Reverse glacier motion during iceberg calving and the cause of glacial earthquakes

Murray, Tavi; Nettles, M.; Selmes, N.; Cathles, L. M.; Burton, Justin; James, T. D.; Edwards, Stuart; Martin, Ian; O’Farrell, T.; Aspey, Robin; Rutt, I. C.; Bauge, T.

doi:10.1126/science.aab0460

Cited by 40 publications

(92 citation statements)

References 39 publications

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“…It produced a force of maximum amplitude 5.4 × 10 10 N in the radial direction, normal to the terminus that is well reproduced by our model (computed maximum amplitude of 5.9 × 10 10 N). Event B is due to the BO capsize of an iceberg with L ≈ 2,500 m, H ≈800 m, and ε ≈0.23 (volume 0.37 km 3 ) from Helheim glacier, on 25 July 2013 (Murray, Nettles, et al, ). It produced a force amplitude of 3 × 10 10 N also very well reproduced by the proposed approach (amplitude of 2.95 × 10 10 N).…”

Section: Force Variations With Iceberg Dimensions (εH)supporting

confidence: 92%

Numerical Modeling of Iceberg Capsizing Responsible for Glacial Earthquakes

et al. 2018

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The capsizing of icebergs calved from marine‐terminating glaciers generate horizontal forces on the glacier front, producing long‐period seismic signals referred to as glacial earthquakes. These forces can be estimated by broadband seismic inversion, but their interpretation in terms of magnitude and waveform variability is not straightforward. We present a numerical model for fluid drag that can be used to study buoyancy‐driven iceberg capsize dynamics and the generated contact forces on a calving face using the finite‐element approach. We investigate the sensitivity of the force to drag effects, iceberg geometry, calving style, and initial buoyancy. We show that there is no simple relationship between force amplitude and iceberg volume, and similar force magnitudes can be reached for different iceberg sizes. The force history and spectral content varies with the iceberg attributes. The iceberg aspect ratio primarily controls the capsize dynamics, the force shape, and force frequency, whereas the iceberg height has a stronger impact on the force magnitude. Iceberg hydrostatic imbalance generates contact forces with specific frequency peaks that explain the variability in glacial earthquake dominant frequency. For similar icebergs, top‐out and bottom‐out events have significantly different capsize dynamics leading to larger top‐out forces especially for thin icebergs. For realistic iceberg dimensions, we find contact‐force magnitudes that range between 5.6 × 1011 and 2 × 1014 kg·m, consistent with seismic observations. This study provides a useful framework for interpreting glacial earthquake sources and estimating the ice mass loss from coupled analysis of seismic signals and modeling results.

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Section: Force Variations With Iceberg Dimensions (εH)supporting

confidence: 92%

Numerical Modeling of Iceberg Capsizing Responsible for Glacial Earthquakes

et al. 2018

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“…Murray et al, 2015aMurray et al, , 2015b; and (v) the large uncertainties in the bed data, discussed in J14 and evidenced by the disparate measurements shown in Figure 3a, present a further complication: instead of a steadily sloped bed, the glacier might encounter a pinning point (e.g., in the form of retrograde bed slope) or an abrupt deepening in bathymetry. Murray et al, 2015aMurray et al, , 2015b; and (v) the large uncertainties in the bed data, discussed in J14 and evidenced by the disparate measurements shown in Figure 3a, present a further complication: instead of a steadily sloped bed, the glacier might encounter a pinning point (e.g., in the form of retrograde bed slope) or an abrupt deepening in bathymetry.…”

Section: Figures 3 and 4 Show Comparisons Between Previously Reportedmentioning

confidence: 99%

On the role of buoyant flexure in glacier calving

Wagner

James

Murray

et al. 2016

Geophysical Research Letters

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Interactions between glaciers and the ocean are key for understanding the dynamics of the cryosphere in the climate system. Here we investigate the role of hydrostatic forces in glacier calving. We develop a mathematical model to account for the elastic deformation of glaciers in response to three effects: (i) marine and lake‐terminating glaciers tend to enter water with a nonzero slope, resulting in upward flexure around the grounding line; (ii) horizontal pressure imbalances at the terminus are known to cause hydrostatic in‐plane stresses and downward acting torque; (iii) submerged ice protrusions at the glacier front may induce additional buoyancy forces that can cause calving. Our model provides theoretical estimates of the importance of each effect and suggests geometric and material conditions under which a given glacier will calve from hydrostatic flexure. We find good agreement with observations. This work sheds light on the intricate processes involved in glacier calving and can be hoped to improve our ability to model and predict future changes in the ice‐climate system.

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“…Increasing dynamic ice loss from the Greenland Ice Sheet reflects a combination of increased ice velocities and icefront retreat [4,[17][18][19]. Correlations between ice-front position change, and air and sea temperatures suggest that tidewater glaciers are sensitive to both atmospheric and oceanic forcing ( [20][21][22]; Fig.…”

Section: Ice-front Variations Of Calving Glaciersmentioning

confidence: 99%

Glacier Calving in Greenland

Benn

Cowton

Todd

et al. 2017

Curr Clim Change Rep

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In combination, the breakaway of icebergs (calving) and submarine melting at marine-terminating glaciers account for between one third and one half of the mass annually discharged from the Greenland Ice Sheet into the ocean. These ice losses are increasing due to glacier acceleration and retreat, largely in response to increased heat flux from the oceans. Behaviour of Greenland's marine-terminating ('tidewater') glaciers is strongly influenced by fjord bathymetry, particularly the presence of 'pinning points' (narrow or shallow parts of fjords that encourage stability) and overdeepened basins (that encourage rapid retreat). Despite the importance of calving and submarine melting and significant advances in monitoring and understanding key processes, it is not yet possible to predict the tidewater glacier response to climatic and oceanic forcing with any confidence. The simple calving laws required for ice-sheet models do not adequately represent the complexity of calving processes. New detailed process models, however, are increasing our understanding of the key processes and are guiding the design of improved calving laws. There is thus some prospect of reaching the elusive goal of accurately predicting future tidewater glacier behaviour and associated rates of sea-level rise.

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Reverse glacier motion during iceberg calving and the cause of glacial earthquakes

Cited by 40 publications

References 39 publications

Numerical Modeling of Iceberg Capsizing Responsible for Glacial Earthquakes

Numerical Modeling of Iceberg Capsizing Responsible for Glacial Earthquakes

On the role of buoyant flexure in glacier calving

Glacier Calving in Greenland

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