexure in response to the filling/drainage of meltwater features on the Larsen B ice shelf, Antarctica, contributed to the fragmentation process that accompanied its collapse in 2002.

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Ice-shelf fracture due to viscoelastic flexure stress induced by fill/drain cycles of supraglacial lakes

Antarctic Science ◽

10.1017/s0954102015000292 ◽

2015 ◽

Vol 27 (6) ◽

pp. 587-597 ◽

Cited By ~ 23

Author(s):

Alison F. Banwell ◽

Douglas R. Macayeal

Keyword(s):

Lake Basin ◽

Ice Shelf ◽

Successive Cycle ◽

Thin Beam ◽

Ice Shelves ◽

Supraglacial Lakes ◽

Lake Bottom ◽

Extended Zone ◽

Plate Analysis ◽

Power Law Creep

AbstractUsing a previously derived treatment of viscoelastic flexure of floating ice shelves, we simulated multiple years of evolution of a single, axisymmetric supraglacial lake when it is subjected to annual fill/drain cycles. Our viscoelastic treatment follows the assumptions of the well-known thin-beam and thin-plate analysis but, crucially, also covers power-law creep rheology. As the ice-shelf surface does not completely return to its un-flexed position after a 1-year fill/drain cycle, the lake basin deepens with each successive cycle. This deepening process is significantly amplified when lake-bottom ablation is taken into account. We evaluate the timescale over which a typical lake reaches a sufficient depth such that ice-shelf fracture can occur well beyond the lake itself in response to lake filling/drainage. We show that, although this is unlikely during one fill/drain cycle, fracture is possible after multiple years assuming surface meltwater availability is unlimited. This extended zone of potential fracture implies that flexural stresses in response to a single lake filling/drainage event can cause neighbouring lakes to drain, which, in turn, can cause lakes farther afield to drain. Such self-stimulating behaviour may have accounted for the sudden, widespread appearance of a fracture system that drove the Larsen B Ice Shelf to break-up in 2002.

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Normal modes of a coupled ice-shelf/sub-ice-shelf cavity system

Journal of Glaciology ◽

10.3189/2013jog12j096 ◽

2013 ◽

Vol 59 (213) ◽

pp. 76-80 ◽

Cited By ~ 17

Author(s):

Olga V. Sergienko

Keyword(s):

Water Flow ◽

Thin Plate ◽

Normal Modes ◽

Coupled System ◽

Ocean Waves ◽

Ice Shelf ◽

Cavity Depth ◽

Ice Shelves ◽

Iceberg Calving ◽

Cavity System

AbstractIce shelves and ice tongues are dynamically coupled to their cavities. Here we compute normal modes (eigenfrequencies and eigenfunctions) of this coupled system using a thin-plate approximation for the ice shelf and potential water flow in the ice-shelf cavity. Our results show that normal modes depend not only on the ice-shelf parameters (length, thickness, Young’s modulus, etc.) but also on the cavity depth. The dominant eigenmodes are higher for ice shelves floating over deeper cavities; they are also higher for shorter ice shelves and ice tongues (<50 km long). The higheigenfrequency eigenmodes are primarily controlled by the ice flexure and have similar periods to sea swell. These results suggest that both long ocean waves with periods of 100–400 s and shorter sea swell with periods of 10–20 s can have strong impacts on relatively short ice shelves and ice tongues by exciting oscillations with their eigenfrequencies, which can lead to iceberg calving and, in some circumstances, ice-shelf disintegration.

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A statistical fracture model for Antarctic ice shelves and glaciers

The Cryosphere ◽

10.5194/tc-12-3187-2018 ◽

2018 ◽

Vol 12 (10) ◽

pp. 3187-3213 ◽

Cited By ~ 3

Author(s):

Veronika Emetc ◽

Paul Tregoning ◽

Mathieu Morlighem ◽

Chris Borstad ◽

Malcolm Sambridge

Keyword(s):

Large Scale ◽

Damage Mechanics ◽

Ice Sheets ◽

Continuum Damage Mechanics ◽

Ice Shelf ◽

Ice Shelves ◽

Flow Models ◽

Iceberg Calving ◽

Antarctic Continent ◽

Average Success Rate

Abstract. Antarctica and Greenland hold enough ice to raise sea level by more than 65 m if both ice sheets were to melt completely. Predicting future ice sheet mass balance depends on our ability to model these ice sheets, which is limited by our current understanding of several key physical processes, such as iceberg calving. Large-scale ice flow models either ignore this process or represent it crudely. To model fractured zones, an important component of many calving models, continuum damage mechanics as well as linear fracture mechanics are commonly used. However, these methods have a large number of uncertainties when applied across the entire Antarctic continent because the models were typically tuned to match processes seen on particular ice shelves. Here we present an alternative, statistics-based method to model the most probable zones of the location of fractures and demonstrate our approach on all main ice shelf regions in Antarctica, including the Antarctic Peninsula. We can predict the location of observed fractures with an average success rate of 84 % for grounded ice and 61 % for floating ice and a mean overestimation error rate of 26 % and 20 %, respectively. We found that Antarctic ice shelves can be classified into groups based on the factors that control fracture location.

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Widespread distribution of supraglacial lakes around the margin of the East Antarctic Ice Sheet

Scientific Reports ◽

10.1038/s41598-019-50343-5 ◽

2019 ◽

Vol 9 (1) ◽

Cited By ~ 12

Author(s):

Chris R. Stokes ◽

Jack E. Sanderson ◽

Bertie W. J. Miles ◽

Stewart S. R. Jamieson ◽

Amber A. Leeson

Keyword(s):

Ice Sheet ◽

Ice Shelf ◽

Typically Develop ◽

Ice Shelves ◽

Supraglacial Lakes ◽

Marginal Areas ◽

Surface Slopes ◽

Highly Sensitive ◽

Ice Sheet Mass Balance ◽

High Resolution Satellite Imagery

Abstract Supraglacial lakes are important to ice sheet mass balance because their development and drainage has been linked to changes in ice flow velocity and ice shelf disintegration. However, little is known about their distribution on the world’s largest ice sheet in East Antarctica. Here, we use ~5 million km2 of high-resolution satellite imagery to identify >65,000 lakes (>1,300 km2) that formed around the peak of the melt season in January 2017. Lakes occur in most marginal areas where they typically develop at low elevations (<100 m) and on low surface slopes (<1°), but they can exist 500 km inland and at elevations >1500 m. We find that lakes often cluster a few kilometres down-ice from grounding lines and ~60% (>80% by area) develop on ice shelves, including some potentially vulnerable to collapse driven by lake-induced hydro-fracturing. This suggests that parts of the ice sheet may be highly sensitive to climate warming.

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Efficient Location and Extraction of the Iceberg Calved Areas of the Antarctic Ice Shelves

Remote Sensing ◽

10.3390/rs12162658 ◽

2020 ◽

Vol 12 (16) ◽

pp. 2658

Author(s):

Mengzhen Qi ◽

Yan Liu ◽

Yijing Lin ◽

Fengming Hui ◽

Teng Li ◽

...

Keyword(s):

Extraction Process ◽

Ice Shelf ◽

Extraction Area ◽

Ice Shelves ◽

Textural Characteristics ◽

Iceberg Calving ◽

Ice Velocity ◽

The Antarctic ◽

Omission Errors

Continuous, rapid, and precise monitoring of calving events contributes to an in-depth understanding of calving mechanisms, which have the potential to cause significant mass loss from the Antarctic ice sheet. The difficulties in the precise monitoring of iceberg calving lie with the coexistence of ice shelf advances and calving. The manual location of iceberg calving is time-consuming and painstaking, while achieving precise extraction has mostly relied on the surface textural characteristics of the ice shelves and the quality of the images. Here, we propose a new and efficient method of separating the expansion and calving processes of ice shelves. We visualized the extension process by simulating a new coastline, based on the ice velocity, and detected the calved area using the simulated coastline and single-temporal post-calving images. We extensively tested the validity of this method by extracting four annual calving datasets (from August 2015 to August 2019) from the Sentinel-1 synthetic aperture radar mosaic of the Antarctic coastline. A total of 2032 annual Antarctic calving events were detected, with areas ranging from 0.05 km2 to 6141.0 km2, occurring on almost every Antarctic ice shelf. The extraction accuracy of the calved area depends on the positioning accuracy of the simulated coastline and the spatial resolution of the images. The positioning error of the simulated coastline is less than one pixel, and the determined minimum valid extraction area is 0.05 km2, when based on 75 m resolution images. Our method effectively avoids repetition and omission errors during the calved area extraction process. Furthermore, its efficiency is not affected by the surface textural characteristics of the calving fronts and the various changes in the frontal edge velocity, which makes it fully applicable to the rapid and accurate extraction of different calving types.

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Viscous and elastic buoyancy stresses as drivers of ice-shelf calving

Journal of Glaciology ◽

10.1017/jog.2020.35 ◽

2020 ◽

Vol 66 (258) ◽

pp. 643-657 ◽

Cited By ~ 1

Author(s):

Cyrille Mosbeux ◽

Till J. W. Wagner ◽

Maya K. Becker ◽

Helen A. Fricker

Keyword(s):

Ice Sheet ◽

Elastic Model ◽

Ice Shelf ◽

Ice Shelves ◽

Bending Stresses ◽

Iceberg Calving ◽

Basal Melting ◽

The Antarctic ◽

The Impact ◽

Maximum Stresses

AbstractThe Antarctic Ice Sheet loses mass via its ice shelves predominantly through two processes: basal melting and iceberg calving. Iceberg calving is episodic and infrequent, and not well parameterized in ice-sheet models. Here, we investigate the impact of hydrostatic forces on calving. We develop two-dimensional elastic and viscous numerical frameworks to model the ‘footloose’ calving mechanism. This mechanism is triggered by submerged ice protrusions at the ice front, which induce unbalanced buoyancy forces that can lead to fracturing. We compare the results to identify the different roles that viscous and elastic deformations play in setting the rate and magnitude of calving events. Our results show that, although the bending stresses in both frameworks share some characteristics, their differences have important implications for modeling the calving process. In particular, the elastic model predicts that maximum stresses arise farther from the ice front than in the viscous model, leading to larger calving events. We also find that the elastic model would likely lead to more frequent events than the viscous one. Our work provides a theoretical framework for the development of a better understanding of the physical processes that govern glacier and ice-shelf calving cycles.

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The Recent Advance of the Ross Ice Shelf Antarctica

Journal of Glaciology ◽

10.3189/s0022143000012181 ◽

1986 ◽

Vol 32 (112) ◽

pp. 464-474 ◽

Cited By ~ 1

Author(s):

S. S. Jacobs ◽

D. R. Macayeal ◽

J. L. Ardai

Keyword(s):

Large Scale ◽

Melting Rate ◽

Spreading Rate ◽

Ice Shelf ◽

Ice Shelves ◽

Ross Ice Shelf ◽

Front Position ◽

Iceberg Calving ◽

Basal Melting ◽

Available Information

AbstractThe seaward edge of the Ross Ice Shelf advanced northward at a minimum average velocity of 0.8 km a–1 between 1962 and 1985. That advance approximated velocities that have been obtained from glaciological data, indicating little recent wastage by iceberg calving. West of long. 178° E., the ice shelf has attained its most northerly position in the past 145 years, and has not experienced a major calving episode for at least 75 years. Since 1841 the ice-front position has advanced and retreated within a zone from about lat. 77° 10’S. (near long. 171° E.) to lat. 78° 40’ S. (near long. 164° W.). The central ice front is now farthest south but has the highest advance rate. Calving may occur at more frequent intervals in that sector, which also overlies the warmest ocean currents that flow into the sub-ice-shelf cavity. Available information on ice-shelf advance, thickness, spreading rate, and surface accumulation indicates a basal melting rate around 3 m a–1 near the ice front. These data and independent estimates imply that basal melting is nearly as large a factor as iceberg calving in maintaining the ice-shelf mass balance. In recent years, the Ross, Ronne, and Filchner Ice Shelves have contributed few icebergs to the Southern Ocean, while projections from a contemporaneous iceberg census are that circumpolar calving alone may exceed accumulation on the ice sheet. Large-scale ice-shelf calving may have preceded historical sightings of increased numbers of icebergs at sea.

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Seasonal evolution of Antarctic supraglacial lakes in 2015–2021 and links to environmental controls

10.5194/tc-2021-203 ◽

2021 ◽

Author(s):

Mariel Christina Dirscherl ◽

Andreas J. Dietz ◽

Claudia Kuenzer

Keyword(s):

Antarctic Peninsula ◽

Time Lags ◽

Ice Shelf ◽

Ice Shelves ◽

Shelf Stability ◽

Air Content ◽

Supraglacial Lakes ◽

Environmental Controls ◽

Lake Formation ◽

Increased Risk

Abstract. Supraglacial meltwater accumulation on ice shelves may have important implications for future sea-level-rise. Despite recent progress in the understanding of Antarctic surface hydrology, potential influences on ice shelf stability as well as links to environmental drivers remain poorly constrained. In this study, we employ state-of-the-art machine learning on Sentinel-1 Synthetic Aperture Radar (SAR) and optical Sentinel-2 satellite imagery to provide new insight into the inter-annual and intra-annual evolution of surface hydrological features across six major Antarctic Peninsula and East Antarctic ice shelves. For the first time, we produce a record of supraglacial lake extent dynamics for the period 2015–2021 at unprecedented 10 m spatial resolution and bi-weekly temporal scale. Through synergetic use of optical and SAR data, we obtain a more complete mapping record enabling the delineation of also buried lakes. Our results for Antarctic Peninsula ice shelves reveal below average meltwater ponding during most of melting seasons 2015–2018 and above average meltwater ponding throughout summer 2019–2020 and early 2020–2021. Meltwater ponding on investigated East Antarctic ice shelves was far more variable with above average lake extents during most of melting seasons 2016–2019 and below average lake extents during 2020–2021. This study is the first to investigate relationships with climate drivers both, spatially and temporally including time lag analysis. The results indicate that supraglacial lake formation in 2015–2021 is coupled to the complex interplay of varying air temperature, solar radiation, snowmelt, wind and precipitation, each at different time lags and directions and with strong local to regional discrepancies, as revealed through pixel-based correlation analysis. Southern Hemisphere atmospheric modes as well as the local glaciological setting including melt-albedo feedbacks and the firn air content were revealed to strongly influence the spatio-temporal evolution of supraglacial lakes as well as below or above average meltwater ponding despite variations in the strength of forcing. Recent increases of Antarctic Peninsula surface ponding point towards a further reduction of the firn air content implying an increased risk for ponding and hydrofracture. In addition, lateral meltwater transport was observed over both Antarctic regions with similar implications for future ice shelf stability.

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SYNOPTIC OBSERVATIONS OF CALVING EVENTS IN ANTARCTICA USING SPACEBORNE IMAGES

ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences ◽

10.5194/isprs-archives-xlii-5-531-2018 ◽

2018 ◽

Vol XLII-5 ◽

pp. 531-536

Author(s):

S. D. Jawak ◽

S. S. Singh ◽

A. J. Luis

Keyword(s):

Satellite Images ◽

Google Earth ◽

Natural Phenomenon ◽

Ice Shelf ◽

Ice Shelves ◽

The Past ◽

Abnormal Rate ◽

Iceberg Calving ◽

Synoptic Observations ◽

Landsat Satellite

Abstract. Iceberg calving is the detachment of ice from ice shelves or glaciers. Although calving is a natural phenomenon, an abnormal rate of calving can be a threat to ice shelves. Some of the events were so large, that an iceberg of approximately 150&times;50km area was calved in a single event. The most recent reported iceberg calving event was Larsen C and it took place in July 2017. In addition to the large and widely reported calving events, there are several small calving events, which are also of great significance and contribute to the overall mass loss from Antarctica. This study focuses on small calving events in Antarctica along various coasts. Three calving events are studied here, all of them have occurred in the past. This study was performed using Google Earth and Landsat satellite imageries. The first event is identified to have occurred at the Knox coast in 2016. Even after the icebergs were calved, they remained intact with the ice shelf due to ice fronts. The second event took place at the Queen Mary Coast in the year 2014. This event was studied from 2009 to 2016 using Landsat satellite images and many rifts were observed. The third event took place at the Princess Astrid Coast in the year 2016. This event was monitored from 2014 and three icebergs were calved between the years 2014 to 2016. This study emphasizes the exploitation of optical satellite data for studying calving events in Antarctica. Various crevasses and rifts are observed on Landsat imageries, which can be the first sign of a calving process.

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Detecting Calving Events of Icebergs D-28 and B-49 using High Resolution Sentinel-1A SAR Data

10.5194/egusphere-egu21-16264 ◽

2021 ◽

Author(s):

Kavita Mitkari ◽

Jayaprasad Pallipad ◽

Deepak Putrevu ◽

Arundhati Misra

Keyword(s):

Image Interpretation ◽

Terrain Correction ◽

West Antarctica ◽

Ice Shelf ◽

Ice Shelves ◽

Amery Ice Shelf ◽

Time Series Dataset ◽

Iceberg Calving ◽

Canny Edge ◽

Speckle Filtering

Detecting iceberg calving events and subsequently tracking their movement is important because large icebergs can create problem in shipping and navigation. This study discusses two calving events that took place at 1) Amery ice shelf (East Antarctica) in September 2019 and 2) Pine Island Glacier&#8217;s floating ice shelf (West Antarctica) in February 2020. Though the calving that occurred in September 2019 does not have any impact on climate change, it is considered to be the most significant calving event on Amery ice shelf since 1963-64. The gigantic tabular iceberg officially named D-28 measures more than 600 square-miles. On the other hand, Pine Island is considered as the fastest retreating glaciers in Antarctica. This calving event gave rise to smaller icebergs, the largest of which was 120 square-miles, big enough to earn it a name: B-49. Though ice calving is a normal phenomenon at the ice shelves, the front of the glacier is stable if the rate of calving is in synchronization with the glacier&#8217;s forward flow. But, at Pine Island, the rate of disintegration has increased more than the glacier's speed to push the inland ice into Pine Island Bay. On-screen digitization approach of analysing time series dataset of glacier front positions is conventional, time consuming and subjective. To track the movement of icebergs D-28 and B-49, present study has detected rifts using canny edge detection filter and textural measures. We have utilized the Sentinel 1A SAR C-band (GRD) EW mode (Resolution (Rg x Az): 93 x 87 m and pixel spacing 40 x 40 m) images pertaining to the Amery ice shelf for Sep 2020-Mar 2020 and Pine Island Glacier with Pine Island Bay for Dec 2019-Mar 2020. All the images were processed for calibration (sigma0), speckle filtering (refined Lee), terrain correction (Range Doppler) and dB conversion using SNAP tool. Terrain correction has been performed using RAMP v2 DEM (200 m) and all the images have been projected to WGS 84/Antarctic Polar Stereographic projection and converted into dB. Through image interpretation, it is revealed that as of Mar 2020, iceberg D-28 has rotated almost 90 degrees anti-clockwise and drifted slightly northward away from Cape Darnley. In case of iceberg B-49, it is observed that the western portion of the calved ice, including the largest iceberg, has rapidly rotated out into Pine Island Bay, whereas the eastern half, including many smaller shards of ice, is following in similar fashion.

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