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
analyzed in the field, emphasizing (i) the extreme runout of boulders transported by snow
avalanches, i.e. point α in this study and its corresponding angle to the top of the snow
avalanche starting zone, and (ii) to the path steepness or angle β, measured in the field from
the position at which the slope angle equals 10°, using a Suunto inclinometer (0.5° precision).
According to McClung and Schaerer (1993) who observed a proportional relationship
between parameters α and β, the following expression has been formulated for each
investigated path:
α = x·β
Figure 2 Location of the reference paths: A – Botn í Dýrafjörður, B – Reykjaströnd, C –
Fnjóskadalur and D – Bleiksmýrardalur.
3. RESULTS OF THE TRANSFER TESTS IN INHABITED AREAS
3.1 The case study of Patreksfjörður, Northwestern Iceland
Patreksfjörður is a small town (622 inhabitants on December 1, 2007) in the Northwestern
Peninsula. The extent of all reported snow avalanches that reached the village are shown in
Figure 4A. Several major events are reported in the beginning of the 20 th century (Ágústsson
and others, 2003), reaching the sea at the location of the present-day harbor. Although the
runout of these two events, occurring before 1930 is not exactly known, their runout crosses
some of the present-day residence and industrial buildings. Since then, three shorter snow
avalanches reached or approached the settlement area and two slushflows devastated the areas
by the rivers (another event is known from the mid 19 th century). The most recent snow
avalanche events, in 1989, 1995 and 2000, were of lower magnitude.
The application of the determined α/β relationship locates the lower part of the runout zone,
from where the slope angle reach 10° to the furthest expected reach of transported rocky
material. Almost the whole settlement is located within the runout zone of potential snow
avalanches, either below or above the β isoline. This highlights the high hazard degree of
Decaulne and others 133