Jökull - 01.12.1966, Blaðsíða 54

b?
Sc
O0
Oöv-v
L~'—i o <3 O
Q CD G> O
o_ . —O
o
*/-
2 -
."'/- oSo
t>l°a| °al°7
^T.-.-l-'l'-'--
A A A
S>. 8/8'65
H 1693
H 1300
H| (1104)
Vlla+b -
H 4
3 —
Legend:
Black tephra
Light tephra
H 1766
K 1721
H 1693
V II a+ b
— • • —1 Loessial Soil
fine Sandy
Loessial Soil
Sandy
C3~Q°
A A A
Moroine
and Soil
Ground
moraine
A A A
S> '48
Fig. 2. Two soil profiles, one beneath, the
other just south of the moraine which marks
the max. extension of Hagafellsjökull eystri in
postglacial times. The location of the profiles
is shown on fig. 1.
Tvö jarðvegssnið, annað undir, hitt rétt sunnan
við þá jökulurð, er sýnir mestu útbreiðslu Haga-
fellsjökuls eystri siðan ísöld lauk. Lega sniða?ina
er sýnd á 1. mynd.
when the level of Hagavatn was lowered 6 m and
9,5 m respectively (Wright 1935, Thorarinsson
1939). On my suggestion he tried to find and
identify in the lake sediments some of the
dated tephra lavers I liad observed in the Haga-
vatn area. In the western part of the basin
Green could identify the typical tephra layer
succession H 1693, K 1721 and H 1766. Below
H 1693 there was only a thin layer of sedi-
ments, containing 10 to 12 varves. Consequent-
lv the glacier did not block the present outlet
of Hagavatn, viz. exceed its 1939 position, un-
til maximally two or three decades before 1693
(Green 1952).
On the lake shore east. of the big end-mo-
raines which run through the lake basin Green
(op. cit.) found upthrusted varved lake sedi-
ments containing the tephra layer Vlla + b,
which was deposited between 850 and 900 A.D.
This is a proof that at that time the glacier
was smaller than in 1929 and in all probability
the outlet of the lake was then the same as now.
On August 7 and 8, 1965, I again led an ex-
cursion of Scandinavian geologists and geo-
graphers to the Hagavatn area. This gave me
an opportunity to look again at the loessial
soil layer below the ablation moraine between
the Far river-beds. Assisted by G. Sigbjarnar-
son, who is working on a monograph on the
area between Geysir and Hagavatn, I measured
a soil section just west of the Far-bridge (pro-
file 1 on Fig. 2, cf. also the photo Fig. 3). In
this section we found four of Hekla’s rhyolitic
layers, HI, H3, H4 and H5, age respectively
860, 2800, 4000 and 6600 years. Above H1
there is a finegrained dark tephra laver, in
all probability H 1300, which I have found in
other profiles in the Hagavatn—Sandvatn area.
The uppermost part of the loessial soil profile
has been more or less disturbed by the over-
running glacier, but in that part we found a
208 JÖKULL