Landsliding and the Evolution of Mountainous Landscapes

滑坡是大多数山地景观的主要侵蚀机制。我们对气候和构造作用力、河网特征和基岩性质等因素如何控制坡度调整的时空格局了解很少；高地地区本质上主要是侵蚀，因此没有保留过程动力学的直接“记录”。此外，还没有定量模型来预测大型滑坡在地貌时间尺度上的动态。因此，关于滑坡在景观演变中的作用的基本问题仍然存在：o大型滑坡在景观中持续多久？是什么控制着他们的长期活动？O大型山泥倾泻如何影响地形发展和泥沙产生？O滑坡引起的泥沙产生如何影响河道形态和河谷切割？这项建议的目的是通过量化滑坡为主的集水区斜坡不稳定的空间和时间模式，量化滑坡对泥沙产生和山坡形态的影响。加利福尼亚州的红木溪上游流域(约200平方公里)是这项工作的理想实验室，因为：超过80%的集水区由易发生滑坡的地形组成，该地区经历了高速率的岩石抬升，并且广泛的研究利用摄影测量和基于现场的方法记录了与缓慢、间歇的泥石流和塌方相关的地貌过程速率和变形。尽管红木溪的几个斜坡崩塌显示出重大的历史活动，但随处可见的休眠滑坡(即凹凸不平的山坡)具有不同程度的退化，是先前广泛存在的斜坡不稳定阶段的遗留问题。利用机载激光条带测绘(ALSM)产生的高分辨率地形数据，我们建议通过量化易发生滑坡的山坡的详细形态来记录构造和气候强迫如何影响红木溪斜坡失稳的长期模式。滑坡的类型和相对年龄可以通过对地形粗糙度的统计分析来限制；米级的陡坡、碎石堤坝和褶皱在最近的破坏中是新鲜的和明确的，在较老的滑坡上变得越来越柔和和平滑。我们将通过对滑坡活动时间的估计(通过对未排水凹陷的放射性测年来确定)来校准地形粗糙度的定量测量，以记录整个研究区的斜坡变形的年表和风格。当结合山谷动力学、古气候和古地震的研究时，我们的分析将使我们能够检验将斜坡失稳的历史和模式与各种外部扰动联系起来的假说。更广泛的影响拟议中的研究对寻求了解山脉规模的剥蚀、土地利用的影响以及气候变化对地表过程的影响的地球科学家具有重大影响。由于滑坡产生的泥沙对颗粒大小和河道性质有深远的影响，我们对坡面失稳的全流域分析将有助于建立山坡过程和水生生境之间的联系。在Redwood Creek，与土地利用实践(如沟壑、泥石流和浅层滑坡)相关的集中历史侵蚀带被系统地叠加在由大型山体滑坡形成的复杂马赛克形成的山坡上。我们的分析将使土地管理者能够更好地预测和补救木材采伐和气候变化的影响。ALSM数据集还将作为描述未来坡度和渠道系统动态的基线。在更广泛的范围内，这些结果将有助于激发对整个大陆边缘的沉积物路线、扩散和沉积的模拟，在沉积物生产和海洋沉积物之间建立直接联系。这项研究将通过与联邦和州土地管理机构的直接合作得到加强。

ABSTRACTLandsliding is the dominant erosional mechanism in most mountainous landscapes. We have a poor understanding of how factors such as climatic and tectonic forcing, channel network characteristics and bedrock properties govern the spatial and temporal pattern of hillslope adjustment; upland regions are predominantly erosional in nature and thus do not retain a direct 'record' of process dynamics. Furthermore, no quantitative models exist to predict the dynamics of large landslides over geomorphic timescales. As a result, fundamental questions regarding the role of landslides in landscape evolution remain: o How long do large landslides persist in the landscape? What controls their long-term activity? o How do large landslides affect topographic development and sediment production? o How does landslide-driven sediment production affect channel morphology and valley incision? The objective of this proposal is to quantify the effects of landsliding on sediment production and hillslope morphology by quantifying spatial and temporal patterns of slope instability in a landslide-dominated catchment. The upper Redwood Creek drainage basin (~200 km2), California, is an ideal laboratory for this endeavor because: over 80% of the catchment is comprised of landslide-prone terrain, the region experiences high rates of rock uplift, and extensive studies have documented geomorphic process rates and deformation associated with slow, intermittent earthflows and slumps using photogrammetric and field-based methods. Although several slope failures in Redwood Creek exhibit significant historical activity, ubiquitous dormant landslides (i.e., hummocky hillslopes) with varying degrees of degradation are the legacy of prior phases of widespread slope instability. Using high-resolution topographic data generated via airborne laser swath mapping (ALSM), we propose to document how tectonic and climatic forcing affect the long-term pattern of slope instability in Redwood Creek by quantifying the detailed morphology of landslide-prone hillslopes. The style and relative age of landsliding can be constrained via statistical analyses of terrain roughness; meter-scale scarps, debris levees, and folds are fresh and well defined in recent failures and become increasingly subdued and smooth on older landslides. We will calibrate quantitative measures of terrain roughness with estimates for the timing of slide activity (established via radiometric dating of undrained depressions) to document the chronology and style of slope deformation across the study area. When coupled with studies of valley dynamics, paleoclimate, and paleoseismicity, our analysis will permit us to test hypotheses relating the history and pattern of slope instability with various external perturbations. Broader Impacts The proposed research has significant implications for earth scientists seeking to understand mountain-scale denudation, land-use impacts, and the effect of climate change on surficial processes. Because landslide-derived sediment production profoundly affects grain size and channel properties, our catchment-wide analysis of slope instability will be useful for establishing linkages between hillslope processes and aquatic habitat. In Redwood Creek, zones of focused historical erosion related to land-use practices (such as gullys, earthflows, and shallow landslides) are systematically superimposed on hillslopes shaped by a complex mosaic of large landslides. Our analyses will enable land managers to better predict and remediate impacts of timber harvesting and climate change. The ALSM dataset will also serve as a baseline for characterizing future hillslope and channel system dynamics. On a broader scale, the results will serve to excite simulations of sediment routing, dispersal, and deposition across continental margins, establishing direct linkages between sediment production and marine deposits. The research will be strengthened through direct collaboration with federal and state land management agencies.