NSFGEO-NERC: Collaborative Research: Coupling Erosion, Weathering, and Hydrologic Function in an Active Orogenic System

在地球板块运动的推动下，大陆的碰撞形成了地球上最大的山脉。这对大陆大片地区的可居住性以及控制其地质演化和缓和全球气候具有根本性影响。现代大陆碰撞的主要例子是印度板块向北运动与亚洲板块的碰撞，在过去的5000万年里，印度板块与亚洲板块的碰撞抬升了喜马拉雅山和西藏。该地区为全球五分之一以上的人口提供淡水，而流经该地区的河流泛滥平原为他们提供食物。喜马拉雅和西藏对以夏季季风性降雨为主的东亚和东南亚气候有重大影响。该山脉是该地区主要自然灾害的源头，包括地震、山体滑坡和洪水。大陆碰撞对地质演化也有重要的影响，大陆地壳的变形、掩埋、加热和融化以及相关的隆升和侵蚀提供了大量的沉积物。大陆碰撞也被认为在超过百万年的时间尺度上对缓和全球气候起着重要作用，因为雨水中溶解的二氧化碳和被侵蚀的沉积物之间的化学反应增加了溶解的二氧化碳和钙的流量，这些二氧化碳和钙以石灰石的形式沉积到海洋中，从而消除了大气中的二氧化碳，限制了全球气温。然而，碰撞山脉的演化涉及构造、侵蚀和气候之间复杂的相互作用。碰撞使大陆变厚，使其表面地形升高，加强了山体滑坡的侵蚀和更陡峭的河流轮廓。地形海拔也改变了当地的气候，例如，通过增加降雨，通过增加滑坡频率和河流运输沉积物的能力来加强侵蚀。山带地形的演变被认为代表了大陆地壳在碰撞作用下的增厚与地形和局部气候影响下的侵蚀之间的平衡。碰撞作用由增厚的地壳在自身重量下的扩张趋势所平衡。该项目将通过研究尼泊尔的Melamchi Khola河流域，研究构造过程、滑坡主导的侵蚀过程和气候影响之间的复杂相互作用。集水区跨越了从丘陵到高山的巨大地形梯度，这种梯度反映在对高山的侵蚀率显著增加上。在一个地点的详细研究将使我们了解控制过程之间的相互作用。例如，挖掘速度如何控制滑坡的形成和侵蚀速度。当地气候，特别是降雨，是如何影响这种关系的？岩石的侵蚀作用如何影响控制构造和地震和滑坡的倾向？这项工作将包括：1)确定岩石的物理和化学性质是如何通过破裂和地下水流经裂缝被带到地表时的化学变化而变化的，以及这些变化与当地构造和气候的关系。2)量化地形是如何在构造驱动的隆升和滑坡侵蚀的竞争过程中形成的。这些主要过程如何受到岩体演化和地下水流的影响。3)确定雨水落在山上，然后进入破碎的岩石，然后流入下面的河流的流动路径。4)量化岩石的化学变化如何取决于当地气候（温度和降雨）、地下水流动路径和侵蚀速率。

The collision of continents driven by the movement of the Earth's tectonic plates raises the Earth's greatest mountain ranges. This has fundamental impacts on the habitability of large areas of the continents as well as controlling their geological evolution and moderating global climate. The prime modern example of a continental collision is the northward movement of India colliding with Asia which has raised the Himalayas and Tibet over the last 50 million years. This region sources freshwater for more than one-fifth of the global population and the floodplains of the rivers draining the region provide their food. The Himalayas and Tibet have a major impact on the climate of east and south-east Asia dominated by the summer monsoonal rains. The mountain range is the source of the major natural hazards in the region including earthquakes, landslides and floods. Continental collisions also have a major impact on the geological evolution the continental crust deforming, burying, heating and melting the crust and the associated uplift and erosion provides large amounts of sediment. The continental collisions are also thought to play an important part in moderating global climate on the greater than million-year timescales as the chemical reactions between carbon-dioxide dissolved in rainwater and the eroded sediment enhance the flux of dissolved carbon-dioxide and calcium to the oceans to be deposited as limestone removing carbon-dioxide from the atmosphere and limiting global temperatures.However the evolution of collisional mountain ranges involves complex interactions between tectonics, erosion and climate. The collision thickens the continents which elevates their surface topography, enhances erosion by landslides and the steeper river profiles. The topographic elevation also alters the local climate, for example by increasing rainfall which enhances erosion by increasing landslide frequency and the ability of rivers to transport sediments. The evolving topography of mountain belts is thought to represent a balance between the thickening of the continental crust by the collision balanced by the tendency of the thickened crust to spread under its own weight and the erosion of the crust forced by the topography and local climatic impacts. This project will study these complex interactions between the tectonic processes, the erosive processes dominated by landslides and the impact of climate by studying the Melamchi Khola river catchment in Nepal. The catchment spans the dramatic gradient in topography from the foothills to the high mountains, a gradient which is reflected by a marked increase in erosion rates towards the high mountains. The detailed study in one location will enable us to understand the interactions between the controlling processes. For example how does the exhumation rate control landslide formation and the erosion rate. How does the local climate, particularly rainfall, impact this relationship? How does removal of rock by erosion impact the controlling tectonics and propensity for earthquakes and landslides? The work will involve: 1) Determining how the physical and chemical properties of rock change by fracturing and chemical alteration as groundwater flows through the fractures as they are brought to the surface and the relationship of these changes to both the local tectonics and to climate. 2) Quantify how the topography is shaped by the competing processes of tectonically-driven uplift and erosion by landslides. How are these major processes impacted by the evolution of the rock mass and the groundwater flow through the subsurface. 3) Determine the flow paths of water as rain falls on the mountains and then enters fractured rock before feeding rivers below. 4) Quantify how the chemical alteration of the rock depends on the local climate (temperature and rainfall), groundwater flow paths and erosion rate.