From Peaks to Prairie: Two Natural Experiments in Decadal Landscape Evolution

侵蚀和沉积不断地重塑地球表面。随着地质时间的推移，这些过程会磨损山脉，并将大量破碎的岩石运往大海。在人类的时间尺度上，这些速度往往如此之慢，以至于几乎察觉不到。但当干扰以野火、洪水、地震、牲畜过度放牧或气候变化等形式袭击地形时，侵蚀和泥沙输送的速度可能会发生戏剧性的变化。地质学家和工程师长期以来一直在寻求开发景观演变的数学模型，以预测给定的景观将如何对干扰做出反应。这些模型对于理解地质循环是如何运作的，以及在较短的时间尺度上预测景观可能对环境变化做出何种反应是至关重要的。然而，这些模型需要根据实际的现场数据进行严格的测试。该项目将测量科罗拉多州两个地点的历史和当代侵蚀和沉积，以提供用于测试模型的案例研究。第一个遗址位于丹佛以东的高平原上，在20世纪显示出异常快速的沟壑增长。航道网络的历史将被重建，使用的方法包括历史上的航拍照片、对20世纪60年代初修建的土坝后面沉积物体积的测量、山谷内沉积物的年代测定，以及测量冷战时期核武器试验释放的外来放射性核素在土壤中的浓度。此外，高精度地面激光扫描新技术将以前所未有的分辨率提供通道头逐年增长的图像。第二个地点位于科罗拉多州落基山脉的一个流域，1996年强烈的野火和暴雨引发了戏剧性的侵蚀和沉积。火灾后重复的实地测量详细记录了分水岭地区的戏剧性变化。这些原始测量将得到机载和地面激光绘制的地形图的补充。来自这两个地点的数据将被用来测试一个领先的景观响应计算机模型。随着模型的不断完善，这些数据库将为现在和未来的科学界提供资源。侵蚀和沉积是自然过程，在整个地球的存在过程中帮助塑造了它，它们对社会产生了直接和广泛的影响。源源不断的泥沙从山上流向大海，填满了水电站，降低了它们的发电能力和运行寿命。河道内的淤积会增加周围社区的洪水风险，而沿溪流和沟渠网络切割可能会破坏道路和其他基础设施，并降低农地的质量。河流携带的泥沙数量或大小的变化将改变河流生态系统的健康。侵蚀甚至会挖出埋在地下的危险废物，将它们释放到河流网络中，在那里它们可能会污染供水。所有这些过程往往都受到人类发展的影响。为此，需要建立景观对自然和人类干扰的响应的计算模型，以支持仔细的规划，以减轻未来土地利用和气候变化的潜在影响。该项目支持继续开发和完善这些模型，并将进行实地测试，以促进在不断变化的地貌中的可持续生活。

Erosion and sedimentation constantly re-shape the Earth's surface. Over geologic time, these processes wear down mountains and move vast quantities of broken rock to the sea. On human time scales, the rates are often so slow as to be barely perceptible. But when disturbance strikes a landscape such as in the form of wildfire, flooding, earthquakes, livestock overgrazing,or climate change, the pace of erosion and sediment transport can be altered dramatically. Geologists and engineers have long sought to develop mathematical models of landscape evolution that can predict how a given landscape will response to disturbance. Such models are crucial to understanding how the geological cycle operates and, on shorter time scales, for predicting how landscapes are likely to react to environmental changes. However, these models need to be tested rigorously against actual field data. This project will measure historical and contemporary erosion and sedimentation at two sites in Colorado to provide case studies with which to test models. The first site, located on the High Plains east of Denver, has shown unusually rapid gully growth during the 20th century. The history of the channel network will be reconstructed using a combination of historic aerial photographs, measurements of the volume of sediment trapped behind earthen dams built in the early 1960s, dating of sediments within the valleys, and measuring the concentration in soils of exotic radionuclides that were released by Cold-War era nuclear weapons testing. In addition, the new technology of high-precision ground-based laser scanning will provide images at unprecedented resolution of the year-by-year growth of channel heads. The second site lies in a drainage basin in the Colorado Rockies where intense wildfire followed by heavy rainfall in 1996 triggered dramatic erosion and sedimentation. Repeated field measurements following the fire provide a detailed record of dramatic changes in the watershed area. These original measurements will be supplemented with airborne and ground-based laser-derived maps of the terrain. Data from both sites will be used to test one of the leading computer models of landscape response. The databases will provide a resource for the scientific community now and into the future as models continue to become more sophisticated.Erosion and sedimentation are natural processes that have helped shape our planet throughout its existence, and they have direct and wide-ranging impacts on society. The constant flow of sediment from mountains to the sea fills in hydropower reservoirs, decreasing their generating capacity and operational lifespan. Sedimentation within river channels can increase flood risk to surrounding communities, while incision along streams and gully networks can damage roadways and other infrastructure and reduce the quality of agricultural land. Changes in the amount or size of sediment carried by streams will alter the health of river ecosystems. Erosion can even exhume buried hazardous wastes, releasing them to stream networks where they can contaminate water supplies. All of these processes are often affected by human development. For this reason, computational models of landscape response to both natural and human disturbance are needed to support careful planning that mitigates the potential effects of future changes in land use and climate. This project supports the continued development and refinement of these models and will result in field-based tests that will contribute to sustainable living in an ever-changing landscape.