Collaborative Research: RAPID: The fate of landslide-derived sediment following tropical cyclones: a case study of Hurricane Fiona in Puerto Rico

2022年9月18日至20日，飓风菲奥娜给波多黎各岛带来了超过64厘米的降雨。这种过度的降水导致了整个岛屿的大规模浪费和洪水，类似于2017年飓风María的影响。这两个事件都为研究热带气旋对高海拔热带景观演变的影响提供了难得的机会。该项目将支持两次科学家和设备的部署，以便从波多黎各南部受飓风后大规模浪费严重影响的两个集水区收集具有时效性和易腐性的数据。利用这些集水区作为模型研究区域，研究人员将：利用基于无人机的运动结构摄影测量技术调查滑坡沉积物、疤痕和滑坡后河流的地形；2. 2 .采集滑坡区下游河流沉积物样本，进行滑坡源沉积物粒度分析和宇宙成因核素示踪；用延时相机监测和记录不稳定的滑坡和河道淤积的运动。该项目将与设在波多黎各的共同调查人员合作，并与从事危害评估和预防工作的联邦和地方科学家协调。实地工作部署将涉及至少3名研究生和3名本科生。60多年来，地质学家一直在争论大型但不常见的风暴事件对侵蚀景观长期演变的影响。对于像热带周期这样的大风暴，对热带景观的直接地貌影响可能是显而易见的：大量的浪费和洪水。然而，热带景观对风暴事件的扩展响应往往更为复杂，景观响应的测量需要在风暴事件发生后立即开始在整个集水区重复观测。该项目支持收集对时间敏感和易腐烂的数据，以探索热带景观对热带气旋引起的山体滑坡和洪水的反应的三种假设。具体而言，调查人员将解决以下问题：1。风暴事件在哪里（以及为什么）破坏了山坡的稳定？通过实地调查滑坡疤痕和沉积物，用定时相机监测仍然不稳定的山坡，并利用遥感图像绘制区域滑坡地图；2. 河网如何适应滑坡沉积物的涌入？通过重复无人机地形调查测量河道淤积/侵蚀模式，利用滑坡区下游河道的时移影像直接跟踪粗沙输运；和3。在热带景观中，滑坡沉积物的停留时间是多久？通过对河流沉积物中宇宙成因放射性核素浓度的反复测量，以探测次年滑坡沉积物通量的变化。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。

From September 18-20, 2022 Hurricane Fiona delivered more than 64 cm of rainfall to the island of Puerto Rico. This excessive precipitation caused mass wasting and flooding across the island, similar to the effects of Hurricane María in 2017. Both events represent extraordinary opportunities to study the impact of tropical cyclones on the evolution of a high relief, tropical landscape. This project will support two deployments of scientists and equipment to collect time-sensitive and perishable data from two catchments in southern Puerto Rico strongly impacted by mass wasting after the hurricane. Using these catchments as a model study area the investigators will: 1. survey the topography of landslide deposits, scars, and post-landslide river aggradation using drone-based structure-from-motion photogrammetry; 2. collect samples of river sediment downstream of landslide areas for grain size analysis and cosmogenic nuclide tracing of landslide-derived sediment, 3. monitor and record the movement of still-unstable landslides and actively aggrading river channels with time-lapse cameras. The project will be collaborative with co-investigators based in Puerto Rico and coordinated in concert with federal and local scientists working in hazards assessment and prevention. Field work deployments will engage at least 3 graduate and 3 undergraduate students.For more than sixty years, geologists have debated the contribution of large, yet infrequent storm events to the long-term evolution of eroding landscapes. For large storms like tropical cycles, the immediate geomorphic impact to tropical landscapes may be obvious: mass wasting and flooding. However, the extended response of tropical landscapes to the storm event is often more complex, and measurement of landscape response requires repeated observations across a catchment area, beginning immediately after the storm event. This project supports collection of time-sensitive and perishable data to explore three hypotheses concerning the response of a tropical landscape to landslides and flooding caused by a tropical cyclone. Specifically, the investigators will address the questions: 1. Where (and why) do storm events destabilize hillslopes? by surveying landslide scars and deposits in-person, monitoring still-unstable hillslopes with time-lapse cameras, and mapping landslides regionally with remotely-sensed imagery; 2. How do river networks adjust to an influx of landslide-derived sediment? by measuring channel aggradation/erosion patterns with repeat drone-based topographic surveys and direct tracking of coarse sediment transport using time-lapse images of channels downstream of landslide areas; and 3. What is the residence time of landslide-derived sediment in a tropical landscape? by repeated measurement of cosmogenic radionuclide concentrations in river sediment to detect changes in the flux of landslide-derived sediment over the following year.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.