Jökull - 01.12.2006, Side 10

Haraldsdóttir et al.
NE. Heavy snowfall and persistent strong winds may
result in enormous snow accumulation in many of the
starting zones of avalanches in N-Vestfirðir. Intensive
snowfall during winds from SE can cause avalanche
hazard on slopes facing north in parts of Ísafjörður
and Hnífsdalur. In all of the towns in N-Vestfirðir
there is frequently a serious threat of dry avalanches,
with the exception of Suðureyri.
Siglufjörður
The most severe avalanche hazard in Siglufjörður
(Figure A9) is related to heavy snowfall with strong
winds from northerly directions. Some of the
avalanches with the longest run-outs (from Skolla-
skál, Ytra-Strengsgil and Jörundargil) have been pre-
ceded by persistent snowfall during moderate winds
and cold weather followed by strong winds leading to
very rapid snow accumulation in the starting zones.
Ólafsfjörður
Avalanches with long run-out zones are uncommon
along the mountainside above the town (Figure A10).
The main dry avalanche threat is considered to be as-
sociated with snowfall during easterly winds. Addi-
tionally, the town is threatened by mudflows.
Seyðisfjörður
Analysis of weather related to avalanches in Seyð-
isfjörður (Figure A11) is more complicated than in
most of the other towns in Iceland. Hazard may arise
in some of the avalanche source areas in most wind
conditions during snowfall or sleet, but the most com-
mon circumstances are associated with snowfall dur-
ing winds from NE or E.
Although often warm, winds from SE may bring
snow to the mountains above Seyðisfjörður. During
intense snow or sleet and moderate winds from E,
snow can accumulate on both sides of the fjord, caus-
ing wet avalanche hazard. Threat by wet avalanches
and slush flows mainly occurs on the south side of
town below Strandartindur. The town is also threat-
ened by debris flows and an area of large mass-creep.
Neskaupstaður
Avalanche hazard can arise along the entire mountain-
side at Neskaupstaður (Figure A12) in snowfall during
winds between N and E. The most frequent circum-
stances creating avalanche hazard is intense snowfall,
sometimes during calm weather in the town but strong
winds in the mountains and out on the open sea. Tem-
perature at sea level is often slightly above freezing
during snow accumulation preceding the most severe
avalanche events. North-easterly winds can lead to ac-
cumulation of snow on parts of the mountains above
the town as well as erosion of snow from other parts.
During avalanche weather, temperatures usually drop
as one gets farther away from the coast, and conse-
quently, the limits of snow and rain tend to be at a
lower level inland than at the coast. Intensive wet
snow accumulation sometimes occurs during ESE-
and SE-winds.
Most of the largest avalanches since 1885 seem
to have been dry avalanches, triggered after several
days of NE-winds with snowfall on top of hard snow
surface in the mountains, and temperatures just be-
low 0◦C in the lowland. Debris-flow hazard is also
present, especially from the Urðarbotn area.
Eskifjörður
The main threat in Eskifjörður is due to slush flows,
debris flows and flooding (Figure A13), which is most
likely to occur during intense precipitation. Monitor-
ing is necessary if snow has accumulated in gullies.
SUMMARY
An overview of the outlines of recorded avalanches
in the vicinity of all major towns in Iceland that are
endangered by avalanches has been presented graphi-
cally, together with a short description of the relevant
elements of the weather prior to the avalanches. The
overview is based on avalanche records, which have
been reliable during decades in some towns, whereas
in other towns there was no record until after 1995,
except for avalanches causing fatalities and/or dam-
age to property.
The main characteristics of the weather prior to
avalanches is heavy precipitation and strong winds.
The most severe avalanche hazard is generally also
associated with strong winds in the mountains and
heavy precipitation during the days preceding a catas-
trophic avalanche. Avalanche hazard in N-Vestfirðir,
8 JÖKULL No. 56