Collaborative Research: Orogeny, orography, and unsteady erosion: evolution of the Himalaya

这项研究试图了解喜马拉雅地区的侵蚀速率是如何随时间和空间而变化的。一些初步数据表明，在较长的时间尺度上，侵蚀速率变得更加稳定。本研究假设，降雨分布的空间变化调节了侵蚀速率的差异，而特定的水流功率（流量和河道坡度的乘积）为现代侵蚀速率提供了可靠的代理。该项目将使用非常高分辨率的降雨遥感数据以及数字地形来预测水流功率的变化。对侵蚀速率的影响将通过宇宙生成核素（CRN）分析来自流域的样品，对比水流功率来评估。将使用热动力学模型分析集水区样带中各种矿物的冷却年龄，以在更长的时间尺度上创建侵蚀速率时间变化的可靠重建。喜马拉雅山脉处于一个活跃的构造区，该建议提出了地形横向平流的假设，以响应构造板块的持续碰撞。据推测，这种平流导致了喜马拉雅流域和相关地形的重大重组。由于平流导致水流被捕获并形成新的跨喜马拉雅河流，侵蚀力大大增强，其他干流将被切断，从而失去动力。这种水流动力的变化应该通过侵蚀速率和地形起伏的变化来表示。该项目将通过使用基岩冷却年龄从地形起伏样带和等高样带重建地形起伏变化来验证这些想法。这个项目的重点是研究山带的生长和衰减，以及气候调节的侵蚀如何影响地震发生的地方。最近的理论表明，在积极变形的山带中，降雨的空间变化模式导致侵蚀速率的差异，而这些侵蚀的差异影响变形发生的地方。喜马拉雅山脉具有强烈的季风降雨、大面积的地形和快速的构造变形，是探索这些相互作用的理想场所。卫星数据和地面观测显示，降雨量在喜马拉雅山脉的长度和宽度上都发生了突然变化。通过将降雨数据与喜马拉雅地形相结合，这个项目的数值模型将预测哪里的侵蚀应该是快是慢。目前喜马拉雅地区降雨的大部分空间变化似乎是由横贯喜马拉雅的大型河谷的作用造成的：它们提供了将降水引导到山区的地形导管，因此，似乎影响了侵蚀程度强弱的地区。该提案认为，这些山谷并不是永久锁定的，但它们可以移动并改变排水模式。实地和实验室调查将记录随着时间的推移侵蚀速率的变化以及喜马拉雅地形的变化。超过3亿人生活在喜马拉雅下游，并利用从这里流出的水。这项工作将深入了解偏远地区（目前鲜为人知）的降雨、降雪和水平衡情况，并有助于更好地预测河流的行为，这对印度和尼泊尔的人民来说是一个重大的利益。

This research attempts to understand how Himalayan rates of erosion vary as a function of space and time. Some initial data suggest that erosion rates become much steadier at longer time scales. This research hypothesizes that spatial variations in rainfall distributions modulate differences in erosion rates and that specific stream power (the product of discharge and channel gradient) provides a reliable proxy for modern erosion rates. This project will use very high resolution remote-sensing data on rainfall along with digital topography to predict variations in stream power. The effect on erosion rates will be evaluated through cosmogenic nuclide (CRN)analyses of samples from catchments with contrasting stream power. Cooling ages of various minerals from transects in the catchments will be analyzed using thermokinematic models to create reliable reconstructions of temporal changes in erosion rates over longer time scales. The Himalayas are in an active tectonic region, and the proposal presents the hypothesis that topography advects laterally in response to the ongoing collision of tectonic plates. This advection is hypothesized to cause major re-organization of Himalayan drainages and related topography. As advection leads to stream capture and creation of new Transhimalayan rivers with greatly enhanced erosive power, other trunk channels will be beheaded, thereby losing power. Such changes in stream power should be expressed by changes in both erosion rates and topographic relief. The project will test these ideas by reconstructing changes in topographic relief using bedrock cooling ages both from their relief transects and from equal-elevation transects. This project focuses on how mountain belts grow and decay and how climatically modulated erosion may affect where earthquakes occur within them. Recent theory suggests that, in actively deforming mountain belts, spatially varying patterns of rainfall cause contrasts in erosion rates and that these differences in erosion influence where deformation occurs. The Himalayas, with their strong monsoonal rains, large-scale topography, and rapid rates of tectonic deformation, are an ideal setting in which to explore these proposed interactions. Satellite data ground-based observation reveal that the amount of rainfall changes abruptly both along the length and breadth of the Himalaya range. By combining the rainfall data with the topography of the Himalaya, this project's numerical models will predict where erosion should be rapid or slow. Much of the current spatial variation in rainfall along the Himalaya appears to result from the role of large river valleys that slice across the Himalaya: they provide topographic conduits that guide precipitation into the mountains and, thereby, appear to influence where erosion is more or less intense. This proposal contends that these valleys are not permanently locked in place, but they can shift and change drainage patterns. The field and laboratory investigation will document changes in erosion rates through time and changes in the topography of the Himalaya. Over 300 million people live downstream from the Himalaya and utilize the waters that flow from it. This work will provide insight on rainfall, snow, and water balance in remote (and currently poorly known) areas, and it will help facilitate better forecasting of river behavior, a significant benefit for the people of India and Nepal.