Development of topographic asymmetry: Insights from dated cinder cones in the western United States
Development of topographic asymmetry: Insights from dated cinder cones in the western United States
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地形不对称的发展：来自美国西部过时的煤渣锥的见解
DOI：
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发表时间：
2014
期刊：
影响因子：
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通讯作者：
J. Roering
中科院分区：
文献类型：
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作者：
L. McGuire;J. Pelletier;J. Roering
地形的不对称性，也就是说，地形地貌的差异作为一个功能的坡度，可以用来推断生态水文地貌反馈关系。在这项研究中，我们记录的地形梯度和排水密度的依赖性的坡度和时间/年龄在亚利桑那州，俄勒冈州和加州的四个第四纪的锥场。火山灰锥作为地貌演化的自然实验特别有用，因为它们开始它们的演化在过去的一个已知时间（许多已经被辐射测定），因为它们通常具有简单的，良好约束的初始形态。北向的部分有陡峭的地形梯度和较高的平均植被覆盖（即，归一化植被指数（NDVI）值）与每个火山区内相应的朝南部分的火山锥进行比较。在四个火山区中的三个中，锥体的北向部分的排水密度也较高。这些地形上的差异最初并不存在，但随着时间的推移逐渐发展，表明这种不对称是喷发后地貌过程的结果。为了测试地形的坡度控制的替代假设，我们开发了一个数值模型，用于植被锥的演变和方法，用于估计当地的古植被覆盖作为海拔，坡度和第四纪内的时间的函数。数值模型结果表明，崩积物运输率较高的朝南的山坡上，至少有三个四个锥领域。我们的古植被分析表明，在我们研究的两个亚利桑那州火山区，朝南的山坡上崩积物运输速率较高，这是由于时间平均植被覆盖率较高，因此植物生物扰动导致沉积物运输速率较高。我们的研究结果表明，相对较小的太阳辐射的变化可以通过水文，植被覆盖和泥沙输运之间的反馈景观的深刻影响。
Topographic asymmetry, that is, differences in the morphology of landscapes as a function of slope aspect, can be used to infer ecohydrogeomorphic feedback relationships. In this study, we document the dependence of topographic gradients and drainage densities on slope aspect and time/age in four Quaternary cinder cone fields in Arizona, Oregon, and California. Cinder cones are particularly useful as natural experiments in geomorphic evolution because they begin their evolution at a known time in the past (many have been radiometrically dated) and because they often have simple, well‐constrained initial morphologies. North‐facing portions of cinder cones have steeper topographic gradients and higher mean vegetation cover (i.e., Normalized Difference Vegetation Index, or NDVI, values) under current climatic conditions compared with corresponding south‐facing portions of cones within each volcanic field. Drainage density is also higher on north‐facing portions of cones in three of the four volcanic fields. These differences in topography were not present initially but developed progressively over time, indicating that the asymmetry is a result of post‐eruption geomorphic processes. To test alternative hypotheses for the slope‐aspect control of topography, we developed a numerical model for cinder cone evolution and a methodology for estimating local paleovegetation cover as a function of elevation, slope aspect, and time within the Quaternary. The numerical model results demonstrate that rates of colluvial transport were higher on south‐facing hillslopes in at least three of the four cinder cones fields. Our paleovegetation analysis suggests that in the two Arizona volcanic fields we studied, higher rates of colluvial transport on south‐facing hillslopes were the result of greater time‐averaged vegetation cover and hence higher rates of sediment transport by floral bioturbation. Our results illustrate the profound impact that relatively small variations in solar insolation can have on landscapes via feedbacks among hydrology, vegetation cover, and sediment transport.