MCA: Multi-scale considerations of climatic signatures on debris flows and alluvial fans

在世界范围内，人们正经历着风暴频率和强度的历史性变化，这些变化摧毁了家园和生命。频繁和/或强烈风暴最具破坏性的影响之一是，相关的降雨可以破坏土质材料的稳定，并使自然和建筑基础设施的基础液化。在这样的条件下，这些材料可以下坡流动，随后夹带额外的材料，并急剧增加尺寸。它们的生长速度和进化令人震惊，因为它们添加了泥土、岩石，甚至一米大小的巨石，成为巨大的泥石流河流。这些泥石流可能会在流动时突然改变方向，甚至会形成自己的沟道墙或堤防，从而在相对于周围环境的“超级提升”中保持高速。这些泥石流的时间、方向和规模的不可预测性会增加其破坏性，例如，2018年加利福尼亚州蒙特西托县泥石流造成的死亡和破坏就是显而易见的。为了更好地减轻灾害，科学家需要了解当地材料、湿度和当地气候条件等细节是如何决定这些行为的。该项目包括利用以往水流及其沉积物的数据、物理实验和计算模拟进行研究，以帮助我们更好地预测和预测在不同气候条件下可能出现的未来水流的行为。该项目结合了实地工作、实验室实验、颗粒物理理论和计算模型，以了解特定泥石流事件外部气候条件的综合影响以及这些条件下的流动物理。这将涉及一个与沉积物流体特性和边界条件有关的新框架，因为它与不同条件下的泥石流行为有关。实验工作将包括：(1)在简单的基础条件下控制滑塌-浆体实验；(2)侵蚀河道化实验；(3)冲积扇实验。计算工作将建立在多相离散元法（DEM）模型中嵌入的沉积物流体流变学基础上。实地工作将包括泥石流沉积物，这些沉积物选择在具有独特气候和物理信号的地点，以帮助识别每种信号：(1)与达特茅斯学院的Marisa Palucis教授合作，研究理查森山脉的冰缘沉积物（随着气候变化改变沉积物供应）；(2)台湾老农河流域湿暖湿沉积（高泥沙供给、湿润条件、不同流域岩性）；(3)在欧文斯谷较为干燥、温度较高的沉积物中，具有明显的气候和岩性差异特征。与土著社区计划开展的工作将在土著社区的积极参与和社区记录下为科学作出贡献。该奖项由地貌与土地利用动力学项目和颗粒与多相过程项目共同资助。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。

Worldwide, communities are experiencing historic changes in storm frequencies and magnitudes that destroy homes and lives. One of the most devastating effects of frequent and/or intense storms is the way in which associated rainfall can destabilized earthen materials and liquefy the very foundation of natural and built infrastructure. Under such conditions, these materials can flow downslope, subsequently entrain additional materials, and increase in dramatically size. Their growth rate and evolution can be alarming as they add mud, rocks, and even meter-sized boulders to become massive rivers of debris flows. These debris flows may abruptly change direction as they flow, and even create their own channel walls, or levees, thus maintaining a high speed as they “super-elevate” relative to their surroundings. The unpredictability of the timing, directions, and magnitudes of these flows can add to their devastation as evident, for example, in the deaths and destruction of the 2018 debris flows in Montecito County, California. For better hazard mitigation scientists need to understand how details such as local materials, moisture, and local climate conditions dictate these behaviors. This project involves research using data from previous flows and their deposits, physical experiments, and computational simulations to help us better anticipate and predict behaviors of likely future flows under varying climatic conditions. This project combines field work, laboratory experiments, granular physics theory, and computational modeling to understand combined effects climate conditions external to specific debris flow events and flow physics embedded in those conditions. This will involve a new framework relating sediment-fluid specifics and boundary conditions as it relates to debris flow behaviors under varying conditions. Experimental work will include: (1) controlled slump-slurry experiments with simplistic basal conditions; (2) erosional channelized experiments, and (3) alluvial fan experiments. Computational work will build on sediment-fluid rheology embedded in a multi-phase discrete-element-method (DEM) model. Field work will include debris flow deposits at sites selected for their distinct climatic and physics-based signals to help identify signals from each: (1) on periglacial deposits in the Richardson Mountains (changing sediment supply with climate changes) with collaborative partner Professor Marisa Palucis of Dartmouth College; (2) on wetter warmer deposits along the Laonong River Valley, Taiwan (high sediment supplies, moist conditions, distinct catchment lithologies); (3) in drier hotter deposits in Owens Valley that contain signatures of distinct climate and lithology differences. Planned work with indigenous communities will contribute to the science with their active involvement and community records. This award is jointly funded by the Geomorphology and Land-use Dynamics Program and the Particulate and Multiphase Processes Program.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.