Jökull - 01.01.2001, Side 19

Changes in the Gígjukvísl river channel during the November
1996 jökulhlaup, Skeiðarársandur, Iceland
Óskar Knudsen

, Helgi Jóhannesson


, Andrew J. Russell

and Hreinn Haraldsson



Klettur Consulting Engineers, Bíldshöfða 12, IS 112 Reykjavík, Iceland. E-mail: ok@isl.is.

Public Roads Administration, Borgartún 7, IS 105 Reykjavík, Iceland. E-mail: hej@vegag.is.

Department of Earth Sciences & Geography, Keele University, Keele, Staffordshire,
ST5 5BG, UK. E-mail: a.j.russell@keele.ac.uk.
Abstract — Aerial photographs taken in 1992 and 1997 enabled the production of maps of Skeiðarársandur
before and after the November 1996 jökulhlaup. This paper presents pre- and post-jökulhlaup maps of the
Gígjukvísl river channel, providing an excellent opportunity to examine geomorphological change resulting
from the jökulhlaup. The Gígjukvísl channel system underwent spectacular transformation from a complex
system of low capacity channels and proglacial lakes to a large high capacity channel, scaled to the November
1996 jökulhlaup flows. The overall size of the Gígjukvísl channel increased, reducing flood flow resistance and
decreasing future potential for the formation of backwater lakes. Specific change within the Gígjukvísl channel,
upstream of the Little Ice Age moraines, consists of bank erosion of up to 300 m at the main Gígjukvísl outlet and
within channel deposition of between 6 and 12 m. Downstream of the Little Ice Age moraines channel change
consists of bank erosion of 600 m and localised within–channel aggradation of 4 m. Comparison of 1992 and
1997 aerial photographs also provides a clear picture of the glacier snout retreat of 300 m and thinning of
50–60 m during this period. Drastic change within the Gígjukvísl channel was brought about by the recent
(post-1954) creation of a proglacial trench within the river system. Prior to the November 1996 jökulhlaup, the
proximal Gígjukvísl river channel had never experienced a high–magnitude jökulhlaup. Extensive bank erosion
during the jökulhlaup drasticly changed the channel so it is now well–adjusted to high–magnitude flood flows
reducing the geomorphological impact of future jökulhlaups.
INTRODUCTION
There are many areas in Iceland where changes in
landscape are, or can be expected to be, rapid even
within the typical design lifetime (50–100 years) of
man-made structures. Understanding and monitor-
ing these changes is necessary for the design and
maintenance of these structures. Recently, the Pub-
lic Roads Administration has produced maps of some
of the areas where rapid natural changes can influ-
ence road transportation. Maps have been produced
of Breiðamerkursandur (aerial photographs from Au-
gust, 1996, height of flight 5500 m), Skeiðarársand-
ur (aerial photographs from August, 1997, height of
flight 3000 m) and Mýrdalssandur (aerial photographs
from September, 1997, height of flight 3000 m).
These areas are large glacial outwash plains as indi-
cated by the Icelandic word sandur.
On Breiðamerkursandur (Figure 1) the glacier has
retreated throughout the last century and a proglacial
lake, Jökulsárlón, has emerged (Price, 1982). As the
proglacial lake emerged, the sediment load carried by
the river, Jökulsá, to the sea changed from approxi-
mately 9 million m

per year to a negligible amount
(Björnsson, 1996). This is the cause of coastal ero-
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