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
The Icelandic Meteorological Office (IMO) has used the SAMOS model for various
applications since the year 2000. In the following, some results of this work are summarised
and methods and operational guidelines which have been developed are outlined briefly.
2. SIMULATION OF AVALANCHES OVER A WIDE SIZE RANGE
The concept of the standard path was introduced by Jónasson and others (1999) to define a
general scale for measuring the run-out distance of avalanches. This measure of run-out is
called the run-out index and is defined as the horizontal distance, in [hm], to the stopping
position of an avalanche that has been transferred to the standard path from its original path.
The run-out index is traditionally a scalar since the avalanche path is represented by a single
flow-line on which the stopping position is a single point that can be explicitly defined by the
one-dimensional system horizontal distance along the flow-line [hm]. The evaluation of runout
indices relies on a slight modification of the traditional 2-parameter PCM snow avalanche
model. Run-out indices have proved to be useful both to simplify the comparison of different
avalanches and to carry out a statistical analysis of the run-out of avalanches in a collection of
different avalanche paths. The run-out index scale has been used extensively at the IMO and
has gained an increased expectance since its introduction.
2.1 2D run-out index
A two-dimensional model for snow avalanche motion may be used to extend the run-out
index concept to two dimensions. It is possible to create run-out index isolines by determining
run-out indices on multiple flow-lines along a mountainside and interpolate between matching
values. This could be suggested as a two-dimensional run-out index. However, this method is
limited because of the inherent limitations of flow-line models.
Figure 1 A birds view of the three-dimensional standard path. The parallel lines in red
mark horizontal distance from the top in 100 m increments in the range
1000−2000 m. The corresponding run-out indices are defined as the distance in
[hm] and are thus in the range from 10−20.
Flow-line models only consider the geometry of the path in the downstream direction. This
might be sufficient in an unconfined mountainside, but frequently, topographical features such
as gorges, gullies and ridges stretch along avalanche paths. These features, which tend to
channelise or spread the flow of the avalanche, can either magnify or reduce the run-out
164 Application of two-dimensional avalanche model simulations at the IMO