Jökull - 01.12.2003, Side 9

The 1783–1785 Laki-Grímsvötn eruptions
counts the surge advanced one Danish mile beyond
the hillock Orustuhóll on that day. This inconsis-
tency in the dates given for the lava emerging from
the Hverfisfljót River gorge can be explained by con-
sidering the geographic condition around the mouth
of the gorge, which was and still is located at the
southern tip of Mt. Dalsfjall, 7 km north-northeast of
the hillock Orustuhóll. The north-south trending Mt.
Þverárfjall is approximately 1 km north of Orustuhóll
and because of that mountain the mouth of the Hverf-
isfljót River gorge is not visible from the Síða dis-
trict. However, the mouth of the gorge is clearly visi-
ble from the Fljótshverfi district in the east (see Figure
2 in Thordarson et al., this issue).
I conclude that the description in Eldrit 2, when
the lava is said to have emerged from the gorge on
9 August, refers to the time when Steingrímsson saw
the lava advance beyond the southern tip of Þverár-
fjall from the Síða district. On the other hand, the
description in Eldrit 3 about the surge emerging from
the gorge on 7 August, is most likely based on obser-
vations by inhabitants of the Fljótshverfi district and
Steingrímsson did not get news of that until after he
wrote Eldrit 2.
Another way of evaluating the veracity of these
descriptions is by reconstructing the flow rate of the
lava during this period. The distance the lava flowed
from the vents until it reached the mouth of the gorge
is ∼28 km. According to Eldrit 3 it took the flow 8
days to flow this distance, i.e. from 30 July to 7 Au-
gust. According to the description in Eldrit 2 it took
the lava 10 days to flow the same distance. If the state-
ment in Eldrit 2 that the lava emerged from the gorge
on the 9th is correct, then the lava advanced about
10 km in less than a day. If the lava emerged out from
the gorge on the 7th, as stated in Eldrit 3, the flow
advanced the same distance in 3 days, or about 3 km
per day. As the lava emerged from the gorge, where it
had been confined to a narrow passageway, and spread
out onto the sandur plain, its flow rate would be ex-
pected to decrease but not increase as is the case if the
description in Eldrit 2 is assumed to be correct.
This discussion on the inconsistency between the
Eldrit written by Steingrímsson is by no means ex-
haustive, but demonstrates that the discrepancies are
minor and does not have substantial effects on our re-
construction of the events of the eruption.
HÓLM’S DESCRIPTIONS
Om Jordbranden paa Island i Aret 1783 (About the
Eruption in Iceland in the year 1783) by Sæmundur
Magnússon Hólm was published in both Danish and
German in Copenhagen 1784 (Table 1). An extract
from his Eldrit was also printed in the Ephemerides
Societatis Meteorologicae Palatinae, Observationes
Anni 1783 published in Mannheim 1785. The author
was born and raised in Meðalland, one of the Fire dis-
tricts. In 1771 he drew up a map of the area featuring
the local landscape and farming communities (Figure
1). This map is a valuable source about local con-
ditions in the Fire district before the Laki eruption
and the inhabitants’ perception of geographic direc-
tions (see Thordarson et al., this issue). At the time of
the eruption Hólm was located in Copenhagen, thus
in writing his compendium of the eruption he had to
rely on news, letters and reports sent to Copenhagen
via the trading vessels from Iceland in fall of 1783.
His main sources appear to be the Eldrit of Jón Eir-
íkssonII (Table 1) and a report by Skúli Magnússon,
Governor of Iceland (Rafnsson, 1984), along with per-
sonal letters sent to him and other Icelanders living
in Copenhagen. Consequently, Hólm’s descriptions
on the progress of the Laki eruption are often exag-
gerated and thus not a reliable source on the details
of the course of eruption events. However, his writ-
ings provide useful information about the occurrence
of the Laki haze and its effects in Denmark. The Eldrit
included a map, showing very inaccurately the distri-
bution of the Laki lava flow.
STEPHENSEN’S DESCRIPTIONS AND
OBSERVATIONS
Magnús Stephensen and H. C. D. W. von Levetzow
were sent to Iceland in the summer 1784 by the Dan-
ish government to investigate the Laki eruption and
its effect on the Icelandic community. Stephensen
published the results of his investigations in 1785,
along with a map of the lava flow (Table 1). The de-
scriptions of the eruptive events are largely based on
Steingrímsson’s documentation of the eruption, and
as pointed out by Pálsson (1794), facts are often dis-
JÖKULL No. 53, 2003 7