Jökull - 01.12.2006, Side 6

Haraldsdóttir et al.
Weather related to avalanches at Neskaupstaður
(Ólafsson, 1998), showed connections between pre-
cipitation, maximum wind speed and the occurrence
of large avalanches. A prerequisite for avalanches
with a long run-out was either a high value of accu-
mulated precipitation over 5 days or moderate precip-
itation, but strong winds from the north-east. Stud-
ies for Siglufjörður (Björnsson, 2001), Seyðisfjörður
(Karlsdóttir, 2003) and for the northern part of Vest-
firðir (Björnsson, 2002) also revealed a connection
between high wind speeds and avalanches. Prior to
the avalanches in Seyðisfjörður, a high amount of pre-
cipitation was also observed. Much precipitation was
usually observed before the largest avalanches in the
northern part of Vestfirðir, as well as in Siglufjörður.
Strong winds as well as heavy precipitation are the
most important parameters to consider when attempt-
ing to predict regional avalanche hazard with the help
of sophisticated numerical modeling of the snowpack
(Haraldsdóttir et al., 2004).
GEOGRAPHICAL SETTING
Several coastal towns are endangered by avalanches
in Iceland (Figure 2). Fishing is the economic foun-
dation for these towns, which were established in the
late 1800’s. Above the towns are steep 400–800 m
high mountains. As the towns grew bigger in the late
1900’s, they gradually expanded towards the moun-
tain slopes and today there are many houses that
are located within presently-defined avalanche haz-
ard zones. The slopes of the mountains in the start-
ing zones of avalanches are typically 30–40◦. The
mountain tops are either relatively sharp peaks or flat
with relatively extensive fetch for blowing snow. Both
types exist in most parts of the country, but the peak
form is more common in Austfirðir, E-Iceland, and the
plateau form in Vestfirðir, NW-Iceland. Many starting
zones are in gullies or bowls, while others are on more
open slopes.
Previous awareness of the potential hazard de-
pended mainly on people’s experience of avalanches.
During the late 1800’s there were cold winters. In
Neskaupstaður in the 1890’s (translated to English):
“avalanches struck every winter down to the ocean”
(unpublished memoirs of Pálmason, as referred to
by Haraldsdóttir (1997). At that time, there were
few houses in the present location of Neskaupstaður,
where in 1885 three lives were lost. During the same
year, an avalanche took the lives of 24 people in Seyð-
isfjörður. During most of the 20th century the cli-
mate was warmer and there are no registered major
catastrophic avalanches in the Neskaupstaður area un-
til 1974, when 12 fatalities occurred. More than half
a century without any significant avalanche activity in
vicinity of the inhabited area had resulted in careless-
ness in planning new residential areas.
The present avalanche hazard zones extend down
to the ocean in many towns, enclosing industrial as
well as inhabited areas. Several farms and many roads
are threatened by avalanches, but this overview con-
cerns only towns and their immediate surroundings.
Figure 3 shows an overview of avalanche acci-
dents in Iceland. The incidents are mostly clustered
in Vestfirðir, NW-Iceland, in central N-Iceland and in
Austfirðir, E-Iceland with some scatter elsewhere. As
Björnsson (1980) points out, the data is discontinuous.
Records are inaccurate up to the year 1800, but af-
ter 1800 reports on damage from avalanches are quite
complete.
Most of the fatal, catastrophic avalanches dur-
ing the last 30 years striking towns or farms in Ice-
land have been dry slab avalanches. Examples in-
clude Neskaupstaður on 20 December 1974, causing
12 casualties, an avalanche striking approximately 40
summer cottages close to Ísafjörður on 5 April 1994
killing one person, Súðavík on 16 January 1995 caus-
ing 14 casualties, a farmhouse in Reykhólasveit on 18
January 1995 killing one person, Flateyri on 26 Oc-
tober 1995 causing 20 casualties and the most recent
one destroying a farm in Ólafsfjörður on 13 January
2004 killing the farmer.
Slush flows killed four people in Patreksfjörður on
22 January 1983. Assessments of the avalanche haz-
ard at several locations, as well as recommendations
for actions to be taken, were made after the Neskaup-
staður 1974 avalanches (Quervain, 1975), and also
after the Patreksfjörður 1983 slush flows (Hestnes,
1985). Besides dry slab avalanches, slush flows cause
a major threat to several towns. Powder avalanches
on the other hand are rare, due to prevailing strong
4 JÖKULL No. 56