Jökull - 01.11.1998, Page 10

Katla tephra layer (K-1918). The thickness of the
Leiðólfsfell scoria layer decreases rapidly away from
source (Figs. 1 and 4) and at locations beyond -500 m
it is covered by top soil that also includes the 1845
AD Hekla tephra (H-1845). In the underlying soil,
which contains tephra layers that pre-date the
Leiðólfsfell scoria, the 1755 AD Katla tephra (K-
1755) is the youngest tephra layer found in all pro-
files. Thus, the tephra stratigraphy shows that the
Leiðólfsfell scoria formed within the time period 1755
to 1845 AD. The interval between the deposition of
K-1918 and H-1845 tephra layers represents 73 years.
Although the soil thickness between the pairs K-
1918/H-l 845 and H-1845/LeiðólfsfelI-scoria varies
slightly from one location to another, it is almost
identical at any one location. This suggests that the
time interval between the formation of the successive
pairs is of similar in length. The Leiðólfsfell scoria
and the underlying K-1755, however, are separated by
a much thinner (0.5-1.0 cm) soil layer, indicating that
these two tephras are closer in age. The layer that con-
firms the exact age of the Leiðólfsfell scoria is a thin
(0.3-0.5 cm) strombolian tephra that occours at its
base. It contains clasts that are chemically and physi-
cally indistinguishable from the strombolian tephra
that was erupted from the Laki fissures in 1783
(Þórðarson et al., 1996). The close association of these
two tephra layers demonstrates that they are contem-
poraneous and without doubt from the same eruption.
The age of the Leiðólfsfell cones and scoria is fur-
Fig. 2. The Laki lava flow resting directly on the Leiðólfsfell scoria deposit; the arrow points towards the boundary between the
two formations. The dark area in the upper middle is the new road ballast quarry. The Leiðólfsfell cones are visible on the sky-
line to the left. Photograph is taken near location 2 and the view is to the NE. Person for scale.
- Ljósmyndin sýnir Skaftáreldahraun beint ofan á Leiðólfsfellsgjóskunni; örin bendir á lagamót gjósku og hrauns. Dökka
svœðið rétt ofan við miðju myndarinnar er gjallnáman og Leiðólfsfellsgíga ber við himin efst til vinstri. Myndin er tekin til
norðausturs við sniðstað 2.
JOKULL, No. 46, 1998