Les systèmes fluviaux à chenaux anastomosés en milieu périglaciaire : la Léna et ses principaux affluents (Sibérie centrale)
This study deals with Siberian rivers dominated by outburst flood within a continuous and deep permafrost zone. The Lena basin rivers (Lena, Aldan and Vilioui) present specific fluvial forms: they consist of multiple wide channels separated by sandy bars and vegetated allu- vial islands; sinuous and...
| Published in: | Géographie physique et Quaternaire |
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| Main Authors: | , |
| Format: | Text |
| Language: | French |
| Published: |
Les Presses de l'Université de Montréal
2000
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| Subjects: | |
| Online Access: | http://id.erudit.org/iderudit/005647ar https://doi.org/10.7202/005647ar |
| Summary: | This study deals with Siberian rivers dominated by outburst flood within a continuous and deep permafrost zone. The Lena basin rivers (Lena, Aldan and Vilioui) present specific fluvial forms: they consist of multiple wide channels separated by sandy bars and vegetated allu- vial islands; sinuous and narrow branches can be observed in the floodplain and on the islands. The objective of this preliminary study is to understand the dynamics of these hydro- systems on the basis of a sedimentary processes analysis. Firstly, the study of the channels deposits reveals that the thickness of sediments remobilised during the annual flood is more important in the case of the anastomosed branches than in the main channels. Furthermore, Passega's method (1957) allows the determination of depositional mechanisms for the active fluvial units. Secondly, the analysis of sections located at the interface between active channels and stabilised units provide information about the channels' sedimentary processes. Specific deposits bordering the channels, that could be associated with log-jams and ice-jams, are also identified as major sedimentation processes. Finally, the effect of thermal and mechanical erosion on the banks is examined. It appears that the narrowly graded sediments deposited in the river bars derive mainly from the remobilisation of ancient aeolian deposits. During the summer low discharge, the dewatered channels are subject to aeolian deflation, building younger dunes on the banks. Cette étude concerne les rivières à régime de débâcle en milieu périglaciaire à pergélisol épais et continu. La Léna et ses principaux affluents (Aldan, Vilioui) présentent des formes fluviales spécifiques : on distingue dans le lit mineur des chenaux larges et peu profonds, qui enserrent des bancs sableux et des îles boisées, tandis que dans la plaine et les îles se développent des bras anastomosés plus sinueux et plus étroits. L'objectif de cette étude préliminaire est la compréhension du fonctionnement de ces hydrosystèmes, en se ... |
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