International Symposium on Mitigative Measures against Snow ...

<strong>International</strong> <strong>Symposium</strong> on Mitigative Measures against Snow Avalanches
Egilsstaðir, Iceland, March 11–14, 2008
depending on lateral position in the run-out area. Two-dimensional models do not rely on a
single longitudinal profile, but simulate the flow on a three-dimensional surface representing
the actual landscape. A two-dimensional model may, thus, be used to compute a twodimensional
run-out index, which describes the effect of various landscape features on the
run-out. One may expect a run-out index of this kind to have a more distinctive shape than
interpolated points of flow-line models indices. The line representing a two-dimensional runout
index will stretch farther away from the mountain below channels in the topography and
then retreat farther uphill below ridges compared with the corresponding isoline of run-out
indices along multiple flow-lines determined by 1D model calculations.
Identically to the original approach, the two-dimensional run-out indices are determined by
transferring an avalanche from its original path to the standard path, which has been
transformed to a surface, maintaining the original longitudinal profile. Figure 1 shows the 3D
standard path.
2.2 Parameter axis
It was concluded from the experimental simulations that in order to simulate avalanches that
vary in size it is advisable to change release snow depth, d, and the friction angle,
δ, simultaneously but keep other model parameters constant. An important point to consider is
that a unique backcalculation of the model parameters, d and δ, based on information about
run-out distance solely, is impossible because an infinite number of parameter pairs can
explain a given avalanche run-out. In other words, increased friction, δ, can be compensated
by an increase in snow depth, d. It is of practical interest to define a single d/δ pair corresponding
to each run-out index. Similarly to the approach of Jónasson and others (1999), a
way to get around this problem has been developed. This is achieved by defining a so called
parameter axis in the d/δ plane on which d/δ pairs for simulations of avalanches with run-out
indices in the range from 10 to 20 are located (Gíslason, 2007). The parameter axis currently
used for systematic two-dimensional avalanche simulations at the IMO is plotted on Figure 2.
Figure 2 A set of parameter pairs that can be used to simulate avalanches with run-out
indices in the range 10−20.
Gíslason 165