Block-controlled hillslope form and persistence of topography in rocky landscapes
Block-controlled hillslope form and persistence of topography in rocky landscapes
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DOI：
10.1130/g38665.1
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发表时间：
2017-04
期刊：
影响因子：
5.8
通讯作者：
R. Glade;R. Anderson;G. Tucker
中科院分区：
文献类型：
--
作者：
R. Glade;R. Anderson;G. Tucker
岩石山坡上点缀着巨石大小的石块，覆盖着薄而不均匀的土壤，在地球上陡峭的地形和干旱环境中都很常见，在其他星球上也是如此。虽然人们对均匀岩性中土质覆盖的凸起向上坡体的演化有了较好的认识，但非均质岩性和地质结构对坡体形态和演化的影响还没有得到很好的解决。层状沉积岩中发育的地貌以陡峭的地貌为特征，如台地和驼背，呈现陡峭的线性到凹形向上的坡道，零星的地块来自较软的地层上覆盖的抵抗岩层的崩解。在这里，我们表明，块体可以控制地形的持续性和这些景观中山坡的形成和演变。我们提出了一个数值模型，说明了块体释放、块体对土壤蠕变的中断以及块体的零星下坡运动之间的反馈作用对于捕捉这些景观的形态和演变是必要的，也是充分的。数值结果由一个简单的解析解再现，该解析解根据块体大小和间距预测稳态凹形山坡形状和平均坡角。我们的结果阐明了以前未被识别的山坡反馈，促进了我们对岩石山坡地貌的理解。在景观尺度上，我们的发现建立了一种定量方法来解决分层景观中尖锐边缘的迁移和地形的持久性。
Rocky hillslopes dotted with boulder-sized blocks and covered by a thin, nonuniform soil are common in both steep landscapes and arid environments on Earth, as well as on other planets. While the evolution of soil-mantled, convex-upward hillslopes in uniform lithology is reasonably well understood, the influence of heterogeneous lithology and geologic structure on hillslope form and evolution has yet to be properly addressed. Landscapes developed in layered sedimentary rocks feature sharp-edged landforms such as mesas and hogbacks that exhibit steep, linear to concave-upward ramps with scattered blocks calved from resistant rock layers overlying softer strata. Here we show that blocks can control the persistence of topography and the form and evolution of hillslopes in these landscapes. We present a numerical model demonstrating that incorporation of feedbacks between block release, interruption of soil creep by blocks, and sporadic downslope movement of blocks are necessary and sufficient to capture the morphology and evolution of these landscapes. Numerical results are reproduced by a simple analytical solution that predicts steady-state concave hillslope form and average slope angle from block size and spacing. Our results illuminate previously unrecognized hillslope feedbacks, advancing our understanding of the geomorphology of rocky hillslopes. On a landscape scale, our findings establish a quantitative method to address the migration of sharp edges and the persistence of topography in layered landscapes.