Abstract. The development and evolution of confined outwash fans in high Arctic regions depend on the rate of meltwater discharge, which is directly related to the glacier ablation rate, in turnassociated with climate conditions. Other factors controlling outwash fan morphology (e.g. depth and width of distributive channels) are processes of fluvial erosion, and the transport and deposition of sediments. These factors have not previously been considered together in relation to the evolution of the confined outwash fans which are commonly incised into the top of permafrost in the forefields of subpolar glaciers and in mountains in high Arctic regions. Morphology and surficial sediments of a confined outwash fan of the Waldemar River (NW Spitsbergen, Svalbard) were analysed on the basis of geomorphological and sedimentological studies. The results of our investigations show multiple relations between the depth and width of distributary channels, fan slope and textural features of glaciofluvial surficial sediments supplied into the fluvial system from the glacier and from lateral fluvial erosion of permafrost Morphology and surficial sediments of the Waldemar River confined outwash fan (Kaffiøyra, Svalbard)
The dynamics of fluvial system evolution depend on fluvial processes and their driving forces associated with climatic variations, which affect changes in the morphology of river channels and floodplains. Neither channel slope and morphology, nor the properties of fluvial sediment have previously been considered as determinants of active braidplain widening on outwash plains (formed from valley/alpine glaciers and confined by pre-existing topography) in the High Arctic region and in the forefields of retreating glaciers. Factors determining widening of braidplain activity of the Waldemar River outwash (north-western Spitsbergen, Svalbard) were analysed on the basis of geomorphological, sedimentological, glaciological and meteorological research, and indicate significant multiple correlations between meltwater discharge, precipitation, braidplain width, morphology of the braided channel and the textural features of braidplain deposits. The capability of multivariate adaptive regression splines to detect these relationships was described, and threshold values were identified. The results indicate that the rate of active braidplain widening is proportional to the meltwater outflow in proglacial rivers, which can decrease despite a growing rate of glacial ablation. A proposed model enables us to predict zones of braidplain prone to widening activity in the High Arctic (humid) outwash fans and plains as well as fans developed in arid intermountain basins. The necessary conditions to activate braidplain widening processes were (1) spatial changes in the outwash feeding system due to glacier terminus retreat and (2) crossing the thresholds in passive factors (S and d 50 ) controlling lateral erosion intensity. As a result, the braidplain reached a new dynamic equilibrium, in which high-magnitude-low-frequency extreme meltwater discharges were of particular importance in terms of braidplain dynamics and are the dominant controls on the pattern of distributary channels.
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