What?
Characteristics
A wave‐like formation of soft or hard wind drifted snow, often overhanging.
Avalanche type and trigger
Cornice collapse can trigger new snow avalanches, wind slabs, persistent slabs, or wet avalanches on steep slopes below.
Where?
Spatial distribution
Cornices occur on the leeward sides of wind‐exposed ridgelines or sharp terrain breaks.
Position of the weak layer in the snowpack
Snow drift extends the cornice outward, so the fresher, sensitive, and more easily triggered part of the cornice is generally near its outer edge.
Why?
Release characteristics
- Natural cornice collapses are common during windy midwinter storms, as cornices rapidly build outward and become unstable with drifting storm snow.
- Rapid warming, rainfall or prolonged melt can cause cornices to become unstable, to buckle and calve.
When?
Duration
Once built, cornices can be an issue throughout the season, generally from midwinter through spring.
How to manage?
Identification of the problem in the field
Cornices occur on ridgelines or sharp terrain breaks and are usually easy to recognize. However, while standing on the top of cornices it is sometimes difficult to estimate their size. Cornices often break further back than expected, even onto flat terrain, and are the cause of many unexpected falls in the mountains.
Travel advice
Avoid travel on and below large ridge top cornices, especially during periods with drifting snow or the onset warm temperatures.
