Deconstructive metamorphosis

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Snow, from its fall until its full melting, undergoes a structural metamorphism governed by local temperature and humidity fields. Among them, the isothermal metamorphism seems the most accessible to modeling. In this work, we tried to simulate the microstructural transformations of a dry snow sample, placed in isothermal conditions, near 0 degree C. In these conditions, the vapor pressure of water is high: the metamorphism can be considered, in first approximation, as fully curvature-driven. A simple numerical model was implemented on this basis and applied to simulated data and 3-D images from X-ray microtomography. From  Snow Microstructure / MANTO Team Centre d'Etudes de la Neige - French Snow Research Center [1]
Snow, from its fall until its full melting, undergoes a structural metamorphism governed by local temperature and humidity fields. Among them, the isothermal metamorphism seems the most accessible to modeling. In this work, we tried to simulate the microstructural transformations of a dry snow sample, placed in isothermal conditions, near 0 degree C. In these conditions, the vapor pressure of water is high: the metamorphism can be considered, in first approximation, as fully curvature-driven. A simple numerical model was implemented on this basis and applied to simulated data and 3-D images from X-ray microtomography. From Snow Microstructure / MANTO Team Centre d'Etudes de la Neige - French Snow Research Center [1]

Deconstructive metamorphosis begins as the snow makes its way to the ground often melting, refreezing, and settling. Water molecules become reordered causing the snowflakes to become more spherical in appearance. These melting snowflakes fuse with others around them becoming larger until all are uniform in size. While the snow is on the ground the melting and joining of snow flakes reduces the height of snow pack by shrinking air spaces and causing the density and mechanical strength of the snow pack to increase. Freshly fallen snow with a density of 0.1/cm3 has very good insulating properties; however as time goes on, due to destructive metamorphism the insulating property of the snow pack decreases because the air spaces between snowflakes disappear. Snow that has been residing on the ground for a long period of time has an average density of 0.40g/cm3 and conducts heat well; however, once a base of 50 cm of snow with a density around 0.3g/cm3 has accumulated, temperatures under the snow remain relatively constant because the greater depth of snow compensates for its density. Destructive metamorphosis is a function of time, location, and weather. It occurs at a faster rate with higher temperatures, in the presence of water, under larger temperature gradients (e.g., warm days followed by cold nights), at lower elevations and on slopes that receive large amounts of solar radiation. As time goes on snow settles compacting air spaces, a process expedited by the packing force of the wind.


Image:Snow density.jpg

Reference

  • 1 The Snow Life-Cycle [2]

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