Rates of Evacuation of Bedload Sediment From an Alpine Glacier Control Proglacial Stream Morphodynamics

IF 3.5 2区 地球科学 Q1 GEOSCIENCES, MULTIDISCIPLINARY Journal of Geophysical Research: Earth Surface Pub Date : 2024-08-10 DOI:10.1029/2024JF007727
D. Mancini, M. Roncoroni, M. Dietze, M. Jenkin, T. Müller, B. Ouvry, F. Miesen, Q. Pythoud, M. Hofmann, F. Lardet, A. P. Nicholas, S. N. Lane
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Abstract

Proglacial forefields commonly include highly dynamic fluvial systems associated with the fundamental instability between topography, flow hydraulics and sediment transport. However, there is limited knowledge of how these systems respond to changing subglacial hydrology and sediment supply. We investigated this relationship using the first continuous field-collected data sets for both suspended and bedload sediment export and proglacial river dynamics for an Alpine glacier forefield, the Glacier d’Otemma, Switzerland. The results show a strong sensitivity of fluvial morphodynamics to the balance between sediment transport capacity and supply. When subglacial bedload export rates exceeded fluvial transport capacity, we found bar construction leading to net forefield aggradation and surficial coarsening, especially on bar heads. This intensified braiding buffered the downstream transport of coarse sediment. When subglacial bedload export rates were lower than transport capacity, incision occurred, with reduced braiding intensity, net erosion and important amounts of bedload leaving the proglacial system. We found a net fining of surficial deposits except for very isolated coarsening patterns on bar heads. Thus, proglacial forefield morphodynamics are strongly conditioned by subglacial hydrology and sediment supply, but this conditioning is also influenced by the response of the forefield itself. Proglacial forefields have an important influence on the longitudinal connectivity of sediment flux in regions sensitive to climate change, such as recently deglaciated high mountain areas. The linkages we report between subglacial processes and river morphodynamics are critical for understanding the development of embryonic forefield ecosystems.

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阿尔卑斯冰川床载沉积物的蒸发率控制冰川溪流形态动力学
冰川前场通常包括与地形、流动水力学和沉积物运移之间的基本不稳定性有关的高度动态河川系统。然而,人们对这些系统如何应对冰川下水文和沉积物供应变化的了解十分有限。我们利用首次为阿尔卑斯冰川前场--瑞士奥特玛冰川--采集的悬浮和床载沉积物输出以及冰川河流动力学的连续实地数据集,研究了这种关系。结果表明,河流形态动力学对沉积物输送能力和供给之间的平衡非常敏感。当冰川下的床面负荷输出率超过了河道的运输能力时,我们发现条带的形成会导致前场的净扩张和表层的粗化,尤其是在条带头部。这种加剧的辫状结构缓冲了粗沉积物的下游搬运。当冰川下沉积物的输出率低于运输能力时,就会发生切裂,导致辫状强度降低、净侵蚀和大量沉积物离开冰川系统。我们发现,除了极个别的棒头粗化模式外,表层沉积物出现了净细化。因此,冰川前场形态动力学受到冰川下水文和沉积物供应的强烈制约,但这种制约也受到前场本身反应的影响。在对气候变化敏感的地区,如近期冰川消融的高山地区,冰川前场对沉积通量的纵向连通性具有重要影响。我们所报告的冰川下过程与河流形态动力学之间的联系对于了解前场生态系统雏形的发展至关重要。
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来源期刊
Journal of Geophysical Research: Earth Surface
Journal of Geophysical Research: Earth Surface Earth and Planetary Sciences-Earth-Surface Processes
CiteScore
6.30
自引率
10.30%
发文量
162
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