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.