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Snow metamorphism as revealed by scanning electron microscopy.
Florent Dominé1, Thomas Lauzier, Axel Cabanes
1CNRS, Laboratoire de Glaciologie et Géophysique de l'Environnement, 38402 Saint Martin d'Hères, cedex, France. florent@lgge.obs.ujf-grenoble.fr
Microscopy Research and Technique
|August 26, 2003
Summary
Current snow metamorphism theories are mostly verified, but new findings show rounded shapes dominate even at colder temperatures. Some newly formed crystal faces contradict existing growth models.
Area of Science:
- Snow science
- Crystallography
- Geophysics
Background:
- Snow crystal shapes are theorized to depend on growth rates and temperature.
- Sublimating crystals are expected to be rounded, while growing crystals vary from rounded to faceted.
- A transition temperature of -10.5°C is proposed for equilibrium shape changes.
Purpose of the Study:
- To investigate snow crystal shapes under natural and laboratory metamorphic conditions.
- To test the validity of current snow metamorphism theories regarding crystal morphology.
- To identify discrepancies between theoretical predictions and observed snow crystal shapes.
Main Methods:
- Scanning Electron Microscopy (SEM) was used for detailed crystal morphology analysis.
- Snow samples underwent natural metamorphism.
- Laboratory experiments involved isothermal metamorphism at -4°C and -15°C.
Main Results:
- Observed snow crystal shapes generally align with existing theories on growth rates and sublimation.
- Contrary to theory, rounded crystal shapes predominated after extended metamorphism at -4°C and -15°C.
- Small faceted crystals with sharp angles, newly formed at -15°C, were observed, contradicting current models.
Conclusions:
- Existing theories on snow crystal growth and sublimation are largely supported by observations.
- The predicted temperature-dependent transition from rounded to faceted equilibrium shapes was not confirmed.
- The formation of new, sharp-angled faces under specific conditions suggests alternative growth or sublimation mechanisms, possibly involving dislocations.