Valley-floor widths across the Himalayan orogen [dataset]

Himalayan rivers transport ~10^3 Mt of sediment annually to ocean basins. Mountain valleys are an important component of this routing system: sediment storage in these valleys acts to buffer climatic and tectonic signals recorded by downstream sedimentary systems. Despite a critical need to understand the spatial distribution, volume and longevity of these valley fills, controls on valley location and geometry are unknown, and estimates of sediment volumes are based on never-tested assumptions of valley widening processes. Here we extract 1,644,215 valley-floor width measurements across the Himalaya to determine the dominant controls on valley-floor morphology, and to assess sediment storage processes. We use random forest regression to estimate the importance of potential controlling variables, and find that channel steepness, a proxy for rock uplift, is a first-order control on valley-floor width. We also analyse a novel dataset of 1,797 exhumation rates and find that valley-floor width decreases as exhumation rate increases. We therefore suggest that valley-floor width is adjusted to long-term tectonically driven exhumation rather than being controlled by water discharge or bedrock erodibility, and that valley widening predominantly results from sediment deposition along low-gradient valley floors rather than lateral bedrock erosion.

喜马拉雅河流每年向海洋盆地输送约10^3百万吨沉积物。山地河谷是该沉积物输运系统的重要组成部分：河谷内的沉积物储存可缓冲下游沉积系统所记录的气候与构造信号。尽管学界亟需明确这些河谷充填物的空间分布、体积与留存时长，但河谷位置与几何形态的控制因素仍不明晰，且沉积物体积的估算均基于未经验证的河谷展宽过程假设。本研究在喜马拉雅全域提取了1,644,215组河谷谷底宽度测量数据，以明确谷底地貌的主导控制因素，并评估沉积物储存过程。本研究采用随机森林回归（Random Forest Regression）模型估算潜在控制变量的重要性，结果表明作为岩石抬升替代指标的河道陡度，是控制谷底宽度的一级影响因素。此外，本研究还分析了包含1,797个剥露速率的全新数据集，发现谷底宽度随剥露速率升高而减小。据此，本研究提出：谷底宽度是对长期构造驱动剥露的响应，而非受水流量或基岩可蚀性控制；且河谷展宽主要源于低坡度河谷谷底的沉积物堆积，而非基岩侧向侵蚀。