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
Figure 3 The mountain Brellur above Patreksfjörður with its flat and extensive
mountaintop. The Urðir area is located on the left side of the photo where there is
a gap in the residential area (photo: Kristín Martha Hákonardóttir).
The mountaintop acts as a huge catchment area for snow drift. Northeasterly winds, which
seem to be dominating in the area according to available data on weather conditions, can
cause strong snow drift into the starting zone and the formation of big cornices (Margreth,
2006). Snow drift is the main reason for snow accumulation in starting zones of avalanches in
the area and the break up of cornices, as those shown in Figure 4, is known to have initiated
some of the largest avalanches in the area (Jóhannesson and others, 1996). Installation of
snow fences and wind baffles is therefore considered to be an effective way of reducing the
risk of avalanches at the Urðir area in Patreksfjörður.
Figure 4: Cornices in the cliffs in the avalanche starting zone in Patreksfjörður in 1995. The
height of the cornices is estimated 5−10 m (photo: courtesy of Þröstur Reynisson).
Margreth (2006) designed a scheme combining snow fences and wind baffles for the Urðir
area in an appraisal study for avalanche defences for the Urðir and Klif areas in Patreksfjörður.
The proposed snow drift measures are shown in Figure 5. They consist of 25−30 wind
baffles to break up cornice formation and 1700 m of snow fences positioned normal to the
prevailing wind direction in multiple rows. The wind direction, wind speed and the local snow
distribution need to be analysed in advance for an effective application of the snow drift
measures, followed by testing the function of a small portion of snow fences and wind baffles
prior to the final construction.
88 Snow drift measures as protection against snow avalanches in Iceland