Jökull - 01.12.1953, Side 17

then the 1702 m peak and Svíahnúkur vestri
(W. Svíahnúkur) the 1681 m peak (cf. my map).
To a conspicuous angle of Grímsfjall NW of
Svíahnúkur eystri, where the mountain bends
towards E, I have given the name Gríðarhorn
(Giantess’ Corner) in remembrance of the giant-
ess in Grímsvötn mentioned in Jón Árnason’s
folk tales, and for the nearly vertical NW face
of Gríðarhorn I propose the name Stórkonu-
þil (Giantess’ Gable). The icefree cliff rising
behind the nearly permanently open water in
the westernmost part of the depression I call
Vatnshamar (Lake’s Cliff).
The raising of the water level. — As men-
tioned above, there is open water along Vatns-
hamar in the westernmost part of the depres-
sion. On our arrival on 1 July 1953, this water
was 20—50 m wide and ab. 300 m in length,
but when I flew over Grímsvötn on 18 Aug.
1953 the open lake was considerably bigger.
Pictures taken on 28 Aug. 1950 show that the
firn-ice surface in the SW part of the depression
was then very plain. This plain area was much
smaller when we were there last summer, and
east of this flat area the surface was undulated.
The measured heights above the water level at
Vatnshamar varied between 5 and 13 metres
along our route, and a high ridge extending
SW-wards some few hundred metres NW of
Gríðarhorn was ab. 19 m above the water level.
Generally speaking, the surface rose eastwards
and northeastwards (cf. the map). Along the
foot of Gríðarhorn was a small strip of open
water between the nearly vertical cliff on one
side and vertical firn wall on the other side.
We did not reach the water level, but from
altimeter readings on the snowfield just W of
the open water we estimated the level to be
in the same height as at Vatnshamar.
The height of the water level on 1 July 1953
is based on the following altimeter readings:
I. Level of open water at Vatnshamar (Temp.
of the air 4.5—5.0° C):
13:45 hrs. 4575 feet j
15:15 - 4580 feet [■ Mean value 4578 feet.
15:30 - 4580 feet j
II. Camp IV, 1.5 km NE of Gríðarhorn
(Temp. of the air 4.0—3.0° C):
20:20 hrs. 4675 feet ]
23:18 — 4675 feet l Mean value 4677 feet.
23:45 - 4680 feet j
III. Svíahnúkur eystri (Temp. of the air ab.
2.0° C):
21:34 hrs. 5540 feet 1
22:40 - 5540 feet f Mean value 5540 feet’
Height difference II—I: 99 feet. Correction
negligible.
Height difference III—II: 863 feet + correc
tion (— 10 feet) = 853 feet.
Height difference III-I: 952 feet = 290 metres.
Presupposing that the height of Svíahnúkur
eystri is 1702 m, the height of the water level
in Grímsvötn on 1 July 1953 was 1412 m (++a.
2 m).
On 7 April 1951, S. Rist measured with a
Paulin altimeter the height difference between
the cairn on Svíahnúkur eystri and the water
level at Gríðarhorn. He found the difference
to be 337 m, or a water level 47 m lower than
during our visit 26 months later.
On 2 April 1951, J. Eythórsson determined by
barometric observations the height difference
between sea level and the firn surface in the
Grímsvötn depression, and found it to be
1360 m. The height of the open water level
af Gríðarhorn he found in the same way to be
1351 m (corr. values). Eythórsson has similarly
calculated the absolute height of the water level
at Vatnshamar according to my altimeter read-
ings and found it to be 1400 m. Difference in
height of the water level according to these cal-
culations is thus 49 m, or nearly the same as
when calculated by the height difference bet-
ween Svíahnúkur eystri and the water level.
During my flight over Grímsvötn on 28 Aug.
1950 I took a picture of Vatnshamar (Fig. 7).
During my flight on 18 Aug. 1953 I again photo-
graphed Vatnshamar (Fig. 8). Comparing these
pictures, we find that between these flights the
raising of the lake is of the order of 60 m
(corr. +_ 5 a 10 m).
In this connection it may also be mentioned
that viewing Vatnshamar in fieldglasses during
my flight on 18 Aug. 1953 I found that the
white spots of lime deposited around the hot
springs observed at Vatnshamar ab. 1.5 m above
the water level, when we were there on 1 July
(cf. p. 18), were now submerged by the rising
water level.
From the above-mentioned measurements and
calculations we can draw the conclusion that
between the beginning of April 1950 and 1
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