Jökull


Jökull - 01.12.1980, Page 23

Jökull - 01.12.1980, Page 23
Comparison of Sediment load Transport in the Skeiðará Jökulhlaups in 1972 and 1976 HAUKUR TÓMASSON, SVANUR PÁLSSON AND PÁLL INGÓLFSSON, National Energy Authority, 108 Reykjavík ABSTRACT The charactenstics of the Skeiðará jökulhlaups are briefly descnbed. A summary of the data on the quantity of suspended sediment load is presented in Table 1. The three methods which have been used in the sampling of sediment are found to give highly different amounts of 'coarse sediment load. The jökul- hlaup of 1976 was the first one in Skeiöará in which more than one sampling method was applied. In the jökulhlaup of 1976 a good dis- charge/sediment rating curve and a fairly uniform spatial distribution of the sediment were obtained. On the other hand in 1972 the rating curve was poorly defined and the spatial distribution non-uniform. In the jökulhlaup of 1972 a layer of sand and coarse silt was deposited in the flood channel, but not in 1976. The deposit is too fine-grained to have been laid down by running water. The present authors explain it as having been deposited by way of anchor ice which is also considered responsible for the vanation in the sedimenl concentration from one place to another. Similarly, such deposition may explain some very fine-grained layers in ancient alluvial sedimenls. INTRODUCTION The Grímsvötn jökulhlaups are vast floods caused by draining of the Grímsvötn sub- glacial lake which is situated in the western part of the Vatnajökull ice-cap. The floods appear in the glacier rivers Skeiðará, Gígju- kvísl and Súla on Skeiðarársandur and some- times they spread over a great part of the sandur plain, see Fig. 1. Because of these jök- ulhlaups the above rivers were first bridged as late as 1973 — 74. Skeiðará is by far the most voluminous of the glacier streams on Skeiðar- ársandur. Floods in that particular stream are hlaups. Key: SKO: Skeiðará at glacier outlet, SKG: Skeiðará at dikes. — Mynd 1. Yfirlits- mynd. Hlaupfarvegir Skeiðarárhlaupa. SKÚ: Skeið- ará við Útfall. SKG: Skeiðará við garða. JÖKULL 30. ÁR 21

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Jökull

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