Three-Dimensional Heterogeneous Structures of Newly Formed Wind Slabs and its Implications for Avalanche Release

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.