Avalanche risk assessment - Ministry of Forests, Lands and Natural ...

figure 87 Avalanche mapping for Val d’Isère, France (scale 1:25 000). Mapping in orange is from air photo
interpretation. Mapping in magenta is based on field surveys, interviews with local witnesses including Forest Service
rangers, and ski patrollers. Solid cross-hatching implies more certainty than areas delineated with broken cross-hatching.
(After Borrel 1992)
New Zealand
Avalanche mapping has been completed on many high-use alpine hiking
trails in New Zealand and on one tourist highway. Avalanche mapping
was undertaken at 1:30 000 on a 28 km length of the Milford Road where
50 major avalanche paths plunge from alpine areas subject to very high
precipitation (8000–10 000 mm/yr) through remnants of forest to a narrow
valley floor (Fitzharris and Owens 1980).
For a time, the mapping undertaken along the route was considered by
road authorities to over-estimate avalanche runout distances but a series
of heavy winters in the mid-1990s, when additional areas of old forest
were destroyed, proved the mapping to be conservative. No frequency
was implied in the mapping, but estimates were given in an accompanying
technical report. Active avalanche control undertaken above the
highway in heavy winters increased the frequency of major avalanching
on most paths by at least an order of magnitude above the estimates
made by the mappers.
68 Snow Avalanche Management in Forested Terrain