Following today's tragic avalanche near Termignon in the Haute-Maurienne it is interesting to read this report field by the Hautes-Alples avalanche forecasters who were on the ground in the Nevache.
Avalanche Conditions and Snowpack Stability Report (Summary)
Recent Avalanche Activity: No recent or past slab avalanches observed in the sector. Some small (size 1) wet snow avalanches were seen on steep, sun-exposed slopes near rocks.
Snowpack Observations: A crust layer from Monday’s warming extends up to around 2400m beneath recent snowfall. A snow profile was conducted at 2570m on a N/NE-facing slope, revealing:
145 cm total snow depth, with 45 cm of recent snow showing some wind impact. Beneath that, 50 cm of older snow increasing in density. Around 20 cm of faceted grains, starting to gain cohesion. 20 cm of weak depth hoar (sugar-like crystals) at the bottom.
Stability Tests:
Compression Test (CT11@25SP): A clean fracture occurred in the depth hoar layer after 11 taps. Extended Column Test (ECT P 12@25): Full propagation occurred after 12 taps, indicating a persistent weak layer.\
Key Risks & Recommendations:
No clear surface instability in the tested area, but conditions could be worse in more wind-affected zones. The weak layer at the bottom is relatively easy to trigger and has the potential for full-depth avalanches. Extra caution is needed on shaded high-altitude slopes (north-facing), particularly near slope edges or couloirs where snow cover is shallower—these areas are more prone to triggering deep slab avalanches.
Conclusion:
While surface conditions seem stable, deep persistent weak layers pose a significant risk. In case of an avalanche, it could release the entire snowpack. Skiers should avoid wind-loaded areas and terrain traps and be especially cautious in shallow snowpack zones.
See: https://skitour.fr/sorties/176149
and in the Vanoise
surface instabilities but a weak layer which the forecaster qualified as "inaccessible" due to layers of crust - at that spot.