Collaborative Research: Distribution and Evolution of Geomorphic Process Zones in Large Mountain Ranges

大型山脉在区域尺度上表现出显著的地貌异质性，这反映在山脉不同部位的不同地貌过程占主导地位。这些过程的时空分布，并影响沉积物从山脉中撤离的速度和方式，这些速度和方式反馈给构造过程，并影响山脉前缘以外的河流的行为，那里往往是人口集中的地方。该研究的目的是记录和机械地解释在玻利维亚安第斯山脉的东科迪勒拉这一重要的大山脉中，主要的下游、盆地间和时间趋势的形态和地貌过程。河流切割造成地形起伏，这强烈地调节了作用于山坡的地貌过程的类型和速率，河流运输泥沙负荷的相对能力决定了切割和沉积的位置、河流的行为，从而决定了山谷的形态。因此，了解大山脉的形态和地貌过程的时空格局需要有能力定量地描述河流对山脉的切割，并将切割产生的山坡和河流特征与特定的地貌过程联系起来。这些要求决定了本研究要采用的方法，其中包括四个主要步骤。首先，地貌区域的现代格局必须在东部科迪勒拉的贝尼和皮科马约两个大流域内记录下来。这些盆地具有相似的岩石类型和总体构造历史，但南北降水和总缩短（因此河流切割历史）的变化产生了截然不同的形态。将通过实地观测和图像解译确定以特定山坡和河流地貌过程为主的区域。将对每个区域进行形态计量学表征，以确定：1)哪些指标最能反映特定处理的发生；2)大型山地流域的总体趋势是什么？该研究的第二个主要任务是开发和应用由现场数据校准的河道网络切口模型，以说明河道坡度如何随时间变化和起伏。在该模型中，下降速率与水流功率成正比，隆升的时空格局受到区域构造地质研究、古高程研究和地球动力学模型的约束。第三，从河流切口模型中获得的信息将用于“离线”计算，以确定1)山坡如何随时间变化形状和局部地形的增减；2)切割和沉积制度发生的位置以及河流制度对山谷形态的影响。例如，深层基岩滑坡导致的山坡下降的几何形状和速率将通过对已知河流切割速率产生的陡峭山坡的连续Culmann楔形稳定性分析来计算。计算将在河流切口模型运行期间的选定时间和网络中选定的地点进行。最后，河流切口模型和离线计算中的预测将用几个独立数据来源进行验证。模拟景观的一般地貌格局和形态特征将与现代贝尼盆地和皮科马约盆地的地貌格局和形态特征进行比较。预测的长期地表下降速率将与来自两个盆地的火成岩和变质岩的裂变径迹分析确定的挖掘速率进行比较，而来自两个盆地的火成岩和变质岩的裂变径迹分析确定的速率预测将与来自不同规模的流域的沉积物输出净速率的预测将与来自冲积层宇宙成因同位素丰度的分析得出的速率进行比较。拟议的研究有许多应用，从确定当地地质灾害的性质到预测由于气候变化而导致的全球侵蚀和沉积模式的变化。

Dunne 9628737 Large mountain ranges exhibit striking regional scale morphologic heterogeneity which is reflected in the dominance of different geomorphic processes in different parts of the range. The spatial and temporal distribution of these processes and affects the rate and manner in which sediment is evacuated from the range, which feeds back on tectonic processes and affects the behavior of rivers beyond the range front, where human populations are often concentrated. The objectives of the proposed study are to document and mechanistically explain major downstream, inter basinal, and temporal trends in morphology and geomorphic process within a large, important mountain range: the Eastern Cordillera of the Bolivian Andes. Fluvial incision creates relief, which strongly modulates the type and rate of geomorphic processes acting on hillslopes, and the relative ability of a river to transport its sediment load governs loci of incision and deposition, behavior of the river, and therefore morphology of the valley. Understanding spatial and temporal patterns of morphology and geomorphic process in large mountain ranges therefore requires the ability to quantitatively describe fluvial incision into mountain ranges, as well as to link hillslope and fluvial characteristics resulting from incision to specific geomorphic processes. These requirements dictate the methodology to be employed in this study, which involves four major steps. First, the modern pattern of geomorphic regions must be documented within two large drainage basins, the Beni and Pilcomayo, in the Eastern Cordillera. These basins share similar rocktypes and general tectonic histories, but north-south variation in precipitation and total shortening (and therefore fluvial incision history) has produced strikingly different morphologies. Regions dominated by particular hillslope and fluvial geomorphic processes will be identified from field observations and image interpretation. Each region will be characterized morphometrical ly to determine: 1) which indices best reflect the occurrence of particular processed; and 2) what general trends characterize large mountain drainage basins. The second major task of the study is to develop and apply a channel network incision model calibrated with field data to illustrate how channel slopes vary and relief is generated through time. In this model, downcutting rate is proportional to stream power, and the spatial and temporal pattern of uplift is constrained by regional structural geology studies, paleoelevation studies, and a geodynamic model. Third, information derived from the fluvial incision model will be used in "off-line" calculations to determine 1) how hillslopes change shape and local relief grows and diminishes through time; and 2) where incisional and depositional regimes occur and how fluvial regime affect valley morphology. For example, the geometry and rate of hillslope lowering by deep-seated, bedrock landsliding will be calculated using successive Culmann wedge stability analyses on steep hillslopes produced by a known rate of fluvial incision. Calculations will be made at selected times during a fluvial incision model run and at selected places down the network. Finally, the fluvial incision model and the predictions made in off-line calculations will be checked with several sources of independent data. The general geomorphic patterns and morphometric characteristics of simulated landscapes will be compared to those of the modern Beni and Pilcomayo basins. Predicted long-term surface lowering rates will be compared with exhumation rates determined from fission track analysis of igneous and metamorphic rocks from both basins, while predictions of the rates determined from fission track analysis of igneous and metamorphic rocks from both basins, while predictions of the net rate of sediment export from drainage basins of various sizes will be compared with rates obtained from analysis of cosmogenic isotopic abundance in alluvium. The proposed study has many applications ranging from defining the nature of local geologic hazards to anticipating shifts in gobal erosion and sedimentation patterns due to climatic change.