Jökull - 01.12.1957, Blaðsíða 28

G. R. ELLISTON:
A Study of the Ogives on Some of the Outlet Glaciers
of Öræfajökull
The observations which form the basis of
the article were made as part of the programme
of the Cambridge South-East Iceland Expedi-
tion, which spent nine weeks in Austur-Skafta-
fellssýsla in the summer of 1957. The first one
to draw attention to the ogives of the outlet
glaciers of Öræfajökull and interprete them
as probably annual was S. Thorarinsson (1, 2).
Several of the outlet glaciers in this area were
visited by Ives and King in 1953 and 1954
(3, 4), and a particular study was made of the
ogives on Morsárjökull (5) and reference made
to the ogives on Svínafellsjökull and Falljökull
(6). The main object of the Cambridge Ex-
pedition was the study of the ogives on Svína-
fellsjökull and their relationship to the wave
ogives (sometimes called “pressure waves”)
found below the icefall.
The ogives on Svínafellsjökull are not easy
to distinguish from the surface of the glacier,
and it is necessary to climb about fOO m up
the sides of the valley to see them clearly.
Measurements indicate that they are annual
in origin, and they extend from the waves at
the foot of the icefall to below the badly
crevassed region near the glacier tongue; there
are 38 in all. They are very broad, averaging
twice the width of the white spaces between
them, but both their width and their intensity
varies greatly. The widths of the first 31 ogives
were taped, and were found to vary between
40 m and 13 m, while the white spaces be-
tween measured from only 18 m to 80 m. A
wide black ogive might be followed by either
a wide or a narrow white space. From the
foot of the icefall to. the position of the velo-
city measurements (see fig. 1) they are of a
fairly uniform grey, but between the velocity
line and the badly crevassed region they are
almost indistinguishable and very difficult to
measure. The ogives in the crevassed region
and on the tongue are very dense and dark,
and can be seen from the surface of the
glacier.
The black ogives are not homogeneous, but
are formed of a number of narrow bands, very
close together and often merging with each
other. Above the crevassed region the annual
Fig. 1. A plan of Svínafellsjökull. The straight
line across the middle of the glacier indicates
the position of the velocity measurements.
Riss af Svinafellsjökli.
ogives are very faint, and only distinguishable
near the edges of the glacier, but the individual
bands show up clearly in the centre and this
led Ives and King to the conclusion that Svína-
fellsjökull possessed two distinct sets of ogives
— the small bands in the centre, 35 m apart,
and the annual ogives at the edges of the
moraine. However, over the rest of the glacier
the bands making up the annual ogives are
not so regularly distributed and do not appear
in the white spaces between, and it is our
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