Life, death and afterlife of the extrusion flow theory

Waddington, Edwin D.

doi:10.3189/002214311796406022

Cited by 11 publications

(7 citation statements)

References 125 publications

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“…Notwithstanding, non-basal deformation of ice requires 183 stresses at least 60 times larger than those for basal slip at the same strain rate, so 184 that large internal stresses are expected in ice undergoing dislocation creep (Duval 185 et al, Wilson and Zhang, 1996). ics of glaciers and ice sheets (Sharp, 1954;Waddington, 2010 Glen (1955) and others, including the corroboration of the suitability of 234 such a power law for modeling glacier flow (Nye, 1953(Nye, , 1957 consists of a recoverable "delayed-elastic" strain (sometimes also called "anelas-…”

mentioning

confidence: 99%

The microstructure of polar ice. Part II: State of the art

Faria

Weikusat

Azuma

2014

Journal of Structural Geology

110

189

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Besides the obvious relevance of glaciers and ice sheets for climate-related issues, another important feature of natural ice is its ability to creep on geological time scales and low deviatoric stresses at temperatures very close to its melting point, without losing its polycrystalline character. This fact, together with its strong mechanical anisotropy and other notable properties, makes natural ice an interesting model material for studying the high-temperature creep and recrystallization of rocks in Earth's interior. After having reviewed the major contributions of deep ice coring to the research on natural ice microstructures in Part I of this work (Faria et al., this issue), here in Part II we present an up-to-date view of the modern understanding of natural ice microstructures and the deformation processes that may produce them. In particular, we analyse a large body of evidence that reveals fundamental flaws in the widely accepted tripartite paradigm of polar ice grains is also observed at various depths, provided that the local concentration of strain energy is high enough (which is not seldom the case). As a substitute for the tripartite paradigm, we propose a novel dynamic recrystallization diagram in the three-dimensional state space of strain rate, temperature, and mean grain size, which summarizes the various competing recrystallization processes that contribute to the evolution of the polar ice microstructure.

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mentioning

confidence: 99%

The microstructure of polar ice. Part II: State of the art

Faria

Weikusat

Azuma

2014

Journal of Structural Geology

110

189

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“…Extrusion flow, a velocity pattern for which maximum horizontal velocity occurs below the surface (Waddington, 2010), is clearly visible in Fig. 4 in the vicinity of the calving front for the low water level cases.…”

Section: Water Level Heightmentioning

confidence: 95%

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Mercenier¹

2017

Preprint

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Ocean-terminating glaciers in Arctic regions have undergone rapid dynamic changes in recent years, which have been related to a dramatic increase in calving rates. Iceberg calving is a dynamical process strongly influenced by the geometry at the terminus of tidewater glaciers. We investigate the effect of varying water level, calving front slope and basal sliding on the state of stress and flow regime for an idealized grounded ocean-terminating glacier and scale these results with ice thickness and velocity. Results show that water depth and calving front slope strongly affect the stress state while the effect from spatially uniform variations in basal sliding is much smaller. An increased relative water level or a reclining calving front slope strongly decrease the stresses and velocities in the vicinity of the terminus and hence have a stabilizing effect on the calving front. We find that surface stress magnitude and distribution for simple geometries are determined solely by the water depth relative to ice thickness. Based on this scaled relationship for the stress peak at the surface, and assuming a critical stress for damage initiation, we propose a simple and new parametrization for calving rates for grounded tidewater glaciers that is calibrated with observations.

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“…These soft layers are located in the lower part of the NEEM ice core, which is dominated by simple shear (Dansgaard and Johnson, 1969;Montagnat et al, 2014). The soft layers can therefore be seen as depths where a high rate of simple shear occurs, instead of layers with enhanced extrusion (Waddington, 2010). However, it is likely that not all soft layers that are caused by finer grains have been identified since the available sampling rate of 615 LM images along 2207 m of depth of the NEEM ice core leaves many depth intervals not studied.…”

Section: Variability Of Predicted Strain Rates With Depthmentioning

confidence: 99%

Using a composite flow law to model deformation in the NEEM deep ice core, Greenland: Part 1 the role of grain size and grain size distribution on the deformation of Holocene and glacial ice

Kuiper

Weikusat

Bresser

et al. 2019

Preprint

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Abstract. The effect of grain size on strain rate of ice in the upper 2207 m in the North Greenland Eemian Ice Drilling (NEEM) deep ice core was investigated using a rheological model based on the composite flow law of Goldsby and Kohlstedt (1997, 2001). The grain size was described by both a mean grain size and a grain size distribution, which allowed the strain rate to be calculated using two different model end members: (i) the micro-scale constant stress model where each grain deforms by the same stress and (ii) the micro-scale constant strain rate model where each grain deforms by the same strain rate. The model results show that basal slip accommodated by grain boundary sliding produces almost all of the deformation in the upper 2207 m of the NEEM ice core, while dislocation creep (basal slip accommodated by non-basal slip) hardly contributes to deformation. The difference in calculated strain rate between the two model end members is relatively small. The calculated strain rate in the fine grained glacial ice (1419–2207 m) varies strongly with depth and is about 4–5 times higher than in the coarser grained Holocene ice (0–1419 m). Two peaks in strain rate are predicted at about 1980 and 2100 m of depth. The results from the rheological model and microstructures in the glacial ice indicate that fine grained layers in the glacial ice will act as internal preferential sliding zones in the Greenland ice sheet.

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Life, death and afterlife of the extrusion flow theory

Cited by 11 publications

References 125 publications

The microstructure of polar ice. Part II: State of the art

The microstructure of polar ice. Part II: State of the art

Final author response

Using a composite flow law to model deformation in the NEEM deep ice core, Greenland: Part 1 the role of grain size and grain size distribution on the deformation of Holocene and glacial ice

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