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

由地球构造板块运动驱动的大陆碰撞升起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变和调节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向北运动与亚洲碰撞，在过去的5000万年里，喜马拉雅山和西藏上升了。该地区为全球五分之一以上的人口提供淡水资源，该地区河流的洪泛平原为他们提供食物。喜马拉雅山脉和西藏对东亚和东南亚的气候有重大影响，这些地区的夏季季风雨占主导地位。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大影响，大陆地壳变形、掩埋、加热和熔化地壳，以及相关的隆起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在缓和全球气候方面发挥了重要作用，因为溶解在雨水中的二氧化碳与侵蚀沉积物之间的化学反应增强了溶解的二氧化碳和钙到海洋的通量，并以石灰石的形式沉积，从而去除了碳。然而，碰撞山脉的演变涉及构造、侵蚀和气候之间复杂的相互作用。碰撞使大陆变厚，从而抬高了它们的表面地形，加剧了滑坡和更陡的河流剖面造成的侵蚀。地形海拔也改变了当地气候，例如降雨量增加，增加了滑坡频率和河流输送沉积物的能力，从而加剧了侵蚀。山区地形的演变被认为是大陆地壳因碰撞而增厚与增厚的地壳在自身重量作用下扩展的趋势相平衡，以及地形和当地气候影响造成的地壳侵蚀之间的平衡。该项目将通过研究尼泊尔的Melamchi Khola河流域，研究地质构造过程、以山崩为主的侵蚀过程和气候影响之间的复杂相互作用。集水区从山麓丘陵到高山，地形有很大的梯度，这一梯度反映在向高山的侵蚀率明显增加。在一个地方的详细研究将使我们能够了解控制过程之间的相互作用。例如，折返速率如何控制滑坡的形成和侵蚀速率。当地的气候，特别是降雨量，如何影响这种关系？侵蚀作用对岩石的移动如何影响控制性构造和地震及滑坡的倾向？这项工作将涉及：1）确定当地下水被带到地表时，岩石的物理和化学性质如何通过断裂和化学蚀变而变化，以及这些变化与当地构造和气候的关系。2)量化地形是如何形成的构造驱动隆起和滑坡侵蚀的竞争过程。这些主要过程是如何受到岩体演化和地下水流的影响的。3)当雨水福尔斯落在山上，然后进入断裂的岩石，然后流入下面的河流时，确定水的流动路径。4)量化岩石的化学变化如何取决于当地气候（温度和降雨量），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.