EAR-PF: Evolution of landscapes buried by Quaternary sediments

Jeffrey Kwang博士获得了NSF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博士的指导下开展研究。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。河流及其网络驱动着景观演化的变化;它们根据气候、构造和岩石类型的变化进行重组，极大地重组了地球表面。实地观察表明，岩石对侵蚀的敏感性决定了河流如何侵蚀成景观，这一假设基于景观是由单一材料构成的想法。由于天然河流穿过多种物质，因此研究具有对比侵蚀性的景观非常重要。该项目的重点是以前被冰川覆盖的地区，那里的古代河流网络被埋在冰川沉积的数十至数百米的沉积物之下。埋藏后，地表上形成了一个新的河流网络，其几何形状可能与古代河流网络截然不同。随着河流侵蚀冰川沉积物，它们重新暴露了旧景观，引发了古代和新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清除所需的时间尺度。由于可蚀性的对比在其他地貌中很常见，这项研究将提供重要的见解，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。PI还旨在通过设计有关河流演变的互动数字模型/游戏来促进地球科学教育和多样性。在UMN和马萨诸塞大学，Kwang博士将与当地的女孩公司合作。组织为尤里卡！举办夏季讲习班，一个旨在缩小STEM领域性别差距的项目。此外，PI将与明尼苏达州立大学的菲利普拉森博士共同指导一名本科研究生。由树枝状网络切割的景观在地球的大陆表面无处不在。了解这些地貌是如何出现和重组的，揭示了地貌过程是如何创造地貌的。处于动态平衡状态的景观中，水系网络很少发生变化，而处于非平衡状态的景观中，水系网络正在积极地形成和重组。美国中西部以前曾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络切割的沉积岩。冰川作用后，沉积岩被第四纪沉积物掩埋，即冰碛物，基本上，景观被重置。这样的景观是研究排水网络的理想场所，因为（1）新的排水网络正在耕作覆盖的表面上积极形成，（2）来自埋藏地形的旧排水网络正在被挖掘出来。在该地区，PI将使用数值景观演变模型来测试排水网络重组如何受到以下因素的影响：（1）冰川冰碛和埋藏沉积岩之间的岩石可蚀性对比，以及（2）地表排水网络相对于埋藏的方向排水网络。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。利用实地工作和遥感，PI还将校准一个数值模型，以预测从这些景观中完全撤离冰川所需的时间尺度。更广泛地说，PI预计，这项研究将有利于我们了解其他地质环境与对比基板侵蚀。实地研究发现，可蚀性的变化有一个一阶控制景观的演变和形态，而且，它已被确定，对比侵蚀性的基板是陆地地貌的规范，而不是例外。因此，这项研究可以提供一个变革性的洞察岩性变化和地层如何影响表面过程，驱动排水重组，并创建martatrium.This奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

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.