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Eric Rignot - One of the best experts on this subject based on the ideXlab platform.
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Iceberg Calving of Thwaites Glacier, West Antarctica: Full-Stokes modeling combined with linear elastic fracture mechanics
2016Co-Authors: Eric Rignot, Mathieu Morlighem, Helene SeroussiAbstract:Abstract. Thwaites Glacier (TG), West Antarctica, has been losing mass and retreating rapidly in the past few decades. Here, we present a study of its Calving dynamics combining a two-dimensional flowband Full Stokes (FS) model of its viscous flow with linear elastic fracture mechanics (LEFM) theory to model crevasse propagation and ice fracturing. We compare the results with those obtained with the higher-order (HO) and the shallow-shelf approximation (SSA) models coupled with LEFM. We find that FS/LEFM produces surface and bottom crevasses that match the distribution of crevasse depth and width observed from NASA's Operation IceBridge radar depth sounders, whereas HO/LEFM and SSA/LEFM do not generate crevasses that match observations. We attribute the difference to the non-hydrostatic condition of ice near the grounding line, which facilitates crevasse formation, and is accounted for by the FS model but not by the HO or SSA model. We also find that Calving is enhanced when pre-existing surface crevasses are present, when the ice shelf is shortened or when the ice shelf front is undercut. The role of undercutting depends on the time scale of Calving events. It is more prominent for glaciers with rapid Calving rates than glaciers with slow Calving rates. Glaciers extending into a shorter ice shelf are more vulnerable to Calving than glaciers developing a long ice shelf, especially as the ice front retreats close to the grounding line region, which leads to a positive feedback. We conclude that the FS/LEFM combination yields substantial improvements in capturing the stress field near the grounding line for constraining crevasse formation and Iceberg Calving.
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Iceberg Calving of thwaites glacier west antarctica full stokes modeling combined with linear elastic fracture mechanics
The Cryosphere, 2016Co-Authors: Eric Rignot, Mathieu Morlighem, Helene SeroussiAbstract:Abstract. Thwaites Glacier (TG), West Antarctica, has been losing mass and retreating rapidly in the past few decades. Here, we present a study of its Calving dynamics combining a two-dimensional flow-band full-Stokes (FS) model of its viscous flow with linear elastic fracture mechanics (LEFM) theory to model crevasse propagation and ice fracturing. We compare the results with those obtained with the higher-order (HO) and the shallow-shelf approximation (SSA) models coupled with LEFM. We find that FS/LEFM produces surface and bottom crevasses that are consistent with the distribution of depth and width of surface and bottom crevasses observed by NASA's Operation IceBridge radar depth sounder and laser altimeter, whereas HO/LEFM and SSA/LEFM do not generate crevasses that are consistent with observations. We attribute the difference to the nonhydrostatic condition of ice near the grounding line, which facilitates crevasse formation and is accounted for by the FS model but not by the HO or SSA models. We find that Calving is enhanced when pre-existing surface crevasses are present, when the ice shelf is shortened or when the ice shelf front is undercut. The role of undercutting depends on the timescale of Calving events. It is more prominent for glaciers with rapid Calving rates than for glaciers with slow Calving rates. Glaciers extending into a shorter ice shelf are more vulnerable to Calving than glaciers developing a long ice shelf, especially as the ice front retreats close to the grounding line region, which leads to a positive feedback to Calving events. We conclude that the FS/LEFM combination yields substantial improvements in capturing the stress field near the grounding line of a glacier for constraining crevasse formation and Iceberg Calving.
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Full-Stokes modeling of grounding line dynamics, ice melt and Iceberg Calving for Thwaites Glacier, West Antarctica
2016Co-Authors: Eric Rignot, Mathieu Morlighem, Helene SeroussiAbstract:Abstract. Thwaites Glacier (TG), West Antarctica, has been losing mass and retreating rapidly in the past three decades. Here we present a two-dimensional, Full-Stokes (FS) modeling study of the grounding line dynamics and Iceberg Calving of TG. First, we compare FS with two simplified models, the higher-order (HO) model and the shallow-shelf approximation (SSA) model, to determine the impact of changes in ice shelf basal melt rate on grounding line dynamics. Second, we combine FS with the Linear Elastic Fracture Mechanics (LEFM) theory to simulate crevasse propagation and Iceberg Calving. In the first experiment, we find that FS requires basal melt rate consistent with remote sensing observations to reach steady state at TG’s current geometry while HO and SSA require unrealistically high basal melt rate. The grounding line of FS is also more sensitive to changes in basal melt rate than HO and SSA. In the second experiment, we find that only FS can produce surface and bottom crevasses that match radar sounding observations of crevasse width and height. We attribute the difference to the non- hydrostatic conditions of ice near the grounding line, which facilitate crevasse formation and are not accounted for in HO and SSA. Additional experiments using FS indicate that Iceberg Calving is significantly enhanced when surface crevasses exist near the grounding line, when ice shelf is shortened, or when the ice shelf front is undercut. We conclude that FS yields substantial improvements in the description of ice flow dynamics at the grounding line under high basal melt rate and in constraining crevasse formation and Iceberg Calving.
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observation of ocean tides below the filchner and ronne ice shelves antarctica using synthetic aperture radar interferometry comparison with tide model predictions
Journal of Geophysical Research, 2000Co-Authors: Eric Rignot, Douglas R Macayeal, L Padman, Marjorie SchmeltzAbstract:Tides near and under floating glacial ice, such as ice shelves and glacier termini in fjords, can influence heat transport into the subice cavity, mixing of the under-ice water column, and the Calving and subsequent drift of Icebergs. Free-surface displacement patterns associated with ocean variability below glacial ice can be observed by differencing two synthetic aperture radar (SAR) interferograms, each of which represents the combination of the displacement patterns associated with the time-varying vertical motion and the time-independent lateral ice flow. We present the pattern of net free-surface displacement for the Iceberg Calving regions of the Ronne and Filchner Ice Shelves in the southern Weddell Sea. By comparing SAR-based displacement fields with ocean tidal models, the free-surface displacement variability for these regions is found to be dominated by ocean tides. The inverse barometer effect, i.e., the ocean's isostatic response to changing atmospheric pressure, also contributes to the observed vertical displacement. The principal value of using SAR interferometry in this manner lies in the very high lateral resolution (tens of meters) obtained over the large region covered by each SAR image. Small features that are not well resolved by the typical grid spacing of ocean tidal models may contribute to such processes as Iceberg Calving and cross-frontal ventilation of the ocean cavity under the ice shelf.
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Comparison of Ice-shelf Creep Flow Simulations with Ice-front Motion of Filchner-Ronne Ice Shelf, Antarctica, Detected by SAR Interferometry
Annals of Glaciology, 1998Co-Authors: Christina L. Hulbe, Eric Rignot, Douglas R MacayealAbstract:Comparison between numerical model ice-shelf flow simulations and synthetic aperture radar (SAR) interferograms is used to study the dynamics at the Hemmen Ice Rise (HIR) and Lassiter Coast (LC) corners of the Iceberg-Calving front of the Filchner-Ronne Ice Shelf (FRIS).
Shad O'neel - One of the best experts on this subject based on the ideXlab platform.
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Tidal and seasonal variations in Calving flux observed with passive seismology
Journal of Geophysical Research: Earth Surface, 2015Co-Authors: Timothy C. Bartholomaus, Christopher F Larsen, Shad O'neel, Michael West, Erin C. Pettit, Martin TrufferAbstract:The seismic signatures of Calving events, i.e., Calving icequakes, offer an opportunity to examine Calving variability with greater precision than is available with other methods. Here using observations from Yahtse Glacier, Alaska, we describe methods to detect, locate, and characterize Calving icequakes. We combine these icequake records with a coincident, manually generated record of observed Calving events to develop and validate a statistical model through which we can infer Iceberg sizes from the properties of Calving icequakes. We find that the icequake duration is the single most significant predictor of an Iceberg's size. We then apply this model to 18 months of seismic recordings and find elevated Iceberg Calving flux during the summer and fall and a pronounced lull in Calving during midwinter. Calving flux is sensitive to semidiurnal tidal stage. Large Calving events are tens of percent more likely during falling and low tides than during rising and high tides, consistent with a view that deeper water has a stabilizing influence on glacier termini. Multiple factors affect the occurrence of mechanical fractures that ultimately lead to Iceberg Calving. At Yahtse Glacier, seismology allows us to demonstrate that variations in the rate of submarine melt are a dominant control on Iceberg Calving rates at seasonal timescales. On hourly to daily timescales, tidal modulation of the normal stress against the glacier terminus reveals the nonlinear glacier response to changes in the near-terminus stress field.
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Calving seismicity from Iceberg–sea surface interactions
Journal of Geophysical Research: Earth Surface, 2012Co-Authors: Timothy C. Bartholomaus, Christopher F Larsen, Shad O'neel, Michael WestAbstract:[1] Iceberg Calving is known to release substantial seismic energy, but little is known about the specific mechanisms that produce Calving icequakes. At Yahtse Glacier, a tidewater glacier on the Gulf of Alaska, we draw upon a local network of seismometers and focus on 80 hours of concurrent, direct observation of the terminus to show that Calving is the dominant source of seismicity. To elucidate seismogenic mechanisms, we synchronized video and seismograms to reveal that the majority of seismic energy is produced during Iceberg interactions with the sea surface. Icequake peak amplitudes coincide with the emergence of high velocity jets of water and ice from the fjord after the complete submergence of falling Icebergs below sea level. These icequakes have dominant frequencies between 1 and 3 Hz. Detachment of an Iceberg from the terminus produces comparatively weak seismic waves at frequencies between 5 and 20 Hz. Our observations allow us to suggest that the most powerful sources of Calving icequakes at Yahtse Glacier include Iceberg-sea surface impact, deceleration under the influence of drag and buoyancy, and cavitation. Numerical simulations of seismogenesis during Iceberg-sea surface interactions support our observational evidence. Our new understanding of Iceberg-sea surface interactions allows us to reattribute the sources of Calving seismicity identified in earlier studies and offer guidance for the future use of seismology in monitoring Iceberg Calving.
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Analysis of low‐frequency seismic signals generated during a multiple‐Iceberg Calving event at Jakobshavn Isbræ, Greenland
Journal of Geophysical Research: Earth Surface, 2012Co-Authors: Fabian Walter, Jason M. Amundson, Martin Truffer, Mark Fahnestock, Shad O'neel, Helen A. FrickerAbstract:[1] We investigated seismic signals generated during a large-scale, multiple Iceberg Calving event that occurred at Jakobshavn Isbrae, Greenland, on 21 August 2009. The event was recorded by a high-rate time-lapse camera and five broadband seismic stations located within a few hundred kilometers of the terminus. During the event two full-glacier-thickness Icebergs calved from the grounded (or nearly grounded) terminus and immediately capsized; the second Iceberg to calve was two to three times smaller than the first. The individual Calving and capsize events were well-correlated with the radiation of low-frequency seismic signals (
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Analysis of low-frequency seismic signals generated during a multiple-Iceberg Calving event at Jakobshavn Isbræ, Greenland
Journal of Geophysical Research, 2012Co-Authors: Fabian Walter, Jason M. Amundson, Martin Truffer, Mark Fahnestock, Shad O'neel, Helen Amanda FrickerAbstract:[1] We investigated seismic signals generated during a large-scale, multiple Iceberg Calving event that occurred at Jakobshavn Isbrae, Greenland, on 21 August 2009. The event was recorded by a high-rate time-lapse camera and five broadband seismic stations located within a few hundred kilometers of the terminus. During the event two full-glacier-thickness Icebergs calved from the grounded (or nearly grounded) terminus and immediately capsized; the second Iceberg to calve was two to three times smaller than the first. The individual Calving and capsize events were well-correlated with the radiation of low-frequency seismic signals (
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Iceberg Calving as a primary source of regional‐scale glacier‐generated seismicity in the St. Elias Mountains, Alaska
Journal of Geophysical Research, 2010Co-Authors: Shad O'neel, Natalia Rupert, Christopher F Larsen, Roger A. HansenAbstract:[1] Since the installation of the Alaska Regional Seismic Network in the 1970s, data analysts have noted nontectonic seismic events thought to be related to glacier dynamics. While loose associations with the glaciers of the St. Elias Mountains have been made, no detailed study of the source locations has been undertaken. We performed a two-step investigation surrounding these events, beginning with manual locations that guided an automated detection and event sifting routine. Results from the manual investigation highlight characteristics of the seismic waveforms including single-peaked (narrowband) spectra, emergent onsets, lack of distinct phase arrivals, and a predominant cluster of locations near the Calving termini of several neighboring tidewater glaciers. Through these locations, comparison with previous work, analyses of waveform characteristics, frequency-magnitude statistics and temporal patterns in seismicity, we suggest Calving as a source for the seismicity. Statistical properties and time series analysis of the event catalog suggest a scale-invariant process that has no single or simple forcing. These results support the idea that Calving is often a response to short-lived or localized stress perturbations. Our results demonstrate the utility of passive seismic instrumentation to monitor relative changes in the rate and magnitude of Iceberg Calving at tidewater glaciers that may be volatile or susceptible to ensuing rapid retreat, especially when existing seismic infrastructure can be used.
Helene Seroussi - One of the best experts on this subject based on the ideXlab platform.
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Iceberg Calving of thwaites glacier west antarctica full stokes modeling combined with linear elastic fracture mechanics
The Cryosphere, 2016Co-Authors: Eric Rignot, Mathieu Morlighem, Helene SeroussiAbstract:Abstract. Thwaites Glacier (TG), West Antarctica, has been losing mass and retreating rapidly in the past few decades. Here, we present a study of its Calving dynamics combining a two-dimensional flow-band full-Stokes (FS) model of its viscous flow with linear elastic fracture mechanics (LEFM) theory to model crevasse propagation and ice fracturing. We compare the results with those obtained with the higher-order (HO) and the shallow-shelf approximation (SSA) models coupled with LEFM. We find that FS/LEFM produces surface and bottom crevasses that are consistent with the distribution of depth and width of surface and bottom crevasses observed by NASA's Operation IceBridge radar depth sounder and laser altimeter, whereas HO/LEFM and SSA/LEFM do not generate crevasses that are consistent with observations. We attribute the difference to the nonhydrostatic condition of ice near the grounding line, which facilitates crevasse formation and is accounted for by the FS model but not by the HO or SSA models. We find that Calving is enhanced when pre-existing surface crevasses are present, when the ice shelf is shortened or when the ice shelf front is undercut. The role of undercutting depends on the timescale of Calving events. It is more prominent for glaciers with rapid Calving rates than for glaciers with slow Calving rates. Glaciers extending into a shorter ice shelf are more vulnerable to Calving than glaciers developing a long ice shelf, especially as the ice front retreats close to the grounding line region, which leads to a positive feedback to Calving events. We conclude that the FS/LEFM combination yields substantial improvements in capturing the stress field near the grounding line of a glacier for constraining crevasse formation and Iceberg Calving.
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Iceberg Calving of Thwaites Glacier, West Antarctica: Full-Stokes modeling combined with linear elastic fracture mechanics
2016Co-Authors: Eric Rignot, Mathieu Morlighem, Helene SeroussiAbstract:Abstract. Thwaites Glacier (TG), West Antarctica, has been losing mass and retreating rapidly in the past few decades. Here, we present a study of its Calving dynamics combining a two-dimensional flowband Full Stokes (FS) model of its viscous flow with linear elastic fracture mechanics (LEFM) theory to model crevasse propagation and ice fracturing. We compare the results with those obtained with the higher-order (HO) and the shallow-shelf approximation (SSA) models coupled with LEFM. We find that FS/LEFM produces surface and bottom crevasses that match the distribution of crevasse depth and width observed from NASA's Operation IceBridge radar depth sounders, whereas HO/LEFM and SSA/LEFM do not generate crevasses that match observations. We attribute the difference to the non-hydrostatic condition of ice near the grounding line, which facilitates crevasse formation, and is accounted for by the FS model but not by the HO or SSA model. We also find that Calving is enhanced when pre-existing surface crevasses are present, when the ice shelf is shortened or when the ice shelf front is undercut. The role of undercutting depends on the time scale of Calving events. It is more prominent for glaciers with rapid Calving rates than glaciers with slow Calving rates. Glaciers extending into a shorter ice shelf are more vulnerable to Calving than glaciers developing a long ice shelf, especially as the ice front retreats close to the grounding line region, which leads to a positive feedback. We conclude that the FS/LEFM combination yields substantial improvements in capturing the stress field near the grounding line for constraining crevasse formation and Iceberg Calving.
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Full-Stokes modeling of grounding line dynamics, ice melt and Iceberg Calving for Thwaites Glacier, West Antarctica
2016Co-Authors: Eric Rignot, Mathieu Morlighem, Helene SeroussiAbstract:Abstract. Thwaites Glacier (TG), West Antarctica, has been losing mass and retreating rapidly in the past three decades. Here we present a two-dimensional, Full-Stokes (FS) modeling study of the grounding line dynamics and Iceberg Calving of TG. First, we compare FS with two simplified models, the higher-order (HO) model and the shallow-shelf approximation (SSA) model, to determine the impact of changes in ice shelf basal melt rate on grounding line dynamics. Second, we combine FS with the Linear Elastic Fracture Mechanics (LEFM) theory to simulate crevasse propagation and Iceberg Calving. In the first experiment, we find that FS requires basal melt rate consistent with remote sensing observations to reach steady state at TG’s current geometry while HO and SSA require unrealistically high basal melt rate. The grounding line of FS is also more sensitive to changes in basal melt rate than HO and SSA. In the second experiment, we find that only FS can produce surface and bottom crevasses that match radar sounding observations of crevasse width and height. We attribute the difference to the non- hydrostatic conditions of ice near the grounding line, which facilitate crevasse formation and are not accounted for in HO and SSA. Additional experiments using FS indicate that Iceberg Calving is significantly enhanced when surface crevasses exist near the grounding line, when ice shelf is shortened, or when the ice shelf front is undercut. We conclude that FS yields substantial improvements in the description of ice flow dynamics at the grounding line under high basal melt rate and in constraining crevasse formation and Iceberg Calving.
Irena Vaňková - One of the best experts on this subject based on the ideXlab platform.
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Rapid Iceberg Calving following removal of tightly packed pro-glacial mélange
Nature Communications, 2019Co-Authors: Timothy H. Dixon, David M. Holland, Denis Voytenko, Irena VaňkováAbstract:Observation systems are not sufficient to determine the relationship between mélange strength and Calving frequency. Here the authors used the derivation of digital elevation models from radar interferometry data to study Jakobshavn Isbræ and show an inverse correlation between mélange thickness and Calving rate. Iceberg Calving is a major contributor to Greenland’s ice mass loss. Pro-glacial mélange (a mixture of sea ice, Icebergs, and snow) may be tightly packed in the long, narrow fjords that front many marine-terminating glaciers and can reduce Calving by buttressing. However, data limitations have hampered a quantitative understanding. We develop a new radar-based approach to estimate time-varying elevations near the mélange-glacier interface, generating a factor of three or more improvement in elevation precision. We apply the technique to Jakobshavn Isbræ, Greenland’s major outlet glacier. Over a one-month period in early summer 2016, the glacier experienced essentially no Calving, and was buttressed by an unusually thick mélange wedge that increased in thickness towards the glacier front. The extent and thickness of the wedge gradually decreased, with large-scale Calving starting once the mélange mass within 7 km of the glacier front had decreased by >40%.
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Rapid Iceberg Calving following removal of tightly packed pro-glacial mélange.
Nature communications, 2019Co-Authors: Surui Xie, Timothy H. Dixon, David M. Holland, Denis Voytenko, Irena VaňkováAbstract:Iceberg Calving is a major contributor to Greenland’s ice mass loss. Pro-glacial melange (a mixture of sea ice, Icebergs, and snow) may be tightly packed in the long, narrow fjords that front many marine-terminating glaciers and can reduce Calving by buttressing. However, data limitations have hampered a quantitative understanding. We develop a new radar-based approach to estimate time-varying elevations near the melange-glacier interface, generating a factor of three or more improvement in elevation precision. We apply the technique to Jakobshavn Isbrae, Greenland’s major outlet glacier. Over a one-month period in early summer 2016, the glacier experienced essentially no Calving, and was buttressed by an unusually thick melange wedge that increased in thickness towards the glacier front. The extent and thickness of the wedge gradually decreased, with large-scale Calving starting once the melange mass within 7 km of the glacier front had decreased by >40%. Observation systems are not sufficient to determine the relationship between melange strength and Calving frequency. Here the authors used the derivation of digital elevation models from radar interferometry data to study Jakobshavn Isbrae and show an inverse correlation between melange thickness and Calving rate.
Roger A. Hansen - One of the best experts on this subject based on the ideXlab platform.
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Iceberg Calving as a primary source of regional‐scale glacier‐generated seismicity in the St. Elias Mountains, Alaska
Journal of Geophysical Research, 2010Co-Authors: Shad O'neel, Natalia Rupert, Christopher F Larsen, Roger A. HansenAbstract:[1] Since the installation of the Alaska Regional Seismic Network in the 1970s, data analysts have noted nontectonic seismic events thought to be related to glacier dynamics. While loose associations with the glaciers of the St. Elias Mountains have been made, no detailed study of the source locations has been undertaken. We performed a two-step investigation surrounding these events, beginning with manual locations that guided an automated detection and event sifting routine. Results from the manual investigation highlight characteristics of the seismic waveforms including single-peaked (narrowband) spectra, emergent onsets, lack of distinct phase arrivals, and a predominant cluster of locations near the Calving termini of several neighboring tidewater glaciers. Through these locations, comparison with previous work, analyses of waveform characteristics, frequency-magnitude statistics and temporal patterns in seismicity, we suggest Calving as a source for the seismicity. Statistical properties and time series analysis of the event catalog suggest a scale-invariant process that has no single or simple forcing. These results support the idea that Calving is often a response to short-lived or localized stress perturbations. Our results demonstrate the utility of passive seismic instrumentation to monitor relative changes in the rate and magnitude of Iceberg Calving at tidewater glaciers that may be volatile or susceptible to ensuing rapid retreat, especially when existing seismic infrastructure can be used.
