Discharge and suspended sediment dynamics during two jökulhlaups in the Skaftá river, Iceland

Abstract

AbstractThis paper investigates the dynamics and significance of discharge and suspended sediment transport (SST) during two jökulhlaups (glacier outburst floods) in the Skaftá River, south Iceland. Jökulhlaups occur frequently in many glacial environments and are highly significant in the geomorphological evolution of river basins and coastal environments. However, direct high‐resolution monitoring of jökulhlaups has rarely been accomplished and hardly ever at more than one station in a downstream sequence. Here we present detailed data on jökulhlaup discharge and water quality from an intensive monitoring and sampling programme at two sites in summer 1997 when two jökulhlaups occurred. Evidence is discussed that supports the origin of both jökulhlaups being subglacial reservoirs, produced over several months by subglacial geothermal activity. At the downstream site, Ása‐Eldvatn, the larger jökulhlaup (1) had a peak discharge of 572 m3 s−1 and a peak suspended sediment flux of 4650 kg s−1 (channel‐edge value) or 4530 kg s−1 (cross‐sectional). These values compare to the non‐jökulhlaup flow of 120 m3 s−1 and suspended sediment flux of 190 kg s−1 (channel‐edge) or 301 kg s−1 (cross‐sectional). Significantly, the jökulhlaups transported 18·8 per cent of the annual runoff and 53 per cent of the annual suspended sediment transport in 6·6 per cent of the year. Furthermore, water chemistry, suspended sediment and seismic data suggest that volcanic activity and geothermal boiling (possibly including steam explosions) may have occurred during Jökulhlaup 1. The research illustrates the value of integrating high‐resolution, multi‐point field monitoring of meteorological, hydrological, hydrochemical, geomorphological and seismological data for understanding the dynamics, significance and downstream translation of jökulhlaups. Copyright © 2005 John Wiley & Sons, Ltd.