Jökull - 01.12.1956, Blaðsíða 6

on the whole been receding since ab. 1870,
although the recession has now and then been
interrupted by stagnation and minor advances.
According to Eythórsson (1949, p. 251), the front
of Svínafellsjökull was as a whole very near the
same in 1932 as in 1904. The variations of the
glaciers until 1932 may by summed up as
follows:
Beginning of 18th century: Glaciers consider-
ably larger than in 1935.
1740’s: Glaciers larger than in 1935.
Years or decades immediately preceding 1794:
Advance.
1794: Glaciers larger than in 1935.
1830’s: Probably advance.
1865: Svínafellsjökull probably as large as in
1904.
1932: Svínafellsjökull about the same as in
1904.
The variations since 1932 are, according to
Eythórsson measurements (1949, p. 251, 1951, p.
16, 1952, p. 31, 1953, p. 49, 1954, p. 46, 1955,
p. 40; Mercanton 1952, p. 117) as follows:
Skaftaf.jök. Svinaf.jök. Svínaf.jök.
■ (N) (S)
1932-34 + 60 — 65 — 33
1934-35 - 45 — 15 — 20
1935-36 -155 0 — 10
1936-37 - 71 + 3 + 7
1937-38 - 21 — 15 — 10
1938-39 - 5 — 10 — 13
1938-40 - 65 — 20.5 — 7
1940-41 - 80 — 33 — 16
1941-42 -133 — 27 — 26
1942-43 - 17 — 2 — 2
1943-44 - 49 — 43 — 3
1944-45 - 65 — 50 + 3
1945-46 - 22 — 4 — 3
1946-47 - 63 — 58 — 3
1947-48 - 29 — 5 0
1948-49 - 20 — 3 — 1
1949-50 - 50 — 2 — 6
1950-51 + 28 — 18 — 13
1951-52 + 4 + 5.5
1952-53 + 20 (N) - 12 (S) + 9 + 8
1953-54 - 49 + 3 + 7
1954-55 - 31 — 15 + 3
1955-56 - 47 — 1 + 4
Probably it would be possible to correlate
stagnations and advances of Svínafellsjökull
with terminal moraine ridges found within the
1904 limit of the glacier front but no attempt
has hitherto been made at such a correlation.
THE AGE OF STÓRALDA.
Fig 3 shows soil profiles dug ancl measured
in Öræfi in September 1955. Profile De 18a was
measured on the crest of Stóralda proper near
its highest point. Three tephra (= volcanic ash)
layers could be identified in this profile. The
thickest layer is without doubt the tephra from
the eruption of Öræfajökull 1727 A.D. This
layer is black, bastaltic and — due to the vic-
inity of the volcano — more coarse grained than
other recent tephra layers in the Öræfi profiles
(particle diam. 5= 1 cm). During this erup-
tion the main tephra fall was carried WNW-
wards and the layer increases in thickness and
coarseness towards N in the western part of
Öræfi. The two black medium-coarse sandy
layers immediately above the 1727 layer in this
profile can hardly be other than the layers for-
med by the eruption of Katla 1755 and the
Laki eruption 1783. During the eruption of
Katla in October 1755, one of the biggest from
that volcano in historical time, the tephra was
mainly carried eastwards. The tephra fall had
a devastating effect in most of the inhabited
area between Katla and Skeidarársandur and
the tephra fall was also heavy in entire Austur-
Skaftafellssýsla. (Safn t. s. fsl. IV, p. 243). The
tephra layer from the Laki eruption 1783 is
in Öræfi more finegrained than the 1755 tephra
and the layer is thinner than one would expect
from descriptions of this eruption. Upon the
whole, the tephra production of the Laki fissure
seems to have been much less than assumed by
Thoroddsen. The devastating effect this erup-
tion had on the vegetation nearly all over the
country has partly been caused by poisonous
gases such as affected the vegetation in the vici-
nity of the jökulhlaup (glacier burst) in Skeid-
ará 1954 (Thorarinsson 1954) ancl from which
originated the bluish mist after which the 1783
disaster was called Móðuharðindi (The Mist
Disaster).
The black tephra layer found beneath the
1727-layer in profile De 18a has not yet been
identified but it is likely to be from the erup-
tion of Katla in 1625.
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