Jökull - 01.12.2003, Side 11

The 1783–1785 Laki-Grímsvötn eruptions
torted. On his two-day exploratory trip into the Síða
highlands, Stephensen conducted some observations
on the eruptive products from the Laki event and at-
tempted to locate the source vents. He notes that
the moors above the Síða district and most of the
Síða highlands were covered with a 10 to 15 cm-thick
tephra deposit. Stephensen’s descriptions of land-
marks in the highlands, and his map of the lava flow
and vent locations in the northern part of the high-
lands, were very inaccurate (Stephensen, 1785; Páls-
son, 1794). Stephensen states that he could not get a
clear view of this part of the highlands due to smoke
and mist that filled the air. Pálsson (1794) noted that
it was rumoured in the Fire districts that Stephensen
never went far into the Síða highlands and the in-
completeness of Stephensen’s descriptions in that area
supports this.
PÁLSSON’S DESCRIPTIONS AND
OBSERVATIONS
In the spring of 1784, Sveinn Pálsson wrote a
short compendium about the Laki eruption (Table
1), mostly describing the distal effects of the erup-
tion in northern Iceland, i.e. ash fall, sulfuric haze
and how these phenomena affected vegetation and
weather. He relates the severe frost in the fall and
winter of 1783–1784 to the sulfuric haze produced by
Laki because it reduced the solar radiation flux to the
Earth’s surface. This is similar to the explanation put
forth by Pálsson’s contemporaries Mourgue de Mon-
tredon (1784), Johann L. Christ (1783), and Benjamin
Franklin (1784). Pálsson’s brief descriptions concern-
ing the progress of the eruption are based on a letter
from a friend living in the Síða district.
In 1794, eleven years after the eruption, Pálsson
explored the Fire districts and the Síða highlands. His
travel log, written in 1791–1797 but not printed until
1945, gives a detailed description of his observations
in the area, along with a map which fairly accurately
depicts the distribution of the Laki lava flow, vent lo-
cations and prominent landmarks (Pálsson, 1794). He
noted that the tephra at that time had completely dis-
appeared into the bogs. Furthermore he states that
where the tephra had fallen on bare ground in the
northern part of the highlands, it was largely removed
by wind and surface runoff. The western slopes of Mt.
Galti, however, were completely covered with tephra
and the fall deposit was about 15 cm thick.
Pálsson and his partner were the first to reach and
investigate the Laki cone-row, July 31st 1794. Af-
ter a difficult walk across the lava flow they reached
the cone-row midway between the Laki and Hnúta
mountains (See Figure 3 in Thordarson et al., this
issue). Pálsson’s descriptions are remarkably accu-
rate and the cones he describes have been identified
as those situated on fissure segment 3. He estimated
the length of the cone-row between Laki and Hnúta to
be 2 Danish miles, or ∼15 km. The correct length is
13 km. From his observations, Pálsson correctly con-
cluded that the lava in the Skaftá River gorge was de-
rived from the fissures southwest of Laki and the lava
filling the Hverfisfljót River gorge originated from the
fissures northeast of Laki. He also suggested that the
fissures southwest of Laki were formed during the ini-
tial phase of the eruption and that the fissures north-
east of Laki were formed on 29 July, when activity
was first noticed in the eastern part of the Síða high-
lands.
It is obvious from Pálsson’s conjecture on the
progress of the eruption that he considered the cone
rows on either side of Mt. Laki to be two discrete fis-
sure segments, one opening at the beginning of the
eruption and the other about two months later. Later
geologists (Helland, 1886; Thoroddsen, 1879, 1894,
1925; Thorarinsson, 1967, 1969) adopted this idea
without question, as the basic reasoning appeared log-
ical, although erroneous as demonstrated by Thordar-
son and Self (1993).
Another important contribution was Pálsson’s
documentation of the location of the Úlfarsdalur Val-
ley, which was eradicated by the Laki lava and is
wrongly placed on modern topographic maps. The
first outbreaks of the Laki eruption were reported to
be in the Úlfarsdalur Valley, therefore it is important
to know the exact location of this valley. According to
Pálsson, Úlfarsdalur trended north along the western
slopes of Úlfarsdalssker, separated from the Skaftá
River gorge by a low lava ridge. The lava that ran
westwards from the craters at Hnúta (see Figure 2 in
Thordarson et al., this issue) and dammed the Skaftá
River gorge on the third day of the eruption now cov-
JÖKULL No. 53, 2003 9