Jökull - 01.12.1955, Síða 10

In the present case the initial condition is
h = h s that is, u = 0, and by putting p (0) = 0
we get simply Cj = 0 for all i. The initial
perturbation o£ the stable form is therefore
independent of x, which is a very simple result.
The function u is thus obtained by the inte-
gration of (28).
Two cases will be treated here, that is, (1)
the change of the height of the firn line by the
constant g, and (2) the periodic change g =
Ae where A is a constant. The solutions of
(28) are:
(1) g = consfarir. U“yf/-ea'j (33)
(2) W
The instability of the ice-sheet is clearly revea-
led by these eqations.
As these relations are obtained by the linea-
rized equation (26) they holcl only as long as u
is small compared to h, that is, they will not be
true at the snout of the glacier.
In order to get some numerical data we will
turn to the conditions at the Vatnajökull, where
the total ablation gradient is approximately
0.01 per year. The equation (33) shows that
an increase in the height of the firn line by
a constant amount will in approximately 70
years have lowered the ice-sheet by the same
amount.
On the other hand a climatic cycle of the
amplitude 0.5 °C and having the total period of
200 years, starting with an increase in the height
of tlie firn line, will after one total period
have lowered the ice-sheet by 150 meters.
The first approximation above leads naturally
to a second step by the inserting of the u-values
obtained into (25). This gives a new differen-
tial equation which is again linearized and a
second u computed.
The response to climatic variations of large
glaciers, as for instance the Vatnajökull, can
theoretically be treatecl in the above manner,
but the computational work will be very great
and the practical aspects of this work will not
be discussed in the present paper.
LITERATURE:
1. Glen, J. W. Experiments on the deformation
of ice. Journal of Glaciology, Vol. 2, No. 12,
1952, p. 111-114.
2. Nye, J. F. The mechanics of glacier flow.
Journal of Glaciology Vol. 2, No. 12, 1952,
p. 82-93.
3. Orvig, Svenn: The Glaciological studies of
the Baffin Island Expedition 1950, Part 5:
On the variation of the shear stress on the
bed of an ice cap. Journal of Glaciology,
Vol. 2. No. 14, 1953, p. 242-247.
4. Somigliana, C. Sulla profonditá dei ghiacc-
ini. Atti della Reale Academia. Nationale
dei Lincei, Rendiconti, Classe di Scienze
fisiche, matematiche e naturali. Vol. 30,
Serie 5, 1921.
Ubersicht iiber die Eisrandlagen
in Kringilsárrani von 1890-1955
von E. M. Todtmann, Hamburg
Nachdem ich das westliche Vorfeld des Brúar-
jökull zwischen Ivringilsá um Kverká seit 1950,
das östliche Vorfeld, Maríutungur, seit 1953
kannte, untersuchte ich 1955 das Vorfeld
Kringilsárrani, das umgrenzt wird von der
Kringilsá, der Jökulsá á Brú mit ihrem Neben-
fluss Ulakvisl und vom Eisrand.
I’áll Hjarðar aus Hjarðarhagi im Jökulclal
brachte uns mit dem Lastwagen, auf den wir
ein kleines Boot geladen hatten, bis an die
Kringilsá. Dicht siidlich der Endmoráne von
1890 setzten wir mit dem Boot úber den Fluss.
Mit mir blieb Þorleifur Einarsson aus Reykja-
vik. Student der Geologie in Erlangen.
Das Sclirifttum gibt nur geringe Kenntnisse
úber Kringilsárrani. Thoroddsen ist selber
nicht dort gewesen, zu seiner Zeit lag der Eisrand
noch an der Moráne von 1890. Th. Ivjerulf (nach
Thoroddsen) beobachtete 1890 eine gewaltige
Spalte im Gletscher súdwestlich vom Snæfell.
Pálmi Hannesson, (nach Thorarinsson) be-
suchte Kringilsárrani 1933. Er sah im Morán-
eníelcl radial verlaufencle lange Rúcken, die er
als Spaltenausfúllungen deutet, eine reiche Vege-
tation uncl Anfánge von Palsen, (dysjar).
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