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Response of transient rock uplift and base level knickpoints to erosional efficiency contrasts in bedrock streams
Earth Surface Processes and Landforms ( IF 2.8 ) Pub Date : 2021-05-05 , DOI: 10.1002/esp.5146 Joshua A. Wolpert 1 , Adam M. Forte 1
Earth Surface Processes and Landforms ( IF 2.8 ) Pub Date : 2021-05-05 , DOI: 10.1002/esp.5146 Joshua A. Wolpert 1 , Adam M. Forte 1
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Knickpoints in bedrock streams are often interpreted as transient features generated by a change in boundary conditions. It is typically assumed that knickpoints propagate upstream with constant vertical velocities, though this relies on a stream being in erosional steady state (erosion rate equals rock uplift rate) prior to the knickpoint's formation. Recent modeling and field studies suggest that along-stream contrasts in rock erodibility perturb streams from erosional steady state. To evaluate how contrasts in rock erodibility might impact knickpoint interpretations, we test parameter space (rock erodibility, rock contact dip angle, change in rock uplift rate) in a one-dimensional (1D) bedrock stream model that has variable rock erodibility and produces a knickpoint with a sudden change in rock uplift rate. Upstream of a rock contact, the vertical velocity of a knickpoint generated by a change in rock uplift rate is strongly correlated with how the rock contact has previously perturbed erosion rates. These knickpoints increase vertical velocity upon propagating upstream of a hard over soft contact and decrease vertical velocity upon propagating upstream of a soft over hard contact. However, interactions with other transient perturbations produced by rock contacts make for nuances in knickpoint behavior. Rock contacts also influence the geometry of knickpoints, which can become particularly difficult to identify upstream of soft over hard rock contacts. Using our simulations, we demonstrate how a contact's along-stream horizontal migration rate and cross-contact change in rock strength control how much an upstream reach is perturbed from erosional steady state. When simulations include multiple contacts, the knickpoint is particularly prone to colliding with other transient perturbations and can even disappear altogether if rock contact dips are sufficiently shallow. Caution should be taken when analyzing stream profiles in areas with significant changes in rock strength, especially when rock contact dip angles are near the stream's slope.
中文翻译：
基岩流中瞬态岩石隆起和基面临界点对侵蚀效率对比的响应
基岩流中的断点通常被解释为由边界条件变化产生的瞬态特征。通常假设拐点以恒定的垂直速度向上游传播，尽管这依赖于在拐点形成之前处于侵蚀稳态（侵蚀速率等于岩石隆起速率）的流。最近的建模和实地研究表明，岩石可蚀性的沿流对比扰乱了侵蚀稳态的流。为了评估岩石可蚀性的对比如何影响拐点解释，我们在具有可变岩石可蚀性并产生岩石隆起速率突然变化的拐点。岩石接触的上游，由岩石隆起速率变化产生的临界点的垂直速度与先前岩石接触如何扰乱侵蚀速率密切相关。这些断点在硬接触软接触上游传播时增加垂直速度，并在软接触硬接触上游传播时降低垂直速度。然而，与岩石接触产生的其他瞬态扰动的相互作用会导致小点行为的细微差别。岩石接触也会影响断点的几何形状，这会变得特别难以识别软硬岩石接触的上游。使用我们的模拟，我们展示了接触的沿流水平迁移率和岩石强度的交叉接触变化如何控制上游河段受到侵蚀稳态的影响。当模拟包括多个接触时，临界点特别容易与其他瞬态扰动碰撞，如果岩石接触倾角足够浅，临界点甚至可能完全消失。在岩石强度发生显着变化的区域分析河流剖面时应谨慎，尤其是当岩石接触倾角接近河流坡度时。
更新日期：2021-05-05
中文翻译：
基岩流中瞬态岩石隆起和基面临界点对侵蚀效率对比的响应
基岩流中的断点通常被解释为由边界条件变化产生的瞬态特征。通常假设拐点以恒定的垂直速度向上游传播，尽管这依赖于在拐点形成之前处于侵蚀稳态（侵蚀速率等于岩石隆起速率）的流。最近的建模和实地研究表明，岩石可蚀性的沿流对比扰乱了侵蚀稳态的流。为了评估岩石可蚀性的对比如何影响拐点解释，我们在具有可变岩石可蚀性并产生岩石隆起速率突然变化的拐点。岩石接触的上游，由岩石隆起速率变化产生的临界点的垂直速度与先前岩石接触如何扰乱侵蚀速率密切相关。这些断点在硬接触软接触上游传播时增加垂直速度，并在软接触硬接触上游传播时降低垂直速度。然而，与岩石接触产生的其他瞬态扰动的相互作用会导致小点行为的细微差别。岩石接触也会影响断点的几何形状，这会变得特别难以识别软硬岩石接触的上游。使用我们的模拟，我们展示了接触的沿流水平迁移率和岩石强度的交叉接触变化如何控制上游河段受到侵蚀稳态的影响。当模拟包括多个接触时，临界点特别容易与其他瞬态扰动碰撞，如果岩石接触倾角足够浅，临界点甚至可能完全消失。在岩石强度发生显着变化的区域分析河流剖面时应谨慎，尤其是当岩石接触倾角接近河流坡度时。
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