In situ X-ray tomography densification of firn: The role of mechanics and diffusion processes

Burr, Alexis; Lhuissier, Pierre; Martín, Christophe; Philip, Armelle

doi:10.1016/j.actamat.2019.01.053

Cited by 13 publications

(26 citation statements)

References 47 publications

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“…This is consistent with a mass transport occurring from regions of high curvature toward regions of low curvature, as exemplified in Figure 10. While Burr et al (2019) report that letting firn samples evolve at rest in a relatively hightemperature environment (−2 • C) without compression leads to pore splitting, we did not observe such phenomenon in our simulation.…”

Section: Surface Diffusion Onlycontrasting

confidence: 91%

“…This number increased from 39 to 57 pores, showing the ability of the ice creep mechanism to split and isolate pores from the atmosphere. The same observation of pore splitting was made by Burr et al (2019). They report pore separations of a sample during ongoing densification that is subject to solely mechanical loading.…”

Section: Ice Creep Onlysupporting

confidence: 56%

“…The goal of this model is to explicitly simulate the evolution of the ice/pore interface in firn. This evolution notably includes topological changes, resulting from pore closure or coalescence (Burr et al, 2019). In the model, the bi-phasic nature of the firn is replaced by a mono-phasic medium with the addition of a characteristic function retaining the position of the ice/pore interface, the so called Level-Set (LS) function φ (Osher and Sethian, 1988;Gibou et al, 2018).…”

Section: The Level-set Methodsmentioning

confidence: 99%

“…In a recent article, Burr et al (2019) performed different types of cold-room experiments to study the decoupled contributions of ice creep and curvature-driven diffusion to the evolution of firn and its porosity. They conclude that both compression and diffusive mechanisms contribute to the separation of pores.…”

Section: Contributions Of Dislocation Creep and Surface Diffusion To mentioning

confidence: 99%

“…In this section, we modeled the equivalent of Burr et al (2019) experiments to study the individual contributions of dislocation creep and surface diffusion to the densification of firn and the closure of pores. In total, we run four different experiments, all initialized with the same porous network.…”

Section: Contributions Of Dislocation Creep and Surface Diffusion To mentioning

confidence: 99%

See 4 more Smart Citations

A Micro-Mechanical Model for the Transformation of Dry Polar Firn Into Ice Using the Level-Set Method

et al. 2020

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Interpretation of greenhouse gas records in polar ice cores requires a good understanding of the mechanisms controlling gas trapping in polar ice, and therefore of the processes of densification and pore closure in firn (compacted snow). Current firn densification models are based on a macroscopic description of the firn and rely on empirical laws and/or idealized geometries to obtain the equations governing the densification and pore closure. Here, we propose a physically-based methodology explicitly representing the porous structure and its evolution over time. In order to handle the complex geometry and topological changes that occur during firn densification, we rely on a Level-Set representation of the interface between the ice and the pores. Two mechanisms are considered for the displacement of the interface: (i) mass surface diffusion driven by local pore curvature and (ii) ice dislocation creep. For the latter, ice is modeled as a viscous material and the flow velocities are solutions of the Stokes equations. First applications show that the model is able to densify firn and split pores. Using the model in cold and arid conditions of the Antarctic plateau, we show that gas trapping models do not have to consider the reduced compressibility of closed pores compared to open pores in the deepest part of firns. Our results also suggest that the mechanism of curvature-driven surface diffusion does not result in pore splitting, and that ice creep has to be taken into account for pores to close. Future applications of this type of model could help quantify the evolution and closure of firn porous networks for various accumulation and temperature conditions.

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Section: Surface Diffusion Onlycontrasting

confidence: 91%

Section: Ice Creep Onlysupporting

confidence: 56%

Section: The Level-set Methodsmentioning

confidence: 99%

Section: Contributions Of Dislocation Creep and Surface Diffusion To mentioning

confidence: 99%

Section: Contributions Of Dislocation Creep and Surface Diffusion To mentioning

confidence: 99%

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A Micro-Mechanical Model for the Transformation of Dry Polar Firn Into Ice Using the Level-Set Method

et al. 2020

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Metamorphism observation and model of snow from summit, Greenland under both positive and negative temperature gradients in a micro computed tomography

Baker

2022

Hydrological Processes

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Three sets of snow specimens with different initial densities ranging from 311 to 486 kg m À3 , which were collected from depths of 7, 40 and 57 cm at Summit, Greenland (72 35 0 N, 38 25 0 W) in June 2017, were subjected to the temperature gradient (TG) of $160 K m À1 in opposing directions. The snow metamorphism was characterized using both X-ray micro computed tomography and optical microscopy. The formation of depth hoar is evident as the snow grains transformed from the initial approximately rounded particles to needles, broad-plates, columns and cup-shapes.The de-densification process of snow is also reflected in various microstructural parameters, viz., the density and the structure thickness (the feature size of ice particle) generally decreased with time, while the area-equivalent circle diameter (the feature size of pore), the total porosity, the specific surface area and the structure model index (a measure of convexity/concavity of ice surface) increased. Based on an icesphere pair of equal size, a vapour transport model, which depends on the initial particle radius, r p , and the ratio of the initial particle-bond radius to the initial particle radius, α, was constructed to simulate the main characteristics of change in the density with time under the TG metamorphism. We found critical values of r p = 0.1 mm and α = 0.1 that determine how fast the geometric coefficient, ψ (a tuning parameter used in this model at the cone angle θ ¼ 45 between the two ice spheres), changes.We propose a conceptual model in which an ice-sphere pair can be regarded as a volume element of morphogenesis of depth hoar. This model can be used to explain the formation of the needle-like, broad-plate and column depth hoar by combining particle-by-particle with inter-layer vapour transport.

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A grain-size driven transition in the deformation mechanism in slow snow compression

Sundu,

Ottersberg,

Jaggi

et al. 2024

Acta Materialia

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In situ X-ray tomography densification of firn: The role of mechanics and diffusion processes

Cited by 13 publications

References 47 publications

A Micro-Mechanical Model for the Transformation of Dry Polar Firn Into Ice Using the Level-Set Method

A Micro-Mechanical Model for the Transformation of Dry Polar Firn Into Ice Using the Level-Set Method

Metamorphism observation and model of snow from summit, Greenland under both positive and negative temperature gradients in a micro computed tomography

A grain-size driven transition in the deformation mechanism in slow snow compression

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