LINKS BETWEEN PROGLACIAL STREAM SUSPENDED SEDIMENT DYNAMICS, GLACIER HYDROLOGY AND GLACIER MOTION AT MIDTDALSBREEN, NORWAY

Two-hourly suspended sediment concentration variations observed during the summer of 1987 in the proglacial stream draining Midtdalsbreen, N orway are modelled using multiple regression and time series technique s. Suspended sediment fluctuations are influenced by stream discharge variations, diurnal hysteresis effects, medium-term sediment supply an d transport variations and the recent suspended sediment concentration history of the stream. They do not appear to be influenced by seasona l exhaustion or rainfall variations. Possible reasons for this are dis cussed. Large positive residuals from the fitted models are major puls es of suspended sediment unrelated to discharge variations; these sedi ment flushes correlate with periods of enhanced glacier motion. They c annot be explained by enhanced sediment production by subglacial erosi on, but are probably due to the tapping of subglacially stored sedimen t during sudden changes in the hydraulics and/or configuration of the subglacial hydrological system. Seasonal changes in the lag between gl acier motion peaks and suspended sediment flushes suggest that the sub glacial hydrological system evolves over the summer from a distributed to a more channelized configuration.