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

侵蚀和沉积不断地重塑着地球表面。随着地质时间的推移，这些过程磨损了山脉，并将大量破碎的岩石转移到海洋中。在人类的时间尺度上，速度往往很慢，几乎察觉不到。但是，当野火、洪水、地震、牲畜过度放牧或气候变化等形式的干扰袭击景观时，侵蚀和沉积物运输的速度可能会发生巨大变化。长期以来，地质学家和工程师一直在寻求开发景观演化的数学模型，以预测给定景观对干扰的反应。这样的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，对于预测景观如何可能对环境变化作出反应是至关重要的。然而，这些模型需要根据实际的现场数据进行严格的测试。该项目将在科罗拉多州的两个地点测量历史和当代的侵蚀和沉积，为测试模型提供案例研究。第一个地点位于丹佛东部的高平原，在20世纪显示出异常快速的沟壑增长。水道网的历史将通过综合使用历史航空照片、对20世纪60年代初建造的土坝后沉积物体积的测量、对山谷内沉积物的年代测定以及对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的测量来重建。此外，高精度地面激光扫描的新技术将提供前所未有的分辨率图像，以逐年增长的通道头。第二个地点位于科罗拉多落基山脉的一个流域，1996年，这里发生了强烈的野火和暴雨，引发了剧烈的侵蚀和沉积。火灾后反复进行的实地测量提供了流域地区剧烈变化的详细记录。这些原始测量结果将由机载和地面激光绘制的地形图加以补充。来自这两个地点的数据将用于测试景观响应的一种领先的计算机模型。随着模型变得越来越复杂，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，在地球存在的整个过程中帮助塑造了地球，它们对社会产生了直接和广泛的影响。泥沙不断从山上流入海洋，填满了水电站水库，降低了水库的发电能力和运行寿命。河道内的沉积会增加周边社区的洪水风险，而沿着溪流和沟壑网络的切割会破坏道路和其他基础设施，并降低农业用地的质量。河流携带沉积物的数量或大小的变化将改变河流生态系统的健康。侵蚀甚至会把埋在地下的危险废物挖出来，释放到水流网络中，污染供水系统。所有这些过程往往受到人类发展的影响。因此，需要计算景观对自然和人为干扰的响应模型来支持谨慎的规划，以减轻未来土地利用和气候变化的潜在影响。该项目支持这些模型的不断发展和完善，并将进行实地测试，这将有助于在不断变化的景观中实现可持续生活。

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.