Collaborative Research: Steepland dynamics and steady-state forms resulting from debris flows

景观编码了关于构造和气候的有价值的信息，以及形成它们的过程的频率、大小和类型。然而，要可靠地提取这些信息，我们需要了解在地球表面输送沉积物的过程与它们所创造的景观之间的关系。该项目的首要目标是了解泥石流在形成陡峭地貌方面的作用。泥石流是泥浆、岩石和其他附带碎片(如树木)的混合物，可以沿着山谷网络高速移动。它们体型庞大、运动迅速、行为时断时续，对生命和基础设施构成了危险。它们还侵蚀了它们所经过的山谷，形成了陡峭的地形。泥石流被认为是在陡峭地形中输送泥沙和侵蚀基岩的主要机制，但目前我们缺乏一个数学框架来描述地貌对泥石流侵蚀的反应。在这个项目中，研究人员将开发一个模型来预测泥石流如何侵蚀地貌，并应用这个模型来了解构造、气候和土地利用的变化如何影响地形和传递到下游河流和水库的泥沙量。该项目将提高我们从地形数据中提取有关构造和气候信息的能力，并将有助于解决关于泥石流和以水为主的水流在塑造基岩沟渠网络方面的相对重要性的长期争论。该项目将培养一名博士后研究员、一名博士生、一名硕士研究生和三名本科生。其中两名本科生将通过亚利桑那大学ASEMS(亚利桑那州科学工程和数学学者)项目招收，该项目旨在支持STEM领域代表性不足的学生。研究人员还将制作在线社区学习工具，领导面对面的诊所，支持学生和研究人员使用在项目过程中开发的模型和分析工具，并在公立高中进行客座讲座。泥石流被认为是许多高原侵蚀的主要驱动因素，但我们目前缺乏一种在景观演变模型中量化泥石流侵蚀的通用、机械化的方法。因此，我们预测高原的动态，包括它们对构造、气候和人为强迫的地貌响应的能力是有限的。该项目将解决与泥石流侵蚀的地貌作用有关的三个基本问题：1)如何在地质时间尺度上量化泥石流的侵蚀？2)泥石流侵蚀如何影响准稳态景观的形态？3)泥石流侵蚀如何影响通过河网传播的瞬变信号(例如临界点)？为了解决这些问题，研究人员建议分析俄勒冈海岸山脉(OCR)和圣加布里埃尔山脉(SGM)以泥石流为主的景观，开展一项旨在将景观形态变化与构造强迫和环境因素联系起来的实地活动，并开发一种新的包含泥石流侵蚀的景观演变模型。泥石流侵蚀模型将采用基于过程的泥石流运动方程，这些方程尊重泥石流的离散性质、瞬变流动动力学和有限的流动性，将它们与以水为主的河流区分开来。从这张非局部泥石流动力学的详细图片中，研究人员将计算出地质时期内整合的基岩渠道内的泥石流侵蚀。该模型将通过与OCR和SGM中以泥石流为主的山谷的河道网络特性和千年尺度侵蚀速率的地形分析进行比较来验证。他们将应用基于过程的建模方法，结合我们研究地点的数据和观测，得出泥石流侵蚀的地貌运移规律，量化泥石流侵蚀对稳态景观形式的影响，并探索泥石流如何影响瞬变信号在渠道网络中的传播。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Landscapes encode valuable information about tectonics and climate, as well as the frequency, size, and types of processes that shape them. Reliable extraction of this information, however, requires that we understand the relationships between the processes that transport sediment over the Earth’s surface and the landscapes that they create. The overarching goal of this project is to understand the role of debris flows in shaping steep landscapes. Debris flows are mixtures of mud, rocks, and other incidental debris (such as trees) that can travel at high speeds down valley networks. Their large size, rapid motion, and episodic behavior pose hazards to life and infrastructure. They also erode the valleys they travel through, contributing to the shape of steep landscapes. Debris flows are thought to be a dominant mechanism for transporting sediment and eroding bedrock in steep terrain, but we currently lack a mathematical framework to describe how landscapes respond to erosion by debris flows. In this project, the investigators will develop a model to predict how debris flows erode landscapes and apply this model to understand how changes in tectonics, climate, and land-use influence topography and the sediment volumes passed on to downstream rivers and reservoirs. The project will improve our ability to extract information about tectonics and climate from topographic data and will contribute to resolving a long-standing debate regarding the relative importance of debris flows and water-dominated flows in sculpting bedrock channel networks. This project will train one postdoctoral researcher, one PhD student, one MS student, and three undergraduate students. Two of the undergraduate students will be recruited through the University of Arizona ASEMS (Arizona’s Science Engineering and Math Scholars) program, which is designed to support underrepresented students in STEM fields. The investigators will also produce online community learning tools, lead in-person clinics that support students and researchers in using the model and analysis tools developed through the course of the project, and give guest lectures at a public high school.Debris flows are thought to be a primary driver of erosion in many steeplands but we currently lack a generalizable, mechanistic approach for quantifying debris flow erosion within landscape evolution models. As such, our ability to predict the dynamics of steeplands, including their geomorphic responses to tectonic, climatic, and anthropogenic forcing, is limited. This project will address three fundamental questions related to the geomorphic role of debris flow erosion: 1) How can we quantify erosion by episodic debris flows over geologic timescales?, 2) How does debris flow erosion influence the morphology of quasi-steady state landscapes?, and 3) How does debris flow erosion influence transient signals (e.g. knickpoints) propagating through the channel network? To address these questions, the investigators propose to analyze debris flow dominated landscapes in the Oregon Coast Range (OCR) and the San Gabriel Mountains (SGM), conduct a field campaign designed to relate changes in landscape morphology to tectonic forcing and environmental factors, and develop a novel landscape evolution model that incorporates debris flow erosion. The debris flow erosion model will employ process-based equations for debris flow motion that honor the discrete nature, transient flow dynamics, and limited mobility of debris flows that differentiates them from water-dominated flows. From this detailed picture of nonlocal debris-flow dynamics, the investigators will then calculate debris flow erosion within bedrock channels integrated over geologic time. The model will be validated through comparisons with topographic analyses of channel network properties and millennial-scale erosion rates in debris-flow-dominated valleys in the OCR and SGM. They will apply their process-based modeling approach in combination with data and observations from our study sites to derive a geomorphic transport law for debris flow erosion, quantify the impact of debris flow erosion on the form of steady state landscapes, and explore how debris flows influence the propagation of transient signals through the channel network.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.