Avalanche management

New Zealand – South Island

training programme with Otago Polytechnic

Avalanches are common on steep, snow-covered mountain slopes and play a significant role in landscape evolution. Although most avalanches occur in remote locations, a few affect people directly by causing injury or death. Statistics show that most skiers or climbers caught in avalanches trigger the slide themselves. Avalanches also delay travellers and often cause damage to property. The cost of highway closures, avalanche defense structures and avalanche control can be high. For example in western Canada the annual bill for operational control and forecasting is about $10 million.

Avalanche debris is typically well compacted and hard as a result of frictional heating and work hardening.

Heavy equipment is needed to clear avalanche debris, which may also contain rocks and trees.

Albert Dow rescue cache at the floor of Huntington Ravine

Mount Washington

Albert Dow cache in spring (pushed over by an avalanche)

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Avalanche Risk Assessment - Longyearbyen

www.unis.no/RESEARCH/GEOLOGY/Geo_research/Ole/SnowAvalanches.htm

Car hit by the wind blast associated with a large loose snow avalanche and subsequently folded around a tree.

Cornice formed in upper Vandledningsdalen, late June 2000. The snow accumulated by snow drift across the mountain plateau by prevalent SE winter winds. The height from the valley bottom to the mountain plateau above is about 70 m

Avalanche boulder tongue in Endalen, Spitsbergen, Svalbard, August 2000. The avalanche track is seen as a light-colored deposit of debris, extending from the small valley in the upper right to the lower left corner of the photograph. The mountain rises to about 580 m asl., while the valley bottom is at about 200 m asl. This avalanche track extents all the way to the river plain, signaling even the valley bottom beyond to be within the avalanche risk zone during winter.

Buildings on Haugen destroyed by a wet snow avalanche from Vandledningsdalen, June 1953. By this event 3 persons were killed and 30 other persons were injured. The old hospital was destroyed and several other buildings damaged. Another wet snow avalanche occurred in 1989, resulting in loss of property but no casualties. Avalanche defense structures have since been constructed at the mouth of Vandledningsdalen

Avalanches often follow the almost same path from year to year. Local knowledge on high- and low risk zones may with considerable success be used to locate buildings and other structures in the landscape. The picture shows an example from Switzerland.

www.eng.ucalgary.ca/Civil/Avalanche/Civil_Site/avalanche.htm

Protective Forest for Village of Andermatt, Switzerland. Large avalanches run down the slopes on both sides of the protective forest. The forest prevents large avalanches from starting above the village. The interaction between the forest and avalanches is a part of many project to mitigate avalanche hazards.

This house in Davos, Switzerland has been designed and reinforced to mitigate the avalanche risk to the occupants. The windows have strong shutters and the walls are reinforced. The kitchen and garage of such houses are often placed facing the avalanche slope. The rooms where people spend the most time, such as the bedrooms, are located on the opposite side of the house. Some houses have a bunker in the basement for temporary occupancy during extreme storms. Precautionary evacuations are also used in areas where destructive avalanches have long return intervals such as 100 years.

Gas exploder in French Alps. The exploder is filled with propane and oxygen from cylinders in a control shelter (not shown). When ignited by a spark plug in the exploder, the explosion releases unstable snow near the exploder. There are approximately 20 of these exploders in Canada.

The berm on the left side of the photo diverts avalanches parallel to the highway through Rogers Pass in Glacier National Park. The height and curvature of the berm are determined from calculations of avalanche motion.

Snowpack support structures near Andermatt, Switzerland. When constructed in avalanche starting zones, such structures reduce the frequency of large dry slab avalanches. These and similar wooden structures can be used to mitigate large avalanches while the forest regrows.

Summary of Hazard Management:

Prediction / Forecast

Education

Planning /Zoning

Protection

Abatement