Ground deformation and gravity variations modelled from present-day ice thinning in the vicinity of glaciers

Mémin, Anthony; Rogister, Yves; Hinderer, J.; Llubes, Muriel; Boy, Jean‐Paul

doi:10.1016/j.jog.2009.09.006

Cited by 9 publications

(6 citation statements)

References 45 publications

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“…We observe left‐handed block displacement along steeply dipping joints on the western slope and right‐handed shearing on the eastern slope, resulting in uphill‐facing counterscarps (inset in Figure a). These calculated uplift values are within the same order of magnitude as determined in previous studies; e.g., Memin et al [] estimated 5–9 mm uplift for 30–50 m ice loss in the Mont Blanc region. Our predicted post‐LIA uplift at Aletsch corresponds to a mean uplift rate of 0.4–1.1 mm yr −1 , which is in good agreement with a rebound modeling study at Aletsch estimating an uplift rate of up to 1.5 mm yr −1 due to recent glacier retreat [ Melini et al , ].…”

Section: Numerical Study Of Paraglacial Rock Slope Damage and Displacmentioning

confidence: 99%

Beyond debuttressing: Mechanics of paraglacial rock slope damage during repeat glacial cycles

et al. 2017

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Cycles of glaciation impose mechanical stresses on underlying bedrock as glaciers advance, erode, and retreat. Fracture initiation and propagation constitute rock mass damage and act as preparatory factors for slope failures; however, the mechanics of paraglacial rock slope damage remain poorly characterized. Using conceptual numerical models closely based on the Aletsch Glacier region of Switzerland, we explore how in situ stress changes associated with fluctuating ice thickness can drive progressive rock mass failure preparing future slope instabilities. Our simulations reveal that glacial cycles as purely mechanical loading and unloading phenomena produce relatively limited new damage. However, ice fluctuations can increase the criticality of fractures in adjacent slopes, which may in turn increase the efficacy of fatigue processes. Bedrock erosion during glaciation promotes significant new damage during first deglaciation. An already weakened rock slope is more susceptible to damage from glacier loading and unloading and may fail completely. We find that damage kinematics are controlled by discontinuity geometry and the relative position of the glacier; ice advance and retreat both generate damage. We correlate model results with mapped landslides around the Great Aletsch Glacier. Our result that most damage occurs during first deglaciation agrees with the relative age of the majority of identified landslides. The kinematics and dimensions of a slope failure produced in our models are also in good agreement with characteristics of instabilities observed in the field. Our results extend simplified assumptions of glacial debuttressing, demonstrating in detail how cycles of ice loading, erosion, and unloading drive paraglacial rock slope damage.

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Section: Numerical Study Of Paraglacial Rock Slope Damage and Displacmentioning

confidence: 99%

Beyond debuttressing: Mechanics of paraglacial rock slope damage during repeat glacial cycles

et al. 2017

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“…6 shows large differences between the SVAL and DCW models for the areas located above and under the horizon of the station. We thus use Green's function for the Newtonian gravity variation as defined by Merriam (1992) and Boy et al (2002) and applied to specific glaciers in the Alps by Mémin et al (2009).…”

Section: Namementioning

confidence: 99%

Secular gravity variation at Svalbard (Norway) from ground observations and GRACE satellite data

Mémin¹,

Rogister²,

Hinderer³

et al. 2011

Geophysical Journal International

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S U M M A R YThe Svalbard archipelago, Norway, is affected by both the present-day ice melting (PDIM) and Glacial Isostatic Adjustment (GIA) subsequent to the Last Pleistocene deglaciation. The induced deformation of the Earth is observed by using different techniques. At the Geodetic Observatory in Ny-Ålesund, precise positioning measurements have been collected since 1991, a superconducting gravimeter (SG) has been installed in 1999, and six campaigns of absolute gravity (AG) measurements were performed between 1998 and 2007. Moreover, the Gravity Recovery and Climate Experiment (GRACE) satellite mission provides the time variation of the Earth gravity field since 2002. The goal of this paper is to estimate the present rate of ice melting by combining geodetic observations of the gravity variation and uplift rate with geophysical modelling of both the GIA and Earth's response to the PDIM. We estimate the secular gravity variation by superimposing the SG series with the six AG measurements. We collect published estimates of the vertical velocity based on GPS and VLBI data. We analyse the GRACE solutions provided by three groups (CSR, GFZ, GRGS). The crux of the problem lies in the separation of the contributions from the GIA and PDIM to the Earth's deformation. To account for the GIA, we compute the response of viscoelastic Earth models having different radial structures of mantle viscosity to the deglaciation histories included in the models ICE-3G or ICE-5G. To account for the effect of PDIM, we compute the deformation of an elastic Earth model for six models of ice-melting extension and rates. Errors in the gravity variation and vertical velocity are estimated by taking into account the measurement uncertainties and the variability of the GRACE solutions and GIA and PDIM models. The ground observations agree with models that involve a current ice loss of 25 km 3 water equivalent yr −1 over Svalbard, whereas the space observations give a value in the interval [5, 18] km 3 water equivalent yr −1 . A better modelling of the PDIM, which would include the precise topography of the glaciers and altitude-dependency of ice melting, is necessary to decrease the discrepancy between the two estimates.

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“…So far, we have considered that the remote unloaded/loaded area is located beneath the horizontal plane passing through the observation point (JAMES and IVINS 1998;LE MEUR and HUYBRECHTS 2001;MÄ KINEN et al 2007). However, since the Newtonian part of the gravity depends on the relative position of the observation point and location where mass changes occur (MERRIAM 1992;BOY et al 2002;MÉMIN et al 2009), it depends on the topography of the loaded area. In the next section, we examine the influences of the geophysical context, topography and load variation on C e,N .…”

Section: Separation Between the Geodetic Consequences Of Gia And Pdimmentioning

confidence: 99%

Separation of the Geodetic Consequences of Past and Present Ice-Mass Change: Influence of Topography with Application to Svalbard (Norway)

Mémin

Hinderer

Rogister

2011

Pure Appl. Geophys.

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Polar regions such as Greenland, Svalbard and Antarctica are deforming today because of both the present-day ice-mass (PDIM) change of glaciers and the glacial isostatic adjustment (GIA) following the Pleistocene deglaciation. Observations handled in these areas contain both the contributions from the PDIM change and GIA. This study aims at separating them by considering two specific gravity variation-to-vertical displacement ratios. We first review the case of the viscoelastic rebound (GIA) subsequent to the Pleistocene deglaciation leading to a ratio C v . The outcome of previous studies is that C v is approximately equal to -0.15 lGal/mm and almost independent of the deglaciation history, ice geometry and viscosity profile of the mantle. Similarly we consider the elastic deformation resulting from PDIM change which leads to a second ratio C e,N . Several studies have shown that C e;N % À0:26 lGal/mm if one assumes that the changing glaciers are thin layers over the surface of a spherical Earth model. In this case, we show that the separation between the contributions from PDIM change and GIA is unique if both gravity and height changes observations are available at the same station. Next, we focus on C e,N and show that according to the deglaciation/glaciation context and from colocated gravity variation and ground vertical velocity measurements one can deduce a range of possible values for C e,N . Studying the influence of the topography on C e,N we first show that it tends to positive values if most of surrounding ice-mass changes above the altitude of the observation site and to values lower than -0.26 lGal/mm if changes are below. We next apply our general formalism to the case of the past and PDIM changes in Svalbard, Norway. We compute the ratio C e,N at the geodetic observatory at Ny-Å lesund and show the influence of the topography of the surrounding glaciers on the measured gravity and uplift rates. We show that if the ice-mass change is spatially uniform, C e, N does not depend on the speed of ice-mass change, and hence the separation of the contributions from PDIM changes and GIA can still be done univocally. However, if the ice-mass change is not spatially uniform, C e, N depends on both the speed of ice-mass change and the volume of ice-change rate.

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Ground deformation and gravity variations modelled from present-day ice thinning in the vicinity of glaciers

Cited by 9 publications

References 45 publications

Beyond debuttressing: Mechanics of paraglacial rock slope damage during repeat glacial cycles

Beyond debuttressing: Mechanics of paraglacial rock slope damage during repeat glacial cycles

Secular gravity variation at Svalbard (Norway) from ground observations and GRACE satellite data

Separation of the Geodetic Consequences of Past and Present Ice-Mass Change: Influence of Topography with Application to Svalbard (Norway)

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