Jökull - 01.12.2003, Side 28

Thordarson et al.
to come out of the gorge. Throughout November, lava
continued to issue from the fissures but the new flows
were confined to the highlands (C49). Rainfall, con-
taining ash and sand occurred frequently in late Oc-
tober to November (B83). On 24 November, a strong
earthquake was felt in the Fire districts (A25), which
was followed by increased activity at Austur-Land-
norðursgjá, such that the fire column was seen to rise
above Mt. Kaldbakur (Figure 5g). In the beginning of
December the fire glow above the Laki fissures, which
so far had been seen every night, began to diminish
(B83). However, lava was still emerging from the fis-
sures and the bluish haze continued to hover over the
Fire districts (C49).
In summary: Three tephra falls are described in the
chronicles for this period of the eruption (Figure 5e
and f). Two of these tephra falls (29 August and 7
September) are traced back to the Laki fissures and
one (i.e., 14 September) is inferred to have originated
at the Austur-Landnorðursgjá. Also, distinctive ex-
plosive eruptions occurred at the Austur- Landnorð-
ursgjá on 26 September, 25 October and 24 Novem-
ber (Figure 5g). Similar to the occurrences early on in
the eruption, the explosive activity is closely associ-
ated with occurrences of earthquake swarms and lava
surges. This time the lava surges emerged fromHverf-
isfljót River gorge because of the northeast shift in the
location of the most active vents (Figures 2 and 3).
THE FINAL SCENARIO
A sulfuric stench filled the air in the Fire districts fre-
quently throughout 1784, especially when the wind
was blowing off the vent areas. This was also com-
monly noted in calm weather and on rainy days (B86).
The residents of the farm Skaftárdalur in Skaftártunga
saw fires at the Laki fissures until 14 January 1784.
According to Steingrímsson, no activity was observed
on the fissures after 7 February 1784 (C50).
The Austur-Landnorðursgjá continued to erupt
through the winter of 1784 (B86–87; Figure 5h).
Flash flooding (jökulhlaup) occurred in the Núpsvötn
(Súla) River on 8 April and at the same time a huge
black volcanic cloud rose from Austur-Landnorðurs-
gjá. Steingrímsson reports that ash from this erup-
tion site fell twice in the Fire districts, but most of
the time the plume was directed away from the dis-
tricts by southerly wind (B87). Steingrímsson’s de-
scriptions indicate that this activity lasted for a consid-
erable time, possibly throughout the spring of 1784.
Activity at Austur-Landnorðursgjá was observed off
and on through the year 1784 and in the winter 1785,
especially from the Öræfi district. The last day when
fires were seen at Grímsvötn was 26 May 1785 (B89).
Strong earthquakes were felt in the Fire districts
sometime in February 1784 and were described by
Steingrímsson as follows:
“After a long period of freezing and heavy winds which
lasted through January, strong earthquakes were felt again,
though different than previous ones. Some moved the earth
slightly up and down, others travelled like oceanic waves
from northwest to southeast. The frozen ground cracked
with the sound of thumps and claps.” (A26)
The cracks were most numerous in the Fljóts-
hverfi district and Steingrímsson notes that the spring
water in the Fire districts, which had been strongly
contaminated up to this time, tasted much better after
these earthquakes.
DISCUSSION
NATURE OF ERUPTIVE ACTIVITY AND
RELATED PHENOMENA
The Laki eruption began on 8 June 1783 and 7 Febru-
ary 1784 was the last day when activity was noticed
at the fissures. This day is taken to mark the end of
the Laki eruption and accordingly the eruption lasted
for 8 months. Despite the termination of activity on
the Laki fissures, activity continued at the Grímsvötn
volcano until 26 May 1785, indicating an∼2 year du-
ration for this eruption episode on the Grímsvötn vol-
canic system (Thordarson and Self, 1993).
For almost 200 years the accepted view on the
progress of the Laki eruption was based on the idea
put forth in 1794 by Sveinn Pálsson (see Thordarson,
this issue). The view was that the eruption featured
two main eruption episodes, the first commencing on
8 June on the fissures to the southwest of Mt. Laki
and a second one that commenced on 29 July on the
fissures to the northeast of mountain (Figure 3). Both
episodes where thought to have begun with explosive
26 JÖKULL No. 53, 2003