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

合作研究：大山脉地貌过程带的分布与演化

• 批准号: 9628737
• 负责人: Thomas Dunne
• 金额: --
• 依托单位: University of California-Santa Barbara
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1996
• 资助国家: 美国
• 起止时间: 1996-09-01 至 1999-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9628737&HistoricalAwards=false
• 关键词: Collaborative; Research; Distribution; Evolution; Geomorphic

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.

Dunne 9628737 大山脉表现出惊人的区域尺度形态异质性，这反映在该山脉不同部分不同地貌过程的主导地位。这些过程的空间和时间分布会影响沉积物从山脉中排出的速度和方式，从而反馈构造过程并影响山脉前沿以外的河流的行为，而人口通常集中在那里。本研究的目的是记录并机械地解释玻利维亚安第斯山脉东科迪勒拉山脉内形态和地貌过程的主要下游、盆地间和时间趋势。河流切割产生地形，强烈调节作用于山坡的地貌过程的类型和速率，河流输送沉积物的相对能力控制切割和沉积的位置、河流的行为，从而控制山谷的形态。因此，了解大山脉形态和地貌过程的时空模式需要能够定量描述山脉的河流切割，以及将切割产生的山坡和河流特征与特定地貌过程联系起来。这些要求决定了本研究中采用的方法，包括四个主要步骤。首先，地貌区域的现代模式必须记录在东科迪勒拉山脉的贝尼和皮尔科马约这两个大型流域盆地内。这些盆地具有相似的岩石类型和一般构造历史，但南北降水量和总缩短（以及因此河流切割历史）的变化产生了截然不同的地貌。将通过实地观察和图像解释来识别以特定山坡和河流地貌过程为主的区域。每个区域都将在形态学上进行表征，以确定：1）哪些指数最能反映特定处理的发生； 2) 大型山区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用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以及地形如何产生。在该模型中，下切率与河流功率成正比，抬升的时空模式受到区域构造地质学研究、古海拔研究和地球动力学模型的约束。第三，从河流切割模型获得的信息将用于“离线”计算，以确定：1）山坡如何改变形状以及局部地形如何随着时间的推移而增大和减小； 2) 切割和沉积形态发生的位置以及河流形态如何影响山谷形态。例如，深部基岩滑坡造成的山坡下降的几何形状和速率将通过对由已知的河流切割速率产生的陡峭山坡进行连续卡尔曼楔形稳定性分析来计算。将在河流切割模型运行期间的选定时间和网络下游的选定位置进行计算。最后，将使用多个独立数据源来检查河流切割模型和离线计算中所做的预测。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尔科马约盆地进行比较。预测的长期地表下降速率将与根据两个盆地的火成岩和变质岩的裂变径迹分析确定的折返速率进行比较，同时预测根据两个盆地的火成岩和变质岩的裂变径迹分析确定的折返速率，同时预测不同规模流域的沉积物净输出率将与冲积层宇宙成因同位素丰度分析获得的速率进行比较。拟议的研究有许多应用，从定义当地地质灾害的性质到预测气候变化导致的全球侵蚀和沉积模式的变化。