We present 17 new 10Be erosion rates from southern Peru sampled across an extreme orographic rainfall gradient. Using a rainfall-weighted variant of the normalized channel steepness index, ksnQ, we show that channel steepness values, and thus topography, are adjusted to spatially varying rainfall. Rocks with similar physical characteristics define distinct relationships between ksnQ and erosion rate (E), suggesting ksnQ is also resolving lithologic variations in erodibility. However, substantial uncertainty exists in parameters describing these relationships. By combining our new data with 38 published erosion rates from Peru and Bolivia, we collapse the range of compatible parameter values and resolve robust, nonlinear ksnQ–E relationships suggestive of important influences of erosional thresholds, rock properties, sediment characteristics, and temporal runoff variability. In contrast, neither climatic nor lithologic effects are clear using the traditional channel steepness metric, ksn. Our results highlight that accounting for spatial rainfall variations is essential for disentangling the multiple influences of climate, lithology, and tectonics common in mountain landscapes, which is a necessary first step toward greater understanding of how these landscapes evolve.

中文翻译：

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安第斯山脉中北部地形和侵蚀的控制

我们展示了秘鲁南部在极端地形降雨梯度范围内采样的 17 个新的 10Be 侵蚀率。使用归一化河道陡度指数的降雨加权变体 ksnQ，我们表明河道陡度值以及地形会根据空间变化的降雨量进行调整。具有相似物理特征的岩石定义了 ksnQ 和侵蚀率 (E) 之间的不同关系，表明 ksnQ 也解决了侵蚀性的岩性变化。然而，描述这些关系的参数存在很大的不确定性。通过将我们的新数据与来自秘鲁和玻利维亚的 38 个已发表的侵蚀率相结合，我们缩小了兼容参数值的范围，并解决了稳健的非线性 ksnQ-E 关系，表明侵蚀阈值、岩石特性、沉积物特征和时间径流变化的重要影响。相比之下，使用传统的河道陡度度量 ksn 时，气候和岩性影响都不清楚。我们的研究结果强调，考虑空间降雨变化对于理清山地景观中常见的气候、岩性和构造的多重影响至关重要，这是更好地了解这些景观如何演变的必要的第一步。