Avanzi, Francesco; Petrucci, Giacomo; Matzl, Margret; Schneebeli, Martin; De Michele, Carlo (2017): Specific surface area (SSA) and thickness distribution measured during X-ray microtomographic observations of wet-snow metamorphism in a cold laboratory, link to Zip archive [dataset]. PANGAEA, https://doi.org/10.1594/PANGAEA.874393,

---

Supplement to: Avanzi, F et al. (2017): Early formation of preferential flow in a homogeneous snowpack observed by micro-CT. Water Resources Research, https://doi.org/10.1002/2016WR019502

We performed X-ray microtomographic observations of wet-snow metamorphism during controlled continuous melting and melt-freeze events in the laboratory. Three blocks of snow were sieved into boxes and subjected to cyclic, superficial heating or heating-cooling to reproduce vertical water infiltration patterns in snow similarly to natural conditions. Periodically, samples were taken at different heights and scanned. Results suggest that wet-snow metamorphism dynamics are highly heterogeneous even in an initially homogeneous snowpack. Consistent with previous work, we observed an increase with time in the thickness of the ice structure, which is a measure of grain size. However, this was coupled with large temporal scatter between consecutive measurements of the specific surface area and of the statistical moments of grain thickness distributions. Because of marked differences in the right tail, grain thickness distributions did not show shape invariance with time, contrary to previous analyses. In our experiments, wet-snow metamorphism showed two strikingly different patterns: homogeneous coarsening superimposed by faster heterogeneous coarsening in areas that were affected by preferential percolation of water. Liquid water movement in snow and fast structural evolution may be thus intrinsically coupled by early formation of preferential flow at local scale. These observations suggest that further experiments are highly needed to fully understand wet-snow metamorphism and infiltration patterns in a natural snowpack.

This .zip folder contains data of Specific Surface Area (SSA) and thickness distribution measured during X-ray microtomographic observations of wet-snow metamorphism in a cold laboratory. Three experiments were performed. Experiments M1 and M2 reproduced a melt-only process, where snow was kept in isothermal state at 0°C; experiment MF included several melt-freeze cycles. Additional information may be found in the mentioned paper (including positions, labels, and time of all the samples analysed).

Directory organization:

- Folder SSA contains three .csv files (comma-separated) reporting data of SSA measured during the three experiments. Time is relative to the beginning of each experiment (in days). Three heights were probed: surface, middle and base (see the paper for details). In M1, two different data of SSA are available at middle height for instants = 5.58, 7.58, and 8.54 days. Data in column SSA_middle_1 (m²/kg) refer to samples L (time = 5.58 days), OA (time = 7.58 days) and PA (time = 8.54 days), respectively. Data in column SSA_middle_2 (m²/kg) refer to samples M (time = 5.58 days), OB (time = 7.58 days), and PB (time = 8.54 days), respectively.

- Folder Thickness contains the thickness distributions of all the samples analysed (one folder for each experiment). Data are tab-separated. Order of columns: Binstart (incl) [mm], Counts, Vol [mm³], in-%.

Contact: In case of questions, please contact Francesco Avanzi (francesco.avanzi@mail.polimi.it)

Micro-CT data are available upon request to Martin Schneebeli (schneebeli@slf.ch)