Jökull - 01.12.2003, Page 17

The 1783–1785 Laki-Grímsvötn eruptions
Skaftá
kilometers
0 1.0
Laki
10
10
a
Ulfarsdalssker
Ul
fa
rs
da
lur
Sk
aft
a
Hnuta
Blaengur Innri-Eyrar
Varmardalur
TC-1
TC-2
Lambavatn
Laki
Varmarfell
Sid
ujokul
l
N
H
ve
rfi
sf
ljo
t
10987654321
0
8 June
11 June 14 June
27 June 9 July 29 July
28 August? 7 September? 26 Sept?
24 October?
5 10 15 20 25 27km
Tephra
Lava
Other features
Cone and crater outlines
Lambagigar cone row
Individual fissures (1-10)
Scoria and spatter cones
Tuff cones
Proximal tephra sectors
Lava channel
Lava flow
Rootless cone groups
Laki graben
Older faults
Bedrock
b
..
Figure 3. Map of the Laki fissures: demonstrating the main features of the cone-row and surrounding lavas.
TC-1 and TC-2 indicate the tuff cones SW and NE of Laki, respectively. Extent of individual fissures, labelled
1 through 10, shown schematically. Cones on fissure 3 (arrow) where first visited and described by Sveinn
Pálsson in 1794. – Lakagígar, gjóskukeilur, gígaraðir og sprungur. Örin bendir á gígana sem Sveinn Pálsson
kannaði og lýsti 1794.
Typically, each fissure is delineated by a row of scoria
and spatter cones, although two tuff cones on fissures
4 and 6 interrupt this pattern. Mt. Laki is an older
subglacial volcanic edifice, which coincidently sub-
divides the vent system into two almost equally long
segments (Figures 2 and 3). These segments, how-
ever, should not be equated with the termsÚtnorðurs-
gjá and Landnorðursgjá used by Steingrímsson in his
accounts because he did not know this natural sub-
division of the vent system at the time of the erup-
tion. These terms simply refer to on which side of Mt.
Kaldbakur the vent activity was visible from the Síða
district (Figure 4).
Lava produced on the vents to the southwest of
Mt. Laki flowed south over the western part of the
Síða highlands in two main lobes; one confined to
the Skaftá River gorge and the other to the Varm-
árdalur and Hellisá river valleys (Figure 2). As the
lava emerged from the Skaftá River gorge, it spread
out onto the cultivated lowlands of Síða, Landbrot
and Meðalland. The vents to the northeast of Mt.
Laki issued lava to the south and north away from the
fissures. Lava flowing to the south advanced down
the Hverfisfljót River gorge, a distance of 25 km, be-
fore reaching the lowlands of Síða and Fljótshverfi.
Lava flowing to the north spread over the outwash
JÖKULL No. 53, 2003 15