Reversal of ice motion during the outburst of a glacier-dammed lake on Gornergletscher, Switzerland

Sugiyama, Shin; Bauder, Andreas; Weiss, Patrik; Funk, Martin

doi:10.3189/172756507782202847

Cited by 55 publications

(61 citation statements)

References 42 publications

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“…However, it is interesting to note that the shear-type events occur at the onset of the drainage of Gornersee. This observation suggests that shear failure is a response to the lake drainage, which is known to have the potential to significantly alter the glacier's flow direction (P. Riesen, unpublished manuscript, 2007;Sugiyama et al, 2007). In order to support this conjecture, a procedure to search the entire data set has to be developed.…”

Section: Discussionmentioning

confidence: 99%

“…The data used for the present analysis were acquired as part of an investigation of the yearly subglacial drainages of Gornersee, a nearby ice-marginal lake (e.g., Huss et al, 2007;Sugiyama et al, 2007;Walter et al, 2008). The instrumentation for the 2004 and 2006 seismic arrays consisted of 14 and 24 seismometers, respectively, most of which were installed at the glacier surface (Fig.…”

Section: Introductionmentioning

confidence: 99%

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Moment Tensor Inversions of Icequakes on Gornergletscher, Switzerland

Walter

Clinton²,

Deichmann³

et al. 2009

Bulletin of the Seismological Society of America

109

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We have determined seismic source mechanisms for shallow and intermediate-depth icequake clusters recorded on the glacier Gornergletscher, Switzerland, during the summers of 2004 and 2006. The selected seismic events are part of a large data set of over 80,000 seismic events acquired with a dense seismic network deployed in order to study the yearly rapid drainage of Gornersee lake, a nearby icemarginal lake. Using simple frequency and distance scaling and Green's functions for a homogeneous half-space, we calculated moment tensor solutions for icequakes with M w 1:5 using a full-waveform inversion method usually applied to moderate seismic events (M w > 4) recorded at local to regional distances (≈50-700 km). Inversions from typical shallow events are shown to represent tensile crack openings. This explains well the dominating Rayleigh waves and compressive first motions observed at all recording seismograms. As these characteristics can be observed in most icequake signals, we believe that the vast majority of icequakes recorded in the 2 yr is due to tensile faulting, most likely caused by surface crevasse openings. We also identified a shallow cluster with somewhat atypical waveforms in that they show less dominant Rayleigh waves and quadrantal radiation patterns of first motions. Their moment tensors are dominated by a large double-couple component, which is strong evidence for shear faulting. Although less than a dozen such icequakes have been identified, this is a substantial result as it shows that shear faulting in glacier ice is generally possible even in the absence of extreme flow changes such as during glacier surges. A third source of icequakes was located at 100 m depth. These sources can be represented by tensile crack openings. Because of the high-hydrostatic pressure within the ice at these depths, these events are most likely related to the presence of water lenses that reduce the effective stress to allow for tensile faulting.Online Material: Background information and results of moment tensor inversions.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Moment Tensor Inversions of Icequakes on Gornergletscher, Switzerland

Walter

Clinton²,

Deichmann³

et al. 2009

Bulletin of the Seismological Society of America

109

View full text Add to dashboard Cite

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“…In recent field observations on an Alpine glacier (Gornergletscher, Switzerland), repeated near-reversal of flow, accompanied by reversed displacement direction was observed (Sugiyama et al, 2007(Sugiyama et al, , 2008. The change of motion takes place within a few days during the periodical drainage of a supra-glacial lake, and is possibly related to the unloading and stress redistribution during the rapid drainage.…”

Section: Introductionmentioning

confidence: 99%

A viscoelastic Rivlin-Ericksen material model applicable to glacier ice

Riesen¹,

Hutter²,

Funk³

2010

Nonlin. Processes Geophys.

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Abstract. We present a viscoelastic constitutive relation which describes transient creep of a modified second grade fluid enhanced with elastic properties of a solid. The material law describes a Rivlin-Ericksen material and is a generalization of existing material laws applied to study the viscoelastic properties of ice. The intention is to provide a formulation tailored to reproduce the viscoelastic behaviour of ice ranging from the instantaneous elastic response, to recoverable deformation, to viscous, stationary flow at the characteristic minimum creep rate associated with the deformation of polycrystalline ice. We numerically solve the problem of a slab of material shearing down a uniformly inclined plate. The equations are made dimensionless in a form in which elastic effects and/or the influence of higher order terms (i.e., strain accelerations) can be compared with viscous creep at the minimum creep rate by means of two dimensionless parameters. We discuss the resulting material behaviour and the features exhibited at different parameter combinations. Also, a viable range of the non-dimensional parameters is estimated in the scale analysis.

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“…Pressurisation greater than the ice overburden pressure is another important element of the glacier response as it causes hydraulic jacking of the glacier, stress redistribution at the glacier bed and mechanical uplift of the glacier surface (Bartholomaus et al, 2008). This mechanical response of the ice is little studied, however, and current models are unable to accurately reproduce observations (Sugiyama et al, 2007;Pimentel and Flowers, 2011).…”

Section: Introductionmentioning

confidence: 99%

Stress Redistribution Explains Anti-correlated Subglacial Pressure Variations

et al. 2018

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We used a finite element model to interpret anti-correlated pressure variations at the base of a glacier to demonstrate the importance of stress redistribution in the basal ice. We first investigated two pairs of load cells installed 20 m apart at the base of the 210 m thick Engabreen glacier in Northern Norway. The load cell data for July 2003 showed that pressurisation of a subglacial channel located over one load cell pair led to anti-correlation in pressure between the two pairs. To investigate the cause of this anti-correlation, we used a full Stokes 3D model of a 210 m thick and 25-200 m wide glacier with a pressurised subglacial channel represented as a pressure boundary condition. The model reproduced the anti-correlated pressure response at the glacier bed and variations in pressure of the same order of magnitude as the load cell observations. The anti-correlation pattern was shown to depend on the bed/surface slope. On a flat bed with laterally constrained cross-section, the resulting bridging effect diverted some of the normal forces acting on the bed to the sides. The anti-correlated pressure variations were then reproduced at a distance >10-20 m from the channel. In contrast, when the bed was inclined, the channel support of the overlying ice was vertical only, causing a reduction of the normal stress on the bed. With a bed slope of 5 degrees, the anti-correlation occurred within 10 m of the channel. The model thus showed that the effect of stress redistribution can lead to an opposite response in pressure at the same distance from the channel and that anti-correlation in pressure is reproduced without invoking cavity expansion caused by sliding.

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Reversal of ice motion during the outburst of a glacier-dammed lake on Gornergletscher, Switzerland

Cited by 55 publications

References 42 publications

Moment Tensor Inversions of Icequakes on Gornergletscher, Switzerland

Moment Tensor Inversions of Icequakes on Gornergletscher, Switzerland

A viscoelastic Rivlin-Ericksen material model applicable to glacier ice

Stress Redistribution Explains Anti-correlated Subglacial Pressure Variations

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