Collaborative Research: Testing Critical Zone Controls on Mountain-Scale Relief in a Tropical Climate

合作研究：测试热带气候下山区救援的关键区域控制

• 批准号: 2139895
• 负责人: Kenneth Hughes
• 金额: $ 28.45万
• 依托单位: University of Puerto Rico Mayaguez
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-06-01 至 2025-05-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2139895&HistoricalAwards=false
• 关键词: Collaborative; Research; Testing; Critical; Zone

The Critical Zone is the thin layer of Earth that extends from the base of the soil layer to treetops and supports most terrestrial life on our planet. This project examines how differences in Critical-Zone processes influence topography through a comparative experiment of two different bedrock units on the tropical island of Puerto Rico. On the island, ancient volcanic rocks form steep, high peaks and have clay-rich soils, whereas granitic rocks underlie relatively more subdued, rolling hills covered by sandier soils. This study will evaluate the impact of these differences on the occurrence of landslides, the size of sediment grains that populate river channels, and the size and frequency of floods. The principal hypothesis is that landslides cut more deeply in the clay-rich soils and, as a result, deliver coarser sediment to rivers. The coarser sediment, in turn, better shields the river channel from erosion such that larger floods are needed to carve the underlying bedrock. In addition, the clay-rich volcanic soils retain more rainwater, resulting in fewer floods than areas covered by sandy granitic soils. The net result is that the volcanic rocks maintain a higher elevation and steeper topography than the granitic terrain. This project will test these ideas through detailed landslide mapping, grain-size measurements, statistical analyses of streamflow gaging data, and measurements of long-term landscape erosion rates. This project will form the basis for graduate and undergraduate research experiences and also engage additional students at the University of Puerto Rico, Mayagüez and Colorado State University in an experiential learning, research, and cultural exchange program centered on comparing and contrasting the landscapes in Puerto Rico and Colorado.Variations in topographic relief, steepness, and height are often observed to correlate with differences in bedrock geology. Most often, these changes are interpreted to result from differences in the erodibility of the underlying bedrock. On the tropical island of Puerto Rico intermediate-to-mafic volcaniclastic units underlie high relief, steep mountains, whereas felsic-rich granitic-to-granodioritic rocks are characterized by gentler, rolling hills. Preliminary results indicate that unweathered bedrock strength and fracture density between these two rock units is similar, implying the differences in primary rock strength or erodibility cannot explain the stark contrast in topography. Previous studies show that the soils developed atop each of these rock units are distinct, with the more mafic units comprised of clay-rich soils and sandier soils developed in the more felsic units. These differences in soil characteristics and associated Critical Zone architecture promote relief production in the volcaniclastic units relative to the granitic units. Specifically, differences in the Critical Zone affect the magnitude of incision thresholds by controlling bedload grain size distributions and the frequency of floods that breach these thresholds by modulating shallow, subsurface hydrology. These hypotheses will be tested by mapping landslide locations, measuring grain size distributions in sediment deposits, analyzing flood statistics from existing stream gaging stations, and calculating long-term erosion rates from cosmogenic radionuclides. Datasets will be synthesized into a modeling framework that predicts fluvial landscape relief as a function of rock strength, the magnitude of incision thresholds, and the frequency of threshold breaching floods. This project is jointly funded by the Geomorphology & Land-use Dynamics program in Earth Sciences and the Established Program to Stimulate Competitive Research (EPSCoR).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.

临界区是地球的薄层，从土壤层的底部延伸到树梢，并支持我们星球上的大多数陆地生命。本项目通过对热带岛屿波多黎各上两个不同基岩单元的对比实验，研究临界区过程的差异如何影响地形。在岛上，古老的火山岩形成陡峭的高峰，并有丰富的粘土，而花岗岩岩石下相对较柔和，起伏的山丘覆盖着沙质土壤。这项研究将评估这些差异对滑坡发生的影响，填充河道的沉积物颗粒的大小，以及洪水的大小和频率。主要的假设是，滑坡在富含粘土的土壤中切割得更深，因此，将较粗的沉积物输送到河流中。而较粗的沉积物又能更好地保护河道不受侵蚀，因此需要更大的洪水来雕刻下面的基岩。此外，富含粘土的火山土壤保留了更多的雨水，导致洪水比桑迪花岗岩土壤覆盖的地区少。最终的结果是，火山岩保持了比花岗岩地形更高的海拔和更陡峭的地形。该项目将通过详细的滑坡测绘、粒度测量、流量测量数据的统计分析和长期景观侵蚀率的测量来检验这些想法。该项目将形成研究生和本科生研究经验的基础，并吸引更多的学生在波多黎各，马亚圭斯和科罗拉多州立大学的体验式学习，研究和文化交流计划集中在比较和对比的景观在波多黎各和科罗拉多。地形起伏，陡度和高度的变化往往被观察到与基岩地质的差异相关。大多数情况下，这些变化被解释为由于下伏基岩的可蚀性的差异。在热带岛屿波多黎各，中等至镁铁质火山岩单元位于高起伏、陡峭的山脉之下，而富长英质的花岗岩至花岗闪长质岩石则以平缓、起伏的山丘为特征。初步结果表明，这两个岩石单元之间的未风化基岩强度和断裂密度是相似的，这意味着原生岩石强度或可蚀性的差异不能解释地形的鲜明对比。以前的研究表明，这些岩石单元顶部的土壤是不同的，与更多的镁铁质单位组成的粘土丰富的土壤和砂质土壤中开发的长英质单位。土壤特性和相关临界带结构的这些差异促进了火山岩单元相对于花岗岩单元的救灾生产。具体而言，在临界区的差异影响切口阈值的大小，通过控制推移质粒度分布和洪水的频率，通过调制浅，地下水文突破这些阈值。这些假设将通过绘制滑坡位置图、测量沉积物中的粒度分布、分析现有河流测量站的洪水统计数据以及计算宇宙成因放射性核素的长期侵蚀率来进行检验。数据集将被合成到一个建模框架中，该框架预测河流景观地形作为岩石强度的函数，切口阈值的大小和阈值突破洪水的频率。 该项目由地球科学地貌土地利用动力学项目和激励竞争性研究的既定项目（EPSCoR）共同资助。该奖项反映了NSF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。