Item: Spatial Variations in Snowslope Stability: Insights from Observations During Active Control on the Milford Road, New Zealand
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Title: Spatial Variations in Snowslope Stability: Insights from Observations During Active Control on the Milford Road, New Zealand
Proceedings: 2010 International Snow Science Workshop
Authors:
- Zach M. Guy [ Department of Earth Sciences, Montana State University, Bozeman, MT, USA ]
- Karl W. Birkeland [ Department of Earth Sciences, Montana State University, Bozeman, MT, USA ] [ USDA Forest Service National Avalanche Center, Bozeman, MT, USA ]
Date: 2009
Abstract: Slab avalanches initiate from relatively small (1-10m length) zones of basal weakness. Knowledge of the location of these “deficit zones†or “sweet spots†is needed to help travelers evaluate slope stability, and also for avalanche technicians placing charges for effective avalanche control. Widespread avalanche activity is common within minutes after the onset of rain on freshly deposited snow. These avalanches typically release as slabs several hours or more before liquid water has penetrated to the sliding layer; analyses indicate that a small perturbation at the surface can have a large effect on the stress distribution deeper in the snowpack. An important implication is that new snow is often in a metastable condition, which is consistent with the view that caution is needed when travelling during or soon after storms. Another implication is that control work with explosives is most likely to be effective during or soon after storms. Experiences on the Milford Road, New Zealand indicate good results with large (25kg) charges and large (900g) boosters. In many cases charges placed at a specific location in a start zone consistently yield good results. However, the most effective location can and does vary depending on snow conditions; large charges placed less than 100m apart often produce different results. Key is to persist and dig out all potential deep instabilities to minimize “nasty surprises†such as post-control releases and/or earthquake-triggered avalanches.
Object ID: ISSW_O-017.pdf
Language of Article: English
Presenter(s): Unknown
Keywords: milford road, spatial variations, snowslope stability
Page Number(s): 95-101
Subjects: new zealand slab avalanches
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