Bedrock fracture density controls on hillslope erodibility in steep, rocky landscapes with patchy soil cover, southern California, USA
Bedrock fracture density controls on hillslope erodibility in steep, rocky landscapes with patchy soil cover, southern California, USA
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DOI：
10.1016/j.epsl.2019.06.011
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发表时间：
2019-09
影响因子：
5.3
通讯作者：
Alexander B. Neely;R. DiBiase;L. Corbett;P. Bierman;M. Caffee
中科院分区：
文献类型：
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作者：
Alexander B. Neely;R. DiBiase;L. Corbett;P. Bierman;M. Caffee
尽管许多陡峭的景观由土壤覆盖的和裸露基岩的山坡拼凑而成，但模型通常假设山坡完全是土壤覆盖的或裸露的基岩，这使得预测岩石特性如何影响山坡的可蚀性和景观演变具有挑战性。在这里，我们研究了加利福尼亚州南部圣加布里埃尔山脉和圣哈辛托山脉北部的水源集水区；这两个陡峭的地貌气候和岩性相似，但基岩裂缝密度截然不同，在圣加布里埃尔山脉，∼高出5倍。我们将新公布的碎屑原位宇宙侵蚀速率10Be与高分辨率图像和地形分析相结合，以量化裸露基岩和土壤覆盖的山坡的形态和丰度如何随这两个景观内部和之间的侵蚀速率而变化。对于相似的平均坡度(35-46°)，NSJM的集水区的侵蚀速度为KYR−1的0.1m-0.6m，而SGM的KYR−1的侵蚀速度为0.2m-2.2m。在这两种景观中，裸露的基岩山坡随着侵蚀速率的增加而增加；然而，NSJM中暴露的基岩更多、更陡峭，这表明更大的基岩裂隙间距降低了土壤生产效率，支撑了更陡峭的悬崖。此外，SGM中较高的侵蚀速率要求土壤运移效率提高3倍，这反映了基岩裂隙密度对沉积物装甲坡面大小的间接控制。我们的数据突显了陡峭景观中的山坡地貌动力学如何依赖于土壤和基岩的强度以及土壤生产和运输的效率，所有这些都对岩石性质有不同的敏感性，并影响山坡上土壤和裸露基岩的划分。
Although many steep landscapes comprise a patchwork of soil-mantled and bare-bedrock hillslopes, models typically assume hillslopes are entirely soil-mantled or bare-bedrock, making it challenging to predict how rock properties influence hillslope erodibility and landscape evolution. Here, we study headwater catchments across the San Gabriel Mountains (SGM) and Northern San Jacinto Mountains (NSJM) in southern California; two steep landscapes with similar climate and lithology, but with distinctly different bedrock fracture densities, ∼5× higher in the SGM. We combine new and published detrital in-situ cosmogenic10Be-derived erosion rates with analysis of high resolution imagery and topography to quantify how the morphology and abundance of bare-bedrock and soil-mantled hillslopes vary with erosion rate within and between the two landscapes. For similar mean hillslope angles (35-46°), catchments in the NSJM erode at rates of 0.1-0.6 m kyr−1, compared to 0.2-2.2 m kyr−1in the SGM. In both landscapes, bare-bedrock hillslopes increase in abundance with increasing erosion rate; however, more and steeper bedrock is exposed in the NSJM, indicating that wider bedrock fracture spacing reduces soil production efficiency and supports steeper cliffs. Additionally, higher erosion rates in the SGM require a 3× higher soil transport efficiency, reflecting an indirect control of bedrock fracture density on the size of sediment armoring hillslopes. Our data highlight how hillslope morphodynamics in steep landscapes depend on the strength of soil and bedrock and the efficiency of soil production and transport, all of which are variably sensitive to rock properties and influence the partitioning of soil and bare-bedrock on hillslopes.