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Evolutionary geomorphology: thresholds and nonlinearity in landform response to environmental change

机译：演化地貌学：地形响应环境变化的阈值和非线性

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Geomorphic systems are typically nonlinear, owing largely to theirthreshold-dominated nature (but due to other factors as well). Nonlineargeomorphic systems may exhibit complex behaviors not possible in linearsystems, including dynamical instability and deterministic chaos. The latterare common in geomorphology, indicating that small, short-lived changes mayproduce disproportionately large and long-lived results; that evidence ofgeomorphic change may not reflect proportionally large external forcings;and that geomorphic systems may have multiple potential responsetrajectories or modes of adjustment to change. Instability and chaos do notpreclude predictability, but do modify the context of predictability. Thepresence of chaotic dynamics inhibits or excludes some forms ofpredicability and prediction techniques, but does not preclude, and enables,others. These dynamics also make spatial and historical contingencyinevitable: geography and history matter. Geomorphic systems are thusgoverned by a combination of "global" laws, generalizations andrelationships that are largely (if not wholly) independent of time andplace, and "local" place and/or time-contingent factors. The more factorsincorporated in the representation of any geomorphic system, the moresingular the results or description are. Generalization is enhanced byreducing rather than increasing the number of factors considered. Predictionof geomorphic responses calls for a recursive approach whereby global lawsand local contingencies are used to constrain each other. More specificallya methodology whereby local details are embedded within simple but morehighly general phenomenological models is advocated. As landscapes andlandforms change in response to climate and other forcings, it cannot beassumed that geomorphic systems progress along any particular pathway.Geomorphic systems are evolutionary in the sense of being path dependent,and historically and geographically contingent. Assessing and predictinggeomorphic responses obliges us to engage these contingencies, which oftenarise from nonlinear complexities. We are obliged, then, to practiceevolutionary geomorphology: an approach to the study of surface processesand landforms which recognizes multiple possible historical pathways ratherthan an inexorable progression toward some equilbribrium state or along acyclic pattern.
机译：地貌系统通常是非线性的，这在很大程度上是由于其阈值主导的性质（但也由于其他因素）。非线性地貌系统可能表现出线性系统中不可能发生的复杂行为，包括动态不稳定性和确定性混乱。后者在地貌学中很常见，表明微小的，短暂的变化可能会产生不成比例的较大和长期的结果。地貌变化的证据可能未按比例反映出较大的外在强迫;并且地貌系统可能具有多种潜在的响应轨迹或变化的调整模式。不稳定和混乱并不能排除可预测性，但是会改变可预测性的环境。混沌动力学的存在抑制或排除了某些形式的可预测性和预测技术，但并不排除或支持其他形式。这些动力还使得空间和历史偶然性不可避免：地理和历史至关重要。因此，地貌系统由“全局”定律，概括和关系的组合管理，这些定律在很大程度上（如果不是全部）独立于时间和地点，以及“局部”地点和/或时变因素。包含在任何地貌系统表示中的因素越多，结果或描述就越奇异。通过减少而不是增加所考虑因素的数量来增强概括性。对地貌响应的预测要求采用递归方法，在这种方法中，全球法律和局部突发事件可相互制约。更具体地，提倡一种方法，该方法将局部细节嵌入到简单但更为普遍的现象学模型中。由于景观和地貌因气候和其他强迫而变化，因此不能假定地貌系统沿任何特定路径发展。地貌系统在依赖路径的意义上是进化的，并且在历史和地理上具有偶然性。评估和预测地貌响应使我们不得不参与这些偶然性，这通常是由于非线性复杂性而引起的。因此，我们有义务实践进化的地貌学：一种研究地表过程和地貌的方法，它认识到多种可能的历史路径，而不是不可避免地向某种平衡态或沿着无环态发展。

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