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带来了超过厘米的降雨量。这种过度的降水造成了全岛的大规模浪费和洪水泛滥，类似于2017年飓风玛丽亚的影响。这两个事件都是研究热带气旋对高地热带地貌演变的影响的非同寻常的机会。该项目将支持两次部署科学家和设备，以从波多黎各南部两个受飓风后大规模浪费严重影响的集水区收集时间敏感和易腐烂的数据。以这些流域为模型研究区，调查人员将：1.利用无人机动态结构摄影测量技术调查滑坡堆积、疤痕和滑坡后河流淤积的地形；2.采集滑坡区下游河流沉积物样品，用于滑坡成因沉积物的粒度分析和宇宙核素示踪；3.利用时移相机监测和记录仍不稳定的滑坡和积极淤积的河道的运动。该项目将与设在波多黎各的联合调查员合作，并与从事危害评估和预防工作的联邦和当地科学家协调。野外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罕见的风暴事件对侵蚀地貌长期演变的贡献。对于像热带风暴这样的大风暴，地貌对热带景观的直接影响可能是显而易见的：大规模浪费和洪水泛滥。然而，热带地貌对风暴事件的延伸反应往往更为复杂，测量景观反应需要在风暴事件发生后立即开始在整个集水区进行重复观测。该项目支持收集对时间敏感和易腐烂的数据，以探索关于热带地貌对热带气旋引起的山体滑坡和洪水的反应的三个假设。具体地说，调查人员将解决以下问题：1.风暴事件在哪里(以及为什么)破坏山坡的稳定？通过亲自调查滑坡的伤痕和沉积物，使用延时相机监测仍然不稳定的山坡，并使用遥感图像绘制区域滑坡地图；2.河网如何适应滑坡产生的泥沙的涌入？通过重复无人机地形测量测量河道淤积/侵蚀模式，并利用滑坡地区下游河道的时间推移图像直接跟踪粗泥沙输送；以及3.滑坡产生的沉积物在热带地貌中的停留时间是多少？通过反复测量河流沉积物中的宇宙成因放射性核素浓度，以检测下一年滑坡引发的沉积物通量的变化。该奖项反映了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。

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.