Fracture density and grain size controls on the relief structure of bedrock landscapes

量化岩石材料特性和山脉地形之间的联系对于了解气候和构造如何影响地形和预测自然灾害至关重要。然而，将岩石强度纳入景观演化模型一直是一个具有挑战性的问题。这在一定程度上是因为很难确定描述岩石强度的适当指标，而且决定岩石强度的因素因侵蚀过程的不同而不同。该项目旨在通过检验以下假设来解决这一认识差距：在陡峭的地貌中，岩石强度通过基岩山坡上的裂隙密度和由此产生的输送到渠道的泥沙的粒度分布，对景观规模的可蚀性施加一级控制。通过比较山坡和沟渠起伏的地形指标与由水系沉积物中宇宙成因核素浓度确定的侵蚀率，该项目将表征南加州两个地貌相似、岩石类型和气候相似、但构造历史和基岩裂缝密度强烈对比的景观在可蚀性方面的差异。该项目将利用新的陆基摄影测量技术和对高分辨率机载激光雷达数据的分析，以提高对整个地貌的实地观测和测量。开发和测试新的点云和基于图像的分析技术将通过课堂、实验室练习和独立研究项目为地球科学本科生提供培训和经验。该项目的成果将提供一个框架，在这项具有挑战性的任务上取得进展，这项任务是将地形和侵蚀率之间的具体地点相关性扩大到具有不同岩石强度和气候的地区，并提供关于构造环境和基岩破裂之间潜在反馈的挑衅性假设，这些假设限制了山脉的高度。

Quantifying the connection between rock material properties and the topography of mountain ranges is critical for understanding how climate and tectonics influence landscapes and for predicting natural hazards. However, incorporating rock strength into landscape evolution models has been a challenging problem. This is due in part to difficulties in defining appropriate metrics to describe rock strength, and because the factors that determine rock strength vary in importance depending on erosion process. This project aims to address this knowledge gap by testing the hypothesis that in steep landscapes, rock strength exerts a first order control on landscape-scale erodibility through the influence of fracture density on bedrock hillslopes and the resulting grain size distribution of sediment delivered to channels. By comparing topographic metrics of hillslope and channel relief with erosion rates determined from cosmogenic nuclide concentrations in stream sediment, this project will characterize differences in erodibility between two landscapes in Southern California with similar topography, rock type, and climate, but strongly contrasting tectonic history and bedrock fracture density. This project will take advantage of new ground-based photogrammetry techniques and analysis of high-resolution airborne lidar data to upscale field observations and measurements to entire landscapes. Development and testing of novel point-cloud and image-based analysis techniques will provide training and experience for geoscience undergraduates through classroom laboratory exercises and independent research projects. Results from this project will provide a framework for making progress on the challenging task of expanding site-specific correlations between relief and erosion rate to regions with differing rock strength and climate, and inform provocative hypotheses regarding potential feedbacks between tectonic setting and bedrock fracturing that limit the height of mountain ranges.