Avalanche Mechanics Faculty
Snowpack boundary conditions, snowpack properties, metamorphism of snow and intergranular bonding, deformation and failure of weak layers, avalanche initiation and fracture propagation.
Tests of snow slab stability.
Applied Snow and Avalanche Research website
|A large powder avalanche on Mt. Blanc, France. Such avalanches can
reach 200 km/h. A dense-flowing component of similar speed may be
hidden by the powder component. Although the greatest impact pressures
are created by the dense-flowing component, both the dense-flowing and
the powder components are considered for hazard mapping and for design
|Two graduate students at Rogers Pass, British Columbia observe a
profile of all snowpack layers before measuring the strength of the
weak layers. Some avalanche forecasting operations in Canada use the
strength of weak layers, along with the load due to the overlying slab,
to calculate stability indices. Other stability indices include the
stress due to an average skier.
|Researcher approaches a crown fracture of a dry slab avalanche in the
Cariboo Mountains. The avalanche was remotely triggered by a
snowmobiler on the gentle slopes above the crown fracture.
|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 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.
|Snowboarder doing a shovel tilt test to help assess the stability of
near surface layers. Professional forecasters and recreationists use
this and other mechanical tests of snow stability. However, because
snow stability varies within snow slopes and changes over time, too
much emphasis should not be placed on any point observation of the
|To test the strength of a weak snow layer or weak interface at the base
of a slab, the snow is gripped with a shear frame that is placed a few
mm above the weak layer or interface, and pulled to fracture within a
second. The results of such simple mechanical tests are used to
calculate stability indices for avalanche forecasting. Improving
stability indices is an active research topic.
|Dry slab avalanche in the Purcell Mountains of British Columbia. The
avalanche released naturally (no artificial trigger) on a weak layer of
surface hoar crystals (frost). Once buried by subsequent snowfalls,
layers of surface hoar sometimes remain unstable for a month or more.
|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.
|A 3-metre high crown fracture of a dry slab avalanche in the Columbia
Mountains of British Columbia. Natural dry slab avalanches start with a
ductile failure and then fracture within a weak layer or weak interface
at the base of the slab. Many weak layers are less than 1 cm thick, and
can only be located by careful observations.
|A small dry slab avalanche in the Columbia Mountains of British
Columbia. Although relatively small, such avalanches can be hazardous
to backcountry recreationists.
|A dry slab avalanche in the Rocky Mountains near Fernie, British
Columbia. The avalanche has descended a vertical distance of
approximately 150 m and generated sufficient impact pressure to destroy
a wood frame building. Such avalanches are common in Canada, however,
most occur away from people and property.
|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
|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
|This close-up photo shows the weak structure of a layer of buried
surface hoar (frost) crystals. The layer is 20 mm thick. Such layers
can remain unstable for several weeks.