Stability Tests

The Forest Service National Avalanche Center, in cooperation with Ron Johnson of the Gallatin National Forest Avalanche Center, has developed and tested the Stuffblock stability test.  This simple and effective test involves dropping a stuff sack filled with 10 lbs (4.5 kg) of snow from various heights onto an isolated column of snow in the snow pit.  For more detailed information, including statistical comparisons between the stuffblock and the rutschblock and experience with the stuffblock in different snow climates, check out the Stuffblock Technical Report (complete with photographs) or you can find an article we published in Cold Regions Science and Technology here.

Ron Johnson demonstrates the stuffblock snow stability test

 

 

The Forest Service National Avalanche Center has also worked with Chris Landry, a 2002 MSc graduate of the Department of Earth Sciences at Montana State University, on the development and testing of the quantified loaded column test (QLCT).  The QLCT involves testing an isolated column of snow on a sloping test site, leaving as much of the snowpack intact as possible.  Rapid vertical loading is applied to the column by pressing a mechanical force gauge onto a plywood load plate until shear fracture or collapse occurs at the weakest layer. The load plates define the size of the column and distribute the loading evenly over the weak layer. Total shear stress produced by the snow overlying the weak layer, the weight of the plywood plate, and the measured vertical force is compared, in a stability ratio, to the shear stress produced by the in-situ slab overlying the weak layer.   Test results can also be expressed as the water equivalent of the additional loading required to produce shear fracture. A paper describing the mechanics, procedures and initial trials of the quantified loaded column test were presented at ISSW 2000 at Big Sky, Montana. The QLCT was used for Chris's thesis, which is posted here.

Chris Landry demonstrates the quantified loaded column test

 

 

For more information about stability tests, check out Effectively using and interpreting snow stability tests, a paper by Ron Johnson and Karl Birkeland that was presented at the 1998 International Snow Science Workshop.