Wind slabs, a major cause of dry slab avalanches, frequently develop during drifting-snow events in mountainous terrain. However, their three-dimensional internal structure remains poorly understood because of limited observations and is often assumed to be relatively homogeneous. This study examined recently deposited wind slabs using samples collected from Mt. Niseko Annupuri, Japan, in Februray and March 2024 and March 2025. High-resolution X-ray micro-computed tomography (µCT) was used to quantify three-dimensional snow-density distributions and spatial heterogeneity. Two avalanches associated with consecutive blizzard events were also examined to assess the potential implications of the observed structures for avalanche release. The µCT observations revealed pronounced three-dimensional heterogeneity, including band-like structures with distinct density contrasts. Similar features occurred in samples from both years despite differing deposition conditions. This heterogeneity likely results from interactions between drifting-snow deposition and locally variable airflow over irregular snow surfaces. The results demonstrate that newly formed wind slabs develop as three-dimensionally heterogeneous depositional bodies rather than homogeneous layers. Such structures may affect fracture initiation and crack propagation and contribute to avalanche release, particularly where no distinct weak layer is evident. These findings highlight the importance of three-dimensional observations for understanding wind-slab formation and avalanche processes.

1. [1] J. Schweizer, J. B. Jamieson, and M. Schneebeli, “Snow avalanche formation,” Rev. Geophys., Vol.41, No.4, Article No.1016, 2003. https://doi.org/10.1029/2002RG000123
2. [2] D. McClung and P. Schaerer, “The avalanche handbook (3rd edition),” The Mountaineers Books, 2006.
3. [3] G. Statham et al., “A conceptual model of avalanche hazard,” Nat. Hazards, Vol.90, No.2, pp. 663-691, 2018. https://doi.org/10.1007/s11069-017-3070-5
4. [4] M. Schneebeli, “Numerical simulation of elastic stress in the microstructure of snow,” Ann. Glaciol., Vol.38, pp. 339-342, 2004. https://doi.org/10.3189/172756404781815284
5. [5] B. Reuter, J. Schweizer, and A. van Herwijnen, “A process-based approach to estimate point snow instability,” Cryosphere, Vol.9, No.3, pp. 837-847, 2015. https://doi.org/10.5194/tc-9-837-2015
6. [6] J. Gaume, A. van Herwijnen, G. Chambon, N. Wever, and J. Schweizer, “Snow fracture in relation to slab avalanche release: Critical state for the onset of crack propagation,” Cryosphere, Vol.11, pp. 217-228, 2017. https://doi.org/10.5194/tc-11-217-2017
7. [7] J. W. Pomeroy and D. M. Gray, “Snowcover: Accumulation, relocation and Management,” National Hydrology Research Institute (NHRI) Science Report No.7, 1995.
8. [8] G. E. Liston and M. Sturm, “A snow-transport model for complex terrain,” J. Glaciol., Vol.44, No.148, pp. 498-516, 1998. https://doi.org/10.3189/S0022143000002021
9. [9] M. Lehning, H. Löwe, M. Ryser, and N. Raderschall, “Inhomogeneous precipitation distribution and snow transport in steep terrain,” Water Resour. Res., Vol.44, No.7, Article No.W07404, 2008. https://doi.org/10.1029/2007WR006545
10. [10] H. Hirashima, K. Nishimura, E. Baba, A. Hachikubo, and M. Lehning, “SNOWPACK model simulations for snow in Hokkaido, Japan,” Ann. Glaciol., Vol.38, pp. 123-129, 2004. https://doi.org/10.3189/172756404781815121
11. [11] K. Nishimura, E. Baba, H. Hirashima, and M. Lehning, “Application of the snow cover model SNOWPACK to snow avalanche warning in Niseko, Japan,” Cold Reg. Sci. Technol., Vol.43, Nos.1-2, pp. 62-70, 2005. https://doi.org/10.1016/j.coldregions.2005.05.007
12. [12] A. Komatsu and K. Nishimura, “Calculation of snowdrift distribution over complex topography to improve the accuracy of snow avalanche warning systems,” SOLA, Vol.18, pp. 71-75, 2022. https://doi.org/10.2151/sola.2022-012
13. [13] S. Yamaguchi et al., “Co-creation with local governments and ski resorts to generate scientific information that contributes to ski resort avalanche safety management,” Bull. Glaciol. Res., Vol.42, pp. 9-17, 2024. https://doi.org/10.5331/bgr.23R02