Jökull - 01.12.1970, Blaðsíða 29

The Evolution of the Drainage System (1904—1965)
Infront of Breidamerkurjökull, Iceland
R. J. PRICE AND P. J. HOWARTH1,
DEPARTMENT OF GEOGRAHY, UNIVERSITY OF GLASGOW
The area of study is located in south-east
Iceland (Fig. 1) approximately 80 km west of
Höfn. On the southern side of Vatnajökull,
glaciers descend from the ice cap almost to
sea level. One of these gJaciers, Breidamerkur-
jökull, and its proglacial area has been the
subject of detailed study by members of the
Department of Geography, University of Glas-
gow, during the period 1964/1967 (Howarth
1968, Price 1969, Welch 1967, Welch and Ho-
warth 1968). This paper is concerned with the
whole of the proglacial area of Breidamerkur-
jökull. The authors carried out fieldwork in
this area during the summers of 1965 and 1966
when Price mapped the area to the west of
Jökulsárlón (Fig. 1) and Howarth mapped the
area to the east of Jökulsárlón.
Breidamerkurjökull is a valley glacier some
20 km in length and generally 10 to 12 km
wide which broadens into a lobe towards its
terminus to give an ice front nearly 20 km in
length. This glacier originates in the extensive
accumulation area of Vatnajökull and is fed
by several disdnct tributaries. The confining
walls of Breidamerkurjökull are high ridges
(600—800 m) of extrusive volcanic rocks, mainly
basaltic lavas. Since 1890 the front of Fjalls-
jökull has retreated westwards and that of
Breidamerkurjökull north-westwards, although
it was not until 1945 that the two ice fronts
became completely separated (Fig. 1). In this
paper the development of the drainage system
produced during the retreat of the glaciers
over the last 61 years will be discussed.
All but two of the meltwater channels ob-
served in the area of study were cut in the
1) At present, assistant professor, Department
of Geography, McMaster University, Hamilton,
Ontario.
drift deposits. In that part of the area inside
the outermost moraine ridge (Fig. 1) most of
the fluvioglacial erosion was confined to di-
stinct channel systems with individual channels
ranging between 10 m and 200 m in width and
1 and 3 m in depth. Only where the channels
have been cut through moraine ridges do they
exceed 10 m in depth. There are areas of sand-
ar2) inside the moraine system on which large
numbers of anastomosing channels up to 1 m
in depth were observed.
Beyond the outermost moraine, formed
about 1890, which represents the greatest ex-
tent of Breidamerkurjökull in historical times
(Thorarinsson 1943, p. 29), fluvioglacial erosion
was associated with the development of the
drainage systems on the sandar. Presumably the
development of the great Breidamerkursandar
must be related to the advance and retreat of
Breidamerkurjökull on numerous occasions
prior to the advance which reached its maxim-
um in 1890. Almost certainly, a considerable
thickness of sand and gravel would have been
deposited in this area when large volumes of
meltwater were realised during the eruptions
of Öraefajökull in 1362 and 1727 (Thorarins-
son 1958). The thickness of the deposits form-
ing the present sandur is unknown but it is
assumed that the present surface form is the
product of fluvioglacial erosion and deposition
taking place during the last advance and re-
treat of Breidamerkurjökull. The channel
systems on these sandar surfaces are complex
and represent the changing pattern of the
drainage system at the time the ice stood at
the position of the 1890 moraine. The drainage
system established beyond the moraine system
2) Sandur: Icelandic word (singular) mean-
ing outwash plain. Sandar: plural.
JÖKULL 20. ÁR 27