EAR-PF: Evolution of landscapes buried by Quaternary sediments

Jeffrey Kwang博士被授予NSF EAR博士后奖学金，在明尼苏达大学（UMN）的Andrew Wickert博士和马萨诸塞大学阿默斯特分校（UMass）的Isaac Larsen博士指导下进行研究。该项目旨在了解被近期沉积物掩埋的景观如何随着时间的推移而演变。河流及其网络推动景观演变的变化；它们会随着气候、构造和岩石类型的变化而重组，从而彻底改变地球表面。实地观察表明，岩石对侵蚀的敏感性在决定河流如何侵蚀成景观方面发挥着控制作用，这一假设基于景观是由单一物质构成的观点。由于天然河流穿过多种材料，因此研究具有不同可蚀性的景观非常重要。这个项目的重点是以前被冰川覆盖的地区，在那里，古老的河流网络被埋在冰川沉积的几十到几百米的沉积物下。埋葬后，新的河网在地表形成，其几何形状可能与古代河网大不相同。随着河流侵蚀冰川沉积物，它们重新暴露了旧的景观，引发了新旧河流网络之间的竞争。利用数值模型和现场技术，PI将(1)确定控制这些竞争网络结果的重要指标，(2)预测冰川沉积物完全移除所需的时间尺度。由于可蚀性的差异在其他地形中也很常见，这项研究将为我们提供重要的见解，了解我们脚下的岩石结构如何在广泛的地质环境中决定河流的形成和景观的演变。该计划亦旨在透过设计有关河流演变的互动数值模型/游戏，促进地球科学教育和多样性。在UMN和UMass， Dr. Kwang将与当地的Girls Inc.组织合作，为Eureka！该项目旨在缩小STEM领域的性别差距。此外，PI将与明尼苏达州立大学的Phillip Larson博士共同指导一名本科生。树突状网络分解的景观在地球大陆表面无处不在。了解这些地质模式是如何出现和重组的，揭示了地貌过程是如何创造地貌的。在动态平衡的景观中，排水网络很少发生变化，而在非平衡的景观中，排水网络却在积极地形成和重组。美国中西部以前被冰川覆盖的地区是不平衡景观的典型例子。在更新世冰期之前，这些地区通常含有被树枝状河流网切割的沉积岩。冰川作用结束后，沉积岩被第四纪沉积物掩埋，即被掩埋，从本质上讲，景观被重置。这些景观是研究排水网络的理想地点，因为(1)新的排水网络正在未被覆盖的表面上积极形成，(2)埋藏地形中的旧排水网络正在被挖掘出来。在该地区，PI将使用数值景观演化模型来测试排水网络重组如何受到以下因素的影响：(1)冰碛物与埋藏沉积岩之间岩石可蚀性的对比；(2)地表排水网络相对于埋藏排水网络的方向。研究结果还将详细说明倒刺支流形成的新机制，为这些河网特征提供新的地质解释。通过实地工作和遥感，PI还将校准一个数值模型，以预测从这些景观中完全清除冰川积雪所需的时间尺度。更广泛地说，PI预计这项研究将有助于我们理解其他地质环境中基材可蚀性的对比。实地研究发现，可蚀性的变化对景观的演化和形态具有一级控制作用，而且已经确定，具有不同可蚀性的底物是陆地地貌的常态，而不是例外。因此，该研究可以对岩性变化和地层如何影响地表过程、驱动排水重组和创造地质格局提供变革性的见解。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Dr. Jeffrey Kwang has been awarded an NSF EAR Postdoctoral Fellowship to carry out research under the mentorship of Dr. Andrew Wickert at the University of Minnesota (UMN) and Dr. Isaac Larsen at the University of Massachusetts-Amherst (UMass). This project aims to understand how landscapes buried by recent sediments evolve over time. Rivers and their networks drive change in landscape evolution; they reorganize in response to changing climate, tectonics, and rock type, drastically restructuring the Earth’s surface. Field observations have shown that a rock’s susceptibility to erosion exerts control in determining how rivers erode into landscapes, an assumption based in the idea that landscapes are made of a single material. Because natural rivers cut through multiple materials, it is important to study landscapes with contrasting erodibilities. This project focuses on regions that were previously glaciated where ancient river networks are buried under tens to hundreds of meters of sediments deposited by glaciers. After burial, a new river network is established on the surface that may have a geometry that is quite different from the ancient river network. As rivers erode into the glacial sediments, they re-expose the old landscape, triggering a competition between the ancient and new river networks. Using numerical models and field techniques, the PI will (1) determine important metrics that control the outcome of these competing networks and (2) predict timescales required for glacial sediments to be fully removed. Because contrasts in erodibility are common in other landforms, this research will provide important insight into how the structure of the rock below our feet determines rivers formation and landscape evolution in a broad spectrum of geologic settings. The PI also aims to promote Earth science education and diversity by designing interactive numerical models/games about river evolution. At UMN and UMass, Dr. Kwang will collaborate with local Girls Inc. organizations to develop summer workshops for Eureka!, a program that aims to close the gender-gap in STEM. In addition, the PI will co-mentor an undergraduate research student with Dr. Phillip Larson at the Minnesota State University. Landscapes dissected by dendritic networks are ubiquitous across the continental surfaces of Earth. Understanding how these geopatterns emerge and reorganize reveals how geomorphic processes create landforms. Drainage networks seldom change in landscapes that are in dynamic equilibrium, but drainage networks are actively forming and reorganizing in landscapes in disequilibrium. Regions in the American Midwest that were previously glaciated are classic examples of disequilibrium landscapes. Before Pleistocene glaciation, these regions generally contained sedimentary rock dissected by dendritic river networks. After glaciation, the sedimentary rock was buried by Quaternary sediments, i.e. till, and essentially, the landscape was reset. Such landscapes are ideal locations to study drainage networks because (1) new drainage networks are actively forming on the till-covered surfaces, and (2) old drainage networks from the buried topography are being exhumed. In this region, the PI will use numerical landscape evolution models to test how drainage network reorganization is affected by (1) rock erodibility contrasts between the glacial till and buried sedimentary rock and (2) the orientation of the surface drainage network with respect to the buried drainage network. The results will also detail a new mechanism for the formation of barbed tributaries, offering a new geologic interpretation for these river network features. Using field work and remote sensing, the PI will also calibrate a numerical model to predict timescales that are required for the full evacuation of glacial till from these landscapes. More broadly, the PI anticipates that this research will benefit our understanding of other geologic settings with contrasts in substrate erodibility. Field studies have found that variability in erodibility has a first-order control on landscape evolution and morphology, and moreover, it has been determined that substrates with contrasting erodibilities are the norm in terrestrial landforms, not the exception. Therefore, this research can provide a transformative insight into how lithologic variation and stratigraphy affect surface processes, drive drainage reorganization, and create geopatterns.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.