Jökull - 01.12.1977, Blaðsíða 12

too, that basaltic activity was directly associated
with tlie eruption (Sparlts et al. 1977), as borne
out by a basaltic tephra layer in the Bárdar-
bunga core.
The íollowing quotation is from Thorarins-
son’s (1963) book on Askja
“On Jan. 3 1875 a fiery column rising in the
south was seen from the Mývatn region; clouds
of srnoke had been observed earlier. About the
middle of February an expedition of farmers
from around Lake Mývatn set out for Dyngju-
fjöll. When it reached Askja on February 16,
huge solfataras were active in the south-east
corner of the depression, “flinging rocks and
mud several hundred feet into the air”. The
report of the expedition does not indicate tliat
any volcanic eruption occurred during their
stay in Askja, nor does it appear to warrant the
conclusion (which some have, nevertheless,
drawn from it) that there was freshly poured-
out lava anywhere around. Water was flowing
from the solfataras, and what seems to be
generally indicated is an overture to an erup-
tion very similar to that which preceded the
eruption of 1961, except that the activity ap-
pears to liave been rather more violent; very
likely some sort of explosive eruption had taken
place.”
Thorarinsson (op. prox. cit.) states further
that apparently several centuries preceding the
1875 eruption “constituted an intermission in
Askja’s activity. But then Dyngjufjöll were an
unexplored region practically up to the year
1874. The smoke that was sometimes seen rising
above Dyngjufjöll strengthened the popular be-
lief in the existence of outlaws in the highlands.
.... Tlie first person known to have visited
Askja was the surveyor Björn Gunnlaugsson,
who came there in 1838, but could see only
little because of fog”.
Another inaccessable and little-explored vol-
canic area is tlie DYNGJUHÁLS region, 30 to
40 km north of thc Bárdarbunga site. According
to Jónsson (1945) several fresh-looking lava
flows in this region attest to vigorous activity
in recent centuries. However, the only eruption
that Jónsson (1945) attributes with certainty to
this region, that of 1862—64, has now been
shown to have taken place in Tröllahraun, west
of Vatnajökull (Thorarinsson & Sigvaldason
1 0 JÖKULL 27. ÁR
1972). Another type of possible indicators of
eruptions on Dyngjuháls, where 7 crater rows
extend beneath the glacier Dyngjujökull, could
be the floods in Jökulsá between 1655 and 1729.
But, as already indicated, it seems most reason-
able to attribute them to volcanic activity in
Kverkfjöll. Tlierefore, as matters now stand, it
appears that the activity in Dyngjuháls may be
considerably older than hitherto supposed.
ÞÓRDARHYRNA, within the Vatnajökull
ice cap some 40 km SW of Grímsvötn, erupted
in 1903, and probably in 1823 (Thorarinsson
1974) . Tephra from the 1903 eruption was col-
lected aboard a ship off Langanes (NE Iceland)
and analyzed by Alouritzen and Noe-Nygaard
(1950. Table II, nr. 6).
Other active volcanoes may exist beneath tlie
Vatnajökull ice sheet, as indicated by hydro-
thermal activity and periodic jökulhlaups issu-
ing from underneath the ice sheet. Two such
places have especially been suggested as vol-
canoes, “Sigin” (the cauldrons) NW of Gríms-
vötn, from which issue floods in Skaftá, charged
witli hydrogen sulphide and other fumes, and
another location NE of Pálsfjall, where depres-
sions in the glacier attest to thermal activity
underneath. The latter place may have been
the site of an eruption in 1753 (Thorarinsson
1974, pp. 57—58). However, next to nothing is
so far known of tlieir volcanic liistories.
ÖRÆFAJÖKULL, 25 km SE of Bárdarbunga,
erupted in 1727 and 1362 (Thorarinsson 1958).
Öræfajökull is a typical central volcano, with a
caldera at the summit. Its products in these two
eruptions have been silicic to intermediate in
composition (Table II, no. 11).
Finally, HEKLA and KATLA, both some 130
km to the south-west of Bárdarbunga, have
erupted many times during the last centuries.
The volcanic history of Hekla in particular is
well known due to the researches of Thorarins-
son (1967), and recent studies have cast much
light on that of Ivatla as well (Thorarinsson
1975) .
As seen from this list, only a fraction of the
tephras in the Bárdarbunga core could be ex-
pected to be from known eruptions, having a