Meandering river evolution in an unvegetated permafrost environment
Meandering river evolution in an unvegetated permafrost environment
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DOI：
10.1016/j.geomorph.2023.108705
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发表时间：
2023-04-25
期刊：
影响因子：
3.9
通讯作者：
Cvijanovich，Bronson
中科院分区：
文献类型：
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作者：
Levy，Joseph S.;Cvijanovich，Bronson
曲流河沉积相与岩石记录中陆地植被的兴起有关，但在许多现代无植被环境中也发现了现代高度弯曲的单线河流的例子。先前的工作人员推测，永久冻土或冰胶结沉积物可以提供所需的凝聚力，以产生单线程，蜿蜒的渠道，然而，在绝大多数的陆地永久冻土站点中，蜿蜒的河流存在的银行植被的存在，使得它不可能解开的相对影响，银行凝聚力所提供的冻结沉积物提供的根。在这里，我们研究地形变化超过13年的玛瑙河，一个无植被的，受多年冻土影响，砂和砾石底的河流在南极洲的麦克默多干谷（MDV），支持的图像数据。激光雷达变化检测和卫星/机载图像分析的基础上，我们发现，曲流河过程（切岸侵蚀，点坝的增长，曲流迁移）可以发生在这个冰胶结，无植被的多年冻土河流系统。我们发现，玛瑙河的上游，单线程的河段是曲折的，和银行的凝聚力是由冰胶结永久冻土。Onyx蜿蜒河段内的蜿蜒迁移率非常接近根据其他无植被河流中蜿蜒迁移率的观察结果预测的值，但是，Onyx河排放的持续时间很短（约70天），这表明这些迁移率应被视为低估计值，在短暂的夏季侵蚀季节，可能高达2.55倍。总之，这些观察结果表明，冰胶结的永久冻土是一种弱形式的银行凝聚力，可以导致快速的景观变化，以应对热岩溶河流侵蚀，产生动态河道，特别是在温暖的融水遇到富含冰的永久冻土沉积物。
Meandering river sedimentary facies are associated with the rise of terrestrial vegetation in the rock record, but modern examples of highly sinuous, single-threaded streams are also found in many modern non-vegetated environments. Prior workers have speculated that permafrost or ice-cemented sediment could provide the cohesion needed to generate single-threaded, meandering channels, however, the presence of bank vegetation in the overwhelming majority of terrestrial permafrost sites in which meandering rivers are present has made it impossible to disentangle the relative impact of bank cohesion provided by frozen sediments from that provided by roots. Here, we examine topographic change over 13 years at the Onyx River, an unvegetated, permafrost-affected, sand-and-gravel-bottomed river in the McMurdo Dry Valleys (MDV) of Antarctica, supported by ∼40 years of image data. On the basis of lidar change detection and satellite/airborne image analysis, we find that meandering river processes (cut bank erosion, point bar growth, and meander migration) can occur in this ice-cemented, unvegetated permafrost river system. We find that the Onyx River's upper, single-threaded reach is meandering, and that bank cohesion is provided by ice-cemented permafrost. Meander migration rates within the Onyx's meandering reach are extremely close to values predicted based on observations of meander migration rates in other unvegetated rivers, however, the short (∼70 day) duration of Onyx River discharge suggests these migration rates should be considered low estimates, which could be up to ∼5 times greater during the short, summer erosion season. Together, these observations suggest that ice-cemented permafrost is a weak form of bank cohesion that can result in rapid landscape change in response to thermokarstic fluvial erosion, producing dynamic river channels, especially where warm meltwater encounters ice-rich permafrost deposits.