EAR-PF: Revisiting Megafloods: Insights From Glacial Isostatic Adjustment on Flood Size, Flow Routes, and Climate Response

Tamara Pico博士被授予NSF EAR博士后奖学金，研究冰川均衡调整对晚更新世灾难性洪水的影响，以提高我们对大洪水发生时间和路线的理解。这项工作将在加州理工学院和俄勒冈州立大学进行。在2.2万至1.4万年前的上一次冰河时代，数十场灾难性的巨型洪水从冰坝覆盖的米苏拉湖涌出，冲刷了爱达荷州和华盛顿州东部的风景，形成了人们所熟知的沟渠疤地。这些冰川湖的爆发是地球上已知的最大的洪水。重建这些事件的规模有助于我们理解洪水如何塑造地球的景观，以及与气候突变的关系。在洪水期间，冰盖融化导致地壳以大约10毫米/年的速度变形，比区域构造抬升速率高出几个数量级，导致区域地形与今天有很大不同。这一冰川均衡调整过程在先前的洪水量或流量估计中被忽略，带来了尚未量化的潜在的巨大误差。这项研究将对洪水事件期间的总排放量提供更准确的估计，这反过来将有助于量化海洋和更广泛的气候系统对大洪水的反应。此外，这项研究将通过研究过去灾难性洪水的性质和应对气候变化的冰盖稳定性，为突发洪水规划提供信息。国际和平协会在科学界的妇女和代表性不足的少数群体方面拥有广泛的领导和外联经验，并将继续坚定地参与这些社区。发生在22,000到14,000年前的米苏拉湖冰川爆发的特大洪水是地球上已知的最大的洪水。在这些洪水事件期间，先前对水量和流量的估计依赖于基于现代地形的坡度。在此期间，冰川均衡调整引起的地壳形变速率约为10毫米/年，比区域抬升速率高出数量级，并使当地斜坡改变了约30%。因此，先前对洪水量的估计包含一个潜在的大误差，而这个误差还没有被量化。此外，在米苏拉洪水期间，由于冰川均衡调整导致的隆起和下沉模式发生了显著变化，这种地形重塑可能解释了观察到的洪水路线随时间的变化。这项建议在地貌学和地球物理学的学科范围内，试图调查冰川均衡调整对米苏拉大洪水事件过程中形成的沟渠沙地景观的影响。该项目提出了三个相互关联的目标：(1)根据冰川均衡调整重建洪水事件间隔期间的排水路径演变；(2)使用经冰川均衡调整校正的斜率准确估计洪水流量；(3)将海洋和更广泛的气候系统的响应与最新改进的总淡水流量估计联系起来。将进行冰川均衡调整模拟，以预测沟渠荒地的古地形和古坡度。将使用经冰川均衡调整后的地形来计算洪水排放路径和洪水流量估计值。最后，这些对淡水流量的新估计将与俄勒冈州海岸收集的沉积物岩心的地球化学记录进行比较，以评估海洋生物系统对大洪水事件的反应。这项拟议的研究通过使用冰川均衡调整模型超越多个尺度，将地貌过程与地幔对冰负荷的响应的小波长和大波长特征联系起来，最终将局部短期爆发的洪水与更长期的全球气候变化联系起来。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。

Dr. Tamara Pico has been awarded an NSF EAR Postdoctoral Fellowship to investigate the influence of glacial isostatic adjustment on late Pleistocene catastrophic flooding to improve our understanding of the timing and routing of mega-floods. The work will be conducted at the California Institute of Technology and Oregon State University. During the last ice age, 22,000 to 14,000 years ago, dozens of catastrophic mega-floods from an ice-dammed Glacial Lake Missoula scoured the landscapes of Idaho and eastern Washington, forming what are known as the Channeled Scablands. These glacial lake outbursts are the largest known floods on Earth. Reconstructing the magnitude of these events informs our understanding of how floods shape Earth's landscapes and relate to abrupt changes in climate. Over the period of flooding, ice sheet melting caused crustal deformation with rates of about 10 mm/yr, which is orders of magnitude above regional tectonic uplift rates, resulting in a substantially different regional topography relative to today. This process of glacial isostatic adjustment has been neglected in prior estimates of flood volumes or discharge, introducing a potentially large error, which has not yet been quantified. This study will provide a more accurate estimates of total discharge during flood events which in turn will help quantify the response of the ocean and broader climate system to mega-floods. In addition, the research will help inform for outburst flood planning by studying the nature of past catastrophic flooding and the stability of ice sheets in response to climate change. The PI has extensive leadership and outreach experience in women in science and underrepresented minority groups and will continue a committed involvement in these communities. Outburst mega-floods from glacial Lake Missoula, occurring from 22,000 to 14,000 years ago, are the largest known floods on Earth. Prior estimates of water volume and flow discharge during these flood events rely on slopes based on modern topography. Over this time period, glacial isostatic adjustment caused crustal deformation with rates of about 10 mm/yr, orders of magnitude above regional uplift rates, and changed local slopes by about 30%. Thus, prior estimates of flood volumes include a potentially large error, which has not yet been quantified. Furthermore, over the interval of Missoula flooding, patterns of uplift and subsidence due to glacial isostatic adjustment evolved significantly, and this reshaping of topography may explain observed changes in flood routing over time. This proposal, within disciplines of Geomorphology and Geophysics, seeks to investigate the influence of glacial isostatic adjustment on the Channeled Scablands landscape as it developed over the course of Missoula mega-flood events. Three interconnected goals for this project are proposed: (1) reconstruct drainage path evolution across the interval of flood events in response to glacial isostatic adjustment; (2) accurately estimate flood discharge using slopes corrected for glacial isostatic adjustment; and (3) connect the response of ocean, and broader climate system, to newly-refined estimates of total freshwater flux. Glacial isostatic adjustment simulations will be performed to predict paleo-topography and paleo-slopes in the Channeled Scablands. Flood drainage pathways and flood discharge estimates will be calculated using the resulting topography corrected for glacial-isostatic adjustment. Finally, these new estimates of freshwater flux will be compared to the geochemical record of sediment cores collected off the Oregon coast, to assess the response of the ocean's biological system to mega-flood events. The proposed research, which transcends multiple scales by using glacial-isostatic adjustment modeling to connect geomorphic processes to both small and large wavelength features of the mantle's response to ice loading, ultimately linking local short-lived outburst flooding to longer global climate changes.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.