Informace o publikaci
Comparing the effects of material sources and fluvial processes on the gravel fraction of the Muninelva braided stream, Central Svalbard
| Autoři | |
|---|---|
| Rok publikování | 2016 |
| Druh | Článek ve sborníku |
| Konference | Polar Ecology Conference 2016 |
| Fakulta / Pracoviště MU | |
| Citace | |
| Obor | Zemský magnetismus, geodesie, geografie |
| Klíčová slova | gravel bed braided river, sediment sources, clast shape characteristics, Muninelva, Svalbard |
| Popis | Muninelva River flows down a narrow mountain valley (Munindalen) in Dickson Land, Western Spitsbergen, 7 km west of Petuniabukta. Muninelva River flows from two connected glacier tongues (Muninbreen Glacier) in the NNW part of the valley and flows along the valley axis down to its mouth in Mimerdalen Valley at the SSE end of the valley. The river is 6 km long and its channel belt is 50–250 m wide. It has a nature of a valley-train sensu Hambrey (1995). It changes into a braided outwash fan (sensu Hambrey 1995) at its mouth to the wide Mimerdalen valley. First-order channel in the valley train delimits bar assemblages with compound and unit bars and second-order channels cutting across the bar surfaces (Lunt and Bridge 2004). The first-order channel is branching on the outwash fan. The river is dominantly pebble-cobble gravely along the entire stream. Muninelva River has the two main material sources according to their position in respect of the stream: I. head source – Muninbreen Glacier and its terminal moraine-mound complexes; II lateral sources – colluvial and alluvial fans, terminoglacial fan from a lateral glacier and bedrock in the channel belt banks (Devonian sandstone and conglomerate). All sources differ in the shape of their clastic material. Important effect of the fluvial transport on the size and shape of the clasts (downstream fining and increased roundness) could be assumed basing on the length of Muninelva River and well-developed channels and bars. This assumption has been studied using the analysis of the clast in the fraction 64–256 mm, which were sampled along the entire length of the river, as well as from source sediments. Bedrock provides implicitly angular debris and well-rounded clasts originates from conglomerates, so they could not be confused with the material originating from other sediments. Our results show that the clast grain size and roundness are dominantly controlled by material sources and not by the fluvial activity. Significant fluvial effects could only be found in the distal and axial part of the stream. Long morphologically developed braided stream is therefore not sufficiently competent to significantly modify the material from their sources, which resembles braided outwash fans of Horbyebreen and Bertilbreen in the same area (Hanáček et al. 2013). This fact is of great interest for possible interpretations of fossil gravely braided streams without a preserved morphology, which could resemble alluvial fans basing on clast shape characteristics. |