Nomination of

SURTSEY – NOMINATION FOR THE UNESCO WORLD HERITAGE LIST
surface temperatures of about 5° C. On average,
the minimum temperature drops below 0° C on
80 days of the year; however, since the maximum
exceeds 0° C on most of those days, round-theclock
freezing is only experienced for 18 days per
year, on average. The frost-free period lasts on
average for 5 to 7 months; during the last 50
years, the longest frost-free period lasted 8
months and the shortest about 15 weeks.
Maximum temperatures in excess of 20° C are
quite rare; Stórhöfði has experienced only 2 such
days during the last 85 years. Frost below -15° C
is also extremely rare.
Stórhöfði receives ample precipitation,
totalling annually about 1600 mm. Whereas June
is the driest month of the year (93 mm), October
comes out on average as the wettest month (156
mm), though in fact the entire fall and winter
period from August to March resembles October
(Fig. 2.8). Snowfall is rather slight; in fact, its sum
(60 mm) comprises only around 4% of the total
annual precipitation. A mixture of snow and rain
falls frequently, resulting in approximately
another 30% of the overall precipitation, while
the remaining 66% falls as rain. During the
summer, there is no snowfall. Humidity is
generally high, with frequent overcast and lowcloud
conditions.
Winds are strong at the nearby Stórhöfði
lighthouse, where on over 130 days per year the
10-minute average exceeds 20 m/s at least once,
and a sustained 10-minute hurricane force (>32.7
m/s) is exceeded on an average of 15 days per
year (Fig. 2.8). Concurrent measurements at
Surtsey and Stórhöfði indicate that the ridge wind
at Surtsey is even stronger than at Stórhöfði;
presumably, however, Surtsey's lower-level winds
are considerably less violent. In any case, the sea
state is often highly agitated.
Most of the weather systems affecting Surtsey
arise out of the west (SW to NW). However, the
westerlies aloft are usually undercut by shallow
air masses from the northeast, so for most of the
year easterly winds prevail in the area and are
reinforced by the barrier of the South Iceland
glaciers (Fig. 2.9).
Offshore waves
Iceland's wave climate is severe, including
measured offshore significant wave heights (the
26
°C
m/s
mm
mm/day
mm
10
8
6
4
2
0
14
12
10
8
6
160
140
120
100
80
140
120
100
80
60
40
20
0
Average temperature
Wind speed
Average monthly precipitation
Absolute daily maxima
(precipitation)
Snow total
J F M A M J J A S O N D
Month
Fig. 2.8. Average temperature (red trace) and wind
speed (yellow trace) at Stórhöfði, 1971–2000; average
monthly precipitation (blue trace); snow totals (light
blue trace) and absolute daily maxima (shown by
green dots, in mm per day. (Modified from the
Icelandic Meteorological Office.)
average height of one-third of the waves observed
during a given period of time) of over 16 m and
wave peak periods of up to 20 seconds. Cyclones
from North America pass over Iceland from the
southwest, generating high waves upon reaching
Southwest Iceland. Deep cyclones sometimes
stagnate east or north of the country for several
days and also generate high waves.
In January 1990, for example, an extreme
storm hit the south coast of Iceland. At its peak
intensity, the atmospheric pressure plunged to