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Aerial photographs taken in 1992 and 1997 allowed the production of maps of Skeiðarársandur before and after the November 1996 jökulhlaup. This paper presents pre- and post-jökulhlaup maps of the Gígjukvísl channel, providing an excellent opportunity to examine geomorphological change resulting from the November 1996 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. Overall size of the Gígjukvísl channel increased and the channel cross-sectional areas became much more compact, reducing flood flow resistance and decreasing future potential for the formation of backwater lakes. Specific change within the Gígjukvísl channel consists of channel change consisting of bank erosion of up to 300 m at the main Gígjukvísl outlet and within channel deposition of between 6 and 12 m. Aggradation rates decrease markedly downstream with bank erosion of 600 m downstream of the Little Ice Age moraines and localised within-channel aggradation of only 4 m. Comparison of 1992 and 1997 aerial photographs also provides a clear picture of 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 which the river system. As the proximal Gígjukvísl channel had never experienced a high magnitude jökulhlaup, the present Gígjukvísl channel is now well-adjusted to high -magnitude flood flows reducing the geomorphological impact of any subsequent jökulhlaups in the near future. The geomorphological impact of the November 1996 jökulhlaup on the Gígjukvísl channel was highly varied, controlled by downstream variations in jökulhlaup channel-scale flow conditions. This work We have demonstratesd theat tremendous value of pre- and post- jökulhlaup maps for improved understanding of both jökulhlaup processes and consequent channel impacts.
Author(s): Knudsen Ó, Jóhannesson H, Russell AJ, Haraldsson H
Publication type: Article
Publication status: Published
Journal: Jökull
Year: 2001
Volume: 50
Pages: 19-32
ISSN (print): 0449-0576
Publisher: Joklarannsoknafelag Islands
