Collaborative Research: The effects of weathering on bedrock channel erosion and form

该奖项是根据2009年《美国复苏和再投资法案》(公法111-5)提供资金的。河道基岩侵蚀是控制地貌演变的一个基本过程，但尚未得到充分评价。这种侵蚀的速度及其在河道中的位置取决于河流可用于在河床上做功的能量、沉积物覆盖的分布以及河道下面的基岩类型。最近的几项模拟研究考察了河道横断面和纵向剖面的耦合演化，但基于现场的研究基岩河道侵蚀的研究很少。此外，很少有研究明确考虑风化对基岩河道几何形状和长期河道演变的影响。本项目将检验四个假设，重点评估风化对基岩河道侵蚀的影响：1)基岩沿河道边缘的风化程度高于河道中心附近；2)沉积物覆盖下的风化程度没有增强；3)基岩的磨损率随着风化程度的增加而增加；4)在风化程度较大的地方，河道断面宽而浅，随着风化效率的降低，河道断面变得更窄、更深。这些假设将通过测量三种水文气候环境中易风化岩石(如弱砂岩、石灰岩)和耐风化岩石(如石英岩、花岗岩)的河流地点岩石风化的跨海峡分布来检验。风化程度将使用两种地球化学风化指数来量化，一种是现场使用施密特锤子和裂缝密度和长度，另一种是在实验室使用巴西拉伸劈裂试验。岩石的可擦除性将通过实验室中的研磨机实验进行测量。这些调查的结果将使风化作用能够纳入现有的基岩侵蚀数值模型中。河流对岩石的侵蚀形成了地球上一些最壮观的地形(如大峡谷)，是活跃在非冰川景观中的最有效的侵蚀过程。因此，了解造成河流侵蚀岩石的过程以及这些过程的速度对于解释地球表面的历史是至关重要的。利用实地调查、实验室测量和数值模拟，将检验几个假设，这些假设对记录不同条件下河道基岩侵蚀的性质和速度具有重要影响。该项目将提供大量的教育和人才发展好处，包括支持本科生、研究生和博士后研究员。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). Erosion of bedrock in river channels is a fundamental process governing the evolution of landscapes that has not yet been evaluated fully. The rate of this erosion and its location within a river channel depend on a river's energy available to do work on the river bed, the distribution of sediment cover, and the type of bedrock underlying the channel. Several recent modeling studies have examined the coupled evolution of channel cross-sections and longitudinal profiles, but field-based studies investigating bedrock channel erosion are rare. Moreover, few studies have explicitly considered the effects of weathering on bedrock channel geometry and long-term channel evolution. This project will test four hypotheses focused on evaluating how weathering affects bedrock channel erosion 1) bedrock is more highly weathered along channel margins than near the channel center; 2) the degree of weathering is not enhanced beneath sediment cover; 3) the abrasion rate of bedrock increases as the degree of weathering increases; and 4) where weathering is substantial, channel cross-sections are wide and shallow, and as weathering efficiency decreases, channel cross-sections become narrower and deeper. These hypotheses will be tested by measuring the cross-channel distribution of rock weathering at stream sites with both easily weathered rocks (e.g., weak sandstones, limestone) and weathering-resistant rocks (e.g., quartzite, granite) in three hydro-climatic settings. The degree of weathering will be quantified using two geochemical weathering indices, in situ using Schmidt hammers and fracture density and length, and in the laboratory using Brazilian tension splitting tests. Rock erodability will be gauged via abrasion mill experiments in the laboratory. The results from these investigations will allow weathering to be incorporated into existing numerical models of bedrock erosion. Rock erosion by river channels forms some of the most spectacular topography on Earth (e.g., Grand Canyon), and is the most effective erosion process active in non-glaciated landscapes. Understanding the processes responsible for rock erosion by rivers and the rates at which these processes work is therefore fundamental to interpreting the history of Earth's surface. Using field investigations, laboratory measurements, and numerical modeling, several hypotheses will be tested that have important implications for documenting the nature and rate of bedrock erosion in river channels under various conditons This project will provide substantial educational and personnel development benefits, including support of undergaraduates, a graduate student, and a post-doctoral research fellow.